CN117305731A

CN117305731A - High-strength high-reaming steel and manufacturing method thereof

Info

Publication number: CN117305731A
Application number: CN202210714666.8A
Authority: CN
Inventors: 王焕荣; 张晨; 杨阿娜; 庞厚君; 范佳杰
Original assignee: Baoshan Iron and Steel Co Ltd
Current assignee: Baoshan Iron and Steel Co Ltd
Priority date: 2022-06-22
Filing date: 2022-06-22
Publication date: 2023-12-29

Abstract

A high-strength high-reaming steel and a manufacturing method thereof, the components in percentage by weight are as follows: 0.01 to 0.10 percent of C, less than or equal to 0.2 percent of Si, 0.5 to 2.0 percent of Mn, less than or equal to 0.02 percent of P, less than or equal to 0.003 percent of S, 0.01 to 0.08 percent of Al, less than or equal to 0.004 percent of N, 0.05 to 0.2 percent of Ti, 0.10 to 0.50 percent of V, less than or equal to 0.003 percent of O, less than or equal to 0.5 percent of Mo, and the balance of Fe and other unavoidable impurities; wherein, when V is 0.10-0.20%, the tensile strength of the high-reaming steel is 590MPa grade, and the hole-enlarging rate is more than or equal to 70%; when V is 0.20-0.35%, the tensile strength of the high-reaming steel is 780MPa, and the hole expansibility is more than or equal to 50%; when V is 0.35-0.50%, the tensile strength of the high-reaming steel is 980MPa, and the reaming rate is more than or equal to 30%. The high-reaming steel has high strength, high plasticity and high reaming rate, is well matched, is particularly suitable for manufacturing parts such as automobile chassis structures and the like which need high strength thinning and reaming flanging forming, and has wide application prospect.

Description

High-strength high-reaming steel and manufacturing method thereof

Technical Field

The invention belongs to the field of high-strength steel, and particularly relates to high-strength high-reaming steel and a manufacturing method thereof.

Background

Automobiles occupy a very important position in national economy development. Many parts in passenger cars, especially chassis and parts of the car body, often require hot rolled pickled products. The weight reduction of passenger cars is not only a development trend of the automobile industry, but also a requirement of laws and regulations. The law and regulation prescribes oil consumption, and the actual requirement is that the weight of a vehicle body is reduced in a phase-change manner, and the requirement reflected on materials is that the vehicle body is high-strength, thin and light. High strength and weight reduction are the necessary requirements of the subsequent new vehicle, which tend to lead to higher steel grade, and the chassis structure also has the necessary change: if the parts are more complex, the requirements on material performance, surface and the like and the forming technology are improved, such as hydroforming, hot stamping, laser welding and the like, so that the performances of high strength, stamping, flanging, rebound, fatigue and the like of the materials are converted.

Compared with overseas, the development of the domestic high-strength high-reaming steel has relatively low strength level and poor performance stability. The high-hole-enlarging steel used by domestic automobile spare part enterprises is basically high-strength steel with the tensile strength of below 600MPa, and the high-hole-enlarging steel with the grade of below 540MPa competes for white heat. High-hole-expansion steel with tensile strength of 780MPa is gradually used in batches at home at present, but high requirements are also put forward on important indexes in two forming processes of elongation and hole expansion rate, and meanwhile, the requirements on performance stability are also stricter. In order to reduce the process cost, passenger car enterprises further improve the performance requirements of materials. For example, in the production of automobile chassis parts, in order to reduce the stamping process, the material is required to have high strength and high plasticity, and simultaneously, the hole expansion rate index is required to be higher. If the reaming rate of 780 MPa-level high reaming steel is required to be further improved to be more than or equal to 70 percent on the basis of ensuring the current capability to be more than or equal to 50 percent. The existing high-reaming steel, in particular 780MPa high-reaming steel, mostly adopts the thought of hot rolling bainite and precipitation strengthening, the process path is medium-temperature coiling, the temperature control precision and the structure uniformity are poor, the index fluctuation of the hole expansibility and the like is large, and the punching cracking is easy to occur at a user side.

