阅读说明：本技术 一种具有超高强度微合金化渗碳齿轮钢及其制备方法 (Microalloyed carburized gear steel with ultrahigh strength and preparation method thereof ) 是由 申勇峰 王月莉 薛文颖 于 2021-06-24 设计创作，主要内容包括：一种具有超高强度微合金化渗碳齿轮钢及其制备方法,属于齿轮钢生产技术领域,通过合理的成分设计及工艺控制,使所制备的Cr-Mo系齿轮钢具有超高抗拉强度和屈服强度,并且其表面为针状马氏体组织,具有高硬度,芯部为板条状马氏体组织,保持超高韧性,使该齿轮钢在具有超高抗拉强度的同时具备“芯韧”的综合力学性能。采用本发明方法具体工艺步骤及参数,可得到微观组织由针状马氏体和板条状马氏体组成,室温条件下的屈服强度为1272～1497MPa,抗拉强度为2072～2251MPa,延伸率为7±5％的具有超高强度微合金化的渗碳齿轮钢。(A microalloyed carburized gear steel with ultrahigh strength and a preparation method thereof belong to the technical field of gear steel production, and the prepared Cr-Mo gear steel has ultrahigh tensile strength and yield strength through reasonable component design and process control, the surface of the Cr-Mo gear steel is a needle-shaped martensite structure and has high hardness, the core part of the Cr-Mo gear steel is a lath-shaped martensite structure, and the ultrahigh toughness is maintained, so that the gear steel has the comprehensive mechanical property of 'core toughness' while having ultrahigh tensile strength. By adopting the specific process steps and parameters of the method, the ultra-high strength microalloyed carburized gear steel with the microstructure composed of acicular martensite and lath martensite, the yield strength of 1272-1497 MPa, the tensile strength of 2072-2251 MPa and the elongation of 7 +/-5% under the room temperature condition can be obtained.)

1. The microalloyed carburized gear steel with the ultrahigh strength is characterized by comprising the following chemical components in percentage by weight: (0.19-0.215)% C, (0.2-0.3)% Si, (1.1-1.2)% Mn, (1.4-1.5)% Cr, (1.5-1.8)% Ni, (0.3-0.5)% Mo, (0.1-0.2)% V, and the balance Fe element and inevitable impurities.

2. The ultra-high strength microalloyed carburized gear steel according to claim 1, wherein the gear steel has a needle-like martensitic structure in its surface and a lath-like martensitic structure in its core; the yield strength is 1272-1497 MPa, the tensile strength is 2072-2251 MPa, and the elongation is 7 +/-5% at room temperature.

3. A method of making an ultra-high strength microalloyed carburized gear steel in accordance with claim 1, characterized by the steps of:

weighing (0.19-0.215)% of C, (0.2-0.3)% of Si, (1.1-1.2)% of Mn, (1.4-1.5)% of Cr, (1.5-1.8)% of Ni, (0.3-0.5)% of Mo, (0.1-0.2)% of V and the balance of Fe by weight percentage, smelting the alloy raw materials in a vacuum furnace, introducing protective gas into the vacuum furnace, and casting the smelted molten steel into steel ingots;

carrying out solution treatment on the steel ingot, then rolling, and air-cooling the obtained hot rolled plate to room temperature;

carrying out preliminary heat treatment on the steel plate, and then air-cooling to room temperature;

carrying out carburizing treatment, carrying out oil quenching after the carburizing treatment, carrying out annealing treatment on the oil-quenched gear steel, and cooling to room temperature;

then carrying out secondary oil quenching;

and annealing again, and cooling to room temperature to obtain the carburized gear steel with ultrahigh strength.

4. The method for preparing an ultra-high strength microalloyed carburized gear steel according to claim 3, characterized in that the protective gas introduced in said step is argon.

5. The method for preparing the ultra-high strength microalloyed carburized gear steel according to claim 3, characterized in that in the step, the steel ingot is heated to 1200 plus or minus 10 ℃ and kept warm for 2-4h for solution treatment, 6 passes of rolling are carried out at 1100 plus or minus 10 ℃, the total deformation is 82.5 percent, the final rolling temperature is 900 plus or minus 50 ℃, and then the steel ingot is air-cooled to room temperature.

6. The method for preparing an ultra-high strength microalloyed carburized gear steel according to claim 3, characterized in that, in the step, the steel plate is subjected to the preliminary heat treatment in a manner that: keeping the temperature at 500 plus or minus 10 ℃ for 2 to 3 hours, and then keeping the temperature at 700 plus or minus 10 ℃ for 5 to 7 hours.

