CN102586681A

CN102586681A - Method for reducing martensite formation critical cooling rate of automobile boron steel

Info

Publication number: CN102586681A
Application number: CN2012100766153A
Authority: CN
Inventors: 高志国; 白雅琼; 程德富; 康利明
Original assignee: Baotou Iron and Steel Group Co Ltd
Current assignee: Baotou Iron and Steel Group Co Ltd; Inner Mongolia Baotou Steel Union Co Ltd
Priority date: 2012-03-22
Filing date: 2012-03-22
Publication date: 2012-07-18

Abstract

The invention relates to a method for reducing the martensite formation critical cooling rate of automobile boron steel. A plate comprises the following chemical constituents by weight percent: 0.20 to 0.42 percent of C, 0.15 to 0.9 percent of Si, 1.1 to 1.85 percent of Mn, 0.015 or less percent of P, 0.002 or less percent of S, 0.01 to 0.06 percent of Ti, 0.0010 to 0.0050 percent of B, 0.001 to 0.09 percent of RE, and Fe and inevitable impurities in balancing amount. The thickness of a finished plate is 5 to 30 mm. The boron steel plate produced by using the method has excellent hardenability, and the martensite formation critical cooling rate can be reduced from 33 DEG C/s to below 10 DEG C/s. The invention changes the microstructure of material through the solid solution and the solid-state reaction of rare-earth elements, so that the martensite formation critical cooling rate of the boron steel plate for impact resistance is remarkably reduced, and the hardenability is remarkably improved.

Description

A kind of method that reduces automobile with the martensite formation critical cooling rate of boron steel

Technical field

The invention belongs to the material heat treatment field, particularly steel plate process for cooling technology.

Background technology

The automobile that the crashworthiness shock resistance is superior can be through the remarkable characteristics of strengthening of thermal treatment because of having with the thermoforming boron steel; Exploitation of the SSAB company of Sweden and the hot rolling of the having produced Domex series boron plate of can quenching; The hot rolling of the Docal series of the Mittal Steel exploitation boron plate of can quenching; Can be with ys 400MPa; The hot rolling attitude sheet material of tensile strength 600MPa obtains tensile strength after through the heating shrend and reaches the excellent properties more than the 1500MPa, is widely used in the production of the stamping parts such as A post, B post, front and back collision bumper of several sedans such as domestic Sagitar, Magotan, Bora, Audi.Motor corporations such as a domestic vapour, Cherry, lucky, Chang'an are urgently seeking to make the automobile shock resistance with this technology and are using stamping parts.Because the production line construction of this product is expensive very huge, at present domestic only have several companies from external introducing technology.The main supplier of domestic automobile steel plate pays much attention to the thermoforming technology; Carried out the research of thermoforming high-strength vehicle plate; And successfully develop commercial thermoforming with HS boron alloy steel plate, this will promote the thermoforming technology and be equipped in greatly developing and using of China.In order to make the anti-popularization and application of hitting in producing at home with thermoforming boron steel technology of automobile, press for automobile that exploitation has China's independent intellectual property right and resist and hit production technology and design concept with the thermoforming boron steel.

This patent discloses a kind of automobile forms critical cooling rate with the martensite of boron steel method that reduces; Mainly the mode through microalloying of rare earth reduces the anti-martensite that hits with boron steel of automobile and forms critical cooling rate, resists and hits the hardening capacity with boron steel thereby improved automobile.Not only can avoid causing the anti-ballistic work that hits with boron steel to descend through the enforcement of aforesaid method because of the too much adding of boron, and the facility investment expense that quenching apparatus causes because of the rate of cooling deficiency after the saving thermoforming.

Summary of the invention

The objective of the invention is to disclose a kind of automobile forms critical cooling rate with the martensite of boron steel method that reduces.

Technical scheme of the present invention is such, and anti-(weight percent) chemical composition content that hits with boron steel sheet material should meet: C 0.20%-0.42%, Si 0.15%-0.9%; Mn 1.1%-1.85%, P≤0.015%, S≤0.002%; Ti 0.01%-0.06%; B 0.0010%-0.0050%, RE 0.001%-0.09%, surplus is Fe and unavoidable impurities.Be shaped through hot rolling or forge hot post-heat-treated, production board thickness is 5-30mm.