780 MPa-grade acid-washed high-reaming steel has been disclosed in many patents, such as:

chinese patent CN103602895A relates to a low-carbon Nb-Ti microalloyed high-reaming steel, which is characterized in that the component design is low-carbon high-silicon Nb-Ti microalloyed, the reaming ratio guarantee value is more than or equal to 50%, the high-silicon component design generally brings about red iron scales on the surface of a steel plate, and the coiling temperature interval required for forming bainite is about 500 ℃, so that the control difficulty of the total length temperature of a steel coil is large, and the fluctuation of the total length performance is easy to cause.

Chinese patent CN105821301A relates to 800 MPa-grade hot rolled high-strength high-reaming steel, and has the characteristics of low-carbon high-silicon Nb-Ti microalloying, wherein the Ti content reaches a very high degree of 0.15-0.18 percent, and in the actual production process, the component design thought has the defects of red iron scale and the like on the surface of strip steel, and the high Ti is easy to form coarse TiN and has adverse stability on the reaming ratio.

Chinese patent CN108570604A relates to 780MPa grade hot rolled and pickled high-reaming steel, which has the characteristics of low carbon, high aluminum and high chromium in component design, and adopts a three-section cooling process in process design. Although the surface of the strip steel is free of red iron sheet, the design of high aluminum is easy to cause the blockage of a casting nozzle in the actual production process, the process is complex, the control difficulty of the three-stage cooling process is high, and the hole expansion rate is low.

The 780 MPa-grade high-hole-enlarging steel adopts high Ti as a precipitation strengthening element, and patent documents on the aspect of adopting high-V high-hole-enlarging steel are not found according to the results of searching the existing 780 MPa-grade patents.

The problems of red iron sheet, difficult steelmaking, large control difficulty of the temperature uniformity of the whole strip steel and the like exist in the above patents.

Disclosure of Invention

The invention aims to provide high-strength high-reaming steel and a manufacturing method thereof, wherein the high-strength high-reaming steel has good surface quality; when the vanadium content is 0.10-0.20%, the yield strength is more than or equal to 500MPa, the tensile strength is more than or equal to 590MPa, the elongation A50 is more than or equal to 18%, and the hole expansion rate is more than or equal to 70%; when the vanadium content is 0.20-0.35%, the yield strength is more than or equal to 600MPa, the tensile strength is more than or equal to 780MPa, the elongation A50 is more than or equal to 18%, and the hole expansion rate is more than or equal to 50%; when the vanadium content is 0.35-0.50%, the yield strength is more than or equal to 800MPa, the tensile strength is more than or equal to 980MPa, the elongation A50 is more than or equal to 13%, the hole expansion rate is more than or equal to 30%, excellent surface, strength, plasticity and hole expansion performance matching are realized, and the method can be applied to parts needing high-strength thinning, such as control arms, auxiliary frames and the like, of chassis parts of passenger vehicles.

In order to achieve the above purpose, the technical scheme of the invention is as follows:

in order to meet the requirements of users for higher surface quality, higher strength, plasticity, hole expansibility matching and the like, subversion changes are required to be made on the traditional high-hole-expansion steel.

It is well known that in general, the elongation of a material is inversely related to the hole expansion ratio, i.e., the higher the elongation, the lower the hole expansion ratio; conversely, the lower the elongation, the higher the hole expansion ratio. Under the same strengthening mechanism, the higher the strength of the material, the lower the hole expansion ratio. In order to obtain a steel product with good plasticity and reaming and flanging properties, the relationship between the two needs to be balanced better. On the other hand, in order to obtain good matching of strength, plasticity and hole expansibility, the addition of more silicon elements is indispensable for high-strength high-plasticity high-hole-expansion steel, but the composition design of high silicon brings poor steel plate surface, namely, the red iron sheet defects formed in the hot rolling link are difficult to remove thoroughly in the subsequent pickling process, so that streaky red iron sheets appear on the surface of the pickled high-strength steel, and the surface quality is seriously affected.

Therefore, the invention adopts the design of low carbon, high titanium and high vanadium components, does not add silicon element, and is completely different from the traditional high-reaming steel which adopts high titanium and micro-alloy elements.

