CN114107793B - 1180 MPa-grade low-carbon martensitic high-reaming steel and manufacturing method thereof - Google Patents

1180 MPa-grade low-carbon martensitic high-reaming steel and manufacturing method thereof Download PDF

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CN114107793B
CN114107793B CN202010896479.7A CN202010896479A CN114107793B CN 114107793 B CN114107793 B CN 114107793B CN 202010896479 A CN202010896479 A CN 202010896479A CN 114107793 B CN114107793 B CN 114107793B
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steel
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CN114107793A (en
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王焕荣
张晨
杨峰
杨阿娜
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Baoshan Iron and Steel Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

Abstract

A1180 MPa grade low-carbon martensite high-reaming steel and a manufacturing method thereof comprise the following chemical components in percentage by weight: c0.05-0.10%, si<0.8 percent, 1.5 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, 0.02 to 0.08 percent of Al, less than or equal to 0.004 percent of N, 0.1 to 0.5 percent of Mo, 0.01 to 0.05 percent of Ti, less than or equal to 0.0030 percent of O, and the balance of Fe and other unavoidable impurities. The yield strength of the high-reaming steel is more than or equal to 900MPa, the tensile strength is more than or equal to 1180MPa, and the transverse elongation A is the same as that of the high-reaming steel 50 More than or equal to 8 percent and the hole expansion rate is more than or equal to 70 percent. The yield strength of the high-reaming steel is more than or equal to 900MPa, the tensile strength is more than or equal to 1180MPa, and the high-reaming steel can be applied to the parts of chassis parts of passenger vehicles, such as control arms, auxiliary frames and the like, which need high-strength thinning.

Description

1180 MPa-grade low-carbon martensitic high-reaming steel and manufacturing method thereof
Technical Field
The invention relates to the field of high-strength steel, in particular to 1180 MPa-level low-carbon martensitic high-reaming steel and a manufacturing method thereof.
Background
With the development of national economy, the production of automobiles is greatly increased, and the use amount of plates is continuously increased. The original design of parts of various automobile types in the domestic automobile industry requires hot-rolled or pickled plates, such as parts of chassis parts, torsion beams, auxiliary frames, wheel spokes and rims of automobiles, front and rear axle assemblies, automobile body structural parts, seats, clutches, safety belts, truck box plates, protective nets, automobile girders and the like. Wherein, the steel for the chassis accounts for 24-34% of the total steel of the car.
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. For example, the high-hole-enlarging steel used by domestic automobile spare part enterprises is basically high-strength steel with the tensile strength below 600MPa and high-hole-enlarging steel with the grade below 440MPa competing for white-heat. High-hole-expansion steel with tensile strength of 780MPa grade is gradually used in batches at present, but high requirements are also put forward on important indexes of elongation and hole expansion rate for two forming. The 980 MPa-level high-reaming steel is still in the research and development authentication stage at present, and does not reach the batch use stage yet. High-hole-enlarging steels of higher strength grade, such as 1180MPa, have not been developed by manufacturers. Based on the trend of high-bore steel, in order to better meet the potential demands of users, it is necessary to develop 1180MPa high-bore steel with a higher strength level.
The 980 MPa-grade high-hole-enlarging steel has few documents, while 1180 MPa-grade high-hole-enlarging steel is blank. Most of the related patent documents are high-hole-enlarging steel of 780MPa and below. Numerous studies indicate that 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. Also, the higher the strength of the material, the lower the hole expansion ratio. In order to obtain a steel product with better plasticity and reaming and flanging performance, the relation between the two needs to be balanced better. A single uniform tissue is advantageous for achieving higher hole expansion rates, whereas a dual or multi-phase tissue is generally disadvantageous for improved hole expansion rates.
Disclosure of Invention
The invention aims to provide 1180 MPa-grade low-carbon martensitic high-reaming steel and a manufacturing method thereof, wherein the yield strength of the high-reaming steel is more than or equal to 900MPa, the tensile strength is more than or equal to 1180MPa, and the transverse elongation A is higher than or equal to 50 More than or equal to 8 percent, and the hole expansion rate is more than or equal to 70 percent, and can be applied to zero chassis of a passenger carParts such as control arms and auxiliary frames and the like which need high strength and thinning.
