CN114107793A - 1180 MPa-grade low-carbon martensite high-reaming steel and manufacturing method thereof - Google Patents

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

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CN114107793A
CN114107793A CN202010896479.7A CN202010896479A CN114107793A CN 114107793 A CN114107793 A CN 114107793A CN 202010896479 A CN202010896479 A CN 202010896479A CN 114107793 A CN114107793 A CN 114107793A
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hole
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CN114107793B (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

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  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)
  • Heat Treatment Of Sheet Steel (AREA)

Abstract

1180 MPa-grade low-carbon martensite high-reaming steel and a manufacturing method thereof, wherein the low-carbon martensite high-reaming steel comprises the following chemical components in percentage by weight: 0.05 to 0.10% of C, Si<0.8 percent of Mn, 1.5-2.0 percent of Mn, less than or equal to 0.02 percent of P, less than or equal to 0.003 percent of S, 0.02-0.08 percent of Al, less than or equal to 0.004 percent of N, 0.1-0.5 percent of Mo, 0.01-0.05 percent of Ti, less than or equal to 0.0030 percent of O, and the balance of Fe and other inevitable impurities. The invention is as describedThe yield strength of the high-hole-expansion steel is more than or equal to 900MPa, the tensile strength is more than or equal to 1180MPa, and the transverse elongation A50Not less than 8% and hole expansion rate not less than 70%. The high-hole-expansion steel has the yield strength of more than or equal to 900MPa and the tensile strength of more than or equal to 1180MPa, and can be applied to parts of a chassis of a passenger vehicle, such as a control arm, an auxiliary frame and the like, which need high strength thinning.

Description

1180 MPa-grade low-carbon martensite high-reaming steel and manufacturing method thereof
Technical Field
The invention relates to the field of high-strength steel, in particular to 1180 MPa-grade low-carbon martensite 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 requirements of parts of many vehicle types in the domestic automobile industry require the use of hot-rolled or pickled plates, such as chassis parts, torsion beams, auxiliary frames of cars, wheel spokes and rims, front and rear axle assemblies, body structural parts, seats, clutches, safety belts, truck box plates, protective nets, automobile girders and other parts of automobiles. Wherein, the proportion of the chassis steel to the total steel used by the car can reach 24 to 34 percent.
The light weight of passenger cars is not only a development trend in the automotive industry, but also a requirement of legal regulations. The fuel consumption is regulated by laws and regulations, the weight of a vehicle body is required to be reduced in a phase-changing manner, and the requirement reflected on materials is high strength, thinning and light weight. High strength subtracts heavy is the inevitable requirement of follow-up new motorcycle type, and this must lead to the fact with the steel grade higher, also must bring the change on the chassis structure: if the parts are more complex, the requirements on material performance, surface and the like and the forming technology are improved, such as hydraulic forming, hot stamping, laser welding and the like, and the performances of high strength, stamping, flanging, resilience, fatigue and the like of the material are further converted.
Compared with the foreign countries, the development of domestic high-strength high-hole-expansion steel has relatively lower strength level and poor performance stability. For example, high-expansion-hole steel used by domestic automobile part enterprises is basically high-strength steel with the tensile strength of below 600MPa, and high-expansion-hole steel with the tensile strength of below 440MPa competes for whitening. High hole expansion steel with 780 MPa-grade tensile strength is gradually used in batch at present, but higher requirements are provided for two important indexes of forming elongation and hole expansion rate. And 980 MPa-grade high-reaming steel is still in a research and development certification stage at present and does not reach a batch use stage. High hole expansion steel with higher strength grade such as 1180MPa has not been developed by manufacturers. Based on the development trend of high-hole-expansion steel, in order to better meet the potential requirements of users, 1180MPa high-hole-expansion steel with higher strength level needs to be developed.
The documents related to 980MPa grade high-hole-expansion steel are few, and 1180MPa grade high-hole-expansion steel is blank. Most of the related patent documents are high-hole-expansion steels of 780MPa or less. A large number of researches indicate that the elongation rate of the material is in inverse proportion to the hole expansion rate, namely the higher the elongation rate is, the lower the hole expansion rate is; 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 material having good plasticity and hole-enlarging and flanging performance, the relationship between the two needs to be better balanced. A single homogeneous structure is advantageous for achieving higher porosities, whereas a bi-or multiphase structure is generally disadvantageous for increasing the porosities.
