ssina - designer's handbook - stainless steel fasteners

STAINLESS

STEEL

FASTENERS

D E S I G N E R

HAN DBOOK

with Directory of

Fastener Manufacturers

A SYSTEMATIC APPROACH

TO THEIR SELECTION

StainlessSteel

TheValueOption

Fasteners 3/28/00 8:25 AM Page 3

suitability for any general and specificuse. The SSINA assumes no liabilityor responsibility of any kind in con-nection with the use of this informa-tion. The reader is advised that thematerial contained herein should notbe used or relied on for any specificor general applications without firstsecuring competent advice.

PREFACE/ACKNOWLEDGEMENT 1

A SYSTEMATIC APPROACH TO STAINLESS STEEL

FASTENER SELECTION 1

MANUFACTURE OF STAINLESS STEEL FASTENERS 1

WHAT IS STAINLESS STEEL 2

IDENTIFICATION 2

STAINLESS STEEL CHARACTERISTICS

(CORROSION RESISTANCE, STRENGTH, MACHINABILITY,

COLD HEADING QUALITY, APPEARANCE/AESTHETICS) 3

STAINLESS STEEL NO PROTECTIVE COATING NECESSARY 6

CHOOSING THE RIGHT STAINLESS STEEL 6

TENSILE AND YIELD STRENGTH 7

ANCHORS 8

DESIGNING AND ENGINEERING CONSIDERATIONS 8

DESIGNING FOR OPTIMUM CORROSION RESISTANCE 12

HIGH TEMPERATURE SERVICE 14

LOW TEMPERATURE SERVICE 16

STAINLESS STEEL PHYSICAL PROPERTIES 17

FASTENER MARKINGS 18, 19

FASTENER BASICS 20

DIRECTORY OF FASTENER

MANUFACTURERS INSIDE BACK COVER

The Specialty Steel Industry of NorthAmerica (SSINA) and the individualcompanies it represents have madeevery effort to ensure that the infor-mation presented in this handbook istechnically correct. However, neitherthe SSINA nor its member companieswarrants the accuracy of the informa-tion contained in this handbook or its

T A B L E O F C O N T E N T S


1P R E F A C EThere was a time when the periodic repairof mechanical and electrical componentswas taken for granted. Today, with laborcosts at record levels and going up,greater consideration at the design levelis being given to the reductionor eveneliminationof maintenance.

In cases where a joint must be takenapart and reassembled, the corrosionresistance of the fastener is particularlyimportant so that corrosion will in no wayhamper or prevent its removal. The costof removing rusty bolts, and replacingthem with new ones, is more expensivethan using corrosion resistant fasteners tobegin with.

Other costs resulting from fastenerfailure, such as downtime and lost pro-duction, make an even stronger case forconsideration of high integrity fastenersystems.

The 300 series stainless steels offerexcellent corrosion resistance to mostfreshwater environments, but their yieldstrengths are low for some applications.

The 400 series stainless steels offerhigh mechanical strength, but have a ten-dency to pit and corrode in many fresh-water systems.

The precipitation hardened stainlesssteels (e.g. 17-4 PH) provide alternativematerial considerations to meet both setsof criteriastrength and corrosion resis-tancewhile the duplex stainless steelsand super austenitic stainless steels offerexcellent solutions for handling moreaggressive environments.

Consequently, the designer needsto consider a fastener as a system, andregard the assembled joint as a critical andintegral portion of the design, since thejoint is normally an area under the higheststress and often the place where failure ismost likely to occur. A designer shouldstart with the optimum fastener and designthe joint around that, rather than startingwith the joint and then looking for thefastener that seems most adequate.

A C K N O W L E D G E M E N TThe SSINA wishes to acknowledge thatsome of the data contained in this hand-book were originally prepared by thecommittee of Stainless Steel Producers,American Iron and Steel Institute.

A S Y S T E M A T I CA P P R O A C H T O S T A I N L E S S S T E E L F A S T E N E R S E L E C T I O NSelecting the optimum fastener can be anawesome task for any designer. There isa staggering diversity of fastener typesavailable (over 500,000 standard items),and for any one type there can be a largenumber of sizes from which to choose.For example, one of the smallest stan-dard fasteners has a head of 0.01 inch(.254mm) in diameter; the largest has ahead of 4 feet (1.219m).

Stainless steel is used extensivelythroughout industry for both originalequipment manufacture as well as forreplacement. The purpose of this publica-tion is to help designers trace an orderlypath through the fastener complexity toarrive at a stainless steel fastener systemthat best fills the need.

S T A I N L E S S S T E E LF A S T E N E R SThe stainless steel fastener materials areidentified as the B8 class of alloys and areidentified in the ASTM SpecificationA193/193M (Standard Specification forAlloy Steel and Stainless Steel BoltingMaterials for High Temperature Service).The corresponding nut specification isASTM Specification A194/194M.

ASTM Specification F593 (StandardSpecification for Stainless Steel Bolts,Hex Cap Screws and Studs) covers the

broad range of commercial ferritic,martensitic and precipitation hardenedgrades of stainless steel, 0.25 to 1.5 inchnominal diameter.

These specifications cover the 300series stainless steels and high man-ganese and high silicon austeniticgrades, all of which are essentially 18-8(18% chromium and 8% nickel) materials,with compositions very close to the nomi-nal composition for Type 304. Becausethey have similar corrosion resistanceproperties, these 18-8 materials are ofteninterchanged in fastener applications. Ifan application calls for Type 304, thedesigner can generally specify an 18-8(Grade 8) fastener material.

M A N U F A C T U R E O FS T A I N L E S S S T E E LF A S T E N E R SWhile designers seldom get involved inthe manufacture of fasteners, it can beuseful to know something about theprocesses involved. This can be espe-cially true if the product requires a fas-tener of special design, such as the manyspecials illustrated in the photographsthroughout this booklet.

SYMBOL

B8/B8A

B8C/B8CA

B8M/B8MA/B8M2/B8M3

B8P/B8PA

B8N/B8NA

B8MN/B8MNA

B8MLCuN/B8MLCuNA

B8T/B8TA

B8R/B8RA

B8S/B8SA

ALLOY

Type 304

Type 347

Type 316

Type 305

Type 304N

Type 316N

6% molybdenum alloy

Type 321

Nitronic 50

Nitronic 60

Table 1 GRADE 8 FASTENER MATERIALS

Source: Stainless Steel Industry Data


There are two basic methods for pro-ducing fastenersmachining and coldheadingboth of which are applicable tostainless steels.

MACHINING is the oldest method offastener production, and it is still specifiedfor very large diameters and for small pro-duction runs. Machining, however, has asignificant disadvantage, as illustrated inFigure 1a. It disrupts metal grain flow andcreates planes of weakness in the criticalhead-to-shank fillet area. The result issome loss in load-carrying ability and adrastic reduction in fatigue resistance.

COLD HEADING is a method of formingwire into various shapes by causing it toplastically flow into die and punch cavitieswithout preheating the material (Figure1b). Bolts, screws, nails and rivets havelong been made by cold heading, butrecent developments in this field have

expanded the market for specialfasteners.

Cold heading has many importantadvantages in both quality and economy.Production rates, for example, canexceed 12,000 parts per hour. Coldheading also cold works stainless steels,which results in significant increases instrength for the 300 Series types.

