Steel for axle housing and method for producing the same

Abstract

The application provides a kind of axle housing steel and its production method, the axle housing steel is as follows weight percentage content component: C is 0.06wt%-0.15wt%, Mn is 0.8wt%-1.50wt%, Si is 0.05wt%-0.50wt%, Nb is 0.01wt%-0.06wt%, V is 0.01wt%-0.05wt%, S≤0.005wt%, P≤0.015wt%, Alt is 0.015wt%-0.06wt%, the rest is Fe and trace element.The axle housing steel of the application has high fatigue strength while having high strength, meets the requirement of QC / T533 and QC / T534 standard ≥800,000 times, also meets the fatigue performance requirement of engineering vehicle at least ≥300,000 times.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-strength steel production, and particularly relates to a steel for axle housing and a production method thereof. BACKGROUND

[0002] Fatigue performance is a technical difficulty in the application of the steel for axle housing. No matter cold or hot working, the axle housing produced needs to meet the requirements of QC / T533 and QC / T534 standards, and the vertical fatigue life is greater than or equal to 800,000 times. However, with the increase of the strength grade, the plasticity and toughness of the material decrease, and it is difficult to meet the requirements of fatigue performance. SUMMARY

[0003] The application provides a steel for axle housing, which has high strength and high fatigue strength, meets the requirements of QC / T533 and QC / T534 standards of greater than or equal to 800,000 times, and also meets the fatigue performance requirements of engineering vehicles of greater than or equal to 3,000,000 times.

[0004] The first aspect of the application provides a steel for axle housing, which comprises the following components in weight percentage: C is 0.06wt% to 0.15wt%, Mn is 0.8wt% to 1.50wt%, Si is 0.05wt% to 0.50wt%, Nb is 0.01wt% to 0.06wt%, V is 0.01wt% to 0.05wt%, S is less than or equal to 0.005wt%, P is less than or equal to 0.015wt%, Alt is 0.015wt% to 0.06wt%, and the rest is Fe and trace elements.

[0005] In a feasible implementation manner of the first aspect of the application, the microstructure of the steel for axle housing comprises ferrite, pearlite and bainite; in the microstructure, the volume fraction of the ferrite is 80% to 92%, the volume fraction of the pearlite is 7% to 15%, and the volume fraction of the bainite is 1% to 5%; and the average grain size of the steel for axle housing is less than or equal to 6μm.

[0006] In a feasible implementation manner of the first aspect of the application, the D-type inclusions of the steel for axle housing are less than or equal to 1.0 level, the Ds-type inclusion size is less than or equal to 13μm, and the B-type inclusions are less than or equal to 0.5 level.

[0007] In a feasible implementation manner of the first aspect of the application, the yield strength of the steel for axle housing is greater than or equal to 460MPa, the elongation after fracture is greater than or equal to 24%, the low-temperature impact toughness at-20℃ is greater than or equal to 80J, and the number of cyclic loads that can be borne in the fatigue performance test is greater than or equal to 800,000 times.

[0008] The second aspect of the application provides a preparation method of the above-mentioned steel for axle housing of the first aspect of the application, which comprises the following steps:

[0009] Converter smelting: smelting the molten iron in a converter, controlling the end point of the converter smelting to have [O] content ≤800ppm and [N] content ≤45ppm, to obtain molten steel;

[0010] LF refining: refining the molten steel in a LF, controlling the soft blowing time of the inert gas to be ≥8min, the molten steel to be ≥10min, and the [N] content to be ≤45ppm, to obtain refined molten steel;

[0011] Casting: casting the refined molten steel at a casting speed of 1.1m / min to 1.4m / min, to obtain a casting blank; the casting blank comprises the following components in weight percentage: C is 0.06wt% to 0.15wt%, Mn is 0.8wt% to 1.50wt%, Si is 0.05wt% to 0.50wt%, Nb is 0.01wt% to 0.06wt%, V is 0.01wt% to 0.05wt%, S ≤0.005wt%, P ≤0.015wt%, Alt is 0.015 to 0.06wt%, and the rest is Fe and trace elements;

[0012] Rolling and cooling: rolling and cooling the casting blank, to obtain the axle housing steel.

