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National Standard of the People’s 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 Chemical composition，% Type

Grade

P

Deoxidization method

0.045

F、b、Z

0.045

F、b、Z

0.045

F、b、Z

0.040

0.040

Z

0.035

0.035

TZ

0.045

Z

0.045

Z

Si C

S

Mn maximum

Q195

-

0.06～0.12

0.25～0.50

0.30

0.09～0.15

0.25～0.55

0.30

A Q215

0.050

B

Q235

0.045 1)

0.050

1)

0.045

A

0.14～0.22

0.30～0.65

B

0.12～0.20

0.30～0.70

C

≤0.18

D

≤0.17

0.30 0.35～0.80

A Q255

0.050 0.18～0.28

0.40～0.70

0.30

B Q275

-

0.050

0.045 0.28～0.38

0.50～0.80

0.35

0.050

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 Stretching test Yield pointσs，N/mm

Charpy

，%

2

Type Grade

Impact test Elongationδ5

V-Notc

Tensile

Thickness（Diameter） ，mm >16 ≤16 ～ 40

>40 ～ 60

>60 ～ 100

>100 ～ >150 150

strengthσ 2

N/mm

Thickness（Diameter） ，mm >16 >40 ≤16 ～ ～ 40 60

>60 ～ 100

>100 >15 ～ 0 150

Temperature ℃

h Impact Test

J

minimum Q195 Q215

A B

(195) (185) 215

205

-

-

-

-

315～390

33

32

-

-

-

-

195

185

175

165

335～410

31

30

29

28

27

26

A Q235

B C

235

225

215

205

195

185

375～460

26

25

24

23

22

Q275

A B -

-

-

20

27

-

-

20

21

0

D Q255

-

minim um -

minimum

-20 255

245

235

225

215

205

410～510

24

23

22

21

20

19

275

265

255

245

235

225

490～610

20

19

18

17

16

15

-

-

20

27

-

-

Table 3 Cold bend test B=2α 180° Type

Sample direction

Thickness（Diameter） ，mm 60

>60～100

>100～200

the diameter of curve center d Q195

longitudinal

0

lateral

0.5α

longitudinal

-

-

0.5α

1.5α

2α

lateral

α

2α

2.5α

longitudinal

α

2α

2.5α

lateral

1.5α

2.5α

3α

Q255

2α

3α

3.5α

Q275

3α

4α

4.5α

Q215

Q235

27

Note: “B” is the width of the sample, “α” 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

1

Chemical analysis

2

tension

3

Cold bend

4 5

Samples quantity， Sampling method pcs 1 （each furnace number）

1

Normal temperature impact Low-temperature

GB 222

Test method GB 223.1～223.5 GB 223.8～223.12 GB 223.18～223.19 GB 223.23～223.24 GB 223.31～223.32 223.366397 GB GB 228、GB GB 232

GB 2975

GB 2105

3

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 “α” 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.