Method for producing 20CrMnTiH high-sulfur free-cutting narrow-hardenability gear steel for automobiles

Abstract

The invention discloses a method for producing 20CrMnTiH high-sulfur free-cutting narrow-hardenability gear steel for an automobile, and particularly relates to a method for producing the 20CrMnTiH high-sulfur free-cutting narrow-hardenability gear steel for the automobile by using a converter, LF refining, VD vacuum treatment, phi 180 round billet continuous casting and round steel hot rolling. The high-quality gear steel which is high in grade, narrow in hardenability bandwidth, high in purity, fine in grain and good in machining performance (such as easy cutting, cold extrusion and forging) is efficiently produced at low cost. And the economic benefit is improved.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to a method for producing 20CrMnTiH high-sulfur, easy-to-cut, narrow hardenability gear steel for automobiles. Background Art

[0002] Automobile gear is one of the important parts of automobiles, which plays the role of transmitting power. At present, people's requirements for automobile high speed, safety, comfort, energy saving, environmental protection and other performance are becoming more and more stringent. The transmission system is developing towards miniaturization, light weight and high power, which requires improving gear life, transmission accuracy and reducing gear cost. Therefore, the load on automobile gears is getting bigger and bigger, and the requirements for the quality of automobile gear steel are getting higher and higher. Representative steel grades of gear steel: 20CrMnTiH, 20CrMoH, SCM822H (Japanese brand Cr-Mo series steel), 20Cr, 40Cr, 28MnCr5 (German brand Mn-Cr series steel), SAE8620H (American brand Cr-Ni-Mo series steel). Automobile gear steel belongs to structural steel, among which alloy structural steel is the main one, and the proportion of carburized gear steel is constantly expanding. Although various types of gear steel have been developed and introduced, my country has abundant manganese, chromium and titanium resources, which enables my country to produce gear steel at low cost, so 20CrMnTiH gear steel is still widely used. There are basically two production processes for gear steel in my country: 1. EF (or BOF) + LFV (or VAD, RH) refining - die casting - initial rolling and blanking - horizontal rolling mill or semi-continuous rolling to make products. 2. UHP (EBT) + LF\VD refining - continuous casting of alloy steel billets - semi-continuous rolling to make products. Comparing the two processes, it is obvious that continuous casting has gradually replaced the die casting process. Compared with electric furnace steelmaking, converter steelmaking has the advantages of simple raw materials, high hit rate of terminal temperature and composition, and short production cycle. The scrap steel used in electric furnace steelmaking has a high residual element content, which limits the production of high-quality steel, so converter steelmaking can improve product quality and reduce production costs. The use of converter-LF\VD refining-continuous casting smelting process has changed the history of special steels that were mostly produced by electric furnaces in the past. Summary of the invention

[0003] The purpose of the present invention is to provide a method for producing 20CrMnTiH high-sulfur easy-to-cut narrow hardenability gear steel for automobiles by using converter-LF refining-VD vacuum treatment-Φ180 round billet continuous casting-hot rolled round steel. Through the converter-LF\VD refining-continuous casting smelting process, high-grade narrow hardenability bandwidth, high purity, fine grains, good processing performance (such as easy chipping, cold extrusion, forging, etc.) high-quality gear steel can be produced efficiently and at low cost, achieving improved economic benefits.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] The invention discloses a method for producing 20CrMnTiH high-sulfur free-cutting narrow hardenability gear steel for automobiles. The high-sulfur free-cutting narrow hardenability gear steel comprises the following components in percentage by weight: C: 0.18-0.21%, Si: 0.20-0.30%, Mn: 0.85-0.95%, P: ≤0.020%, S: 0.020-0.030%, Cr: 1.00-1.20%, Ti: 0.05-0.075%, Al: 0.010-0.030%, Mo: ≤0.003%, Cu: ≤0.001%, Ni: ≤0.008%, W: ≤0.003%, and the remainder is Fe and unavoidable impurities.

[0006] The process flow is: blast furnace molten iron - 120 tons top and bottom composite blowing converter - LF refining - VD vacuum treatment - Φ180mm round billet continuous casting - semi-continuous rolling of bars into Φ50~Φ75 round steel; among which:

[0007] The composition and temperature of the molten iron in the converter are as follows: Si 0.47-0.62%, Mn 0.51-0.57%, P 0.088-0.096%, S 0.04-0.052%, T 1274-1275℃;

[0008] Considering that the finished molten steel must have a certain sulfur content, the molten iron does not need to be desulfurized. The sulfur element in the molten iron can be partially removed in the converter, LF, and VD.

