CN104060164B - A kind of hot rolled steel plate for cold formation and manufacture method thereof - Google Patents

Abstract

The invention discloses a hot-rolled steel plate for cold forming and a manufacturing method thereof. The preparation method of the hot-rolled steel plate for cold forming includes a steelmaking step, a continuous casting step, a heating step, a hot continuous rolling step and a coiling step. That is, the composition of the molten steel after steelmaking is: 0.05-0.1% by weight of C, ≤0.1% by weight of Si, 1.7-1.95% by weight of Mn, 0.03-0.07% by weight of Nb, and 0.09-0.14% by weight of Ti , 0.1-0.3% by weight of Mo, ≤0.025% by weight of P, ≤0.01% by weight of S, the balance being Fe and unavoidable impurities; the finishing rolling temperature in the hot continuous rolling step is 850-900 °C; the coiling temperature in the coiling step is 530-580 °C. According to the method of the present invention, a high-strength hot-rolled steel sheet for cold forming with a yield strength of 750 MPa can be provided.

Description

A kind of hot-rolled steel plate for cold forming and its manufacturing method

technical field

The invention relates to a hot-rolled steel plate for cold forming and a manufacturing method thereof, in particular to a high-strength hot-rolled steel plate for cold forming with a yield strength of 750 MPa and a preparation method thereof.

Background technique

In order to avoid the influence of hot-forming process on the softening of hot-rolled steel plate material, in practical application, it is an economical and practical method to use cold-forming process to process cold-bent parts for hot-rolled steel plate with small thickness. Hot-rolled steel sheets for forming have been greatly developed, and hot-rolled steel sheets for cold forming are widely used in automobiles, engineering machinery, steel structures, construction and other fields.

The yield strength of the hot-rolled steel plate first used in the cold forming process is within 400MPa. With the development of various industries, in order to reduce production costs and improve component safety, this strength level of steel can no longer meet the requirements of users. Higher-level hot-rolled steel sheets for cold forming are adopted. In the automotive field, in order to reduce the weight of automobiles, reduce fuel consumption, improve the strength of automobile components, and ensure safety performance, the strength level of hot-rolled steel sheets for automobile beams has been increased to yield strength. More than 650MPa; with the increase of building height and the improvement of safety performance requirements, the level of cold-formed hot-rolled steel sheets for construction has also increased from 345MPa to 420MPa or even 460MPa.

Zhou Suihua of Dongfeng Motor Company analyzed the Domex 700MC hot-rolled steel plate produced by SSAB in Sweden, and its chemical composition requirements were ≤0.12 wt% C, ≤2.1 wt% Mn, ≤0.07 wt% Nb, ≤0.1 wt% % Ti, ≤0.5% by weight Mo, the mechanical properties of a typical finished steel plate are Rel=735MPa, Rm=820MPa, A=16%, Domex 700MC contains Mo precious elements, the production cost is high, and the Domex 700MC hot-rolled steel plate The elongation is low; Zhang Fengquan of Beijing University of Science and Technology discussed the TS780 hot-rolled steel plate developed by Kawasaki Corporation of Japan in the article on the status quo and development of low-alloy steel for automobiles. Its chemical composition is 0.08% by weight of C, 1.5% by weight of Si, With 1.8% by weight of Mn and 0.1% by weight of Ti, the mechanical properties of the finished steel plate are Rm≥800MPa, A≥20%, and the titanium precipitation strengthening of the ferrite phase and the multiphase structure of ferrite+martensite have been achieved. Good overall performance, but the final rolling temperature and coiling temperature for producing this kind of steel plate are low, and the production process is difficult; Chen Yan from the Technology Center of Anshan Iron and Steel Co., Ltd. wrote an article on the product development strategy of JFE Iron and Steel Company in Japan about the NANO-HITEN developed by NKK The steel has been studied, the chemical composition is 0.2% by weight of C, 1.46% by weight of Si, 1.45% by weight of Mn, the mechanical properties are Rel=670MPa, Rm=830MPa, A=39%, the final rolling temperature of NANO-HITEN steel plate The temperature is 800°C, the coiling temperature is 380°C, the low carbon level and the addition of molybdenum avoid the formation of pearlite, but the final rolling temperature and coiling temperature are low, and the production process is difficult; Hunan Valin Lianyuan Iron and Steel Co., Ltd. Jiao Guohua and other inventions A method for producing high-strength steel with a yield strength of 700MPa grade, the chemical composition content of which is 0.03-0.08% by weight of C, 0.2-0.5% by weight of Si, 1.4-2% by weight of Mn, and 0.1-0.15% by weight of Ti, 0.02-0.08% by weight of Nb, 0-0.03% by weight of V, using thin slab continuous casting and rolling process, the final rolling temperature is 820-880 ° C, after laminar cooling, the coiling temperature is 550-620 ° C, the product The yield strength range is 690-760MPa, the crimping temperature is low, and the production process is difficult; a 700MPa-grade composite strengthened bainite steel invented by Mao Xinping, Guangzhou Zhujiang Iron and Steel Co., Ltd. and its preparation method adopt thin slab continuous casting Continuous rolling process, its chemical composition content is 0.03-0.07% by weight of C, 1.51-2.1% by weight of Mn, 0.5-0.8% by weight of Cr, 0.1-0.15% by weight of Ti, the structure of steel is fine bainite Mainly, the yield strength of the product can reach more than 700MPa. The steel plate contains Cr, and the Ti content is high, the production cost is high, the coiling temperature is low, and the production process is difficult.

