CN102747295B - Bainite sheet steel produced by controlled rolling and cooling method and preparation method thereof - Google Patents

Abstract

The invention belongs to the field of single rolled steel plate rolling processes in metallurgy industry, in particular relates to a bainite sheet steel produced by controlled rolling and cooling technology, and is characterized by comprising the following chemical components by weight: 0.02-0.08% of C, 0.25-0.55% of Si, 1.65-1.85% of Mn, not more than 0.015% of P, not more than 0.008% of S, 0.05-0.08% of Nb+Ti, 0.30-0.50% of Mo+Cr, 0.015-0.05% of Als and the balance of Fe and trace impurity elements, wherein C+Si/30+(Mn+Cr)/20+Mo/15 is not more than 0.25. According to the bainite sheet steel, the thickness specification range is 10-20 mm, the width of a finished product is not less than 0.85 time of nominal width of a rolling mill, unevenness of the steel plate is not more than 6 mm/m, the intensity index ReL is not less than 550 MPa, Rm is not less than 670 MPa, A is not less than 20%, and -20 DEG C Akv is not less than 200 J.

Description

A kind of bainite steel sheet that utilizes controlled rolling and controlled cooling method production and preparation method thereof

Technical field

The invention belongs to metallurgy industry list rolled steel plate rolling technology field, particularly a kind of bainite steel sheet that utilizes controlled rolling and controlled cooling method production and preparation method thereof.

Background technology

According to the difference of tissue topography, the kind of steel is generally divided into the heterogeneous type that pearlite type, bainite type, martensite type and heterogeneous structure thereof form.Wherein, bainitic steel is the steel class of tool development and application prospect, and it has kept high tenacity, good welding property, cold formability, erosion resistance and other application performance when intensity improves.In production, the steel of yield strength 460 ~ 620MPa rank mainly adopts bainite type tissue, be mainly used in the economic construction every field such as starting material exploitation, energy development, communications and transportation, construction of water conservancy works, town and country construction, become of paramount importance structured material, wherein thin specification (thickness≤20mm) market requirements of steel plates amount is very large.

At present, in the high-strength steel of uni-tension rolling is produced, realize by controlled rolling and controlled cooling (TMCP) technology generations and having implemented for traditional hardening and tempering process, thereby reduce production costs, reduce energy consumption, enhance productivity, its deficiency is as reaching bainite structure control target, generally to each processing parameter in production process, as Heating temperature, each stage rolling temperature, draft and roll rear cooling parameter etc. and all have stricter requirement, technology controlling and process difficulty, especially for thin specification wide plate width steel plate, in existing given process parameters range, be difficult to according to production practical situation adjusting process to meet steel-plate shape requirement, therefore to exceed standard be the maximum factor that affects this type of Plate Production to the roughness of thin specification (10-20mm) wide plate width steel plate (finished width is >=0.85 times of milling train nominal width) steel plate.

Summary of the invention

Technical problem to be solved by this invention is to overcome the deficiency of prior art and product quality level, from the angle of the market requirement, provides a kind of bainite steel sheet that utilizes controlled rolling and controlled cooling method production and preparation method thereof.

For solving the problems of the technologies described above, the present invention by the following technical solutions:

A kind of bainite steel sheet that utilizes Controlled Rolling And Controlled Cooling to produce, it is characterized in that: its chemical composition by weight percentage content is: C:0.02 ~ 0.08%, Si:0.25 ~ 0.55%, Mn:1.65 ~ 1.85%, P :≤0.015%, S :≤0.008%, Nb+Ti:0.05 ~ 0.08%, Mo+Cr:0.30 ~ 0.50%, Als:0.015 ~ 0.05%, all the other are Fe and micro impurity element, and C+Si/30+ (Mn+Cr)/20+Mo/15≤0.25.

Press such scheme, described bainite steel sheet thickness specification limit is 10 ~ 20mm, finished width >=0.85 times milling train nominal width, roughness≤6mm/m.

