CN111057964B - Steel for high-strength knuckle of new energy automobile and preparation method and application thereof - Google Patents

Steel for high-strength knuckle of new energy automobile and preparation method and application thereof Download PDF

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CN111057964B
CN111057964B CN201911386181.5A CN201911386181A CN111057964B CN 111057964 B CN111057964 B CN 111057964B CN 201911386181 A CN201911386181 A CN 201911386181A CN 111057964 B CN111057964 B CN 111057964B
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steel
knuckle
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CN111057964A (en
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安金敏
顾金海
彭冬晋
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Shanghai Cotech Automotive Engineering Co ltd
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Shanghai Cotech Automotive Engineering 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D7/00—Steering linkage; Stub axles or their mountings
    • B62D7/18—Steering knuckles; King pins
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/52—Manufacture of steel in electric furnaces
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/10—Handling in a vacuum
    • 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
    • C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
    • 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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • 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
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • 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
    • C21D2211/003—Cementite
    • 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
    • C21D2211/005—Ferrite
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

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Abstract

The invention relates to a steel for a high-strength knuckle of a new energy automobile, and a preparation method and application thereof, wherein the steel comprises the following components: 0.40-0.44%, si:0.31-0.37%, mn:0.50-0.59%, P: less than or equal to 0.015 percent, S:0.031-0.037%, cr:0.90-0.99%, ni: less than or equal to 0.25 percent, cu: less than or equal to 0.15 percent, mo: less than or equal to 0.10 percent, al:0.017-0.033%, ti:0.003-0.02%, N:0.008-0.014%, wherein Al%. Gtoreq.27N%/14-9 Ti%/16; the preparation method comprises the steps of primary smelting of furnace burden in an electric arc furnace, ladle refining, vacuum degassing, continuous casting, pouring and hot working rolling to obtain finished steel. Compared with the prior art, the invention has the advantages of wide sources of steel components, low cost, stable and reliable process control and the like.

Description

Steel for high-strength knuckle of new energy automobile and preparation method and application thereof
Technical Field
The invention belongs to the technical field of alloy steel, and relates to steel for a high-strength knuckle of a new energy automobile, and a preparation method and application thereof.
Background
The knuckle is one of important parts in an automobile and a steering system, and is required to bear bending force of up-and-down swing of the automobile during running, reaction force of the ground, torsion force during steering and impact force during automobile braking (particularly sudden braking), so that the knuckle is required to have certain tensile strength and yield strength and higher plasticity and toughness. In the prior art, cast iron, aluminum alloy or steel materials are generally adopted, the strength of an iron casting is low, the application range is limited, the light weight effect of the aluminum alloy steering knuckle is obvious, but the cost is high, the strength is low, the steel materials are currently two main types, namely CrMo series quenched and tempered steel, and the other type is microalloyed non-quenched and tempered steel, and both the strength and the toughness of the steering knuckle are improved by adding certain alloy elements, so that the alloy cost is increased.
Chinese patent CN102886642a discloses a method for manufacturing a knuckle for automobiles, the manufactured steel ingot comprises C:0.37-0.44%, si:0.15-0.35%, mn:0.70-0.90%, P:0.15-0.25%, S:0.015-0.025%, cr:0.70-0.95%, mo:0.30-0.40%, ni:1.6-2%, cu:0.10-0.20%, wherein the tensile strength Rm of the finished product is more than or equal to 830MPa, the yield strength Rp0.2 is more than or equal to 690MPa, the elongation A is more than or equal to 14%, and the reduction of area Z is more than or equal to 30%, the steel is produced by adopting a die casting steel ingot method, so that the yield is low, and Ni element is added in the raw materials, so that the processing cost of the steel ingot is higher, meanwhile, P element is added, and the cold-embrittlement cracking tendency of the material is enhanced.
Chinese patent CN110129656a discloses a method for producing steel for automobile steering knuckles, the steel produced includes C:0.37-0.39%, si:0.20-0.30%, mn:0.75-0.80%, P: less than or equal to 0.020 percent, S: less than or equal to 0.015 percent, cr:1.05-1.10%, ni: less than or equal to 0.3 percent, al:0.0015 to 0.0040%, cu+Ni+V+Sn: less than or equal to 0.80 percent, H: less than or equal to 0.0002 percent, O: less than or equal to 0.0020 percent, and the balance of Fe and unavoidable impurities. The hardening and tempering hardness of the finished product part is 30-36HRC, the grain size is 5-8 grade, the fatigue life is 50 ten thousand times without damage, the steel prepared by the patent is essentially coarse grain steel, the grain uniformity is poor, and the performance is unstable.