[0013] In an implementable embodiment of the second aspect of the present application, in the step of casting, the casting speed is 1.2m / min, and the constant ratio under this casting speed is ≥98%.

[0014] In an implementable embodiment of the second aspect of the present application, in the step of rolling and cooling, the casting blank obtained by casting is sent into a heating furnace, the out-furnace temperature is controlled to be 1180 to 1250℃, and then rolling is performed, the rolling includes finish rolling, the inlet temperature of the finish rolling is 950 to 1080℃, and the outlet temperature of the finish rolling is 820 to 900℃.

[0015] In an implementable embodiment of the second aspect of the present application, in the step of rolling and cooling, the cumulative reduction rate of the ferrite region is controlled to be ≥18%.

[0016] In an implementable embodiment of the second aspect of the present application, in the step of rolling and cooling, after the casting blank is heated and rolled, coiling is performed, and the coiling temperature is 550 to 630℃.

[0017] In an implementable embodiment of the second aspect of the present application, in the step of rolling and cooling, the cooling is a front-end concentrated laminar flow cooling mode, and the cooling speed is controlled to be ≤30℃ / s. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The microstructure diagram of the 500MPa high-strength housing steel described in Embodiment 1 of the present application;

[0019] Figure 2Inclusion map for the 500 MPa high strength case steel described in Example 1 of the present invention;

[0020] Figure 3 Microstructure map for the 500 MPa high strength case steel described in Example 2 of the present invention;

[0021] Figure 4 Inclusion map for the 500 MPa high strength case steel described in Example 2 of the present invention. DETAILED DESCRIPTION

[0022] In order to make the inventive purposes, technical solutions and beneficial technical effects of the present application clearer, the present application will be further described in detail below in combination with examples. It should be understood that the examples described in the specification are only for the purpose of explaining the present application, and are not intended to limit the present application.

[0023] For the sake of brevity, only some numerical ranges are explicitly recited herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with any other lower limit to form a range not explicitly recited, and likewise any upper limit can be combined with any other upper limit to form a range not explicitly recited. Further, although a range is recited, it is to be understood that every point or individual number within the range is also specifically recited. Thus, every point or individual number can be combined with every other point or individual number to form a range not explicitly recited.

[0024] In the description herein, where a composition is described as containing, including, or comprising specific components, or where a process is described as having, including, or comprising specific process steps, it is contemplated that the application composition can also consist essentially of, or consist of, the recited components, and that the application processes can also consist essentially of, or consist of, the recited process steps.

[0025] The use of the terms "including," "comprising," "having," "containing," "involving," and variations thereof, is typically intended to be broad and understood as open-ended.

[0026] In the description herein, it is to be understood that the terms "above," "below," "upper," "lower," and the like, can be used with respect to the orientation of the figures, and are not intended to be limiting.

[0027] The above summary of the application is not intended to describe every disclosed embodiment or implementation of the present application. The example embodiments are described more fully below. Throughout this application the use of a series of examples provides guidance to the broadest scope of the application. In various instances, the recitation of a representative group is merely illustrative and should not be construed as exhaustive.

[0028] With the development of micro-alloy steel smelting technology and controlled rolling and controlled cooling technology, the application adopts clean steel platform construction to develop the axle housing steel, obtain fine and dispersed inclusions, and improve the fatigue performance. In addition, combined with the controlled rolling and controlled cooling technology, the microstructure of the high-strength steel is regulated to obtain stable microstructure of the high-strength steel, good strength and plasticity, realize the stamping process, and reduce the failure rate of the drive axle.

[0029] The application provides an axle housing steel with high strength and high fatigue performance, which meets the requirements of ≥800,000 times of QC / T533 and QC / T534 standards.