A bainite steel-sheet preparation method who utilizes Controlled Rolling And Controlled Cooling to produce, is characterized in that: it comprises the following steps:

(1) smelt by predetermined composition, obtain continuously cast bloom;

(2) rolling:

Continuously cast bloom, in 1180 ℃～1240 ℃ equal thermal treatments, is then carried out to two-stage control rolling on milling train, and start rolling temperature >=1070 ℃ of described first stage, are guaranteeing to adopt as far as possible heavy reduction rolling under milled sheet shape prerequisite; 950 ℃～980 ℃ of subordinate phase start rolling temperatures, finishing temperature >=850 ℃, rolling pass is controlled at 6 ~ 8 passages, and every time draft is not less than 15%, and last passage employing draught is that 1 ~ 2mm gently presses;

(3) accelerate cooling:

Adopt Mulpic to accelerate cooling, described final cooling temperature is controlled at 400 ℃～450 ℃, 10～20 ℃/s of rate of cooling, and upper lower collector pipe water is than being 1:1.2 ~ 1.8;

(4) waste heat self-tempering and straightening process:

Before aligning after accelerating cooling completing and to steel plate, by aforementioned processing and steel plate on roller-way, swing 80 ~ 120s, to carry out waste heat self-tempering, then carry out light reduction multi-pass aligning according to steel-plate shape situation, till leveling.

Press such scheme, accumulation draft >=35% of first stage in described rolling technology, the 3-4 that the workpiece thickness after rolling is finished product thickness is doubly.

C, Mn are the most effective solution strengthening elements, the content that increases Mn in steel will reduce the transformation temperature of steel, crystal grain thinning, in the time that the content of Mn exceedes 1.5%, also there is the effect that promotes steel bainite, and the bainite productivity in steel improves with the increase of Mn, considers welding property factor, therefore to adopt low-carbon high-manganese be basic chemical composition design in the present invention.

Cr is medium carbide forming element, dissolves in austenitic Cr and strongly improve hardening capacity when heating.Cr part displacement iron in steel forms alloyed cementite, improves its stability; A part is dissolved in bainite ferrite, produces solution strengthening, improves intensity and the hardness of matrix.Cr can not only make C curve obviously move to right, and makes bainite and bainite transformation region disconnecting, can significantly postpone perlitic transformation, makes steel obtain bainite structure within the scope of larger cooling rate.

Mo is present in the sosoloid and carbide of steel, has solution strengthening effect, and can improve the bainite hardening capacity of steel.Mo has significant retardation function to perlitic transformation, and less on the impact of bainite transformation, thereby can obtain whole bainite structures within the scope of sizable cooling rate.Cr and Mo add in steel simultaneously, strongly stop polygonal ferrite to be separated out, and for obtaining, full bainite structure effect is more obvious.Thereby guarantee that Plate Steel obtains uniform bainite structure within the scope of wider cooling rate.

In steel, add Nb, can by Nb (CN) not solute point and strain inducing separate out the recrystallize that suppresses high temperature deformation process, expand non-recrystallization district scope so that the execution of TMCP technique, thereby reach the object of refinement ferrite crystal grain; The interpolation of Ti, can play the effect of growing up that suppresses austenite crystal in heat-processed, and meanwhile, micro-alloy low-temperature district precipitate also can play the effect of precipitation strength.

In steel, can form acid-soluble aluminium (Als) and sour insoluble aluminium adding of Al, and Als comprises solid solution aluminium and AlN, and the AlN particle of disperse can stop growing up of austenite crystal, crystal grain thinning.

In steel, S, P are detrimental impurity elements, and P in steel, S content are more low better.In the time that S content is more in steel, when hot rolling, easily produce the problems such as hot-short; And when in steel, P content is more, it is cold short that steel easily occurs, in addition, also easily there is segregation in phosphorus.

Preparation technology of the present invention comprises that by the control of rolling technology slab heats in advance, optimization distribution to rolling pass and draught etc., the cooling front increase relaxation time can accelerated, be conducive to separating out and structure refinement of carboritride, and under certain External Force Acting, reducing the dislocation desity causing due to high-temperature reply reduces, be conducive to the raising of steel plate over-all properties, on the other hand, pass through to control draft or the draught of each passage in rolling technology subordinate phase, can utilize the capacity of equipment of milling train to carry out high-temperature straightening to steel plate, reach certain smooth effect, improve rolled sheet material plate shape, can guarantee that by adjusting Mulpic accelerated cooling process parameter steel plate is evenly cooling, thereby avoid steel plate to occur that in process of cooling wooden dipper song waits the problems such as plate shape is bad, controlling process of cooling steel-plate shape does not worsen, then the structural stress that utilizes the cooling rear waste heat self-tempering of acceleration that middle temperature phase transformation is produced fully discharges, adopt again light reduction multi-pass straightening process can avoid increasing steel plate unrelieved stress, can guarantee that the bent plate shape problem that waits of wooden dipper can not appear because of stress relief in steel plate in cold bed process of cooling, and it is final by controlling steel high temperature austenite tissue morphology, phase transition process, control the organization type of steel, form, distribute and separate out equal factor, make the bainite steel sheet meeting the demands.

