CN104561790A

CN104561790A - 1500MPa-grade high-strength steel and production method thereof

Info

Publication number: CN104561790A
Application number: CN201510033919.5A
Authority: CN
Inventors: 田玉新
Original assignee: Baosteel Special Steel Co Ltd
Current assignee: Baowu Special Metallurgy Co Ltd
Priority date: 2015-01-23
Filing date: 2015-01-23
Publication date: 2015-04-29
Anticipated expiration: 2035-01-23
Also published as: CN104561790B

Abstract

The invention relates to 1500MPa grade high-strength steel and a production method thereof. The 1500MPa grade high-strength steel comprises the following chemical ingredients in percentage by weight: 0.20-0.30% of C, 1.50-1.80% of Si, 2.00-2.50% of Mn, 0.02-0.06% of Ti, 0.002-0.005% of B, 0.015-0.06% of Al and the balance of Fe and inevitable impurities, wherein the total content of impurity elements is less than or equal to 0.05%, and the elements also meet the relationship that Ti/C is more than or equal to 0.04 and less than or equal to 0.3. The production method of the 1500MPa grade high-strength steel comprises the following steps: steelmaking, rolling, carrying out forced cooling to the temperature of 300 DEG C or below from the temperature of 820 DEG C or above, then carrying out air cooling to room temperature, and finally tempering at low temperature of 200-250 DEG C, so that high-strength steel with tensile strength of 1500MPa grade and impact toughness more than or equal to 50J is obtained, and good combination of high strength and high toughness is realized.

Description

A kind of 1500MPa grade high-strength steel and production method thereof

Technical field

The invention belongs to field of alloy steel, be specifically related to a kind of 1500MPa grade high-strength steel and production method thereof.

Background technology

At present, in each fields such as the energy, traffic, machineries, the ferrous materials used all requires to have higher intensity and good impelling strength.Along with equipment develops to maximization and lightness, the intensity of material, toughness and cost performance are had higher requirement.Hardening high-strength steel, owing to having good combination of strength and toughness and stability, has been widely used in all kinds of engineering machinery.But most of hardening high-strength steel is usually containing a certain amount of noble element Cr, Mo, V etc., and needs out-line quenching+tempering heat treatment just can reach good performance, therefore causes production cost higher, and manufacturing process is complicated.

Existing 1500MPa level alloy steel is by increasing C content, or by adding a certain amount of noble element Cr, Mo etc., or could high performance requirements be met by off-line modifier treatment.

Chinese patent CN102534387 discloses a kind of 1500MPa level high-strong toughness bainite/martensite rail and manufacture method thereof, the main component of this steel is: C 0.10-0.40%, Si 0.80-2.00%, Mn 1.20-2.40%%, Cr 0.50-1.20%, Mo 0.20-0.60%.This invention steel obtains 1500MPa high strength and high tenacity by with the addition of a certain amount of Cr and Mo, but the interpolation of the noble elements such as Cr, Mo, the increase greatly of cost of alloy certainly will be caused.

Chinese patent CN101586207 discloses a kind of 1600MPa level physical construction hot rolling wire and manufacture method thereof, its main chemical compositions is: C 0.20-0.30%, Si 1.5-3.0%, Mn2.0-4.0%, Mo 0.2-0.3%, this invention is by the cooperation of Composition Design and rolling technology, take needle type martensite as Main Tissues, and be the hot rolling wire of feature containing bainite, ensure that wire rod has higher intensity, its tensile strength is at more than 1600MPa.But this invention steel Si, Mn content is relatively high, and improves obdurability and the solidity to corrosion of steel by adding a certain amount of noble element Mo, the cost of alloy is caused to increase.

The tensile strength that Chinese patent CN1900343 discloses a kind of excellent in delayed fracture resistance is the steel of 1600MPa level or more and the manufacture method of products formed thereof, its main chemical compositions is: C0.20-0.60%, Si≤0.50%, Mn 0.10-3.0%, Al 0.005-0.1%, Mo 3.0-10%, adds the alloying elements such as a certain amount of Cr, Ni, W, V, B, Ti, Nb, Cu in addition and carrys out improving SNR, because the content of the noble elements such as Mo is higher, production cost significantly increases.

Summary of the invention

The object of the present invention is to provide a kind of 1500MPa grade high-strength steel and production method thereof, this high-strength steel is not containing elements such as Cr, Mo, V, do not need out-line quenching can reach tensile strength in 1500MPa level, impelling strength AKu >=50J, there are good plasticity and toughness, and production cost is lower, manufacturing process is simple, can be widely used in the component manufacturing automobile, engineering machinery.