[0030] The first aspect of the application provides an axle housing steel, which comprises the following components by weight percentage: C is 0.06wt%-0.15wt%, Mn is 0.8wt%-1.50wt%, Si is 0.05wt%-0.50wt%, Nb is 0.01wt%-0.06wt%, V is 0.01wt%-0.05wt%, S≤0.005wt%, P≤0.015wt%, Alt is 0.015wt%-0.06wt%, and the rest is Fe and trace elements.

[0031] In the axle housing steel, the carbon content is between 0.06% and 0.15%, the carbon and iron form carbide, which can significantly improve the strength and hardness of the steel; the manganese content is between 0.8% and 1.50%, which can expand the austenite region, reduce the critical cooling rate of the steel, and make the steel more easily obtain martensite structure, thereby improving the strength of the steel; the silicon content is between 0.05% and 0.50%, silicon can form stable silicate inclusions in the steel, which helps to improve the strength of the steel; the niobium content is between 0.01% and 0.06%, niobium can form stable carbonitride with carbon, nitrogen and other elements, prevent austenite grain growth, refine the grain, and thereby improve the strength of the steel; the vanadium content is between 0.01% and 0.05%, vanadium can form stable carbide and nitride, refine the grain, and improve the strength of the steel. On this basis, the application controls the sulfur content to be ≤0.005%, the phosphorus content to be ≤0.015%, reduces the number and size of inclusions, so that the axle housing steel has high strength and high fatigue performance.

[0032] In some embodiments, the thickness of the axle housing steel is 4.0mm-16.0mm.

[0033] In some embodiments, the microstructure of the axle housing steel includes ferrite, pearlite and bainite; in the microstructure, the volume fraction of ferrite is 80%-92%, the volume fraction of pearlite is 7%-15%, and the volume fraction of bainite is 1%-3%; the average grain size of the axle housing steel is ≤6μm.

[0034] The internal microstructure is mainly ferrite-based, and there are pearlite and a small amount of granular bainite. The bainite has high strength and good toughness, which can make the steel have good strength and toughness. On this basis, the grain size of the axle housing steel is small, and the average grain size is ≤6μm, which can reduce the initiation and propagation of fatigue cracks and improve the fatigue life of ferrite steel.

[0035] In some embodiments, the D-type inclusions of the axle housing steel are ≤1.0 grade, the Ds-type inclusion size is ≤13μm, and the B-type inclusions are ≤0.5 grade.

[0036] The inclusion grade of the axle housing steel of the present application belongs to fine inclusions, mainly D-type inclusions ≤1.0 grade, Ds-type inclusion size ≤13μm, a small amount of B-type inclusions ≤0.5 grade, no other type of inclusions, high fatigue strength.

[0037] In some embodiments, the yield strength of the axle housing steel is ≥460MPa, the elongation after fracture is ≥24%, the low temperature impact toughness at -20℃ is ≥80J, and the number of cycles that can be tolerated in the fatigue performance test is ≥800,000 times.

[0038] The second aspect of the present application provides a preparation method of the above-mentioned axle housing steel of the first aspect of the present application, which comprises molten iron-converter smelting-LF furnace external refining-casting-continuous casting billet-heating furnace heating-rough rolling+precision rolling-rolling cooling-coiling.

[0039] Specifically, the preparation method of the axle housing steel provided by the second aspect of the present application comprises:

[0040] Converter smelting: smelting the molten iron in a converter, controlling the end point [O] content of the converter smelting to be ≤800ppm and the [N] content to be ≤45ppm, to obtain molten steel;

[0041] LF refining: LF refining the molten steel, controlling the soft blowing time of the inert gas to be ≥8min, the setting time of the molten steel to be ≥10min, and the [N] content to be ≤40ppm, to obtain refined molten steel;

[0042] Casting: casting the refined molten steel at a casting speed of 1.1m / min-1.4m / min to obtain a casting billet; the casting billet comprises the following components in weight percentage: C is 0.06wt%-0.15wt%, Mn is 0.8wt%-1.50wt%, Si is 0.05wt%-0.50wt%, Nb is 0.01wt%-0.06wt%, V is 0.01wt%-0.05wt%, S≤0.005wt%, P≤0.015wt%, Alt is 0.015-0.06wt%, and the rest is Fe and trace elements;

[0043] Rolling and cooling: the cast blank is rolled and cooled to obtain the axle housing steel.

