CN111321346B - Ultrahigh-strength spring steel with excellent hydrogen-induced delayed fracture resistance and production method thereof - Google Patents
Ultrahigh-strength spring steel with excellent hydrogen-induced delayed fracture resistance and production method thereof Download PDFInfo
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Abstract
The invention discloses an ultrahigh-strength spring steel with excellent hydrogen-induced delayed fracture resistance and a production method thereof, wherein the tensile strength is more than or equal to 2300MPa, and the ultrahigh-strength spring steel comprises the following chemical components in percentage by weight: 0.75 to 0.85 percent of C, 1.60 to 2.00 percent of Si, 0.40 to 0.60 percent of Mn, 0.80 to 1.00 percent of Cr, 0.20 to 0.30 percent of V, 0.03 to 0.05 percent of Nb, 0.10 to 0.30 percent of Mo, 0.01 to 0.03 percent of Re, 0.015 to 0.040 percent of Al, 0.005 to 0.008 percent of N, less than or equal to 0.015 percent of P, less than or equal to 0.015 percent of S, less than or equal to 0.0015 percent of O, and the balance of Fe and other inevitable impurities; and Al/N is more than or equal to 3.5 percent, 29.1C +5.2Si +1.8Mn +3.5Cr +2.6V +0.8Nb +4.9Mo is more than or equal to 36 percent; the high-strength spring steel is produced by electric furnace smelting, an LF furnace, vacuum degassing, continuous casting, cogging and wire rolling, a large amount of noble metal elements Ni and Cu which are easy to cause brittle cracking of steel and copper are avoided, and the high-strength spring steel with the tensile strength of more than or equal to 2300MPa is produced at low cost under the interaction of C, Si, Mn, Cr, V, Nb, Mo, Re and N by a specific process, and has excellent delayed fracture resistance and fatigue performance.
Description
Technical Field
The invention belongs to the technical field of spring steel, and particularly relates to ultrahigh-strength spring steel with excellent hydrogen-induced delayed fracture resistance and a production method thereof.
Background
The light weight technology is a future development trend of automobiles, springs are one of safety parts of automobiles, and in order to reduce the self weight, the design stress of the springs is required to be improved continuously. The development trend of the spring to high stress, light weight and long service life is irreversible in the future, but the performance of the material for manufacturing the high-stress spring is limited at present, the use stress of the spring is further improved, and the research and development of a new material with high obdurability is urgent.
In recent years, the development of high-strength spring steel has been a hot issue. Chinese patent CN 103725984 a discloses a high-toughness high-strength spring steel, which is characterized in that the chemical components (weight percentage) of the material are: 0.35 to 0.50 percent of C, 1.50 to 2.50 percent of Si, 0.35 to 1.00 percent of Mn, less than or equal to 0.025 percent of P, less than or equal to 0.015 percent of S, 0.50 to 1.20 percent of Cr, 0.15 to 0.50 percent of Ni, 0.10 to 0.30 percent of Cu, 0.04 to 0.10 percent of V, 0.03 to 0.10 percent of Ti, and the balance of Fe and other inevitable impurities. The grain size of the treated material is 8.0 grade or above, when the tensile strength is more than 1920MPa, the reduction of area Z is more than or equal to 40 percent, and the elongation after fracture is more than or equal to 10 percent. When the method is insufficient, the tensile strength is not obviously improved compared with the strength of national standard 55SiCrV and other marks.
Chinese patent CN 103667983A discloses a high-strength spring steel and a preparation method thereof, which is characterized in that the chemical components (weight percentage) of the material are as follows: 1.0 to 1.3 portions of C, 0.6 to 0.9 portion of Si, 0.4 to 0.5 portion of Cu0.0 to 14.5 portions of Ni14.0 to 14.5 portions of Ni, 1.7 to 2.1 portions of Mn, 0.03 to 0.05 portion of Ce0.006 to 0.008 portion of Ti, 0.02 to 0.05 portion of Zn0.004 to 0.005 portion of Sn0.0 to 1.3 portions of Cr, less than or equal to 0.030 portion of P, less than or equal to 0.030 portion of S, and the balance of Fe. The formed alloy material has excellent comprehensive mechanical properties, especially ultrahigh strength, hardness, toughness, plasticity and fatigue resistance, and also has corrosion resistance. However, the method adds a large amount of noble metal element Ni, so the cost is extremely high, and the method is not suitable for mass production and application.