Following heading, the blank is readyfor threading, which is frequently done byroll threading, another cold forming tech-nique that preserves grain flow patterns.

There are other operations involved infastener production, such as head slot-ting, shank slotting (for thread-cuttingscrews), head drilling, etc. But the makingof and threading the blank are the twomajor processes.

The markings for stainless steel fas-teners are defined in ASTM SpecificationA193/193M. The grades of stainlesssteel are also organized within classes,1 through 2C. The grade, listed in Table 1on page 1, and manufacturers identifica-tion symbols can be found on the endof the stud or bolt that indicates confor-mance to the specification.

W H A T I SS T A I N L E S S S T E E LStainless steel is a family of iron-basedalloys containing about 10.5% chromiumor more, plus other alloying elementssuch as nickel, manganese, molybde-num, sulfur, selenium, titanium, etc. (SeeTable 2 on page 3.) The chromium is

chiefly responsible for corrosion and heatresistance; the other alloying elementsare present in stainless steel to enhancecorrosion resistance and to impart certaincharacteristics with respect to strengthand fabricability.

A total of 60 commercial stainlesssteel types were originally recognized bythe American Iron and Steel Institute(AISI) as standard compositions. A com-plete listing of all stainless steels and adescription of each are contained in theSSINA publication, Design Guidelines forthe Selection and Use of Stainless Steel.

In addition to the standard AISI types,many special analysis and proprietarystainless steels are produced in theUnited States and Canada.

I D E N T I F I C A T I O NMost AISI stainless steels are identified bya system of numbers in either 200, 300,or 400 Series. In addition, all are identifiedby the Unified Numbering System (UNS).For example, Type 304 is Type S30400 inUNS. Special analysis and proprietarystainless steels are identified by tradenames, some of which may resembleAISI numbers.

There are five primary classifications of stainless steel:

AusteniticMartensiticFerriticPrecipitation hardeningDuplexEach characterizes its metallurgical

structure, which, in turn, reflects differentcharacteristics with respect to corrosionresistance, hardenability and fabricability.

AUSTENITIC stainless steels arechromium-nickel-manganese andchromium-nickel compositions identifiedby 200 and 300 Series numbers, respec-tively. They can only be hardened by coldwork and are non-magnetic in theannealed condition. Typical of theaustenitic group is Type 304, which con-tains nominally 18% chromium and 8%nickel; hence the 18-8 name.

FERRITIC stainless steels are straight-chromium steels in the 400 Series that arenot hardenable by heat treatment and onlyslightly hardenable by cold working. All aremagnetic. Type 430 is typical of this group.

MARTENSITIC stainless steels arestraight-chromium, 400 Series that can be

2

Figure 1a METALLURGICAL METAL FLOW FOR MACHINED MATERIALS

Figure 1b METALLURGICAL METAL FLOW FOR COLD HEADED MATERIALS


3hardened by heat treatment only. All aremagnetic. Type 410 is typical of this group.

PRECIPITATION HARDENING stainlesssteels are hardenable by a combination ofa low-temperature aging treatment andcold working. The AISI types are identifiedby UNS numbers only, e.g. Type S17400,although many are referred to in literatureby proprietary trade names such as 17-4PH. The precipitation hardening stainlesssteels are especially useful because fabri-cation can be completed in an annealed

condition and uniform hardening achievedwithout a high-temperature treatment thatmay result in distortion and scaling.

DUPLEX stainless steels are character-ized by their 50% austenitic 50% ferriticstructures which allow these materials tooffer the corrosion resistance for theaustenitic grades of material while provid-ing higher design properties.

SUPER-AUSTENITIC stainless materialsshould be given consideration in thosecases where aggressive chloride environ-

ments are encountered. They have highernickel and molybdenum contents forimproved pitting and crevice corrosionresistance.

S T A I N L E S S S T E E LC H A R A C T E R I S T I C SThe austenitic stainless steels are charac-terized as having excellent corrosionresistance. For example, Type 304 is themost widely used material that withstandsordinary rusting. It is virtually immune to

303

304

305

316

XM7*

384

410

416

430

17-4 PH

2205

AusteniticStainlessSteel






MartensiticStainlessSteel

MartensiticStainlessSteel

FerriticStainlessSteel

PrecipitationHardenedAustenitic Stainless

DuplexStainlessSteel

C Mn P S Si Cu Mo Ni Cr Other

ASTM A276 Type 303QQ-S-764 Class 303AISI 303




ASTM A493 Type XM7

AISI 384




ASTM A564AISI 630

ASTM A479ASTM A276

GENERAL SPECIFICATIONS 1DESCRIPTION COVERING

OF RAW MATERIALS CHEMICAL COMPOSITION, % MAXGRADE MATERIAL REQUIREMENTS (UNLESS SHOWN AS MIN OR MAX/MIN LIMITS GIVEN)

STAINLESS STEEL

0.15

0.08

0.12

0.08

0.10

0.08

0.15

0.15

0.12

0.07

0.03

2.00

2.00

2.00

2.00

2.00

2.00

1.00

1.25

1.00

1.00

2.00

0.20

0.045

0.045

0.045

0.045

0.045

0.040

0.060

0.040

0.040

0.030

0.15min

0.030

0.030

0.030

0.030

0.030

0.030

0.15min

0.030

0.030

0.015

1.00

1.00

1.00

1.00

1.00

1.00

1.00

1.00

1.00

1.00

1.00

3.0to4.0

3.0to5.0

0.603

2.00to

3.00

0.602

3.20

8.00to

10.00

8.00to

12.00

10.00to

13.00

10.00to

14.00

8.00to

10.00

17.00to

19.00

3.0to5.0

5.50

17.00to

19.00

18.00to

20.00

17.00to

19.00

16.00to

18.00

17.00to

19.00

15.00to

17.00

11.50to

13.50

12.00to

14.00

14.00to

18.00

15.00to

17.50

22.00

SeeNote(4)

N0.18

NOTES TO TABLE 21. Legend of specification designations

ASTMAmerican Society for Testing and MaterialsAISIAmerican Iron and Steel InstituteQQ-X-XXXFederal Government

2. May be added at manufacturers option.3. ASTM A276 permits addition of molybdenum, and also

0.12/0.30% lead at manufacturers option. AISI requiresthe addition of molybdenum but permits no lead.

4. Cb & Ta 0.15 to 0.45

*Type S30430

Table 2 CHEMICAL COMPOSITION LIMITS OF RAW MATERIAL (ASTM F593-91)


4foodstuffs, sterilizing solutions, mostorganic chemicals and dyestuffs, and awide variety of inorganic chemicals. Infact, the 18-8 austenitic stainless steelsare used in the food and beverage, phar-maceutical and electronic chip industries,because they maintain product purity,with the minimum of contamination.

A general characterization for stainlesssteels in handling these environments issummarized as follows:

CorrosionCategory Type ResistanceAustenitic 316 Superior

304 ExcellentDuplex 2205 SuperiorPrecipitationHardened 17-4 ExcellentFerritic 430 GoodMartensitic 410 Fair

This guideline can be helpful in nar-rowing down the choice of materials forany given corrosive environment. The finaldetermination, however, should be basedon tests conducted under actual workingconditions. If this is not practical for adesigner, he should consult with a corro-sion engineer having experience withstainless steels.

