CN114574770B - Preparation method of high-strength fatigue-resistant 60Si2MnA spring steel - Google Patents
Preparation method of high-strength fatigue-resistant 60Si2MnA spring steel Download PDFInfo
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Abstract
The invention discloses a preparation method of high-strength fatigue-resistant 60Si2MnA spring steel, which requires accurate control of each element, reduces steel billet segregation and banded shape of rolled material, mainly eliminates subsurface pinholes of continuous casting billets in surface quality, and solves the problem of Al production in pure steel production 2 O 3 The generation of the inclusion is realized by adopting a method without adding aluminum in the component design. The process route comprises molten iron desulfurization treatment, top-bottom combined blown converter smelting, tapping slag washing, LF refining, RH vacuum treatment, square billet continuous casting and hot continuous rolling; the composition is C:0.58 to 0.61wt%, si:1.65 to 1.75wt%, mn:0.68 to 0.78wt%, P: less than or equal to 0.012wt%, S: less than or equal to 0.0030wt%, 0.12 to 0.15wt% of Cr, cu: 0.10-0.15 wt%, ni:0.10 to 0.15wt%, N: less than or equal to 0.0040wt%; after RH treatment, hydrogen in the molten steel is determined, and the hydrogen content in the molten steel is less than 1.0 PPm; the preparation method of the material comprises the following steps: molten iron desulphurization pretreatment → top and bottom combined blown converter blowing → LF refining → RH vacuum treatment → billet continuous casting → billet feeding into furnace and soaking again → rolling and cooling → shearing, finished product inspection and performance detection.
Description
Technical Field
The invention relates to a preparation method of high-strength fatigue-resistant 60Si2MnA spring steel, belonging to the field of steel material manufacturing.
Background
The 60Si2MnA spring steel is classified into a plate spring, a round spring, and a spring steel for drawing according to the purpose. The main factors affecting its fatigue life and drawing performance are steel purity, material hardness after heat treatment, strength and surface and internal quality. Brittle inclusions in steelBecomes the main cause of fatigue fracture of the spring in the service life. The control method for inclusions in high-silicon spring steel at home and abroad mainly comprises the following three methods. The first scheme is that an LF refining scheme without adding aluminum, controlling the content of aluminum and controlling the medium alkalinity is adopted; the second scheme adopts a process scheme of low aluminum and low alkalinity, adopts a deoxidation mode of Si and Mn, has the Al content in steel not more than 0.005 percent, the slag alkalinity of 1.0 to 1.5 and Al content in steel 2 O 3 The content is below 5%, the scheme is difficult to desulfurize, acid slag seriously wets the ladle slag line position due to the position of the ladle slag line being a magnesia carbon brick, high-melting-point MgO is more contained in impurities in steel, low-alkalinity desulfuration is difficult, and LF refining electrifying treatment time is long, so that nitrogen increase of molten steel is serious; the steel tapping of the third scheme adopts ferrosilicon deoxidation and does not add aluminum deoxidation, the Al content in the steel is 0.005-0.015 percent, the binary basicity of the slag is 2.0-4.0, and the steel produced by the method has more inclusions and is easy to generate large-particle inclusions of B-type oxides. The low-alkalinity slag is easy to corrode refractory materials; the slag system refining process has high desulfurization difficulty, poor submerged arc effect and low molten steel temperature rise speed; this scheme is unstable in oxide inclusion control.
One of the main factors causing the low fatigue life of the spring steel is that the subcutaneous bubbles on the surface of the continuously cast steel billet are rolled into superficial microcracks of the material, which become corrosion sources or cracking sources in the use process of the material.
Because 60Si2MnA is high-silicon spring steel, the silicon content in the steel reaches 1.7 percent, a large amount of ferrosilicon is needed to be used for increasing silicon in the molten steel, the aluminum content in low-aluminum ferrosilicon is usually 0.8 percent, the ferrosilicon is added in the converter tapping process or the LF refining treatment process, the aluminum in the ferrosilicon is oxidized to generate Al 2 O 3 B-type composite inclusions serving as a matrix exist in the molten steel, in addition, a calcium-containing wire is adopted to carry out calcium treatment at the final stage of LF refining to carry out modification treatment on non-metallic inclusions, and the molten steel is turned over and exposed in a steel ladle due to violent reaction in the wire feeding process, so that the molten steel is oxidized and increases nitrogen due to contact with air. Therefore, the above three proposals have difficulty solving the B group in the steelClass D and DS brittle inclusions.