Specifically, the high-strength high-reaming steel comprises the following components in percentage by weight: 0.01 to 0.10 percent of C, less than or equal to 0.2 percent of Si, 0.5 to 2.0 percent of Mn, less than or equal to 0.02 percent of P, less than or equal to 0.003 percent of S, 0.01 to 0.08 percent of Al, less than or equal to 0.004 percent of N, 0.05 to 0.2 percent of Ti, 0.10 to 0.50 percent of V, less than or equal to 0.003 percent of O, less than or equal to 0.5 percent of Mo, and the balance of Fe and other unavoidable impurities; wherein,

when V is 0.10-0.20%, the tensile strength of the high-reaming steel is 590MPa, and the hole expansibility is more than or equal to 70%;

when V is 0.20-0.35%, the tensile strength of the high-reaming steel is 780MPa, and the hole expansibility is more than or equal to 50%;

when V is 0.35-0.50%, the tensile strength of the high-reaming steel is 980MPa, and the reaming rate is more than or equal to 30%.

Further, the alloy also comprises one or more than one component of less than or equal to 0.5 percent of Mo, less than or equal to 0.1 percent of Nb, less than or equal to 0.5 percent of Cu, less than or equal to 0.5 percent of Ni, less than or equal to 0.5 percent of Cr and less than or equal to 0.002 percent of B.

The structure of the steel is ferrite and bainite, wherein the ferrite contains nano TiC, and the bainite contains nano VC.

In the composition design of the high-strength high-reaming steel, the invention comprises the following components:

carbon, which is a basic element in steel, is one of the important elements in the present invention. Carbon expands the austenite phase region, stabilizing austenite. Carbon plays a very important role in improving the strength of steel as a interstitial atom in steel, and has the greatest influence on the yield strength and tensile strength of steel. In the invention, as the structure to be obtained in the hot rolling stage is low-carbon bainite, the carbon content is required to be ensured to be more than 0.01 percent in order to obtain the high-strength steel with the final tensile strength of 780 MPa; at the same time, the carbon content cannot be higher than 0.10%. The carbon content is too high, and low-carbon martensite is easy to form during low-temperature coiling. Thus, the present invention controls the carbon content to be between 0.01 and 0.10%, preferably between 0.03 and 0.07%;

silicon is a basic element in steel. In order to meet the requirements of high strength, high plasticity and high hole expansion rate, which are proposed by users, more silicon is generally added during component design, but the high silicon component design brings about the reduction of the surface quality of the steel plate and has more red iron sheet defects. In the present invention, in order to ensure that good surface quality is obtained, the silicon content should be strictly controlled in the composition design. In other words, silicon is an impurity element in the present invention, and it seems difficult to completely avoid addition of silicon in consideration of the need to deoxidize silicon manganese in actual steelmaking. According to a large amount of statistical data of actual production, when the silicon content is below 0.2%, the defect of surface red iron sheet can be avoided during hot rolling, and the red iron sheet can be prevented from appearing usually below 0.10%. Therefore, the silicon content in the steel of the present invention is controlled to be within 0.2%, preferably within 0.10%;

manganese is also the most basic element in steel and is one of the most important elements in the present invention. Mn is known to be an important element for enlarging the austenite phase region, and can reduce the critical quenching speed of steel, stabilize austenite, refine grains, and retard the transformation of austenite to pearlite. In the invention, in order to ensure the strength and grain refining effect of the steel plate, the Mn content is generally controlled to be more than 0.5 percent; meanwhile, the Mn content is not more than 2.0% generally, otherwise Mn segregation is easy to occur during steelmaking, and hot cracking is easy to occur during slab continuous casting. Therefore, the Mn content in the steel of the present invention is generally controlled to be 0.5 to 2.0%, preferably 0.8 to 1.6%;

phosphorus is an impurity element in steel. P (P)Is extremely easy to be biased to grain boundary, and Fe is formed when the content of P in steel is higher (more than or equal to 0.1 percent) ₂ P is precipitated around the crystal grains, so that the plasticity and toughness of the steel are reduced, the lower the content is, the better the content is generally controlled within 0.02 percent, and the steelmaking cost is not increased;