Chinese patent CN104087819B discloses an as-cast low-temperature tough ferrite ductile iron material for car steering knuckles and a preparation method thereof, the ferrite ductile iron material prepared comprises C:3.1-3.4%, si:3.1-3.3%, mn:0.2-0.30%, P: <0.040%, S: <0.015%, cu: <0.1%, sn: <0.01%, cr: <0.1%, mo: <0.1%, ni: <0.1%, mg:0.03-0.05%, and the balance Fe and unavoidable impurities, wherein the tensile strength Rm is more than or equal to 480MPa, the yield strength Rp is 0.2 and more than or equal to 360MPa, the elongation A is more than or equal to 18%, the hardness is HBW165-200, the ferrite ductile iron material prepared by the method has low strength and is not suitable for a front knuckle of a new energy automobile with large bearing capacity, and the added low-melting-point element increases the difficulty of material preparation.
Chinese patent CN109097644a discloses a high strength aluminum alloy for automobile steering knuckles and a method for preparing automobile steering knuckles, the prepared aluminum alloy comprising Si:0.45-0.75%, cu:0.15-0.35%, mn: less than or equal to 0.05 percent, mg:0.90-1.10%, zn: less than or equal to 0.20 percent, ti: less than or equal to 0.10 percent, cr:0.04-0.35%, and the balance of Al. The tensile strength Rm is more than or equal to 400MPa, the yield strength Rp0.2 is more than or equal to 358MPa, the elongation A is more than or equal to 13%, the hardness HBW is more than or equal to 115, and the strength is lower.
In summary, in the prior art, the steel material has high alloy element content, coarse grains, increased cost and unstable performance; the mechanical properties of ductile iron and aluminum alloy are low, smelting difficulty or cost control is not ideal, and the performance requirements of the new energy automobile on the front steering knuckle cannot be met.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide the steel for the high-strength knuckle of the new energy automobile as well as the preparation method and the application thereof, which are used for solving the problems of high difficulty, high cost and unstable finished product performance of the steel for the knuckle.
The aim of the invention can be achieved by the following technical scheme:
the steel for the high-strength knuckle of the new energy automobile comprises the following components in percentage by weight:
c:0.40-0.44%, si:0.31-0.37%, mn:0.50-0.59%, P: less than or equal to 0.015 percent, S:0.031-0.037%, cr:0.90-0.99%, ni: less than or equal to 0.25 percent, cu: less than or equal to 0.15 percent, mo: less than or equal to 0.10 percent, al:0.017-0.033%, ti:0.003-0.020%, N:0.0080-0.0140%, and the balance of Fe and unavoidable impurities.
C is an element necessary for guaranteeing the using strength of the steering knuckle and is one of main elements influencing the hardenability, the strength of the steering knuckle is poor due to the fact that the content of C is too low, and good hardenability requirements cannot be guaranteed.
Si can well eliminate the adverse effect of ferric oxide on steel, and can dissolve in ferrite, strengthen the ferrite and improve the strength, hardness, elasticity, elastic limit and wear resistance of the steering knuckle; in addition, si can also improve the Ac3 temperature of the steel, has great positive influence on the tempering stability and oxidation resistance of the steering knuckle, but Si has poor thermal conductivity, is easy to cause cracking of the steel, and has serious decarburization tendency. Therefore, the Si content is controlled to be 0.31-0.37% in the invention.
Mn is an effective element for deoxidation and desulfurization, is one of main elements affecting hardenability, and can play a role in deoxidation and desulfurization when being added during smelting, and in addition, mn can be dissolved in ferrite to play a role in solid solution strengthening; when the Mn content is less than 0.50%, the deoxidization and desulfurization effects are smaller, and after the Mn content is more than 0.59%, the hardenability and segregation of the steering knuckle are not well controlled, and meanwhile, the thermoplastic property is poor, so that the production is influenced, and therefore, the Mn content is controlled to be 0.50-0.59%.
P is a harmful element, and an excessive amount of P increases cold brittleness of steel, so that the P content in the invention is not more than 0.015%.
