GB/T 20887.2-2022Continuously hot rolled high strength steel sheet and strip for automobile—Part 2: High hole expansion steel (English PDF)

Foreword

This document is drafted in accordance with GB/T 1.1-2020 "Directives for standardization - Part 1: Rules for the structure and drafting of standardizing documents".

This document is Part 2 of GB/T 20887 "Continuously hot rolled high strength steel sheet and strip for automobile". GB/T 20887 has issued the following parts.

- Part 1: High yield strength steel for cold forming;

- Part 2: High hole expansion steel;

- Part 3: Dual phase steel;

- Part 4: Transformation induced plasticity steel;

- Part 5: Martensitic steel;

- Part 6: Complex phase steel;

- Part 7: Steels for hydraulic forming.

This document replaces GB/T 20887.2-2010 "Continuously hot rolled high strength steel sheet and strip for automobile - Part 2: High hole expansion steel". Compared with

GB/T 20887.2-2010, in addition to structural adjustments and editorial changes, the main technical changes are as follows.

a) Change the term and definition of high hole expansion steel (see 3.1; 3.1 of the 2010 edition);

b) Add HR380/540HE, HR520/680HE, and HR780/980HE designations and their corresponding technical requirements (see Table 1 and Table 2);

c) Add the provisions for chemical composition (see Table 1);

d) Add the provisions for the guaranteed time of mechanical properties (see 7.4);

e) Add the provisions for the upper limit of tensile strength (see Table 2);

f) Change HR440/580HE upper limit of yield strength AND elongation after fracture with gauge length of 80 mm (see Table 2; Table 1 of the 2010 edition);

g) Add the provisions for elongation after fracture with a gauge length of 50 mm; add the regulation that the specified minimum elongation after fracture is reduced by 2% when the thickness is <=3 mm (see Table 2);

h) Add the requirement that the quality of pickled surface after negotiation can also be implemented in accordance with the provisions of GB/T 38813 (see 7.5.4);

i) Add special requirements that tensile strain hardening exponent and metallographic microstructure inspection can be added (see 7.6);

j) Change the lot grouping weight from 40 t to 60 t (see 9.2; 8.5 of the 2010 edition);

k) Add the provisions for inspection document type (see Clause 10).

1 Scope

This document specifies the terms and definitions, classification and designation representation method, order content, dimension, shape, weight, technical requirements, test methods, inspection rules, package, mark and certification of continuously hot rolled high-strength high hole expansion steel sheet and strip for automobile.

This document applies to continuously hot rolled steel strips with high hole expansion property with a thickness of not more than 6.0 mm, steel sheets cross-cut from them, and longitudinally-cut steel strips (hereinafter referred to as "steel sheets and strips").

2 Normative references

The contents of the following documents, through normative references in this text, constitute indispensable provisions of this document. Among them, for dated references, only the edition corresponding to that date applies to this document. For undated references, the latest edition (including all amendments) applies to this document.

GB/T 222 Permissible Tolerances for Chemical Composition of Steel Products

GB/T 223.5 Steel and Iron - Determination of Acid-Soluble Silicon and Total Silicon Content - Reduced Molybdosilicate Spectrophotometric Method

GB/T 223.9 Iron, steel and alloy - Determination of aluminium content - Chrome azurol S photometric method

GB/T 223.12 Methods for chemical analysis of iron, steel and alloy - The sodium carbonate separation-diphenyl carbazide photometric method for the determination of chromium content

GB/T 223.23 Iron, steel and alloy - Determination of nickel content - The dimethylglyoxime spectrophotometric method

GB/T 223.26 Iron, steel and alloy - Determination of molybdenum content - The thiocyanate spectrophotometric method

3 Terms and definitions

The following term and definition applies to this document.

4 Classification and designation representation method

5 Order content

5.1 Contracts or orders placed according to this document shall include the following.

5.2 If the information such as surface state and thickness accuracy is not specified in the order contract, it shall supply those with hot rolled surface and ordinary thickness accuracy.

6 Dimension, shape, weight

The dimension, shape, weight and tolerance of steel sheets and strips shall comply with the provisions of GB/T 709.

7 Technical requirements

8 Test methods

8.1 The chemical composition tests of steel are generally carried out according to the chemical analysis methods of GB/T 4336, GB/T 20123, GB/T 20125 or general methods.

8.2 The inspection items and test methods of steel sheets and strips shall comply with the requirements of Table 4.

9 Inspection rules

9.1 The inspection and acceptance of steel sheets and strips shall be carried out by the quality inspection department of the supplier.

9.4 The re-inspection and determination rules for steel sheets and strips shall comply with the provisions of GB/T 17505.

9.5 The test results of chemical composition and mechanical properties are rounded according to the rounding value comparison method. The rules of rounding off shall be in accordance with the provisions of GB/T 8170.

10 Package, mark and certification

The package, mark and certification of steel sheets and strips shall comply with the provisions of GB/T 247.

Appendix A (Informative)

Comparison of similar designations at home and abroad The comparison between the designations in this document and those in GB/T 20887.2- 2010 and similar designations in foreign standards is shown in Table A.1.