PNL-SA--19953

DE93 004834

MECHANICALPROPERTIESOF MARTENSITICALLOY AlSl 422

M. L. HamiltonF. H HuangW. Hu

June 1992

Presented at the

16th International _,_ . _Symposium on £ffects of ...." _ ' ....Radiation on MaterialsJune 22-24, 1992Denver, Colorado

Prepared forthe U.S. Department of Energyunder Contract DE-ACO6-76RLO 1830

i,¸, . ,. .

Pacific Northwest Laborator__-,_._ ,_Richland, Washington 99352 _,::_,_x.:_.,,

,| D|STRIBUTION OF THIS DOCUMENT I$ UNLI_

Margaret L. Hamilton, 1'2 FraiLk II. }lual_g, 3 axld Wan-l.iang Hu 3

I

MECIIANICAL PROPEl{TIES OF MAICI'ENSI'/'IC ALI.OY AISI 4"22

REFERENCE: Hamilton, M. L., Huang, F. H., and Hu, W. L., "Mechanical

Properties of Martensitic Alloy AISI 422," Effects of Radiation on

Materials: 16th_/International Symposium, ASTM STP 1175, Arvind S.Kumar, David S. Gelles, and Randy K. Nanstad, Editors, American Society

for Testing and Materials, Philadelphia,_1993.

ABSTRACT: HT9 is a martensitic stainless steel that has been considered

for structural applications in liquid me,_al 1-eactors (LMRs) as well asin fusion reactors._ AISI 422 is a commercially available martensitic

stainless steel that closely resembles HT9, and was studied briefly

under the auspices of the U.S. LMR prog_'am. P1-eviously unpublishedtensile, fracture tougl,ness and cl_a[py impact data ol, AISI 422 were

_:_xamined for- potential insights il-lto tl_e col,sequences of tl_e,kcompositional diffe_-e,:ces between the two alloys, pa_-ticularly with

respect to current questions concerning the o_-igin of the radiation-induced embrittlement observed in HT9.

KEYWORDS: ferritic/ma['tensitic stainless steels, mechanical properties,

tensile prope_'ties, toughness, impact bellavior, _-adi at ion- inducedemb_- it t iement

INTRODUCTION

}|T9 is a martensitic sta]llle_ _tu_] tl,at ll_s t._n consJdeL'ed fo_-

structural applications in liquid metal reactors (LHRs) and is curL'ently

under consideration for similar- _pplications in fusion reactors. The

U.S. LMR program was interested in establishing the properties and

irradiation-induced changes in behavior- of ai_ American alloy that

closely _esembles HT9, referred to as AISI 422. Only a fraction of the

work originally pr-oposed u1_der the U.S. L_.IR p_-og_'am was completed prior" p._to the termination of the p_-ogram. Due to the sJ.miiaritie__-_4_&_._,

composition between HT9 and 422, however-, and _he _P_ 1h_ HT9 exhibits

irradiation-induced embrittlement)the source of wllich is not completely

understood, it appeared that re, x-amination of the AISI 422 databaseA

iSenior" research scientist, Pacific Northwest Laboratory, P.O. Box

999, Richland, WA 99352

2pacific Northwest Labo_atory is operated _o_- the U.S. Department

of Energy by Battelle Memorial Institute under Coutract DE-AC06-76RLO1830.

3Senior scientists, Westinghouse llanford Company, P.O. Box 1970,

Richland, WA 99352

-i_r

establislled under tl_e 12.H{ [_ogra._ migl_t provide so,,e useful insights

into tlle post-irr_diatiox_ embrittl_m_llt o_ tl_]s class o_ _]]oy.

BACKGROUND

AISI 422 is also referred to as Carpenter 636, AISI 616 and

Unitemp 1420 WM. lt is a hardenable steel that was designed for service

at temperatures up to 650°C. lt is a modification of AISI 420, withadditions of nickel, molybdenum, tungsten and vanadium to impL_ove t|,e

elevated temperature strength and r_sistance to stress corrosioz_

cracking. If,2] The composition of the LMR heat of AISI 422 is compared

to that of a typical LMR heat of HT9 in ']'able i. Note that relative toHT9, AISI 422 contains 60% more manganese, 30% more silicon ax,d nickel,

and more than double the amounts of pliosphorus and tungsten.