[0044] The application can effectively remove harmful gases and inclusions in the molten steel by controlling the atmosphere of converter smelting, LF refining and casting process parameters, and the duration of soft blowing operation is more than or equal to 8 minutes, and the static time is greater than or equal to 10 minutes, which is helpful for the floating and removal of inclusions in the molten steel, and the fine inclusion level control is realized, combined with the fine grain strengthening effect of the controlled rolling and controlled cooling process, to produce high-strength housing steel with yield strength greater than or equal to 460 MPa, elongation greater than or equal to 24%, and low-temperature impact toughness at -20℃ greater than or equal to 80 J. Moreover, the inclusion level of the high-fatigue high-strength axle housing steel belongs to fine inclusions, mainly D-type inclusions less than or equal to 1.0 level, Ds-type inclusion size less than or equal to 13 μm, a small amount of B-type inclusions less than or equal to 0.5 level, and no other type of inclusions, which can obtain higher fatigue strength and meet the requirements of QC / T533 and QC / T534 standards greater than or equal to 800 million times.

[0045] In some embodiments, in the step of casting, the casting speed is 1.2 m / min, and the constant ratio at this casting speed is greater than or equal to 98%.

[0046] The casting speed of the axle housing steel of the application is maintained at 1.2 m / min, and the constant ratio at this casting speed is greater than or equal to 98%, which can reduce the fluctuations and uncertainties in the production process, obtain stable crystallization organization and size precision, and improve the quality of the product.

[0047] Moreover, although the casting speed is large, the axle housing steel obtained by the embodiments of the application has less cracks and inclusions, and the axle housing steel has good performance.

[0048] In some embodiments, in the step of rolling and cooling, the cast blank obtained by casting is sent to a heating furnace, the furnace temperature is controlled to be 1180℃-1250℃, and then rolling is performed, which includes finish rolling, the inlet temperature of the finish rolling is 950℃-1080℃, and the outlet temperature of the finish rolling is 820℃-900℃.

[0049] The heating temperature is controlled to be 1180℃-1250℃, which mainly affects the size of the original austenite grains. The heating temperature can be selected to be 1200℃-1220℃, and the size of the austenite grains is appropriate, so that a steel with better mechanical strength and fatigue performance can be obtained.

[0050] The entry temperature of the finish rolling is 950-1080°C, and the exit temperature of the finish rolling is controlled at 820-900°C, large reduction is adopted in the non-recrystallization zone, so as to fully play the principle of fine-grain strengthening rolling of the micro-alloy, and the grain boundaries or deformation bands of the deformed austenite are the nucleation sites of ferrite, so as to achieve the effect of refining the grain. The entry temperature of the finish rolling can be selected as 979-989°C, and the exit temperature of the finish rolling can be selected as 880-890°C, combined with the appropriate discharge temperature, the billet rolled at the temperature range has fine grain, good microstructure and excellent fatigue performance, and the mechanical strength is also high.

[0051] In some embodiments, in the step of rolling and cooling, the ferrite region control cumulative reduction rate is ≥18%, and can be selected as 20-22%.

[0052] The ferrite region control cumulative reduction rate is high, and large deformation is carried out in the ferrite region, which can increase the deformation bands and dislocation density inside the austenite grain, refine the ferrite grain, and the refined ferrite grain can significantly improve the strength and toughness of the bridge shell steel.

[0053] In some embodiments, in the step of rolling and cooling, the cast billet is heated and rolled, and then coiled, and the coiling temperature is 550-630°C.

[0054] The coiling temperature is controlled at 550-630°C, so that the micro-alloy CN compound is fully analyzed and discharged in the cooling process, and the strength and plasticity of the product are ensured. The coiling temperature can be selected as 580-610°C, and if the coiling temperature is too high, the ferrite grain will be coarse, the amount of proeutectoid ferrite will gradually increase, and the amount of pearlite will gradually decrease, which will reduce the tensile strength and yield strength of the steel; if the coiling temperature is too low, the interlamellar spacing of the pearlite will be refined, which will reduce the toughness of the steel.