[0009] Converter endpoint composition and temperature control: C ≥ 0.06%, P ≤ 0.015%, T ≥ 1630℃;

[0010] Converter end point deoxidation alloying:

[0011] The steel is deoxidized by aluminum-manganese-iron deoxidizer at the end of the converter;

[0012] Silicon manganese and ferrochrome are added into the ladle to alloy the steel, the amount of slag in the converter is strictly controlled, pneumatic slag blocking is used during the steel tapping process, and the thickness of the slag layer after steel tapping is controlled within 80mm;

[0013] LF refining process control and slag making process:

[0014] After the ladle enters the LF station, 550-750 kg of lime, 200 kg of bauxite and 150-200 kg of fluorite are added to make a refining slag with high basicity, good reducibility and fluidity; during the LF refining process, 100 kg of calcium carbide is added to the slag surface for continuous deoxidation to ensure that the slag color becomes white and has good fluidity; using this slag-making process and adding a small amount of 15 kg of aluminum-manganese-iron deoxidation, the slag basicity is controlled at 2.4-2.6, with strong reducibility, belonging to the typical white slag, which can play a strong role in deoxidation, desulfurization and inclusion removal.

[0015] Alloys are added according to the composition of molten steel, and the alloy composition is adjusted and controlled according to internal control standards; LF refining is stirred with argon blowing throughout the process, so that steel and slag react fully, and degassing, inclusion removal and sulfur removal are strengthened;

[0016] VD vacuum treatment process control:

[0017] The average time for deep space vacuum treatment in VD furnace is 11-13min, the average vacuum degree is 0.008-0.012kpa, the average soft blowing time is 13-15min, and the soft blowing flow rate is 86-90L / min;

[0018] After vacuum degassing in the VD furnace, titanium-iron alloy is added;

[0019] After the vacuum treatment of the VD furnace is completed, 100 to 170 meters of sulfur wire is fed according to the sulfur content in the molten steel to make the sulfur content in the molten steel reach the target value; then about 200 meters of silicon calcium wire is fed;

[0020] Continuous casting process control:

[0021] The casting process is protected throughout the process. The electromagnetic stirring of the crystallizer adopts the stirring mode of forward brick → stop → reverse. The stirring current is 100-320A, the stirring frequency is 2.0-3.0Hz, and the secondary cooling water volume is controlled at 0.45L / kg. The billet specification is Φ180mm. The average value of continuous casting superheat control is 30.6℃. The average pulling speed is 1.68m / min. There are no defects such as scars, pits and bubbles on the surface of the continuous casting billet, and there is no obvious component segregation inside. The continuous casting billet is stacked and slowly cooled for 24 hours. No hydrogen white spots and thermal stress cracks are found in the billet inspection.

[0022] Bar semi-continuous rolling process control:

[0023] The heating process is carried out in a walking beam furnace, with a preheating temperature of 850-900°C; a heating section temperature of 1200-1250°C; a soaking section temperature of 1180-1230°C, and a total heating time of 4 hours and 50 minutes. The heating process requires that the temperature of the ingot is uniform, the temperature difference between the inside and outside of the ingot is controlled within 20°C, and the steel tapping speed is uniform.

[0024] The starting rolling temperature is 1090-1190℃; the rolling time for each piece is 1 minute 25 seconds - 1 minute 35 seconds, and the final rolling temperature is 880-980℃; after the rolled material comes off the cooling bed, it is stacked and slowly cooled for 24 hours at 600-700℃.

[0025] Furthermore, the converter temperature is 1274.6°C.

[0026] Furthermore, the average time for deep space vacuum treatment in the VD furnace is 12 min, the average vacuum degree is 0.01 kPa, the average time for soft blowing is 14 min, and the soft blowing flow rate is 88 L / min.

[0027] Furthermore, the components of the high-sulfur free-cutting narrow hardenability gear steel are as follows by weight percentage: C: 0.205%, Si: 0.234%, Mn: 0.89%, P: 0.017%, S: 0.027%, Cr: 1.11%, Ti: 0.06%, Al: 0.029%, Mo: 0.003%, Cu: 0.001%, Ni: 0.008%, W: 0.003%, and the rest is Fe and unavoidable impurities.

