CN102212743A - Low-yield-ratio hot-rolled dual-phase steel plate with tensile strength of 600MPa and manufacturing method thereof - Google Patents

Abstract

The invention relates to a low-yield-ratio hot-rolled dual-phase steel plate with tensile strength of 600MPa and a manufacturing method thereof. The low-yield-ratio hot-rolled dual-phase steel plate comprises the following chemical components in percentage by weight: 0.05-0.08% of C, 0.20-0.40% of Si, 1.30-1.60% of Mn and the balance of Fe. The organizational structure of the steel plate comprises a ferritic structure and a martensitic structure, wherein the volume fraction of the ferrite is 85-90% and the volume fraction of the martensite is 10-15%; the yield strength Rp0.2 is 340-365MPa; the tensile strength Rm is 600-675MPa, and the total elongation A50 after fracture is 26-30%; and the yield ratio (Rp0.2/Rm) is 0.50-0.60, and the product of strength and elongation (Rm*A50) is 15,000-20,000. In the manufacturing method, a controlled rolling and controlled cooling process is adopted for producing the steel plate in a sheet billet continuous casting and rolling production line. The manufacturing method has the advantages that while the tensile strength of the steel plate is maintained at 600MPa, the yield strength of the steel plate is lowered to below 365MPa and the yield ratio of the steel plate is controlled at 0.50-0.60, thereby solving the problem that the service life of a stamping die is shortened to cause increment in the costs of tools and dies when a user uses the steel plate.

Description

A kind of tensile strength 600MPa level low yield strength ratio hot rolling biphase plate and manufacture method

Technical field

The present invention relates to a kind of high-strength steel manufacturing of automobile structure, be specifically related to a kind of tensile strength 600MPa level low yield strength ratio hot rolling biphase plate and manufacture method, belong to technical field of steel rolling.

Technical background

High-strength vehicle is one of domestic and international investigation of materials focus with the exploitation of hot rolling biphase plate always.The tissue characteristic of hot-rolled dual-phase steel is about 15% volume ratio martensitic phase that distributes on ferrite matrix.Before more than 20 year, international and domestic by ways such as Cr-Mo microalloyings, on the old process production line, develop 600MPa level hot-rolled dual-phase steel, on short-flow production line, Mr. Liu Yanchun once developed the low-cost 600MPa level of the C-Mn composition hot rolling biphase plate (patent No.: ZL200610045846.2) in 2006, since 2007, produce in batches in CSP factory of Baogang (CSP line), steam supply car wheel shop makes spoke, in use, because this steel yield strength (Rp0.2) higher (greater than 365MPa) makes press tool shortening in work-ing life to cause the tool and mould cost to improve.By and the user between technical intelligence feedback, through the adjustment to the product processing parameter, yield strength is reduced to below the 365MPa the most at last, exceeds former patented technology indication range fully, yield tensile ratio is controlled between 0.50～0.60, has fundamentally solved user's use problem.

Summary of the invention

The objective of the invention is at above-mentioned the deficiencies in the prior art, provide a kind of tensile strength that keeps steel plate, yield strength is reduced to tensile strength 600MPa level low yield strength ratio hot rolling biphase plate and manufacture method below the 365MPa in the 600MPa level.

The present invention is a composition of steel based on common C-Mn, on sheet billet continuous casting and rolling production line, adopts cooling controlling and rolling controlling process, exploitation tensile strength 600MPa level, low yield strength ratio hot rolling biphase plate.

Steel plate of the present invention be organized as ferrite and martensitic phase, its chemical ingredients by mass percent is: 0.05～0.08%C, 0.20～0.40%Si, 1.30～1.60Mn, surplus is Fe; Be organized as ferrite and martensitic stucture, wherein: it is 85～90% that ferrite accounts for volume fraction, and it is 10～15% that martensite accounts for volume fraction; Yield strength Rp _0.2Be 340～365MPa; Tensile strength Rm is 600～675MPa, and percentage of total elongation A has no progeny ₅₀Be 26～30%; Especially, yield tensile ratio (Rp0.2/Rm) between 0.50～0.60, strength and ductility product (Rm * A ₅₀) between 15000～20000.