And (3) document retrieval:
(1) Patent application No. 2021110210453 discloses a "controlling method for oxide inclusions of high-silicon series spring steel". High alumina high alkalinity slag is manufactured through an LF ladle furnace external refining process, and the binary alkalinity of the slag is 5.0-7.0; argon is adopted for weak stirring, the stirring flow is controlled to be 100-600 NL/min, and the Al content of the aluminum deoxidation refining ladle is controlled to be 0.025-0.040%; and performing soft blowing for the time after VD vacuum treatment and vacuum treatment. The oxygen content in the steel is less than or equal to 7.0 ppm, and the average oxygen content is 6.0 ppm; the grade of the B-type coarse inclusion and the grade of the B-type fine inclusion are both less than or equal to 0.5 grade; the grade of D coarse and fine inclusions is less than or equal to 0.5 grade.
(2) Patent application No. 202010448939X discloses a high stress spring steel and a preparation process thereof, and the production process flow adopted comprises molten iron desulphurization pretreatment, converter smelting, LF refining and slab continuous casting. The components are as follows: : 0.47 to 0.52 percent of C, 0.1 to 0.32 percent of Si, 1.2 to 1.5 percent of Mn, 0.9 to 1.1 percent of Cr, 0.15 to 0.25 percent of Mo, 0.03 to 0.05 percent of V, 0.02 to 0.05 percent of Nb, 0.25 to 0.35 percent of Ni, 0.15 to 0.25 percent of Cu, less than or equal to 0.02 percent of P, less than or equal to 0.015 percent of S, and the balance of Fe and inevitable impurities. The spring steel produced by the method does not show aluminum deoxidation, but the sulfur and phosphorus content in the steel is high, the LF refining reducing slag is not fully desulfurized, and the effect of removing impurities by desulfurization is not obvious.
(3) Patent application No. 2021113695136 discloses a production process of a vehicle damping spring steel 65Mn wire rod, and the invention discloses a production process of a vehicle damping spring steel 65Mn wire rod, wherein the damping spring steel 65Mn wire rod comprises the following chemical components in percentage by weight: 0.62-0.68% of C, si: 0.17% -0.30%, mn: 0.90% -1.00%, P: less than or equal to 0.015 percent, S: less than or equal to 0.015 percent, and the balance of Fe and inevitable impurities. The production process comprises molten iron desulphurization, converter smelting, argon blowing, LF refining, continuous casting, square billet heating, high-speed wire unit rolling and stelmor controlled cooling. The invention uses a high-speed wire-drawing machine set to roll the billet into a wire rod at high temperature, and adopts a finishing mill and a reducing sizing mill set of 8+4 machine type. By optimizing the heating system before rolling, controlling rolling and controlling the cooling process, the surface decarburization of the wire rod is reduced, the fatigue life of the finished spring is prolonged, the metallographic structure is improved, the high sorbite is obtained, the strength and the plasticity of the vehicle damping spring steel wire rod are improved, and the purpose of optimizing the metallographic structure and the comprehensive performance of the vehicle damping spring steel 65Mn hot rolled wire rod is achieved. However, the sulfur content in steel is 0.015 percent, the sulfur content is high, the purity of steel is low, and the fatigue life of the material is seriously influenced.
(4) The statistical study on the appearance and size of inclusions in the whole process of the steelmaking process was published in the modern metallurgy, no. 2 of 2010, 60Si2CrVA spring steel converter smelting process, and the analysis shows that the main type of the inclusions is Al 2 O 3 And 4-type inclusions such as MnS, tiN, and complex oxides.
(5) The special steel 2008 2 published the inclusion research of the ultra-low oxygen spring steel 60Si2Mn, the LD, LF (VD) and CC are adopted TO produce the high-quality spring steel 60Si2Mn for automobiles, the Al is adopted TO deoxidize, the high-alkalinity low-oxidizability refining slag is rapidly produced during tapping, the refining time of slag steel is prolonged as much as possible, the argon blowing stirring is enhanced, and the TO content of the final casting blank is 10 multiplied by 10 -6 ，[S]The content is 0.005%, [ P ]]0.010% gave a cast slab of higher purity.
(6) The theory and practice of oxide inclusion composition and form control of spring steel are published in No. 1 of 2002 in special steel, and the oxide inclusion composition and form control are researched by taking 60Si2MnA as spring steel as an example, low-aluminum ferrosilicon is adopted for alloying, and the content of acid-soluble aluminum in the steel is controlled to be 0.0012-0.0014%. And the spring steel was subjected to a rotary bending fatigue test. But does not show the type, size and grade of inclusions.