Disclosure of Invention
The invention aims to provide 1180 MPa-grade low-carbon martensite high-hole-expansion steel and a manufacturing method thereof, wherein the yield strength of the high-hole-expansion steel is more than or equal to 900MPa, the tensile strength of the high-hole-expansion steel is more than or equal to 1180MPa, and the transverse elongation A of the high-hole-expansion steel is50The hole expanding rate is more than or equal to 8 percent, and the hole expanding rate is more than or equal to 70 percent, so that the hole expanding agent can be applied to parts of a chassis of a passenger car, such as a control arm, an auxiliary frame and the like, which need high strength thinning.
In order to achieve the purpose, the technical scheme of the invention is as follows:
in the aspect of component design, the low C content is adopted, so that excellent weldability can be ensured when a user uses the steel, and the obtained martensite structure has good hole expansibility and impact toughness; on the basis of meeting the requirement that the tensile strength is more than or equal to 1180MPa, the lower the carbon content is, the better the carbon content is; adopting high manganese-stabilized austenite, and matching with the process to obtain the near-equiaxial deformed austenite after rolling; a certain amount of molybdenum can remarkably delay the phase transformation of ferrite and pearlite, so as to avoid the formation of ferrite and pearlite; by adopting a low-carbon martensite design idea, adopting a relatively low finish rolling temperature and air cooling or direct water cooling after rolling, fine and uniform original austenite grains can be obtained, and finally, the low-carbon martensite with uniform structure is obtained.
Specifically, the 1180 MPa-grade low-carbon martensite high-hole-expansion steel comprises the following chemical components in percentage by weight: 0.05 to 0.10 percent of C, less than 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 inevitable impurities.
Further, the alloy also comprises one or more of Cr less than or equal to 0.5 percent, B less than or equal to 0.002 percent, Ca less than or equal to 0.005 percent, Nb less than or equal to 0.06 percent, V less than or equal to 0.05 percent, Cu less than or equal to 0.5 percent and Ni less than or equal to 0.5 percent, wherein the content of Nb and V is respectively preferably less than or equal to 0.03 percent, the content of Cu and Ni is respectively preferably less than or equal to 0.3 percent, the content of Cr is preferably 0.2 to 0.4 percent, the content of B is preferably 0.0005 to 0.0015 percent and the content of Ca is preferably less than or equal to 0.002 percent.
The microstructure of the high-reaming-hole steel is online low-carbon tempered martensite.
The yield strength of the high-hole-expansion steel is more than or equal to 900MPa, the tensile strength is more than or equal to 1180MPa, and the transverse elongation A50Not less than 8% and hole expansion rate not less than 70%.
The high hole expansion steel of the invention comprises the following components:
carbon is an essential element in steel and is also one of the important elements in the present invention. Carbon expands the austenite phase region and stabilizes austenite. Carbon, which is an interstitial atom in steel, plays a very important role in increasing the strength of 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 the high-strength steel with the tensile strength reaching 1180MPa, the carbon content is required to be ensured to be more than 0.05 percent, otherwise, the carbon content is less than 0.05 percent, and the tensile strength can not reach 1180MPa even if the steel is completely quenched to the 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 both low. Therefore, the carbon content should be controlled to be between 0.05 and 0.10%, and preferably in the range of 0.07 to 0.09%.
Silicon, which is the basic element in steel, is the main element in the present invention, Si being the conventional additive element, mainly aimed at deoxidation. 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, usually not more than 0.8%, preferably less than 0.5%;
manganese, the most basic element in steel, is also one of the most important elements in the present invention. It is known that Mn is an important element for expanding the austenite phase region, and can reduce the critical quenching rate of steel, stabilize austenite, refine grains, and delay transformation of austenite to pearlite. In the present invention, in order to ensure the strength of the steel sheet and at the same time, in order not to form ferrite during cooling, the Mn content should be generally controlled to be more than 1.5%; meanwhile, the Mn content is generally not more than 2.0%, otherwise Mn segregation is likely to occur during steel making, and hot cracking is also likely to occur during slab continuous casting. Therefore, the Mn content in the steel is generally controlled to 1.5 to 2.0%, preferably in the range of 1.6 to 1.9%.
