CN100488649C - Technology method for using thin slab for continuous casting and rolling to produce low-carbon high-niobium high-strength toughness steel belt - Google Patents

Abstract

The invention belongs to the preparing field of continuous casting and rolling of an abbreviated bar strip, in particular to the technique which utilizes continuous casting and rolling of the bar strip to produce a steel strip of low-carbon, high-niobium and high-obdurability. The specific procedures includes that the soaking temperature of a casting blank is controlled between 1100-118 DEG C in the process of continuous casting and rolling of an abbreviated bar strip, the open rolling temperature is <=1050 DEG C, the deformations is between 40%-50%, the final rolling temperature is between 800-900 DEG C, and the coiling temperature is between 500-65 DEG C. In the process of continuous casting and rolling of an abbreviated bar strip, 5-7 suites of racks are hot-rolled, the relative draft is F1-F2:40-50%, F3-F4:20-40%, F5-F7:5-30%. Controlled cooling is adopted to achieve quick controlled cooling to further reach the coiling temperature after the final rolling, and rate of cooling is more than 10 DEG C/s. Compared to the present techniques, the invention has the advantages that cost is low, technique is simple, polymorphy is simultaneously eliminated, and the final steel strip structure is even and thin, thereby the mechanic performance is fine.

Description

Adopt the process of thin slab for continuous casting and rolling to produce low-carbon high-niobium high-strength toughness steel band

Technical field

The invention belongs to the CSP preparation field, be particularly related to the process that adopts the thin slab for continuous casting and rolling to produce low-carbon high-niobium high-strength toughness steel band, be mainly used in the preparation of the high-strength toughness steel band of industries such as petrochemical industry, facilities for transport and communication and engineering machinery.

Background technology

In the prior art, niobium is as suppressing one of the most significant microalloy element of austenite recrystallization effect, is the most ripe micro alloying element of technology during the hot continuous rolling steel band is produced.Its mechanism of action is by making the austenite flattening after the distortion, increasing dislocation density and Zona transformans distributes, improve effective grain boundary area of γ-α phase transformation, and the microalloy carbonitride pinning effect of separating out by the effect of dragging and the deformation inductdion of solid solution niobium, thereby suppress phase transformation ferrite/bainite grain growth and obtain even and tiny tissue.

The technology path that CSP production contains the niobium steel band is: distortion makes austenite that crystallization again, refine austenite crystal grain fully take place in the recrystallization zone; The multi-pass large deformation is rolling in the non-recrystallization district, forms " pancake " shape austenite, to increase dislocation and Zona transformans, for follow-up ferrite transformation provides more forming core point; After the finish to gauge by controlling the cold structure refinement that makes.Yet, be prone to mixed crystal phenomenon and be one of subject matter that CSP production contains the niobium steel band, the main cause that mixed crystal occurs is that original thick casting dendrite austenite recrystallization is incomplete or recrystallized structure is inhomogeneous, and then causes the mechanical performance of finished product steel belt to worsen.For example: be published in " iron and steel " the 38th volume in August, 2003, the 8th phase, 16-19 page or leaf, " mixed crystal problem and the improvement method that contain the Nb steel in the csp technology " and be published in " iron and steel " the 40th volume in February, 2005, the 2nd phase, 69-71 page or leaf, " research that continuous casting billet tissue influence mixed crystal produces ".

Summary of the invention

The object of the invention is to provide that a kind of cost is low, technology is simple, has eliminated mixed crystal phenomenon, makes final steel band even tissue refinement, thus the process of the thin slab for continuous casting and rolling to produce low-carbon high-niobium high-strength toughness steel band of satisfactory mechanical property.

According to above-mentioned purpose, the technical scheme of integral body of the present invention is:

The present invention utilizes ripe thin plate blank continuously casting and continuously rolling technology and the technological process of using of China, under the condition that does not increase any equipment in addition, produce low-carbon high-niobium high-strength toughness steel belt, make austenite avoid crystallization again to take place by setting the controlled rolling parameter in the high temperature open rolling, keep austenite to be in non-recrystallization district as-rolled condition all the time, austenite is flattening gradually in multi-pass deformation, increase along with Strain Accumulation, flat austenite crystal inside has formed a large amount of dislocation tangle and Zona transformans, because crystalline polamer does not more take place from start to finish, dislocation and Zona transformans are not eliminated but are increased gradually, for the ferrite/bainite phase transformation after the finish to gauge provides sufficient forming core point, therefore in phase transition process, austenite grain boundary and the intracrystalline forming core situation of growing up reach unanimity, finally obtained the tissue of even refinement, eliminate mixed crystal phenomenon, obtained well behaved high-strength toughness steel band.