Chinese patent CN 105648332 a discloses a high-performance spring steel, which is characterized in that the chemical composition (weight percentage) of the material is: c: 1.9-2.2 parts of Cu: 5-6 parts of Si: 1-1.2 parts of Cr: 0.8-1.2 parts of Nb: 0.2-0.5 part, V: 0.2-0.3 part of Al: 0.5-0.8 part, and the balance of Fe and impurities which cannot be removed. The high-performance spring steel plate material is subjected to heating, forming, waste heat quenching, medium temperature tempering and final product shape forming. The invention has the beneficial effects that: the elasticity is good, is fit for normally working under the load environment, has higher yield strength to making the spring material to have longer life-span. However, the method adds 5% or more of copper element, which is very easy to cause copper brittle cracking of steel.
The tensile strength of the high-strength spring steel used at home and abroad is basically between 1800 and 2000MPa, the steel grade of 2000 and 2100 grade has been developed and tried on high-grade cars, but the steel grade of higher grade with ultrahigh obdurability has not been developed. And some spring enterprises improve the strength of the existing steel grade by reducing the tempering temperature, so that the plasticity and toughness are deteriorated, and the fatigue life is also reduced. New steel materials with higher strength and toughness for springs are urgently needed to be developed so as to improve the stress and the fatigue strength of the springs and meet the development requirements of the automobile industry.
Disclosure of Invention
The invention aims to provide an ultrahigh-strength spring steel with excellent hydrogen-induced delayed fracture resistance and a production method thereof. The high-strength spring steel is produced by reasonably controlling the content range of each component in the spring steel and combining a proper production process.
The technical scheme adopted by the invention is as follows:
the ultrahigh-strength spring steel with excellent hydrogen-induced delayed fracture resistance has the tensile strength of more than or equal to 2300MPa and comprises the following chemical components in percentage by weight: 0.75 to 0.85 percent of C, 1.60 to 2.00 percent of Si, 0.40 to 0.60 percent of Mn, 0.80 to 1.00 percent of Cr, 0.20 to 0.30 percent of V, 0.03 to 0.05 percent of Nb, 0.10 to 0.30 percent of Mo, 0.01 to 0.03 percent of Re, 0.015 to 0.040 percent of Al, 0.005 to 0.008 percent of N, less than or equal to 0.015 percent of P, less than or equal to 0.015 percent of S, less than or equal to 0.0015 percent of O, and the balance of Fe and other inevitable impurities;
in order to ensure that the austenite grain size of the steel is less than or equal to 10 mu m and the size of the precipitated carbide after quenching and tempering heat treatment is less than or equal to 25 mu m so as to obtain excellent hydrogen-induced delayed fracture resistance and fatigue life, the Al/N is required to be ensured to be more than or equal to 3.5 percent;
in order to ensure that the tensile strength is more than or equal to 2300MPa, the A value is more than or equal to 36 percent: a is 29.1C +5.2Si +1.8Mn +3.5Cr +2.6V +0.8Nb +4.9 Mo.
The invention also provides a production method of the ultrahigh-strength spring steel with the tensile strength of more than or equal to 2300MPa, which comprises the following steps: electric furnace smelting, LF furnace, vacuum degassing, continuous casting, cogging and wire rolling.
Further, in the continuous casting step, a bloom of 250mm × 250mm is continuously cast.
In the cogging step, a large square billet with the thickness of 250mm multiplied by 250mm is heated and rolled into a square billet with the thickness of 150mm multiplied by 150mm, then the square billet is piled and cooled, a small square billet is rolled through the large square billet, the compression ratio of steel is improved, and therefore the internal quality of finished wire rods is improved.
The heating temperature is 1220-1250 ℃, the surface decarburization can be generated in the heating furnace when the heating temperature is higher than 1250 ℃, and the tapping temperature is insufficient when the heating temperature is lower than 1220 ℃, so that the rolling difficulty is caused. In addition, the total heating time is more than or equal to 230min, preferably 235-262 min.
The process for rolling the wire rod comprises the following steps: peeling a 150mm × 150mm square billet → heating → high-speed wire controlled rolling → stelmor cooling by wire → phi 5.5-10 mm wire rod finished product.