Phosphorus, an impurity element in steel. P is easy to be partially gathered on the grain boundary, and Fe is formed when the content of P in steel is higher (more than or equal to 0.1 percent)2P is precipitated around the crystal grains to reduce the plasticity and toughness of the steel, so the lower the content of the P is, the better the P content is generally controlled within 0.02 percent, and the steelmaking cost is not increased;
sulfur, an impurity element in steel. S in steel is usually combined with Mn to form MnS inclusions, and particularly when the contents of S and Mn are high, the steel forms more MnS, and 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 structural anisotropy is increased, and the hole expansion performance is not favorable. Therefore, the lower the S content in the steel, the better, considering that the Mn content in the present invention must be at a high level, the S content is strictly controlled in order to reduce the MnS content, and the S content is required to be controlled to be within 0.003%, and preferably to be within 0.0015%.
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., Al mainly functions to deoxidize and refine grains. In the invention, Al is taken as a common deoxidizing element and an element for refining grains, and the content of Al is usually controlled to be 0.02-0.08%; the Al content is lower than 0.02 percent, and the effect of refining grains is not achieved; similarly, when the Al content is higher than 0.08%, the effect of refining grains is saturated. Therefore, the Al content in the steel may be controlled to be 0.02 to 0.08%, and preferably 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 unavoidable element in the steel making process. Although the content thereof is small, the formed TiN particles, in combination with a strong carbide forming element such as Ti or the like, have a very adverse effect on the properties of the steel, particularly on the hole expansibility. Because TiN is square, great stress concentration exists between the sharp corner and the substrate, and cracks are easily formed by the stress concentration between the TiN and the substrate in the reaming deformation process, so that the reaming performance of the material is greatly reduced. On the premise of controlling the nitrogen content as much as possible, the lower the content of the element forming strong carbide such as Ti, the better. In the present invention, a trace amount of Ti is added to fix nitrogen, and the adverse effect of TiN is minimized. Therefore, the nitrogen content should be controlled to 0.004% or less, and preferably 0.003% or less.
Titanium is one of important elements in the present invention. Ti plays two main roles in the present invention: firstly, the nitrogen-fixing agent is combined with impurity element N in steel to form TiN, and plays a part of the role of nitrogen fixation; secondly, a certain amount of TiN with fine dispersion is formed in the subsequent welding process of the material, thereby inhibiting the size of austenite grains, refining the structure and improving the low-temperature toughness. Therefore, the Ti content in the steel is controlled in the range of 0.01 to 0.05%, and preferably in the range of 0.01 to 0.03%.
Molybdenum, is one of the important elements in the present invention. The addition of molybdenum to the steel can greatly retard ferrite and pearlite transformation. The effect of the molybdenum is beneficial to adjusting various processes in the actual rolling process, such as sectional cooling after finishing the final rolling, air cooling before 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 structures such as ferrite or pearlite and the like cannot be formed in the air cooling process, and meanwhile, deformed austenite can be dynamically restored in the air cooling process, thereby being beneficial to improving the uniformity of the structures; molybdenum has strong resistance to solder softening. Because the invention mainly aims to obtain the 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 softening degree of welding. Therefore, the content of molybdenum should be controlled between 0.1-0.5%, preferably in the range of 0.15-0.35%.
Chromium is one of the elements that can be added in the present invention. The addition of a small amount of chromium element is not for improving the hardenability of the steel, but for combining with B, which is beneficial to forming an acicular ferrite structure in a welding heat affected zone after welding, and can greatly improve the low-temperature toughness of the welding heat affected zone. Since the final application parts related by the invention are passenger car chassis products, the low-temperature toughness of the welding heat affected zone is an important index. Besides ensuring that the strength of the welding heat affected zone cannot be reduced too much, the low-temperature toughness of the welding heat affected zone also meets certain requirements. In addition, chromium itself has some resistance to solder softening. Therefore, the addition amount of chromium in the steel is generally less than or equal to 0.5%, and the preferable range is 0.2-0.4%.
