CN101353761A - A kind of high-strength cold-rolled hot-dip galvanized TRIP steel plate and its preparation method - Google Patents

Abstract

The invention belongs to the field of metal material processing, and in particular provides a high-strength cold-rolled hot-dip galvanized TRIP steel plate and a preparation method thereof. The composition mass percentage of TRIP steel plate is: C: 0.1-0.4%, Si: ≤0.06%, Mn: 0.5%-2.5%, Al: 0.5%-2.0%, P: ≤0.03%, S: ≤0.02%, Nb: 0.01% to 0.10%, Ti: 0.01% to 0.10%, Cu: 0.1 to 1.0%, Ni: 0.1 to 0.6%, and the balance is iron. In the preparation process, the comprehensive performance of TRIP steel plate was improved by controlling the content of C, Mn, Nb, Ti and other elements in the steel, as well as the temperature and time of hot rolling, coiling, cold rolling and annealing. Compared with the traditional phase change induced plastic steel, the present invention has the following advantages: 1) has excellent platability, because low silicon is used, it can meet the coating requirements of hot-dip pure zinc and alloyed galvanized coating, and obtain excellent coating performance ; 2) The grain refinement effect is good, because the use of Nb microalloying can effectively refine the grains.

Description

A kind of TRIP steel plate for high strength cold rolling hot dip galvanizing and preparation method thereof

The invention belongs to the metal material processing field, a kind of high strength cold rolling hot dip galvanizing phase-change induced plastic (TRIP) steel plate and preparation method thereof particularly is provided.

Background technology:

The car industry requirement loss of weight, this means the material that working strength is higher, so that can under the prerequisite of not abandoning security and functional requirement, reduce the thickness of parts. ultrahigh-strength steel (UHSS) light sheet products, especially phase-change induced plastic (TRIP) product made from steel has outstanding high strength and good plasticity combination, therefore can provide terms of settlement for this problem. in addition, often requirement improves the corrosion resistance nature of above-mentioned steel sheet product by electro-galvanizing or pot galvanize.

In the tradition TRIP steel, composition is mainly 0.12-0.55%C, 0.2-2.5%Mn, 0.4-1.8%Si (mass percent).In these alloying elements, Si is a kind of solution strengthening element, is insoluble to cementite, can hinder separating out and improving ferritic intensity of cementite strongly.But silicone content is higher in steel, and steel surface is easy to form layer of oxide layer during hot rolling, even these zone of oxidation are handled by dephosphorization, also is difficult to it is thoroughly removed.In the operation of rolling subsequently, these zone of oxidation are broken, and part enters the surface of steel, causes the reduction of surface quality of steel.After cold rolling and continuous annealing, these zone of oxidation significantly reduce the coating of material, must just can carry out last zinc-plated processing through electroplating technology.These problems have limited the widespread use in practice of high Si-TRIP steel.

Al and Si are insoluble to cementite, can both stop the formation of cementite strongly, and therefore, the eighties in last century, many scholars proposed to substitute Si and the Al-Mn that grows up is the TRIP steel with Al.Compare with the Si element, aluminium is a kind of weak solution strengthening element, when silicon is replaced fully by aluminium, will produce negative influence to the balance of the intensity-plasticity of TRIP steel, though this moment steel unit elongation can keep par, the tensile strength of steel greatly reduces.

There is scholar (adding the influence of 0.5% bronze medal and bainiteization) to discover to 0.2C_1.5Mn_1.5Si deformation induced plasticity TRIP steel plate tissue and mechanical property, add the Cu element, can sacrifice under a little plasticity condition, improve intensity 50～100MPa, so, can significantly improve the over-all properties of material by adding a small amount of alloying element.

Summary of the invention:

The object of the present invention is to provide the Al-TRIP steel material of a high strength, microalloying, and be easy to galvanized product made from steel by cold rolling being prepared into.

A kind of TRIP steel plate for high strength cold rolling hot dip galvanizing, it is characterized in that TRIP steel plate composition quality percentage composition is: C:0.1～0.4%, Si :≤0.06%, Mn:0.5%～2.5%, Al:0.5%～2.0%, P :≤0.03%, S :≤0.02%, Nb:0.01%～0.10%, Ti:0.01%～0.10%, Cu:0.1～1.0%, Ni:0.1～0.6%, surplus is an iron.