In order to achieve the above purpose, the technical scheme of the invention is as follows:
in the invention, the lower C content is adopted in component design, so that excellent weldability can be ensured when a user uses the composition, and the obtained martensitic structure is ensured to have good hole expansibility and impact toughness; on the basis of meeting the tensile strength of more than or equal to 1180MPa, the lower the carbon content is, the better; adopting higher manganese to stabilize austenite, and obtaining the near equiaxial deformed austenite after rolling by matching with the process; the transformation of ferrite and pearlite can be obviously delayed by a certain amount of molybdenum, so that ferrite and pearlite are avoided; the low-carbon martensite design thought is adopted, the relatively low final rolling temperature and the air cooling or direct water cooling after rolling are adopted, fine and uniform original austenite grains can be obtained, and finally the low-carbon martensite with uniform structure is obtained.
Specifically, the 1180MPa low-carbon martensitic high-hole-enlarging steel comprises the following chemical components in percentage by weight: 0.05 to 0.10 percent of C, 0.8 percent of Si, 1.5 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, 0.02 to 0.08 percent of Al, less than or equal to 0.004 percent of N, 0.1 to 0.5 percent of Mo, 0.01 to 0.05 percent of Ti, less than or equal to 0.0030 percent of O, and the balance of Fe and other unavoidable impurities.
Further, the alloy also comprises one or more than one of less than or equal to 0.5% of Cr, less than or equal to 0.002% of B, less than or equal to 0.005% of Ca, less than or equal to 0.06% of Nb, less than or equal to 0.05% of V, less than or equal to 0.5% of Cu, and less than or equal to 0.5% of Ni, wherein the content of Nb and V is preferably less than or equal to 0.03%, the content of Cu and Ni is preferably less than or equal to 0.3%, the content of Cr is preferably 0.2-0.4%, the content of B is preferably 0.0005-0.0015%, and the content of Ca is preferably less than or equal to 0.002%.
The microstructure of the high-reaming steel is online low-carbon tempered martensite.
The yield strength of the high-reaming steel is more than or equal to 900MPa, the tensile strength is more than or equal to 1180MPa, and the transverse elongation A is the same as that of the high-reaming steel 50 More than or equal to 8 percent and the hole expansion rate is more than or equal to 70 percent.
In the composition of the high-reaming steel of the invention, the following components are involved:
carbon, which is a basic element in steel, is also 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, because the structure to be obtained is low-carbon martensite, in order to obtain high-strength steel with tensile strength reaching 1180MPa, the carbon content must be ensured to be more than 0.05%, otherwise, the carbon content is less than 0.05%, and the tensile strength of the steel is less than 1180MPa even if the steel is completely quenched to room temperature; but the carbon content cannot be higher than 0.10%. The carbon content is too high, the strength of the formed low-carbon martensite is too high, and the elongation and the hole expansion rate are low. Therefore, the carbon content should be controlled to be between 0.05 and 0.10%, preferably within the range of 0.07 to 0.09%.
Silicon is a basic element in steel, but in the present invention, si is a conventional additive element, mainly aimed at deoxidization. In order to improve the surface quality of the steel, and to reduce the actual rolling force, the Si content in the steel is not too high, preferably not more than 0.8%, and preferably not more than 0.5%;
manganese, the most basic element in steel, 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 present invention, in order to ensure the strength of the steel sheet and to prevent ferrite formation during cooling, the Mn content should generally be controlled to be 1.5% or more; 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 is generally controlled to be 1.5-2.0%, preferably in the range of 1.6-1.9%.
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 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, and in view of the fact that the Mn content in the present invention must be at a higher level, the S content is strictly controlled to be within 0.003%, preferably within a range of 0.0015% or less, in order to reduce the MnS content.
