National Standard of the Peoples Republic of China

GB 700-88

Carbon structural steels ( extract )

5 Technical requirements

5.1 Type and chemical composition

5.1.1 Steel type and chemical composition (melting analysis) shall accord with Table 1.

Table 1

Type Grade

Chemical composition% Deoxidization

method C Mn Si S P

maximum

Q195 - 0.060.12 0.250.50 0.30 0.050 0.045 FbZ

Q215 A

0.090.15 0.250.55 0.30 0.050

0.045 FbZ B 0.045

Q235

A 0.140.22 0.300.651)

0.30

0.050 0.045 FbZ

B 0.120.20 0.300.701) 0.045

C 0.18 0.350.80

0.040 0.040 Z

D 0.17 0.035 0.035 TZ

Q255 A

0.180.28 0.400.70 0.30 0.050

0.045 Z B 0.045

Q275 - 0.280.38 0.500.80 0.35 0.050 0.045 Z

Note: 1) For Q235A.B boiling steel the upper limit of Mn Content is 0.60%.

5.1.1.1 For boiling steel the Si shall be not more than 0.07%, for solid steel the Si shall be not

more than 0.17%,for solid steel the minimum content of Si is 0.12%.

5.1.1.2 D grade steel shall has adequate elements which could come into being crystal pattern, for

instance Als shall not less than 0.015% or Alt is not less than 0.020%.

5.1.1.3 For contents of impurities Cr, Ni, Cu shall all be not more than 0.30%, for Oxygen

converter steel N shall not more than 0.008%, it could not make analysis in case the supplier

promised.

For A grade steel the content of Cu may not more than 0.35% in case the demander accepted,

meanwhile the supplier shall finish Cu analysis of steel and indicate the content in the Quality

Certificate.

5.1.1.4 Residual content of As of steel shall not more than 0.080%. For steel that formed from

pig-iron smelting with mineral rich of As , the As content could be negotiated by both supplier and

demander. In case there is no As in the raw material, the As analysis is not necessary.

5.1.1.5 For content of C, Mn of all types of A grade steel and other class steel, the lower limit is

not conditions of delivery, and the content of C, Mn (melting analysis) shall be indicated in the

Quality Certificate, however the prior basis is the mechanical properties of steel shall accord with

this standard.

5.1.1.6 The supplier shall guarantee the chemical composition (melting analysis) accord with the

table 1 while they supply the steel ingot (including continuous casting blank) and billet steel. To

make the properties of rolled steel comply with this standard, the chemical composition of all

types of A, B grade steel could be adjusted according to the demander` s requirements which

could sign other agreements.

5.1.2 The chemical composition tolerance of finished steel and billet steel shall accord with table 1

of standard GB 222.

It shall not guarantee the chemical composition tolerance of finished steel which made from

boiling steel, so does the billet steel.

5.2 Smelting method

Steel shall be smelted by oxygen converter, open hearth furnace, or electric furnace and indicated

in the contract. The smelting method generally determined by the supplier.

5.3 Delivery status

It generally delivery the steel with hot rolled steel status (including controlled rolling). In case the

demander require, normalizing treatment status is accepted under the negotiation(A grade steel

excluded).

5.4 Mechanical properties

5.4.1 Tensile test and impact test shall accord with table 2, bend test shall accord with table 3.

Table 2

Type Grade

Stretching test Impact test

Yield pointsN/mm2 Tensile

strength

N/mm2

Elongation5%

Temperature

Charpy

V-Notc

h

Impact

Test

J

ThicknessDiametermm ThicknessDiametermm

16

>16

40

>40

60

>60

100

>100

150

>150 16

>16

40

>40

60

>60

100

>100

150

>15

0

minimum minimum minim

um Q195 - (195) (185) - - - - 315390 33 32 - - - - - -

Q215 A

215 205 195 185 175 165 335410 31 30 29 28 27 26 - -

B 20 27

Q235

A

235 225 215 205 195 185 375460 26 25 24 23 22 21

- -

B 20

27 C 0

D -20

Q255 A

255 245 235 225 215 205 410510 24 23 22 21 20 19 - -

B 20 27

Q275 - 275 265 255 245 235 225 490610 20 19 18 17 16 15 - -

Table 3

Type Sample direction

Cold bend test B=2 180

ThicknessDiametermm

60 >60100 >100200

the diameter of curve center d

Q195 longitudinal 0

- - lateral 0.5

Q215 longitudinal 0.5 1.5 2

lateral 2 2.5

Q235 longitudinal 2 2.5

lateral 1.5 2.5 3

Q255 2 3 3.5

Q275 3 4 4.5

Note: B is the width of the sample, is the thickness of the steel (diameter).