sulfur is an impurity element in steel. S in steel is usually combined with Mn to form MnS inclusion, more MnS is formed in the steel especially when the contents of S and Mn are high, the MnS has certain plasticity, and the MnS deforms along the rolling direction in the subsequent rolling process, so that the transverse plasticity of the steel is reduced, the tissue anisotropy is increased, and the reaming performance is unfavorable. Therefore, the lower the S content in the steel, the better, in order to reduce the MnS content, the S content needs to be strictly controlled, and the S content is required to be controlled within 0.003 percent, preferably below 0.0018 percent;

the role of aluminum in steel is mainly deoxidation and nitrogen fixation. In the presence of strong carbide forming elements such as Ti and the like, al has the main functions of deoxidizing and refining grains. In the invention, al is used as a common deoxidizing element and an element for refining grains, and the content of the Al is usually controlled to be 0.01-0.08%; al content is less than 0.01%, and the effect of refining grains is not achieved; also, when the Al content is higher than 0.08%, the effect of refining the crystal grains is saturated. Therefore, the Al content in the steel of the present invention is controlled to be 0.01-0.08%, preferably 0.02-0.05%;

nitrogen, which is an impurity element in the present invention, is preferably contained in a lower amount. Nitrogen is an inevitable element in the steelmaking process. Although the content thereof is small, the formed VN particles, in combination with strong carbide forming elements such as V and the like, have a detrimental effect on the properties of the steel, especially on the reaming properties. Because VN is square, there is very big stress concentration between its closed angle and the base member, and in the reaming deformation's in-process, the stress concentration between VN and the base member easily forms the crack source to greatly reduced the reaming performance of material. Because the invention adopts the high vanadium design on the component system, the adverse effect on reaming caused by VN is reduced as much as possible. Therefore, the nitrogen content is controlled to be less than 0.004%, preferably less than 0.003%;

titanium is an important element in the present invention. Titanium is added into steel, on one hand, the titanium can be combined with N to form TiN in a high-temperature stage, so that the nitrogen fixation effect is realized, and the subsequent reduction of VN formation is facilitated; on the other hand, the excessive titanium combined with N can be combined with carbon to form nano TiC in an air cooling stage after the water cooling in the first stage, so that the effect of strengthening ferrite is achieved. The content of titanium is at least more than 0.05 percent, so that the titanium has stronger precipitation strengthening effect; when the titanium content is higher than 0.20%, the precipitation strengthening effect of titanium reaches a saturated state. Therefore, the titanium content in the steel of the present invention is controlled to be 0.05 to 0.20%, preferably 0.08 to 0.15%;

vanadium is an important element in the present invention. Vanadium, like titanium, niobium, is also a strong carbide forming element. However, the vanadium carbide has a low solution or precipitation temperature, and is usually entirely dissolved in austenite in the finish rolling stage. Vanadium starts to form in ferrite only when the temperature decrease starts to change phase. In order to fully utilize the precipitation strengthening effect of vanadium, the addition of vanadium in the steel is at least more than 0.10 percent to have obvious precipitation strengthening; with the increase of the vanadium content, the precipitation strengthening effect of vanadium is gradually enhanced, and when the vanadium content exceeds 0.50%, the precipitation strengthening effect of vanadium is saturated, the size of the formed vanadium carbide is larger, and the contribution to the strength is reduced instead. Therefore, the addition amount of vanadium in the steel of the invention is generally less than or equal to 0.50%; when the vanadium content is between 0.10 and 0.20 percent, 590 MPa-grade high-reaming steel can be obtained; when the V content is between 0.20 and 0.35, 780MPa grade high-reaming steel can be obtained; when the V content is between 0.35 and 0.50, 980MPa high-reaming steel can be obtained;

molybdenum is one of the important elements in the present invention. The addition of molybdenum to steel can significantly delay ferrite and pearlite transformation, which is beneficial to obtaining bainitic structures. In addition, molybdenum has strong weld softening resistance. Since the main purpose of the invention is to obtain low carbon ferrite and bainite structures, and the low carbon ferrite and bainite are easy to soften in a heat affected zone after welding, the softening degree of the heat affected zone of the welding can be effectively reduced by adding a certain amount of molybdenum. However, too much molybdenum is not added, so that on one hand, the alloy cost is increased, and on the other hand, the iron element body formation in the sectional cooling process is inhibited to a certain extent. Therefore, the molybdenum content is controlled to be less than or equal to 0.5 percent, preferably less than or equal to 0.3 percent;