Boron is one of the elements that can be added in the present invention. Boron mainly has the function of being segregated at the original austenite grain boundary in the steel and inhibiting the formation of proeutectoid ferrite; boron added to steel can also greatly improve the hardenability of steel. However, in the present invention, the trace amount of boron is added not mainly for the purpose of enhancing hardenability but for the purpose of improving the structure of the weld heat affected zone in combination with chromium to obtain an acicular ferrite structure having good toughness. The addition of boron in the steel is generally controlled below 0.002%, and the preferred range is 0.0005-0.0015%.
Calcium, an added element in the present invention. Calcium can improve the form of sulfides such as MnS, so that elongated sulfides such as MnS and the like are changed into spherical CaS, the inclusion form is favorably improved, the adverse effect of the elongated sulfides on the hole expanding performance is further reduced, but the addition of excessive calcium can increase the amount of calcium oxide, and is adverse to the hole expanding performance. Therefore, the addition amount of calcium in steel grades is usually less than or equal to 0.005%, and the preferable range is less than or equal to 0.002%.
Oxygen, which is an inevitable element in the steel making process, is an essential element in the present invention, and the content of O in steel after deoxidation is generally 30ppm or less, and does not cause significant adverse effects on the properties of the steel sheet. Therefore, the O content in the steel is controlled to be within 30 ppm.
Niobium, is one of the elements that may be added in the present invention. Niobium is similar to titanium and is a strong carbide element in steel, niobium is added into the steel to greatly improve the non-recrystallization temperature of the steel, deformed austenite with higher dislocation density can be obtained in the finish rolling stage, and the final phase change structure can be refined in the subsequent transformation process. However, the addition amount of niobium is not too much, and on the one hand, the addition amount of niobium exceeds 0.06%, 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, the anisotropy of hot-rolled austenite structures is easily caused, and the anisotropy is transmitted to final structures in the subsequent cooling phase change process, so that the reaming performance is not good. Therefore, the niobium content in the steel is usually controlled to 0.06% or less, and preferably in the range of 0.03% or less.
Vanadium, is an additive element in the present invention. Vanadium, like titanium and niobium, is also a strong carbide former. However, vanadium carbides are low in solid solution or precipitation temperature, and are usually all solid-dissolved in austenite in the finish rolling stage. Vanadium only begins to form in ferrite when the temperature decreases to initiate phase transformation. In the present invention, the main purpose of adding vanadium is to improve the resistance of the weld heat affected zone to softening together with molybdenum. Molybdenum and vanadium are most effective from the viewpoint of the effect of resistance to solder softening, and in the case of molybdenum, vanadium may be selectively added. Therefore, the amount of vanadium added to the steel is usually 0.05% or less, preferably 0.03% or less.
Copper, which is an additive element in the present invention. The corrosion resistance of the steel can be improved by adding the copper into the steel, and the corrosion resistance effect is better when the copper and the P element are added together; when the addition amount of Cu exceeds 1%, an epsilon-Cu precipitated phase can be formed under certain conditions, and a strong precipitation strengthening effect is achieved. However, addition of Cu is likely to cause the phenomenon of "Cu embrittlement" during rolling, and in order to fully utilize the effect of Cu on improving corrosion resistance in some applications without causing significant "Cu embrittlement", the content of Cu element is usually controlled to be within 0.5%, preferably within 0.3%.
Nickel, which is an additive element in the present invention. The nickel added into the steel has certain corrosion resistance, but the corrosion resistance effect is weaker than that of copper, the nickel added into the steel has little influence on the tensile property of the steel, but the structure and the precipitated phase of the steel can be refined, and the low-temperature toughness of the steel is greatly improved; meanwhile, in the steel added with copper element, a small amount of nickel is added to inhibit the generation of Cu brittleness. The addition of higher nickel has no significant adverse effect on the properties of the steel itself. If copper and nickel are added simultaneously, not only can the corrosion resistance be improved, but also the structure and precipitated phase of the steel are refined, and the low-temperature toughness is greatly improved. However, both copper and nickel are relatively expensive alloying elements. Therefore, in order to minimize the cost of alloy design, the amount of nickel added is usually 0.5% or less, preferably 0.3% or less.
