Axle housing steel and production method thereof

Abstract

The invention provides steel for an axle housing and a production method of the steel. The steel for the axle housing comprises the following components in percentage by weight: 0.06 to 0.15 weight percent of C, 0.8 to 1.50 weight percent of Mn, 0.05 to 0.50 weight percent of Si, 0.01 to 0.06 weight percent of Nb, 0.01 to 0.05 weight percent of V, less than or equal to 0.005 weight percent of S, less than or equal to 0.015 weight percent of P, 0.015 to 0.06 weight percent of Alt and the balance of Fe and trace elements. The steel for the axle housing has high strength and high fatigue strength, meets the requirement that QC / T533 and QC / T534 standards are greater than or equal to 80000 times, and also meets the requirement that an engineering vehicle is at least greater than or equal to 300000 times of fatigue performance.

Description

Technical Field

[0001] The present application belongs to the technical field of high-strength steel production, and specifically relates to a steel for a bridge shell and a production method thereof. Background Art

[0002] Fatigue performance is a technical difficulty in the application of bridge housing steel. Regardless of hot or cold processing, the bridge housing shell must meet the requirements of QC / T533 and QC / T534 standards, with a vertical fatigue life of ≥ 800,000 times. However, as the strength grade increases, the plasticity and toughness of the material decrease, making it difficult to meet the fatigue performance requirements. Summary of the invention

[0003] The present application provides a steel for a bridge shell, which has high strength and high fatigue strength, meets the requirements of QC / T533 and QC / T534 standards of ≥800,000 times, and also meets the fatigue performance requirements of engineering vehicles of at least ≥300,000 times.

[0004] In a first aspect, the present application provides a steel for a bridge housing, comprising 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.

[0005] In a feasible implementation scheme of the first aspect of the present application, the microstructure of the steel for the bridge housing includes ferrite, pearlite and bainite; in the microstructure, the volume fraction of ferrite is 80% to 92%, the volume fraction of pearlite is 7% to 15%, and the volume fraction of bainite is 1% to 5%; the average grain size of the steel for the bridge housing is ≤6μm.

[0006] In a feasible implementation manner of the first aspect of the present application, the D-type inclusions of the steel for the bridge housing are ≤ level 1.0, the size of the Ds-type inclusions is ≤ 13 μm, and the B-type inclusions are ≤ level 0.5.

[0007] In a feasible implementation manner of the first aspect of the present application, the yield strength of the steel used for the bridge shell is ≥460MPa, the elongation after fracture is ≥24%, the low-temperature impact toughness at -20°C is ≥80J, and the number of cyclic loadings that can be withstood in fatigue performance tests is ≥800,000 times.

[0008] The second aspect of the present application provides a method for preparing the axle housing steel according to the first aspect of the present application, comprising:

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

[0010] LF refining: LF refining is performed on the molten steel, and the soft blowing time of the inert gas is controlled to be ≥8min, the calming time of the molten steel is ≥10min, and the [N] content is ≤45ppm to obtain refined molten steel;

[0011] Casting: Casting the refined molten steel at a pulling speed of 1.1m / min to 1.4m / min to obtain a casting billet; the casting billet 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: The ingot is rolled and cooled to obtain steel for the bridge housing.

[0013] In a feasible implementation manner of the second aspect of the present application, in the casting step, the pulling speed is 1.2 m / min, and the constant ratio at this pulling speed is ≥98%.

[0014] In a feasible implementation manner of the second aspect of the present application, in the rolling and cooling steps, the ingot obtained by casting is sent to a heating furnace, the furnace outlet temperature is controlled to be 1180-1250°C, and then rolling is carried out, and the rolling includes finish rolling, the inlet temperature of the finish rolling is 950-1080°C, and the outlet temperature of the finish rolling is 820-900°C.

[0015] In a feasible implementation manner of the second aspect of the present application, in the steps of rolling and cooling, the cumulative reduction rate in the ferrite region is controlled to be ≥18%.

[0016] In a feasible implementation manner of the second aspect of the present application, in the rolling and cooling steps, the ingot is heated and rolled before being coiled, and the coiling temperature is 550-630°C.