The role of aluminum in steel is mainly deoxidation and nitrogen fixation. In the presence of strong carbide forming elements such as Ti, nb, V, etc., the primary role of Al is to deoxidize and refine the 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 controlled to be between 0.02 and 0.08 percent; al content is less than 0.02%, 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 is controlled to be 0.02-0.08%, 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 TiN particles have a very adverse effect on the properties of steel, particularly on the reaming properties, in combination with strong carbide forming elements such as Ti and the like. Because TiN is square, a large stress concentration exists between the sharp angle and the matrix, and cracks are easily formed due to the stress concentration between the TiN and the matrix in the reaming deformation process, so that the reaming performance of the material is greatly reduced. The lower the content of the strong carbide forming element such as Ti is, the better the nitrogen content is controlled as much as possible. In the invention, trace Ti is added to fix nitrogen, so that adverse effects caused by TiN are reduced as much as possible. Therefore, the nitrogen content should be controlled to be 0.004% or less, preferably to be 0.003% or less.
Titanium is one of the important elements in the present invention. Ti plays two main roles in the present invention: firstly, the titanium alloy is combined with impurity element N in steel to form TiN, which plays a part of role of nitrogen fixation; secondly, a certain amount of dispersed and fine TiN is formed in the subsequent welding process of the material, the size of austenite grains is restrained, the structure is thinned and the low-temperature toughness is improved. Therefore, the Ti content in the steel is controlled to be in the range of 0.01 to 0.05%, preferably in the range of 0.01 to 0.03%.
Molybdenum is one of the important elements in the present invention. Molybdenum addition to steel can greatly delay ferrite and pearlite transformation. The effect of the molybdenum is beneficial to the adjustment of various processes in the actual rolling process, such as sectional cooling after finishing rolling, air cooling and water cooling, and the like. In the invention, a process of air cooling and then water cooling or direct water cooling after rolling is adopted, the addition of molybdenum can ensure that ferrite or pearlite and other structures are not formed in the air cooling process, and meanwhile, deformed austenite can be dynamically recovered in the air cooling process, thereby being beneficial to improving the uniformity of the structure; molybdenum has very strong weld softening resistance. Since the main purpose of the invention is to obtain a structure of single low-carbon martensite and a small amount of residual austenite, the low-carbon martensite is easy to soften after welding, and the addition of a certain amount of molybdenum can effectively reduce the welding softening degree. Therefore, the content of molybdenum should be controlled between 0.1 and 0.5%, preferably in the range of 0.15 to 0.35%.
Chromium is one of the additive elements in the present invention. The addition of a small amount of chromium element is not used for improving the hardenability of steel, but is combined with B, so that the acicular ferrite structure is formed in a welding heat affected zone after welding, and the low-temperature toughness of the welding heat affected zone can be greatly improved. Because the final application part related to the invention is a chassis product of a passenger car, the low-temperature toughness of a welding heat affected zone is an important index. In addition to ensuring that the strength of the weld heat affected zone does not decrease too much, the low temperature toughness of the weld heat affected zone also meets certain requirements. In addition, chromium itself has a certain resistance to weld softening. Therefore, the chromium element content in the steel is generally not more than 0.5%, preferably in the range of 0.2 to 0.4%.
Boron is one of the additive elements in the present invention. Boron in steel mainly gathers at the original austenite grain boundary, and inhibits the formation of proeutectoid ferrite; boron addition to steel can also greatly improve the hardenability of the steel. However, in the present invention, the main purpose of adding the trace boron element is not to improve hardenability, but to improve the weld heat affected zone structure by combining with chromium, and to obtain a needle-like ferrite structure having good toughness. The boron addition to the steel is generally controlled to be less than 0.002%, preferably in the range of 0.0005-0.0015%.
Calcium is an additive element in the present invention. Calcium can improve the forms of sulfides such as MnS, so that long-strip-shaped sulfides such as MnS are changed into spherical CaS, the forms of inclusions are improved, and further the adverse effect of long-strip-shaped sulfides on reaming performance is reduced, but the addition of excessive calcium can increase the quantity of calcium oxide, and is adverse to reaming performance. Therefore, the addition amount of the steel grade calcium is usually not more than 0.005%, preferably in the range of not more than 0.002%.