The invention relates to a manufacturing method of 1180 MPa-grade low-carbon martensite high-reaming steel, which comprises the following steps of:
1) smelting and casting
Smelting the components by a converter or an electric furnace, secondarily refining the components by a vacuum furnace, and then casting the components 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 ℃, heat preservation time: 1-2 hours;
3) hot rolling
The initial rolling temperature: at 950-1100 ℃, under 3-5 times of large reduction at 950 ℃ and the accumulated deformation is more than or equal to 50%, then the intermediate blank is heated to 920-950 ℃, and then the final 3-7 times of rolling are carried out, and the accumulated deformation is more than or equal to 70%; the finishing temperature is 800-920 ℃;
4) cooling down
Firstly, air cooling is carried out for 0-10 seconds, then the steel plate is water cooled to a certain temperature below the Ms point at the cooling speed of more than or equal to 30 ℃/s, and the steel plate is cooled to the room temperature after being coiled;
5) acid pickling
The pickling speed of the strip steel is adjusted within the range of 30-90 m/min, the pickling temperature is controlled within the range of 75-85 ℃, the withdrawal and straightening rate is controlled to be less than or equal to 1.5% so as to reduce the elongation loss of the strip steel, and then the strip steel is rinsed, dried on the surface of the strip steel and oiled.
Preferably, after the acid washing in the step 5), rinsing is carried out at the temperature of 35-50 ℃ to ensure the surface quality of the strip steel, and the surface of the strip steel is dried and oiled at the temperature of 120-140 ℃.
In the aspect of component design, the low C content is adopted, so that excellent weldability can be ensured when a user uses the steel, and the obtained martensite structure has good hole expansibility and impact toughness; on the basis of meeting the requirement that the tensile strength is more than or equal to 1180MPa, the lower the carbon content is, the better the carbon content is; adopting high manganese-stabilized austenite, and matching with the process to obtain the near-equiaxial deformed austenite after rolling; a certain amount of molybdenum can remarkably delay the phase transformation of ferrite and pearlite, so as to avoid the formation of ferrite and pearlite; by adopting a low-carbon martensite design idea, adopting a relatively low finish rolling temperature and air cooling or direct water cooling after rolling, 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 is required to be completed as fast as possible in the stages of rough rolling and finish rolling. After finishing rolling, air cooling is firstly carried out for a certain time or direct water cooling is carried out after finishing rolling. The main purposes of air cooling are as follows: because of the higher manganese and molybdenum content in the composition design, the manganese is an element for stabilizing austenite, and the molybdenum greatly delays ferrite and pearlite phase transformation. Therefore, during the air-cooling for a certain period of time, the rolled deformed austenite does not undergo phase transformation, i.e., ferrite structure, but dynamic recrystallization and relaxation processes. The deformed austenite is dynamically recrystallized to form nearly equiaxial austenite with uniform structure, the dislocation in the austenite grains is greatly reduced after relaxation, and the combination of the two can obtain martensite with uniform structure in the subsequent water-cooling quenching process. In order to obtain a martensite structure, the water cooling speed is higher than the critical cooling speed of the low-carbon martensite, and in the invention, in order to ensure that the martensite can be obtained by all component designs, the water cooling speed after rolling the strip steel is required to be more than or equal to 30 ℃/s.
Since the microstructure according to the present invention is low-carbon martensite, the strip steel may be cooled to a temperature not higher than the martensite transformation start point Ms at a cooling rate higher than the critical cooling rate after the finish rolling. The cooling temperature is different, and the content of residual austenite at room temperature is different. There is usually an optimum quenching stop temperature range, which varies depending on the alloy composition, and is generally between 150 ℃ and 350 ℃. In order to obtain high-strength steel with good plasticity and hole expansion rate, the strip steel needs to be quenched to a certain temperature range below the Ms point, and the structure with excellent comprehensive performance can be obtained by quenching the strip steel to a range not more than the Ms point according to theoretical calculation and actual test verification. When the quenching temperature is more than or equal to Ms, a bainite structure appears in the structure, and the strength requirement of 1180MPa cannot be met. For the above reasons, the coiling temperature needs to be controlled to be less than or equal to Ms. Based on the innovative components and process design thought, 1180 MPa-grade low-carbon martensite high-hole-expansion steel with excellent strength, plasticity, toughness and hole expansion performance can be obtained.