[0017] In a feasible implementation manner of the second aspect of the present application, in the rolling and cooling steps, the cooling is a front-end concentrated laminar layer cooling mode, and the cooling rate is controlled at ≤30°C / s. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a microstructure diagram of the 500MPa high-strength shell steel described in Example 1 of the present invention;

[0019] Figure 2This is the inclusion map of the 500MPa high-strength shell steel described in Example 1 of the present invention;

[0020] Figure 3 This is a microstructure diagram of the 500MPa high-strength shell steel described in Example 2 of the present invention;

[0021] Figure 4 This is the inclusion diagram of the 500MPa high-strength shell steel described in Example 2 of the present invention. DETAILED DESCRIPTION

[0022] In order to make the invention purpose, technical scheme and beneficial technical effect of the present application clearer, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the embodiments described in this specification are only for explaining the present application, not for limiting the present application.

[0023] For simplicity, only some numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form an unambiguous range; and any lower limit can be combined with other lower limits to form an unambiguous range, and any upper limit can be combined with any other upper limit to form an unambiguous range. In addition, although not explicitly stated, each point or single value between the range endpoints is included in the range. Thus, each point or single value can be combined with any other point or single value as its own lower limit or upper limit or with other lower limits or upper limits to form an unambiguous range.

[0024] In the description herein, when a composition is described as containing, comprising or including specific components, or when a process is described as containing, comprising or including specific process steps, it is expected that the composition of the present application also consists essentially of or consists of the components, and the process of the present application also consists essentially of or consists of the process steps.

[0025] The use of the terms "including," "comprising," "containing," and "having" should generally be interpreted as open ended and non-limiting unless expressly stated otherwise.

[0026] In the description of this article, it should be noted that, unless otherwise specified, “above” and “below” are inclusive of the number itself, and the “multiple” in “one or more” means more than two.

[0027] The above-mentioned summary of the invention of the present application is not intended to describe each disclosed embodiment or each implementation in the present application. The following description more specifically illustrates exemplary embodiments. In many places throughout the application, guidance is provided by a series of examples, which can be used in various combinations. In each example, enumeration is only used as a representative group and should not be interpreted as exhaustive.

[0028] With the development of microalloy steel smelting technology and controlled rolling and controlled cooling technology, this application adopts the clean steel platform to develop bridge shell steel, obtain fine dispersed inclusion level, and improve fatigue performance. In addition, combined with controlled rolling and controlled cooling technology, the organization of high-strength steel is regulated to obtain a stable high-strength steel organization, obtain good strength and plasticity, realize stamping process, and reduce the defective rate of drive axles.

[0029] The present application provides a bridge housing steel having both high strength and high fatigue performance, which meets the requirements of QC / T533 and QC / T534 standards of ≥ 800,000 times.

[0030] In a first aspect, the present application provides a steel for a bridge housing, comprising 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 0.015wt%~0.06wt%, and the rest is Fe and trace elements.

[0031] In the steel for the bridge housing of the present application, the carbon content is between 0.06% and 0.15%. Carbon forms carbides with iron, 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 it easier for the steel to obtain a martensitic structure, thereby improving the strength of the steel. The silicon content is between 0.05% and 0.50%, and 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 carbonitrides with elements such as carbon and nitrogen to prevent the growth of austenite grains, refine the grains, and thus improve the strength of the steel; the vanadium content is between 0.01% and 0.05%, vanadium can form stable carbides and nitrides, refine the grains, and improve the strength of the steel. On this basis, the present application controls the sulfur content to ≤0.005%, and the phosphorus content to ≤0.015%, reduces the number and size of inclusions, and makes the bridge housing steel have both high strength and high fatigue performance.

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

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

[0034] The internal microstructure is mainly ferrite-based, with pearlite and a small amount of granular bainite. Bainite has high strength and good toughness, which can make the steel have good strength and toughness. On this basis, the grains of the steel used for the bridge shell are fine, with an average grain size of ≤6μm, which can reduce the initiation and expansion of fatigue cracks and improve the fatigue life of ferrite steel.

[0035] In some embodiments, the steel for the axle housing has a D-type inclusion of ≤1.0 level, a Ds-type inclusion size of ≤13 μm, and a B-type inclusion of ≤0.5 level.