S as an impurity element in steel can obviously reduce the plasticity and toughness of the steel, but a proper amount of sulfur can effectively improve the cutting performance of the steel, so that the S content is controlled to be 0.031-0.037 percent in the invention.
Cr can obviously improve the hardenability, strength, wear resistance and other properties of steel, is favorable for reducing the activity of C, and can prevent decarburization phenomenon from occurring in the processes of heating, rolling and heat treatment of knuckle forgings, but the excessively high Cr content can obviously reduce the toughness of the knuckle after quenching and tempering, so that the Cr content is controlled to be 0.90-0.99%.
Ni and Mo have the effect of improving the fatigue strength of the material, but too high content can reduce machinability after hot working, and increase alloy cost; cu can improve the strength and toughness of the material, but too high content of Cu can enhance the hot brittleness of the material at high temperature, so that the fatigue performance of the steering knuckle is reduced, and therefore, the content of Ni is not more than 0.25%, the content of Mo is not more than 0.10% and the content of Cu is not more than 0.15%.
Further, the weight percentage of Al, the weight percentage of N% of N and the weight percentage of Ti in the steel satisfy the following relation: al is more than or equal to 27N%/14-9Ti%/16.
Al, ti and N are main refined grain elements, and in the technical scheme of the invention, one or more precipitated phase particles of carbide, nitride and carbonitride of (Al and Ti) are formed by controlling the mass percentages of Al, ti and N in steel and the mass relation of Al, ti and N, so that the positive effects of pinning grain boundaries and refining grains are achieved. For this reason, it is necessary to ensure proper Al, ti and N contents in the steel, and at the same time, ensure Al/N and Ti/N contents in the steel, and avoid that too much or too little content of a certain element affects the performance of the steel. In the initial stage of smelting, al is mainly used as deoxidizer to be added and formed into Al 2 O 3 The inclusion floats up, enters slag, is fed with Al wires after VD vacuum treatment, and the Al mainly serves as an alloying element to play a role in microalloying under the condition of low oxygen. Al combines with N in steel to form AlN phase, and plays a role in pinning the grain boundary to inhibit the growth of austenite grains at the austenite grain boundary, but the excessive Al or the unreasonable atomic number ratio of Al/N is mixed, so that Al is easily formed in the steel 2 O 3 Inclusions are difficult to remove, while Al 2 O 3 And CaS are easily adsorbed at the tundish nozzle "nodulation", resulting in poor molten steel castability. The other element N forming AlN is added in an alloy form, but excessive N can cause high gas content, subcutaneous bubbles are easy to form, and the quality of steel is affected. In addition, alN particles are unstable at high temperature and are easy to grow or dissolve, and the pinning effect on grain boundaries is weakened, so that trace Ti and N elements are added in a compound way to preferentially form a TiN precipitated phase which is more stable at high temperature, thereby inhibiting austenite grain growth at a high temperature stage, but if the Ti content is too high, coarse TiN inclusion is easy to form in steel, and the fatigue strength of a steering knuckle is influencedDegree, etc.
In summary, in the invention, the weight percentage of Al is controlled to be 0.017-0.033%, the weight percentage of Ti is controlled to be 0.003-0.020%, the weight percentage of N is controlled to be 0.008-0.014%, and the Al%. Gtoreq.27N%/14-9 Ti%/16 is satisfied.
Further, in the steel, the grade of sulfide nonmetallic inclusion is less than or equal to 2.5.
The preparation method of the steel for the high-strength knuckle of the new energy automobile comprises the following steps of:
1) Preparing furnace burden according to the components and weight percentage of the steel, and sequentially performing primary smelting in an electric arc furnace, ladle refining, vacuum degassing and continuous casting pouring on the furnace burden to obtain a continuous casting blank;
2) And (3) adopting a rolling mill hot working rolling method, and sequentially heating and rolling the continuous casting billet in the step (1) to obtain the finished steel product.