Oxygen is an unavoidable element in the steelmaking process, and for the invention, the content of O in the steel can generally reach below 30ppm after deoxidization, and the performance of the steel plate is not obviously adversely affected. Therefore, the O content in the steel may be controlled to 30ppm or less.
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 0.06%, so that relatively coarse niobium carbonitride is easily formed in the structure, part of carbon atoms are consumed, and the precipitation strengthening effect of carbide 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 is usually controlled to be 0.06% or less, preferably in the range of 0.03% or less.
Vanadium is an additive 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 the ferrite when the temperature decrease starts to change phase. In the present invention, the main purpose of adding vanadium is to improve the weld heat affected zone softening resistance in combination with molybdenum. From the viewpoint of the anti-weld softening effect, the effect of molybdenum and vanadium is strongest, and in the case of molybdenum, vanadium can be selectively added. Therefore, the addition amount of vanadium in steel is usually not more than 0.05%, and the preferable range is not more than 0.03%.
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 added to easily form a "Cu embrittlement" phenomenon during rolling, and in order to make full use of the corrosion resistance improving effect of Cu in some applications, the Cu element content is usually controlled to be within 0.5%, preferably within 0.3%, without causing a significant "Cu embrittlement" phenomenon.
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 is usually not more than 0.5%, and the preferable range is not more than 0.3%.
The invention relates to a 1180 MPa-level low-carbon martensitic high-reaming steel manufacturing method, 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 the casting blank or the cast ingot, wherein the heating temperature is as follows: 1100-1200 ℃, and the heat preservation time is as follows: 1 to 2 hours;
3) Hot rolling
Start rolling temperature: 950-1100 ℃, 3-5 passes of high reduction at 950 ℃ and accumulated deformation more than or equal to 50%, then the intermediate blank is heated to 920-950 ℃, and then the final 3-7 passes of rolling are carried out and accumulated deformation more than or equal to 70%; the final rolling temperature is 800-920 ℃;
4) Cooling
Firstly performing air cooling for 0-10 seconds, then cooling the steel plate to a certain temperature below an Ms point at a cooling rate of more than or equal to 30 ℃/s, and cooling to room temperature after coiling;
5) Acid washing
The strip steel pickling operation speed is regulated within the interval of 30-90 m/min, the pickling temperature is controlled between 75-85 ℃, the withdrawal straightening rate is controlled to be less than or equal to 1.5%, so as to reduce the strip steel elongation loss, and then the strip steel is rinsed, dried and oiled.
Preferably, after the step 5) of pickling, rinsing is carried out at a temperature of between 35 and 50 ℃ to ensure the surface quality of the strip steel, and the strip steel surface is dried and oiled at a temperature of between 120 and 140 ℃.
In the invention, the lower C content is adopted in component design, so that excellent weldability can be ensured when a user uses the composition, and the obtained martensitic structure is ensured to have good hole expansibility and impact toughness; on the basis of meeting the tensile strength of more than or equal to 1180MPa, the lower the carbon content is, the better; adopting higher manganese to stabilize austenite, and obtaining the near equiaxial deformed austenite after rolling by matching with the process; the transformation of ferrite and pearlite can be obviously delayed by a certain amount of molybdenum, so that ferrite and pearlite are avoided; the low-carbon martensite design thought is adopted, the relatively low final rolling temperature and the air cooling or direct water cooling after rolling are adopted, fine and uniform original austenite grains can be obtained, and finally the low-carbon martensite with uniform structure is obtained.