[0055] In some embodiments, in the step of rolling and cooling, the cooling is a front-end concentrated laminar cooling mode, and the cooling speed is controlled at ≤30°C / s.

[0056] Examples

[0057] The following examples more specifically describe the present disclosure, which are only illustrative and various modifications and variations can be made within the scope of the present disclosure, which will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used directly without further purification, and the instruments used in the examples are commercially available.

[0058] Example 1

[0059] The chemical components and contents of the high fatigue high strength axle housing steel continuous casting billet of the embodiment are as follows: C is 0.0692wt%, Mn is 1.0386wt%, Si is 0.1535wt%, Nb is 0.0203wt%, V is 0.031wt%, S is 0.0022wt%, P is 0.0123wt%, Alt is 0.0352%, and the rest is Fe and inevitable impurities.

[0060] The preparation method of the high fatigue high strength axle housing steel of the embodiment comprises the following steps:

[0061] Converter smelting: the molten iron is subjected to converter smelting, the converter end point [O] is controlled to be 780ppm, the [N] is controlled to be 42ppm, and the tapping adopts a double-block control method.

[0062] LF refining: the ladle is not allowed to be drained during LF refining, the soft blowing time is 9min, the quieting time is 12min, and the [N] is 38ppm when leaving the station.

[0063] Pouring: protective pouring is adopted, the constant pulling speed is 1.21m / min, and the proportion is greater than or equal to 98.5%.

[0064] Rolling and cooling: the continuous casting billet is heated in the furnace, and the discharge temperature is 1220℃; the finish rolling inlet temperature is 987℃, the finish rolling outlet temperature is 880℃, and the coiling temperature is controlled to be 580℃. The reduction of the last stand of finish rolling is 20%.

[0065] The laminar cooling mode is front-end concentrated cooling, the second group and the seventh group of ultra-fast cooling manifolds are appropriately opened when producing 12mm, and the small flow is spaced apart; and the post-coiling slow cooling is to room temperature.

[0066] After the transverse detection of the mechanical properties, the yield strength of the 12mm high fatigue high strength drive axle housing steel produced in the embodiment is 541MPa, the tensile strength is 620MPa, the elongation after fracture is 26%, and the low temperature impact energy at-20℃ is 228J. In the fatigue performance test, the number of cycles that can be tolerated is 870,000 times.

[0067] The 12mm high fatigue high strength drive axle housing steel produced in the embodiment has the following inclusion grade: 0.5 of D-type inclusions, 0 of Ds-type inclusions, and no other inclusions.

[0068] The microstructure of the 12mm high fatigue high strength drive axle housing steel produced in the embodiment mainly includes 90% of ferrite in volume fraction, a small amount of bainite in volume fraction of 1.5%, and 8.5% of pearlite in volume fraction, and the average grain size is 4.2μm.

[0069] Embodiment 2

[0070] The chemical components and contents of the high fatigue high strength axle housing steel continuous casting billet of the embodiment are as follows: C is 0.1371 wt%, Mn is 1.4187 wt%, Si is 0.1669 wt%, Nb is 0.012 wt%, V is 0.018 wt%, S is 0.0017 wt%, P is 0.0142 wt%, Alt is 0.0361%, and the rest is Fe and inevitable impurities.

[0071] The preparation method of the high fatigue high strength axle housing steel of the embodiment comprises the following steps:

[0072] Converter smelting: the molten iron is subjected to converter smelting, the converter end point [O] is controlled to be 792 ppm, the [N] is controlled to be 44 ppm, and the tapping adopts a double-block control method.

[0073] LF refining: the ladle is not allowed to be drained during LF refining, the soft blowing time is 9 min, the quieting time is 11 min, and the [N] is 39 ppm when leaving the station.

[0074] Pouring: protective pouring is adopted, the constant pulling speed is 1.15 m / min, and the proportion is greater than or equal to 99%.

