CN103451523A - Niobium-containing high-strength fine-grain 700MPa-level hot-rolled dual-phase steel and production method thereof - Google Patents

Abstract

The invention discloses a niobium-containing high-strength fine-grain 700MPa-level hot-rolled dual-phase steel and a production method thereof. A steel plate with a polygonal ferrite and martensite dual-phase structure is obtained by a hot rolling and sectional control cooling process. The dual-phase steel comprises the following chemical components in percentage by weight: 0.07-0.10% of C, 0.20-0.50% of Si, 1.20-1.50% of Mn, less than or equal to 0.03% of P, less than or equal to 0.03% of S, 0.08-0.11% of Nb and the balance of Fe and unavoidable impurities. The production method of the dual-phase steel comprises the following steps: preparing materials according to the chemical components of the dual-phase steel; smelting in a vacuum induction furnace, and pouring the molten steel to obtain a steel ingot; heating the steel ingot and starting rolling; controlling the rolling at two stages; after the rolling, performing sectional cooling; and finally conveying the product to a coil storehouse. The dual-phase steel disclosed by the invention has the advantages of good strength-toughness match of steel plate, high tensile strength of steel plate, low yield ratio and good stamping property.

Description

The thin brilliant 700MPa level hot-rolled dual-phase steel of a kind of niobium-containing high-strength and production method thereof

Technical field:

The present invention relates to high-strength thin-crystal hot-rolled dual-phase steel and production method thereof, particularly the thin brilliant 700MPa level hot-rolled dual-phase steel of a kind of niobium-containing high-strength and production method thereof.

Background technology:

Ferrous materials remains main structured material in 21 century, and high performance and cost degradation are the developing direction of following ferrous materials, is also the prerequisite of sustainable economic development.To future developments such as high security, economic environmental protection, high life, intensity, plasticity, the solidity to corrosion of auto sheet proposed to more and more higher requirement along with Hyundai Motor.Hot-rolled dual-phase steel can be widely used for manufacturing the members such as automobile reinforcing plate, wheel, chassis, collision bumper, the various frameworks of car body with its high strength and high formability.But weight reduction 20～30%, meet the development topic of automotive material lightweight, high-performance, safety environment protecting energy saving, becomes gradually one of first-selected steel grade of automobile steel.Dual phase steel refers to that soft steel or low-carbon alloy steel obtain through critical zone thermal treatment or controlled rolling technique, the AHSS (AHSS, Advanced High-Strength Steel) mainly formed by a small amount of (volume fraction the is less than 20%) martensite (M) of ferrite F+.Common high-strength steel is by the controlled rolling crystal grain thinning, and the carbonitride by microalloy element separate out the strengthening matrix, and dual phase steel is at pure ferrite crystal boundary or the intracrystalline disperse harder martensitic phase that distributing, so its strength and toughness has obtained good coordination.

The Mechanical Properties of Dual Phase Steels characteristics: (1) stress-strain curves is without discontinuous yield phenomenon; (2) there is high preliminary work hardening rate, especially the initial manufacture hardening rate; (3) low yield strength and high tensile strength; (4) higher unit elongation.

In existing disclosed Patents document, the ferrito-martensite dual phase steel has following characteristics: (1) adds more Si element and the alloying elements such as Cr, Mo, as: Chinese patent open (bulletin) number CN102766812A, disclosed a kind of 700MPa level low yield strength ratio hot-rolled dual-phase steel steel plate and manufacture method thereof.When Si content is higher, hot-rolled sheet quality control on the surface difficulty strengthens, and adds the alloying elements such as Cr, Mo, and cost is high; (2) adopt the syllogic process for cooling, as: Chinese patent open (bulletin) number CN102703815A, disclosed a kind of 600MPa level hot-rolled dual-phase steel and preparation method thereof.Because it is had relatively high expectations to process for cooling, adopt the syllogic process for cooling, industrial production is restricted.

In summary it can be seen, there are various defects in existing hot-rolled dual-phase steel and production method.Therefore, preparation technology is simple in exploitation, the cost cheapness, and the ferrito-martensite dual phase steel of surface quality and satisfactory mechanical property has become the emphasis of common concern.