The invention has the beneficial effects that:
the method can be used for manufacturing the high-hole-expansion steel with yield strength not less than 900MPa, tensile strength not less than 1180MPa and thickness of 2-6mm, and has good elongation (transverse A)50Not less than 8%), impact toughness and hole expansion performance (the hole expansion rate is not less than 70%), shows excellent matching of strength, plasticity, toughness and hole expansion performance, and therefore has the following beneficial effects:
(1) by adopting a relatively economic component design idea and an innovative cooling process path, 1180MPa grade high-hole-expansion steel with excellent strength, plasticity, toughness and hole expansion performance can be obtained;
(2) the steel coil or the steel plate has excellent ultrahigh strength, plasticity and toughness matching, and simultaneously has good hole expansion performance, can be applied to manufacturing of parts such as automobile chassis, auxiliary frames and the like which need high-strength thinning and hole expansion flanging, and has very wide application prospect.
Drawings
FIG. 1 is a process flow diagram of a 1180MPa grade low-carbon martensite high-hole-expansion steel manufacturing method of the invention;
FIG. 2 is a schematic view of a rolling process in the 1180 MPa-grade low-carbon martensite high-hole-expansion steel manufacturing method of the invention;
FIG. 3 is a schematic view of a cooling process in the 1180 MPa-grade low-carbon martensitic high-expansion steel manufacturing method of the present invention;
FIG. 4 is a typical metallographic picture of a high hole expansion steel according to example 1 of the present invention;
FIG. 5 is a representative metallographic picture of a high hole expansion steel of example 3 according to the invention;
fig. 6 is a typical metallographic picture of a high hole expansion steel example 5 according to the present invention.
Detailed Description
Referring to fig. 1 to 3, the method for manufacturing 1180MPa grade hot-rolled or pickled high-hole-expansion steel comprises the following steps:
1) smelting and casting
Smelting by adopting a converter or an electric furnace, secondarily refining by adopting a vacuum furnace, and then 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 ℃, heat preservation time: 1-2 hours;
3) hot rolling
The initial rolling temperature: at 950-1100 ℃, under 3-5 times of large reduction at 950 ℃ and the accumulated deformation is more than or equal to 50%, then the intermediate blank is heated to 920-950 ℃, and then the final 3-7 times of rolling are carried out, and the accumulated deformation is more than or equal to 70%; the finishing temperature is 800-920 ℃;
4) cooling down
Air cooling is carried out for 0-10 seconds, then the steel plate is water cooled to a certain temperature below the Ms point at the cooling speed of more than or equal to 30 ℃/s, and the steel plate is cooled to the room temperature after being coiled.
5) Acid pickling
The pickling speed of the strip steel can be adjusted within the range of 30-90 m/min, the pickling temperature is controlled within the range of 75-85 ℃, the withdrawal and straightening rate is controlled to be less than or equal to 1.5% so as to reduce the elongation loss of the strip steel, rinsing is carried out within the temperature range of 35-50 ℃, and surface drying and oiling are carried out within the temperature range of 120-140 ℃.
The components of the high hole expansion steel embodiment of the invention are shown in table 1, and tables 2 and 3 are production process parameters of the steel embodiment of the invention, wherein the thickness of a billet in a rolling process is 120 mm; table 4 shows the mechanical properties of the steel sheets of examples 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 relatively stable, the impact energy at the low temperature of minus 40 ℃ is stabilized between 90 and 120J, and the hole expansion ratio is more than or equal to 70 percent. The embodiments show that the 1180MPa high-strength steel has good matching of strength, plasticity, toughness and hole expansion performance, is particularly suitable for parts such as automobile chassis structures and the like which need high-strength thinning and hole expansion flanging forming, such as control arms and the like, can also be used for parts such as wheels and the like which need hole expansion, and has wide application prospect.
