Novel carburizing gear steel based on high-temperature carburizing process and preparation method

Abstract

The invention discloses novel carburized gear steel based on a high-temperature carburizing process and a preparation method thereof. The novel carburized gear steel comprises the following chemical elements in percentage by mass: 0.19-0.25% of C; 0.15 to 0.35 percent of Si; 0.80% to 1.20% of Mn; p is less than or equal to 0.03%; s is 0.010% to 0.030%; 0.40 to 0.60 percent of Cr; 0.10 to 0.18% of Mo; 0.02 to 0.050 percent of Al; 0.005% to 0.025% of Nb; 0.01-0.02% of N, and the balance Fe and other inevitable residual elements. Through the reasonable design of carbon, silicon, manganese, chromium, molybdenum and sulfur and the adoption of aluminum, niobium and nitrogen matched second-phase particle refined grain and high-temperature rolling technology, the prepared carburizing gear steel meets the requirement of a high-temperature carburizing process, the carburizing time is obviously shortened, the alloy cost is obviously reduced, the energy consumption is effectively reduced, and the austenite grain size is fine and uniform.

Description

Technical Field

[0001] The present invention relates to the technical field of metal materials, and in particular to a novel carburized gear steel based on a high temperature carburizing process and a preparation method thereof. Background Art

[0002] In the field of modern industrial manufacturing, gear steel is one of the key mechanical structural materials, and its performance is directly related to the operating efficiency, durability and reliability of mechanical equipment. Although traditional carburized gear steel has good hardness and wear resistance, its production process is energy-intensive, costly, and imposes a certain burden on the environment. With the improvement of global awareness of energy conservation, emission reduction and green environmental protection, the development of a low-cost, high-temperature carburized new type of gear steel has become an urgent need in the industry. Summary of the invention

[0003] The purpose of the present invention is to provide a new type of carburized gear steel and a preparation method based on a high temperature carburizing process, so as to solve the problems existing in the prior art of high material alloy cost, low carburizing temperature, long time, high energy consumption and low efficiency.

[0004] To achieve the above-mentioned purpose, the present invention provides the following technical solution: a new type of carburizing gear steel based on a high-temperature carburizing process, wherein the mass percentage content of chemical elements in the carburizing gear steel is in the following range: C 0.19-0.25%; Si 0.15-0.35%; Mn 0.80-1.20%; P≤0.02%; S0.010-0.030%; Cr 0.40-0.60%; Mo 0.10-0.18%; Al 0.02-0.050%; Nb 0.005-0.025%; N 0.01-0.02%; the rest are Fe and other inevitable residual elements.

[0005] Preferably, the carburized gear steel meets the technical requirement of being kept at 1000° C. for 6 hours and having an austenite grain size not coarser than grade 6.0.

[0006] The present invention also provides a method for preparing a novel carburized gear steel based on a high temperature carburizing process, the method sequentially comprising the steps of converter primary refining, LF refining, RH vacuum degassing, continuous casting, hot rolling, and inspection and verification.

[0007] Further, the converter primary refining comprises the following steps:

[0008] 1) Batching and charging: Use molten iron and scrap steel, charging ratio: 80% molten iron + 20% scrap steel, total charging volume 120±10 tons, first charge scrap steel and then molten iron;

[0009] 2) Oxygen blowing: The blowing adopts staged fixed flow and variable gun operation. The ignition gun position is set at 1400-1700mm. After the ignition is normal, it is raised to the normal blowing gun position of 1500-1700mm; the ignition oxygen flow rate is 10000Nm 3 / h, increase oxygen supply step by step to a working oxygen flow rate of 16000~26000Nm 3 / h; before starting the converter, the deep blowing time should be ≥40s, and the oxygen supply should be increased to 23000Nm 3 / h or more, the deep blowing gun position shall not be lower than 900mm, which is conducive to deep decarburization;

[0010] 3) Slag making: After the ignition is normal, add the first batch of lime, the amount of which is 1 / 3 to 1 / 2 of the total amount. According to the slag-forming situation, limestone or dolomite can be added to balance the temperature. After the first batch of materials is added, lime or self-produced return ore or steelmaking dust removal briquette and other iron-containing oxides are continuously added. The amount of slag added in each batch is 200 to 400 kg to prevent the converter from overflowing slag or the temperature from rising too fast; the amount of magnesium material added is 200 to 400 kg each time, and the final slag target is controlled at 8 to 12%; fluorite or fluorite balls are generally added as flux when the slag is dried and the slag-forming is poor in the later stage. A single batch of fluorite or fluorite balls shall not be greater than 100 kg;