Summary of the invention:

The invention provides the thin brilliant 700MPa level hot-rolled dual-phase steel of a kind of niobium-containing high-strength and production method thereof, by hot rolling and segmentation Controlled cooling process, obtain having the steel plate of polygonal ferrite and martensite duplex structure.

The thin brilliant 700MPa level hot-rolled dual-phase steel of a kind of niobium-containing high-strength, its chemical composition and weight percentage are: C:0.07% ~ 0.10%; Si:0.20% ~ 0.50%; Mn:1.20% ~ 1.50%; P :≤0.03%; S :≤0.03%; Nb:0.08% ~ 0.11%, all the other are Fe and inevitable impurity.

The thin brilliant 700MPa level hot-rolled dual-phase steel of described a kind of niobium-containing high-strength has following mechanical property:

Yield strength 480 ~ 540MPa, tensile strength 700 ~ 750MPa, unit elongation 18 ~ 25%, yield tensile ratio is less than 0.75.

The thin brilliant 700MPa level hot-rolled dual-phase steel of described a kind of niobium-containing high-strength, have martensitic stucture and a small amount of residual austenite that polygonal ferrite and disperse distribute.

The production method of the thin brilliant 700MPa level hot-rolled dual-phase steel of a kind of niobium-containing high-strength, the method comprises the following steps:

A. according to chemical composition and the weight percentage of the thin brilliant 700MPa level hot-rolled dual-phase steel of a kind of niobium-containing high-strength, prepare burden;

B. by the alloy for preparing at vacuum induction furnace smelting, pass into shielding gas Ar gas in stove, pouring molten steel becomes steel ingot;

C. by Heating Steel Ingots to 1200 ~ 1250 ℃, start rolling after being incubated 2 ~ 3h;

D. adopt the two-stage control rolling, austenite recrystallization district rolling temperature scope is 950 ~ 1050 ℃, controls austenite recrystallization district deflection 60%; Austenite non-recrystallization district rolling temperature scope is 850 ~ 950 ℃, controls the non-recrystallization zone of austenite deflection 50% ~ 60%, and finishing temperature is 840 ~ 880 ℃;

E. adopt the segmentation process for cooling after rolling, the first stage: after finish to gauge, with the speed of 45 ℃/s, be cooled to 700 ℃; Subordinate phase: treat temperature 10 ~ 15s in air, batch after finally with the speed of 100 ℃/s ~ 150 ℃/s, being cooled to 400 ~ 450 ℃, deliver to the coiled sheet storehouse.

The present invention compares with existing similar technology, and its significant beneficial effect is embodied in:

1. owing at simple C-Si-Mn, only having added alloy element Nb in steel, with low cost;

2. in composition of steel, Si content, by weight percentage lower than 0.50%, has guaranteed plate surface quality and coating performance;

3. armor plate strength and toughness match, and steel plate tensile strength is high, and yield tensile ratio is low, and punching performance is good.

Composition Design characteristics of the present invention are that low Si contains Nb, and its effect and strengthening mechanism are as follows:

Silicon: Si is solution strengthening element commonly used in the ferrite/martensite dual phase steel, can the reinforced ferrite matrix, dwindle ferrite/martensite two-phase difference of hardness; In addition, Si is non-carbide forming element, can suppress the formation of cementite, hinders pearlitic transformation, enlarges the ferrite transformation temperature range, thereby enlarges rolling and cooling temperature window, is conducive to the realization of production technique.But Si content height can cause the quality control on the surface difficulty of steel to strengthen, simultaneously, the plating poor performance of steel plate.The Si content of described hot-rolled dual-phase steel in 0.10 ~ 0.50% scope, has guaranteed plate surface quality and plating performance by weight percentage.

Niobium: Nb is the carbonitride forming element, and Main Function is: in rolling and process of cooling, tiny niobium carbonitrides is separated out, and significantly improves the intensity of steel.Except adding the Nb element, usually also add the elements such as Ti, V with same purpose in existing dual phase steel, when this dvielement addition is many, although can improve the intensity of steel, damaged the processability of steel.Described hot-rolled dual-phase steel only adds by weight percentage the Nb element 0.06 ~ 0.11%, is improving intensity and also guaranteed the plasticity of steel simultaneously.