Further, in the step 1), during primary smelting of the electric arc furnace, P is removed from the slag during the oxidation period, and slag discharging conditions comprise: the slag tapping temperature is 1630-1660 ℃, and the weight percentage of P is not more than 0.013 percent; the tapping conditions include: the tapping temperature is 1630-1650 ℃, the weight percentage of P is not more than 0.010 percent, and the weight percentage of C is not less than 0.03 percent;
adding aluminum in the ladle refining process to enable the weight percentage of Al in molten steel to reach 0.038-0.042%, adding other metal alloys, stirring for 5-10min, and adjusting chemical components to be controlled internally;
when the temperature of molten steel in the ladle refining process reaches 1650-1670 ℃, entering a vacuum degassing process;
in the vacuum degassing process, the vacuum degree is 60-70Pa (preferably 66.7 Pa), and the vacuum degassing time is not less than 15min;
after the vacuum degassing process, adding titanium alloy into molten steel until the weight percentage of Ti reaches 0.003-0.020%, so as to ensure the yield, and then enabling the molten steel to enter a continuous casting process through a hanging ladle when the temperature of the molten steel reaches 1550-1570 ℃ (hanging ladle temperature) and the weight percentage of each component meets the corresponding requirement.
Wherein the furnace burden comprises low P, S scrap steel, crop ends, high-quality pig iron, metal alloy and reducing agent, and the metal alloy comprises ferrochrome, low-phosphorus ferromanganese and other metal element-containing materials ferrosilicon and titanium alloy which are commonly used in steel making technology and can meet the metal element types of steel materials in the invention; the reducing agent comprises calcium carbide, carbon powder and aluminum powder, and the arc furnace is preferably a 30-150 ton arc furnace;
furthermore, the ladle refining process is performed in a ladle refining furnace adapted to the capacity of an electric arc furnace, comprising: refining molten steel, seating a ladle, measuring temperature and analyzing, adjusting argon pressure according to conditions, and removing harmful gases and inclusions in the molten steel through the ladle refining process.
Further, in the step 1), in the continuous casting pouring process, high-temperature molten steel is poured into a tundish through a protective sleeve, and then a continuous casting blank is poured out through a continuous casting crystallizer in combination with electromagnetic stirring and light pressing technologies;
wherein the inner surface of the tundish is a refractory coating, the inner surface is completely cleaned and checked before use, cracks cannot be formed on the inner surface, and the superheat degree of the tundish is 20-40 ℃;
the casting speed of the continuous casting blank is 0.6-2.1m/min, the preferable section size of the continuous casting blank is 140mm multiplied by 320mm multiplied by 425mm, and the casting speed of the continuous casting blank is adjusted according to the section size;
and (3) placing the obtained continuous casting blank in a slow cooling pit, and then executing the step (2) after the slow cooling process, wherein the slow cooling time of the slow cooling process is not less than 24 hours.
Further, in step 2), the heating process is performed in a continuous furnace, and the heating process sequentially comprises: the preheating section, the first heating section, the second heating section and the soaking section;
the temperature of the preheating section is not higher than 700 ℃;
the heating temperature of the first heating section is 700-980 ℃;
the heating temperature of the second heating section is 950-1200 ℃;
the heating temperature of the soaking section is 1100-1200 ℃;
the total heating time of the continuous casting billet in the continuous furnace is not less than 195min.
Compared with the prior art, the soaking temperature is increased by 20 ℃ to implement the diffusion process of billet heating, which is beneficial to improving the composition and tissue uniformity of the continuous casting billet. At the same time, at this temperature, the precipitated phase particles have the fastest solid solution speed, so the high heating temperature will make the original undissolved Al, N, ti compounds in the steel have more dissolution, make the Al, N, ti concentration in the matrix increase, precipitate more dispersed particles at the later cooling, in addition, only after the heating furnace temperature is lifted upwards, the finishing temperature can be raised, the austenite recovery recrystallization after rolling is more sufficient, the precipitated phase particles are distributed more uniformly.
As the preferable technical scheme, the steel blank obtained after the soaking section can be discharged from the furnace to enter the rolling process when the temperature difference between the negative surface and the positive surface of the steel blank is not more than 30 ℃.
As a preferable technical scheme, the surface of the continuous casting blank is cleaned before the continuous casting blank is heated; and (3) removing phosphorus and oxide skin of the steel blank obtained after the heating process by high-pressure water, and then entering a rolling process.
Further, in the rolling process, the initial rolling temperature is 1100-1200 ℃, and the final rolling temperature is not lower than 900 ℃.