[0011] 4) Steel tapping: The steel tapping temperature is 1600-1640°C, and the steel tapping amount is controlled at 110±5 tons. Slag making and ladle alloying are performed during the steel tapping process. The adding sequence is: aluminum ingot→pre-melted slag→alloy→lime; the proportion of the steel tapping slag is: 600kg lime, 450kg pre-melted slag, and 160kg aluminum ingot; the alloy content in the obtained primary steel water is: C 0.12-0.16%, P≤0.015%, Si 0.14-0.18%, Mn 0.80-1.00%, Cr 0.40-0.50%, Mo 0.10-0.15, and Al 0.06-0.08%.

[0012] Further, the LF refining comprises the following steps:

[0013] 1) Entering LF refining: The temperature of the molten steel entering the LF station is ≥1500℃, and the argon flow rate before power supply is 300-400NL / min;

[0014] 2) Adjust slag temperature: supply power to increase temperature for 2-3 minutes, add 100-200kg of lime and 0-100kg of slag dissolving agent to adjust slag according to the slag condition; add 30kg of Al particles and 160-240kg of silicon carbide powder to diffuse and deoxidize the slag, and add them several times according to the slag condition;

[0015] 3) LF refining process: The first component sample entering LF refining is tested for Al content of 0.045-0.060%; if the Al content is not within the range, the Al line is fed in time according to the target of 0.060%, nitrogen is blown at the bottom of the whole LF process, and alloy is added according to the component requirements. After LF refining, the chemical composition is sampled and analyzed, and the chemical composition of the alloy meets the following standards: C 0.19-0.25%; Si 0.15-0.35%; Mn 0.80-1.20%; P≤0.02%; Cr 0.40-0.60%; Mo 0.10-0.18%; Al 0.02-0.050%; Nb 0.005-0.025%. When the temperature is 1600-1610°C, it enters the RH treatment station.

[0016] Furthermore, the RH vacuum degassing step is as follows: the RH station adopts nitrogen circulation, and the high vacuum is maintained for ≥20 minutes; the high vacuum refers to the situation where the vacuum degree is ≤67Pa; after the RH is completed, a nitrogen sample is taken for analysis, and according to the N content in the steel, a nitrogen-manganese wire is fed by a wire feeder so that the N content reaches 0.01-0.02%; in addition, according to the S content in the steel, an S wire is fed by a wire feeder so that the S content reaches the requirement of 0.010-0.030%; after the vacuum treatment, a weak argon stirring operation is performed, and the argon flow rate is 30-50NL / min, and the molten steel shall not be exposed.

[0017] Furthermore, the continuous casting step is: using a 5-machine 5-stream arc continuous casting unit for casting, controlling the continuous casting superheat at 15-25°C, and controlling the casting speed at 0.70-0.75m / min.

[0018] Furthermore, the heating rolling steps are: heating temperature and time, heating stage 1 temperature 1000-1150°C; heating stage 2 temperature 1220-1240°C; soaking stage temperature 1220-1250°C; total heating time ≥4.5-6.5h; final rolling temperature ≥960°C.

[0019] Furthermore, the inspection and verification steps are as follows: cut a 1 / 4 circle with a thickness of 20 mm from the rolled steel, heat it to 1000°C in a box-type resistance furnace, keep it warm for 6 hours, quench it with water after it is taken out of the furnace, then grind and polish the cross section, corrode it with 5% picric acid ethanol solution, and observe the austenite grain size of the sample under an optical microscope at 100 times.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The present invention designs a new type of carburizing gear steel with a reasonable ratio based on a high-temperature carburizing process according to the material requirements for high-temperature carburizing, high hardness, high fatigue life, low cost and good processing performance. By rationally designing carbon, silicon, manganese, chromium, molybdenum and sulfur, the content of expensive chromium and molybdenum alloys is reduced compared with traditional chromium-molybdenum series carburizing gear steels, and the content of cheap carbon and manganese is increased, which significantly reduces the alloy cost while ensuring the material performance.