TABLE 1--Compositions of AIS] 422 (heat 20818) and HT9 (heat 91353).

, •....

ALLOY C Mn Si I' Cr Ni Mo V I W....... ,_ •

HT9 0.21 0.49 0.22 0.008 11.97 0.57 1.03 0.33 0.52, ,, , ,

422 0.22 0.80 0.29 0.018 11.79 0.80 1.05 0.29 1.16

It is well known that martensitic stainless steels such as HT9 can

exhibit significant embrittle|l|ent following i_'radiation, particularly at

temperatures on the order of 350 to 385_C, where a pronounced increasein strength occurs, lt is not w_ll ui_derstood, |_owever, w_lether the

embrittlement arises primarily fro,t_ the helium-induced cavities or the

precipitation that develops during ir_-adiatioq. Both factors arerelated to the level of nickel present in the alloy, and as suclL are

very difficult to separate clearly. The purpose of this work was

therefore to use the slight compositional variation between }{'I'9and AIS]

422 to glean some insight into the bellavior of HT9 followingirradiation.

EXPERIMENTAL PROCEDURE

A 9½-inch (241.3 mm) long piece of 5_-_-incll (533.35 mm) diameter

AISI 422 bar- stock was purcl_ased in a normalized and tempered condition.

The original ingot, produced by AiTecl; Specialty Steel, was melted in an

electric furnace and refined by argoi_-oxygen decarburization (AOD). A

*-_-round piece of the bar was rolled to two thicknesses (_.4and 1/8 inch

[6.35 and 3.18 nm_]) with intermediate heat treatments similar to those

used for processing HT9. Tl_e final heat treatment for- botl_ thicknesses

comprised austenitizing at i038_C for- 5 minutes aud tempering at 760°Cfor 30 minutes. Both treatments were followed by an air cool. The

final tempered martensite structure had an ASTM grain size of about 8and a Vickers hardness of about 298 DPH (500 g load). No delta ferrite

was present in tl_e heat--treated AISI 422 microstructure, whereas HT9

generally contains about 1% delta ferrite at prior austenite grainboundaries.

Miniature (_-_-size) charpy specimens were maciiined from the tllickersheet stock, while miniature tellsile and compact tension specimens were

machined from the thinner sheet stock according to the drawings given in

Figure i and in the orientations given in Figure 2. Tensile specimens

"x

were tested in tl,e unirradiated condition only at te,uperatu[es rax_ging (_/_# >from 25 to 540_C ax,d a t_omil,a] strall, r_te of 1.5 >."10 -4 s -i. Com[_ac_--tension specimens were irradiated il_ tl,c Fast Flu_: Test F_cility_-400

and -540uC bu_ _ tested Q/fly in tl_e uu_dial e_l +condinJorl, at

temperatures ranging from 25 to 42 /_C, usi£+_g a si**gle specimen

electropotential techr_ique. Char_Jy sl_ecimenb were irradiated at -400°6:in a precracked condition to a fluence of --4 x ]022 n/cm _ (E > 0.i MEV),

or about 17 dpa. Impact tests were performed o[, botl, irradiated ai1d

unirradiated specimens in an itlst_-u,nented dt-op tower. The fracture

energy was normalized against tile area of tl,e f_-actuL-e sub-face. Theductile-brittle transition te|upeL-ature (DBTT) is determined as tli_

midpoint between the upper shelf (USE) and the lower shelf. More

details on each of the test techniques, demonstrating their validity as

applied to miniature specimens, are given in references 3-5.

RESULTS AND DISCUSSION

The tensile data obtained on AISI 422 are slJown in Figure 3 irl

comparison with similar data on }|Tg. lt is evident that AISI 422 is

slightly stronger and somewllat more ductile tl_a,_ 11'i'9in the unirradiatedcondition.