Under the process, N is favorable to be desolventized from gamma solid solution and combined with Ti and Al in steel into one or more precipitated phase particles of (Ti, al) carbide, nitride and carbonitride. If the finishing temperature is low, the peak precipitation of the precipitated phase particles may cause uneven distribution of the precipitated phase particles and insufficient recovery recrystallization to cause structural anisotropy, so the finishing temperature is not lower than 900 ℃. In addition, the finishing temperature is increased, finer grains can be obtained, the grain size increases the difference between the average grain diameter d of ferrite after supercooling austenite transformation and the spacing s of the Mn-rich strip, and the trend of forming pearlite by the Mn-rich strip is lightened, so that the tissue segregation is lightened.
The steel can be used for preparing new energy automobile steering knuckles.
Further, the tensile strength Rm of the steering knuckle is more than or equal to 870MPa, the yield strength Rp0.2 is more than or equal to 730MPa, and the elongation A is more than or equal to 14%;
the metallographic structure of the steering knuckle is tempered sorbite, and the austenite grain size is 7.5-8.0 grade.
Compared with the prior art, the invention has the following characteristics:
1) The steel and the knuckle prepared based on the steel have the advantages of low cost and good comprehensive mechanical properties, can meet the technical requirements of the knuckle on braking force durability, lateral force durability, steering force impact, durability and the like, and also have the advantages of wide sources of component elements, stable and reliable process control and the like;
2) According to the invention, by adjusting the absolute weight percentage and the relative weight percentage of Al, ti and N in the steel, one or more precipitated phase particles of carbide, nitride and carbonitride of (Al and Ti) are formed, so that the positive effects of pinning grain boundaries and refining grains are achieved, and the tensile strength, yield strength and extensibility of the finished steel are obviously improved;
3) The invention adopts a hot working rolling method to prepare finished steel, and improves the temperature of a soaking section in a heating process to promote the component distribution and the tissue uniformity of the steel, and improves the final rolling temperature in the rolling process, so that austenite recovery and recrystallization after rolling are more sufficient, and precipitated phase particles are more uniformly distributed;
4) The invention prolongs the calm time by reducing the ladle temperature (20 ℃ lower than the conventional ladle temperature), promotes the floating of the inclusions, improves the removal rate of the impurities in the steel, and further improves the strength and toughness of the finished steel.
Drawings
Fig. 1, 2, 3 and 4 are schematic diagrams of metallographic structures with different magnifications in example 3.
Detailed Description
The invention will now be described in detail with reference to the drawings and specific examples. The present embodiment is implemented on the premise of the technical scheme of the present invention, and a detailed implementation manner and a specific operation process are given, but the protection scope of the present invention is not limited to the following examples.
A preparation method of steel material comprises the following steps:
1) Preparing furnace burden according to the components and weight percentage of the designed steel, and sequentially performing primary smelting, ladle refining, vacuum degassing and continuous casting pouring on the furnace burden in a 150t electric arc furnace to obtain a continuous casting blank;
2) And (3) adopting a rolling mill hot working rolling method, and sequentially carrying out surface cleaning, heating, high-pressure water phosphorus removal and scale removal on the continuous casting billet in the step (1) to obtain the finished steel product.
Wherein, in step 1), during primary smelting of the electric arc furnace, P is removed from the slag stream in the oxidation period, and slag discharging conditions comprise: the slag tapping temperature is 1630-1660 ℃, and the weight percentage of P is not more than 0.013 percent; the tapping conditions include: the tapping temperature is 1630-1650 ℃, the weight percentage of P is not more than 0.010 percent, and the weight percentage of C is not less than 0.03 percent;
in the ladle refining process, adding aluminum alloy to enable the weight percentage of Al in molten steel to reach 0.038-0.042%, adding other metal alloy, stirring for 5-10min, and adjusting chemical components to be controlled internally;
when the temperature of molten steel in the ladle refining process reaches 1650-1670 ℃, entering a vacuum degassing process;
in the vacuum degassing process, the vacuum degree is 66.7Pa, and the vacuum degassing time is not less than 15min;
after the vacuum degassing process, adding titanium alloy into molten steel until the weight percentage of Ti reaches 0.003-0.020%, so as to ensure the yield, and then enabling the molten steel to enter a continuous casting process through a hanging ladle when the temperature of the molten steel reaches 1550-1570 ℃ and the weight percentage of each component meets the corresponding requirement;
in the continuous casting pouring process, high-temperature molten steel is poured into a tundish through a protective sleeve, and then a continuous casting blank is poured out through a continuous casting crystallizer by combining electromagnetic stirring and soft reduction technology,
the inner surface of the tundish is a refractory coating, the inner surface is completely cleaned and checked before use, cracks cannot be formed on the inner surface, and the superheat degree of the tundish is 20-40 ℃;
the casting speed of the continuous casting blank is 0.6-2.1m/min, the preferable section size of the continuous casting blank is 140mm multiplied by 320mm multiplied by 425mm, and the casting speed of the continuous casting blank is adjusted according to the section size;
and (3) placing the obtained continuous casting blank in a slow cooling pit, and then executing the step (2) after the slow cooling process, wherein the slow cooling time of the slow cooling process is not less than 24 hours.