[0036] The inclusion grade of the steel used for the bridge shell in this application belongs to fine inclusions, mainly D-type inclusions ≤1.0 level, Ds-type inclusion size ≤13μm, a small amount of B-type inclusions ≤0.5 level, no other types of inclusions, and high fatigue strength.

[0037] In some embodiments, the yield strength of the steel used for the bridge housing is ≥460MPa, the elongation after fracture is ≥24%, the low-temperature impact toughness at -20°C is ≥80J, and the number of cyclic loadings that can be withstood in fatigue performance tests is ≥800,000 times.

[0038] The second aspect of the present application provides a method for preparing the steel for the bridge shell according to the first aspect of the present application, which comprises molten iron - converter smelting - LF refining outside the furnace - casting - continuous casting - heating in a heating furnace - rough rolling + finishing rolling - cooling after rolling - coiling.

[0039] Specifically, the second aspect of the present application provides a method for preparing axle housing steel, comprising:

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

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

[0042] Casting: Casting the refined molten steel at a pulling speed of 1.1m / min to 1.4m / min to obtain a casting billet; the casting billet 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;

[0043] Rolling and cooling: The ingot is rolled and cooled to obtain steel for the bridge housing.

[0044] This application controls the atmosphere of converter smelting, LF refining and casting process parameters, and the duration of soft blowing operation reaches or exceeds 8 minutes, which can effectively remove harmful gases and inclusions in molten steel. The calming time ≥10min is conducive to the floating and removal of inclusions in molten steel, and the fine inclusion level control is achieved. Combined with the controlled rolling and controlled cooling process, the effect of fine grain strengthening is used to produce high-strength shell steel with a yield strength of ≥460MPa, a post-fracture elongation of ≥24%, and a low-temperature impact toughness of -20°C of ≥80J. In addition, the inclusion level of high-fatigue and high-strength bridge shell steel belongs to fine inclusions, mainly D-type inclusions ≤1.0 level, Ds-type inclusion size ≤13μm, a small amount of B-type inclusions ≤0.5 level, and no other types of inclusions, which can obtain higher fatigue strength and meet the requirements of QC / T533 and QC / T534 standards ≥800,000 times.

[0045] In some embodiments, in the step of casting, the pulling speed is 1.2 m / min, and the constant ratio at the pulling speed is ≥ 98%.

[0046] The drawing speed of the steel for the bridge shell of the present application is maintained at 1.2 m / min, and the constant ratio at this drawing speed is ≥98%, which can reduce fluctuations and uncertainties in the production process, obtain stable crystal structure and dimensional accuracy, and improve product quality.

[0047] Furthermore, although the casting process has a relatively high pulling speed, the bridge shell steel obtained in the embodiment of the present application has fewer cracks and inclusions, and the bridge shell steel has good performance.

[0048] In some embodiments, during the rolling and cooling steps, the ingot obtained by casting is sent to a heating furnace, the furnace outlet temperature is controlled to be 1180°C to 1250°C, and then rolling is performed, wherein the rolling includes finish rolling, the inlet temperature of the finish rolling is 950°C to 1080°C, and the outlet temperature of the finish rolling is 820°C to 900°C.

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

[0050] The inlet temperature of finishing rolling is 950℃~1080℃, and the outlet temperature of finishing rolling is controlled at 820℃~900℃. The high pressure reduction in the non-recrystallization zone is adopted to give full play to the fine grain strengthening rolling principle of microalloy. The grain boundary or deformation band of deformed austenite is the nucleation site of ferrite, thereby achieving the effect of grain refinement. The inlet temperature of finishing rolling can be selected from 979℃~989℃, and the outlet temperature can be selected from 880℃~890℃. Combined with the appropriate furnace temperature, the billet rolled in this temperature range has fine grains, good organizational structure, excellent fatigue performance, and high mechanical strength.

[0051] In some embodiments, during the rolling and cooling steps, the cumulative reduction ratio in the ferrite region is controlled to be ≥18%, and may be 20% to 22%.

[0052] The ferrite region controls the cumulative reduction rate to be high, and large deformation is performed in the ferrite region, which can increase the deformation band and dislocation density inside the austenite grains and refine the ferrite grains. The refined ferrite grains can significantly improve the strength and toughness of the steel for the bridge housing.