[0075] Rolling and cooling: the continuous casting billet is heated in the furnace, the discharge temperature is 1200°C; the finish rolling inlet temperature is 1005°C, the finish rolling outlet temperature is 890°C, and the coiling temperature is controlled to be 610°C. The reduction of the last stand of the finish rolling is 20%.

[0076] The laminar cooling mode is front-end concentrated cooling, and slow cooling to room temperature after coiling.

[0077] The 14.0 mm high fatigue high strength drive axle housing steel produced in the embodiment has a yield strength of 505 MPa, a tensile strength of 595 MPa, an elongation after fracture of 27%, and a low-temperature impact energy of 232 J at -20°C after transverse mechanical property detection. In the fatigue performance test, the number of cycles that can be tolerated is 840,000 times.

[0078] The 14.0 mm high fatigue high strength drive axle housing steel produced in the embodiment has a D-type inclusion level of 0.5, and no other inclusions.

[0079] The 14.0 mm high fatigue high strength drive axle housing steel produced in the embodiment has a microstructure mainly composed of ferrite and pearlite, a volume fraction of ferrite of 91%, a small amount of bainite with a volume fraction of 1%, and a volume fraction of pearlite of 8%, and an average grain size of 5.6 μm.

[0080] Embodiment 3

[0081] Compared with embodiment 1, the difference lies in that the process parameters for preparation are different, the pulling speed is small, and the discharge temperature and finish rolling treatment temperature are low.

[0082] The different process parameters in this embodiment include:

[0083] Casting: Protective casting is adopted, with a constant casting speed of 1.05m / min and a proportion of ≥98.5%.

[0084] Rolling and cooling: The continuously cast billet is heated in the furnace and exits at a temperature of 1190℃; the entry temperature of the finishing mill is 950℃, the exit temperature of the finishing mill is 860℃, and the coiling temperature is controlled at 570℃.

[0085] The 16mm high-fatigue, high-strength drive axle housing steel produced in this embodiment, after transverse mechanical property testing, exhibits a yield strength of 522MPa, a tensile strength of 610MPa, an elongation after fracture of 25.5%, and a low-temperature impact energy of 184J at -20℃. In fatigue performance testing, it can withstand 820,000 cyclic loading cycles. The inclusion grade is D0.5, B0.5.

[0086] The microstructure of the 16mm high fatigue high strength drive axle housing steel produced in this embodiment is mainly ferrite and pearlite, with a volume fraction of 90% ferrite, a small volume fraction of 1% bainite, and a volume fraction of 9% pearlite, with an average grain size of 5.1μm.

[0087] Example 4

[0088] Compared with Example 1, the difference lies in the different process parameters used in the preparation, with a lower pulling speed and higher furnace exit temperature and finishing rolling temperature.

[0089] The different process parameters in this embodiment include:

[0090] Casting: Protective casting is adopted, with a constant casting speed of 1.05m / min and a proportion of ≥98.5%.

[0091] Rolling and cooling: The continuously cast billet is heated in the furnace and exits at a temperature of 1225℃; the entry temperature of the finishing mill is 1050℃, the exit temperature of the finishing mill is 910℃, and the coiling temperature is controlled at 630℃.

[0092] The 14mm high-fatigue, high-strength drive axle housing steel produced in this embodiment, after transverse mechanical property testing, exhibits a yield strength of 525MPa, a tensile strength of 618MPa, an elongation after fracture of 26.5%, and a low-temperature impact energy of 202J at -20℃. In fatigue performance testing, it can withstand 840,000 cyclic loading cycles. The inclusion class D is 1.0.

[0093] The microstructure of the 14mm high fatigue and high strength drive axle housing steel produced in this embodiment is mainly ferrite and pearlite, with a volume fraction of 92% ferrite, a small volume fraction of 1% bainite, and a volume fraction of 7% pearlite, and an average grain size of 4.8μm.

[0094] Example 5

[0095] The difference compared with Example 1 is that the process parameters for preparation are different, the finishing rolling temperature and coiling temperature are low, and the reduction is lower.