7. The method for preparing the ultra-high strength microalloyed carburized gear steel according to claim 3, characterized in that in the step, the carburizing treatment process parameters are as follows: carburizing for 3-5h at 930-950 ℃, 300Pa at the carburizing pressure of 200-0.9 Pa, 0.7-0.9% of the surface carbon content of the carburized part and 0.8-1.2mm of the thickness of the carburized layer; after the carburization is finished, the temperature is reduced to 860 ℃, the temperature is preserved for 10min, and then oil quenching is carried out.

8. The method for preparing the ultra-high strength microalloyed carburized gear steel according to claim 3, characterized in that, in the step, the annealing treatment process parameters after oil quenching are as follows: the annealing temperature is 160 +/-20 ℃, the heat preservation is carried out for 2-4h, and the cooling mode is air cooling.

9. The method for preparing the ultra-high strength microalloyed carburized gear steel according to claim 3, characterized in that in the step, secondary oil quenching is carried out, the quenching temperature is 810 +/-30 ℃, and the temperature is kept for 2-3 h.

10. The method for preparing the ultra-high strength microalloyed carburized gear steel according to claim 3, characterized in that in the step, annealing is carried out again, the annealing temperature is 160 +/-20 ℃, the temperature is kept for 2-3h, and the cooling mode is air cooling.

Technical Field

The invention belongs to the technical field of production of gear steel, and particularly relates to microalloyed carburized gear steel with ultrahigh strength and a preparation method thereof.

Background

In recent years, with the rapid development of national economy, the industries of aerospace, ships, automobiles and the like are also rapidly developed, so that the demand for shafts, gears and the like of transmission parts of the industries is increasing. These shaft and gear parts work under the conditions of high cyclic load, high impact load and severe friction, so that they have higher requirements for the comprehensive performance of the parts, namely: high surface hardness, good wear resistance, and enough toughness and other comprehensive mechanical properties in the core. The quality of the bearing and the gear directly influences the safety and the service life of equipment and facilities in the operation process, so that the development of high-performance gear steel becomes a focus of traditional structural materials, and the prospect is wide.

At present, the alloying system of the steel for gears in China is the sum of the original Suyi, American, Japanese, Germany, English, France, Italy and the independent innovative alloying system in China, and covers the alloy steel systems of all countries in the world. With the progress of production and technology, the industrial requirements are more and more demanding on the use conditions of gears, and the performance of steel is required to be improved in the aspects of strengthening, improving the rotation fatigue life, preventing the oxidation of grain boundaries, inhibiting softening and the like.

The excellent structure and mechanical property of the gear steel material can be effectively realized by adopting the methods of solid solution strengthening, fine grain strengthening, forging process and heat treatment schedule improvement and the like. At the present stage, in the production process, secondary phases such as carbide, nitride and the like are dispersed and precipitated in steel by mainly adding trace alloy elements, so that the grain boundary is effectively pinned, and the growth of grains is prevented; and by adding trace microalloy elements, when austenite is recrystallized, the recrystallization behavior of the deformed austenite is inhibited by controlling the rolling process and the cooling process, so that the effect of delaying the growth of recrystallized austenite grains is achieved; thereby obtaining the gear steel material with refined grains and higher strength. In recent years, a gear steel piece is placed in a carburized active medium, heated to a single-phase austenite state, and kept warm for a certain time, so that a high carbon content can be obtained on a surface layer, and then the workpiece is quenched and subjected to low-temperature tempering heat treatment under the protection of carbon, so that the surface strength of the steel piece is improved.

At present, most heavy machinery and heavy automobiles adopt Cr-Ni, Cr-Mo or Cr-Ni-Mo series gear steel. The 18CrNiMo7-6 carburized gear steel of German DIN standard series has high impact toughness and good hardenability, the tensile strength of the 18CrNiMo7-6 carburized gear steel is 1185MPa, the tensile strength of 17Cr2Ni2Mo, 20Cr2Ni4, 17CrNiMo6 and 20CrNi2MoV which are used in China in large quantities is 1167-1542 MPa, and a large lifting space is provided.

With the increasingly harsh service conditions of the gear steel, the performance requirements of the gear steel are higher and higher, and the production and development of the gear steel with excellent comprehensive mechanical properties are urgent and are not slow.

Disclosure of Invention

The invention aims to provide a carburized gear steel with ultrahigh strength microalloying and a preparation method thereof. Through reasonable component design and process control, the prepared Cr-Mo gear steel has ultrahigh tensile strength and yield strength, the surface of the Cr-Mo gear steel is an acicular martensite structure and has high hardness, the core part of the Cr-Mo gear steel is a lath-shaped martensite structure, and the ultrahigh toughness is maintained, so that the gear steel has ultrahigh tensile strength and comprehensive mechanical properties of 'core toughness'.