[0053] In some embodiments, in the rolling and cooling steps, the ingot is heated and rolled before being coiled, and the coiling temperature is 550°C to 630°C.

[0054] The coiling temperature is controlled at 550℃~630℃, so that the microalloy CN compounds are fully precipitated during the cooling process to ensure the strength and plasticity of the product. The coiling temperature can be selected as 580℃~610℃. If the coiling temperature is too high, the ferrite grains will be coarse, the amount of proeutectoid ferrite will gradually increase, and the amount of pearlite will gradually decrease, resulting in a decrease in the tensile strength and yield strength of the steel; if the coiling temperature is too low, the pearlite interlamellar spacing will be refined, reducing the toughness of the steel.

[0055] In some embodiments, during the rolling and cooling steps, the cooling is performed in a front-end concentrated laminar layer cooling mode, and the cooling rate is controlled at ≤30°C / s.

[0056] Example

[0057] The following examples more specifically describe the disclosure of the present application, which are intended for illustrative purposes only, as it will be apparent to those skilled in the art that various modifications and variations are possible within the scope of the disclosure of the present application. 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 can be used directly without further processing, and the instruments used in the examples are commercially available.

[0058] Example 1

[0059] The chemical components and contents of the high fatigue and high strength bridge housing steel continuous casting billet in this embodiment are: 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 unavoidable impurities.

[0060] The preparation method of the high fatigue and high strength bridge shell steel in this embodiment comprises the following steps:

[0061] Converter smelting: The molten iron is smelted in a converter, and the converter end point [O] is controlled to be 780ppm, [N] is controlled to be 42ppm, and the double-speed control method is adopted for steelmaking.

[0062] LF refining: During LF refining, the ladle was not allowed to drain, the soft blowing time was 9 minutes, the calming time was 12 minutes, and the [N] was 38ppm when leaving the station.

[0063] Casting: Protected casting is adopted, the constant pulling speed is 1.21m / min, and the ratio is ≥98.5%.

[0064] Rolling and cooling: The continuous casting billet is heated in the furnace, and the temperature out of the furnace is 1220℃; the finishing rolling inlet temperature is 987℃, the finishing rolling outlet temperature is 880℃, and the coiling temperature is controlled at 580℃. The reduction rate of the finishing rolling end stand is 20%.

[0065] The laminar cooling mode is front-end centralized cooling. When producing 12mm, the second and seventh groups of ultra-fast cooling headers are properly opened, separated by small flow rates; after coiling, slowly cool to room temperature.

[0066] The 12 mm high fatigue and high strength drive axle housing steel produced in this embodiment has a yield strength of 541 MPa, a tensile strength of 620 MPa, an elongation after fracture of 26%, and a low temperature impact energy of -20°C of 228 J after transverse mechanical property testing. In the fatigue performance test, it can withstand 870,000 cycles of loading.

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

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

[0069] Example 2

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

[0071] The preparation method of the high fatigue and high strength bridge shell steel in this embodiment comprises the following steps:

[0072] Converter smelting: The molten iron is smelted in a converter, and the converter end point [O] is controlled to be 792ppm, [N] to be 44ppm, and the double-speed control method is adopted for steelmaking.

[0073] LF refining: During LF refining, the ladle was not allowed to drain, the soft blowing time was 9 minutes, the calming time was 11 minutes, and the [N] was 39ppm when leaving the station.

[0074] Casting: Protected casting is adopted, the constant pulling speed is 1.15m / min, and the ratio is ≥99%.

[0075] Rolling and cooling: The continuous casting billet is heated in the furnace, and the temperature out of the furnace is 1200℃; the finishing rolling inlet temperature is 1005℃, the finishing rolling outlet temperature is 890℃, and the coiling temperature is controlled at 610℃. The reduction rate of the finishing rolling end stand is 20%.

[0076] The laminar cooling mode is concentrated cooling at the front end and slow cooling to room temperature after rolling.

[0077] The 14.0 mm high fatigue and high strength drive axle housing steel produced in this 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 -20°C of 232 J after transverse mechanical property testing. In the fatigue performance test, it can withstand 840,000 cycles of loading.

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

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

[0080] Example 3

[0081] Compared with Example 1, the difference lies in that the preparation process parameters are different, the drawing speed is small, and the furnace temperature and the finishing rolling treatment temperature are low.