For achieving the above object, technical scheme of the present invention is:

The present invention adopts cheap C, Si, Mn element, and suitably adds the elements such as Ti, B of trace, by suitable pressure cooling and low-temperaturetempering after hot rolling, can obtain a kind of tensile strength at 1500MPa and have the steel alloy of good plasticity and toughness concurrently.

Concrete, a kind of 1500MPa grade high-strength steel of the present invention, its chemical component weight per-cent is: C:0.20 ~ 0.30%; Si:1.50 ~ 1.80%; Mn:2.00 ~ 2.50%; Ti:0.02 ~ 0.06%; B:0.002 ~ 0.005%; Al:0.015 ~ 0.06%; All the other are Fe and inevitable impurity, total amount≤0.05% of impurity element; And above-mentioned element needs satisfied following relation simultaneously: 0.04≤Ti/C≤0.3.

Further, the tensile strength of described 1500MPa grade high-strength steel in 1500MPa level, impelling strength >=50J.

The microstructure of described 1500MPa grade high-strength steel is the tempered martensite of thin lath-shaped.

In the Composition Design of steel of the present invention:

C: be ensure steel room temperature strength and the necessary composition of hardening capacity.C content is higher, and intensity is higher, and resistance to deformation increases simultaneously, and plasticity and toughness reduce.When C content lower than 0.20% time, hardening capacity and insufficient strength; C is higher than 0.30%, then toughness degenerates.Therefore, C content scope of the present invention is 0.20 ~ 0.30%.

Si: add in steel the effect serving deoxidation and solution strengthening.Solid solution Si in the base can affect interaction of dislocation, increases preliminary work hardening rate.Meanwhile, Si can hinder Carbon diffusion when tempering, delays the agglomeration of martensitic decomposition and carbide, significantly improves steel belt roof bolt stability and intensity.When Si content is lower than 1.50% DeGrain, content more than 1.80% after, processibility and toughness deteriorate.Therefore, Si content range of the present invention is 1.50 ~ 1.80%.

Mn: the effect with solution strengthening, refined crystalline strengthening.Mn makes the intensity of steel increase, and damages minimum element to toughness and plasticity.Increase the Mn content in steel, the intensity of steel can be made to increase, but during its too high levels, transformation temperature can be made to decline more, will bainite be occurred in tissue, and damage its toughness.In order to improve hardening capacity and guarantee intensity, Mn content must more than 2.00%, and on the other hand, if Mn too high levels, then the toughness of steel reduces.Therefore, Mn content range of the present invention is 2.00 ~ 2.50%.

Al: the effect serving deoxidation and crystal grain thinning in steel, adds in steel when smelting simultaneously, ensures that the recovery rate of Ti, B is stablized.When Al add-on lower than 0.015% time, DeGrain; When Al add-on is more than 0.06%, aluminium system inclusion particle can be made to increase, and mechanical property is deteriorated.Therefore, Al content range of the present invention is 0.015 ~ 0.06%.

Ti: mainly in steel form TiC to improve intensity with C, tiny TiC can stop Austenite Grain Growth in heat-processed, thinning microstructure, raising plasticity and toughness.But Ti content can not be too high, otherwise TiC particle is thick, not only effectively can not stop grain growth, and can damage the toughness of steel.Another object adding Ti in steel is the N element in fixing steel, thus avoids the combination of N and B and weaken the effect of B in steel.Therefore, Ti content range of the present invention is 0.02 ~ 0.06% scope.

B: be strongly improve hardening capacity element, the B of trace just significantly can postpone perlitic transformation, improves and obtains martensitic possibility.But B content lower than 0.002% time, it is not obvious to improve the effect of hardening capacity; B content higher than 0.005% time, steel easily produces hot-short, affects hot workability.Therefore, B content range of the present invention is 0.002 ~ 0.005%.

The feature of composition of steel design of the present invention is:

1) in steel of the present invention C content 0.20 ~ 0.30%, ensureing under the prerequisite obtaining certain obdurability, the element of pearlitic transformation is strongly postponed by adding Mn, B etc., be beneficial to produce martensitic transformation strengthening, but in order to give full play to the useful effect of B element, Al, Ti must be added with the N element in fixing steel, reduce B and N in conjunction with probability, increase the effect of solid solution B, under relatively low speed of cooling, obtain martensitic stucture to make steel.Meanwhile, the nitride particle that Al, Ti are formed can stop growing up of crystal grain, plays the effect of refinement martensitic stucture, improves the toughness of steel.