niobium is one of the additive elements of the present invention. Niobium is similar to titanium and is a strong carbide element in steel, the unrecrystallized temperature of the steel can be greatly increased by adding the niobium into the steel, deformed austenite with higher dislocation density can be obtained in the finish rolling stage, and the final phase transformation structure can be refined in the subsequent transformation process. However, the amount of niobium added is not too large, and on the one hand, the amount of niobium added exceeds 0.10%, so that relatively coarse niobium carbonitrides are easily formed in the structure, part of carbon atoms are consumed, and the precipitation strengthening effect of carbides is reduced. Meanwhile, the niobium content is high, anisotropy of a hot rolled austenitic structure is easy to cause, and the hot rolled austenitic structure is inherited to a final structure in a subsequent cooling phase transformation process, so that the reaming performance is not good. Therefore, the niobium content in the steel of the present invention is usually controlled to be not more than 0.10%, preferably not more than 0.06%;

copper is an additive element in the invention. Copper is added into the steel to improve the corrosion resistance of the steel, and when the copper and the P element are added together, the corrosion resistance effect is better; when the Cu addition amount exceeds 1%, an epsilon-Cu precipitated phase can be formed under certain conditions, and a stronger precipitation strengthening effect is achieved. However, cu is easy to form a Cu embrittlement phenomenon in the rolling process, and in order to fully utilize the corrosion resistance improvement effect of Cu in certain application occasions and avoid causing a remarkable Cu embrittlement phenomenon, the Cu content is controlled within 0.5 percent, preferably within 0.3 percent;

nickel is an additive element in the invention. The nickel added into the steel has certain corrosion resistance, but the corrosion resistance effect is weaker than that of copper, and the nickel added into the steel has little influence on the tensile property of the steel, but can refine the structure and the precipitated phase of the steel, so that the low-temperature toughness of the steel is greatly improved; meanwhile, in the steel added with copper element, the occurrence of Cu embrittlement can be restrained by adding a small amount of nickel. The addition of higher nickel has no significant adverse effect on the properties of the steel itself. If copper and nickel are added at the same time, not only the corrosion resistance can be improved, but also the structure and the precipitated phase of the steel are refined, and the low-temperature toughness is greatly improved. But since copper and nickel are both relatively noble alloying elements. Therefore, in order to reduce the cost of alloy design as much as possible, the addition amount of nickel in the steel is less than or equal to 0.5 percent, preferably less than or equal to 0.3 percent;

chromium is an additive element in the present invention. Chromium is added into steel to improve the strength of the steel mainly through solid solution strengthening, tissue refining and other modes. As the structure of the invention is ferrite and bainite and nano precipitated carbide, the ratio of the yield strength to the tensile strength of the steel, namely the yield ratio, is higher and is generally more than 0.90. The addition of a small amount of chromium element can properly reduce the yield strength of steel, thereby reducing the yield ratio. The addition of a small amount of chromium can also play a role in improving corrosion resistance, and the addition amount of the chromium is controlled to be less than or equal to 0.5 percent, preferably less than or equal to 0.3 percent;

boron is an additive element in the present invention. Boron can greatly improve the hardenability of steel, promote the transformation of bainite, and promote the transformation of lath bainite during the transformation of medium-temperature bainite. Therefore, the addition of trace boron to the steel of the invention is beneficial to obtaining fine lath bainite structure, but the boron content is not excessive, and the addition of excessive boron can lead to the formation of martensite and more maolympic islands, which is unfavorable for plasticity and reaming. Therefore, the addition amount of boron in the steel is controlled to be less than or equal to 0.002 percent, preferably less than or equal to 0.001 percent;

oxygen is an impurity element in the invention, and in order to obtain a steel coil with more excellent performance, the lower the oxygen content in the steel is, the better, but the lower the oxidation amount is, the steelmaking cost is increased, and the oxygen content in the steel is controlled within 0.003%, preferably within 0.002% under the condition of ensuring the performance of strip steel.