The fracture toughness data obtained from tl_e compact tension

specimens of unirradiated AISI 422 are show,] in Figure 4 in comparison

with similar HT9 data. The tough_;ess of AISI ,122 is higher than that of

HT9, although it should be FLoted that the tearing modulus is 20 to 40

percent lower in AISI 422, depending on the test temperature, rangingfrom 95 at 70°C to 81 at 427uC.

The impact behavior of unJrradiated AISI 422 is compared to that

of HT9 in Figure 5. While tile two data sets aplJcaL- to be very sir_Lilar

, at first glance+ it should be noted tl_at t|_e o_'ientations and heat

treatments of the two types of specimens are dif£erent. While the AISI

422 specimens were fabricated from rolled sheet in the TL orientatiol_,

the HT9 specimens were fabricated from forged bar in the_CR orientation.The difference between these two orientations is shown in Figure 6. The

orientation of the crack f£'ont ar,d the direction of crack propagation

are parallel to the rolling direction it_ the TL AIS_ 422 specimens,

while they are perpendicular" to the working direction in the CR HT9

specimens. In addition, the lIT9 ba_ from wl,icl, tl,e specimens were

machined was in a sligl,tly diffe_-ent condition than tl,at of t|,e AISI 422

sheet, a mill--annealed condition tl_at comprises normalization at i150°C

for more than one l,our followed by l,ot-xvo_-):J,l(3 and temperit_g at 750_Cfor 1 hour.

The similarity between the HT9 and AiSI 422 impact data in theunirradiated condition is somewhat surprising in light o_ the

differences in delta fe].-rite level arid the fact tl,at the AISI 422 is

stronger as well as tougher. The orientation dif._erence ks the only

factor than could account for the similarity, s_nce the difference in

heat treatment is relatively minor. The CR orientation could be

considered as approximating a crack arrest geometry, particula__-ly in the

presence of delta ferrite stringers in HT9, _;he_'eas the TL orientationcould be considered as approximating a cuack divide geometry, where the

crack might be divided along prior austenite grain bounda_-ies.

The similarity between lIT9 and AISI 422 is maintained w_er, bothare i_-radiated at similar temperatures to approzimately tl,e same _]eutro_

exposure, as shown in Figure 7. The }i'I'9specimens were actually

irradiated at -390°C,[7] but the difference between 390 and 400_C is

_i elative to th_ uncertainties in Theirra_l]atioI_ temperature.l_-ecimens were irradiated only to -3 _ lO _' l_/cm-, but since it i_as

been d_monstrated tll_; tllm _llift i_ D[_T']'saturates at _bout fastfluences of 2-3 x i0 _'" xl/cm- iI_ trois temperature zai_ge, [6] ti_e 11'1'9and

AISI 422 data are considered compa_-able.

The data in Figure 7 indicate tl_at the two alloys exhibit tl_e same

shifts in DBTT and USE independent of tl_e orientation differences. The

data also imply that a s,nal] a,uount of delta ferrite llas no effect onthe irradiation-induced shifts in DBTT and USE.

Other data are available, however, on HT9 specimens in the TL

orientation. [8] These data are shown in Figure 8, and indicate that,

while the shift in DBTT and USE are slightly worse in the CR tllan in theTL orientation, the difference between orientations is small relative to

the effect of irradiation itself. SiI_ce the data suggest that there is

no orientation dependence in the irradiation-induced shifts in DBTT and

USE, and since both HT9 (CR) and AISI 422 (TL) exhibit similar shifts inDBTT and USE, one can surmise that the difference between HT9 (TL) and

AISI 422 (TL) in the irradiated condition reflects a difference in the

original condition of the materials rather tl_an an effect of radiation,

i.e., DBTTIIT9(TL) < DB'l'T422(TL ) for unirradiat_d material.

CONCLUSIONS

AISI 422 appears to be as good an alloy as HT9 on the basis of its

strength and fracture toughness properties, but the impact behavior of

AISI 422 does not appear- to be as good as tl_at of }IT9 when orientation

diffe_'ences ar_ taken ii]to accoullt. In addition, tl_e impact b_llavJor orAISI 422 (TL) is worse than tl_at of HT9 (TL) following irradiation to a

saturation fluence. With the mixture of positive and negative results,

it is not really possible to draw firm conclusions concerning the effect

of composition on irradiation-induced changes in behaviorj and no real

insights can be obtained concerning the origin of the irradiation-induced embrittlement obse_-ved in HT9. lt is possible, however, to

specify that the effect of radiation on this class of steel is a general

phenomenon, albeit one tl,at is influenced by the details of processing

procedures and i rradiatio|_ ex_viLo_,m_i,t.