In the design of the rolling process, the rhythm of the rolling process should be completed as fast as possible in the rough rolling and finish rolling stages. After finishing the finish rolling, air cooling is carried out for a certain time or water cooling is directly carried out after finishing the finish rolling. The main purpose of air cooling is as follows: manganese is an element that stabilizes austenite due to its high content in composition design, and molybdenum greatly delays ferrite and pearlite transformation. Therefore, during air cooling for a certain period of time, the rolled deformed austenite does not undergo transformation, i.e., does not form ferrite structure, but rather undergoes dynamic recrystallization and relaxation. The deformed austenite is dynamically recrystallized to form austenite with a uniform structure and nearly equiaxial shape, dislocation in austenite grains can be greatly reduced after relaxation, and martensite with a uniform structure can be obtained in the subsequent water-cooling quenching process by combining the austenite with the relaxed austenite. In order to obtain a martensitic structure, the water cooling speed is greater than the critical cooling speed of low-carbon martensite, and in the invention, the water cooling speed after strip steel rolling is required to be more than or equal to 30 ℃/s in order to ensure that martensite can be obtained by all component designs.
Since the microstructure according to the present invention is low-carbon martensite, the steel strip is cooled to the martensite start point Ms or less at a cooling rate higher than the critical cooling rate after finishing rolling. The cooling temperature is different, and the content of the residual austenite is different at room temperature. There is generally an optimum quench stop temperature range which varies from one alloy composition to another, typically between 150 and 350 ℃. In order to obtain high-strength steel with good plasticity and hole expansibility, the strip steel needs to be quenched to a certain temperature range below an Ms point, and according to theoretical calculation and practical test verification, the strip steel is quenched to be within the range of not more than Ms, so that a tissue with excellent comprehensive performance can be obtained. When the quenching temperature is more than or equal to Ms, bainite structure appears in the structure, and the strength requirement of 1180MPa can not be met. For the above reasons, the winding temperature needs to be controlled to be between +.Ms. Based on the innovative components and the technological design thought, 1180MPa grade low-carbon martensitic high-reaming steel with excellent strength, plasticity, toughness and reaming performance can be obtained.
The invention has the beneficial effects that:
the method can be used for manufacturing the high-reaming steel with the yield strength more than or equal to 900MPa, the tensile strength more than or equal to 1180MPa and the thickness of 2-6mm, and has good elongation (transverse direction A) 50 Not less than 8%), impact toughness and reaming performance (the reaming rate is not less than 70%), and shows excellent matching of strength, plasticity, toughness and reaming performance, thereby bringing the following beneficial effects:
(1) The 1180 MPa-grade high-reaming steel with excellent strength, plasticity, toughness and reaming performance can be obtained by adopting a relatively economical component design thought and adopting an innovative cooling process path;
(2) The steel coil or the steel plate has excellent ultrahigh strength, plasticity and toughness matching, and also has good reaming performance, can be applied to manufacturing 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 process flow diagram of a 1180MPa grade low-carbon martensitic high-reaming steel manufacturing method according to the invention;
FIG. 2 is a schematic drawing of a rolling process in the 1180 MPa-grade low-carbon martensitic high-reaming steel manufacturing method of the invention;
FIG. 3 is a schematic diagram of a cooling process in the 1180 MPa-level low-carbon martensitic high-reaming steel manufacturing method according to the invention;
FIG. 4 is a typical metallographic photograph of example 1 of the high-hole-enlarging steel of the invention;
FIG. 5 is a typical metallographic photograph of example 3 of the high-hole-enlarging steel of the invention;
fig. 6 is a typical metallographic photograph of example 5 of the high-hole-enlarging steel of the invention.
Detailed Description
Referring to fig. 1 to 3, the 1180 MPa-level hot rolled or pickled high-reaming steel manufacturing method of the invention 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 the casting blank or the cast ingot, wherein the heating temperature is as follows: 1100-1200 ℃, and the heat preservation time is as follows: 1 to 2 hours;
3) Hot rolling
Start rolling temperature: 950-1100 ℃, 3-5 passes of high reduction at 950 ℃ and accumulated deformation more than or equal to 50%, then the intermediate blank is heated to 920-950 ℃, and then the final 3-7 passes of rolling are carried out and accumulated deformation more than or equal to 70%; the final rolling temperature is 800-920 ℃;
4) Cooling
Air cooling is carried out for 0-10 seconds, then the steel plate is cooled to a certain temperature below the Ms point by water at a cooling speed of more than or equal to 30 ℃/s, and the steel plate is cooled to room temperature after coiling.