C O R R O S I O NR E S I S T A N C EChromium is the element that providesthe stainless steel with its stainlessname. Generally those alloys with greaterthan 12% chromium in their compositionwill not rust. The martensitic grades ofmaterial (such as Type 400) offer marginalor lower corrosion resistance than the300 series stainless steel for this reason.

However, type 410, performed wellin mild atmospheres, fresh water, mine

water, steam, carbonic acid, crude oil,gasoline, blood, alcohol, ammonia,mercury, soap, sugar solutions and otherreagents. It also has good scaling andoxidation resistance up to 1000F (649C).Type 416 is a free-machining variation ofType 410 and has similar characteristics.

If an application calls for a materialwith corrosion resistant properties betterthan that of Type 304, Type 316 is thenext logical candidate. Type 316 stainlesssteel is a higher alloyed material contain-ing 2-3% molybdenum, which provides

improved pitting and crevice corrosion-resistant properties, especially in environ-ments containing chlorides. It has wideapplication in pulp and paper mills andwater treatment plants (see photographof clarifier construction, bolted weirs andhandrail). It is also widely used in phos-phoric and acetic acids that tend tocause pitting corrosion in the 18-8 types.

In more aggressive pitting environ-ments, those materials with higher levelsof molybdenum should be considered.For further guidance on material selec-tion, consult with a corrosion engineer.

S T R E N G T HNickel is added to the iron-base alloys toprovide fabricability and improved ductil-ity. It is a primary austenite former thatdirectly benefits the workability character-istics for these alloys. Carbon and nitro-gen directly impact the strength of thesealloys. The nitrogen variant of these alloyswill offset the loss of mechanical proper-ties of low carbon grades of austeniticstainless steels.

Alternatively, the addition of aluminum,titanium and/or columbium to theaustenitic stainless steel chemistry cansignificantly increase the mechanicalproperties for these materials throughheat treatment (ageing). Types UNSS13800, UNS S15500, UNS S17400 andUNS S17700 are used to advantage bydesigners in the aerospace industry or inthe manufacture of large diameter boltingfor major civil engineering requirements.

Mixed structures (ferrite/austenite),typical of the duplex stainless steels, willalso provide higher strength characteris-tics than those of the fully austeniticgrades, while retaining excellent corrosionproperties.

This photograph shows a secondary clarifier retrofitat a municipal wastewater treatment plant.

This is a close up of the weirs of the clarifier andshows the use of 316 stainless steel bolting.


KEYS TO TABLE 31. Legend of grade designations:

Asolution annealedSHstrain hardened

Hhardened and tempered at 1100 F min.HThardened and tempered at 525 F 50 F

2. Yield strength is the stress at which an offset of 0.2% of gauge length occurs for all stainless steels.

3. Elongation is determined using a gauge length of 2 in. or 4 diametersof test specimen in accordance with Federal Standard 151, Method 211.

NOTES4. Loads at minimum yield strength and minimum ultimate tensile

strength for full size products may be computed by multiplying the yield strength and tensile strength stresses as given in Table 3 by the stress area for the product size and thread series as given in Table 5.

5. Proof loads of nuts (in pounds) may be computed by multiplying the proof load stress as given in Table 3 by the stress area for the nut size and thread series given in Table 5.

6. Ausenitic stainless steel, strain hardened bolts, screws, studs and nuts shall have the following strength properties:

PRODUCT SIZEin .

to 58 in.over 58 to 1 in.over 1 to 112 in.

YIELD STRENGTHmin ks i

1007050

TENSILE STRENGTHmin ksi

12510590

YIELD STRENGTHmin ks i

906545

TENSILE STRENGTHmin ksi

11510085

PROOF LOADSTRESS

ks i

12510590

TESTED FULL SIZE MACHINED TEST SPECIMENS

BOLTS, SCREWS, STUDS NUTS

303-A304-A

304305316384

XM7*

305-A316-A384-A

XM7-A*

304-SH305-SH316-SH

410-H416-H

410-HT416-HT

430

AusteniticStainless Steel-Sol. Annealed

AusteniticStainless Steel-Cold Worked

AusteniticStainless Steel-Sol. Annealed

AusteniticStainless Steel-Strain Hardened

MartensiticStainless Steel-Hardened andTempered

MartensiticStainless Steel-Hardened andTempered

FerriticStainless Steel-

YIELD 2STRENGTH

min ks i

TENSILESTRENGTH

min ks i

YIELD 2STRENGTH

min ks i

TENSILESTRENGTH

min ks i

ELON-GATION 3

% Min

HARDNESSROCKWELL

Min

PROOFLOAD

STRESSks i

HARDNESSROCKWELL

Min

MECHANICAL REQUIREMENTS

BOLTS, SCREWS AND STUDS NUTS

FULL SIZE BOLTS, MACHINED TEST SPECIMENS OFSCREWS, STUDS BOLTS, SCREWS, STUDS

GENERALGRADE 1 DESCRIPTION

30

50

30

SeeNote 6

95

135

40

75

90

75

SeeNote 6

125

180

70

30

45

30

SeeNote 6

95

135

40

75

85

75

SeeNote 6

125

180

70

20

20

20

15

20

12

20

B75

B85

B70

C25

C22

C36

B75

75

90

75

SeeNote 6

125

180

70

B75

B85

B70

C20

C22

C36

B75

Table 3 MECHANICAL REQUIREMENTS FOR STAINLESS STEEL BOLTS, SCREWS, STUDS AND NUTS (ASTM F593-91)

* Type 30430

5

M A C H I N A B I L I T YThe addition of sulfur and selenium to theaustenitic grades of material improves themachinability of these alloys. These ele-ments, in combination with the chromiumand manganese in these alloys, formstringer like inclusions in the structure,which allow better chip removal.

For instance, Type 303 has a consid-erably higher sulfur content that enhancesmachining characteristics. This propertymight be very beneficial in the productionof large bolts or where small productionruns or specials are needed.

However, it should be recognized thatwhile the 18-8 stainless steels are consid-

ered to have similar corrosion resistanceto one another, the sulfide stringers inType 303 can result in end grain attack atcut ends, especially when exposed towater or some chemical solutions.Accordingly, a designer should specifyType 304 when it is known that Type 303is not suitable for the application. When in


6doubt, the designer should consult with acorrosion engineer.

Type 416-ferritic stainless steel alsohas sulfur in its composition in order toprovide improved machinability for themartensitic grades of stainless steel.

C O L D H E A D I N GQ U A L I T YThe addition of copper in Type 302 stain-less steel (UNS S30430) and higher levelsof nickel in Types 305 (UNS S30500) and384 (UNS S38400) results in lower work-hardening rates, which allows improvedcold heading and workability for thesegrades of material. This is very desirable forlower costs and for large production runs.

These materials have been used for fas-teners, cold headed bolts, screws, upsetnuts, instrument parts and jobs involvingsevere coining, extrusion and swaging.

A P P E A R A N C E /A E S T H E T I C SType 304 and 316 fasteners have beenused extensively in architectural applica-tions for both their eye appeal and theirstructural and corrosion properties (seephotograph of handrails and sign sup-ports at Ronald Reagan WashingtonNational Airport).