Wherein, the furnace burden comprises low P, S scrap steel, cut ends, high-quality pig iron, metal alloy and reducing agent, and the metal alloy comprises ferrochrome, low-phosphorus ferromanganese and other metal element-containing materials ferrosilicon and titanium alloy which are commonly used in steel making technology and can meet the metal element types of steel materials; the reducing agent comprises calcium carbide, carbon powder and aluminum powder, and the arc furnace is preferably a 30-150 ton arc furnace;
furthermore, the ladle refining process is performed in a ladle refining furnace adapted to the capacity of an electric arc furnace, comprising: refining molten steel, seating a ladle, measuring temperature and analyzing, adjusting argon pressure according to conditions, and removing harmful gases and inclusions in the molten steel through the ladle refining process.
In step 2), the heating process is carried out in a continuous furnace, comprising in order: the preheating section, the first heating section, the second heating section and the soaking section;
wherein the temperature of the preheating section is not higher than 700 ℃;
the heating temperature of the first heating section is 700-980 ℃;
the heating temperature of the second heating section is 950-1200 ℃;
the heating temperature of the soaking section is 1100-1200 ℃;
the total heating time of the continuous casting blank in a continuous furnace is not less than 195min, and when the temperature difference of the negative surface and the positive surface of the steel blank obtained after the heat equalizing section is not more than 30 ℃, discharging the steel blank from the furnace and entering a rolling process;
in the rolling process, the initial rolling temperature is 1100-1200 ℃ and the final rolling temperature is not lower than 900 ℃.
Example 1:
in this example, 5 kinds of round bars with a diameter of 80mm were prepared by the above steps in combination with corresponding technical parameters, wherein the technical parameters for preparing 5 kinds of round bars are shown in table 1.
Table 1 technical parameters for preparing 5 kinds of round bars
Example 2:
in this example, the 5 round bars in example 1 were sequentially heated, pre-forged, finish-forged, trimmed, quenched, and tempered to prepare knuckle parts, and the chemical composition and mechanical properties of the knuckle parts were tested after the tie rod was sampled and compared with those of the knuckle parts in the prior art (1:CN104087819B; 2:CN109097644A), and the results are shown in tables 2 and 3, respectively.
TABLE 2 comparison of chemical composition of the steering knuckle parts in this example with the steering knuckle parts of the prior art (wt%)
TABLE 3 mechanical property comparison of the knuckle parts in this example with the knuckle parts of the prior art
Example 3:
in this example, metallographic experiments were performed on the knuckle parts prepared in example 2, and the results are shown in fig. 1, 2, 3 and 4, and it can be seen from the figures that the metallographic structure after heat treatment is tempered sorbite (shown in fig. 1); a large number of precipitated phase particles such as AlN, tiN and the like are uniformly distributed in the matrix (shown in figure 2), and austenite grain boundaries are effectively pinned, so that knuckle grains are fine and uniform, the grain size is 7.5-8 grades (shown in figure 3), the performance is stable, and the grades of sulfide coarse systems and fine systems are not higher than 2.5 grades (shown in figure 4) with reference to GB/T10561-2005.
The previous description of the embodiments is provided to facilitate a person of ordinary skill in the art in order to make and use the present invention. It will be apparent to those skilled in the art that various modifications can be readily made to these embodiments and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above-described embodiments, and those skilled in the art, based on the present disclosure, should make improvements and modifications without departing from the scope of the present invention.