It can be seen that the production technology route of high-strength hot-rolled steel sheets above 700MPa generally adopts the micro-alloying route of adding precious elements such as chromium, niobium, molybdenum and vanadium, and the molybdenum content of some steel types even reaches 0.5 wt% Mo, and the chromium content reaches 0.5-0.8% Cr by weight. In addition, some products adopt thin slab continuous casting and rolling process, low final rolling temperature (such as 800 ℃), low coiling temperature (such as 380 ℃) and conventional cooling process, so that bainite or martensite can be introduced into the finished structure. Body strengthening, the production process is more difficult. At the same time, the Si content of all steel types is more than 0.1% by weight. There is no problem in delivering hot-rolled steel sheets for cold forming with this composition as hot-rolled products, but the Si content of more than 0.1% by weight will definitely reduce the adhesion of the coating. Therefore, steel billets with this silicon content cannot be used as raw materials for cold-rolled coating products. In this way, raw materials with different chemical compositions will be used for hot-rolled products and cold-rolled products, resulting in many steel grades in steel mills, which is difficult for smelting and The production organization arrangement in continuous casting brings great difficulties, which is not conducive to the utilization rate of the slab warehouse and the hot delivery and hot charging rate, and cannot carry out flexible production.

Contents of the invention

The purpose of the present invention is to provide a new high-strength steel plate for cold forming with a yield strength of 750 MPa in order to overcome the defects of high production cost and difficult production process of high-strength hot-rolled steel sheets with a yield strength of 750 MPa for cold forming in the prior art. Hot-rolled steel sheet and its manufacturing method.

The inventors of the present invention unexpectedly discovered in the research that the niobium, titanium, manganese, and molybdenum microalloying methods are used, and the components are controlled within an appropriate content range, and the high finish rolling and finishing rolling at 850-900°C are used. Temperature and high coiling temperature of 535-580°C can make the produced high-strength hot-rolled steel sheet for cold forming have high strength and high toughness without adding precious elements such as Cr and V, and high finish rolling and finishing rolling The high temperature and high coiling temperature make the production process control simple. In addition, by using low content of silicon components, the billet can be used as the raw material for hot rolling steel sheets for cold forming, and can also be used as cold rolled steel sheets and cold rolled coated steel sheets. It can unify the composition of hot-rolled products and cold-rolled products, reduce the mixed pouring between steel types, benefit the utilization rate of slab warehouse and hot delivery and hot charging of steel slabs, and help realize flexible production, reduce Difficulty in the production organization of steel mills, and improve the production efficiency of steel mills.