[0022] (2) The new type of carburizing gear steel based on high temperature carburizing process involved in the present invention adopts the second phase particle refinement of aluminum, niobium and nitrogen and high temperature rolling technology, and adopts the steel prepared by converter primary smelting, LF refining, RH vacuum degassing, continuous casting, hot rolling and inspection and verification steps to meet the high temperature carburizing requirements. The grain size is not coarser than grade 6 when kept at 1000°C for 6 hours, which can significantly shorten the carburizing time and reduce energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is the microstructure diagram of the T1 sample of Example 1;

[0024] Figure 2 The microstructure diagram of the T2 sample of Example 2;

[0025] Figure 3 This is the microstructure diagram of the T3 sample of Example 3. DETAILED DESCRIPTION

[0026] In order to make the purpose and technical solution of the present invention clearly and completely described, and the advantages more clearly understood, the embodiments of the present invention are further described in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are part of the embodiments of the present invention, rather than all of the embodiments, and are only used to explain the embodiments of the present invention, and are not used to limit the embodiments of the present invention. All other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] Embodiment 1

[0028] The present embodiment provides a new carburizing gear steel and a preparation method based on a high temperature carburizing process, wherein the mass percentage content of chemical elements in the new carburizing gear steel is as follows: C 0.20%; Si 0.18%; Mn 0.90%; P0.013%; Cr 0.48%; Mo 0.12%; Al 0.035%; Nb 0.008%; the rest are Fe and other inevitable residual elements.

[0029] The preparation method includes six steps in sequence: converter primary refining, LF refining, RH vacuum degassing, continuous casting, hot rolling, and inspection and verification. The specific operation process is as follows:

[0030] (1) Converter primary refining:

[0031] 1) Batching and charging: Use molten iron and scrap steel, the charging ratio is: 96 tons of molten iron, 24 tons of scrap steel, the total charging volume is 120 tons, first load the scrap steel and then add the molten iron.

[0032] 2) Oxygen blowing: Blowing adopts staged fixed flow and variable gun operation. The ignition gun position is set to 1400mm, and after normal ignition (about 30s), it is raised to the normal blowing gun position of 1500mm; ignition oxygen flow rate is 10000Nm 3 / h, increase oxygen supply step by step to the working oxygen flow rate of 18000Nm 3 / h; before starting the converter, the deep blowing time is ≥40s and the oxygen supply is increased to 23000Nm 3 / h or above, the deep blowing gun position shall not be lower than 900mm, which is conducive to deep decarburization.

[0033] 3) Slag making: After the ignition is normal, add the first batch of lime, the amount of which is 1 / 3 to 1 / 2 of the total amount. Limestone or dolomite can be added to balance the temperature according to the slag-forming situation. After the first batch of materials are added, lime or self-produced return ore or steelmaking dust removal briquette and other iron-containing oxides are continuously added. The amount of slag added in each batch is 200 to 400 kg to prevent the converter from overflowing slag or the temperature from rising too fast; 200 to 400 kg of magnesium material is added each time, and the target of final slag (MgO) is controlled at 8 to 12%; fluorite or fluorite balls are generally added as flux when the slag is dried and the slag-forming is poor in the later stage. A single batch of fluorite or fluorite balls shall not exceed 100 kg.

[0034] 4) Steel tapping: The steel tapping temperature is 1605°C, and the steel tapping amount is controlled at 115 tons. Slag making and ladle alloying are carried out during the steel tapping process. The adding order is: aluminum ingot → pre-melted slag → alloy → lime; the proportion of steel tapping slag is: 600kg lime, 450kg pre-melted slag, and 160kg aluminum ingot; the alloy content in the obtained primary steel water is: C 0.13%, P 0.013%, Si 0.15%, Mn 0.88%, Cr45%, Mo 0.12%, and Al 0.065%.

[0035] (2) LF refining:

[0036] 1) Entering LF refining: The temperature of the molten steel entering the LF station is 1510℃, and the argon flow rate before power supply is 300-400NL / min;

[0037] 2) Adjust slag temperature: supply power to increase temperature for 2-3 minutes, add 100kg lime and 50kg slag dissolving agent to adjust the slag according to the slag condition; add slag material for diffusion deoxidation, add 30kg Al particles and 180kg silicon carbide powder, and add them in multiple times according to the slag condition.