[0028] Furthermore, the components of the high-sulfur free-cutting narrow hardenability gear steel are as follows by weight percentage: C: 0.194%, Si: 0.286%, Mn: 0.901%, P: 0.016%, S: 0.028%, Cr: 1.108%, Ti: 0.069%, Al: 0.029%, Mo: 0.003%, Cu: 0.001%, Ni: 0.008%, W: 0.003%, and the rest is Fe and unavoidable impurities.

[0029] Furthermore, the components of the high-sulfur free-cutting narrow hardenability gear steel are as follows by weight percentage: C: 0.203%, Si: 0.256%, Mn: 0.888%, P: 0.014%, S: 0.023%, Cr: 1.084%, Ti: 0.056%, Al: 0.027%, Mo: 0.003%, Cu: 0.001%, Ni: 0.008%, W: 0.003%, and the rest are Fe and unavoidable impurities.

[0030] Compared with the prior art, the beneficial technical effects of the present invention are:

[0031] The process control of producing 20CrMnTiH high-sulfur easy-cutting narrow hardenability gear steel for automobiles through converter-LF refining-VD vacuum treatment-Φ180 round billet continuous casting-hot rolled round steel can meet the uniform performance of automobile gear steel and appropriate strength and toughness combination, ensuring the reliable performance of the parts made of it. At the same time, it meets the procurement standards and market access conditions for vehicle gear steel stipulated by the Gear Association, namely:

[0032] (1) Hardenability and hardenability bandwidth. Hardenability is the lower and middle limits of hardenability J9 (28-34) and J15 (≤30) of the national standard GB / T5216-2004. Bandwidth ≤6HRC. Three end-quenched samples are taken from different materials of the same furnace number for end quenching. The dispersion of the three end-quenching values ​​is ≤4. The end quenching and hardenability bandwidth results all meet the requirements. (2) Cleanliness. The requirement is T〔O〕≤20ppm. The test result is T〔O〕≤14ppm, which meets all the requirements. (3) Grain size. The austenite grain size of steel is ≥5 levels. The test result shows that the austenite grain size is ≥8.5 levels. (4) Non-metallic inclusion control of steel. The requirements are A≤3.5, B, C, D≤2.0. The test inclusion rating results are A≤2.5, B, C, D≤1.5. The steel has a high purity. (5) The finished product is easy to cut in subsequent processing, which requires a certain sulfur content (0.020% to 0.035%). The test results show that the sulfur content is (0.022-0.030).

[0033] This method has high reliability and practicality, and can use converter-LF refining-VD vacuum treatment-continuous casting-hot rolling round steel to efficiently and low-cost produce high-grade narrow hardenability bandwidth, high purity, fine grains, good processing performance (such as easy chipping, cold extrusion, forging, etc.) high-quality gear steel, so as to achieve economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The present invention will be further described below in conjunction with the accompanying drawings.

[0035] Figure 1 It is the material end hardenability test result;

[0036] Figure 2 This is the result of ordinary low-magnification inspection of gear steel ingot;

[0037] Figure 3 This is the result of banded structure testing on the material. DETAILED DESCRIPTION

[0038] A method for producing 20CrMnTiH high-sulfur free-cutting narrow hardenability gear steel for automobiles, the specific operation of the present invention is as follows:

[0039] 1. The present invention provides a method for producing 20CrMnTiH high-sulfur easy-cutting narrow hardenability gear steel for automobiles by using converter-LF refining-VD vacuum treatment-Φ180 round billet continuous casting-hot rolling round steel. According to the hardenability special requirements J9 (28-34), J15 (≤30), the bandwidth is ≤6HRC, three end quenching samples are taken from different materials of the same furnace number for end quenching, and the dispersion of the three end quenching values ​​is ≤4. The composition of the high-sulfur easy-cutting narrow hardenability gear steel is designed by weight percentage. The ratios are: C: 0.18~0.21, Si: 0.20~0.30, Mn: 0.85~0.95, P: ≤0.020, S: 0.020~0.030, Cr: 1.00~1.20, Ti: 0.05~0.075, Al: 0.010~0.030, Mo: ≤0.003, Cu: ≤0.001, Ni: ≤0.008, W: ≤0.003, and the rest are Fe and unavoidable impurities.

[0040] 2. The process flow is: blast furnace molten iron - 120 tons top and bottom composite blowing converter - LF refining - VD vacuum treatment - Φ180mm round billet continuous casting - bar semi-continuous rolling into Φ50~Φ75 round steel.