ILEFERENCES

[li Aerospace Structural Metals Handl)oo_i, Code ]403, Belfour Stulen,Inc. , 1972.

[2] #_lloy DJqest, Carpenter 636 Alloy, Filing Code 2".'-294, Engineering

Alloys Digest, Inc. , New Jersey, 1974.

[3] Brager, H. R. , Garner, F. A. , and Hamilton,.. M. L. , Jourl_a] ofNuclear Materials, 133 & ]34, !985, pp. 59d-598.

[4] Hu, W. L., and Gelles, D. S., "Miniature Charpy Impact Test

Results for the Irradiated Ferritic Alloys }12'9 and 9Ct-iMo,"Proceedinqs of AIME Topical Conference on Fer_-Jtic Alloys for Use

in Nuclear Enerqy Techno]oc}ies, June 1983, pp. 631-646.

[5] Huang, F. Ii. , and llamilto_,, M. I,. , .lo_,-_,al c,t l_uc:]ea,- Mat;_.;-Ja]_,]87, 1992 5-'29__ , pp. 27 3.

[6] Hu, W. L., a1_d (;elles, D. S., "T|le Ductil_-to-Brittle Tranuition

Behavior of Martensitic Steels Neutro_l Irradiated to 26 d_a,"

ll,fluence of Radiation ox_ Materi_l Prope_-ti_.s: ]3th ],_te1-_,ati(,l,a

Symposium (Part II), ASTM STP 956, 10'razlk A. Garner, Cl,ar]_s li.

Henager, Jr., and Naolliro Igata, Eds., Americal, Society for

Testing aild Materials, P_iladelphia, 1987.

[7] }Iu, W. L., "Alloy Development for Irradiation Performance"

Semiannual Progress Report for Period Ending September 30, 1982,

DOE/ER-0045/9, PW. 255-271.

[8] }iu, W. L., Alloy Development for Irradiation PerformanceSemiannual Progress Report for Period Ending September 30, 1984,

DOE/ER-0045/13, pp. 106-119.

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States

Government. Neither the United States Government nor any agency thereof, nor any of theiremployees, makes any warranty, express or implied, or assumes any legal liability or responsi.bility for the accuracy, completeness, or usefulness of any information, apparatus, product, orprocess disclosed, or represents that its use would not infringe privately owned rights. Refer-ence herein to any specific commercial product, process, or service by trade name, trademark,manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recom-mendation, or favoring by the United States Government or any agency thereof. The viewsand opinions of authors expressed herein do not necessarily state or reflect those of theUnited States Government or a,y agency thereof.

FIGURE CAPTIONS

i. Dimensions of miniatu_'e AISI 422 specimens. (a) Charpy impact

specimen, (b) Compact tension specimeI_, and (c) Tensile specimen.

All dimensions are given in mm.

2. Orientation of miniature AISI 422 specimens relative to tl,e

rolling direction. The tensile specimen axis was parallel to the

rolling direction. Compact tension and cl,arpy impact specimenswere fabricated in the TL orientation.

3 Ten_i _ at _d _wI! S I 422 _ompared with _imi_ar HT9• le da_a/gn unirradi

data_ (a)I0_ength and (_)_tility. _4. Fracture ttTughness data on.irradiated AISI 422 compared with

similar HT9 data.

5. Impact data on unirradiated AISI 422 (TL) compared with HT9 (CR)data.

6. Orientation differences between cllarpy specimens of AISI 422 (TL)

and HT9 (CR) .

7. Impact data on AISI 42?. (TL) i_:_'adiated to -4 x 1022 n/cre 2 at

-400°C, compared to HT9 data (CR).

8. Additional }IT9 charpy impact data, in t_e TL orientation.

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