Some applications do not require thehigh degree of corrosion resistanceoffered by the 18-8 stainless steels or thehigher alloyed types. In these cases, thedesigner can consider types that may belower in cost. For example, Type 430stainless steel contains about 18%chromium, but no nickel. Although it haslower corrosion-resistance propertiesthan the 18-8 types, it has wide applica-tion for decorative trim because when it isbuffed it closely resembles a material thathas been chromium plated. Typical appli-cations include trim on automobiles,

cameras, vending machines, counters,appliances, showcases, and a host ofother products that need dressing up oreye appeal to increase their salability.

S T A I N L E S S S T E E L N O P R O T E C T I V EC O A T I N G N E C E S S A R YSome designers may be inclined to thinkof plated fasteners as a low-cost solutionto corrosion. While plated fasteners doserve a useful purpose in some applica-tions, such as when a plated coating isadded for purposes of creating a specialfinish or color match, it is far more desir-able to use a fastener in which corrosion

protection is inherent within the materialitself and not just added to the surface.

Stainless steels do not need any formof protective coating for resistance to cor-rosion, in contrast with plain steel andsome nonferrous fastener materials.While plated or galvanized steel fastenersare adequate where corrosive conditionsare not severe, many designers considerthe extra cost of stainless steel fastenersas inexpensive insurance against possiblefailure or loss of eye appeal. When thecost of failure is considered, in conjunc-tion with the ease in which damage canoccur to a protective coating, it makesgood sense to specify a fastener made ofa material which is inherently corrosionresistant. Often, a minute discontinuity in aplated surface is all that is needed to leadto corrosive failure. Such discontinuitiesresult from wrench or driver damage,poor plating practices, or simply from theturning action of thread against thread.

Furthermore, while the cost of stain-less steel fasteners may be more thanplated fasteners, the overall cost of thefinished product (from a small applianceto a large plant) will generally be affectedonly by an insignificant amount.

Interestingly, plated coatings areapplied to stainless steels for purposes ofchanging appearance. For instance, thedesigner may want a black fastener, or ahighly reflective chrome plated fastener tomatch the surfaces being joined. Suchrequirements can be accommodated instainless steel.

C H O O S I N G T H E R I G H TS T A I N L E S S S T E E LOnce the design engineer has determinedthe correct candidate fastener materialson the basis of their corrosion-resistantproperties, the next concern probably willbe the mechanical and physical properties

Bolting applications at the Ronald Reagan NationalAirport, Washington, DC.


7of these materials. Once again, the familyof stainless steels offers a wide choice.

Many engineers who have attemptedto design a product using stainless steelfasteners have learned that meaningfuldata on fastener properties are some-times difficult to find. In many situations,the designer has had to rely on technicaldata based on the mechanical propertiesof the materials from which the fastenersare made. All too often these propertiesvary considerably from the actual proper-ties of the manufactured fasteners.

ASTM Specifications A193/193M,A194/194M, F593 and F594 provide thereference base for material selection andspecification purposes.

The original Industrial FastenersInstitute (IFI) specificationIFI-104thatcovered the mechanical, metallurgical andquality requirements of the common stain-

less steels used for bolts, screws, studs,and nuts, has been replaced by therespective ASTM specifications relating tothese materials and their product forms,e.g., ASTM specifications F467/467M,F468/468M, F738M, F836M, F837/837M,F879/879M and F880/880M.

T E N S I L E A N D Y I E L DS T R E N G T HTensile or ultimate strength is that prop-erty of a material which determines howmuch load it can withstand until failure.Yield strength is a measure of the resis-tance of a material to plastic deformation;that is, before assuming a permanent setunder load. For stainless steels, the yieldstrength is calculated on a stress-straindiagram (Figure 2), and it is a point atwhich a line drawn parallel to and offset0.2% from the straight line portion of thecurve intersects the curve. For stainlesssteel, the yield point is not a clear-cut,identifiable point.

It can be seen from the data in Table 3on page 5 that there is a considerablespread between the tensile and yieldstrength values, which is characteristic ofstainless steels. The yield strength is usedfor design calculations and is the stress atwhich the mechanical properties (tensileand yield strengths) can be increased by

cold work or strain hardening.The ASTM specification clearly distin-

guishes these finished conditions as:CLASS 1 - Carbide solution annealedCLASS 2 - Carbide solution annealed andstrain hardened.

For example, full size bolts of 18-8stainless steel in the annealed conditionwill have a minimum yield strength of 30ksi (207 MPa). If the bolt is cold worked15-20%, its yield strength level willincrease to 50 ksi (345 MPa) minimum.Cold worked from 35 to 40%, the mater-ial is considered to be strain-hardenedand the minimum yield strength level is ashigh as 100 ksi (690 MPa), dependingupon size of the fastener. This conditionallows the design engineer to specify andtake advantage of a corrosion resistantmaterial with higher strength criteria.

Likewise, the characteristics of thestress-strain curve can be changed byheat treatment and ageing of the precipi-tation hardened stainless steel and hard-ening and tempering of the martensiticgrades of stainless steel. The differentconditions are designated by a letter;

A - Solution annealedSH - Strain hardenedH- Hardened HT - Hardened and temperedAH - Age hardened

Figure 2 YIELD STRENGTHFigure 2 DETERMINED BY OFFSET

Material

TypicalTensile Strength

ksiDensity

Lbs./Cu. In.Strength-to-WeightRatio Inches x 102

180

60

125

50

12

80

80

75

60

50

.280

.098

.290

.163

.041

.290

.319

.308

.308

.282

6.4

6.1

4.3

3.1

2.9

2.8

2.5

2.4

2.0

1.8

Martensitic StainlessSteel (410, 416)

Aluminum (2024-T4)

Austenitic StainlessSteel (18-8)Strain hardened

TitaniumCommercially pure

Nylon

Austenitic StainlessSteel (18-8), annealed

Monel 400

Silicon Bronze

Brass

Mild Steel

Table 4 STRENGTH-TO-WEIGHT RATIO

Source: ITT Harper


8Figure 3 is a relative comparison ofstrength values between stainless steelsand other corrosion resistant fastenermaterials. In applications where weight isan important consideration, as in aircraftdesign, designers look to strength-to-weight ratios for an indication of the mostefficient material to use. The strength-to-weight ratio is defined as the ratio of tensilestrength to density. Some typical proper-ties of corrosion-resistant fastener materi-als, including strength-to-weight ratios aregiven in Table 4 on page 7. Of particularinterest is the similarity between Type 410stainless steel and aluminum, and the factthat Type 410 has a higher strength-to-weight ratio than aluminum 2024-T4.

A N C H O R SThere are a number of types of mechani-cal anchor systemsinserts; wedge-type; drop-in; shell-type; sleeve-type. Alltypes can be considered for anchorageinto concrete. Sleeve-type anchors canbe considered for use in masonry, groutfilled block and hollow block.

Unlike mechanical anchors, which exertpressure on concrete when expanded,chemical anchors using adhesives providesecure fastening in which the load is dis-tributed along the length of the anchor.These systems are suitable for anchoringconcrete and hollow masonry applications.

The austenitic stainless steels provideexcellent corrosion resistance in a widevariety of masonry and concrete environ-ments, where high alkalinity (pH) is preva-lent. They also provide axial strength inwall tie systems to withstand wind load-ings and tension and compressionstresses in accommodating normal build-ing movement.