Disclosure of Invention
The invention discloses a preparation method of high-strength fatigue-resistant 60Si2MnA spring steel. According to the factors influencing the fatigue strength of the material, firstly, the components require the control of each element to be accurate, the segregation of the steel billet and the banding of the rolled material are reduced, the surface quality is mainly the elimination of the subsurface pinholes of the continuous casting billet, and the production of pure steel fundamentally solves the problem of Al 2 O 3 The generation of inclusion is realized without adding in the design of componentsAluminum is used.
The high-purity spring steel prepared by the method is realized by the following method.
A preparation method of high-strength fatigue-resistant 60Si2MnA spring steel comprises the following process routes of molten iron desulphurization treatment, top-bottom combined blown converter smelting, tapping slag washing, LF refining, RH vacuum treatment, billet continuous casting and hot continuous rolling;
1) The component composition is C:0.58 to 0.61wt%, si:1.65 to 1.75wt%, mn:0.68 to 0.78wt%, P: less than or equal to 0.012wt%, S: not more than 0.0030wt%, cr 0.12-0.15 wt%, cu: 0.10-0.15 wt%, ni:0.10 to 0.15wt%, N: less than or equal to 0.0040wt%, the balance of iron and inevitable impurities, and hydrogen is determined in the molten steel after RH treatment is finished, wherein the hydrogen content in the molten steel is less than 1.0 PPm;
2) The preparation method of the material comprises the following steps: molten iron desulphurization pretreatment → top and bottom combined blown converter blowing → LF refining → RH vacuum treatment → billet continuous casting → billet feeding into furnace and soaking again → rolling and cooling → shearing, finished product inspection and performance detection;
A. the molten iron conditions comprise that the temperature of the molten iron is higher than 1300 ℃, the sulfur content is not more than 0.05 wt percent, and the phosphorus content is not more than 0.12 wt percent;
adopting KR method to make molten iron desulfurization pretreatment, the treated molten iron [ S]The content is less than 0.003 wt%, in order to completely remove the high-sulfur top slag of the iron ladle, the top slag conglomeration agent is added into the iron ladle after the pretreatment is finished to make the top slag become sticky, and the molten iron is pretreated by the conglomeration agent component: al (aluminum) 2 O 3 20 wt% of SiO 2 35wt% of CaO, 42 wt% of MgO, and 1.5-5 mm of slag conglomeration agent;
B. converter smelting, namely, converter smelting is adopted, 20 percent of scrap steel is added into the converter before oxygen blowing smelting, then 80 percent of desulfurized molten iron is added, and the oxygen flow is controlled to be 450Nm 3 Min, intensity 0.50Nm 3 At t.min, rapidly dephosphorizing at low temperature; the converter bottom is blown with argon for stirring, and the air supply intensity is 0.8Nm 3 T.min, the tapping temperature of the converter is 1630-1650 ℃, and the tapping of the converter is [ C]The content is 0.06-0.10 wt%, [ P ]]The content is less than 0.008 wt%; [ S ]]Not more than 0.008wt%, tapping in converter [ N%]The content is less than 0.0020 percent;
C. preparing a steel ladle, namely after removing reducing slag from the steel ladle which is offline in continuous casting, checking and replacing a steel tapping sliding plate, filling drainage sand after the steel tapping sliding plate is qualified, then adding ferrosilicon, and then hoisting and pouring the ferrosilicon into the high-alkalinity reducing slag remained in the continuous casting;
the casting residual slag and the drainage sand are separated by a layer of massive ferrosilicon, so that the drainage sand is prevented from contacting with the slag, continuous casting is prevented from being started and does not flow automatically due to sintering and caking of the drainage sand, and secondly, moisture is eliminated due to the fact that a large amount of added ferrosilicon is baked through high-temperature slag, so that the generation of bubbles under the casting blank is avoided, linear fine cracks on the surface of a rolled material are eliminated, and the method is the most direct method for prolonging the fatigue resistance life.
