CN117305730A

CN117305730A - High-surface high-reaming steel and manufacturing method thereof

Info

Publication number: CN117305730A
Application number: CN202210714629.7A
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

The high-surface high-reaming steel and the manufacturing method thereof comprise 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, 0.10 to 0.50 percent of V, less than or equal to 0.003 percent of O, and the balance of Fe and other unavoidable impurities. The high-reaming steel has the characteristics of high surface strength and high plasticity, has the yield strength of 500-800MPa, the tensile strength of 590-980MPa and the elongation A of 50-18%, and can be applied to parts of chassis parts of passenger vehicles, such as control arms, auxiliary frames and the like, which need high strength thinning.

Description

High-surface high-reaming steel and manufacturing method thereof

Technical Field

The invention belongs to the field of high-strength steel, and particularly relates to high-surface 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 80 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 discloses 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 overall length temperature of a steel coil is high, and the fluctuation of the overall length performance is easy to cause.

Chinese patent CN105821301A discloses 800 MPa-grade hot rolled high-strength high-reaming steel, which is characterized in that the component design is also low-carbon high-silicon Nb-Ti microalloying, the Ti content reaches a very high degree of 0.15-0.18%, 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 discloses 780MPa grade hot-rolled pickled high-reaming steel, which has the characteristics of low carbon, high aluminum and high chromium, and adopts a three-stage 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.

Chinese patent CN114107792a discloses 780MPa grade hot-rolled pickled high-hole-enlarging steel, which is characterized by low carbon and high titanium and adding a proper amount of molybdenum element. Since the transformation process of molybdenum-containing steel is slow, the transformation process mainly occurs after coiling. Therefore, the problems of lower strength of the inner ring and the outer ring of the steel coil and the like exist in the actual production process.

The problems of red iron sheet, difficult steelmaking, high control difficulty of the overall length temperature uniformity of the strip steel, poor performance uniformity and the like exist in the above patents.

Disclosure of Invention

The invention aims to provide high-surface high-reaming steel and a manufacturing method thereof, wherein the high-reaming steel has high strength, high plasticity and high reaming rate, has good matching, has the yield strength of 500-800MPa, the tensile strength of 590-980MPa and the elongation A of 50-18%, has good surface quality, and 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, better performance stability, better 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. The higher the strength of the material, the lower the hole expansion ratio under the same or similar strengthening mechanism. 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.

The invention adopts low carbon and high vanadium in component design, does not add silicon element, can obtain bainite precipitation strengthening high-strength steel with uniform structure and performance on the existing hot continuous rolling production line, and then obtains the bainite precipitation strengthening high-reaming steel through an acid washing process. The nano vanadium carbide which is uniformly and finely dispersed in the bainite endows the steel plate with high strength and high plasticity, and simultaneously has excellent hole expansion rate.

Specifically, the high-surface 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, 0.10 to 0.50 percent of V, less than or equal to 0.003 percent of O, 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 reaming ratio is more than or equal to 80%;

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 hole-enlarging rate is more than or equal to 40%.

Further, the alloy also comprises one or more than one of Mo less than or equal to 0.5%, cu less than or equal to 0.5%, ni less than or equal to 0.5%, cr less than or equal to 0.5%, nb less than or equal to 0.1%, ti less than or equal to 0.2% and B less than or equal to 0.002%.

In the composition design of the high-surface 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 must be above 0.01% in order to obtain high-hole-expansion steel with different final tensile strength levels; 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 carbon content is controlled to be 0.01-0.10%, preferably 0.03-0.07%.

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 controlled to be 0.5 to 2.0%, preferably 0.8 to 1.6%.

Phosphorus is an impurity element in steel. P is easily 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 crystal grains, and the plasticity and toughness of steel are reduced, so that the lower the content is, the better the content is, the phosphorus content is 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, and in order to reduce the MnS content, the S content needs to be strictly controlled, and the S content is controlled to be within 0.003%, preferably below 0.0018% in the invention.

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 may be controlled to be 0.01 to 0.08%, and preferably to be in the range of 0.02 to 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%, and the preferred range is less than 0.003%.

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 present invention is controlled to be not more than 0.50%, preferably not more than 0.30%; when the V content is between 0.10 and 0.20 percent, 590MPa 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, 980 MPa-grade high-reaming steel can be obtained.

Molybdenum is one of the important elements in the present invention. The addition of molybdenum to steel can greatly delay ferrite and pearlite transformation, which is beneficial to obtaining bainite structure. In addition, molybdenum has strong weld softening resistance. Since the main purpose of the invention is to obtain the lower bainite structure, the lower bainite is easy to soften after welding, and the addition of a certain amount of molybdenum can effectively reduce the welding softening degree. Thus, the present invention controls the molybdenum content to be 0.1 to 0.5%, preferably 0.20 to 0.40%.

