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GB/T 20887 consists of the following five parts under the general title Continuously hot rolled high strength steel sheet and strip for automobile:
——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.
This is Part 3 of GB/T 20887.
Annexes A and B of this part are informative.
This part was proposed by China Iron and Steel Association.
This part is under the jurisdiction of National Technical Committee on Iron and Steel of Standardization Administration of China.
Continuously hot rolled high strength steel sheet and strip for automobile - Part 3: Dual phase steel
1 Scope
This part specifies the classification and code, dimension, shape, weight, technical requirements, inspection and test, packaging, marking, quality certificate, etc. of continuously hot rolled dual phase steel sheet and strip.
This part is applicable to the continuously hot rolled dual phase steel strip with thickness not greater than 6mm, as well as the steel sheet and the silt wide strip respectively formed by cutting such steel strip horizontally and vertically (hereinafter referred to as steel sheet and strip).
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this part. For dated references, subsequent amendments (excluding corrections), or revisions, of any of these publications do not apply. However, parties to agreements based on this part are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest editions apply to this part.
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 - Chrom 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 223.53 Methods for chemical analysis of iron, steel and alloy - The flame atomic absorption spectrophotometric method for the determination of copper content
GB/T 223.54 Methods for chemical analysis of iron, steel and alloy - The flame atomic absorption spectrophotometric method for the determination of nickel content
GB/T 223.59 Iron, steel and alloy - Determination of phosphorus content - Bismuth phosphomolybdate blue spectrophotometric method and antimony phosphomolybdate blue spectrophotometric method
GB/T 223.60 Methods for chemical analysis of iron, steel and alloy - The perchloric acid dehydration gravimetric method for the determination of silicon content
GB/T 223.62 Methods for chemical analysis of iron, steel and alloy - The butyl acetate extraction photometric method for the determination of phosphorus content
GB/T 223.63 Methods for chemical analysis of iron, steel and alloy - The sodium (potassium) periodate photometric method for the determination of manganese content
GB/T 223.64 Iron, steel and alloyed - Determination of manganese content - Flame atomic absorption spectrometric method
GB/T 223.78 Methods for chemical analysis of iron, steel and alloy - Curcumin spectrophotometric method for the determination of boron content
GB/T 228 Metallic materials - Tensile testing at ambient temperature
GB/T 247 General rule of package, mark and certification for steel plates (sheets) and strips
GB/T 709 Dimension, shape, weight and tolerance for hot-rolled steel strip, plate and sheet
GB/T 2975 Steel and steel products - Location and preparation of samples and test pieces for mechanical testing
GB/T 4336 Standard test method for spark discharge atomic emission spectrometric analysis of carbon and low - Alloy steel (routine method)
GB/T 5028 Metallic materials - Sheet and strip - Determination of tensile strain hardening exponent (n-values)
GB/T 6394 Metal-methods for estimating the average grain size
GB/T 8170 Rules of rounding off for numerical values & expression and judgment of limiting values
GB/T 10561 Steel - Determination of content of nonmetallic inclusions - Micrographic method using standards diagrams
GB/T 17505 Steel and steel products - General technical delivery requirements
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 20126 Unalloyed steel - Determination of low carbon content - Part 2: Infrared absorption method after combustion in an induction furnace (with preheating)
GB/T 24174 Steel - Determination of bake-hardening-index (BH2)
3 Terms and definitions
For the purposes of this part, the following term and definition apply.
3.1
dual phase steels (DP)
steel with its microstructure mainly composed of ferrite and martensite, with martensite structure dispersively distributed like an island around the ferrite matrix, characterized as no aging, low yield ratio, high work hardening index and bake-hardening-index
4 Classification and code
4.1 The designation of steel is composed of three parts: the initial capital letters of “Hot Rolled”, i.e. “HR”, the specified minimum yield strength/specified minimum tensile strength, and the initial capital letters of “Dual phase”, i.e. “DP”.
Example: HR450/780DP
HR——the initial capital letter of “Hot Rolled”;
450/780——450: the specified minimum yield strength; 780: the specified minimum tensile strength, in MPa;
DP——the initial capital letter of "Dual phase".
4.2 The surface conditions of steel sheet and strip are classified as hot rolled and hot rolled pickled, and the latter is indicated with “P”.
4.3 The surfaces of steel sheet and strip are classified as ordinary (FA) and superior (FB) in accordance with surface quality.
5 Ordering information
5.1 The user shall provide the following information when ordering:
a) product name (steel sheet or strip);
b) number of this part;
c) designation;
d) specification, dimension and unevenness precision;
e) surface condition and surface quality grade;
f) edge condition;
g) packing method;
h) weight;
i) other requirements.
5.2 When ordering, if the surface condition is not stated, the goods shall be delivered with hot rolled surface. The goods with hot rolled pickled surface shall be delivered as oiled unless otherwise specified.
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Classification and code
5 Ordering information
6 Dimension, shape, weight and tolerance
7 Technical requirements
8 Inspection and test
9 Packaging, marking and quality certificate
10 Rounding off of numerical values
11 Comparison of designations in this part and those in foreign standards
Annex A (Informative) Reference value of chemical composition
Annex B (Informative) Comparison of designations in this part and those in foreign standards