D. Deoxidation alloying and impurity removal are carried out during converter tapping, 1.5kg of calcium aluminate/ton of steel synthetic slag washing material is added along with steel flow after 1min from converter tapping, 3kg of a mixture of calcium carbide, active lime and fluorite is added into each ton of steel for pre-deoxidation and slagging, wherein the mass ratio of the calcium carbide to the active lime to the fluorite is 5; according to the requirement of manganese content of components of a smelted finished product, adding silicon-manganese alloy in a sufficient amount, firstly, adding manganese to ensure that the manganese content of molten steel is in the middle-lower limit of a control range, wherein the silicon content of the molten steel is less than a target value, supplementing silicon by ferrosilicon pre-loaded in a steel ladle, adding carbon powder in the tapping process of a converter to carburete the molten steel, adding the alloy before the tapping of the converter is finished, adding a carburant in 70% of the total amount in the later tapping stage of the converter, adding the rest 30% of the alloy into the steel ladle after the tapping of the converter, and blowing argon at the bottom of the steel ladle in the process of adding the carbon powder to stir strongly;
E. LF refining is carried out, the initial refining temperature of the molten steel is more than or equal to 1550 ℃, 120kg of molten steel accelerant CaO content is added in the initial stage of the LF refining, the CaO content is 30wt%, and Al content is higher than 2 O 3 35wt% of SiO 2 Not more than 5wt%, mgO content of 5-8 wt%, caCO 3 Content 10 wt%, caF 2 Less than or equal to 5wt%, silicon carbide content is 5wt%, when the temperature of the molten steel reaches more than 1610 ℃, argon is blown from the bottom of the steel ladle to strongly stir and desulfurize, the stirring time is controlled to be 5-8 min according to the initial sulfur content of refining, the sulfur content of the molten steel is not more than 0.002 wt%, the temperature is raised by electrifying and supplementing, the temperature of the molten steel is controlled to be 1595 +/-1 ℃, and the molten steel can be transported to the RH process to carry out vacuum degassing treatment;
F. RH processing, wherein the duration time of RH vacuum degree less than 120Pa is more than 5 minutes, carbon-oxygen reaction is carried out in an RH vacuum state, inclusions are further deoxidized and removed, dehydrogenation and nitrogen removal are carried out in the RH vacuum state, the RH vacuum processing time is 20-22min, the temperature of molten steel after RH processing is finished is 1558 +/-2 ℃, the hydrogen content in the molten steel is detected by a hydrogen determination instrument, the hydrogen content is not more than 0.0001%, the oxygen content is less than 0.0005%, the RH processing is finished, the bottom blowing argon weak stirring time on the premise that the molten steel cannot be blown open is more than 5 minutes, then the molten steel is lifted to a continuous casting platform to stand for more than 3 minutes;
G. the precise control of the components of the smelted finished product provides guarantee for the calculation of the liquidus temperature, and the liquidus temperature of the molten steel is calculated
1468 ℃, and controlling the temperature of the molten steel of the continuous casting tundish to 1480-1498 ℃; the serious segregation and central porosity of the carbon and manganese in the steel billet are the main factors causing the fatigue resistance of the spring steel to be reduced. A method for controlling the center segregation of elements of a casting blank is characterized in that a 150mm multiplied by 150mm square 10-strand continuous casting machine is used for production, the casting speed of a continuously cast steel blank is set to be 1.45 +/-0.5 m/min, sliding plates are opened from two end flows in sequence during continuous casting start, and finally a middle flow is opened, so that the uniformity of a tundish molten steel temperature field can be ensured, the continuous casting process is kept unchanged after the casting speed of the continuously cast steel blank is set, the gas fog forced cooling is performed after the continuous casting blank is straightened, the isometric crystal of the casting blank is more than 55%, and the center segregation of the steel blank is less than 0.5 level;
H. the method comprises the steps of hot charging and rolling a steel billet, wherein two types of spring steel are rolled, rolled materials comprise spring flat steel and spring round steel, the soaking temperature of the steel billet is 1220 +/-15 ℃, the initial rolling temperature is 1110-1160 ℃, the final rolling temperature is higher than 865 +/-10 ℃, the material is subjected to offline slow cooling, and the decarburized layer thickness of the spring flat steel and the spring round steel material is controlled. The invention adopts the opposite method, adopts the method of increasing the heating temperature of the billet and reducing the residence time of the billet in the heating furnace, properly increases the thickness of the iron scale on the surface of the billet, and the iron scale falls off in the rolling process, thereby reducing the thickness of the decarburized layer, eliminating the microcracks on the surface of the material, rolling the material into spring round steel or plate spring, performing weak cooling after rolling, and performing heat preservation and slow cooling after rolling.