[0096] The different process parameters in this example include:

[0097] Rolling and cooling: the continuous casting billet is heated in a furnace, and the temperature out of the furnace is 1180℃; the finishing rolling inlet temperature is 950℃, the finishing rolling outlet temperature is 820℃, and the coiling temperature is controlled to be 550℃. The reduction of the last stand of finishing rolling is 15%.

[0098] The 16mm high fatigue high strength drive axle housing steel produced in this example has, after transverse detection of mechanical properties, a yield strength of 537MPa, a tensile strength of 641MPa, an elongation after fracture of 24.5%, and a low temperature impact energy at -20℃ of 228J. In the fatigue performance test, the number of cycles that can be tolerated is 810,000. The inclusion level is B1.0, D0.5.

[0099] The 16mm high fatigue high strength drive axle housing steel produced in this example has a microstructure mainly of ferrite and pearlite, 89% of ferrite in volume fraction and a small amount of bainite in volume fraction of 2%, 9% of pearlite in volume fraction, and an average grain size of 4.6μm.

[0100] Example 6

[0101] The difference compared with Example 1 is that the process parameters for preparation are different, and the finishing rolling temperature is high.

[0102] The different process parameters in this example include:

[0103] Rolling and cooling: the continuous casting billet is heated in a furnace, and the temperature out of the furnace is 1180℃; the finishing rolling inlet temperature is 1090℃, the finishing rolling outlet temperature is 900℃, and the coiling temperature is controlled to be 640℃. The reduction of the last stand of finishing rolling is 20%.

[0104] The 16mm high fatigue high strength drive axle housing steel produced in this example has, after transverse detection of mechanical properties, a yield strength of 502MPa, a tensile strength of 585MPa, an elongation after fracture of 26%, and a low temperature impact energy at -20℃ of 165J. In the fatigue performance test, the number of cycles that can be tolerated is 820,000. The D-type inclusion level is 1.0.

[0105] The 16mm high fatigue high strength drive axle housing steel produced in this example has a microstructure mainly of ferrite and pearlite, 92% of ferrite in volume fraction and a small amount of bainite in volume fraction of 1%, 7% of pearlite in volume fraction, and an average grain size of 4.2μm.

[0106] Comparative Example 1

[0107] The composition of the steel for the axle housing of the comparative example is different from that of Example 1, the manganese content is higher, titanium is added, and square titanium nitride inclusions are easily formed in the steel, as follows: C is 0.0891wt%, Mn is 1.5240wt%, Si is 0.1201wt%, Nb is 0.0120wt%, V is 0.0026wt%, Ti is 0.0654wt%, S is 0.0064wt%, P is 0.0187wt%, Alt is 0.0354wt%, and the rest is Fe and inevitable impurities.

[0108] The preparation method of the present comparative example is different from that of Comparative Example 1, as follows:

[0109] The converter end point [O] is 940ppm, [N] is 58ppm, and the tapping adopts double block control method. The ladle is not allowed to be drained during LF refining, the soft blowing time is 8min, the setting time is 12min, and the [N] at the exit is 55ppm. Protective casting is used, and the constant speed is 1.05m / min, and the proportion is ≥98.5%.

[0110] The continuous casting billet is heated, and the discharge temperature is 1205℃; the finish rolling inlet temperature is 967℃, the finish rolling outlet temperature is 890℃, and the coiling temperature is controlled at 580℃. The reduction rate of the last stand of finish rolling is 18%. The laminar cooling mode is front-end concentrated cooling, and when producing 16mm, the second and seventh groups of ultra-fast cooling manifolds are appropriately opened, and the small flow interval is opened; after coiling, slow cooling to room temperature.

[0111] The 16mm high fatigue high strength drive axle housing steel produced in the present comparative example has a yield strength of 584MPa, a tensile strength of 670MPa, an elongation of 22%, and a low temperature impact energy of 97J at -20℃ after transverse detection of mechanical properties. In the fatigue performance test, the number of cycles that can be tolerated is 640,000 times.