D E S I G N I N G & E N G I N E E R I N G C O N S I D E R A T I O N SIn selecting a stainless steel on the basisof mechanical and physical properties,designers should keep in mind the follow-ing considerations. THREAD STRENGTH - Thread forms onfasteners are manufactured by cutting,rolling, or grinding. The best quality high-

est-strength thread, however, is achievedby thread rolling. This is because theplastic deformationor cold workinginvolved in rolling threads results in; (1)more accurate and uniform thread dimen-sions, giving a better fit between threadedparts and fewer concentrated loads atpoints of misfit; (2) smoother thread sur-faces and, thus, fewer scratches andother markings to initiate cracks, orgalling; and (3) higher yield, tensile, andshear properties to better withstand ser-

Figure 3 TENSILE STRENGTH OF NINE FASTENER ALLOYS


9vice loads. Design characteristics arebased on the number of threads per inchof stock and the bolt diameter, as shownin Table 5. This can be important in civilengineering applications as shown in thesluice gate photograph.SHEAR STRENGTH - Shear is transverserupture. It is caused by a pushing orpulling force at 900 from the axis of a part.Thus, a rivet used as a pulley axle will

shear if the load on the pulley exceedsthe shear value of the rivet. Shearstrength is defined as the load in poundsto cause rupture, divided by the crosssectional area in square inches of the partalong the rupture plane.

The allowable shear stresses for stain-less steel bolts are given in Table 6, whichis based on the AISI publication, StainlessSteel Cold-Formed Structural Design

Manual, 1974 Edition. The allowable shearstress for bolts with no threads in the shearplane was taken as 60% of the minimumtensile strength divided by a safety factorof 3.0. This allowable shear stress providesa minimum safety factor of about 1.2against shear yielding of the bolt material.When threads are included in the shearplane, 70% of the nominal allowable shearstress is used due to the fact that the

COARSE THREAD (UNC) FINE THREAD (UNF)

Table 5 TENSILE STRESS AREAS AND THREADS PER INCH

Tensile stress areas are computed using thefollowing formula:

Where As= tensile stress area in square inchesD = nominal size (basic major diameter)

in inchesn = number of threads per inch

PRODUCT SIZEDIA. in.

68

1012

145163871612916583478

1

118114138112

STRESS AREAsq in .

0.009090.01400.01750.0242

0.03180.05240.07750.10630.1419

0.18200.22600.33400.46200.6060

0.76300.96901.15501.4050

THREADSper in .

32322424

2018161413

12111098

7766

STRESS AREAsq in .

0.010150.014740.02000.0258

0.03640.05800.08780.11870.1599

0.20300.25600.37300.50900.6630

0.85601.07301.31501.5810

THREADSper in .

40363228

2824242020

1818161412

12121212

As = 0.7854 [ D 0.9743 ]2n

Type

302**304316

302304316

302**304316

Finish

Hot Finished

Cold Finished

Cold Finished

Condition and Specification

Condition A (Annealed)in ASTM A276-71

Class 1 (solution treated)in ASTM A193-71

Condition A (Annealed)in ASTM A276-71

Condition B (cold-worked)in ASTM A276-71

Class 2 (solution treatedand strain hardened)in ASTM A193-71*

Diameter d (in.)

all

12

34

0.2% YieldStrength (ksi)

30.0

45.0

100.0

TensileStrength (ksi)

75.0

90.0

125.0

No Threadsin Shear Plane

15.0

18.0

25.0

Threadsin Shear Plane

10.5

12.6

17.5

Minimum Tensile Requirements Allowable Shear Stress (ksi)

Table 6 ALLOWABLE SHEAR STRESS FOR STAINLESS STEEL BOLTS

** For Class 2: B8M in ASTM A193, the allowable shear stress** is 22.0 ksi when threading is excluded from the shear plane,** or 15.0 ksi when threads are in the shear plane.** ASTM A276-71 only.

This is a photograph of a sluice gate (open position)on the Thames River Barrier in London. Monel alloyK-500 bolting was used for all the structurals.


10

actual shear stress in bolts is to be calcu-lated on the basis of the gross cross-sec-tional area or nominal area, and that theratios of stress area to nominal area rangefrom 0.65 to 0.76 for diameters of boltsvarying from 1/4 to 3/4 inch (6.3-19.1mm).

This practice is comparable to that forhigh-strength carbon steel structuralbolts. However, it is slightly more liberalbecause of the generally shorter jointlengths in cold-formed stainless steelconstruction. For bolts not listed in Table6, the allowable shear stress can bedetermined in the same manner.TORQUE - Another consideration in aproperly fastened joint is the twistingforce applied to a fastener. Table 7 offerssome suggested maximum torque valuesfor stainless steel fasteners. This table is aguide based on industry tests that pro-vide maximum clamping values with mini-mum risk of seizing. The values are basedon fasteners that are dryfree of anylubricantand wiped clean of chips andforeign matter.

Most production lines are equippedwith assembly tools that can be adjusted

BOLT SIZE

2-56

2-64

3-48

3-56

4-40

4-48

5-40

5-44

6-32

6-40

8-32

8-36

10-24

10-3214"-2014"-28

516"-18516"-2438"-1638"-24716"-14716"-2012"-1312"-20916"-12916"-1858"-1158"-1834"-1034"-1678"-9

78"-14

1"-8

1"-14

118"-7

118"-12

114"-7

114"-12

112"-6

112"-12

TYPE 304 ST. ST.

2.5

3.0

3.9

4.4

5.2

6.6

7.7

9.4

9.6

12.1

19.8

22.0

22.8

31.7

75.2

94.0

132

142

236

259

376

400

517

541

682

752

1110

1244

1530

1490

2328

2318

3440

3110

413

390

523

480

888

703

TYPE 316 ST. ST.

2.6

3.2

4.0

4.6

5.5

6.9

8.1

9.8

10.1

12.7

20.7

23.0

23.8

33.1

78.8

99.0

138

147

247

271

393

418

542

565

713

787

1160

1301

1582

1558

2430

2420

3595

3250

432

408

546

504

930

732

Table 7 TORQUE GUIDE

Source: ITT Harper

Suggested Max Torquing Valuesa guide based upon industry tests on dry products wiped clean. Valuesthru 1" diameter are stated in inch pounds; over 1" diameter, in foot pounds. The 38" diameter and undermetal products were roll-threaded and, where size range permitted, were made on Bolt Maker equipment.


11

to specific torque values. The most trou-ble occurs when replacement is beingmade under conditions where torquetools are not available. There are someguidelines for these circumstances:

1. Tighten the nut finger tightaboutone foot-pound of torque or less.

2. Tighten the nut one additional turn,360 degrees, for proper torque. This is anarbitrary figure that applies primarily to300 Series fasteners. For hardened andtempered 400 Series fasteners, they maybe too high. In any event, a trial testshould be conducted with a torquewrench for best results.

In service at elevated temperature, thebuildup of oxides or scale on fastenersurfaces may fuse threaded surfacestogether. Regular loosening and re-tight-ening can prevent this from happening.

Some engineers are of the opinionthat the only way to avoid seizing andgalling is to lubricate the threaded jointbefore its assembled. Adding a lubricantcan affect the torque-tension relation-ships, as shown in Figure 4. A lubricatedfastener requires less torque to achievethe same degree of tension or clampingforce. Different lubricants have differenteffects also. Wax, for example, on eitherthe bolt or nut, or both, acts to reducethe torque requirements.

