GB/T 20887.4-2022 English PDF (GBT20887.4-2022)

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GB/T 20887.4-2022: Continuously hot rolled high strength steel sheet and strip for automobile -- Part 4: Transformation induced plasticity steel
GB/T 20887.4-2022
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 77.140.50
CCS H 46
Replacing GB/T 20887.4-2010
Continuously hot rolled high strength steel sheet and strip
for automobile - Part 4: Transformation induced plasticity
steel
ISSUED ON: APRIL 15, 2022
IMPLEMENTED ON: NOVEMBER 01, 2022
Issued by: State Administration for Market Regulation;
Standardization Administration of the PRC.
Table of Contents
Foreword ... 3 
Introduction ... 5 
1 Scope ... 7 
2 Normative references ... 7 
3 Terms and definitions ... 9 
4 Classification and designation representation method ... 9 
5 Order content ... 10 
6 Dimension, shape, weight ... 11 
7 Technical requirements ... 11 
8 Test methods ... 13 
9 Inspection rules ... 14 
10 Package, mark and certification ... 14 
Appendix A (Informative) Comparison of similar designations at home and abroad . 16 
Bibliography ... 17 
Continuously hot rolled high strength steel sheet and strip
for automobile - Part 4: Transformation induced plasticity
steel
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.
3.1
Transformation induced plasticity steel
A steel whose microstructure is mainly ferrite, bainite, and retained austenite, and the
retained austenite of which can be transformed into martensite during the forming
process.
Note: Transformation induced plasticity steel has higher work hardening rate, uniform elongation
and tensile strength.
4 Classification and designation representation method
4.1 Classification
4.1.1 According to the surface state, steel sheets and strips are classified into:
a) Hot rolled surface;
b) Hot rolled pickled surface. When the surface state is hot rolled pickled surface, it
is represented by the code "P".
4.1.2 According to the surface quality, steel sheets and strips are classified into:
a) Ordinary surface (FA);
b) Relatively-advanced surface (FB).
4.2 Designation representation method
The designation of the steel sheets and strips is composed of three parts: The initials
"HR" of the English "Hot Rolled"; the specified minimum yield strength value/the
specified minimum tensile strength value; the first two letters "TR" of the English
"Transformation".
Example: HR400/590TR
HR - The initials of the English "Hot Rolled";
400/590 - 400 is the specified minimum yield strength value; 590 is the specified minimum tensile
strength value; in megapascals (MPa);
TR - The first two letters of the English "Transformation".
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.
7.4 Mechanical properties
The supplier shall guarantee that, within 6 months from the date of completion of
manufacture, the mechanical properties of the steel sheet and strip shall comply with
the provisions of Table 2.
Note: Due to the influence of aging, the mechanical properties of steel sheets and strips will change
with the prolongation of storage time; such as the increase of yield strength and tensile
strength, the decrease of elongation after fracture, the deterioration of formability, and the
appearance of tensile strain marks, etc. It is recommended that users use it as soon as possible.
7.5 Surface quality
7.5.1 On the surface of the steel sheet and strip, there shall be no defects such as cracks,
scars, folds, bubbles and inclusions that are harmful to use. There shall be no visible
delamination on the steel sheet and strip.
7.5.2 The surface quality of steel sheets and strips shall comply with the require...