The manufacture method of steel plate of the present invention is: adopt above-mentioned chemical ingredients steel, at sheet billet continuous casting and rolling production line, adopt cooling controlling and rolling controlling process to produce a kind of tensile strength 600MPa level low yield strength ratio hot rolling biphase plate.Specifically carry out according to the following steps:

(1) be 67～72mm, above-mentioned chemical ingredients continuous-casting sheet billet with thickness, through the continuous tunnel furnace soaking, the control tapping temperature is 1100～1150 ℃;

(2) on the tandem rolling unit, carry out hot rolling, 1100～1150 ℃ of control start rolling temperatures, 820～840 ℃ of last frame finishing temperatures;

(3) carry out controlled chilling after the hot rolling, 50～60 ℃/s of controlled chilling speed; Batch 50～130 ℃ of coiling temperatures after the cooling;

(4) steel plate thickness range 3.5～4.0mm.

Advantage of the present invention is: the tensile strength that has kept steel plate is in the 600MPa level, with the yield strength of steel plate reduce to below the 365MPa, yield tensile ratio is controlled between 0.50～0.60, thereby solved the press tool shortening in work-ing life that the user exists in using steel plate, the problem that causes the tool and mould cost to improve.

Description of drawings

Fig. 1 is the typical gold phase constitution Electronic Speculum figure of tensile strength 600MPa level low yield strength ratio ferrite of the present invention and martensite dual-phase steel.Through LEPERA reagent (1at%Na ₂S ₂O ₅+ 4at% picral) dyeing, wherein white portion is a martensite, grey color part is a ferrite.

Embodiment

Option table 1 chemical ingredients steel is a raw material, and continuous-casting sheet billet is of a size of: 67～72mm (thick) * 1250mm (wide) * 8000mm (length).With continuous-casting sheet billet through the continuous tunnel furnace soaking, continuous tunnel furnace length 100m, rolling through 7 frame hot continuous rolling units, control start rolling temperature, finishing temperature are cooled off controlled chilling speed and coiling temperature fast after steel plate rolls.Steel plate thickness specification is limited in 3.5～4.0mm scope.Cooling controlling and rolling controlling process such as table 2, mechanical property and organize mark such as table 3.

Table 1 embodiment surveys chemical ingredients

The composition numbering	C	Mn	Si
				S0	0.05	1.60	0.20
S1	0.06	1.55	0.30
				S2	0.07	1.30	0.40
S3	0.08	1.45	0.35

Table 2 embodiment surveys cooling controlling and rolling controlling process

Table 3 embodiment surveys mechanical property and tissue volume mark

Wherein:

Rp _0.2---nominal yield strength; Rm---tensile strength; A ₅₀---calibration is apart from the 50mm elongation after fracture;

Rp _0.2/ Rm---yield tensile ratio; Rm * A ₅₀---strength and ductility product; The implementation data that composition is numbered the steel correspondence of S0 is numbered S0-1, S0-2, and all the other together.

Claims (2)

1. tensile strength 600MPa level low yield strength ratio hot rolling biphase plate, it is characterized in that: the chemical ingredients of steel plate by mass percent is: 0.05～0.08%C, 0.20～0.40%Si, 1.30～1.60Mn, surplus is Fe; Be organized as ferrite and martensitic stucture, wherein: it is 85～90% that ferrite accounts for volume fraction, and it is 10～15% that martensite accounts for volume fraction; Yield strength Rp _0.2Be 340～365MPa; Tensile strength Rm is 600～675MPa, and percentage of total elongation A has no progeny ₅₀Be 26～30%; Yield tensile ratio (Rp0.2/Rm) between 0.50～0.60, strength and ductility product (Rm * A ₅₀) between 15000～20000.

2. the manufacture method of a tensile strength 600MPa level low yield strength ratio hot rolling biphase plate according to claim 1 is characterized in that: on sheet billet continuous casting and rolling production line, adopt cooling controlling and rolling controlling process, carry out according to the following steps:

(1) be the continuous-casting sheet billet of 67～72mm, the described chemical ingredients of claim 1 with thickness, through the continuous tunnel furnace soaking, the control tapping temperature is 1100～1150 ℃;

(2) on the tandem rolling unit, carry out hot rolling, 1100～1150 ℃ of control start rolling temperatures, 820～840 ℃ of last frame finishing temperatures;

(3) carry out controlled chilling after the hot rolling, 50～60 ℃/s of controlled chilling speed; Batch 50～130 ℃ of coiling temperatures after the cooling;

(4) steel plate thickness range 3.5～4.0mm.

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