The stripping depth is controlled to be more than 1.2mm, the surface defects of the small square billets are fully removed, and the surface quality of finished wire rod products is improved;
controlling the heating temperature to be 1020-1060 ℃, wherein the temperature higher than the temperature range can aggravate the surface decarburization of the blank, the temperature lower than the temperature range cannot be fully austenitized and homogenized, and the preferable temperature is 1037-1041 ℃;
controlling the finishing temperature to be 790-830 ℃, wherein the temperature above the temperature range can cause the structure of the subsequent cooling process to generate network carbide, and the temperature below the temperature range can cause the phase transition temperature of the subsequent cooling process to be too low and cause the bainite abnormal structure, preferably 805-821 ℃;
the spinning temperature is controlled to be 790-830 ℃, and the spinning temperature is preferably 798-816 ℃ for the same reason.
The austenite grain size of the wire rod produced by the method is less than or equal to 10 mu m.
The invention also provides a heat treatment method of the ultrahigh-strength spring steel with excellent hydrogen-induced delayed fracture resistance, which comprises the steps of quenching the spring steel obtained by adopting the components and the production method at 880-930 ℃, carrying out oil cooling, tempering at 420-450 ℃, and carrying out air cooling.
The tensile strength of the spring steel after heat treatment is more than or equal to 2300MPa, the elongation after fracture is more than or equal to 10 percent, the reduction of area is more than or equal to 40 percent, the fatigue strength is more than or equal to 910MPa, and in a hydrogen embrittlement resistance experiment: the hydrogen-resistant delayed fracture life is more than or equal to 1000sec, and the brittle fracture rate is less than or equal to 85 percent.
The ultrahigh-strength spring steel with excellent hydrogen-induced delayed fracture resistance disclosed by the invention has the following elements in components:
c: c is the most effective reinforcing element in steel, and is an important element in spring steel for ensuring fire hardness and wear resistance, and is necessary for obtaining spring steel having high strength and hardness. But too high carbon content deteriorates fatigue resistance and workability of the steel. The content of C is controlled between 0.75 percent and 0.85 percent.
Si: si is an important element for strengthening in steel, and the strong hardness of the steel is improved through the solid solution effect, and meanwhile, the sag resistance of the spring steel is improved. However, the increase of the Si element increases the diffusion of carbon in the steel, and thus the decarburization of the steel is promoted. The Si content is controlled to be 1.60-2.00%.
Mn: mn and Fe form a solid solution, so that the hardness and strength of ferrite and austenite in the steel are improved, and meanwhile, Mn is used for improving the stability of an austenite structure and remarkably improving the hardenability of the steel. However, excessive Mn lowers the plasticity of the steel. The Mn content is controlled to be 0.40-0.60 percent.
Cr: cr and C can form a stable compound, prevent segregation of C or impurities, improve the stability of a matrix and obviously improve the antioxidation of steel. Cr dissolves in ferrite to cause solid solution strengthening, and can significantly increase hardenability and temper resistance of steel, but excessive Cr increases the temper brittleness tendency of steel. The Cr content is controlled to be 0.80-1.00 percent.
V: v is an excellent deoxidizer of steel, and vanadium is added into the steel to refine structure grains and improve the strength and the toughness. V forms fine carbonitrides, and can improve the hydrogen-induced delayed fracture resistance and the fatigue performance. However, too much VC diffuses into the crystal to cause the toughness of the steel to be reduced. The content of V is controlled between 0.20 percent and 0.30 percent.
Nb: nb is a micro-alloying element for refining grains very effectively, forms carbonitride with N through the composite action of Nb and V, particularly can increase nucleation points through increasing a deformation zone, can generate finer ferrite in the phase transformation process, and improves the strength and the fatigue strength of steel. However, the strengthening effect of excess Nb is no longer significant and increases the crack sensitivity of the steel. The Nb content is controlled to be 0.03-0.05 percent.
Mo: after the heat treatment of the steel, Mo is generally dispersed in the matrix material as second phase particles or inclusions, and atoms have a larger adsorption effect on hydrogen, namely, good hydrogen-induced delayed fracture resistance. With the increase of the content of the Mo element, the effect of delaying the internal initiation time of the fatigue crack is more obvious, and the ultrahigh cycle fatigue performance of the material is improved more. However, too much Mo content increases the intergranular corrosion tendency. The content of Mo is controlled to be 0.10-0.30%.
Re: adding proper amount of RE into steel to obtain MnS and A12O3The rare earth inclusions are changed into the metamorphism of the inclusions, thereby improving the mechanical property and fatigue of the steelFatigue life. Re is added into steel to form compact continuous RE composite oxide with high adhesion. In addition, Re improves pitting and intergranular corrosion by purifying the molten steel and deteriorating inclusions. The Re content is controlled to be 0.01-0.03 percent.