5) Acid washing
The strip steel pickling operation speed can be adjusted within the interval of 30-90 m/min, the pickling temperature is controlled between 75-85 ℃, the withdrawal and straightening rate is controlled to be less than or equal to 1.5 percent so as to reduce the strip steel elongation loss, 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 ℃.
The components of the high reaming steel embodiment of the invention are shown in table 1, and table 2 and table 3 are production process parameters of the steel embodiment of the invention, wherein the thickness of a steel billet in the rolling process is 120mm; table 4 shows the mechanical properties of the steel sheet according to the example of the present invention.
As can be seen from Table 4, the yield strength of the steel coil is more than or equal to 900MPa, the tensile strength is more than or equal to 1180MPa, the elongation is usually between 8 and 11 percent, the impact energy is stable, the low-temperature impact energy at-40 ℃ is stable at 90 to 120J, and the reaming ratio is more than or equal to 70 percent. From the embodiment, the 1180MPa high-strength steel has good strength, plasticity, toughness and reaming performance matching, is particularly suitable for parts such as automobile chassis structures and the like which need high-strength thinning and reaming flanging forming, such as control arms and the like, can also be used for parts such as wheels and the like which need hole flanging, and has wide application prospect.
Fig. 4 to 6 show typical metallographic structures of the steel sheets of example 1#,3#, and 5# respectively. As can be seen from metallographic pictures, the structure is single-phase low-carbon martensite, and a small amount of carbide can appear in the structure according to the coiling temperature.
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Claims (14)

1. The 1180MPa low-carbon martensitic high-hole-enlarging steel comprises the following chemical components in percentage by weight: 0.05-0.10% of C, less than 0.8% of Si, 1.5-2.0% of Mn, less than or equal to 0.02% of P, less than or equal to 0.003% of S, 0.02-0.08% of Al, less than or equal to 0.004% of N, 0.1-0.5% of Mo, 0.01-0.05% of Ti, less than or equal to 0.0030% of O, and the balance of Fe and other unavoidable impurities;
the yield strength of the high-reaming steel is more than or equal to 900MPa, the tensile strength is more than or equal to 1180MPa, and the elongation is transverse A 50 More than or equal to 8 percent and the hole expansion rate is more than or equal to 70 percent; and is obtained by a process comprising:
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 the casting blank or the cast ingot, wherein the heating temperature is as follows: 1100-1200 ℃, and the heat preservation time is as follows: 1-2 hours;
3) Hot rolling
Start rolling temperature: 950-1100 ℃, 3-5 passes of high reduction at 950 ℃ and accumulated deformation more than or equal to 50%, then the intermediate blank is heated to 920-950 ℃, and then the final 3-7 passes of rolling are carried out and accumulated deformation more than or equal to 70%; the final rolling temperature is 800-920 ℃;
4) Cooling
Firstly performing air cooling for 2-10 seconds, then cooling the steel plate to a certain temperature below an Ms point at a cooling rate of more than or equal to 30 ℃/s, and cooling to room temperature after coiling;
5) Acid washing
The strip steel pickling operation speed is regulated within the interval of 30-90 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 1.5%, and then the strip steel is rinsed, dried and oiled.
2. The 1180 MPa-grade low-carbon martensitic high-hole-enlarging steel according to claim 1, further comprising one or more of Cr less than or equal to 0.5%, B less than or equal to 0.002%, ca less than or equal to 0.005%, nb less than or equal to 0.06%, V less than or equal to 0.05%, cu less than or equal to 0.5%, and Ni less than or equal to 0.5%.
3. The 1180 MPa-level low-carbon martensitic high-hole-enlarging steel according to claim 2, wherein the Nb and V contents are respectively not more than 0.03%, the Cu and Ni contents are respectively not more than 0.3%, the Cr content is 0.2-0.4%, the B content is 0.0005-0.0015%, and the Ca content is not more than 0.002%.