A kind of as mentioned above TRIP steel plate for high strength cold rolling hot dip galvanizing is characterized in that preparation process is as follows:

1. smelt, cast: in tapping, add alloy element Nb, Ti, by tiny (Nb, Ti) (C, N), pinning austenite grain boundary, refinement strand crystal grain; In cast, carry out rare earth and feed silk.

2. hot rolling steel billet: hot rolling finishing temperature is Ar3+20～150 ℃, obtains hot rolling blank.

3. batch: hot rolling blank is cooled to curling blank under 600～750 ℃ the coiling temperature.

4. oxide compound is removed in pickling.

5. cold rolling: adopt 50～70% the cold rolling above-mentioned hot rolling blank of draught, to reduce thickness.

6. heat tracing: 750～900 ℃ of cold rolling blank holding temperatures, soaking time are 60～200s.

7. pot galvanize: adopt the speed of cooling of 20～50 ℃/s that described cold rolling steel billet is cooled to 450～470 ℃, in this temperature range described cold rolling steel billet is carried out pot galvanize, the time is 10～60s,

8. be cooled to room temperature: adopt the speed of cooling of 20～50 ℃/s that described cold rolling steel billet is cooled to room temperature.

C: carbon is austenite stabilizer element, reduces the Ms point strongly.The austenite that only contains a certain amount of C could be residual in room temperature.And owing to transform inductive plasticity-.When C concentration is little 0.05% the time, almost can't guarantee 5% more residual austenite, thereby can not realize purpose of the present invention.On the other hand, surpass 0.4% and can make the non-constant of weldability, so C content can not be too high.

Mn: manganese plays austenitic function of stabilizer, thereby can reduce the Ms temperature of residual austenite.In addition, manganese can be restrained perlite and form, and, can also improve the intensity aggregate level of steel by solution strengthening.On the other hand, add excessive Mn and can cause when when holding temperature is cooled off, can not fully forming perlite, thereby make the broken concentration deficiency in the residual austenite, cause its stability decreases.The Mn too high levels also will improve the hardness of weld seam, and promote the formation of deleterious banded structure.When the add-on of Mn less than 0.5% the time, must improve rate of cooling for suppressing to resolve into perlite, this is impossible on Industry Control, thereby this add-on is improper.On the other hand, when the Mn amount surpassed 2.5%, zonal structure was remarkable, degradation, thereby also be unfavorable.

Si: silicon is unfavorable to pot galvanize.For fear of requiring,, should further limit Si content to prevent to form crackle to the hot steel bloom material.By restriction Si content, also can avoid red squama occurring at hot rolling surface.

Al: aluminium also is a kind of degree intensive ferrite stablizer, thereby can promote ferritic formation in insulation and from holding temperature cooling period, therefore can the stable residual austenite.The reason that residual austenite is stabilized is being because Al can also restrain during overaging and separate out from residual austenite to a greater extent.Different with Si, Al does not have harmful effect to pot galvanize.Al can improve the A3 point strongly, and when the Al too high levels makes that the temperature of hot rolling open rolling and finish to gauge needs to improve, two-phase region annealed temperature also needs to improve simultaneously.On the other hand, too high Al content is also unfavorable to continuous casting.

Nb: niobium is a kind of strong carbide forming element, the avidity of niobium and carbon is greater than vanadium, niobium commonly used carries out microalloying in ferrous materials, mainly be to utilize niobium to combine to form dispersing carbide with carbon, this carbide formation temperature that contains niobium is higher, may in high-temperature molten steel, exist, and its lattice parameter is close with austenite, can be used as austenitic crystallization nuclei, the niobium that adds trace can thinning solidification structure, in heat treatment process, separate out niobium carbide in addition and generally be the small and dispersed distribution, help dispersion-strengthened, and can stop high temperature austenite to be grown up.((C N), causes the waste of alloying element to form thick Nb for C, N) poly-partially but Nb can take place too much Nb.

Ti: the effect of titanium is similar to niobium, all is microalloy element

The copper content of Cu:1% can improve the intensity of 50MPa, but the dissolving of copper only takes place when high temperature, and almost nil under the room temperature, copper also improves intensity by crystal grain thinning.In ferrite refrigerative process, the solubleness of copper reduces rapidly, produces precipitation strength.