The main purpose of adding microalloy element V in the existing high-strength steel is to refine grains, the addition amount of the microalloy element V is generally within 0.1%, and related patent documents in the aspect of high-reaming steel designed by adopting high V components are not searched.

In the invention, high Ti is added in combination in addition to high V in component design. The main purpose of adding more V is to combine with C to form dispersed nano VC, thereby playing a role in precipitation strengthening. The design of the high Ti and high V components is combined with the sectional cooling process, nano TiC is formed in ferrite grains in a ferrite formation interval, and nano VC is formed in bainite in a bainite formation interval. By matching the components and the process, the nano TiC is introduced into the ferrite, so that the performance difference between the ferrite and the bainite can be reduced, and the hole expansion rate can be improved; the strength of the bainite is controlled through the difference of the V content, so that the high-reaming steel with different strength grades can be obtained, and the requirements of downstream users on the high-reaming steel with different strength grades are met.

The invention relates to a manufacturing method of high-strength high-reaming steel, which comprises the following steps:

1) Smelting and casting

Smelting the components by adopting a converter or an electric furnace, secondarily refining by adopting a vacuum furnace, and casting into a casting blank or an ingot;

2) Reheating of billets or ingots

The heating temperature is more than or equal to 1200 ℃, and the heat preservation time is as follows: 1 to 2 hours;

3) Hot rolling and cooling

The initial rolling temperature of hot rolling is 1050-1150 ℃, rolling is carried out at 3-5 times of high rolling above 1050 ℃ and the accumulated deformation is more than or equal to 50%, then the intermediate billet is heated to 950-1000 ℃, then the final 3-7 times of rolling is carried out and the accumulated deformation is more than or equal to 70%, and the final rolling temperature is 800-950 ℃;

the cooling adopts sectional cooling, after finishing rolling, the steel plate is cooled to 600-750 ℃ at a cooling rate of more than or equal to 30 ℃/s, after air cooling for 1-10 seconds, the steel plate is cooled to 400-550 ℃ at a cooling rate of more than or equal to 10 ℃/s, and then coiled, and then the steel plate is cooled to room temperature at a cooling rate of less than or equal to 20 ℃/h.

Further, step 4) pickling, wherein the running speed of strip steel pickling is 30-140 m/min, the pickling temperature is controlled at 75-85 ℃, the withdrawal and straightening rate is controlled at less than or equal to 3%, rinsing is carried out at a temperature range of 35-50 ℃, surface drying is carried out at a temperature range of 120-140 ℃, and oiling is carried out, so that the pickling high-strength high-reaming steel is obtained.

The method for manufacturing the high-strength high-reaming steel comprises the following steps:

the traditional high-titanium high-reaming steel mostly adopts a high-temperature coiling process, and the invention adopts an innovative sectional cooling and medium-temperature coiling process, and combines with a unique high-titanium high-vanadium component design to develop high-reaming steel series products with different strength levels, namely 590, 780 and 980 MPa.

In the air cooling stage after the first water cooling after rolling, forming ferrite with required quantity and precipitating nano titanium carbide in ferrite grains, so as to improve the performance of the ferrite; in the medium-temperature coiling stage after the second water cooling, nano vanadium carbide is formed in the bainite by utilizing the precipitation effect of vanadium, the strength of the bainite is improved, and the ferrite reinforced by nano titanium carbide and the bainite structure with the strength of the nano vanadium carbide are obtained through innovation of components and processes. By different designs of vanadium content, high-reaming steel series products with different strength grades can be obtained, and the innovativeness of components and processes and the uniqueness of tissues and performances brought by the innovativeness are shown. Nano TiC and VC impart higher strength and more balanced properties to ferrite and bainite, respectively.