If a lubricant is going to be used, testsshould be conducted to determine torquerequirements and to evaluate the com-patibility of the lubricant to the environ-mentsuch as high temperature. Amongthe popular lubricants are those whichcontain substantial amounts of molybde-num disulfide, graphite, mica, talc, cop-

per or zinc fines, or zinc oxide. However,the zinc- and copper-bearing anti-seizelubricants are not recommended for usewith stainless steel.

G A L L I N G & S E I Z I N GTo have an effective fastener system, thedesigner should also be concerned withproper utilization, especially how thefasteners will be installed.

With any product, effective utilizationrequires knowledge of the productscharacteristics as well as its proper use.Failure to follow accepted practices canlead to difficulties, such as seizing andgalling, which can be encountered withfasteners made of any material includingstainless steels. There are severalcourses of action open to designers thatwill minimize or eliminate such difficulties.

One of the common causes for gallingis mismatched threads, or threads that

Figure 4 FASTENER LUBRICATION


12

are not uniform from shank or shoulder topoint. Fasteners made in accordancewith nationally recognized standards,such as those published by the AmericanNational Standards Institute, Inc., (ANSI),will assure that nuts and bolts are uni-formly threaded.

Reasonable care should be exercisedin the handling of fasteners to keepthreads clean and free of dirt, especiallycoarse grime and sand. If threads aretightened down on sand, the chance ofgalling or seizingin any fastener mater-ialincreases significantly.

D E S I G N I N G F O R O P T I M U M C O R R O -S I O N R E S I S T A N C ECorrosion protection for a fastened jointencompasses much more than a consid-eration of the corrosion resistance of thefastener itself. By their very nature, fas-tener systems represent inherent crevices(under aqueous conditions) and notches(fatigue; corrosion fatigue impact), if notdesigned or specified correctly for theconditions of operation. An analysis of theentire assembled joint as a system is

required, which would include evaluationof the structural design, materials,stresses, product life expectancy andenvironmental conditions.

Since corrosion resistance is animportant aspect of product reliability,inherent in any attempt to prevent corro-sion is the careful selection of fastenermaterials. A common practice in industryis to use fasteners made of metals oralloys that are more corrosion resistantthan the materials they join.

The austenitic stainless steels, withmore than 12% chromium in their chem-istry, provide corrosion resistance to awide variety of environments and espe-cially in low chloride waters (less than2000ppm chlorides). Additionally, stainlesssteel is invariably more noble (cathodic)than the structural members they join,and are therefore protected by them.

The stainless characteristics of thesematerials make them ideal fasteners formany architectural applications and suit-able for atmospheric (indoor and outdoor)services.

A Q U E O U S C O R R O S I O NCorrosion is the wearing away or alter-ation of a metal either by direct chemicalattack or by electrochemical reaction.This can lead to a weakened or impairedstructural system, which could result indowntime, replacement and repairs.

Overall corrosion loss, reflected byweight loss, is the most common form ofattack. More serious attack can often beseen in the form of localized pitting andpitting attack. This is especially prevalentin chloride and acid chloride types ofenvironments. If the environment cannotbe controlled, modified or changed, thenmaterials with higher corrosion resistancemay have to be considered.

There are several basic types of corro-sion that may occur, singly or in combi-nation, necessitating an understanding ofmaterial selection for basic designguidelines.

GALVANIC CORROSION can occurwhen dissimilar metals are in contact inthe presence of an electrolyte, which maybe nothing more than a wet industrialatmosphere.

When two different metals are in con-tact with one another, in the presence ofa liquid, a battery cell is created, allowing

Bolting applications at the Ronald Reagan NationalAirport, Washington, DC.

This photograph shows a secondary clarifier retrofitat a municipal wastewater treatment plant.


13

current to flow with corrosion occurring atthe anodic component of the cell. Figure5 provides a guide to the relative anodicand cathodic relationships of metals to

one another when exposed in sea water,which is known as the galvanic series ofmetals and alloys. The further apart thecombination of alloys, the greater is thecorrosion attack at the anodic compo-nent. It is well recognized that magne-sium, zinc and aluminum anodes, whenattached to a steel hull of a ship, will cor-rode preferentially, thereby protecting thestructural integrity of the cathodic com-ponents. By comparison, no serious gal-vanic action will result from the couplingof metals with the same group (stainlessto stainless) or to near alloys in the gal-vanic series (stainless to copper-nickel).

It is also important to have an under-standing of the relative areas of the twodifferent materials that are in direct con-tact with one another (the fastener sys-tem will normally represent the smallestsurface area for materials being joined).Consequently, the fastener systemshould be cathodic to the materials beingjoined. This can be seen in the pho-tographs showing the bolting materialsused in the construction of the ThamesRiver Barrier on page 14.

In the aircraft industry, designersdepend on this area-relationship principlewhen they specify stainless steel fastenersin aluminum structures. The greater therelative area of the anodic (aluminummaterial), the less severe is the corrosion.

By comparison, steel or copper alloystuds for joining stainless steel wouldaccelerate corrosion of the fastener sys-tem, although the extent of the galvanicattack would depend upon the relativearea of each material.

The area relationship depends not onlyon the relative area of the materials in thestructure, but also on the number of fas-teners. Sometimes an acceptable balanceof incompatible metals may be achievedby adjusting the number of fasteners todistribute them more uniformly to avoid alocal condition of low relative area.

A general rule to remember is to usethe more-noble metal for the part with thesmaller surface area. This makes a goodcase for using stainless steel fasteners forjoining metals that are less corrosionresistant. Table 12 on page 20 providesguidelines for the selection of fasteners forvarious base metals. If the potential ishigh for galvanic corrosion in a fastenedjoint, it is possible to insulate the fastener.

CONCENTRATION CELL CORROSION

occurs when two or more areas on thesurface of a metal are exposed to differ-ent concentrations of the same solution,such as under deposits or in crevices.A difference in electrical potential resultsand corrosion takes place. Unlike gal-vanic corrosion, it does not require dis-similar metals.

Figure 5 GALVANIC SERIES OF METALS & ALLOYS IN SEAWATER


14

In the case of very tight stationarycrevices, oxygen depletion at the inter-face of the metals, relative to the aqueousenvironment, can create localized anodicand cathodic differences at the matinginterfaces. Such might be the case atflanged joints where gaskets or o-ringseals are used, or at bolted connections.Underdeposit or crevice attack mayoccur, especially when chlorides are pre-sent in the aqueous system.

In the case of ambient temperature, ithas been determined that this form ofattack is unlikely to occur with Type 304stainless steel systems when the chloridelevels are less than 200ppm, and, in thecase of Type 316 stainless steel systems,when the chloride levels are less than

1000ppm. Higher molybdenum contain-ing alloys offer greater corrosion resis-tance to this form of attack than the 300series stainless steel materials.

To avoid this form of corrosion, keepsurfaces smooth and minimize or elimi-nate lap joints, crevices, and seams.Surfaces should be clean of organicmaterial and dirt. Bolts and nuts shouldhave smooth surfaces, especially in theseating areas. Flush-head bolts should beused where possible.