Al: al element is used for forming AlN in steel and N, and can inhibit the growth of austenite grains and refine carbide on an aggregation grain boundary in the rolling process and the heat treatment process, so that a fine hydrogen trap is formed, the hydrogen-induced delayed fracture resistance of the steel is effectively improved, but the nitride is gradually coarse along with the increase of Al content, a large aluminum carbide inclusion is formed, and the processability of the steel is deteriorated. The Al content is controlled to be 0.015-0.040%.
N: n forms a fine precipitated phase with aluminum in the steel, and improves the hydrogen-induced delayed fracture resistance of the steel. However, excessive N precipitates Fe in the steel4N and the diffusion speed is slow, so that the steel has timeliness, and meanwhile, the cold processing performance of the steel is reduced by the N, and the content of the N is controlled to be 0.005-0.008%.
S and P: the sulfur is easy to form MnS inclusion with manganese in the steel, and the fatigue property of the steel is deteriorated; p is an element with a strong segregation tendency and usually also causes co-segregation of sulphur and manganese, which is detrimental to the homogeneity of the product structure and properties. P is controlled to be less than or equal to 0.015 percent, and S is controlled to be less than or equal to 0.015 percent.
O: o forms oxide inclusions in the steel, the processing performance and the fatigue performance of the steel are damaged, and the content of O is controlled to be less than or equal to 0.0015 percent.
In order to ensure that the austenite grain size of the steel is less than or equal to 10 mu m and the size of the precipitated carbide after quenching and tempering heat treatment is less than or equal to 25 mu m so as to obtain excellent hydrogen-induced delayed fracture resistance and fatigue life, the Al/N is required to be ensured to be more than or equal to 3.5 percent;
in order to ensure that the tensile strength is more than or equal to 2300MPa, the A value is more than or equal to 36 percent: a is 29.1C +5.2Si +1.8Mn +3.5Cr +2.6V +0.8Nb +4.9 Mo.
The value a is an index for evaluating the degree of influence of C, Si, Mn, Cr, V, Nb, and Mo on the tensile strength after the steel quenching and tempering heat treatment and the degree of influence of each element by weighting and adding them. C. Si, Mn, Cr, V, Nb and Mo are the main elements for improving the tensile strength after heat treatment of the steel grade.
The following experiments were performed: 0.75-0.85% of C, 1.60-2.00% of Si, 0.40-0.60% of Mn, 0.80-1.00% of Cr, 0.20-0.30% of V, 0.03-0.05% of Nb, 0.10-0.30% of Mo, 0.01-0.03% of Re, 0.015-0.040% of Al, 0.005-0.008% of N, less than or equal to 0.015% of P, less than or equal to 0.015% of S, less than or equal to 0.0015% of O and the balance of Fe and other inevitable impurities. And various steels meeting the requirements that the Al/N is more than or equal to 3.5 percent and the A value is more than or equal to 36 percent are subjected to heat treatment of 890 ℃ quenching (oil cooling) +430 ℃ tempering after being produced according to the process method of the invention, and then the tensile strength R of the steel is detectedmThe results are shown in FIG. 1.
As can be seen from fig. 1: in order to ensure a tensile strength of 2300MPa or more, it is necessary to maintain the A value at 36% or more.
According to the ultrahigh-strength spring steel with excellent hydrogen-induced delayed fracture resistance and the production method thereof, provided by the invention, a large amount of noble metal elements Ni and Cu elements which are easy to cause brittle fracture of steel copper are avoided, and the ultrahigh-strength spring steel with the tensile strength of more than or equal to 2300MPa is produced at low cost under the interaction of C, Si, Mn, Cr, V, Nb, Mo, Re and N under a specific process, and has excellent delayed fracture resistance and fatigue performance.
Drawings
FIG. 1 is a graph showing the relationship between the tensile strength and the value A of spring steel after heat treatment;
FIG. 2 is a graph of cathodic charge-4 point bend test.
Detailed Description
The present invention will be described in detail with reference to examples.