The microalloyed carburized gear steel with ultrahigh strength comprises the following chemical components in percentage by weight: (0.19-0.215)% C, (0.2-0.3)% Si, (1.1-1.2)% Mn, (1.4-1.5)% Cr, (1.5-1.8)% Ni, (0.3-0.5)% Mo, (0.1-0.2)% V, and the balance Fe element and inevitable impurities. The microstructure of the steel plate consists of acicular martensite and lath martensite, the yield strength of the steel plate under the room temperature condition is 1272-1497 MPa, the tensile strength is 2072-2251 MPa, and the elongation is 7 +/-5%.

A preparation method of microalloyed carburized gear steel with ultrahigh strength comprises the following steps:

weighing (0.19-0.215)% of C, (0.2-0.3)% of Si, (1.1-1.2)% of Mn, (1.4-1.5)% of Cr, (1.5-1.8)% of Ni, (0.3-0.5)% of Mo, (0.1-0.2)% of V and the balance of Fe by weight percentage, smelting the alloy raw materials in a vacuum furnace, introducing protective gas into the furnace, and casting the smelted molten steel into steel ingots;

carrying out solution treatment on the steel ingot, then rolling, and air-cooling the obtained hot rolled plate to room temperature;

carrying out preliminary heat treatment on the steel plate, and then air-cooling to room temperature;

carrying out carburizing treatment, carrying out oil quenching after the carburizing treatment, carrying out annealing treatment on the oil-quenched gear steel, and cooling to room temperature;

then carrying out secondary oil quenching;

and annealing again, and cooling to room temperature to obtain the carburized gear steel with ultrahigh strength.

The preparation method of the microalloyed carburized gear steel with the ultrahigh strength comprises the following steps:

in the step, the introduced protective gas is inert gas such as Ar.

In the step, the steel ingot is heated to 1200 +/-10 ℃ and is kept warm for 2-4h for solution treatment, 6-pass rolling is carried out at 1100 +/-10 ℃, the total deformation is 82.5 percent, the final rolling temperature is controlled at 900 +/-50 ℃, and the obtained hot rolled plate is cooled to room temperature by air.

In the step, the steel plate is subjected to the preliminary heat treatment in a manner that: keeping the temperature at 500 plus or minus 10 ℃ for 2 to 3 hours, and then keeping the temperature at 700 plus or minus 10 ℃ for 5 to 7 hours.

In the step, the carburizing treatment process parameters are as follows: carburizing for 3-5h at 930-950 ℃ with acetylene as carburizing medium, 300Pa for carburizing pressure, 0.7-0.9% of carbon content on the surface of the carburized part and 0.8-1.2mm of carburized layer thickness. After the carburization is finished, the temperature is reduced to 860 ℃, the temperature is kept for 10min, and then oil quenching (namely primary quenching) is carried out.

In the step, the annealing treatment process parameters after oil quenching are as follows: the annealing temperature is 160 +/-20 ℃, and the heat preservation is carried out for 2-4 h. The cooling mode is air cooling.

In the step, secondary oil quenching is carried out, the quenching temperature is 810 +/-30 ℃, and the temperature is kept for 2-3 h.

In the step, annealing is carried out again, the annealing temperature is 160 +/-20 ℃, and the temperature is kept for 2-3 h. The cooling mode is air cooling.

Key point of the invention

1. The method utilizes the traditional vacuum induction melting technology and combines the continuous rolling and the comprehensive factors of component design, hot rolling temperature, hot rolling quantity, preliminary heat treatment process, carburizing process, subsequent heat treatment process and the like so as to control the growth of austenite grains of the gear steel and the precipitation of microalloy elements.

2. The austenite grain growth of the gear steel and the precipitation of micro alloy elements are controlled, so that the gear steel obtains excellent comprehensive mechanical properties, the material has very high room-temperature tensile strength and yield strength, simultaneously the toughness is ensured, and the comprehensive properties are far higher than those of domestic active gear steel.

3. The gear steel has relatively low content of alloy elements and is low in price, the preparation process is simple, and the production cost is greatly saved.

The invention has the following effects:

the invention has the advantages that the carburized gear steel with ultrahigh strength and microalloying and the preparation method thereof utilize the traditional vacuum induction melting technology, and the continuous rolling is combined with the control of comprehensive factors such as components, hot rolling temperature, hot rolling quantity, preheating treatment process, carburization process, quenching temperature, quenching time, quenching mode, annealing temperature, annealing time and the like, so as to control the austenite crystal growth of the gear steel and the precipitation of microalloy elements, so that the gear steel obtains excellent comprehensive mechanical properties. Furthermore, by adopting the specific process steps and parameters of the method, the ultra-high strength microalloyed carburized gear steel with a microstructure composed of acicular martensite and lath martensite, yield strength of 1272-1497 MPa, tensile strength of 2072-2251 MPa and elongation of 7 +/-5% at room temperature can be obtained.