[0041] 3. Composition and temperature of molten iron entering the converter

[0042] Si Mn P S T(℃) Minimum 0.47 0.51 0.088 0.04 1274 Maximum 0.62 0.57 0.096 0.052 1275 average value 0.566 0.546 0.094 0.044 1274.6

[0043] Considering that the finished molten steel must have a certain sulfur content, the molten iron does not need to be desulfurized. Normally, part of the sulfur element in the molten iron can be removed in the converter, LF, and VD.

[0044] 4. Converter endpoint composition and temperature control

[0045] Element C P T(℃) Target control ≥0.06 ≤0.015 ≥1630 Actual control 0.096 0.0094 1628

[0046] 5. Deoxidation and alloying at the end of converter:

[0047] Aluminum-manganese-iron deoxidizer is used for deoxidation at the end of the converter, which can quickly reduce the oxygen activity of the molten steel, and the deoxidation products generated are composite oxides, which are easy to float up and be removed.

[0048] Silicon manganese and ferrochrome are added into the ladle for alloying, the amount of slag discharged from the converter is strictly controlled, pneumatic slag blocking is used in the steel-discharging process, and the thickness of the slag layer is controlled within 80 mm after steel-discharging.

[0049] 6. LF refining process control and slag making process

[0050] After the ladle enters the LF station, 550-750 kg of lime, 200 kg of bauxite, and 150-200 kg of fluorite are added to make a high basicity, reducible, and fluid refining slag. During the LF refining process, 100 kg of calcium carbide is added to the slag surface for continuous deoxidation to ensure that the slag color becomes white and has good fluidity. Using this slag-making process and adding a small amount of 15 kg of aluminum manganese iron for deoxidation, the slag basicity is controlled at about 2.5, with strong reducibility (FeO+MnO<1.25%), which is a typical white slag and can play a strong role in deoxidation, desulfurization and inclusion removal.

[0051] Alloys are added according to the composition of molten steel, and the alloy composition is adjusted and controlled according to internal control standards. Argon is blown and stirred throughout the LF refining process to fully react steel and slag, and strengthen degassing, inclusion removal and sulfur removal.

[0052] 7. VD vacuum treatment process control

[0053] The average deep space vacuum treatment time of the VD furnace is 12 minutes, the average vacuum degree is 0.01kpa, the average soft blowing time is 14 minutes, and the soft blowing flow rate is 88L / min.

[0054] Titanium-ferroalloy is added after vacuum degassing in the VD furnace. The amount of acid-soluble aluminum in the steel after the VD furnace is a sign of the deoxidation level in the steel. The average acid-soluble aluminum in the steel after vacuum deoxidation in the VD furnace is 0.034%, indicating that the oxygen activity in the steel is already very low. According to the Al-O equilibrium relationship, the oxygen activity in the steel is about 2-3ppm; when the acid-soluble aluminum content in the steel is between 0.02% and 0.03%, the titanium recovery rate is 70%.

[0055] After the vacuum treatment of the VD furnace is completed, about 100 to 170 meters of sulfur wire are fed according to the sulfur content in the molten steel to make the sulfur content in the molten steel reach the target value. Then about 200 meters of silicon calcium wire are fed to change Al2O3 and MnS into spherical mCaO·nAl2O3 and CaS through calcium treatment to prevent nozzle blockage.

[0056] 8. Continuous casting process control

[0057] The casting process is fully protected, and the electromagnetic stirring of the crystallizer adopts the forward rotation → stop → reverse stirring mode. The stirring current is 100-320A, the stirring frequency is 2.0-3.0Hz, and the secondary cooling water volume is controlled at 0.45L / kg. The billet specification is Φ180mm. The average value of continuous casting superheat control is 30.6℃, and the average pulling speed is 1.68m / min. There are no defects such as scars, pits and bubbles on the surface of the continuous casting billet, and there is no obvious component segregation inside. The continuous casting billet is stacked and slowly cooled for 24 hours, and no defects such as hydrogen white spots and thermal stress cracks are found in the billet inspection.

[0058] 9. Process control of semi-continuous rolling of bars

[0059] The heating process is carried out in a walking beam furnace, with a preheating temperature of 850-900°C, a heating section temperature of 1200-1250°C, a soaking section temperature of 1180-1230°C, and a total heating time of 4 hours and 50 minutes. The heating process requires that the temperature of the ingot is uniform, the temperature difference between the inside and outside of the ingot is controlled within 20°C, and the steel tapping speed is uniform.

[0060] The starting rolling temperature is 1090-1190℃; the rolling time for each piece is about 1 minute and 30 seconds, and the final rolling temperature is 880-980℃. After the rolled material comes off the cooling bed, it is stacked and slowly cooled for 24 hours at 600-700℃.