Its technological core is high Nb content (being not less than 0.09% usually) and high temperature rolling.By improving Nb content to improve austenite non-recrystallization temperature, the non-recrystallization district is rolling can to carry out under higher temperature thereby make.In addition, utilize the retardation function of solid solution Nb, can obtain to have acicular ferrite/bainite structure than high-strength tenacity to austenite/ferrite transformation.It is reported that this technology is particularly suitable for producing high-strength toughness steel on the lower milling train of rolling power, as X70/X80 pipe line steel etc.

The operation principle of technical scheme of the present invention:

For continuous casting and rolling technique of sheet bar, if with Nb content bring up to higher level (about 0.1wt%, 0.092at%), then austenite recrystallization end temperature will be far above 1000 ℃, and the CSP start rolling temperature is about 1000 ℃.Therefore, in the whole operation of rolling austenitic static state again crystallization might be suppressed fully, promptly rollingly will be in austenite non-recrystallization district all the time.Although the CSP overall reduction is less, improve Nb content and then can make the drafts in austenite non-recrystallization district reach 80-90%, even bigger (relevant with the product thickness specification).In this process, original thick austenite is with flattening gradually, and intracrystalline will produce a large amount of deformation bands simultaneously, and the austenite grain boundary of these flattenings and intracrystalline deformation band will provide a large amount of nucleation sites for phase transformation, thereby be expected to obtain uniform tissue.

Utilize metal material in the correlation of non-recrystallization district distortion with the austenite crystal refinement, parameters such as the rolling temperature in the control CSP process, deflection guarantee, the low-carbon high-niobium high-strength toughness steel belt deformation process is in the district's controlled rolling of austenite non-recrystallization, crystalline polamer does not more all take place in austenite deformation process from start to finish, along with Strain Accumulation, the austenite flattening has increased intracrystalline dislocation and Zona transformans forming core point; After finish to gauge was finished, cold by adding speed control, in the ferrite/bainite phase transition process, crystal boundary and dislocation, Zona transformans etc. were located the forming core situation of growing up and are reached unanimity at austenite, finally obtained metallographic structure even, refinement, had eliminated mixed crystal phenomenon.

In the hot continuous rolling process, high temperature open rolling parameter control is the most important, its main purpose is control deformation temperature and a single pass drafts, with guarantee austenite in high temperature open rolling process, do not take place dynamic recrystallization and subsequently the road minor tick static state crystallization does not more take place.Concrete control deformation temperature is: 1100～1180 ℃ of soaking temperatures, and start rolling temperature≤1050 ℃, deflection is between 40%～50%.The too little meeting of deflection strengthens follow-up drafts, along with temperature reduces, increases mill load; And deflection is too big, is easy to generate partial dynamic crystallization or the crystallization again of road minor tick generation static state again, causes last phase transformation mixed crystal phenomenon to occur.

At the continuous casting and rolling technique of sheet bar flow process of 5～7 frames, the relative reduction ratio principle of each passage is: F1～F2:40～50%; F3～F4:20～40%; F5～F7:5～30%.

The cold process of control after finish to gauge is finished: in order to obtain the comparatively tiny crystallite dimension of grain size, adopt the mode of quickening cooling, the control speed of cooling should be greater than 10 ℃/s.

According to the operation principle of above-mentioned purpose and technical scheme, the concrete technical scheme of the present invention is:

Adopt the process of thin slab for continuous casting and rolling to produce low-carbon high-niobium high-strength toughness steel band, the chemical composition of used steel band (percetage by weight) is: C 0.01%-0.10%; Nb 0.08%-0.20%; Si0.05%-0.5%; Mn 0.1%-2.0%; P 0.005-0.025%; N≤0.01%, surplus is Fe and unavoidable impurities.In the CSP operation, the strand soaking temperature is controlled at 1100～1180 ℃, start rolling temperature≤1050 ℃, and deflection is between 40%～50%; 800～900 ℃ of finishing temperatures, 500～650 ℃ of coiling temperatures.

