CN101921949B - Continuous annealing production method of cold-rolled sheet No.45 steel - Google Patents

Abstract

The invention relates to a continuous annealing production method of cold-rolled sheet No.45 steel. The steel comprises the following components in percentage by weight: 0.47 percent of C, 0.60 percent of Mn, 0.31 percent of Si, less than or equal to 0.035 percent of P, less than or equal to 0.035 percent of S, less than or equal to 0.025 percent of Cr, less than or equal to 0.025 percent of Ni, less than or equal to 0.025 percent of Cu and the balance of Fe. The continuous annealing process comprises the following steps of: putting band steel into a nonoxidative atmosphere consisting of H2 and N2 as a medium in a furnace from room temperature and heating up to 240-260 DEG C through 37-52 seconds; further heating up to 750-770 DEG C through 670-850 seconds; preserving heat for 214-300 seconds; cooling to 590-610 DEG C through 60-85 seconds; cooling to 440-460 DEG C through 13-19 seconds; and cooling to 390-410 DEG C through 789-1,105 seconds, and then cooling to room temperature with water. A continuous annealing steel plate produced by the invention has higher strength and elongation.

Description

No. 45 steel continuous annealing of a kind of cold rolled sheet working method

Technical field

The present invention relates to No. 45 steel continuous annealing of a kind of cold rolled sheet working method, belong to the metal material processing field.

Background technology

It can be used for automotive industry and building field etc. No. 45 steel finished products.The massfraction of carbon is relatively low in No. 45 steel, during annealing in austenite undissolved carbide particle less, nodularization is difficulty comparatively.From the angle of energy, spheroidite unit volume interfacial area is minimum, is tissue the most stable in the steel, so have minimum interfacial energy.Owing to the common continuous annealing of above reason is easy to generate the cementite network tissue ferritic is separated, so low punching press distortion and the cracking of causing of plasticity.Accompanying drawing 1 is No. 45 cold rolling back of steel microtexture photos, and crystal grain obviously becomes the fiber strip.Accompanying drawing 2 is No. 45 steel microtextures behind the traditional continuous annealing process of employing, can find out among the figure that No. 45 structure of steel of traditional technology production are: most sheet perlite+little granular perlite+ferritic.Ferritic is separated in this tissue, will make a very bad impression to macroscopical plasticity.Chinese patent CN200910301238.7 discloses " low-carbon steel cold rolled sheet continuous annealing process ", has narrated the continuous annealing characteristics of low-carbon (LC) thin plate.But require in this patent: " it is that 850 ℃～900 ℃ process furnace further heats that the band steel need get into temperature; be 56～110 seconds heat-up time "; If No. 45 steel will certainly cause final pearlitic structure nodularization difficulty after 850 ℃～900 ℃ heating, therefore be not suitable for No. 45 higher relatively steel productions of carbon content.For obtaining certain toughness and plasticity; Be convenient to the processing of impact briquetting and standard machinery; Need control reasonable component, hot rolling technology, cold rolling draft, annealing process, smooth unit elongation etc., thereby obtain cracked cementite of suitable dispersion and globular pearlite tissue morphology.

The object of the invention provides No. 45 steel continuous annealing of a kind of cold rolled sheet working method, solves that No. 45 steel disperse at continuous annealing production technique Medium pearlite, the problem of nodularization.

Summary of the invention

Technical solution of the present invention: No. 45 steel continuous annealing of a kind of cold rolled sheet of the present invention working method, the chemical ingredients mass percent of this steel grade is: C:0.47%; Mn:0.60%; Si:0.31%; P≤0.035%; S≤0.035%; Cr≤0.25; Ni≤0.25; Cu≤0.25, surplus are Fe, the hot rolling technology control Heating temperature of its steel: 1250 ± 30 ℃; Finishing temperature: 900 ± 20 ℃; Coiling temperature: 730 ± 20 ℃; Cold-rolling process is controlled cold rolling draft at 50%-70%, it is characterized in that: the band steel gets in the stove medium by H by room temperature in the continuous annealing process ₂And N ₂Continuous in the non-oxidizing atmosphere of forming through following process step:

A.. be heated to 240 ℃～260 ℃ through 37～52 seconds;

B. further be heated to 750 ℃～770 ℃ through 607～850 seconds;

C. be incubated 214～300s;

D. be cooled to 590 ℃～610 ℃ through 60～85 seconds;

E. be cooled to 440 ℃～460 ℃ through 13～19 seconds;

F. after being cooled to 390 ℃～410 ℃ in 789～1105 seconds water-cooled to room temperature.

After above-mentioned technology, on average about 450MPa, on average about 680MPa, unit elongation is about 20% for tensile strength for the ys of steel.

Thinking of the present invention is: the height of coiling temperature plays significant effect to the reduction of No. 45 steel plate yss.The present invention adopts coiling temperature: 730 ± 20 ℃, high temperature batches the original grain that helps obtaining large-size, makes that rolling load reduces when cold roller and deformed.

Certain cold rolling draft is the motivating force of continuous annealing recrystallize subsequently, and determined recrystallize forming core point how much.This invention roughly is controlled at the level greater than 50%-70% according to different belt steel thickness specifications with cold rolling draft.

Get into continuous annealing furnace through No. 45 steel of the cold rolled sheet behind hot rolling and the cold rolling process.Through being heated to 240 ℃～260 ℃ through 37～52 seconds, this process is utilized waste heating in the stove in the non-oxidizing atmosphere that H2 and N2 form, and is band steel postheating to high temperature and lays the foundation and can save production capacity; Further be heated to 750 ℃～770 ℃ through 607～850 seconds, this process makes cementite dissolve gradually, and microscopic fibers strip crystal grain after heating recrystallize takes place gradually; Make the abundant recrystallize of structure of steel No. 45 750 ℃～770 ℃ insulation 214～300s these processes, dissolved the cementite diffusion and keep existing and necessarily do not dissolve the cementite particle; Make cementite not dissolve cementite particle place to separate out gradually that through being cooled to 590 ℃～610 ℃ these processes in 60～85 seconds not nodularization process is ready in last process.When keeping the uneven austenite of carbon distribution during do not dissolve cementite to perlitic transformation; Undissolved residual cementite just very easily becomes the forming core particle; Such forming core particle is different with the nuclear that forms at austenite grain boundary; It can to around grow up, and finally make pearlitic spheroidization to greatest extent, improve the nodular cementite ratio.

Being cooled to 440 ℃～460 ℃ these processes through 13～19 seconds makes the band steel be cooled to cementite dispersion, nodularization temperature in the suitable continuous annealing process as early as possible; Be cooled to through 789～1105 seconds and can regulate better after 390 ℃～410 ℃ that cementite is decentralized, the size of pearlitic spheroidization and grain-size, thereby better control tensile strength and unit elongation level.

In order to improve No. 45 steel plate shape conditions and to obtain certain surfaceness, the present invention adopts 0.9 ± 0.3% smooth unit elongation to control.

Effect of the present invention: through optimized composition design, No. 45 band steel than the high-elongation level are successfully produced in adjustment and optimize hot rolling, cold rolling and parameter and annealing, flattening technological parameter.On the basis that technologies such as hot rolling, cold rolling and continuous annealing are optimized, the continuous annealing steel plate of being produced has higher-strength and unit elongation, has improved quality product.Solve that No. 45 steel disperse at continuous annealing production technique Medium pearlite, the problem of nodularization.

Description of drawings

Fig. 1 is No. 45 cold rolling back metallographic structure of steel photos;

Fig. 2 is a metallographic structure photo behind the common annealing in No. 45 steel prior aries;

Fig. 3 is that No. 45 steel adopt metallographic structure photo after the inventive method.