CHLORIDE ION STRESS CORROSION

CRACKING is a recognized phenomenonwith the 300 series stainless steel materi-als. Three conditions must exist before itcan occur; chlorides (environment) mustbe present; stress (inherent with tension-ing of fasteners); and temperature (usuallydoes not occur below 600C). Under thiscombination of conditions, alternativestainless steel materials can be consid-ered, namely the duplex stainless steelsor the more highly alloyed nickel contain-ing materials, typical of 6% molybdenumgrades. The straight chromium 400 series

stainless steels are not subject to thisform of attack, but usually they do notprovide suitable corrosion resistance.

CORROSION FATIGUE is acceleratedfatigue failure occurring in a corrosivemedium. The general fatigue characteris-tics of the ferritic, martensitic and alloysteels are usually significantly reduced,as a result of general aqueous corrosionor pitting attack. The austenitic, duplexand super austenitic stainless steelsexhibit some lowering of their air-fatigueproperties.

Factors extending fatigue perform-ance are application and maintenance ofa high preload, and proper alignment toavoid bending stress.

H I G H T E M P E R A T U R ES E R V I C EThe selection of stainless steel fastenersfor high-temperature service is complexbecause of the many factors involved.Mechanical and physical properties haveto be considered together with corrosionresistance.

Typical stainless steel structural bolting.(Thames River Barrier)

Thames River Barrier

Figure 6 EFFECT OF CHROMIUM CONTENT ON SCALING RESISTANCE OFFigure 6 CHROMIUM-IRON ALLOYS (AT 18000F OR 982 0C)


15

Chromium also plays an importantpart in the high temperature resistancecharacteristics for stainless steels. Figure6 on page 14 shows this effect on thescaling resistance of chromium-iron alloys.Consequently, stainless steel Types 309,310, 314, 442 and 446 would providesuitable performance in many of theseenvironments, while grades with titanium,columbium and tantalum such as type321, 347 and 348 can also be consideredfor elevated temperature service.

In all bolted joints, the fasteners aretightened to some initial elastic stress andcorresponding strain. At elevated temper-atures, creep occurs in which some ofthe elastic strain is transformed to plasticstrain with a corresponding reduction instress. This behavior is termed relaxation.When bolts relax they no longer maintaina tight joint.

Resistance to creep, or relaxation, isan important consideration for fastenersystems at elevated temperature. Table 8

shows creep values for several widelyused stainless steels, some of which arereadily available as off-the-shelffasteners.

Other considerations for elevated-temperature service include thermalexpansion characteristics and oxidationresistance.

The thermal expansion of a fastenershould match the expansion characteris-tics of the materials being fastened (Table9), with a logical conclusion that stainlesssteel fasteners are best for stainless steel

AISI TYPE

303

304

305

309

310

316

321

347

430

446

410

416

1000 F

16.5

20

19

16.5

33

25

18

32

8.5

6.4

11.5

11

1100 F

11.5

12

12.5

12.5

23

17.4

17

23

4.7

2.9

4.3

4.6

1200 F

6.5

7.5

8

10

15

11.6

9

16

2.6

1.4

2

2

1300 F

3.5

4

4.5

6

10

7.5

5

10

1.4

0.6

1.5

1.2

1500 F

0.7

1.5

2

3

3

2.4

1.5

2

0.4

Table 8 CREEP STRENGTHS OF TYPICAL STAINLESS STEEL FASTENER MATERIALS

Source: Industry Data

LOAD FOR 1% ELONGATION IN 10,000 Hr, ks i

Alloy Temperature Range oF

32 to 21232 to 57232 to 1112

32 to 21232 to 57232 to 1112

32 to 21232 to 1000

68 to 572

68 to 572

68 to 572

68 to 212

32 to 6832 to 1600

-76 to 6868 to 21268 to 392

Mean Coefficient ofThermal Expansion

In./In./oF(106)

9.69.9

10.4

8.99.0

10.3

6.17.2

11.3

10.0

11.8

7.8

4.75.6

21.422.823.9

Table 9 THERMAL EXPANSION OF CORROSION-RESISTANT FASTENER ALLOYS

Source: ITT Harper

Type 304 Stainless Steel



Brass

Naval Bronze

Silicon Bronze

Monel

Titanium

Aluminum (2024)


16

base metal joints; otherwise, there can beover-stressing and possible failure, or arapid loss in clamping stress.

The oxidation or scaling resistance ofstainless steels under constant tempera-ture condition is, for the most part,related to chromium content, as illus-trated in Figure 6 on page 14. In Table 10,scale resistance is expressed as temper-ature at maximum continuous service andmaximum intermittent service (in whichtemperature cycling occurs).

As the high-temperature environmentbecomes contaminated by compoundsof sulfur, carbon, hydrogen, and the halo-gens, the problem of materials selection

becomes even more complex.Nevertheless, stainless steels are widelyused in these environments. A fairly com-prehensive discussion of their applicationis found in a publication by TheInternational Nickel Company, CorrosionResistance of the Austenitic Chromium-Nickel Stainless Steels in High-Temperature Environments.

L O W T E M P E R A T U R ES E R V I C EOf primary importance to the develop-ment of the worlds natural gas suppliesis the handling and storage of liquid nat-ural gas (LNG). Fasteners have a role in

LNG processing for piping and heatexchanger flanges, pumps and variousrelated equipment.

Austenitic stainless steels are the mostwidely used materials in cryogenic appli-cations, especially Type 304, because itdoes not become brittle as it is chilled.Not only does Type 304 remain toughand ductile at LNG temperatureminus260F (-162C)but it retains excellentproperties with liquid hydrogen at minus423F (-253C) and liquid helium at minus452F (-268C). Table 11 shows low-tem-perature mechanical properties of severalstainless steels used in cryogenic service.

AISI TYPE

303

304

305

309

310

316

321

347

430

446

410

416

MAX. CONTINUOUSSERVICE, AIR, OF

1650

1650

1650

1950

2050

1650

1650

1650

1550

1950

1300

1250

MAX. INTERMITTENTSERVICE, AIR, OF

1400

1550

1850

1900

1550

1550

1550

1650

2050

1450

1400

Table 10 SCALING (OXIDATION) RESISTANCE OFTable 10 TYPICAL STAINLESS STEEL FASTENER MATERIALS


AISITYPE

304

316

430

410

oF

-40-80-320-423

-40-80-320-423

-40-80-320

-40-80-320

oC

-40-62-196-252

-40-62-196-252

-40-62-196

-40-62-196

ksi

34.034.039.050.0

41.044.075.084.0

41.044.088.0

90.094.0

148.0

kg/mm2

24.024.027.035.0

29.031.053.059.0

29.031.062.0

63.066.0

104.0

ksi

155.0170.0221.0243.0

104.0118.0185.0210.0

76.081.092.0

122.0128.0158.0

kg/mm2

109.0120.0155.0171.0

73.083.0

130.0148.0

53.057.065.0

86.090.0

111.0

Elongation% in 2"

(5.08 cm)

47.039.040.040.0

59.057.059.052.0

36.036.0

2.0

23.022.010.0

% Reductionof Area

64.063.055.050.0

75.073.076.060.0

72.070.0

4.0

64.060.011.0

ft-lb

110110110110

110110

1082

2525

5

kg-m

15.215.215.215.2

15.215.2

1.41.10.3

3.53.50.7

Tensile Strength Izod-ImpactYield Strength0.2% OffsetTest Temperature

Table 11 CRYOGENIC PROPERTIES OF STAINLESS STEELS

Not AvailableNot Available



17

S T A I N L E S S S T E E LP H Y S I C A L P R O P E R T I E SM A G N E T I C P R O P E R T I E SMagnetism, for purposes of this discus-sion, is the ability of a part to be attractedby a magnet and not the parts ability tofunction as a magnet. It is more accu-rately expressed as magnetic permeabil-ity, and it can be an important designconsideration. One reason is the need tohave a magnetic material for automaticassembly operations. On the other hand,some highly sophisticated electronicequipment may require materials withvery low or nil magnetic permeability.Stainless steels can satisfy eitherrequirement.