Therefore, in order to achieve the above object, on the one hand, the present invention provides a method for manufacturing a hot-rolled steel sheet for cold forming, the method comprising a steelmaking step, a continuous casting step, a heating step, a continuous hot rolling step and a coiling step, wherein , the composition of molten steel after steelmaking is: 0.05-0.1% by weight of C, ≤0.1% by weight of Si, 1.7-1.95% by weight of Mn, 0.03-0.07% by weight of Nb, 0.09-0.14% by weight of Ti, 0.1-0.3% by weight of Mo, ≤0.025% by weight of P, ≤0.01% by weight of S, the balance being Fe and unavoidable impurities; the finishing rolling temperature in the hot continuous rolling step is 850-900°C ; The coiling temperature in the coiling step is 535-580°C.

Preferably, the molten steel composition after steelmaking is: 0.05-0.08% by weight of C, ≤0.05% by weight of Si, 1.8-1.95% by weight of Mn, 0.045-0.06% by weight of Nb, 0.1-0.125% by weight Ti, 0.15-0.25% by weight Mo, ≤0.025% by weight P, ≤0.01% by weight S, the balance being Fe and unavoidable impurities.

Preferably, the finish rolling temperature in the hot continuous rolling step is 870-895°C; the coiling temperature in the coiling step is 540-575°C.

Preferably, after finish rolling, it is cooled to the coiling temperature at a cooling rate of 10-30°C/s.

In another aspect, the present invention provides a hot-rolled steel sheet for cold forming produced by the above method.

The present invention adopts niobium, titanium, manganese and molybdenum microalloying method, and controls the composition of molten steel after steelmaking to be: 0.05-0.1% by weight of C, ≤0.1% by weight of Si, 1.7-1.95% by weight of Mn, 0.03-0.07% by weight % by weight of Nb, 0.09-0.14% by weight of Ti, 0.1-0.3% by weight of Mo, ≤0.025% by weight of P, ≤0.01% by weight of S, the balance being Fe and unavoidable impurities. It avoids the addition of precious elements such as Cr and V, and reduces the production cost; at the same time, it adopts high-temperature final rolling, high-temperature coiling and rapid cooling process systems to successfully produce acicular ferrite-based high-strength steel for cold forming with a yield strength of 750MPa. The high-strength hot-rolled steel plate has simple rolling process control and strong adaptability; moreover, the mechanical properties of the high-strength hot-rolled steel plate for cold forming met the requirements of the high-strength hot-rolled steel plate for cold forming.

Other features and advantages of the present invention will be described in detail in the following detailed description.

detailed description

Specific embodiments of the present invention will be described in detail below. It should be understood that the specific embodiments described here are only used to illustrate and explain the present invention, and are not intended to limit the present invention.

The invention provides a method for manufacturing a hot-rolled steel plate for cold forming, the method comprising a steelmaking step, a continuous casting step, a heating step, a hot continuous rolling step and a coiling step, wherein the composition of the molten steel after steelmaking is : 0.05-0.1 wt% C, ≤0.1 wt% Si, 1.7-1.95 wt% Mn, 0.03-0.07 wt% Nb, 0.09-0.14 wt% Ti, 0.1-0.3 wt% Mo, ≤0.025 The P of weight %, the S of ≤0.01 weight %, the balance is Fe and unavoidable impurity; The finish rolling finish rolling temperature in the hot continuous rolling step is 850-900 ℃; The coiling in the coiling step The temperature is 535-580°C.

According to the present invention, as long as the composition of molten steel after steelmaking is: 0.05-0.1% by weight of C, ≤0.1% by weight of Si, 1.7-1.95% by weight of Mn, 0.03-0.07% by weight of Nb, 0.09-0.14% by weight Ti, 0.1-0.3% by weight of Mo, ≤0.025% by weight of P, ≤0.01% by weight of S, the balance being Fe and unavoidable impurities; the finishing rolling temperature in the hot continuous rolling step is 850 -900°C; the coiling temperature in the coiling step is 535-580°C, which can achieve the purpose of the present invention, that is, reduce the production cost, the rolling process is simple to control, and the manufactured hot-rolled steel plate for cold forming meets Requirements for high-strength hot-rolled steel sheets for cold forming. But preferably, the composition of molten steel after steelmaking is: 0.0.05-0.08% by weight of C, ≤0.05% by weight of Si, 1.8-1.95% by weight of Mn, 0.045-0.06% by weight of Nb, 0.1-0.125% by weight % of Ti, 0.15-0.25% by weight of Mo, ≤0.025% by weight of P, ≤0.01% by weight of S, and the balance is Fe and unavoidable impurities, which can further improve the production of high-strength hot-rolled steel sheets for cold forming strength and toughness.