2) the present invention will ensure that steel obtains good mechanical property, also must guarantee TiC amount suitable in steel, because the amount of TiC can affect austenitic alloying level and austenitic grain-size greatly, and the relation between Ti and C decides the amount of TiC in steel, as Ti/C>0.3, intensity disqualification rate increases, and during Ti/C<0.04, plasticity and toughness disqualification rate increases.Therefore, the present invention controls 0.04≤Ti/C≤0.3.

3) the present invention's compound in low alloy steel adds trace Ti+B element, can not only improve the intensity of steel, but also can improve the plasticity of steel and reduce notch sensitivity; Adding higher Si content is consider that Si can hinder Carbon diffusion when tempering, delays the agglomeration of martensitic decomposition and carbide, significantly improves steel belt roof bolt stability and intensity.But be in the steel of 0.20 ~ 0.30% scope in C content, during Si > 1.80%, not only plasticity reduces, and greatly can reduce the impelling strength of steel, and therefore, the present invention's control Si content is 1.50 ~ 1.80%.

The production method of 1500MPa grade high-strength steel of the present invention, comprises the steps:

1) smelt, cast

By mentioned component steel-making, refining, is molded into steel ingot or continuous casting becomes strand, and adopt cast cold, wherein, die casting teeming temperature is 1520 ~ 1530 DEG C, continuous casting temperature 1496 ~ 1506 DEG C;

2) steel ingot or strand heating

Heating temperature is 1180 ~ 1230 DEG C, and soaking time is 2 ~ 4h.

3) rolling

Start rolling temperature is 1080 ~ 1120 DEG C, and finishing temperature is 820 ~ 900 DEG C, and all >=18%, be cooled to less than 300 DEG C with the cooling rate of >=35 DEG C/S after finish to gauge, air cooling is to room temperature subsequently for last two pass deformations of rolling.

4) tempering heat treatment

Tempering temperature is 200 ~ 250 DEG C, and soaking time is 2 ~ 4h, namely obtains tensile strength in 1500MPa level, the high-strength steel of impelling strength >=50J, and its microstructure is the tempered martensite of thin lath-shaped.

Further, step 1) when smelting, molten steel is carrying out alloying again after abundant deoxidation, and alloying order is:

In production method of the present invention:

Step 1 of the present invention) smelting technology: during smelting, make basic slag, ensure that the good and slag look of slag fluidity bleaches.In order to improve the recovery rate of alloying element Ti, B, molten steel is carrying out alloying again after abundant deoxidation, alloying order: add Al before adding Fe-Ti, and Al calculates by 0.6 ~ 0.8Kg/t and adds; Add Al again after adding Fe-Ti, Al calculates by 0.4 ~ 0.6Kg/t and adds; Again Fe-B Al suitcase is added in molten steel well afterwards.After electric furnace steel tapping, reply molten steel carries out sufficient external refining, removes harmful element, non-metallic inclusion and gas in steel to greatest extent, ensures the purity of molten steel, is conducive to the toughness improving steel.

Step 1 of the present invention) pouring technology: adopt cast cold, wherein, die casting teeming temperature is 1520 ~ 1530 DEG C, and continuous casting temperature 1496 ~ 1506 DEG C, to reduce solidifying segregation.

Step 2 of the present invention) heating: in order to improve the plasticity and toughness of steel, should strictly control hot-work condition.In heating process, heating and temperature control, at 1180 ~ 1230 DEG C, carries out high-temperature homogenization process, and insulation enough time, guarantees the abundant dissolving of bulk carbide and the elimination of as cast condition segregation in as-cast structure, is conducive to the plasticity and toughness improving steel.

Step 3 of the present invention) rolling technology: start rolling temperature is 1080 ~ 1120 DEG C, and finishing temperature is 820 ~ 900 DEG C, and finishing temperature is too high easily causes grain growth, is unfavorable for deformation-induced precipitation; Control last two pass deformations, pass deformation controls >=18%, guarantees the abundant fragmentation of as-cast structure and obtains fine grained texture, being conducive to the raising of intensity and toughness; Water cooling after finish to gauge, is cooled to less than 300 DEG C with the cooling rate of >=35 DEG C/S, and ensure that stocking evenly cools fast, air cooling is to room temperature subsequently, obtains martensitic stucture.

The present invention is in the operation of rolling, a large amount of distortion dislocations is produced in deformed austeaite, in process subsequently, a large amount of deformation dislocation rearranges, form a large amount of dislocation cell structure and subgrain, meanwhile, nitride tiny in a large number or carbonitride particle are separated out in dislocation and dislocation cell structure, facilitate the refinement of deformed microstructure.