Drawings

Figure 1 microstructure morphology of ultra-high strength microalloyed carburized gear steel made in example 1 of this invention.

Figure 2 microstructure morphology of ultra-high strength microalloyed carburized gear steel made in example 3 of this invention.

FIG. 3 is a unidirectional tensile engineering stress-strain curve of the ultra-high strength microalloyed carburized gear steel produced in examples 1 to 3 of the present invention; curves 1 to 3 correspond to examples 1 to 3, respectively.

Detailed Description

The hot rolling equipment adopted in the embodiment of the invention isDouble-roller one-way asynchronous rolling mill.

The carburizing equipment adopted in the embodiment of the invention is a DB-433 type vacuum furnace.

The heat preservation equipment adopted in the embodiment of the invention is an SX-8-13 type box type resistance furnace.

The smelting equipment adopted in the embodiment of the invention is a vacuum induction furnace.

The metal raw materials adopted in the embodiment of the invention are all analytical grade, and the weight purities of C powder, Si powder, metal Fe, metal Mn, metal Cr, metal Ni, metal Mo and metal V are all more than or equal to 99.9%.

Example 1

The gear steel has the chemical composition of, by weight, 0.19% of C, 0.2% of Si, 1.1% of Mn, 1.4% of Cr, 1.5% of Ni, 0.3% of Mo, 0.1% of V, and the balance of Fe and inevitable impurities.

The preparation method of the microalloyed carburized gear steel with the ultrahigh strength comprises the following steps:

placing C powder, Si powder, metal Fe, metal Mn, metal Cr, metal Ni, metal Mo and metal V into a smelting furnace, smelting under the condition of argon, and then casting into an ingot, wherein the components of the ingot comprise, by weight, 0.19% of C, 0.2% of Si, 1.1% of Mn, 1.4% of Cr, 1.5% of Ni, 0.3% of Mo, 0.1% of V, and the balance of Fe and unavoidable impurities, and the ingot is cogging into a rectangular billet with the cross section of 80mm multiplied by 80mm and the height of 100 mm;

heating the cast ingot to 1210 ℃, preserving heat for 4 hours, carrying out solution treatment, wherein the hot rolling adopts two-stage controlled rolling, the hot rolling temperature of the first stage is 1110 ℃, the hot rolling temperature of the second stage is 1000 ℃, the final rolling temperature is 950 ℃, the total reduction of the two stages is 82.5%, the plate thickness is 14mm after 6 passes of final rolling, and after the final rolling, placing the steel plate in air and cooling to room temperature;

performing preliminary heat treatment on the steel plate, preserving heat of the steel plate for 2 hours at 510 ℃, then heating to 710 ℃, preserving heat for 6 hours, taking out and cooling to room temperature in air;

carburizing a steel plate, wherein a carburizing medium is acetylene, carburizing is carried out for 4 hours at 940 ℃, the carburizing pressure is set to 300Pa, the carburizing surface concentration is 0.9%, and the carburized layer is 1.2 mm; and then placing the steel plate at 860 ℃ for heat preservation for 10min, and quickly cooling with oil.

Placing the steel plate at 180 ℃ for heat preservation for 3h, and air-cooling to room temperature;

placing the steel plate at 840 ℃ for heat preservation for 2h, and cooling with oil;

and (3) placing the steel plate at 160 ℃ for heat preservation for 2h, and air-cooling to room temperature to obtain the microalloyed carburized gear steel with ultrahigh strength. The obtained product is subjected to performance detection, and has the tensile strength of 2251MPa, the yield strength of 1399MPa, the elongation of 6.97 percent and the hardness of 744.4 HV; the microstructure is austenite grains, the grain size is about 30 μm, the width of a martensite lath is about 0.11 μm, the microstructure appearance is shown in figure 1, and the true stress-true strain curve of the unidirectional stretching is shown in figure 3 (curve 1).

The common gear steel is stretched at room temperature, the yield strength is 1000MPa, the tensile strength is 1200MPa, and the yield strength of the gear steel with the ultrahigh strength prepared by the method is improved by about 400MPa and the tensile strength is improved by 1000MPa compared with the common gear steel.

Example 2

The gear steel has the chemical composition of, by weight, 0.19% of C, 0.2% of Si, 1.1% of Mn, 1.4% of Cr, 1.5% of Ni, 0.3% of Mo, 0.1% of V, and the balance of Fe and inevitable impurities.