The bainite steel-sheet manufacture method the present invention relates to adopts control to prick cooling control technology, by regulating and controlling the processing parameter in each processing step, solve thin specification wide plate width steel-plate shape problem, do not need thermal treatment, and without adding other any equipment, can prepare the bainite steel sheet of excellent performance, the bainite steel sheet thickness specification limit of preparation is 10 ~ 20mm thus, finished width >=0.85 times milling train nominal width, steel plate roughness≤6mm/m, intensity index: ReL(yield strength) >=550MPa, Rm(tensile strength) >=670MPa, A(unit elongation) >=20%,-20 ℃ of Akv (ballistic work) >=200J, compared with domestic and international equal yield strength rank steel grade, there is better low-temperature impact toughness (20 ℃ of Akv >=200J), be applicable to be manufactured on the steel equipment of working in extreme cold environment, expand product applications,

Production technique is easy to be controlled, and production efficiency is high.

Accompanying drawing explanation

Fig. 1 is the bainite steel-sheet rolling pattern figure in the embodiment of the present invention 1;

Fig. 2 is the bainite structure figure of the rich steel plate of bainite in the embodiment of the present invention 1.

Embodiment

Below in conjunction with example, summary of the invention of the present invention is described further:

Embodiment 1

The bainite steel sheet that utilizes Controlled Rolling And Controlled Cooling to produce, thickness is 10mm, width 3800mm, its chemical composition by weight percentage content in table 1, be specially: C:0.05%, Si:0.39%, Mn:1.68%, P:0.013%, S:0.004%, Nb+Ti:0.07%, Mo+Cr:0.35%, Als:0.035%, all the other are Fe and micro impurity element, and in C+Si/30+ (Mn+Cr)/20+Mo/15(table 1 referred to as Pcm) < 0.25;

Concrete preparation method is as follows:

(1), according to predetermined composition, in table 1, produce on line and smelt in 130t converter, and be cast into the continuously cast bloom that specification is 250mm × 1600mm × L.

Table 1 example steel chemical composition of the present invention (wt%)

Example	C	Si	Mn	P	S	Cr+Mo	Nb+ Ti	Als	Pcm
										1	0.05	0.39	1.68	0.013	0.004	0.35	0.07	0.035	＜0.25
2	0.02	0.50	1.70	0.012	0.005	0.40	0.08	0.030	＜0.25
										3	0.08	0.35	1.65	0.012	0.004	0.32	0.05	0.015	＜0.25
4	0.06	0.40	1.72	0.014	0.003	0.36	0.06	0.019	＜0.25

(2) rolling:

By after continuously cast bloom acceptance(check), in 1180 ℃～1240 ℃ equal thermal treatments, then on 4300mm milling train, carry out two-stage control rolling, 1198 ℃ of the start rolling temperatures of described first stage, guaranteeing to adopt as far as possible heavy reduction rolling under milled sheet shape prerequisite, make accumulation draft >=35% of first stage, the workpiece thickness after rolling is 40mm; 968 ℃ of subordinate phase start rolling temperatures, finishing temperature is 860 ℃, and rolling pass is 7 passages, and every time draft is not less than 15%, and last passage employing draught is that 1 ~ 2mm gently presses; Concrete rolling procedure is shown in Fig. 1, and rolling technological parameter condition setting is in table 2;

The control of table 2 controlled rolling process significant parameter

(3) accelerate cooling:

Adopt Mulpic to accelerate cooling, described final cooling temperature is controlled at 420 ℃, 18 ℃/s of rate of cooling, and upper lower collector pipe water is than being 1:1.3, accelerated cooling process Parameter Conditions arranges in table 3.

The control of table 3 cooling control technology significant parameter

Example	Upper lower collector pipe water ratio	Speed of cooling/℃/s	Final cooling temperature/℃
				1	1：1.2	18	420
2	1：1.8	16	440
				3	1：1.4	10	400
4	1：1.6	20	450

(4) waste heat self-tempering and straightening process:

After accelerating cooling completing and before steel plates straightening, by aforementioned processing and steel plate on roller-way, swing 100s, to carry out waste heat self-tempering, then carry out light reduction multi-pass aligning according to steel-plate shape situation, till leveling.Steel plate is cooled to room temperature non-planeness measurement and service check the results are shown in Table 4, and bainite structure figure is shown in Fig. 2.As seen from Figure 2: steel plate is organized as granular bainite and lath-shaped mixed structure, and homogeneous microstructure is tiny.