[0038] 3) LF refining process: The Al content of the first sample entering LF refining is 0.055%; N gas is blown at the bottom of the whole LF process, and alloy is added according to the component requirements. After LF refining, samples are taken for chemical composition analysis. The chemical composition of the alloy meets the following standards: C 0.20%; Si 0.18%; Mn 0.90%; P 0.013%; Cr 0.48%; Mo 0.12%; Al 0.035%; Nb 0.008%. When the temperature is 1608°C, it enters the RH treatment station.

[0039] (3) RH vacuum degassing

[0040] The RH station uses nitrogen circulation, and the high vacuum is maintained for 21 minutes; the high vacuum degree is 57Pa; after the RH is completed, a nitrogen sample is taken for analysis. According to the N content in the steel, a wire feeder is used to feed nitrogen-manganese wire so that the N content reaches 0.010%; in addition, according to the S content in the steel, a wire feeder is used to feed S wire so that the S content reaches the requirement of 0.012%; after vacuum treatment, a weak argon stirring operation is performed, the argon flow rate is 30NL / min, and the molten steel is not exposed.

[0041] (4) Continuous casting

[0042] A 5-machine 5-strand arc continuous casting unit is used to cast square billets with a cross-section of 240mm*300mm. The continuous casting overheat is controlled at 15℃ and the casting speed is controlled at 0.75m / min.

[0043] (5) Heating and rolling

[0044] The temperature of heating section 1 is 1100℃; the temperature of heating section 2 is 1220℃; the temperature of soaking section is 1220℃; the total heating time is 4.5h; the final rolling temperature is 965℃, and the rolling specification is φ75mm steel.

[0045] (6) Inspection and Verification

[0046] A quarter circle with a thickness of 20 mm was cut from the φ75 mm steel after rolling, heated to 1000°C in a box-type resistance furnace, kept warm for 6 hours, and then quenched in water. The cross section was then ground and polished, and corroded with 5% picric acid ethanol solution. The austenite grain size of the sample was observed under an optical microscope at 100 times.

[0047] A group of new carburized gear steels were prepared by the preparation method of Example 1 to obtain test pieces with the test piece number: T1.

[0048] The above-mentioned group 1 test pieces T1 were subjected to characteristic testing, and the specific testing item was austenite grain size.

[0049] The test method for austenite grain size is as follows: cut a 1 / 4 circle with a thickness of 20mm from the φ75mm steel after rolling, heat it to 1000℃ in a box-type resistance furnace, keep it warm for 6h, quench it with water after it is taken out of the furnace, then grind and polish the cross section, corrode it with 5% picric acid ethanol solution, observe the austenite grain size of the sample under an optical microscope at 100 times, and rate it according to GB / T6394-2017.

[0050] The specific test data are shown in Table 1:

[0051] Table 1

[0052] Test piece number Furnace No. Steel Type Specification Generally loose T1 D12400596 22MnCrMoH φ75mm 8.5

[0053] Example 2

[0054] The present embodiment provides a new carburizing gear steel and a preparation method based on a high temperature carburizing process, wherein the chemical element mass percentage content range of the new carburizing gear steel is: C 0.23%; Si 0.23%; Mn 1.10%; P 0.011%; Cr 0.53%; Mo 0.15%; Al 0.031%; Nb 0.015%; the rest is Fe and other inevitable residual elements.

[0055] The preparation method comprises six steps of converter primary refining, LF refining, RH vacuum degassing, continuous casting, hot rolling, and inspection and verification. The specific operation process is as follows:

[0056] (1) Converter primary refining:

[0057] 1) Batching and charging: Use molten iron and scrap steel, the charging ratio is: 94.4 tons of molten iron, 23.6 tons of scrap steel, the total charging volume is 118 tons, first load the scrap steel and then add the molten iron.

[0058] 2) Oxygen blowing: Blowing adopts staged fixed flow and variable gun operation. The ignition gun position is set to 1500mm, and after normal ignition (about 30s), it is raised to the normal blowing gun position of 1600mm; the ignition oxygen flow rate is about 10000Nm 3 / h, increase oxygen supply step by step to a working oxygen flow rate of 26000Nm 3 / h; before starting the converter, the deep blowing time is ≥40s and the oxygen supply is increased to 23000Nm 3 / h or above, the deep blowing gun position shall not be lower than 900mm, which is conducive to deep decarburization.

