GB/T 20887.4-2022Continuously hot rolled high strength steel sheet and strip for automobile—Part 4: Transformation induced plasticity steel (English PDF)

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 transformation induced plasticity steel sheet and strip for automobile.

This document applies to continuously hot rolled transformation induced plasticity steel strips 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

GB/T 8170 Rules of Rounding off for Numerical Values and Expression and Judgement of Limiting Values

GB/T 10561 Steel - Determination of Content of Nonmetallic Inclusions - Micrographic Method Using Standards Diagrams

GB/T 13298 Inspection methods of microstructure for metals

GB/T 17505 Steel and Steel Products - General Technical Delivery Requirements

GB/T 18253-2018 Steel and steel products - Types of inspection documents

GB/T 20066 Steel and iron - Sampling and preparation of samples for the determination of chemical composition

GB/T 20123 Steel and iron - Determination of total carbon and sulfur content - Infrared absorption method after combustion in an induction furnace (routine method)

GB/T 20125 Low-alloy steel - Determination of multi-element contents - Inductively coupled plasma atomic emission spectrometric method

GB/T 24174 Steel - Determination of Bake-Hardening-Index (BH)

GB/T 38813 General requirements for hot-rolled pickled steel sheet and strip

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:

a) Product name (steel sheet or strip);

b) Number of this document;

c) Designation;

d) Specification and dimension, roughness accuracy;

e) Surface state (Pickled surface is represented by the code "P");

f) Surface quality level;

g) Edge state;

h) Tensile specimen's dimension (When the specimen dimension is not specified, use L0=50 mm, b0=25 mm);

7.3.1 Steel sheets and strips are delivered in hot rolled state.

7.3.2 When the steel sheet and strip have a hot rolled pickled surface, they are usually supplied oiled. The oil film applied shall be able to be removed with an alkaline aqueous solution. Under the usual package, transportation, handling, and storage conditions, the supplier shall ensure that, within 3 months from the date of completion of manufacture, the surface of steel sheet and strip will not rust. After negotiation between the supplier and the purchaser, and indicated in the contract, the hot rolled pickled surface can also be supplied without oil.

Note: For non-oiled products required by the purchaser, rust may occur. During transportation, handling, storage and use, the surface is prone to slight scratches.