And (3) detecting the performance of the steel:
rolled spring flat steel with the thickness of 16mm and the width of 90mm, the tensile strength of 1680-1705 MPa, the yield strength of 1542-1566 MPa, the elongation after fracture of 11-16 percent and the surface shrinkage of 41-47 percent; the rolled thickness phi is 14-18 mm, the tensile strength is 1655-1693 MPa, the yield strength is 1547-1572 MPa, the elongation after fracture is 11-17%, and the surface shrinkage is 44-49.5%. The hot rolled steel has excellent elongation after fracture and surface shrinkage.
And (5) analyzing the steel structure and the purity. The steel material has pearlite, sorbite and a small amount of ferrite, the grain size is 8.0-8.5 grade, the hydrogen content in the steel is reduced, the sensitivity of hydrogen embrittlement is reduced, and the atmospheric corrosion resistance of the material is improved due to the trace amount of chromium, nickel and copper in the steel. Secondly, the material is forbidden to contain aluminum in the production process, and Al is not found in the spot inspection of steel 2 O 3 Carrying out inclusion; the sulfur content in the steel reaches an extremely low level after the molten steel is subjected to LF deep desulfurization and RH treatment, and sulfide inclusions and silicate inclusions are almost not existed after the operations of LF and RH double refining, bottom blowing argon soft blowing, standing and the like. The content of nitrogen in the steel is 0.0030-0.0038%, the content of sulfur in the steel is less than or equal to 0.003%, and the content of total oxygen in the steel is less than 5PPm. The surface hardness of the material is less than 310HB.
The 60Si2MnA spring steel square billet produced by the method is rolled into 2 types of products, and is rolled into spring round steel and flat steel, the spring round steel is applied to high-speed rail fasteners, the spring flat steel is applied to heavy-duty automobile plate springs, and various performances after heat treatment meet the use requirements of users.
1. The components of the smelted finished product and the slab quality are 10 furnaces produced by the method, and the product components and the slab detection results are shown in table 1. And (4) performing diagonal sampling analysis on the blank, wherein the maximum carbon segregation sampling inspection is 1.03, and the center segregation of the square blank is not more than 0.5 grade.
2. Mechanical property of rolled steel
3. The structure and the purity of the steel are obtained by selective inspection of the steel after 10-furnace steel rolling, the structure is pearlite, sorbite and a small amount of ferrite, and the grain size is between 8 grades and 8.5 grades. And (4) performing spot inspection on various inclusions, wherein DS inclusions are less than 0.5 grade, and the steel meets the requirement of pure steel. The corrosion resistance of the plate spring is increased because the material contains trace chromium, nickel and copper.
4. The preparation method of the high-strength fatigue-resistant 60Si2MnA spring steel can be popularized in enterprises with molten iron pretreatment, converter, LF refining and RH vacuum refining equipment and equipment for rolling bars and sections.
Detailed Description
A preparation method of high-strength fatigue-resistant 60Si2MnA spring steel comprises the following process routes of molten iron desulphurization treatment, top-bottom combined blown converter smelting, tapping slag washing, LF refining, RH vacuum treatment, billet continuous casting and hot continuous rolling;
1) The component composition is C:0.58 to 0.61wt%, si: 1.65-1.75 wt%, mn: 0.68-0.78 wt%, P: less than or equal to 0.012wt%, S: less than or equal to 0.0030wt%, 0.12 to 0.15wt% of Cr, cu: 0.10-0.15 wt%, ni:0.10 to 0.15wt%, N: less than or equal to 0.0040wt%, the balance of iron and inevitable impurities, and hydrogen is determined in the molten steel after RH treatment is finished, wherein the hydrogen content in the molten steel is less than 1.0 PPm;
2) The preparation method of the material comprises the following steps: molten iron desulphurization pretreatment → top and bottom combined blown converter blowing → LF refining → RH vacuum treatment → billet continuous casting → billet feeding into furnace and soaking again → rolling and cooling → shearing, finished product inspection and performance detection;
A. the molten iron conditions are that the temperature of the molten iron is higher than 1300 ℃, the sulfur content is not more than 0.05 wt percent, and the phosphorus content is not more than 0.12 wt percent;
adopting KR method to make molten iron desulfurization pretreatment, the treated molten iron [ S]The content is less than 0.003 wt%, in order to completely remove the top slag with high sulfur content in the iron ladle, the top slag conglomeration agent is added into the iron ladle after the pretreatment is finished to make the top slag become sticky, and the molten iron is pretreated by the slag conglomeration agent component: al (Al) 2 O 3 20 wt% of SiO 2 35wt% of CaO, 42 wt% of MgO, and 1.5-5 mm of slag conglomeration agent;