The preparation method of the microalloyed carburized gear steel with the ultrahigh strength comprises the following steps:

placing C powder, Si powder, metal Fe, metal Mn, metal Cr, metal Ni, metal Mo and metal V into a smelting furnace, smelting under the condition of argon, and then casting into an ingot, wherein the components of the ingot comprise, by weight, 0.19% of C, 0.2% of Si, 1.1% of Mn, 1.4% of Cr, 1.5% of Ni, 0.3% of Mo, 0.1% of V, and the balance of Fe and unavoidable impurities, and the ingot is cogging into a rectangular billet with the cross section of 80mm multiplied by 80mm and the height of 100 mm;

heating the cast ingot to 1200 ℃, preserving heat for 4 hours, carrying out solution treatment, wherein the hot rolling adopts two-stage controlled rolling, the hot rolling temperature of the first stage is 1100 ℃, the hot rolling temperature of the second stage is 1000 ℃, the final rolling temperature is 900 ℃, the total reduction of the two stages is 82.5%, the plate thickness is 14mm after 6 passes of final rolling, and placing the steel plate in air to be cooled to room temperature;

performing preliminary heat treatment on the steel plate, keeping the temperature of the steel plate at 500 ℃ for 2h, then heating to 700 ℃, keeping the temperature for 6h, taking out the steel plate, and cooling the steel plate to room temperature in the air;

carburizing a steel plate, wherein a carburizing medium is acetylene, carburizing is carried out for 4 hours at 940 ℃, the carburizing pressure is set to 300Pa, the carburizing surface concentration is 0.9%, and the carburized layer is 1.2 mm; and then placing the steel plate at 860 ℃ for heat preservation for 10min, and quickly cooling with oil.

Annealing the steel plate, keeping the temperature of the steel plate at 160 ℃ for 3h, and cooling the steel plate to room temperature in air;

carrying out secondary quenching treatment on the steel plate, placing the steel plate at 810 ℃ for heat preservation for 2h, and carrying out oil cooling;

and annealing the steel plate, placing the steel plate at 160 ℃ for heat preservation for 2h, and air-cooling to room temperature to obtain the microalloying carburized gear steel with ultrahigh strength. The obtained product is subjected to performance detection, and the tensile strength is 2072MPa, the yield strength is 1497MPa, the elongation is 2.2 percent, and the hardness is 720.3 HV; the microstructure is austenite grains, the grain size is about 30 μm, the width of the martensite lath is about 0.13 μm, and the true stress-true strain curve of the uniaxial tension is shown in FIG. 3 (curve 2).

Example 3

The gear steel has the chemical composition of, by weight, 0.19% of C, 0.2% of Si, 1.1% of Mn, 1.4% of Cr, 1.5% of Ni, 0.3% of Mo, 0.1% of V, and the balance of Fe and inevitable impurities.

The preparation method of the microalloyed carburized gear steel with the ultrahigh strength comprises the following steps:

placing C powder, Si powder, metal Fe, metal Mn, metal Cr, metal Ni, metal Mo and metal V into a smelting furnace, smelting under the condition of argon, and then casting into an ingot, wherein the components of the ingot comprise, by weight, 0.19% of C, 0.2% of Si, 1.1% of Mn, 1.4% of Cr, 1.5% of Ni, 0.3% of Mo, 0.1% of V, and the balance of Fe and unavoidable impurities, and the ingot is cogging into a rectangular billet with the cross section of 80mm multiplied by 80mm and the height of 100 mm;

heating the cast ingot to 1190 ℃, preserving heat for 4 hours, carrying out solution treatment, wherein the hot rolling adopts two-stage controlled rolling, the hot rolling temperature of the first stage is 1090 ℃, the hot rolling temperature of the second stage is 1000 ℃, the final rolling temperature is 850 ℃, the total reduction of the two stages is 82.5%, the plate thickness is 14mm after 6 passes of final rolling, and after the final rolling, placing the steel plate in air and cooling to room temperature;

performing preliminary heat treatment on the steel plate, keeping the temperature of the steel plate at 490 ℃ for 2h, then heating to 690 ℃, keeping the temperature for 6h, taking out the steel plate, and cooling the steel plate to room temperature in the air;

carburizing a steel plate, wherein a carburizing medium is acetylene, carburizing is carried out for 4 hours at 940 ℃, the carburizing pressure is set to 300Pa, the carburizing surface concentration is 0.9%, and the carburized layer is 1.2 mm; and then placing the steel plate at 860 ℃ for heat preservation for 10min, and quickly cooling with oil.

Annealing the steel plate, placing the steel plate at 140 ℃ for 3h, and air-cooling to room temperature;

carrying out secondary quenching treatment on the steel plate, placing the steel plate at 780 ℃ and keeping the temperature for 2h, and carrying out oil cooling; and (3) annealing the steel plate, placing the steel plate at 140 ℃ for heat preservation for 2h, and air-cooling to room temperature to obtain the microalloying carburized gear steel with ultrahigh strength. The obtained product is subjected to performance detection, the tensile strength is 2110MPa, the yield strength is 1272MPa, the elongation is 11.44 percent, and the hardness is 736.4 HV; the microstructure is austenite grains, the grain size is about 30 μm, the width of a martensite lath is about 0.16 μm, the microstructure appearance is shown in figure 2, and the true stress-true strain curve of the unidirectional stretching is shown in figure 3 (curve 3).