Other technical scheme is: in the CSP operation, adopt 5～7 cover frame hot rollings, reduction ratio is F1～F2:40～50% relatively, F3～F4:20～40%, F5～F7:5～30%.

Adopt the control cooling, be cooled fast to coiling temperature after the finish to gauge, cooling velocity is greater than 10 ℃/s.

The present invention has compared with prior art that cost is low, technology is simple, has eliminated mixed crystal phenomenon, makes final steel band even tissue refinement, thus the advantage of satisfactory mechanical property.The performance indications that it is concrete: Rp _0.2〉=510Mpa, R _m〉=600Mpa, the summer is than impact absorbing energy (20 ℃) 〉=86J, percentage elongation 〉=24%.

Description of drawings

Fig. 1 adds bainite metallographic structure figure for the embodiment of the invention 1 is resulting for tiny ferrite.

Fig. 2 is the embodiment of the invention 2 resulting tiny even bainite metallographic structure figure of being.

Fig. 3 is the embodiment of the invention 3 resulting tiny even ferrite metallographic structure figure of being.

The specific embodiment

Utilize existing continuous casting and rolling technique of sheet bar flow process to comprise: it is that 70mm, finished product are rolled up wide 1040mm that (electric furnace) converter, ladle refining furnace, thin-slab caster, soaking pit, continuous hot-rolling mill, laminar flow cooling and downcoiler, embodiment of the invention sheet billet continuous casting and rolling production line are about 400 meters, slab thickness.

The embodiment of the invention has prepared 3 batches of low-carbon high-niobium high-strength toughness steel belts, and its chemical composition sees Table 1, and table 2 is routine processing step and technological parameter contrast table for the embodiment of the invention is compared with the prior art, and the performance indications of the embodiment of the invention see Table 3.Table 4 is the chemical composition and the finished product mechanical property contrast table of prior art Comparative Examples.Contrast is listed Comparative Examples in the table in simultaneously for convenience, and in the above-mentioned tabulation, 1-5# is the embodiment of the invention.6# is the prior art Comparative Examples.

Table 1 embodiment of the invention steel is compared with the prior art the chemical composition contrast table (wt%) of example

Embodiment of the invention hot continuous rolling process: after strand goes out even stove, remove surface scale, enter 5～7 frame hot continuous rolling units through descaling mill, 1100～1180 ℃ of strand soaking temperatures, start rolling temperature≤1050 ℃, deflection is between 40%～50%; 800～900 ℃ of finishing temperatures, hot rolled strip thickness are 5mm.Reduction ratio is F1～F2:40～50% relatively, F3～F4:20～40%, F5～F7:5～30%.After finish to gauge is finished, adopt and be as cold as coiling temperature soon, 500～650 ℃ of coiling temperatures, cooling velocity is greater than 10 ℃/s.

The performance indications of table 3 embodiment of the invention are compared with the prior art routine contrast table

Table 4 is the chemical composition and the finished product mechanical property contrast table of prior art Comparative Examples

Claims (1)

1, a kind of process that adopts the thin slab for continuous casting and rolling to produce low-carbon high-niobium high-strength toughness steel band, the chemical composition of used steel band (percetage by weight) is: C 0.01%-0.10%; Nb0.08%-0.20%; Si 0.05%-0.5%; Mn 0.1%-2.0%; P 0.005-0.025%; N≤0.01%, surplus is Fe and unavoidable impurities, it is characterized in that in the CSP operation, the strand soaking temperature is controlled at 1100～1180 ℃, start rolling temperature≤1050 ℃, deflection is between 40%～50%; 800～900 ℃ of finishing temperatures, 500～650 ℃ of coiling temperatures;

In the CSP operation, adopt 5～7 cover frame hot rollings, reduction ratio is F1～F2:40～50% relatively, F3～F4:20～40%, F5～F7:5～30%;

Adopt the control cooling, be cooled fast to coiling temperature after the finish to gauge, cooling velocity is greater than 10 ℃/s.

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