Along with the raising of automobile steel cleanliness factor, the microalloying effect of REE is more for outstanding.Microalloying of rare earth effect size depends on the interaction of solution strengthening, REE and other solute elements of trace rare-earth element, the existence of REE (atom, inclusion or compound), the particularly REE situation of gathering partially at crystal boundary, and REE is to steel surface and matrix effect on structure etc.In different rare earth steels, all observing REE makes structure refinement, changes ferritic content and size, inhibition carbide phenomenons such as gathering alligatoring mutually.Rare earth reduces the rate of cooling that forms martensitic critical temperature (being Ms), and martensitic stucture is changed has tangible influence.The rare earth fining austenite crystal, and be enriched in austenite grain boundary, must influence the martensitic stucture form, austenite crystal is thin more, and martensite lath is also thin more.Rare earth reduces the activity of carbon, nitrogen, increases the solubleness of carbon, nitrogen, reduces its precipitation amount, and they can not be got in internal stress district or the lattice defect by precipitation, has reduced the interstitial atom number of pinning dislocation.Rare earth influences form, size, distribution, quantity and the structure of carbide simultaneously, thereby has improved the mechanical property of steel.

Owing to increased trace rare-earth element in the component, under the effect of microalloying of rare earth, the boron steel sheet material of producing with this method has excellent hardening capacity, the critical cooling rate that can martensite be formed by 33 ℃/s be reduced to 10 ℃/below the s.

The outstanding advantage of the present invention is solid solution and solid state reaction thereof through REE, changes microstructure, tissue and the component of material, thereby the anti-martensite formation critical cooling rate that hits with boron steel sheet material is significantly reduced, and hardening capacity significantly improves.

Description of drawings

Fig. 1 is the boron steel sheet material CCT curve that does not contain rare earth of embodiment 1 correspondence;

Fig. 2 is the CCT curve of the boron steel sheet material that contains rare earth of embodiment 1 correspondence.

Embodiment

Below in conjunction with embodiment the present invention is done further detailed explanation.

Embodiment 1:

Table 1 chemical ingredients (Wt%)

Put into process furnace with intending rolling slab, (weight percent) chemical ingredients of slab is seen table 1, and the CCT curve that the boron steel sheet material under above-mentioned two kinds of member conditions is corresponding is as depicted in figs. 1 and 2.Can know by Fig. 1 and Fig. 2 contrast, observe the stability that rare earth has improved supercooled austenite, make continuous cooling transformation (CCT) curve to the right lower direction move, Ms point descends 34 ℃, rare earth resists to hit with the boron plate effects of phase transition and shows as the influence to stagnation point.The stagnation point of steel is the important evidence of working out heat treating regime.According to rare-earth-iron is phasor, and REE dissolves each other with iron atom in iron liquid, but its partition ratio in iron-based sosoloid is minimum, in iron liquid process of setting, is enriched in interdendritic or crystal boundary at last by the solid/liquid interfaces passing.Because rare earth atom radius ratio iron atom is big, to the solid solution physical efficiency strengthening effect is provided.

Claims

1. an automobile is used boron steel, it is characterized in that chemical ingredients by weight percentage is: C0.20%-0.42%, Si 0.15%-0.9%; Mn 1.1%-1.85%, P≤0.015%, S≤0.002%; Ti0.01%-0.06%; B 0.0010%-0.0050%, RE 0.001%-0.09%, surplus is Fe and unavoidable impurities.

2. characteristic a kind of reduces automobile forms critical cooling rate with the martensite of boron steel method according to claim 1; It is characterized in that through the microalloying of rare earth method; Structure refinement, ferritic content and size change, carbide gathering alligatoring mutually are suppressed, thereby have reduced the critical cooling rate that martensite forms.

3. a kind of automobile as claimed in claim 1 is used boron steel, it is characterized in that the sheet metal thickness scope is 5-30mm.