The austenitic group of stainless steelshave essentially low magnetic permeabil-ity in the annealed condition; i.e., they willnot be attracted by a magnet. Some ofthe austenitic materials, however, areweakly attracted by a magnet after severe

cold working. The effect of cold workingon magnetic properties for a few com-mon 18-8 stainless steels is shown inFigure 7. The magnetic permeability ofthe same group, but expressed as afunction of tensile strength, is shown inFigure 8.

The straight-chromium, 400 Seriesstainless steels are always strongly mag-netic. The degree of magnetic permeabil-ity, however, is affected by chemicalcomposition and heat treatment. Forhighest initial permeability, the carboncontent should be kept low; Types 416and 430 should be fully annealed for thebest magnetic behavior.

During annealing, a dry hydrogenatmosphere should be used to keep sur-faces bright and free of contamination,such as carbon or nitrogen, which candecrease permeability.

Chemical cleaning, which removesiron particles from the surface, may alsoimprove permeability.

Figure 7 WHEN COLD WORKING IS EMPLOYED, SOME Figure 7 NORMALLY NON-MAGNETIC AUSTENITICFigure 7 STEELS BECOME SUBSTANTIALLY MAGNETIC

Figure 8 MAGNETIC PERMEABILITY OF AUSTENITIC ALLOYSFigure 8 SUBJECTED TO COLD WORKING CAN ALSO BE EXPRESSEDFigure 8 AS A FUNCTION OF TENSILE STRENGTH


18

A S T M A L L O Y G R A D ES P E C I F I C A T I O N D E S C R I P T I O N M A R K I N G

Bolts, Screws and Studs Class1(High Temperature Service) I IA IB IC II

ASTM A193 AISI 510 B5AISI 410 B6AISI 304N B8N B8NAAISI 316N B8MNA B8MNUNS 20901 (XM19) B8R2

B8RA3

Bolts, Screws and Studs(High and Low Temperature Service)

ASTM A193 &ASTM A320 AISI 304 B8 B8A B8

AISI 347 B8C B8CA B8CAISI 316 B8M B8MA B8MAISI 305 B8P B8PA B8PAISI 321 B8T B8TA B8TAISI 304N B8LN B8LNA B8NAISI 316N B8MLN BMNLNA B8MN


Nuts Machined Soln. Strain(High Pressure and Temperature Service) From Bar Forged Treat Harden

ASTM A194 AISI 510 3 3A(Heat treated)AISI 410 6 6B(Heat treated)AISI 304 8 8B 8A 8AISI 347 8C 8CB 8CA 8CAISI 316 8M 8MB 8MA 8MAISI 321 8T 8TB 8TA 8TAISI 303 or 303Se 8F 8FB 8FA 8FAISI 305 8P 8PB 8PA 8PAISI 304N 8N 8NB 8NA 8NAISI 316N 8MN 8MNB 8MNA 8MNXM19 8R 8RB 8RAAISI 304 low C 8LN 8LNB 8LNAAISI 316 low C 8MLN 8MLNB 8MLNA

A S T M A L L O Y G R A D E T E M P E RS P E C I F I C A T I O N D E S C R I P T I O N M A R K I N G C O N D I T I O N

Bolts, Hex Cap Screws and Studs(General Corrosion Resistant Service)

ASTM 593 AISI 304, 305, 384, XM7 1 CWAISI 316 2 CWAISI 321, 347 3 CWAISI 430 4 AAISI 431 5 HAlloy 630 6 AH

NOTE: Unless otherwise specified on the inquiry or order, fasteners will be supplied in the above condition.

Key

1. Classes I & IB: Carbide solution1. treated (annealed)

Classes IA & IC: Carbide solution treated in the finished condition.Class II: Strain hardened condition

2. Carbide solution treated.3. Carbide solution treated in the 3. finished condition.

Key

CW coldworkedA annealed or solution annealedH hardened and tempered atH 1050F minimumAH age hardened

F A S T E N E R M A R K I N G S


19


Nuts(General Corrosion Resistant Service)

ASTM A594 AISI 303 or 303Se, 304, 305AISI 384, XM1, XM7 1AISI 316 2AISI 321 3AISI 430, 430F 4AISI 410, 416, 416Se 5AISI 431 6Alloy 630 7

Note: The same markings are used for ASTM Specification F593 (Bolts, Hex Cap Screws and Studs)


Metric Nuts

ASTM A836 AISI 303, 304, 305,AISI 384, XM1, XM7 A1-50 A

A1-70 CWA1-80 M

AISI 321, 347 A2-50 AA2-70 CWA2-80 M

AISI 316 A4-50 AA4-70 CWA4-80 M

AISI 430, 430F F1-45 MC1-70 H565C1-110 H275

AISI 431 C3-80 H565C3-120 H275

AISI 416, 416Se C4-70 H565C4-110 H275

Alloy 630 P1-90 AH


(Metric Bolts, Hex Cap Screws and Studs)

ASTM F738 AISI 303, 303Se, 304, 305,AISI 384, XM1, XM7 A1-70 CW

A1-80 MAISI 321, 347 A2-50 A

A2-70 CWA2-80 M

AISI 316 A4-50 AA4-70 CWA4-80 M

AISI 410 C1-50 MC1-70 H565C1-110 H275

AISI 431 C3-80 H565C3-120 H275

AIAI 416, 416Se C4-50 MC4-70 H565C4-110 H275

AISI 430, 430F F1-45 AF1-60 CW

Key

A Machined from ann. or soln. ann stock and re-annealed

M Machined from strain hardened stock.

CW Cold workedH565 Hardened and tempered

at 565CH275 Hardened and tempered

at 275CAH Solution annealed and age

hardened after forming

Key

A Headed and rolled from annealed stock andre-annealed

M Machined from strain hardened stock

CW Cold WorkedH580 Hardened and tempered

at 565C min.H275 Hardened and tempered

at 275C min.


20

FASTENER BASICS

An analysis of standardfasteners, such as boltsand screws, reveals that allhave certain characteristicsin common. Further, their dif-ferences can be classied asshown here. Each bolt andscrew is, in eect, made up ofa series of component parts;thus, the fasteners may havesome or all of these: (a) ahead; (b) a driving recess; (c)a shoulder; (d) an unthreadedshank; (e) a threaded shank;and (f) a point.

Certain combinations of thesecomponents, because ofusage are considered stan-dard. Others are non-stan-dard, but nearly any combina-tion can be readily produced.

This analysis of fastener partsis presented in the hope thatit will assist the user in under-standing and specifying boltsand screws.

Source: ITT Harper


D I R E C T O R Y O F F A S T E N E R M A N U F A C T U R E R S


ssina - designer's handbook - stainless steel fasteners

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