In addition, in order to further improve the strength and toughness of the produced high-strength hot-rolled steel sheet for cold forming, the finishing rolling temperature in the hot continuous rolling step is preferably 870-895°C, more preferably 875-895°C; preferably The coiling temperature in the coiling step is 540-575°C; more preferably 545-570°C.

In the present invention, there is no special requirement for the steelmaking step, and the steelmaking process commonly used in this field can be adopted, for example, after molten iron desulfurization, converter smelting, and LF furnace Ca treatment, the composition of molten steel is controlled to: 0.05-0.1% by weight of C, ≤0.1% by weight of Si, 1.7-1.95% by weight of Mn, 0.03-0.07% by weight of Nb, 0.09-0.14% by weight of Ti, 0.1-0.3% by weight of Mo, ≤0.025% by weight of P, ≤0.01% by weight S, the balance is Fe and unavoidable impurities.

The continuous casting process commonly used in this field can also be adopted for the continuous casting step, for example, adopt integral argon gas sealing casting, molten steel is injected into the tundish through the sliding nozzle at the bottom of the ladle, and the tundish temperature has no special requirements, which is the conventional temperature used in this field. For example, it is 1530-1560°C, using a funnel-shaped crystallizer, and there is no special requirement for casting slab casting speed, which is a conventionally used casting slab casting speed in this field, for example, 0.7-0.9m/min, and the continuous casting slab obtained in the continuous casting step The thickness is preferably 200-250mm.

In the present invention, the heating step is preferably to heat the slab at a temperature of 1230-1265°C (preferably 1240-1260°C) (heating includes a preheating section, a soaking section, etc.), and the slab can be heated in various conventional It is carried out on the device used for casting slab heating, for example, the device for slab heating can be a walking furnace.

In the present invention, the continuous hot rolling step is to make the heated cast slab go through high-pressure water descaling to remove the oxide scale formed on the surface, then enter the reversible rough rolling unit, and roll through 5-7 passes. Less than 20% (preferably 21-36%), the thickness of the intermediate billet after rough rolling is 40-60mm, and then enters the hot coil box, the strip head and tail are exchanged, and then finish rolling, the thickness of the steel plate after finish rolling Preferably 5-10mm. There is no special requirement for the exit temperature of the rough rolling, and a commonly used temperature in the field can be used, for example, the exit temperature of the rough rolling is 1030-1080°C, preferably 1050-1070°C. The starting temperature of finishing rolling is preferably 950-1000°C, preferably 975-1000°C; in addition, as mentioned above, the finishing rolling temperature is 850-900°C; preferably 870-895°C; more preferably 875-895°C .

In the present invention, the coiling step is a step in which the coil is coiled by a coiler after being cooled. The mode of cooling is preferably laminar cooling, and laminar cooling is preferably cooling from finish rolling and finishing temperature to coiling temperature at a cooling rate of 10-30°C/s, more preferably at a cooling rate of 15-26°C/s The cooling rate is from the finishing rolling temperature to the coiling temperature. The coiling temperature is 535-580°C, preferably 540-575°C; more preferably 545-570°C.

The present invention also provides a high-strength hot-rolled steel plate for cold forming prepared by the method. The structure of the high-strength hot-rolled steel sheet for cold forming is mainly acicular ferrite. The high-strength hot-rolled steel sheet for cold forming has a yield strength of 750 MPa or more, preferably 755-780 MPa, a tensile strength of 800 MPa or more, preferably 820-860 MPa, and an elongation of 17% or more, preferably 17-21%.

The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention. These simple modifications All belong to the protection scope of the present invention.

Example

The following examples will further illustrate the present invention, but do not limit the present invention thereby.