[0059] 3) Slag making: After the ignition is normal, add the first batch of lime, the amount of which is 1 / 3 to 1 / 2 of the total amount. Limestone or dolomite can be added to balance the temperature according to the slag-forming situation. After the first batch of materials are added, lime or self-produced return ore or steelmaking dust removal briquette and other iron-containing oxides are continuously added. The amount of slag added in each batch is 200 to 400 kg to prevent the converter from overflowing slag or the temperature from rising too fast; 200 to 400 kg of magnesium material is added each time, and the target of final slag (MgO) is controlled at 8 to 12%; fluorite or fluorite balls are generally added as flux when the slag is dried and the slag-forming is poor in the later stage. A single batch of fluorite or fluorite balls shall not exceed 100 kg.

[0060] 4) Steel tapping: The steel tapping temperature is 1600°C, and the steel tapping amount is controlled at 114 tons. Slag making and ladle alloying are carried out during the steel tapping process. The adding order is: aluminum ingot → pre-melted slag → alloy → lime; the proportion of steel tapping slag is: 600kg lime, 450kg pre-melted slag, and 160kg aluminum ingot; the alloy content in the obtained primary steel water is: C 0.15%, P 0.010%, Si 0.16%, Mn 0.95%, Cr45%, Mo 0.15%, and Al 0.07%.

[0061] (2) LF refining:

[0062] 1) Entering LF refining: The temperature of the molten steel entering the LF station is 1502℃, and the argon flow rate before power on is 300-400NL / min.

[0063] 2) Adjust slag temperature: supply power to increase temperature for 2-3 minutes, add 150kg lime and 80kg slag reducing agent according to the slag condition to adjust the slag; add slag material for diffusion deoxidation, add 30kg Al particles and 240kg silicon carbide powder, and add them in multiple times according to the slag condition.

[0064] 3) LF refining process: The Al content of the first sample entering LF refining is 0.057%; N gas is blown at the bottom of the whole LF process, and alloy is added according to the component requirements. After LF refining, samples are taken for chemical composition analysis. The chemical composition of the alloy meets the following standards: C 0.23%; Si 0.23%; Mn 1.10%; P 0.011%; Cr 0.53%; Mo 0.15%; Al 0.031%; Nb 0.015. When the temperature is 1610°C, it enters the RH treatment station.

[0065] (3) RH vacuum degassing

[0066] The RH station uses nitrogen circulation, and the high vacuum is maintained for 22 minutes; the high vacuum degree is 40Pa; after the RH is completed, a nitrogen sample is taken for analysis. According to the N content in the steel, a wire feeder is used to feed nitrogen-manganese wire so that the N content reaches 0.015%; in addition, according to the S content in the steel, a wire feeder is used to feed S wire so that the S content reaches the requirement of 0.030%; after vacuum treatment, a weak argon stirring operation is performed, the argon flow rate is 40NL / min, and the molten steel is not exposed.

[0067] (4) Continuous casting

[0068] A 5-machine 5-strand arc continuous casting unit is used to cast square billets with a cross-section of 240mm*300mm. The continuous casting overheat is controlled at 20℃ and the casting speed is controlled at 0.73m / min.

[0069] (5) Heating and rolling

[0070] The temperature of heating section 1 is 1150℃; the temperature of heating section 2 is 1230℃; the temperature of soaking section is 1235℃; the total heating time is 5.5h; the final rolling temperature is 968℃, and the rolling specification is φ75mm steel.

[0071] (6) Inspection and Verification

[0072] A quarter circle with a thickness of 20 mm was cut from the φ75 mm steel after rolling, heated to 1000°C in a box-type resistance furnace, kept warm for 6 hours, and then quenched in water. The cross section was then ground and polished, and corroded with 5% picric acid ethanol solution. The austenite grain size of the sample was observed under an optical microscope at 100 times.

[0073] A group of new carburized gear steels were prepared by the preparation method of Example 2 to obtain test pieces with the test piece number: T2.

[0074] The above-mentioned group 1 test pieces T2 were subjected to characteristic testing, and the specific testing item was austenite grain size.

[0075] The test method for austenite grain size is as follows: cut a 1 / 4 circle with a thickness of 20mm from the φ75mm steel after rolling, heat it to 1000℃ in a box-type resistance furnace, keep it warm for 6h, quench it with water after it is taken out of the furnace, then grind and polish the cross section, corrode it with 5% picric acid ethanol solution, observe the austenite grain size of the sample under an optical microscope at 100 times, and rate it according to GB / T6394-2017.