Claims (8)

1. The steel for the high-strength knuckle of the new energy automobile is characterized by comprising the following components in percentage by weight:
c:0.40-0.44%, si:0.31-0.37%, mn:0.50-0.59%, P: less than or equal to 0.015 percent, S:0.031-0.037%, cr:0.90-0.99%, ni: less than or equal to 0.25 percent, cu: less than or equal to 0.15 percent, mo: less than or equal to 0.10 percent, al:0.017-0.033%, ti:0.003-0.020%, N:0.008-0.014%, and the balance of Fe and unavoidable impurities;
wherein the weight percentage of Al, the weight percentage of N and the weight percentage of Ti satisfy the relation: al is more than or equal to 27N%/14-9Ti%/16;
the tensile strength Rm of the steering knuckle prepared by the steel is more than or equal to 870MPa, the yield strength Rp0.2 is more than or equal to 730MPa, and the elongation A is more than or equal to 14%; the metallographic structure of the steering knuckle is tempered sorbite, and the austenite grain size is 7.5-8.0 grade.
2. The steel for high-strength knuckle of new energy automobile according to claim 1, wherein the grade of sulfide nonmetallic inclusion in the steel is not more than 2.5.
3. The method for producing a steel material for a high-strength knuckle for a new energy automobile according to any one of claims 1 to 2, characterized by comprising the steps of:
1) Preparing furnace burden according to the components and weight percentage of the steel, and sequentially performing primary smelting in an electric arc furnace, ladle refining, vacuum degassing and continuous casting pouring on the furnace burden to obtain a continuous casting blank;
2) And (3) sequentially heating and rolling the continuous casting billet in the step (1) to obtain the finished steel product.
4. The method for producing a steel for a high-strength knuckle for a new energy automobile according to claim 3, wherein in the step 1), slag tapping conditions during primary refining in an electric arc furnace include: the slag tapping temperature is 1630-1660 ℃, and the weight percentage of P is not more than 0.013 percent; the tapping conditions include: the tapping temperature is 1630-1650 ℃, the weight percentage of P is not more than 0.010 percent, and the weight percentage of C is not less than 0.03 percent;
adding aluminum in the ladle refining process to enable the weight percentage of Al in the molten steel to reach 0.038-0.042%, and entering a vacuum degassing process when the temperature of the molten steel in the ladle refining process reaches 1650-1670 ℃;
in the vacuum degassing process, the vacuum degassing time is not less than 15min;
after the vacuum degassing process, adding titanium alloy into molten steel until the weight percentage of Ti in the molten steel reaches 0.003-0.020%, and when the temperature of the molten steel reaches 1550-1570 ℃, enabling the molten steel to enter a continuous casting process through a hanging ladle.
5. The method for producing a steel for a high-strength knuckle for a new energy automobile according to claim 3, wherein in step 1), the degree of superheat of a tundish used in the continuous casting process is 20-40 ℃ and the casting speed is 0.6-2.1m/min;
and (3) performing step 2) after the obtained continuous casting blank is subjected to a slow cooling process, wherein the slow cooling time of the slow cooling process is not less than 24 hours.
6. The method for producing a steel material for a high-strength knuckle for a new energy automobile according to claim 3, wherein in step 2), the heating process is performed in a continuous furnace, comprising, in order: the preheating section, the first heating section, the second heating section and the soaking section;
the temperature of the preheating section is not higher than 700 ℃;
the heating temperature of the first heating section is 700-980 ℃;
the heating temperature of the second heating section is 950-1200 ℃;
the heating temperature of the soaking section is 1100-1200 ℃;
the total heating time of the continuous casting billet in the continuous furnace is not less than 195min.
7. The method for producing a steel for a high-strength knuckle for a new energy automobile according to claim 3, wherein the initial rolling temperature is 1100-1200 ℃ and the final rolling temperature is not lower than 900 ℃.
8. Use of the steel material for high-strength knuckle of new energy automobile according to claim 1 or 2, characterized in that the steel material is used for preparing new energy automobile knuckle.
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CN107012393A (en) * 2017-06-01 2017-08-04 山东寿光巨能特钢有限公司 The production method of carbon chromium steel in a kind of inexpensive high-hardenability
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CN110129656A (en) * 2019-05-22 2019-08-16 湖南华菱湘潭钢铁有限公司 The production method of steel is saved in a kind of motor turning
CN110484837A (en) * 2019-08-16 2019-11-22 江阴兴澄特种钢铁有限公司 A kind of ball-screw steel and its manufacturing method

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CN107012393A (en) * 2017-06-01 2017-08-04 山东寿光巨能特钢有限公司 The production method of carbon chromium steel in a kind of inexpensive high-hardenability
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