The wire rod with specific components is adopted in the invention, the components of the examples and the comparative examples are shown in the table 1, and the production process is as follows:
electric furnace smelting: oxygen is determined before tapping, and steel retaining operation is adopted in the tapping process, so that slag is prevented from being discharged;
and (4) LF furnace: C. adjusting elements such as Si, Cr, Mn, V, Nb, Re, Mo and the like to target values;
vacuum degassing: the pure degassing time is more than or equal to 15 minutes, and the [ H ] is fully removed;
continuous casting: controlling the target temperature of the tundish molten steel to be 10-40 ℃ above the liquidus temperature, and continuously casting a large square billet with the thickness of 250mm multiplied by 250 mm;
cogging: heating a large square billet with the diameter of 250mm multiplied by 250mm → rolling the square billet with the diameter of 150mm multiplied by 150mm → stacking and cooling, controlling the soaking temperature of a heating furnace to be 1220-;
wire rod rolling route: peeling a 150mm × 150mm square billet → heating → high-speed wire controlled rolling → stelmor cooling by wire → phi 5.5-10 mm wire rod finished product. Wherein the peeling depth is controlled to be more than 1.2mm, and the decarburized layer is ensured to be zero after peeling; when the wire rod is rolled, the heating temperature is controlled to be 1020-1060 ℃, the finishing temperature is controlled to be 790-830 ℃, and the spinning temperature is controlled to be 790-830 ℃.
The hot rolling state performance detection method comprises the following steps:
austenite grain size determination: taking a cross section sample on a hot-rolled wire rod, wherein the height of the cross section sample is about 10mm, and carrying out austenitizing treatment, wherein the austenitizing heat treatment process comprises the following steps: 890 ℃ quenching, oil cooling, the temperature of a quenching medium is 18-35 ℃, metallographic sample preparation is carried out after cooling, and austenite grain size measurement is carried out according to GB/T6394 metal average grain size measurement method.
TABLE 1 chemical composition (wt%) of each example and comparative example
TABLE 2 production parameter control, wire structure obtained and mean austenite grain size for each example and comparative example
The performance detection method after quenching and tempering heat treatment comprises the following steps:
tensile property of quenching and tempering heat treatment: processing the wire rod into a blank sample of a standard tension sample (sampling on an intermediate blank in a small specification), and adopting the following quenching and tempering heat treatment process: 890 ℃ quenching, oil cooling, tempering at the temperature of quenching medium of 18-35 ℃, naturally cooling along with air, and then carrying out standard tension sample finish machining and tensile test;
and (3) fatigue test: and (3) quenching and tempering the material, removing the surface iron scale to prepare a sample, and then performing a fatigue bending test. 10 samples were presented with a probability of 60% or more7The maximum load stress of the next or more life is taken as the fatigue strength;
hydrogen-induced delayed fracture resistance test: the intermediate billet in the wire rolling process was used for quenching and tempering treatment, and a flat test piece (65mm long x 10mm wide x 1.5mm thick) was processed from the tempered steel material in the same manner as above to conduct a cathodic charging-4 point bending test. The cathodic charging-4-point bending test is shown in FIG. 2, in which a test piece S having a bending stress (1400MPa) applied thereto was placed in an acid solution (0.5mol/l H)2SO4+0.01mol/l KSCN), at a potential: cathodic charging was carried out at-700V, and the time from the start of charging to the time of rupture was measured as the rupture life, which was used as an index for evaluating the hydrogen-resistant delayed rupture characteristics. Since hydrogen embrittlement resistance under actual circumstances can be achieved if the fracture life is 1000sec or more, hydrogen embrittlement resistance is evaluated on the basis of 1000 sec. In fig. 2, 11 is a platinum electrode and 12 is a standard electrode. In addition, in order to evaluate the hydrogen induced delayed fracture resistance test performance, the fracture morphology of the fractured material of the cathodic charge-4 point bending test was investigated. And after the cathode charging-4-point bending test is finished, observing a fracture surface by adopting a scanning electron microscope at a multiplying power of 500-2000 multiplied by. On the obtained cross-sectional photograph, the ratio of the austenite grain boundary fracture which is the brittle fracture was measured, and this was used as the brittle fracture ratio and an index of the brittle fracture characteristics. The less the austenite grain boundary destruction, i.e., the lower the brittle fracture ratio, the more excellent the brittle fracture resistance. In the evaluation of the brittle fracture ratio, the area ratio of the austenite grain boundary destruction part on the photograph was measured by using image analysis software from a cross-sectional observation photograph of at least 5 fields or more. As for the brittle fracture ratio, the brittle fracture ratio was 85% in terms of 55SiCr which is a general suspension spring steel having a tensile strength of 1750MPa classThis was evaluated on the basis of 85%.