The hot rolling temperature is 1050-1150 ℃, the accumulated deformation is more than or equal to 50% under 3-5 times of high pressure above 1050 ℃, the main purpose is to refine austenite grains, and more solid solution titanium is reserved at the same time; then the intermediate blank is heated to 950-1000 ℃, and then is rolled for the last 3-7 passes, and the accumulated deformation is more than or equal to 70%; after finishing the finish rolling at 800-950 ℃, cooling the steel plate to 600-750 ℃ with water at a cooling rate of more than or equal to 30 ℃/s, air-cooling for 1-10 seconds, continuously cooling the steel plate to 400-550 ℃ with a cooling rate of more than or equal to 10 ℃/s, and slowly cooling to room temperature after coiling.

In the rough rolling and finish rolling stages, the rolling rhythm should be completed as fast as possible, so as to ensure that more solid solution titanium and vanadium are in austenite. After the high-temperature finish rolling is finished, the strip steel is firstly cooled to 600-750 ℃ at a cooling speed of more than or equal to 30 ℃/s, ferrite and intra-ferrite-crystal nano TiC are formed in an air cooling stage, then water is cooled to 400-550 ℃ at a cooling speed of more than or equal to 10 ℃/s to obtain bainite and nano precipitated VC, and finally microstructure mainly comprising ferrite and bainite and nano precipitated TiC and VC inside ferrite and bainite is obtained.

And (5) pickling the coiled hot rolled strip steel to obtain the pickled high-reaming steel. The pickling process is carried out according to the field conventional pickling process, namely the strip steel pickling operation speed is regulated within the interval of 30-140 m/min, the pickling temperature is controlled between 75-85 ℃, the withdrawal and straightening rate is controlled to be less than or equal to 3%, rinsing is carried out within the temperature interval of 35-50 ℃, and surface drying and oiling are carried out at the temperature of 120-140 ℃.

Compared with the prior art, the invention has the advantages that:

compared with the design of high silicon components adopted in Chinese patent CN103602895A and CN105821301A, the invention adopts unique component design without silicon and high aluminum, avoids red iron scales on the surface of strip steel, and improves the surface quality of acid-washed high-strength steel.

Compared with the Chinese patent CN108570604A, the silicon content of the alloy is 0.05-0.5%, but the defect of red iron scale on the surface of the strip steel can not be completely eliminated, the control difficulty of the three-stage cooling process is high, and the performance stability is difficult to ensure.

The Chinese patent CN105154769A contains elements such as molybdenum for inhibiting ferrite transformation in component design, so that the transformation process occurs after coiling, and the problem of large fluctuation of the performance of the inner and outer surfaces of the steel coil exists in actual production.

The invention adopts innovative low-carbon high-titanium high-vanadium component design and combines innovative sectional cooling and medium-temperature coiling processes, so that hot-rolled pickled high-reaming steel with excellent surface, strength, plasticity and reaming performance and good performance stability and different strength grades can be obtained.

The high-strength acid-washing high-reaming steel manufactured by the technology provided by the invention has the tensile strength of more than or equal to 590 to more than or equal to 980MPa, has good elongation (transverse A50 of more than or equal to 13 to more than or equal to 18 percent) and high reaming performance (reaming rate of more than or equal to 30 to more than or equal to 70 percent), shows excellent surface, strength, plasticity and reaming performance matching, can be adjusted according to actual needs, and can be used for manufacturing complex parts such as automobile chassis, auxiliary frames and the like which need high-strength thinning and reaming flanging, thereby having very wide application prospect.

Drawings

FIG. 1 is a schematic diagram of a rolling and cooling process of a high strength high-reaming steel according to the present invention;

fig. 2 is a schematic diagram of a cooling process after rolling of the high strength high hole expansion steel according to the present invention.

Detailed Description

The invention is further described below with reference to examples and figures.

The composition of the inventive example steel is shown in table 1, the balance of the composition comprising Fe and unavoidable impurities.

The process route of the embodiment of the invention is as follows: smelting, casting, reheating of cast billets or ingots, hot rolling and cooling, as shown in fig. 1 and 2. Table 2 shows the production process parameters of the steel according to the example of the invention. Table 3 shows the performance parameters of the steels of the examples of the present invention.

As can be seen from table 1, the components of the examples of the present invention are designed to be low carbon, high titanium, high vanadium and free of silicon, while the components of the comparative examples are designed to be low carbon, high silicon, high titanium and free of vanadium, which are significantly different in terms of component design.