Example 1-5

After the steelmaking step (see Table 1 for the composition of the molten steel after steelmaking), the molten steel is cast in an integral argon gas seal, and the molten steel is injected into the tundish through the sliding nozzle at the bottom of the ladle. The temperature of the tundish is 1538°C. The casting speed of the slab is 0.7m/min, and the thickness of the continuous casting slab is 200mm~230mm; the continuous casting slab is heated in the heating furnace, and the heated slab is dephosphorized by high-pressure water to remove the oxide scale formed on the surface, and then enters the In the reversible rough rolling unit, the intermediate billet after rough rolling enters the hot coil box, the strip head and tail are exchanged, and then the finish rolling is carried out. After the finish rolling, laminar cooling and coiling are carried out to obtain hot-rolled steel plates. Among them, The temperature of slab heating, the exit temperature of rough rolling, the thickness of intermediate slab after rough rolling, the entrance temperature of finish rolling, the finish rolling temperature of finish rolling, the cooling rate of laminar cooling, the coiling temperature and the thickness of steel plate are shown in Table 2 respectively .

Sampling at the end of the steel coil of the hot-rolled steel sheet for cold forming made in the above Examples 1-5, and detecting the yield strength (ReL), tensile strength (Rm) and Elongation (A%); According to the method specified in GB/T232-2010, the cold bending performance is tested (B=35mm, α=180°, d=2a; d represents the diameter of the bending center, a represents the thickness of the sample, and α represents the bending Angle, B represents the width of the sample), and the test results are shown in Table 3.

Table 1

Table 2

table 3

Example Yield strength (MPa) Tensile strength (MPa) Elongation (%) Cold bending performance 1 765 832 19.5 qualified 2 772 849 18.0 qualified 3 756 823 20.5 qualified 4 768 844 19.0 qualified 5 775 857 17.5 qualified

Note: In the cold bending performance test, no cracking is qualified, and cracking is unqualified.

It can be seen from the above Tables 1-3 that the hot-rolled steel sheet for cold forming produced by the method of the present invention has both high strength and high toughness, and its mechanical properties fully meet the requirements of high-strength hot-rolled steel sheet for cold forming.

Claims (9)

1. a manufacturing method of hot-rolled steel plate for cold forming, the method comprises steelmaking step, continuous casting step, heating step, continuous hot rolling step and coiling step, it is characterized in that, the molten steel composition after described steelmaking is : 0.05-0.08 wt% C, ≤0.05 wt% Si, 1.8-1.95 wt% Mn, 0.045-0.06 wt% Nb, 0.1-0.125 wt% Ti, 0.15-0.25 wt% Mo, ≤0.025 The P of weight %, the S of ≤0.01 weight %, the balance is Fe and unavoidable impurity; The finish rolling start temperature in the hot continuous rolling step is 950-1000 ℃, and the finish rolling finish temperature is 870-900°C °C; the coiling temperature in the coiling step is 535-580 °C: after finishing rolling, cool to the coiling temperature at a cooling rate of 10-30 °C/s. 2. The method according to claim 1, wherein the finish rolling temperature in the hot continuous rolling step is 870-895°C; the coiling temperature in the coiling step is 540-575°C. 3. The method according to claim 1, wherein after finish rolling, the coil is cooled to the coiling temperature at a cooling rate of 15-26°C/s. 4. The method according to any one of claims 1-3, wherein the finish rolling start temperature in the hot continuous rolling step is 950-1000°C. 5. The method according to any one of claims 1-3, wherein, in the continuous hot rolling step, the thickness of the intermediate slab after rough rolling is 40-60 mm. 6. The method according to any one of claims 1-3, wherein the thickness of the finish-rolled steel plate is 5-10 mm. 7. The method according to any one of claims 1-3, wherein the heating step is to heat the slab at a temperature of 1230-1265°C. 8. A hot-rolled steel sheet for cold forming, characterized in that the hot-rolled steel sheet for cold forming is produced by the method according to any one of claims 1-7. 9. The hot-rolled steel sheet for cold forming according to claim 8, wherein the hot-rolled steel sheet for cold forming has a yield strength of 755-780 MPa, a tensile strength of 820-860 MPa, and an elongation of 17-21%.