For preventing cracking after rolling of the present invention, temper should be carried out in time, specifically the material after air cooling is entered 200 ~ 250 DEG C of annealing furnaces and carry out low-temperaturetempering, eliminate stress, complete structural transformation, make to organize more stable, obtain the tempered martensite of thin lath-shaped, this martensitic stucture not only intensity is quite high, and has higher toughness.

The present invention, by the synergy between above-mentioned each element, can ensure that the reduction of toughness controls minimum while obtaining high strength by steel.After steel-making, rolling, force to be cooled to less than 300 DEG C more than 820 DEG C, air cooling is to room temperature subsequently, finally low-temperaturetempering at 200 ~ 250 DEG C, can reach tensile strength in 1500MPa level, and impelling strength is at more than 50J, achieves the good combination of high-intensity high-tenacity.Therefore, the present invention is by reasonable component proportioning, and simple rolling and on-line cooling technique obtain the 1500MPa grade high-strength steel of good mechanical performance.

Beneficial effect of the present invention:

1) steel of the present invention is not containing noble elements such as Cr, Mo, V, but by adding Ti, the B element of trace, improving the obdurability of steel, having saved alloy resource.

2) cooling forced by steel of the present invention after rolling, and then can reach the good combination of high-intensity high-tenacity through 200 ~ 250 DEG C of low-temperaturetemperings, its manufacturing process is simple, without the need to out-line quenching, thus save energy, reduce environmental pollution, shorten the production cycle and reduce manufacturing cost.

3) the 1500MPa grade high-strength steel that present component and manufacture method are produced is adopted, its tensile strength Rm is in 1500MPa level, yield strength Rp0.2 >=1235MPa, unit elongation A >=9.5%, relative reduction in area Z >=55%, impelling strength AKu >=50J, there is high strength, have good impelling strength concurrently, mechanical property is high, and low cost of manufacture, the quenched and tempered steel that therefore complete alternative performance is on close level on some engineer applied, its successful design and exploitation will bring huge economic benefit, and its market outlook are by boundless.

Embodiment

Below in conjunction with embodiment, the present invention will be further described.

Chemical composition designed according to this invention and production method produce 6 stove alloys, and the alloying constituent of embodiment 1 ~ 6 is as shown in table 1.

Embodiment 1:

Smelt obtained molten steel by table 1 chemical composition, teeming temperature 1525 DEG C, pours into a mould 2.3 tons of steel ingots, Heating Steel Ingots temperature 1200 DEG C, insulation 3h, start rolling temperature 1090 DEG C, finishing temperature 870 DEG C, control last two pass deformations 25%, mill product Φ 20mm bar, Water cooling to 300 DEG C, average cooling rate is about 38 DEG C/S, then air cooling is to room temperature, 250 DEG C of tempering, insulation 3h.

Embodiment 2:

Smelt obtained molten steel by table 1 chemical composition, teeming temperature 1520 DEG C, pours into a mould 2.3 tons of steel ingots, Heating Steel Ingots temperature 1180 DEG C, insulation 3h, start rolling temperature 1080 DEG C, finishing temperature 820 DEG C, control last two pass deformations 20%, mill product Φ 20mm bar, Water cooling to 293 DEG C, average cooling rate is about 35 DEG C/S, then air cooling is to room temperature, 200 DEG C of tempering, insulation 4h.

Embodiment 3:

Smelt obtained molten steel by table 1 chemical composition, teeming temperature 1530 DEG C, pours into a mould 2.3 tons of steel ingots, Heating Steel Ingots temperature 1220 DEG C, insulation 2h, start rolling temperature 1120 DEG C, finishing temperature 900 DEG C, control last two pass deformations 25%, mill product Φ 20mm bar, Water cooling to 285 DEG C, average cooling rate is about 41 DEG C/S, then air cooling is to room temperature, 240 DEG C of tempering, insulation 2h.

Embodiment 4:

Smelt obtained molten steel by table 1 chemical composition, teeming temperature 1526 DEG C, pours into a mould 2.3 tons of steel ingots, Heating Steel Ingots temperature 1190 DEG C, insulation 3h, start rolling temperature 1110 DEG C, finishing temperature 880 DEG C, control last two pass deformations 20%, mill product Φ 20mm bar, Water cooling to 298 DEG C, average cooling rate is about 39 DEG C/S, then air cooling is to room temperature, 200 DEG C of tempering, insulation 4h.