[0076] The specific test data are shown in Table 2:

[0077] Table 2

[0078] Test piece number Furnace No. Steel Type Specification Generally loose T2 D12401526 22MnCrMoH φ75mm 8.5

[0079] Example 3

[0080] The present embodiment provides a new carburizing gear steel and a preparation method based on a high temperature carburizing process, wherein the chemical element mass percentage content range of the new carburizing gear steel is: C 0.25%; Si 0.33%; Mn 1.18%; P 0.011%; Cr 0.57%; Mo 0.18%; Al 0.045%; Nb 0.024%; the rest is Fe and other inevitable residual elements.

[0081] The preparation method includes six steps: converter primary refining, LF refining, RH vacuum degassing, continuous casting, hot rolling, and inspection and verification. The specific operation process is as follows:

[0082] (1) Converter primary refining:

[0083] 1) Batching and charging: Use molten iron and scrap steel, the charging ratio is: 97.6 tons of molten iron, 24.4 tons of scrap steel, the total charging volume is 122 tons, first load the scrap steel and then add the molten iron.

[0084] 2) Oxygen blowing: Blowing adopts staged fixed flow and variable gun operation. The ignition gun position is set to 1650mm, and after normal ignition (about 30s), it is raised to the normal blowing gun position of 1700mm; ignition oxygen flow rate is 10000Nm 3 / h, increase oxygen supply step by step to a working oxygen flow rate of 26000Nm 3 / h; before starting the converter, the deep blowing time is ≥40s and the oxygen supply is increased to 23000Nm 3 / h or above, the deep blowing gun position shall not be lower than 900mm, which is conducive to deep decarburization.

[0085] 3) Slag making: After the ignition is normal, add the first batch of lime, the amount of which is 1 / 3 to 1 / 2 of the total amount. Limestone or dolomite can be added to balance the temperature according to the slag-forming situation. After the first batch of materials are added, lime or self-produced return ore or steelmaking dust removal briquette and other iron-containing oxides are continuously added. The amount of slag added in each batch is 200 to 400 kg to prevent the converter from overflowing slag or the temperature from rising too fast; 200 to 400 kg of magnesium material is added each time, and the target of final slag (MgO) is controlled at 8 to 12%; fluorite or fluorite balls are generally added as flux when the slag is dried and the slag-forming is poor in the later stage. A single batch of fluorite or fluorite balls shall not exceed 100 kg.

[0086] 4) Steel tapping: The steel tapping temperature is 1640°C, and the steel tapping amount is controlled at 105 tons. Slag making and ladle alloying are performed during the steel tapping process. The adding sequence is: aluminum ingot → pre-melted slag → alloy → lime; the proportion of steel tapping slag is: 600kg lime, 450kg pre-melted slag, and 160kg aluminum ingot; the alloy content in the obtained primary steel water is: C 0.16%, P 0.011%, Si 0.18%, Mn 1.00%, Cr50%, Mo 0.15%, and Al 0.08%.

[0087] (2) LF refining:

[0088] 1) Entering LF refining: The temperature of the molten steel entering the LF station is 1502℃, and the argon flow rate before power on is 300-400NL / min.

[0089] 2) Adjust slag temperature: supply power to increase temperature for 2-3 minutes, add 200kg lime and 100kg slag dissolving agent to adjust the slag according to the slag condition; add slag material for diffusion deoxidation, add 30kg Al particles and 240kg silicon carbide powder, and add them in multiple times according to the slag condition.

[0090] 3) LF refining process: The Al content of the first sample entering LF refining is 0.060%; N gas is blown at the bottom of the whole LF process, and alloy is added according to the component requirements. After LF refining, samples are taken for chemical composition analysis. The chemical composition of the alloy meets the following standards: C 0.25%; Si 0.33%; Mn 1.18%; P 0.011%; Cr 0.57%; Mo 0.18%; Al 0.045%; Nb 0.024%. When the temperature is 1600°C, it enters the RH treatment station.