TABLE 3 tensile properties, fatigue strength and resistance to hydrogen induced delayed fracture after quenching and tempering heat treatment for each of the examples and comparative examples
The examples 1-10 are examples in which chemical components and production processes are reasonably controlled, the strength of the heat-treated steel reaches more than 2300MPa, the elongation reaches more than 12%, and the surface shrinkage reaches more than 40%, which shows that the examples have good strong plasticity, excellent delayed fracture resistance and fatigue performance, can be used for manufacturing 2300MPa grade high-stress springs, and are particularly suitable for ultrahigh-strength springs in a hydrogen-resistant environment. Comparative examples 1 to 5 do not satisfy the conditions of the present invention, and cannot satisfy tensile strength of 2300MPa or more, high fatigue performance, and hydrogen-induced delayed fracture resistance satisfying the reference value, and even if ultra-high strength is realized, application problems may occur as an element requiring stable fatigue life and hydrogen-induced fracture resistance, for example, a high-end automobile spring.
The above detailed description of the ultra-high strength spring steel having excellent hydrogen delayed fracture resistance and the method for producing the same with reference to the examples is illustrative and not restrictive, and several examples can be cited within the limits thereof, and thus, variations and modifications thereof without departing from the general inventive concept should fall within the scope of the present invention.
Claims (4)
1. An ultrahigh-strength spring steel with excellent hydrogen-induced delayed fracture resistance is characterized by comprising the following chemical components in percentage by weight: 0.75-0.85% of C, 1.60-2.00% of Si, 0.40-0.60% of Mn, 0.80-1.00% of Cr, 0.20-0.30% of V, 0.03-0.05% of Nb, 0.10-0.30% of Mo, 0.01-0.03% of Re, 0.015-0.040% of Al, 0.005-0.008% of N, less than or equal to 0.015% of P, less than or equal to 0.015% of S, less than or equal to 0.0015% of O, and the balance of Fe and other inevitable impurities; and Al/N is more than or equal to 3.5 percent, 29.1C +5.2Si +1.8Mn +3.5Cr +2.6V +0.8Nb +4.9Mo is more than or equal to 36 percent;
the method for producing the ultra-high strength spring steel with excellent hydrogen delayed fracture resistance comprises the following steps: electric furnace smelting, LF furnace, vacuum degassing, continuous casting, cogging and wire rolling;
in the cogging step, a large square billet with the thickness of 250mm multiplied by 250mm is heated and rolled into a square billet with the thickness of 150mm multiplied by 150mm, and then the square billet is cooled in a stacking manner; the heating temperature is 1220-;
the process for rolling the wire rod comprises the following steps: peeling a 150mm × 150mm square billet → heating → high-speed wire controlled rolling → stelmor cooling by wire → phi 5.5-10 mm wire rod finished product; controlling the peeling depth to be more than 1.2mm, controlling the heating temperature to be 1020-1060 ℃, the finish rolling temperature to be 790-830 ℃, and the spinning temperature to be 790-830 ℃;
the heat treatment process of the ultrahigh-strength spring steel with excellent hydrogen-induced delayed fracture resistance comprises the following steps: quenching at 880-930 ℃, oil cooling, tempering at 420-460 ℃, and air cooling.
2. The ultra-high strength spring steel having excellent resistance to hydrogen-induced delayed fracture according to claim 1, wherein in the continuous casting step, a 250mm x 250mm bloom is continuously cast.
3. The ultra-high strength spring steel with excellent hydrogen-induced delayed fracture resistance according to claim 1, wherein the scalping depth is controlled to be more than 1.2mm, and the heating temperature is controlled to be 1037-1041 ℃, the finish rolling temperature is controlled to be 805-821 ℃, and the spinning temperature is controlled to be 798-816 ℃.
4. The ultrahigh-strength spring steel with excellent hydrogen-induced delayed fracture resistance as claimed in claim 1, wherein the tensile strength of the spring steel after heat treatment is not less than 2300MPa, the elongation after fracture is not less than 10%, the reduction of area is not less than 40%, the fatigue strength is not less than 910MPa, and in a hydrogen embrittlement resistance experiment: the hydrogen-resistant delayed fracture life is more than or equal to 1000sec, and the brittle fracture rate is less than or equal to 85 percent.
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| JPS63128153A (en) * | 1986-11-18 | 1988-05-31 | Kobe Steel Ltd | Spring steel having superior setting resistance |
| JP3075314B2 (en) * | 1992-01-27 | 2000-08-14 | 株式会社神戸製鋼所 | Manufacturing method of steel wire for ultra high strength spring |
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