[0061] In order to make the method of the present invention more clear, a specific embodiment of the method is described in conjunction with the accompanying drawings.

[0062] Table 1 Chemical composition of materials

[0063]

[0064] Specific implementation 1, the gear steel bar products produced according to 1 to 9 were tested for chemical composition in a certain automobile gear transmission manufacturer. The results are shown in Table 1. The chemical composition of the materials meets the requirements of the Gear Association for vehicle gear steel. Compared with other steel mills, the residual Cu and Ni components are very small, and basically do not contain any.

[0065] Table 2 Cleanliness test

[0066] Furnace No. T〔O〕 N 11705524 14 43 11705525 14 43 11705526 14 51

[0067] Specific implementation 2: The gear steel bar products produced according to 1 to 8 were inspected for cleanliness of finished bars with diameters of Φ55 and Φ75 at a certain automobile gear transmission manufacturer. The Gear Association stipulates that the vehicle gear steel requires T〔O〕≤20ppm, and the inspection results are T〔O〕≤14ppm, which all meet the requirements. As shown in Table 2.

[0068] Table 3 Non-metallic inclusions

[0069]

[0070] Specific implementation 3: The gear steel bar products produced according to 1 to 9 were inspected for non-metallic inclusions and grain size at a certain automobile gear box manufacturer. The results all met the requirements of the gear association and the steel purity was high.

[0071] Specific implementation 4, gear steel bar products produced according to 1 to 9 are tested for end hardenability in a certain automobile gear box manufacturer, such as Figure 1 As shown, the measured end hardenability conforms to the gear specification J9, HRC28-34, bandwidth ≤6HRC, which meets the required range.

[0072] Specific implementation 5: The gear steel ingots produced according to 1 to 8 are basically qualified in the ordinary low-power inspection items, such as Figure 2 shown.

[0073] Specific implementation 6, the gear steel bar products produced according to 1 to 9 were tested for banded structure in a certain automobile gear box manufacturer, and the banded structure was measured to be level 2. Among them, the furnace number 11705526 was slightly worse, reaching level 2.5, but all met the technical requirements of gear coordination less than level 3. Figure 3 shown.