[0112] The 16.0mm high fatigue high strength drive axle housing steel produced in the present comparative example has an inclusion level of B0.5, D1.0, and Ds1.0.

[0113] The 16.0mm high fatigue high strength drive axle housing steel produced in the present comparative example has a microstructure mainly composed of ferrite and pearlite, with a volume fraction of 88% ferrite and a small amount of bainite with a volume fraction of 3%, and a volume fraction of 9% pearlite, and an average grain size of 7.4μm.

[0114] The above embodiments of the present application are merely used for clearly illustrating the present application, but not for limiting the present application. Based on the above description, any modification, equivalent replacement and improvement made by those skilled in the art should be included in the protection scope of the present application.

Claims

1. A method of manufacturing a steel for axle housings, characterized in that, The method comprises the following steps: converter smelting: smelting molten iron in a converter, controlling the end point [O] content of the converter smelting ≤800ppm, and the [N] content ≤45ppm, to obtain molten steel; LF refining: LF refining the molten steel, controlling the soft blowing time of the inert gas ≥8min, the molten steel setting time ≥10min, and the [N] content ≤40ppm, to obtain refined molten steel; casting: casting the refined molten steel at a casting speed of 1.1m / min~1.4m / min to obtain a casting blank, the casting blank comprising the following components in wt%: C 0.06 wt%~0.15wt%, Mn 0.8 wt%~1.50wt%, Si 0.05 wt%~0.50wt%, Nb 0.01wt%~0.06wt%, V 0.01wt%~0.05wt%, S≤0.005wt%, P≤0.015wt%, Alt 0.015~0.06 wt %, and the rest Fe and trace elements; rolling and cooling: rolling the casting blank, and cooling, wherein the cooling is a front-end concentrated laminar flow layer cooling mode, and the cooling rate is controlled to be ≤30℃ / s, to obtain the axle housing steel, the axle housing steel comprising the following components in wt%: C 0.06 wt%~0.15wt%, Mn 0.8 wt%~1.50wt%, Si 0.05 wt%~0.50wt%, Nb 0.01wt%~0.06wt%, V 0.01wt%~0.05wt%, S≤0.005wt%, P≤0.015wt%, Alt 0.015~0.06 wt %, and the rest Fe and trace elements; the microstructure of the axle housing steel comprises ferrite, pearlite and bainite; in the microstructure, the volume fraction of the ferrite is 80%~92%, the volume fraction of the pearlite is 7%~15%, and the volume fraction of the bainite is 1%~5%; the average grain size of the axle housing steel is ≤6μm.

2. Process for the production of a steel for axle housings according to claim 1, characterized in that, In the step of casting, the casting speed is 1.2 m / min, and the constant ratio at this casting speed is ≥98%.

3. Process for the production of a steel for axle housings according to claim 1, characterized in that, In the step of rolling and cooling, the casting blank obtained by the step of casting is sent into a heating furnace, the furnace-out temperature is controlled to be 1180℃~1250℃, and then rolling is performed, the rolling comprising finish rolling, the inlet temperature of the finish rolling is 950℃~1080℃, and the outlet temperature of the finish rolling is 820℃~900℃.

4. Process for the production of a steel for axle housings according to claim 1, characterized in that, In the step of rolling and cooling, the ferrite region control cumulative reduction rate is ≥18%.

5. The method of manufacturing a steel axle housing according to claim 1, characterized in that, In the step of rolling and cooling, coiling is performed after the casting blank is heated and rolled, and the coiling temperature is 550℃~630℃.

6. The method of manufacturing a steel axle housing according to claim 1, characterized in that, The D-type inclusions of the axle housing steel are ≤1.0 grade, the Ds-type inclusion size is ≤13μm, and the B-type inclusions are ≤0.5 grade.

7. Process for the production of a steel for axle housings according to claim 1 or 6, characterized in that, The bridge housing steel has yield strength ≥460 MPa, elongation after fracture ≥24%, low temperature impact toughness ≥80 J at -20 ℃, and can withstand cycle loading ≥800,000 times in fatigue performance test.

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