The accompanying drawing explanation:

Fig. 1 is production method rolling and the process for cooling condition schematic diagram of the thin brilliant 700MPa level hot-rolled dual-phase steel of a kind of niobium-containing high-strength.

In figure, T: once on cooling rear roller-way, treat Wen Wendu; T: time of staying temperature on cooling rear roller-way once; C1: speed of cooling after finish to gauge; C2: on roller-way after temperature ultrafast cold but speed; F: ferrite; P: perlite; MS _:: martensite starts transition point.

Embodiment:

Specifically describe the present invention below in conjunction with accompanying drawing by embodiment.

The thin brilliant 700MPa level hot-rolled dual-phase steel of a kind of niobium-containing high-strength and production method thereof, smelt into steel ingot by the alloy prepared through 50kg vacuum induction process furnace, and its chemical component weight percentage ratio is C:0.08%; Si:0.40%; Mn:1.40%; P :≤0.03%; S :≤0.03%; Nb:0.10%, all the other are Fe and inevitable impurity.Complete hot rolling on 450 milling trains of laboratory.Rolling technology is: by Heating Steel Ingots to 1200 ~ 1250 ℃, after insulation 1h, start rolling; Austenite recrystallization district rolling temperature scope is 1100 ~ 1150 ℃, controls austenite recrystallization district deflection and is controlled at 50%; The non-recrystallization zone of austenite rolling temperature scope is 880 ~ 980 ℃, controls the non-recrystallization zone of austenite deflection 60%; Finishing temperature is 840 ~ 880 ℃; After finish to gauge, temperature is at 850 ℃, and the speed with 45 ℃/s is cooled to 700 ℃ subsequently; Treat temperature 10 ~ 15s in air, batch after finally with the speed of 70 ℃/s ~ 100 ℃/s, being cooled to 450 ~ 520 ℃, deliver to the coiled sheet storehouse.

Claims (3)

1. the thin brilliant 700MPa level hot-rolled dual-phase steel of niobium-containing high-strength is characterized in that this dual phase steel chemical composition and weight percentage are:

C:0.07% ~ 0.10%; Si:0.20% ~ 0.50%; Mn:1.20% ~ 1.50%; P :≤0.03%; S :≤0.03%; Nb:0.08% ~ 0.11%, all the other are Fe and inevitable impurity;

The thin brilliant 700MPa level hot-rolled dual-phase steel of described a kind of niobium-containing high-strength has following mechanical property:

Yield strength 480 ~ 540MPa, tensile strength 700 ~ 750MPa, unit elongation 18 ~ 25%, yield tensile ratio is less than 0.75.

2. the thin brilliant 700MPa level hot-rolled dual-phase steel of a kind of niobium-containing high-strength according to claim 1, is characterized in that this dual phase steel has martensitic stucture and a small amount of residual austenite of polygonal ferrite and disperse distribution.

3. the production method of the thin brilliant 700MPa level hot-rolled dual-phase steel of a kind of niobium-containing high-strength claimed in claim 1 is characterized in that the method comprises the following steps:

A. according to chemical composition and the weight percentage of the thin brilliant 700MPa level hot-rolled dual-phase steel of a kind of niobium-containing high-strength, prepare burden;

B. by the alloy for preparing at vacuum induction furnace smelting, pass into shielding gas Ar gas in stove, pouring molten steel becomes steel ingot;

C. by Heating Steel Ingots to 1200 ~ 1250 ℃, start rolling after being incubated 2 ~ 3h;

D. adopt the two-stage control rolling, austenite recrystallization district rolling temperature scope is 950 ~ 1050 ℃, controls austenite recrystallization district deflection 60%; Austenite non-recrystallization district rolling temperature scope is 850 ~ 950 ℃, controls the non-recrystallization zone of austenite deflection 50% ~ 60%, and finishing temperature is 840 ~ 880 ℃;

E. adopt the segmentation process for cooling after rolling, the first stage: after finish to gauge, with the speed of 45 ℃/s, be cooled to 700 ℃; Subordinate phase: treat temperature 10 ~ 15s in air, batch after finally with the speed of 100 ℃/s ~ 150 ℃/s, being cooled to 400 ~ 450 ℃, deliver to the coiled sheet storehouse.

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