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 controlled to be 0.10% or less, preferably 0.06% or less.

Titanium is an additive element in the present invention. A small amount of Ti is added into the steel, so that on one hand, the Ti can be combined with N to form TiN in a high-temperature stage, the effect of nitrogen fixation is achieved, and the subsequent VN formation is reduced; on the other hand, the excessive Ti combined with N can be combined with carbon in the subsequent process to form nano TiC, and the nano TiC and the nano VC can jointly improve the performance of the steel. When the titanium content is higher than 0.20%, more coarse TiN tends to be formed at a high temperature stage and the impact toughness of the steel is deteriorated. Therefore, the content of the additive element titanium in the steel of the present invention is 0.20% or less, preferably 0.10% or less.

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 during rolling, and in order to fully utilize the corrosion resistance improving effect of Cu in some applications, and at the same time, not to cause a significant "Cu embrittlement" phenomenon, the Cu content is controlled within 0.5%, preferably within 0.3%.

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 of the present invention is not more than 0.5%, preferably not more than 0.3%.

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. Because the structure of the invention is fine bainitic ferrite plus 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. In addition, the addition of a small amount of chromium can also play a role in improving corrosion resistance, and the addition amount of chromium is usually not more than 0.5%, preferably not more than 0.3%.

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 a trace amount of boron to the steel is advantageous for obtaining a fine lath bainitic 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 disadvantageous for plasticity and hole expansion. Therefore, the boron addition amount in the steel of the present invention is controlled to be not more than 0.002%, preferably not more than 0.001%.

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

The existing high-reaming steel generally adopts a high-titanium component design, and alloy elements such as high silicon or molybdenum are sometimes added, while the invention adopts a high-vanadium component design, and the high-titanium component design and the high-vanadium component design are obviously different.

The main purpose of adding micro-alloy element vanadium in the existing high-hole-enlarging steel is to refine grains, the addition amount of the micro-alloy element vanadium is generally within 0.1%, the main purpose of adding the high-vanadium is to combine with carbon to form dispersed nano vanadium carbide, the precipitation strengthening effect is achieved, and related patent documents in the aspect of the high-hole-enlarging steel designed by adopting high-vanadium components are not searched.

Most of the prior high-reaming steel microstructures are ferrite or ferrite plus bainite, and nano titanium carbide is adopted for strengthening in order to obtain higher strength. The microstructure of the high-reaming steel is bainite and nano vanadium carbide in the bainite, and the high-reaming steel with different strength grades can be obtained according to the different vanadium contents, so that 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-surface 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

Heating temperature is more than or equal to 1100 ℃, and heat preservation time is as follows: 1 to 2 hours;

3) Hot rolling and cooling

The initial rolling temperature is 1000-1100 ℃, the accumulated deformation is more than 50% under 3-5 times of rough rolling and high reduction at 950 ℃, then the intermediate billet is air-cooled or water-cooled to 900-950 ℃, then 7 times of finish rolling are carried out, the accumulated deformation is more than 70%, the finish rolling is finished between 800-900 ℃, then the steel plate is water-cooled to 400-550 ℃ at the cooling speed of more than or equal to 10 ℃/s for coiling, and then the steel plate is slowly cooled to room temperature at the cooling speed of less than or equal to 20 ℃/s.

Further, step 4) pickling, wherein the running speed of strip steel pickling is 30-120 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 ℃, and surface drying and oiling are carried out at a temperature range of 120-140 ℃ to obtain the pickling high-reaming steel.

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

the invention adopts a medium-temperature coiling process and combines with innovative low-carbon high-vanadium and low-silicon component design to obtain the high-strength high-reaming steel with excellent performance stability.

In the middle-low temperature bainite transformation zone, the uniformity of the overall length performance of the strip steel is ensured by precisely controlling the coiling temperature. Bainite phase transformation occurs in the medium-temperature coiling process, and simultaneously nano precipitation of vanadium is accompanied. The high-reaming steel series products with different strength levels and different hole expansibility can be obtained by quantitatively designing the carbon content and the vanadium content of key elements and simultaneously matching with specific coiling.

The traditional high titanium type high reaming steel mostly adopts a high temperature coiling process, and the invention adopts a medium temperature coiling process. Therefore, in the rough rolling and finish rolling stages, the rolling rhythm should be completed as fast as possible, so as to ensure that more vanadium is dissolved in austenite. After the high-temperature finish rolling is finished, the strip steel is cooled to a medium temperature region of 400-550 ℃ on line at a cooling speed of more than or equal to 10 ℃/s so as to obtain bainite and nano precipitated tissues.

In the subsequent pickling process, the thermal stress and the structural stress nonuniformity formed in the steel coil in the medium-temperature coiling phase change process are fully released in the pickling withdrawal and straightening process, so that the structural uniformity can be further improved. Based on the innovative components and technological design thought, the invention can obtain high-surface hot-rolled and pickled high-reaming steel series products with different strength grades, plasticity, reaming, performance stability and the like.