4. The 1180 MPa-grade low-carbon martensitic high-reamed steel according to claim 1, wherein the C content is 0.07-0.09%.
5. The 1180 MPa-grade low-carbon martensitic high-reamed steel according to claim 1, wherein the Si content is 0.5% or less.
6. The 1180 MPa-grade low-carbon martensitic high-reamed steel according to claim 1, wherein the Mn content is 1.6-1.9%.
7. The 1180 MPa-grade low-carbon martensitic high-reamed steel according to claim 1, wherein the S content is controlled below 0.0015%.
8. The 1180 MPa-grade low-carbon martensitic high-reamed steel according to claim 1, wherein the Al content is 0.02-0.05%.
9. The 1180 MPa-grade low-carbon martensitic high-reamed steel according to claim 1, wherein the N content is 0.003% or less.
10. The 1180 MPa-grade low-carbon martensitic high-reamed steel according to claim 1, wherein the Ti content is 0.01-0.03%.
11. The 1180 MPa-grade low-carbon martensitic high-reamed steel according to claim 1, wherein the Mo content is 0.15-0.35%.
12. The 1180 MPa-grade low-carbon martensitic high-reamed steel of claim 1, wherein the microstructure of the high-reamed steel is low-carbon tempered martensite.
13. The method for manufacturing 1180 MPa-level low-carbon martensitic high-reaming steel according to any one of claims 1 to 12, characterized by comprising the steps of:
1) Smelting and casting
Smelting the components according to claims 1-11 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 the casting blank or the cast ingot, wherein the heating temperature is as follows: 1100-1200 ℃, and the heat preservation time is as follows: 1-2 hours;
3) Hot rolling
Start rolling temperature: 950-1100 ℃, 3-5 passes of high reduction at 950 ℃ and accumulated deformation more than or equal to 50%, then the intermediate blank is heated to 920-950 ℃, and then the final 3-7 passes of rolling are carried out and accumulated deformation more than or equal to 70%; the final rolling temperature is 800-920 ℃;
4) Cooling
Firstly performing air cooling for 2-10 seconds, then cooling the steel plate to a certain temperature below an Ms point at a cooling rate of more than or equal to 30 ℃/s, and cooling to room temperature after coiling;
5) Acid washing
The strip steel pickling operation speed is regulated within the interval of 30-90 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 1.5%, and then the strip steel is rinsed, dried and oiled.
14. The method for manufacturing 1180 MPa-level low-carbon martensitic high-reaming steel according to claim 13, wherein step 5) after pickling, rinsing at a temperature ranging from 35 ℃ to 50 ℃ and drying the surface of the strip steel at a temperature ranging from 120 ℃ to 140 ℃ and oiling.
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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102227511A (en) * 2008-11-28 2011-10-26 杰富意钢铁株式会社 High-strength cold-rolled steel sheet having excellent workability, molten galvanized high-strength steel sheet, and method for producing same
CN105506494A (en) * 2014-09-26 2016-04-20 宝山钢铁股份有限公司 High-toughness hot-rolled high-strength steel with yield strength being 800 MPa and manufacturing method of high-toughness hot-rolled high-strength steel
CA3110823A1 (en) * 2018-09-20 2020-03-26 Arcelormittal Hot rolled steel sheet with high hole expansion ratio and manufacturing process thereof

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102227511A (en) * 2008-11-28 2011-10-26 杰富意钢铁株式会社 High-strength cold-rolled steel sheet having excellent workability, molten galvanized high-strength steel sheet, and method for producing same
CN105506494A (en) * 2014-09-26 2016-04-20 宝山钢铁股份有限公司 High-toughness hot-rolled high-strength steel with yield strength being 800 MPa and manufacturing method of high-toughness hot-rolled high-strength steel
CA3110823A1 (en) * 2018-09-20 2020-03-26 Arcelormittal Hot rolled steel sheet with high hole expansion ratio and manufacturing process thereof

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