As can be seen from Table 3, the high-reaming steel with three different strength levels, namely, the yield strength of more than or equal to 500 to more than or equal to 800MPa, the tensile strength of more than or equal to 590 to more than or equal to 980MPa, the elongation A50 of more than or equal to 13 to more than or equal to 18 percent and the reaming ratio of more than or equal to 30 to more than or equal to 70 percent, can be obtained by quantitatively designing and accurately controlling the components and the key technological process parameters, has high strength, high plasticity and high reaming ratio, is particularly suitable for manufacturing parts requiring high-strength thinning and reaming flanging forming, such as automobile chassis structures, and has wide application prospect.

Claims

1. The high-strength high-reaming steel comprises the following components in percentage by weight: 0.01 to 0.10 percent of C, less than or equal to 0.2 percent of Si, 0.5 to 2.0 percent of Mn, less than or equal to 0.02 percent of P, less than or equal to 0.003 percent of S, 0.01 to 0.08 percent of Al, less than or equal to 0.004 percent of N, 0.05 to 0.2 percent of Ti, 0.10 to 0.50 percent of V, less than or equal to 0.003 percent of O, less than or equal to 0.5 percent of Mo, and the balance of Fe and other unavoidable impurities; wherein,

2. The high strength, high hole expansion steel of claim 1, further comprising one or more of Mo not more than 0.5%, nb not more than 0.1%, cu not more than 0.5%, ni not more than 0.5%, cr not more than 0.5%, B not more than 0.002%.

3. The high strength, high hole expansion steel according to claim 1, wherein C is 0.03-0.07%.

4. The high strength, high hole expansion steel according to claim 1, wherein Si is less than or equal to 0.10%.

5. The high strength, high hole expansion steel according to claim 1, wherein Mn is 0.8 to 1.6%.

6. The high strength, high hole expansion steel according to claim 1, wherein S is less than or equal to 0.0018%.

7. The high strength, high hole expansion steel according to claim 1, wherein Al is 0.02-0.05%.

8. The high strength, high hole expansion steel according to claim 1, wherein N is not more than 0.003%.

9. The high strength, high hole expansion steel according to claim 1, wherein O is 0.002% or less.

10. The high strength, high hole expansion steel according to claim 1, wherein Mo is 0.3% or less.

11. The high strength, high hole expansion steel according to claim 2, wherein Nb is 0.06%.

12. The high strength, high hole expansion steel according to claim 2, wherein Ti is 0.08-0.15%.

13. The high strength, high hole expansion steel according to claim 2, wherein Cu is 0.3% or less.

14. The high strength, high hole expansion steel according to claim 2, wherein Ni is 0.3% or less.

15. The high strength, high hole expansion steel according to claim 2, wherein Cr is 0.3% or less.

16. The high strength, high hole expansion steel according to claim 2, wherein B is 0.001% or less.

17. The high strength, high hole expansion steel according to any of claims 1 to 16, wherein the structure of the steel is ferrite and bainite, wherein the ferrite contains nano TiC and the bainite contains nano VC.

18. The high strength, high hole-enlarging steel according to any one of claims 1-17 wherein the yield strength of the high strength, high hole-enlarging steel is not less than 500MPa, the tensile strength is not less than 780MPa, and the elongation is not less than 30%.

19. A method of manufacturing a high strength high hole expansion steel according to any one of claims 1 to 18, comprising the steps of:

1) Smelting and casting

Smelting the components according to any one of claims 1 to 16 by using a converter or an electric furnace, secondarily refining by using a vacuum furnace, and casting into a casting blank or an ingot;

2) Reheating of billets or ingots

3) Hot rolling and cooling

20. The method for manufacturing high-strength high-reaming steel according to claim 19, wherein the step 4) is characterized in that the pickling operation speed of the strip steel is 30-140 m/min, the pickling temperature is controlled to be 75-85 ℃, the withdrawal and straightening rate is controlled to be less than or equal to 3%, rinsing is performed at a temperature range of 35-50 ℃, and surface drying and oiling are performed at a temperature range of 120-140 ℃ to obtain the pickling high-strength high-reaming steel.