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GB/T 20887 consists of the following 7 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;
——Part 6: Complex phase steel;
——Part 7: Steels for hydraulic forming.
This is Part 6 of GB/T 20887.
This part is drafted in accordance with the rules given in GB/T 1.1-2009.
This part was proposed by China Iron and Steel Association.
This part was prepared by SAC/TC 183 (Technical Committee on Steel of Standardization Committee of China).
Continuously hot rolled high strength steel sheet and strip for automobile - Part 6: Complex phase steel
1 Scope
This part of GB/T 20887 specifies the classification and designation, order information, dimensions, shape, weight, technical requirements, test methods, inspection rules, packaging, marking and inspection certificate of the continuously hot rolled high strength complex phase steel sheet and strip, hereinafter referred to as steel sheet and strip.
This part is applicable to the steel strip, sheet and slit strip used for making automotive structural parts and reinforcement parts with the nominal thickness less than 8 mm.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
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 223.11 Iron, steel and alloy - Determination of chromium content - Visual titration or potentiometric titration method
GB/T 223.17 Methods for chemical analysis of iron, steel and alloy - The diantipyryl methane photometric method for the determination of titanium content
GB/T 223.26 Iron, steel and alloy - Determination of molybdenum content - The thiocyanate spectrophotometric method
GB/T 223.40 Methods for chemical analysis of iron,steel and alloy; The anion-exchange separation-sulphochlorophenol S photometric method for the determination of niobium content
GB/T 223.58 Methods for chemical analysis of iron, steel and alloy - the extraction-absorption catalytic polarographic method for the determination of manganese 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 223.68 Methods for chemical analysis of iron, steel and alloy-The potassium iodate titration method after combustion in the pipe furnace for the determination of sulfur content
GB/T 223.69 Iron, steel and alloy - Determination of carbon contents - Gas-volumetric method after combustion in the pipe furnace
GB/T 223.75 Iron, steel and alloy - Determination of boron content - Methanol distillation-curcumin photometric method
GB/T 223.76 Methods for chemical analysis of iron, steel and alloy - The flame atomic absorption spectrometric method for the determination of vanadium content
GB/T 228.1-2010 Metallic materials - Tensile testing - Part 1: Method of test at room temperature
GB/T 247 General rule of package, mark and certification for steel plates (sheets) and strips
GB/T 709 Dimensions, shape, weight and tolerances for hot-rol1ed steel plates and sheets
GB/T 2975 Steel and steel products - Location and preparation of test pieces for mechanical testing
GB/T 4336 Carbon and low-alloy steel - Determination of multi-element contents - Spark discharge atomic emission spectrometric method (routine method)
GB/T 6394 Determination of estimating the average grain size of metal
GB/T 8170 Rules of rounding off for numerical values & expression and judgement 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 24524 Metallic materials - Sheet and strip - Hole expanding test
3 Terms and definitions
For the purposes of this part, the following terms and definitions apply.
3.1
complex phase steel; CP
steel with a microstructure containing ferrite or bainite matrix, whereas a small amout of martensite, retained austenite or pearlite may be present as additional phases. The steel was strengthened by fine grained microstructure or precipitates of microalloy elements. Compared to dual phase steels with same tensile strength level, they show a higher yield strength and good hole expansion ratios
4 Classification and designation
4.1 Classification
4.1.1 Steel sheet and strip are classified as hot-rolled and hot-rolled pickled in accordance with surface condition. Hot-rolled pickled surface condition shall be indicated with ‘P’.
4.1.2 Steel sheet and strip are classified as normal (FA) and improved (FB) in accordance with surface quality.
4.2 Designation
Designation of steel sheet and strip shall be indicated with the initial capital letter ‘HR’ of ‘Hot Rolled’, the specified minimum yield strength/specified minimum tensile strength, and the initial capital letter ‘CP’ of ‘Complex Phase’.
Example: HR660/760CP
HR—the initial capital letter of ‘Hot Rolled’.
660/760—the specified minimum yield strength/specified minimum tensile strength, in MPa.
CP—the initial capital letter of ‘Complex Phase’.
5 Order information
5.1 The contract or order covered by this part shall include the following information:
a) product type (sheet or strip);
b) the number of this part;
c) steel grade;
d) nominal dimension, flatness tolerance;
e) surface quality type;
f) surface condition (‘P’ for pickled surface);
g) edge condition;
h) packaging type;
i) mass;
j) application;
k) other requirements.
5.2 In case where the requirements for surface condition, thickness tolerances, surface quality, edge condition and oiling condition are not indicated in the contract, the product shall be supplied in hot-rolled surface, normal thickness tolerances, normal surface quality (FA), cut edge and oiled condition. In case where the requirements for surface quality and oiling condition are not indicated in the contract for pickled surface, the product shall be supplied in improved surface quality (FA) and oiled condition.
6 Dimensions, shape, weight
The nominal dimensions, shape, weight and tolerances shall be in accordance with GB/T 709.
7 Technical requirements
7.1 Chemical composition
7.1.1 For the recommended chemical composition (heat analysis), see Annex A. When requested at the time of ordering, the chemical composition shall be agreed between the manufacturer and purchaser. For the comparison of steel grades among this part and other relevant standards, see Annex B.
7.1.2 The permissible deviations of the product analysis on the specified value of the heat analysis shall be in accordance with GB/T 222.
7.2 Steelmaking process
The steel shall be made by Basic Oxygen Furnace (BOF) or electric furnace. Unless otherwise agreed, the steel making processes shall be at the manufacturer's option.
7.3 Delivery condition
7.3.1 The products are normally supplied in hot-rolled condition.
7.3.2 The pickled products are normally delivered in oiled condition. The layer of oil shall be capable of being removed by alkaline solutions or usual solvents. The manufacturer shall ensure that under normal conditions of packaging, transportation, handling and storing, the products show no corrosion for up to 3 months from the date on which the products are made available at the manufacturer’s work. If the purchaser does not require the pickled surface to be oiled, this shall be agreed by both sides and indicated in the contract.
Note: The product delivered in unoiled condition, required by the purchaser, may show corrosion and light scratches during transportation, handling, storage and application.
7.4 Mechanical properties
The mechanical properties of steel sheet and strip shall be as specified in Table 1.
Foreword I
1 Scope
2 Normative references
3 Terms and definitions
4 Classification and designation
5 Order information
6 Dimensions, shape, weight
7 Technical requirements
8 Test methods
9 Inspection rules
10 Packaging, marking and quality certificate
Annex A (annex informative) Chemical composition
Annex B (annex informative) Comparison of steel grades