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

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

Compared with the Chinese patent CN108570604A, the silicon content is 0.05-0.5%, the defect of red iron scale on the surface of the strip steel can not be completely eliminated, the three-stage cooling process is difficult to control and the performance stability is difficult to ensure, and the invention adopts the multi-path cooling precise control technology, and can ensure the performance uniformity of the strip steel without adopting a complex multi-stage cooling process.

The high-surface high-reaming steel has the tensile strength of more than or equal to 590 to 980MPa and the thickness of 1.5 to 6.0mm, has good elongation (transverse A50 of more than or equal to 14 percent to more than or equal to 18 percent) and high reaming performance (reaming rate of more than or equal to 40 percent to more than or equal to 80 percent), shows excellent matching of surface, strength, plasticity and reaming performance, can be applied to manufacturing complex parts such as automobile chassis, auxiliary frames and the like which need high-strength thinning and reaming flanging, and has very wide application prospect.

Drawings

FIG. 1 is a schematic drawing of a rolling and cooling process for a high surface hot rolled pickled high-hole-enlarging steel according to the 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 slab or ingot, hot rolling, and cooling, as shown in fig. 1. 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 comparative examples 1 to 4 each contained no vanadium element, while the components of comparative examples 1 to 3 also contained high silicon. Therefore, from the viewpoint of the quality of the surface of the steel sheet, the surfaces of the steel sheets of comparative examples 1 to 3 inevitably contain red iron scale, whereas the examples of the present invention are all designed for silicon-free components, and are excellent in surface quality.

In addition, the comparative examples 1-4 all adopt a high titanium component design, which shows that nano titanium carbide precipitation strengthening is adopted; the embodiment of the invention is designed for high vanadium components, and adopts nano vanadium carbide for strengthening, and the components and the strengthening modes have obvious differences.

As can be seen from Table 3, the invention can obtain three high-reaming steels with different strength levels, wherein the yield strength is more than or equal to 500-800MPa, the tensile strength is more than or equal to 590-980MPa, the elongation A50 is more than or equal to 14-18%, and the reaming ratio is more than or equal to 40-80%, by quantitatively designing and accurately controlling the components and the key technological process parameters.

From the embodiment, 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 needing high strength thinning and reaming flanging forming, and has wide application prospect.

Claims

1. The high-surface 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, 0.10 to 0.50 percent of V, less than or equal to 0.003 percent of O, and the balance of Fe and other unavoidable impurities; wherein,

2. The high surface area high-hole-enlarging steel according to claim 1, further comprising one or more of Mo not more than 0.5%, cu not more than 0.5%, ni not more than 0.5%, cr not more than 0.5%, nb not more than 0.1%, ti not more than 0.2%, and B not more than 0.002%.

3. The high surface area high-reaming steel of claim 1, wherein C is 0.03-0.07%.

4. The high surface area high-reaming steel of claim 1, wherein Si is less than or equal to 0.10%.

5. The high surface area high-reaming steel of claim 1, wherein Mn is 0.8 to 1.6%.

6. The high surface area high-reaming steel of claim 1, wherein S is less than or equal to 0.0018%.

7. The high surface area high-reaming steel of claim 1, wherein Al is 0.02-0.05%.

8. The high surface area high-reaming steel of claim 1, wherein N is less than or equal to 0.003%.

9. The high surface area high-reaming steel of claim 1, wherein O is less than or equal to 0.002%.

10. The high surface area high-reaming steel of claim 2, wherein Mo is 0.20 to 0.40%.

11. The high surface area high-reaming steel of claim 2, wherein Nb is 0.06%.

12. The high surface area high-reaming steel of claim 2, wherein Ti is less than or equal to 0.10%.

13. The high surface area high-reaming steel of claim 2, wherein Cu is less than or equal to 0.3%.

14. The high surface area high-reaming steel of claim 2, wherein Ni is less than or equal to 0.3%.

15. The high surface area high-reaming steel of claim 2, wherein Cr is less than or equal to 0.3%.

16. The high surface area high-reaming steel of claim 2, wherein B is less than or equal to 0.001%.

17. The high surface area high pore-enlarging steel according to any one of claims 1-16 wherein the steel structure is bainite and nano-precipitated VC in the bainite.

18. A method of manufacturing a high surface area high reaming steel according to any one of claims 1 to 17, 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

19. The method for manufacturing high surface area high-reaming steel according to claim 18, wherein the step 4) is to perform acid washing, the operation speed of the acid washing of the strip steel is 30-120 m/min, the acid washing temperature is controlled to be 75-85 ℃, the withdrawal 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 acid washing high-reaming steel.