Typical metallographic structures of steel plates of example # 1, # 3 and # 5 are shown in fig. 4 to 6, respectively. According to the metallographic photograph, the structure is single-phase low-carbon martensite, and a small amount of carbide appears in the structure according to different coiling temperatures.
Figure BDA0002658554120000111
Figure BDA0002658554120000121
Figure BDA0002658554120000131
Figure BDA0002658554120000141

Claims (14)

1. A1180 MPa-grade low-carbon martensite high-reaming steel comprises the following chemical components in percentage by weight: 0.05 to 0.10 percent of C, less than 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 inevitable impurities.
2. The 1180 MPa-grade low-carbon martensitic high-hole-expansion steel as claimed in claim 1, further comprising one or more of Cr 0.5% or less, B0.002% or less, Ca 0.005% or less, Nb 0.06% or less, V0.05% or less, Cu 0.5% or less, and Ni 0.5% or less, wherein each of Nb and V is preferably 0.03% or less, each of Cu and Ni is preferably 0.3% or less, each of Cr is preferably 0.2-0.4%, B is preferably 0.0005-0.0015%, and each of Ca is preferably 0.002% or less.
3. The 1180MPa grade low carbon martensitic high bore steel of claim 1, wherein the C content is 0.07-0.09%.
4. The 1180MPa grade low carbon martensitic high bore steel of claim 1, wherein the Si content is less than or equal to 0.5%.
5. The 1180MPa grade low carbon martensitic high bore steel of claim 1, wherein the Mn content is 1.6-1.9%.
6. The 1180MPa grade low carbon martensitic high bore steel of claim 1, wherein the S content is controlled to be below 0.0015%.
7. The 1180MPa grade low carbon martensitic high bore steel of claim 1, wherein the Al content is 0.02-0.05%.
8. The 1180MPa grade low carbon martensitic high bore steel of claim 1, wherein the N content is below 0.003%.
9. The 1180MPa grade low carbon martensitic high bore steel of claim 1, wherein the Ti content is 0.01-0.03%.
10. The 1180MPa grade low carbon martensitic high bore steel of claim 1, wherein the Mo content is 0.15-0.35%.
11. The 1180MPa grade low carbon martensitic high bore steel of claim 1, wherein the microstructure of the high bore steel is low carbon tempered martensite.
12. As claimed in claim 1 or 11The 1180 MPa-grade low-carbon martensite high-hole-expansion steel is characterized in that the yield strength of the high-hole-expansion steel is more than or equal to 900MPa, the tensile strength of the high-hole-expansion steel is more than or equal to 1180MPa, and the elongation percentage of the high-hole-expansion steel is transverse A50Not less than 8% and hole expansion rate not less than 70%.
13. The method for manufacturing 1180MPa grade low carbon martensitic high hole expansion steel as claimed in any one of claims 1 to 12, comprising the steps of:
1) smelting and casting
Smelting by a converter or an electric furnace and performing secondary refining by a vacuum furnace according to the components of the alloy of claims 1-10, and then 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 ℃, heat preservation time: 1-2 hours;
3) hot rolling
The initial rolling temperature: at 950-1100 ℃, under 3-5 times of large reduction at 950 ℃ and the accumulated deformation is more than or equal to 50%, then the intermediate blank is heated to 920-950 ℃, and then the final 3-7 times of rolling are carried out, and the accumulated deformation is more than or equal to 70%; the finishing temperature is 800-920 ℃;
4) cooling down
Firstly, air cooling is carried out for 0-10 seconds, then the steel plate is water cooled to a certain temperature below the Ms point at the cooling speed of more than or equal to 30 ℃/s, and the steel plate is cooled to the room temperature after being coiled;
5) acid pickling
Adjusting the strip steel pickling operation speed within the range of 30-90 m/min, controlling the pickling temperature to be 75-85 ℃, controlling the withdrawal and straightening rate to be less than or equal to 1.5%, rinsing, drying the surface of the strip steel, and oiling.
14. The method for manufacturing 1180MPa grade low carbon martensite high hole expansion steel as claimed in claim 13, wherein the step 5) of pickling is followed by rinsing at a temperature range of 35-50 ℃, and the surface of the strip steel is dried and oiled at a temperature of 120-140 ℃.
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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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