Ni: the similar generation austenite of nickel to Mn, it can also improve intensity and plating performance simultaneously, and in addition, similar with Al to Si, Ni is not dissolved in the cementite. and suppress the cementite precipitation in the maintenance process in 350-600 ℃ of temperature range, and postpone conversion process.Ni can also improve the deterioration that adds the plasticity that Cu brought.

S: sulphur as remnants and harmful element except the machinability that can improve steel, all very unfavorable to extension, impelling strength and the hot-work of steel.So S must be controlled in 0.02%.

P: phosphorus is a kind of harmful element, has seriously destroyed the impelling strength of steel, and is also unfavorable to the hot-work and the weldability of steel.Equally, P also will be strict controlled within 0.03%.

Compare with traditional transformation induced plasticity steel, the present invention has the following advantages:

1) has good platability,, can satisfy hot pure zinc plating, the galvanized coating requirement of alloying, obtain good coating performance because adopt low silicon;

2) grain refining effect is good, because adopt Nb microalloying, effectively crystal grain thinning.

Description of drawings

Fig. 1 is the annealing process synoptic diagram

Embodiment

The high strength cold rolling hot dip galvanizing of the present invention manufacture method of TRIP steel:

At first smelt according to design mix, blank is rolled into thin plate after forging, and 860～900 ℃ of hot rolling finishing temperatures, coiling temperature are 600～700 ℃; Cold rolling draft is 50～70%; The two-phase region annealing temperature is 800～880 ℃, and the two-phase region annealing time is 60～200s, and the cooling rate CR1 that is chilled to zinc pond temperature from annealing temperature is 20～50 ℃/s; Zinc pond temperature is 450～470 ℃, and the zinc-plated time is 10～60s, and speed of cooling CR220～50 after zinc-plated ℃/s is cooled to room temperature, thereby obtains high-strength cold rolling pot galvanize TRIP steel.Fig. 1 is an annealing process, and table 1 is a chemical ingredients, and table 2 is a mechanical property.

Table 1 chemical ingredients

C	Al	Si	Mn	P	S	Cu	Ni	Nb	Ti
										0.24	1.23	0.03	1.7	0.006	0.005	0.54	0.31	0.03	0.015

Table 2 main technique and mechanical property

Embodiment	Annealing temperature/℃	Annealing time/s	Zinc-plated temperature/℃	Zinc-plated time/s	Yield strength/MPa	Tensile strength/MPa	Unit elongation/%
								1	860	80	460	10	368	865	18.5
2	860	80	460	30	418	828	27.0
								3	880	80	460	10	465	908	17.3
4	880	80	460	30	418	838	24.8

Claims (2)

1. A high-strength cold-rolled hot-dip galvanized TRIP steel plate, characterized in that the phase transformation induced plasticity steel plate composition mass percentage is: C: 0.1-0.4%, Si: ≤0.06%, Mn: 0.5%-2.5% , Al: 0.5%～2.0%, P: ≤0.03%, S: ≤0.02%, Nb: 0.01%～0.10%, Ti: 0.01%～0.10%, Cu: 0.1～1.0%, Ni: 0.1～0.6% , and the balance is iron. 2. a kind of high-strength cold-rolled hot-dip galvanized TRIP steel plate as claimed in claim 1, is characterized in that the preparation steps are as follows: 1). Smelting and pouring: alloying elements Nb and Ti are added when tapping, and rare earth wire is fed when pouring; 2). Hot-rolled steel billet: the hot-rolled final rolling temperature is Ar3+20-150°C to obtain a hot-rolled billet; 3). Coiling: Cool the hot-rolled billet to a coiling temperature of 600-750°C and coil the hot-rolled billet; 4). Pickling to remove oxides; 5). Cold rolling: use 50-70% reduction to cold-roll the above-mentioned hot-rolled billet to reduce the thickness; 6).Heating and heat preservation: the heat preservation temperature of the cold-rolled billet is 750-900℃, and the heat preservation time is 60-200s; 7). Hot-dip galvanizing: Cool the cold-rolled billet to 450-470°C at a cooling rate of 20-50°C/s, and perform hot-dip galvanizing on the cold-rolled billet in this temperature range for 10-60s ; 8). Cooling to room temperature: cooling the cold-rolled billet to room temperature at a cooling rate of 20-50° C./s.

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