B. converter smelting is adopted, 20 percent of scrap steel is added into the converter before oxygen blowing smelting, and then the molten iron 8 for desulfurization is added0% and the oxygen flow rate is controlled at 450Nm 3 Min, intensity 0.50Nm 3 T min, fast dephosphorization at low temperature; stirring by blowing argon from the bottom of the converter, with the gas supply intensity of 0.8Nm 3 T.min, the tapping temperature of the converter is 1630-1650 ℃, and the tapping of the converter is [ C]The content is 0.06-0.10 wt%, [ P ]]The content is less than 0.008 wt%; [ S ]]Not more than 0.008wt%, tapping in converter [ N%]The content is less than 0.0020 percent;
C. preparing a steel ladle, namely after the steel ladle which is offline in continuous casting is cleared of reducing slag, checking and replacing a steel tapping sliding plate, filling drainage sand after the steel tapping sliding plate is qualified, then adding ferrosilicon, and then hoisting and pouring the ferrosilicon into the high-alkalinity reducing slag remained in the continuous casting;
the casting residual slag and the drainage sand are separated by a layer of massive ferrosilicon, so that the drainage sand is prevented from contacting with the slag, continuous casting is prevented from being started and does not flow automatically due to sintering and caking of the drainage sand, and secondly, moisture is eliminated due to the fact that a large amount of added ferrosilicon is baked through high-temperature slag, so that the generation of bubbles under the casting blank is avoided, linear fine cracks on the surface of a rolled material are eliminated, and the method is the most direct method for prolonging the fatigue resistance life.
D. Deoxidizing and alloying converter tapping and removing impurities, wherein after 1min of converter tapping, synthetic slag washing materials of 1.5kg of calcium aluminate per ton of steel are added along with steel flow, 3kg of a mixture of calcium carbide, active lime and fluorite is added per ton of steel for pre-deoxidizing and slagging, the mass ratio of the calcium carbide to the active lime to the fluorite is 5; according to the requirement of manganese content of components of a smelted finished product, adding silicon-manganese alloy in a sufficient amount, firstly, adding manganese to ensure that the manganese content of molten steel is in the middle-lower limit of a control range, wherein the silicon content of the molten steel is less than a target value, supplementing silicon by ferrosilicon pre-loaded in a steel ladle, adding carbon powder in the tapping process of a converter to carburete the molten steel, adding the alloy before the tapping of the converter is finished, adding a carburant in 70% of the total amount in the later tapping stage of the converter, adding the rest 30% of the alloy into the steel ladle after the tapping of the converter, and blowing argon at the bottom of the steel ladle in the process of adding the carbon powder to stir strongly;
E. LF refining is carried out, the initial refining temperature of the molten steel is more than or equal to 1550 ℃, and 120kg of molten steel accelerant CaO with the content of 30wt% and Al are added in the initial refining stage of the LF refining 2 O 3 35wt% of SiO 2 Not more than 5wt%, mgO content of 5-8 wt%, caCO 3 Content 10 wt%, caF 2 Less than or equal to 5wt percent, the content of silicon carbide is 5wt percent, when the temperature of the molten steel reaches more than 1610 ℃, argon is blown from the bottom of the steel ladle to strongly stir and desulfurize, the stirring time is controlled to be 5-8 min according to the initial sulfur content of refining, the sulfur content of the molten steel is not more than 0.002 wt percent, the temperature is increased by electrifying and supplementing, the temperature of the molten steel is controlled to be 1595 +/-1 ℃, and the molten steel can be transported to the RH process to carry out vacuum degassing treatment;
F. RH processing, wherein the duration time of RH vacuum degree less than 120Pa is more than 5 minutes, carbon-oxygen reaction is carried out in an RH vacuum state, inclusions are further deoxidized and removed, dehydrogenation and nitrogen removal are carried out in the RH vacuum state, the RH vacuum processing time is 20-22min, the temperature of molten steel after RH processing is finished is 1558 +/-2 ℃, the hydrogen content in the molten steel is detected by a hydrogen determination instrument, the hydrogen content is not more than 0.0001%, the oxygen content is less than 0.0005%, the RH processing is finished, the bottom blowing argon weak stirring time on the premise that the molten steel cannot be blown open is more than 5 minutes, then the molten steel is lifted to a continuous casting platform to stand for more than 3 minutes;