[0074] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for producing 20CrMnTiH high-sulfur free-cutting narrow hardenability gear steel for automobiles, characterized in that: The components of the high-sulfur free-cutting narrow hardenability gear steel are as follows by weight percentage: C: 0.18-0.21%, Si: 0.20-0.30%, Mn: 0.85-0.95%, P: ≤0.020%, S: 0.020-0.030%, Cr: 1.00-1.20%, Ti: 0.05-0.075%, Al: 0.010-0.030%, Mo: ≤0.003%, Cu: ≤0.001%, Ni: ≤0.008%, W: ≤0.003%, and the rest is Fe and unavoidable impurities; The process flow is: blast furnace molten iron - 120 tons top and bottom composite blowing converter - LF refining - VD vacuum treatment - Φ180mm round billet continuous casting - bar semi-continuous rolling into Φ50~Φ75 round steel; among which: The composition and temperature of the molten iron in the converter are as follows: Si 0.47-0.62%, Mn 0.51-0.57%, P 0.088-0.096%, S0.04-0.052%, T 1274-1275℃; Considering that the finished molten steel must have a certain sulfur content, the molten iron does not need to be desulfurized. The sulfur element in the molten iron can be partially removed in the converter, LF, and VD. Converter endpoint composition and temperature control: C ≥ 0.06%, P ≤ 0.015%, T ≥ 1630℃; Converter end point deoxidation alloying: The steel is deoxidized by aluminum-manganese-iron deoxidizer at the end of the converter; Silicon manganese and ferrochrome are added into the ladle to alloy the steel, the amount of slag in the converter is strictly controlled, pneumatic slag blocking is used during the steel tapping process, and the thickness of the slag layer after steel tapping is controlled within 80mm; LF refining process control and slag making process: After the ladle enters the LF station, 550-750 kg of lime, 200 kg of bauxite and 150-200 kg of fluorite are added to make a refining slag with high basicity, good reducibility and fluidity; during the LF refining process, 100 kg of calcium carbide is added to the slag surface for continuous deoxidation to ensure that the slag color becomes white and has good fluidity; using this slag-making process and adding a small amount of 15 kg of aluminum-manganese-iron deoxidation, the slag basicity is controlled at 2.4-2.6, with strong reducibility, belonging to the typical white slag, which can play a strong role in deoxidation, desulfurization and inclusion removal. Alloys are added according to the composition of molten steel, and the alloy composition is adjusted and controlled according to internal control standards; LF refining is stirred with argon blowing throughout the process, so that steel and slag react fully, and degassing, inclusion removal and sulfur removal are strengthened; VD vacuum treatment process control: The average time for deep space vacuum treatment in VD furnace is 11-13min, the average vacuum degree is 0.008-0.012kpa, the average soft blowing time is 13-15min, and the soft blowing flow rate is 86-90L / min; After vacuum degassing in the VD furnace, titanium-iron alloy is added; After the vacuum treatment of the VD furnace is completed, 100 to 170 meters of sulfur wire is fed according to the sulfur content in the molten steel to make the sulfur content in the molten steel reach the target value; then about 200 meters of silicon calcium wire is fed; Continuous casting process control: The casting process is protected throughout the process. The electromagnetic stirring of the crystallizer adopts the stirring mode of forward brick → stop → reverse. The stirring current is 100-320A, the stirring frequency is 2.0-3.0Hz, and the secondary cooling water volume is controlled at 0.45L / kg. The billet specification is Φ180mm. The average value of continuous casting superheat control is 30.6℃. The average pulling speed is 1.68m / min. There are no defects such as scars, pits and bubbles on the surface of the continuous casting billet, and there is no obvious component segregation inside. The continuous casting billet is stacked and slowly cooled for 24 hours. No hydrogen white spots and thermal stress cracks are found in the billet inspection. Bar semi-continuous rolling process control: The heating process is carried out in a walking beam furnace, with a preheating temperature of 850-900°C; a heating section temperature of 1200-1250°C; a soaking section temperature of 1180-1230°C, and a total heating time of 4 hours and 50 minutes. The heating process requires that the temperature of the ingot is uniform, the temperature difference between the inside and outside of the ingot is controlled within 20°C, and the steel tapping speed is uniform. The starting rolling temperature is 1090-1190℃; the rolling time for each piece is 1 minute 25 seconds - 1 minute 35 seconds, and the final rolling temperature is 880-980℃; after the rolled material comes off the cooling bed, it is stacked and slowly cooled for 24 hours at 600-700℃.

2. The method for producing 20CrMnTiH high-sulfur free-cutting narrow hardenability gear steel for automobiles according to claim 1, characterized in that: Converter temperature is 1274.6℃.

3. The method for producing 20CrMnTiH high-sulfur free-cutting narrow hardenability gear steel for automobiles according to claim 1, characterized in that: The average deep space vacuum treatment time of the VD furnace is 12 minutes, the average vacuum degree is 0.01kpa, the average soft blowing time is 14 minutes, and the soft blowing flow rate is 88L / min.

4. The method for producing 20CrMnTiH high-sulfur free-cutting narrow hardenability gear steel for automobiles according to claim 1, characterized in that: The components of the high-sulfur free-cutting narrow hardenability gear steel are as follows by weight percentage: C: 0.205%, Si: 0.234%, Mn: 0.89%, P: 0.017%, S: 0.027%, Cr: 1.11%, Ti: 0.06%, Al: 0.029%, Mo: 0.003%, Cu: 0.001%, Ni: 0.008%, W: 0.003%, and the rest is Fe and unavoidable impurities.

5. The method for producing 20CrMnTiH high-sulfur free-cutting narrow hardenability gear steel for automobiles according to claim 1, characterized in that: The components of the high-sulfur free-cutting narrow hardenability gear steel are as follows by weight percentage: C: 0.194%, Si: 0.286%, Mn: 0.901%, P: 0.016%, S: 0.028%, Cr: 1.108%, Ti: 0.069%, Al: 0.029%, Mo: 0.003%, Cu: 0.001%, Ni: 0.008%, W: 0.003%, and the rest is Fe and unavoidable impurities.

6. The method for producing 20CrMnTiH high-sulfur free-cutting narrow hardenability gear steel for automobiles according to claim 1, characterized in that: The components of the high-sulfur free-cutting narrow hardenability gear steel are as follows by weight percentage: C: 0.203%, Si: 0.256%, Mn: 0.888%, P: 0.014%, S: 0.023%, Cr: 1.084%, Ti: 0.056%, Al: 0.027%, Mo: 0.003%, Cu: 0.001%, Ni: 0.008%, W: 0.003%, and the rest is Fe and unavoidable impurities.

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