[0091] (3) RH vacuum degassing

[0092] The RH station uses nitrogen circulation, and the high vacuum is maintained for 25 minutes; the high vacuum degree is 55Pa; after the RH is completed, a nitrogen sample is taken for analysis. According to the N content in the steel, a wire feeder is used to feed nitrogen-manganese wire so that the N content reaches 0.02%; in addition, according to the S content in the steel, a wire feeder is used to feed S wire so that the S content reaches the requirement of 0.030%; after vacuum treatment, a weak argon stirring operation is performed, the argon flow rate is 50NL / min, and the molten steel is not exposed.

[0093] (4) Continuous casting

[0094] A 5-machine 5-strand arc continuous casting unit is used to cast square billets with a cross-section of 240mm*300mm. The continuous casting overheat is controlled at 25℃ and the casting speed is controlled at 0.70m / min.

[0095] (5) Heating and rolling

[0096] The temperature of heating section 1 is 1000℃; the temperature of heating section 2 is 1240℃; the temperature of soaking section is 1250℃; the total heating time is 6.5h; the final rolling temperature is 964℃, and the rolling specification is φ75mm steel.

[0097] (6) Inspection and Verification

[0098] A quarter circle with a thickness of 20 mm was cut from the φ75 mm steel after rolling, heated to 1000°C in a box-type resistance furnace, kept warm for 6 hours, and then quenched in water. The cross section was then ground and polished, and corroded with 5% picric acid ethanol solution. The austenite grain size of the sample was observed under an optical microscope at 100 times.

[0099] A group of new carburized gear steels were prepared by the preparation method of Example 3 to obtain test pieces with the test piece number: T3.

[0100] The above-mentioned group 1 test pieces T3 were subjected to characteristic testing, and the specific testing item was austenite grain size.

[0101] The test method for austenite grain size is as follows: cut a 1 / 4 circle with a thickness of 20mm from the φ75mm steel after rolling, heat it to 1000℃ in a box-type resistance furnace, keep it warm for 6h, quench it with water after it is taken out of the furnace, then grind and polish the cross section, corrode it with 5% picric acid ethanol solution, observe the austenite grain size of the sample under an optical microscope at 100 times, and rate it according to GB / T6394-2017.

[0102] The specific test data are shown in Table 3:

[0103] Table 3

[0104] Test piece number Furnace No. Steel Type Specification Generally loose T3 D12401539 22MnCrMoH φ75mm 9.5

[0105] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A new type of carburized gear steel based on high temperature carburizing process, characterized by: The mass percentage content range of the chemical elements of the carburized gear steel is: C 0.19-0.25%; Si 0.15-0.35%; Mn 0.80-1.20%; P≤0.02%; S 0.010-0.030%; Cr 0.40-0.60%; Mo 0.10-0.18%; Al 0.02-0.050%; Nb0.005-0.025%; N 0.01-0.02%; the rest are Fe and other inevitable residual elements.

2. The new carburized gear steel based on high temperature carburizing process according to claim 1 is characterized in that: The carburized gear steel meets the technical requirements of being kept at a temperature of 1000° C. for 6 hours and having an austenite grain size not coarser than grade 6.

0.

3. A method for preparing a new type of carburized gear steel based on a high temperature carburizing process, characterized in that: The method comprises the steps of converter primary refining, LF refining, RH vacuum degassing, continuous casting, hot rolling and inspection and verification in sequence.

4. The method for preparing a new type of carburized gear steel based on a high temperature carburizing process according to claim 3, characterized in that: The converter primary refining comprises the following steps: 1) Batching and charging: Use molten iron and scrap steel, charging ratio: 80% molten iron + 20% scrap steel, total charging volume 120±10 tons, first charge scrap steel and then molten iron; 2) Oxygen blowing: The blowing adopts staged fixed flow and variable gun operation. The ignition gun position is set at 1400-1700mm. After the ignition is normal, it is raised to the normal blowing gun position of 1500-1700mm; the ignition oxygen flow rate is 10000Nm 3 / h, increase oxygen supply step by step to a working oxygen flow rate of 16000-26000Nm 3 / h; before starting the converter, the deep blowing time should be ≥40s, and the oxygen supply should be increased to 23000Nm 3 / h or more, the deep blowing gun position shall not be lower than 900mm, which is conducive to deep decarburization; 3) Slag making: After the ignition is normal, add the first batch of lime, the amount of which is 1 / 3 to 1 / 2 of the total amount. According to the slag-forming situation, limestone or dolomite can be added to balance the temperature. After the first batch of materials is added, lime or self-produced return ore or steelmaking dust removal briquette and other iron-containing oxides are continuously added. The amount of slag added in each batch is 200 to 400 kg to prevent the converter from overflowing slag or the temperature from rising too fast; the amount of magnesium material added is 200 to 400 kg each time, and the final slag target is controlled at 8 to 12%; fluorite or fluorite balls are generally added as flux when the slag is dried and the slag-forming is poor in the later stage. A single batch of fluorite or fluorite balls shall not be greater than 100 kg; 4) Steel tapping: The steel tapping temperature is 1600-1640°C, and the steel tapping amount is controlled at 110±5 tons. Slag making and ladle alloying are performed during the steel tapping process. The adding sequence is: aluminum ingot→pre-melted slag→alloy→lime; the proportion of the steel tapping slag is: 600kg lime, 450kg pre-melted slag, and 160kg aluminum ingot; the alloy content in the obtained primary steel water is: C 0.12-0.16%, P≤0.015%, Si 0.14-0.18%, Mn 0.80-1.00%, Cr 0.40-0.50%, Mo 0.10-0.15, and Al 0.06-0.08%.