G. the precise control of the components of the smelted finished product provides guarantee for the calculation of the liquidus temperature, and the liquidus temperature of the molten steel is calculated
1468 ℃, and controlling the temperature of the molten steel of the continuous casting tundish to 1480-1498 ℃; the serious segregation and central porosity of the carbon and manganese in the steel billet are the main factors causing the fatigue resistance of the spring steel to be reduced. A method for controlling the center segregation of elements of a casting blank is characterized in that a 150mm multiplied by 150mm square 10-strand continuous casting machine is used for production, the casting speed of a continuously cast steel blank is set to be 1.45 +/-0.5 m/min, sliding plates are opened from two ends of the continuously cast steel blank in sequence during casting starting, and finally a middle stream is opened, so that the uniformity of a temperature field of tundish molten steel can be ensured, the continuous casting process is kept unchanged after the casting speed of the continuously cast steel blank is set, the gas fog forced cooling is carried out after the continuous casting blank is straightened, the isometric crystal of the casting blank is more than 55%, and the center segregation of the steel blank is less than 0.5 level;
H. the method comprises the steps of hot charging and rolling a steel billet, rolling two types of spring steel, wherein the rolled materials comprise spring flat steel and spring round steel, the soaking temperature of the steel billet is 1220 +/-15 ℃, the initial rolling temperature is 1110-1160 ℃, the final rolling temperature is higher than 865 +/-10 ℃, the materials are subjected to offline slow cooling, and the decarburized layer thickness of the spring flat steel and the spring round steel is controlled. The invention adopts the opposite method, adopts the method of increasing the heating temperature of the billet and reducing the residence time of the billet in the heating furnace, properly increases the thickness of the iron scale on the surface of the billet, and the iron scale falls off in the rolling process, thereby reducing the thickness of the decarburized layer, eliminating the microcracks on the surface of the material, rolling the material into spring round steel or plate spring, performing weak cooling after rolling, and performing heat preservation and slow cooling after rolling.
Claims (1)
1. A preparation method of high-strength fatigue-resistant 60Si2MnA spring steel comprises the following process routes of molten iron desulphurization treatment, top-bottom combined blown converter smelting, tapping slag washing, LF refining, RH vacuum treatment, billet continuous casting and hot continuous rolling; the method is characterized in that:
1) The component composition is C:0.58 to 0.61wt%, si:1.65 to 1.75wt%, mn: 0.68-0.78 wt%, P: less than or equal to 0.012wt%, S: less than or equal to 0.0030wt%, 0.12 to 0.15wt% of Cr, cu: 0.10-0.15 wt%, ni:0.10 to 0.15wt%, N: less than or equal to 0.0040wt%, and the balance of iron and inevitable impurities, and after RH treatment, molten steel is subjected to hydrogen determination, wherein the hydrogen content of the molten steel is less than 1.0 PPm;
2) The preparation method of the material comprises the following steps: molten iron desulphurization pretreatment → top and bottom combined blown converter blowing → LF refining → RH vacuum treatment → billet continuous casting → billet feeding into furnace and soaking again → rolling and cooling → shearing, finished product inspection and performance detection;
A. the molten iron conditions are that the temperature of the molten iron is higher than 1300 ℃, the sulfur content is not more than 0.05 wt percent, and the phosphorus content is not more than 0.12 wt percent;
molten iron desulphurization pretreatment is carried out by adopting KR method, and the treated molten iron [ S ]]The content is less than 0.003 wt%, in order to completely remove the top slag with high sulfur content in the iron ladle, the top slag conglomeration agent is added into the iron ladle after the pretreatment is finished to make the top slag become sticky, and the molten iron is pretreated by the slag conglomeration agent component: al (aluminum) 2 O 3 20 wt% of SiO 2 35wt% of CaO, 42 wt% of MgO, and 1.5-5 mm of slag conglomeration agent;
B. converter smelting, namely, converter smelting is adopted, 20 percent of scrap steel is added into the converter before oxygen blowing smelting, then 80 percent of desulfurized molten iron is added, and the oxygen flow is controlled to be 450Nm 3 A/min, strength of0.50Nm 3 T min, fast dephosphorization at low temperature; blowing argon at the bottom of the converter for stirring, wherein the gas supply intensity is 0.8Nm 3 T.min, the tapping temperature of the converter is 1630-1650 ℃, and the tapping temperature of the converter is [ C ]]The content is 0.06-0.10 wt%, [ P ]]The content is less than 0.008 wt%; [ S ]]Not more than 0.008wt%, tapping in converter [ N%]The content is less than 0.0020 percent;