Steel plate irregularity degree in the each embodiment of table 4 and mechanical properties test result

Example	Roughness/mm/m	ReL/MPa	Rm/Mpa	A/%	-20℃Akv/J	Clod wash d=3a
							1	5	575	705	21.0	230	Qualified
2	4	565	690	21.5	215	Qualified
							3	4	580	710	20.5	220	Qualified
4	5	570	715	21.0	235	Qualified

Embodiment 2-4

With reference to the method for embodiment 1, according to component concentration design and the each bainite steel sheet of the corresponding preparation of processing condition in table 1-table 3, wherein: in embodiment 2-4, the rolling time of waste heat self-tempering light plate on roller-way is respectively 80s, 90s, 120s, the bainite steel sheet chemical composition content preparing is thus in table 1, and steel plate irregularity degree and mechanical properties test the results are shown in Table 4.

Claims (4)

1. a bainite steel sheet that utilizes Controlled Rolling And Controlled Cooling to produce, it is characterized in that: its chemical composition by weight percentage content is: C:0.02 ~ 0.08%, Si:0.25 ~ 0.55%, Mn:1.65 ~ 1.85%, P :≤0.015%, S :≤0.008%, Nb+Ti:0.05 ~ 0.08%, Mo+Cr:0.30 ~ 0.50%, Als:0.015 ~ 0.05%, all the other are Fe and micro impurity element, and C+Si/30+ (Mn+Cr)/20+Mo/15≤0.25, unit elongation >=20% ,-20 ℃ of Akv >=200J; Its preparation method comprises the following steps:

(1) smelt by predetermined composition, obtain continuously cast bloom;

(2) rolling:

Continuously cast bloom, in 1180 ℃～1240 ℃ equal thermal treatments, is then carried out to two-stage control rolling on milling train, and start rolling temperature >=1070 ℃ of described first stage, are guaranteeing to adopt as far as possible heavy reduction rolling under milled sheet shape prerequisite; 950 ℃～980 ℃ of subordinate phase start rolling temperatures, finishing temperature >=850 ℃, rolling pass is controlled at 6 ~ 8 passages, and every time draft is not less than 15%, and last passage employing draught is that 1 ~ 2mm gently presses;

(3) accelerate cooling:

Adopt Mulpic to accelerate cooling, described final cooling temperature is controlled at 400 ℃～450 ℃, 10～20 ℃/s of rate of cooling, and upper lower collector pipe water is than being 1:1.2 ~ 1.8;

(4) waste heat self-tempering and straightening process:

Before aligning after accelerating cooling completing and to steel plate, by aforementioned processing and steel plate on roller-way, swing 80 ~ 120s, to carry out waste heat self-tempering, then carry out light reduction multi-pass aligning according to steel-plate shape situation, till leveling.

2. the bainite steel sheet that utilizes Controlled Rolling And Controlled Cooling to produce according to claim 1, is characterized in that: described bainite steel sheet thickness specification limit is 10 ~ 20mm, finished width >=0.85 times milling train nominal width, roughness≤6mm/m.

3. the bainite steel-sheet preparation method who utilizes Controlled Rolling And Controlled Cooling to produce according to claim 1, is characterized in that: it comprises the following steps:

(1) smelt by predetermined composition, obtain continuously cast bloom; ;

(2) rolling:

Continuously cast bloom, in 1180 ℃～1240 ℃ equal thermal treatments, is then carried out to two-stage control rolling on milling train, and start rolling temperature >=1070 ℃ of described first stage, are guaranteeing to adopt as far as possible heavy reduction rolling under milled sheet shape prerequisite; 950 ℃～980 ℃ of subordinate phase start rolling temperatures, finishing temperature >=850 ℃, rolling pass is controlled at 6 ~ 8 passages, and every time draft is not less than 15%, and last passage employing draught is that 1 ~ 2mm gently presses;

(3) accelerate cooling:

Adopt Mulpic to accelerate cooling, described final cooling temperature is controlled at 400 ℃～450 ℃, 10～20 ℃/s of rate of cooling, and upper lower collector pipe water is than being 1:1.2 ~ 1.8;

(4) waste heat self-tempering and straightening process:

Before aligning after accelerating cooling completing and to steel plate, by aforementioned processing and steel plate on roller-way, swing 80 ~ 120s, to carry out waste heat self-tempering, then carry out light reduction multi-pass aligning according to steel-plate shape situation, till leveling.

4. the bainite steel-sheet preparation method who utilizes Controlled Rolling And Controlled Cooling to produce according to claim 3, is characterized in that: accumulation draft >=35% of first stage in described rolling technology, the 3-4 that the workpiece thickness after rolling is finished product thickness doubly.