Example 4

The gear steel has the chemical composition of, by weight, 0.20% of C, 0.25% of Si, 1.15% of Mn, 1.45% of Cr, 1.6% of Ni, 0.35% of Mo, 0.15% of V, and the balance of Fe and inevitable impurities.

The preparation method of the microalloyed carburized gear steel with the ultrahigh strength comprises the following steps:

placing C powder, Si powder, metal Fe, metal Mn, metal Cr, metal Ni, metal Mo and metal V into a smelting furnace, smelting under the condition of argon, and then casting into an ingot, wherein the components of the ingot comprise, by weight, 0.20% of C, 0.25% of Si, 1.15% of Mn, 1.45% of Cr, 1.6% of Ni, 0.35% of Mo, 0.15% of V, and the balance of Fe and unavoidable impurities, and the ingot is cogging into a rectangular billet with the cross section of 80mm multiplied by 80mm and the height of 100 mm;

heating the cast ingot to 1210 ℃, preserving heat for 4 hours, carrying out solution treatment, wherein the hot rolling adopts two-stage controlled rolling, the hot rolling temperature of the first stage is 1110 ℃, the hot rolling temperature of the second stage is 1000 ℃, the final rolling temperature is 950 ℃, the total reduction of the two stages is 82.5%, the plate thickness is 14mm after 6 passes of final rolling, and after the final rolling, placing the steel plate in air and cooling to room temperature;

performing preliminary heat treatment on the steel plate, preserving heat of the steel plate for 2 hours at 510 ℃, then heating to 710 ℃, preserving heat for 6 hours, taking out and cooling to room temperature in air;

carburizing a steel plate, wherein a carburizing medium is acetylene, carburizing is carried out for 4 hours at 940 ℃, the carburizing pressure is set to be 200Pa, the carburizing surface concentration is 0.7%, and the carburized layer is 0.8 mm; and then placing the steel plate at 860 ℃ for heat preservation for 10min, and quickly cooling with oil.

Placing the steel plate at 180 ℃ for heat preservation for 3h, and air-cooling to room temperature;

placing the steel plate at 840 ℃ for heat preservation for 2h, and cooling with oil;

and (3) placing the steel plate at 180 ℃ for heat preservation for 2h, and air-cooling to room temperature to obtain the microalloyed carburized gear steel with ultrahigh strength. The obtained product is subjected to performance detection, and has the tensile strength of 2251MPa, the yield strength of 1399MPa, the elongation of 6.97 percent and the hardness of 744.4 HV; the microstructure is austenite grain, the grain size is about 25 μm, and the width of martensite lath is about 0.13 μm.

The common gear steel is stretched at room temperature, the yield strength is 1050MPa, the tensile strength is 1150MPa, and compared with the common gear steel, the gear steel with ultrahigh strength prepared by the method has the advantages that the yield strength is improved by about 300MPa, and the tensile strength is improved by 950 MPa.

Example 5

The gear steel has the chemical composition of, by weight, 0.20% of C, 0.25% of Si, 1.15% of Mn, 1.45% of Cr, 1.6% of Ni, 0.35% of Mo, 0.15% of V, and the balance of Fe and inevitable impurities.

The preparation method of the microalloyed carburized gear steel with the ultrahigh strength comprises the following steps:

placing C powder, Si powder, metal Fe, metal Mn, metal Cr, metal Ni, metal Mo and metal V into a smelting furnace, smelting under the condition of argon, and then casting into an ingot, wherein the components of the ingot comprise, by weight, 0.20% of C, 0.25% of Si, 1.15% of Mn, 1.45% of Cr, 1.6% of Ni, 0.35% of Mo, 0.15% of V, and the balance of Fe and unavoidable impurities, and the ingot is cogging into a rectangular billet with the cross section of 80mm multiplied by 80mm and the height of 100 mm;

heating the cast ingot to 1200 ℃, preserving heat for 4 hours, carrying out solution treatment, wherein the hot rolling adopts two-stage controlled rolling, the hot rolling temperature of the first stage is 1100 ℃, the hot rolling temperature of the second stage is 1000 ℃, the final rolling temperature is 900 ℃, the total reduction of the two stages is 82.5%, the plate thickness is 14mm after 6 passes of final rolling, and placing the steel plate in air to be cooled to room temperature;

performing preliminary heat treatment on the steel plate, keeping the temperature of the steel plate at 500 ℃ for 2h, then heating to 700 ℃, keeping the temperature for 6h, taking out the steel plate, and cooling the steel plate to room temperature in the air;

carburizing a steel plate, wherein a carburizing medium is acetylene, carburizing is carried out for 4 hours at 940 ℃, the carburizing pressure is set to 300Pa, the carburizing surface concentration is 0.9%, and the carburized layer is 1.2 mm; and then placing the steel plate at 860 ℃ for heat preservation for 10min, and quickly cooling with oil.