C. preparing a steel ladle, namely after removing reducing slag from the steel ladle which is offline in continuous casting, checking and replacing a steel tapping sliding plate, filling drainage sand after the steel tapping sliding plate is qualified, then adding ferrosilicon, and then hoisting and pouring the ferrosilicon into the high-alkalinity reducing slag remained in the continuous casting;
D. deoxidizing and alloying converter tapping and removing impurities, wherein after 1min of converter tapping, synthetic slag washing materials of 1.5kg of calcium aluminate per ton of steel are added along with steel flow, 3kg of a mixture of calcium carbide, active lime and fluorite is added per ton of steel for pre-deoxidizing and slagging, the mass ratio of the calcium carbide to the active lime to the fluorite is 5; according to the requirement of manganese content of components of a smelted finished product, adding silicon-manganese alloy in a sufficient amount, firstly, adding manganese to ensure that the manganese content of molten steel is in the middle-lower limit of a control range, wherein the silicon content of the molten steel is less than a target value, supplementing silicon by ferrosilicon pre-loaded in a steel ladle, adding carbon powder in the tapping process of a converter to carburete the molten steel, adding the alloy before the tapping of the converter is finished, adding a carburant in 70% of the total amount in the later tapping stage of the converter, adding the rest 30% of the alloy into the steel ladle after the tapping of the converter, and blowing argon at the bottom of the steel ladle in the process of adding the carbon powder to stir strongly;
E. LF refining is carried out, the initial refining temperature of the molten steel is more than or equal to 1550 ℃, and 120kg of molten steel accelerant CaO with the content of 30wt% and Al are added in the initial refining stage of the LF refining 2 O 3 35wt% of SiO 2 Not more than 5wt%, mgO content of 5-8 wt%, caCO 3 Content 10 wt%, caF 2 Less than or equal to 5wt percent, the content of silicon carbide is 5wt percent, when the temperature of the molten steel reaches more than 1610 ℃, argon is blown from the bottom of the steel ladle to strongly stir and desulfurize, the stirring time is controlled to be 5-8 min according to the initial sulfur content of refining, the sulfur content of the molten steel is not more than 0.002 wt percent, the temperature is increased by electrifying and supplementing, the temperature of the molten steel is controlled to be 1595 +/-1 ℃, and the molten steel can be transported to the RH process to carry out vacuum degassing treatment;
F. RH processing, wherein the duration time of RH vacuum degree less than 120Pa is more than 5 minutes, carbon-oxygen reaction is carried out in an RH vacuum state, inclusions are further deoxidized and removed, dehydrogenation and nitrogen removal are carried out in the RH vacuum state, the RH vacuum processing time is 20-22min, the temperature of molten steel after RH processing is finished is 1558 +/-2 ℃, the hydrogen content in the molten steel is detected by a hydrogen determination instrument, the hydrogen content is not more than 0.0001%, the oxygen content is less than 0.0005%, the RH processing is finished, the bottom blowing argon weak stirring time on the premise that the molten steel cannot be blown open is more than 5 minutes, then the molten steel is lifted to a continuous casting platform to stand for more than 3 minutes;
G. the precise control of the components of the smelted finished product provides guarantee for the calculation of the liquidus temperature, and the liquidus temperature of the molten steel is calculated
1468 ℃, and controlling the temperature of the molten steel of the continuous casting tundish to 1480-1498 ℃; a method for controlling the center segregation of elements of a casting blank is characterized in that a 150mm multiplied by 150mm square blank 10-strand continuous casting machine is used for production, the casting speed of a continuously cast steel blank is set to be 1.45 +/-0.5 m/min, sliding plates are opened from two end flows in sequence during continuous casting, finally, a middle flow is opened, the continuous casting process is kept unchanged after the casting speed of the continuously cast steel blank is set, air mist is moved for forced cooling after the continuous casting blank is straightened, the isometric crystal of the casting blank is greater than 55%, and the center segregation of the steel blank is less than 0.5 level;
H. and (3) hot charging and rolling the steel billet, wherein two types of spring steel are rolled, the rolling materials comprise spring flat steel and spring round steel, the soaking temperature of the steel billet is 1220 +/-15 ℃, the initial rolling temperature is 1110-1160 ℃, the final rolling temperature is more than 865 +/-10 ℃, and the material is slowly cooled after being discharged.
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