Embodiment

No. 45 steel continuous annealing of a kind of cold rolled sheet of the present invention working method, the chemical ingredients mass percent of this steel grade is: C:0.47%; Mn:0.60%; Si:0.31%; P≤0.035%; S≤0.035%; Cr≤0.25; Ni≤0.25; Cu≤0.25, surplus are Fe, the hot rolling technology control Heating temperature of its steel: 1250 ± 30 ℃; Finishing temperature: 900 ± 20 ℃; Coiling temperature: 730 ± 20 ℃; Cold-rolling process is controlled cold rolling draft at 50%-70%, it is characterized in that the following process step of process in the continuous annealing process:

Invented technology 1:

A. being with steel to get into medium by room temperature is H ₂And N ₂Be heated to 240 ℃ through 37 seconds in the non-oxidizing atmosphere of forming;

B. subsequently at H ₂And N ₂Further be heated to 750 ℃ through 607 seconds in the non-oxidizing atmosphere of forming;

C. subsequently at 750 ℃ H ₂And N ₂Be incubated 214 in the non-oxidizing atmosphere of forming;

D. subsequently at H ₂And N ₂Be cooled to 590 ℃ through 60 seconds in the non-oxidizing atmosphere of forming;

E. subsequently at H ₂And N ₂Be cooled to 440 ℃ through 13 seconds in the non-oxidizing atmosphere of forming;

F. at H ₂And N ₂After being cooled to 390 ℃ in 789 seconds, adopt WATER AS FLOW MEDIUM to be cooled to room temperature in the non-oxidizing atmosphere of forming.

It is can the result following to handle back No. 45 rigidity according to above-mentioned technology 1:

Invented technology 2:

A. being with steel to get into medium by room temperature is H ₂And N ₂Be heated to 260 ℃ through 52 seconds in the non-oxidizing atmosphere of forming;

B. subsequently at H ₂And N ₂Further be heated to 770 ℃ through 850 seconds in the non-oxidizing atmosphere of forming;

C. subsequently at 770 ℃ H ₂And N ₂Be incubated 300s in the non-oxidizing atmosphere of forming;

D. subsequently at H ₂And N ₂Be cooled to 610 ℃ through 85 seconds in the non-oxidizing atmosphere of forming;

E. subsequently at H ₂And N ₂Be cooled to 460 ℃ through 19 seconds in the non-oxidizing atmosphere of forming;

F. at H ₂And N ₂After being cooled to 410 ℃ in 1105 seconds, adopt WATER AS FLOW MEDIUM to be cooled to room temperature in the non-oxidizing atmosphere of forming.

It is can the result following to handle back No. 45 rigidity according to above-mentioned technology 2:

Accompanying drawing 3 is a microtexture behind the foregoing description, can find out most of perlite nodularization has taken place is the cementite particle and be scattered in the matrix.

The continuous annealing steel plate of producing through the present invention has higher-strength (681N/mm2,688N/mm2) and than high-elongation (17.56%, 22.95%), has improved quality product.

Claims (1)

1. No. 45 steel continuous annealing of cold rolled sheet working method, the chemical ingredients mass percent of this steel grade is: C:0.47%; Mn:0.60%; Si:0.31%; P≤0.035%; S≤0.035%; Cr≤0.25; Ni≤0.25; Cu≤0.25, surplus are Fe, the hot rolling technology control Heating temperature of its steel: 1250 ± 30 ℃; Finishing temperature: 900 ± 20 ℃; Coiling temperature: 730 ± 20 ℃; Cold-rolling process is controlled cold rolling draft at 50%-70%, it is characterized in that: the band steel gets in the stove medium by H by room temperature in the continuous annealing process ₂And N ₂Continuous in the non-oxidizing atmosphere of forming through following process step:

A.. be heated to 240 ℃～260 ℃ through 37～52 seconds;

B.. further be heated to 750 ℃～770 ℃ through 607～850 seconds;

C. be incubated 214～300s;

D. be cooled to 590 ℃～610 ℃ through 60～85 seconds;

E. be cooled to 440 ℃～460 ℃ through 13～19 seconds;

F. after being cooled to 390 ℃～410 ℃ in 789～1105 seconds water-cooled to room temperature.

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