Embodiment 5:

Smelt obtained molten steel by table 1 chemical composition, teeming temperature 1524 DEG C, pours into a mould 2.3 tons of steel ingots, Heating Steel Ingots temperature 1210 DEG C, insulation 4h, start rolling temperature 1110 DEG C, finishing temperature 890 DEG C, control last two pass deformations 25%, mill product Φ 20mm bar, Water cooling to 287 DEG C, average cooling rate is about 40 DEG C/S, then air cooling is to room temperature, 230 DEG C of tempering, insulation 3h.

Embodiment 6:

Smelt obtained molten steel by table 1 chemical composition, teeming temperature 1525 DEG C, pours into a mould 2.3 tons of steel ingots, Heating Steel Ingots temperature 1230 DEG C, insulation 3h, start rolling temperature 1110 DEG C, finishing temperature 840 DEG C, control last two pass deformations 20%, mill product Φ 20mm bar, Water cooling to 286 DEG C, average cooling rate is about 37 DEG C/S, then air cooling is to room temperature, 200 DEG C of tempering, insulation 4h.

Sample embodiment 1 ~ 6 alloy, carry out tensile test at room temperature respectively, its result is as shown in table 2.As shown in Table 2, steel alloy of the present invention just can obtain excellent performance index after smelting, controlled rolling and controlled cooling and low-temperaturetempering process, and its mechanical property reaches the good combination of high-intensity high-tenacity completely.

The chemical composition (wt%) of table 1 embodiment 1 ~ 6

Embodiment	C	Si	Mn	Ti	B	Al
							Embodiment 1	0.21	1.60	2.17	0.03	0.003	0.02
Embodiment 2	0.24	1.52	2.24	0.02	0.002	0.03
							Embodiment 3	0.26	1.75	2.30	0.06	0.005	0.015
Embodiment 4	0.30	1.78	2.45	0.04	0.003	0.04
							Embodiment 5	0.27	1.63	2.50	0.05	0.004	0.03
Embodiment 6	0.29	1.71	2.02	0.03	0.003	0.06

The mechanical property of table 2 embodiment 1 ~ 6

Embodiment

Rm(MPa)

Rp0.2(MPa)

A(％)

Z(％)

AKu(J)

Embodiment 1	1495	1248	11	58	60
						Embodiment 2	1499	1250	10	57	58
Embodiment 3	1581	1344	9.5	55	54
						Embodiment 4	1577	1343	10	56	55
Embodiment 5	1519	1239	10	57	57
						Embodiment 6	1520	1235	10	55	56

Claims

1. a 1500MPa grade high-strength steel, its chemical component weight per-cent is: C:0.20 ~ 0.30%; Si:1.50 ~ 1.80%; Mn:2.00 ~ 2.50%; Ti:0.02 ~ 0.06%; B:0.002 ~ 0.005%; Al:0.015 ~ 0.06%; All the other are Fe and inevitable impurity, wherein, and total amount≤0.05% of impurity element; And above-mentioned element needs satisfied following relation simultaneously: 0.04≤Ti/C≤0.3.

2. 1500MPa grade high-strength steel according to claim 1, is characterized in that, the tensile strength of described 1500MPa grade high-strength steel in 1500MPa level, impelling strength >=50J.

3. 1500MPa grade high-strength steel according to claim 1 and 2, is characterized in that, the microstructure of described 1500MPa grade high-strength steel is the tempered martensite of thin lath-shaped.

4. the production method of 1500MPa grade high-strength steel as claimed in claim 1, comprises the steps:

1) smelt, cast

By composition steel-making described in the claims 1, refining, is molded into steel ingot or continuous casting becomes strand, and adopt cast cold, wherein, die casting teeming temperature is 1520 ~ 1530 DEG C, and continuous casting temperature is 1496 ~ 1506 DEG C;

2) steel ingot or strand heating

Heating temperature is 1180 ~ 1230 DEG C, and soaking time is 2 ~ 4h;

3) rolling

Start rolling temperature is 1080 ~ 1120 DEG C, and finishing temperature is 820 ~ 900 DEG C, and all >=18%, be cooled to less than 300 DEG C with the cooling rate of >=35 DEG C/S after finish to gauge, air cooling is to room temperature subsequently for last two pass deformations of rolling;

4) tempering heat treatment

Tempering temperature is 200 ~ 250 DEG C, and soaking time is 2 ~ 4h.

5. the production method of 1500MPa grade high-strength steel according to claim 4, is characterized in that, the tensile strength of 1500MPa grade high-strength steel that the method obtains in 1500MPa level, impelling strength >=50J.

6. the production method of the 1500MPa grade high-strength steel according to claim 4 or 5, is characterized in that, the microstructure of the 1500MPa grade high-strength steel that the method obtains is the tempered martensite of thin lath-shaped.