Annealing the steel plate, keeping the temperature of the steel plate at 160 ℃ for 3h, and cooling the steel plate to room temperature in air;

carrying out secondary quenching treatment on the steel plate, placing the steel plate at 810 ℃ for heat preservation for 2h, and carrying out oil cooling;

and annealing the steel plate, placing the steel plate at 160 ℃ for heat preservation for 2h, and air-cooling to room temperature to obtain the microalloying carburized gear steel with ultrahigh strength. The obtained product is subjected to performance detection, the tensile strength is 2020MPa, the yield strength is 1380MPa, the elongation is 2.3 percent, and the hardness is 710 HV; the microstructure is austenite grain, the grain size is about 28 μm, and the width of martensite lath is about 0.15 μm.

Example 6

The gear steel has the chemical composition of, by weight, 0.215% of C, 0.3% of Si, 1.2% of Mn, 1.5% of Cr, 1.8% of Ni, 0.5% of Mo, 0.2% of V, and the balance of Fe and inevitable impurities.

The preparation method of the microalloyed carburized gear steel with the ultrahigh strength comprises the following steps:

placing C powder, Si powder, metal Fe, metal Mn, metal Cr, metal Ni, metal Mo and metal V into a smelting furnace, smelting under the condition of argon, and then casting into an ingot, wherein the components of the ingot comprise 0.215 percent of C, 0.3)% of Si, 1.2 percent of Mn, 1.5 percent of Cr, 1.8 percent of Ni, 0.5 percent of Mo, 0.2 percent of V and the balance of Fe and inevitable impurities by weight percent, and the ingot is cogging into a rectangular billet with the cross section of 80mm multiplied by 80mm and the height of 100 mm;

heating the cast ingot to 1210 ℃, preserving heat for 4 hours, carrying out solution treatment, wherein the hot rolling adopts two-stage controlled rolling, the hot rolling temperature of the first stage is 1110 ℃, the hot rolling temperature of the second stage is 1000 ℃, the final rolling temperature is 950 ℃, the total reduction of the two stages is 82.5%, the plate thickness is 14mm after 6 passes of final rolling, and after the final rolling, placing the steel plate in air and cooling to room temperature;

performing preliminary heat treatment on the steel plate, preserving heat of the steel plate for 2 hours at 510 ℃, then heating to 710 ℃, preserving heat for 6 hours, taking out and cooling to room temperature in air;

carburizing a steel plate, wherein a carburizing medium is acetylene, carburizing is carried out for 4 hours at 940 ℃, the carburizing pressure is set to be 200Pa, the carburizing surface concentration is 0.7%, and the carburized layer is 0.8 mm; and then placing the steel plate at 860 ℃ for heat preservation for 10min, and quickly cooling with oil.

Placing the steel plate at 180 ℃ for heat preservation for 3h, and air-cooling to room temperature;

placing the steel plate at 840 ℃ for heat preservation for 2h, and cooling with oil;

and (3) placing the steel plate at 160 ℃ for heat preservation for 2h, and air-cooling to room temperature to obtain the microalloyed carburized gear steel with ultrahigh strength. The obtained product is subjected to performance detection, the tensile strength is 2160MPa, the yield strength is 1330MPa, the elongation is 6.5 percent, and the hardness is 740 HV; the microstructure is austenite grain, the grain size is about 30 μm, and the width of martensite lath is about 0.12 μm.

The common gear steel is stretched at room temperature, the yield strength is 1100MPa, and the tensile strength is 1100 MPa.

Example 7

The gear steel has the chemical composition of, by weight, 0.215% of C, 0.3% of Si, 1.2% of Mn, 1.5% of Cr, 1.8% of Ni, 0.5% of Mo, 0.2% of V, and the balance of Fe and inevitable impurities.