5. The method for preparing a new type of carburized gear steel based on a high temperature carburizing process according to claim 3, characterized in that: The LF refining comprises the following steps: 1) Entering LF refining: The temperature of the molten steel entering the LF station is ≥1500℃, and the argon flow rate before power supply is 300-400NL / min; 2) Adjust slag temperature: supply power to increase temperature for 2-3 minutes, add 100-200kg of lime and 0-100kg of slag dissolving agent to adjust slag according to the slag condition; add 30kg of Al particles and 160-240kg of silicon carbide powder to diffuse and deoxidize the slag, and add them several times according to the slag condition; 3) LF refining process: The first component sample entering LF refining is tested for Al content of 0.045-0.060%; if the Al content is not within the range, the Al line is fed in time according to the target of 0.060%, nitrogen is blown at the bottom of the whole LF process, and alloy is added according to the component requirements. After LF refining, the chemical composition is sampled and analyzed, and the chemical composition of the alloy meets the following standards: C 0.19-0.25%; Si 0.15-0.35%; Mn0.80-1.20%; P≤0.02%; Cr 0.40-0.60%; Mo 0.10-0.18%; Al 0.02-0.050%; Nb0.005-0.025%. When the temperature is 1600-1610°C, it enters the RH treatment station.

6. The method for preparing a new type of carburized gear steel based on a high temperature carburizing process according to claim 3, characterized in that: The steps of RH vacuum degassing are as follows: nitrogen circulation is adopted in the RH station, and the high vacuum is maintained for ≥20 minutes; the high vacuum refers to the situation where the vacuum degree is ≤67Pa; after the RH is finished, a nitrogen sample is taken for analysis, and according to the N content in the steel, nitrogen-manganese wire is fed by a wire feeder to make the N content reach 0.01-0.02%; in addition, according to the S content in the steel, S wire is fed by a wire feeder to make the S content reach the requirement of 0.010-0.030%; after the vacuum treatment, a weak argon stirring operation is performed, and the argon flow rate is 30-50NL / min, and the molten steel shall not be exposed.

7. The method for preparing a new type of carburized gear steel based on a high temperature carburizing process according to claim 3, characterized in that: The continuous casting steps are: using a 5-machine 5-stream arc continuous casting unit for casting, controlling the continuous casting overheat at 15-25° C., and controlling the casting speed at 0.70-0.75 m / min.

8. The method for preparing a new type of carburized gear steel based on a high temperature carburizing process according to claim 3, characterized in that: The steps of heating rolling are: heating temperature and time, heating stage 1 temperature 1000-1150°C; heating stage 2 temperature 1220-1240°C; soaking stage temperature 1220-1250°C; total heating time ≥4.5-6.5h; final rolling temperature ≥960°C.

9. The method for preparing a new type of carburized gear steel based on a high temperature carburizing process according to claim 3, characterized in that: The inspection and verification steps are as follows: cut a 1 / 4 circle with a thickness of 20 mm from the rolled steel, heat it to 1000° C. in a box-type resistance furnace, keep it warm for 6 hours, quench it with water after it is taken out of the furnace, then grind and polish the cross section, corrode it with 5% picric acid ethanol solution, and observe the austenite grain size of the sample under an optical microscope at 100 times.

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