5.4.1.1 The yield point of type Q195 is for reference ,it is not conditions of delivery.

5.4.1.2 It shall use lateral samples of steel sheet and steel strip while carrying out the stretching

and bending tests, percentage of elongation could be 1% less than that of table 2 (absolute value) ,

however, structural steel shall use longitudinal samples.

5.4.1.3 The cold bend test of all types of A grade steel is only carried out the demander required.

The upper limit of tensile strength could not be regarded as conditions of delivery.

5.4.2 Charpy ( V notched specimens) impact test shall accord with the table 2.

5.4.2.1 Charpy ( V notched specimens) absorption energy shall be arithmetic average of one serial

which is three samples` single value, only allow one samples` single value be less than specified

value and could not be less than 70% of specified value.

5.4.2.2 The test result could not be less than 50% of specified values while carrying out the impact

test using small samples of 5mm*10mm*55mm.

5.4.3 The thickness (diameter) generally is not more than 25mm while to get the B grade steel of

all types by rolling boiling steel.

5.5 Surface quality

Surface quality of steel shall accord with the related standards and regulations.

6 Test methods

6.1 The test items, samples quantities, sampling method and test method of each batch steel shall

accord with table 4.

Table 4

No. Item Samples quantity

pcs Sampling method Test method

1 Chemical analysis

1

each furnace

number

GB 222

GB 223.1223.5

GB 223.8223.12

GB 223.18223.19

GB 223.23223.24

GB 223.31223.32

GB 223.36 2 tension 1

GB 2975

GB 228GB 6397

3 Cold bend GB 232

4 Normal temperature

impact 3

GB 2105

5 Low-temperature

impact GB 4159

6.1.1 Making the thickness of samples to 20mm by one side shaping and the diameter of curve

center shall accord with table 3 while the thickness or diameter of cold bend test steel is more than

20mm. The undone side shall be the out side while testing. The diameter of curve center shall add

another thickness than that of table 3 while the samples are undone.

6.1.2 The longitudinal axis of impact samples shall be paralleled to rolling direction.

6.1.3 While carrying out the impact test, if the thickness of steel sheet, steel strip, structural steel

is not less than 12mm or the diameter of bar steel is not less than 16mm, it shall apply

10mm*10mm*55mm samples. While carrying out the impact test, if the thickness of steel sheet,

steel strip, structural steel is 6mm to 12mm or the diameter of bar steel is 12mm to 16mm, it

shall apply 5mm*10mm*55mm samples. Impact samples may maintain one rolling plane.

7 Test rules

7.1 Steel shall be inspected and checked and accepted by bureau of quality and technical

supervision.

7.2 Steel shall be checked and accepted by each batch which is same type, same furnace number,

same grade, same measurement, same delivery status and each batch is not more than 60t.

Steel smelted by furnace which nominal volume is not more than 30t or rolled from

continuous casting blank, which the A grade or B grade steel has same type and same smelting

method and casting method could mix to one batch, however each batch shall has not more than 6

furnace number, the tolerance of C content among different furnace number is not more than

0.02% and Mn is not more than 0.15%.

7.3 It shall choose another serial samples which is same batch to do impact test if Charpy ( V

notched specimens) impact result did not accord with the 5.4.2, the arithmetic average of the six

samples (both former serial and later serial)shall not less than specified values, two samples`

single values are less than specified values is accepted, however , only allow one samples` single

value less than 70% of specified value.

7.4 Re-test and check and acceptance of other items of steel shall accord with GB 247 and

GB2101.