The preparation method of the microalloyed carburized gear steel with the ultrahigh strength comprises the following steps:

placing C powder, Si powder, metal Fe, metal Mn, metal Cr, metal Ni, metal Mo and metal V into a smelting furnace, smelting under the condition of argon, and then casting into an ingot, wherein the components of the ingot comprise, by weight, 0.215% of C, 0.3% of Si, 1.2% of Mn, 1.5% of Cr, 1.8% of Ni, 0.5% of Mo, 0.2% of V, and the balance of Fe and unavoidable impurities, and the ingot is cogging into a rectangular billet with the cross section of 80mm multiplied by 80mm and the height of 100 mm;

heating the cast ingot to 1200 ℃, preserving heat for 4 hours, carrying out solution treatment, wherein the hot rolling adopts two-stage controlled rolling, the hot rolling temperature of the first stage is 1100 ℃, the hot rolling temperature of the second stage is 1000 ℃, the final rolling temperature is 900 ℃, the total reduction of the two stages is 82.5%, the plate thickness is 14mm after 6 passes of final rolling, and placing the steel plate in air to be cooled to room temperature;

performing preliminary heat treatment on the steel plate, keeping the temperature of the steel plate at 500 ℃ for 2h, then heating to 700 ℃, keeping the temperature for 6h, taking out the steel plate, and cooling the steel plate to room temperature in the air;

carburizing a steel plate, wherein a carburizing medium is acetylene, carburizing is carried out for 4 hours at 940 ℃, the carburizing pressure is set to 300Pa, the carburizing surface concentration is 0.9%, and the carburized layer is 1.2 mm; and then placing the steel plate at 860 ℃ for heat preservation for 10min, and quickly cooling with oil.

Annealing the steel plate, keeping the temperature of the steel plate at 160 ℃ for 3h, and cooling the steel plate to room temperature in air;

carrying out secondary quenching treatment on the steel plate, placing the steel plate at 810 ℃ for heat preservation for 2h, and carrying out oil cooling;

and annealing the steel plate, placing the steel plate at 160 ℃ for heat preservation for 2h, and air-cooling to room temperature to obtain the microalloying carburized gear steel with ultrahigh strength. The obtained product is subjected to performance detection, the tensile strength is 2010MPa, the yield strength is 1387MPa, the elongation is 2.3%, and the hardness is 715 HV; the microstructure is austenite grain, the grain size is about 32 μm, and the width of martensite lath is about 0.14 μm.

Example 8

The gear steel has the chemical composition of, by weight, 0.215% of C, 0.3% of Si, 1.2% of Mn, 1.5% of Cr, 1.8% of Ni, 0.5% of Mo, 0.2% of V, and the balance of Fe and inevitable impurities.

The preparation method of the microalloyed carburized gear steel with the ultrahigh strength comprises the following steps:

placing C powder, Si powder, metal Fe, metal Mn, metal Cr, metal Ni, metal Mo and metal V into a smelting furnace, smelting under the condition of argon, and then casting into an ingot, wherein the components of the ingot comprise, by weight, 0.215% of C, 0.3% of Si, 1.2% of Mn, 1.5% of Cr, 1.8% of Ni, 0.5% of Mo, 0.2% of V, and the balance of Fe and unavoidable impurities, and the ingot is cogging into a rectangular billet with the cross section of 80mm multiplied by 80mm and the height of 100 mm;

heating the cast ingot to 1190 ℃, preserving heat for 4 hours, carrying out solution treatment, wherein the hot rolling adopts two-stage controlled rolling, the hot rolling temperature of the first stage is 1090 ℃, the hot rolling temperature of the second stage is 1000 ℃, the final rolling temperature is 850 ℃, the total reduction of the two stages is 82.5%, the plate thickness is 14mm after 6 passes of final rolling, and after the final rolling, placing the steel plate in air and cooling to room temperature;

performing preliminary heat treatment on the steel plate, keeping the temperature of the steel plate at 490 ℃ for 2h, then heating to 690 ℃, keeping the temperature for 6h, taking out the steel plate, and cooling the steel plate to room temperature in the air;

carburizing a steel plate, wherein a carburizing medium is acetylene, carburizing is carried out for 4 hours at 940 ℃, the carburizing pressure is set to 300Pa, the carburizing surface concentration is 0.9%, and the carburized layer is 1.2 mm; and then placing the steel plate at 860 ℃ for heat preservation for 10min, and quickly cooling with oil.

Annealing the steel plate, placing the steel plate at 140 ℃ for 3h, and air-cooling to room temperature;

carrying out secondary quenching treatment on the steel plate, placing the steel plate at 780 ℃ and keeping the temperature for 2h, and carrying out oil cooling;

and (3) annealing the steel plate, placing the steel plate at 140 ℃ for heat preservation for 2h, and air-cooling to room temperature to obtain the microalloying carburized gear steel with ultrahigh strength. The obtained product is subjected to performance detection, the tensile strength is 2000MPa, the yield strength is 1240MPa, the elongation is 11.34 percent, and the hardness is 730 HV; the microstructure is austenite grain, the grain size is about 31 μm, and the width of martensite lath is about 0.17 μm.