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

[0083] Casting: Protected casting is adopted, the constant pulling speed is 1.05m / min, and the ratio is ≥98.5%.

[0084] Rolling and cooling: The continuous casting billet is heated in the furnace and the furnace outlet temperature is 1190℃; the finishing rolling inlet temperature is 950℃, the finishing rolling outlet temperature is 860℃, and the coiling temperature is controlled at 570℃.

[0085] The 16mm high fatigue and high strength drive axle housing steel produced in this embodiment has a yield strength of 522MPa, a tensile strength of 610MPa, an elongation after fracture of 25.5%, and a low temperature impact energy of -20°C of 184J after transverse mechanical property testing. The number of cyclic loadings that can be withstood in the fatigue performance test is 820,000 times. The inclusion grades are D0.5 and B0.5.

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

[0087] Example 4

[0088] Compared with Example 1, the difference lies in that the preparation process parameters are different, the drawing speed is low, and the furnace temperature and the finishing rolling treatment temperature are high.

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

[0090] Casting: Protected casting is adopted, the constant pulling speed is 1.05m / min, and the ratio is ≥98.5%.

[0091] Rolling and cooling: The continuous casting billet is heated in the furnace and the furnace outlet temperature is 1225℃; the finishing rolling inlet temperature is 1050℃, the finishing rolling outlet temperature is 910℃, and the coiling temperature is controlled at 630℃.

[0092] The 14mm high fatigue and high strength drive axle housing steel produced in this embodiment has a yield strength of 525MPa, a tensile strength of 618MPa, an elongation after fracture of 26.5%, and a low temperature impact energy of -20°C of 202J after transverse mechanical property testing. The number of cyclic loadings that can be withstood in the fatigue performance test is 840,000 times. The D inclusion level is 1.0.

[0093] The microstructure of the 14 mm 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 and a small amount of bainite with a volume fraction of 1%, a volume fraction of 7% pearlite, and an average grain size of 4.8 μm.

[0094] Example 5

[0095] Compared with Example 1, the difference lies in that the preparation process parameters are different, the finishing temperature and the coiling temperature are low, and the reduction rate is low.

[0096] The different process parameters of this embodiment include:

[0097] Rolling and cooling: The continuous casting billet is heated in the 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 at 550℃. The reduction rate of the finishing rolling end stand is 15%.

[0098] The 16mm high fatigue and high strength drive axle housing steel produced in this embodiment has a yield strength of 537MPa, a tensile strength of 641MPa, an elongation after fracture of 24.5%, and a low temperature impact energy of -20°C of 228J after transverse mechanical property testing. The number of cyclic loadings that can be withstood in the fatigue performance test is 810,000 times. The inclusion grade is B1.0, D0.5.

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

[0100] Example 6

[0101] Compared with Example 1, the difference lies in that the preparation process parameters are different and the finishing temperature is high.

[0102] The different process parameters of this embodiment include:

[0103] Rolling and cooling: The continuous casting billet is heated in the furnace, and the temperature out of the furnace is 1180℃; the entrance temperature of the finishing rolling is 1090℃, the exit temperature of the finishing rolling is 900℃, and the coiling temperature is controlled at 640℃. The reduction rate of the final stand of the finishing rolling is 20%.

[0104] The 16mm high fatigue and high strength drive axle housing steel produced in this embodiment has a yield strength of 502MPa, a tensile strength of 585MPa, an elongation after fracture of 26%, and a low temperature impact energy of -20°C of 165J after transverse mechanical property testing. The number of cyclic loadings that can be withstood in the fatigue performance test is 820,000 times. The D inclusion level is 1.0.

[0105] The microstructure of the 16 mm 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 and a small amount of bainite with a volume fraction of 1%, a volume fraction of 7% pearlite, and an average grain size of 4.2 μm.

[0106] Comparative Example 1

[0107] Compared with Example 1, the components of the steel for the comparative bridge housing are different, with a higher manganese content. The addition of titanium easily forms square titanium nitride inclusions in the steel. Specifically, C is 0.0891wt%, Mn is 1.5240wt%, Si is 0.1201wt%, Nb is 0.0120wt%, V is 0.0026wt%, Ti is 0.0654%, S is 0.0064wt%, P is 0.0187wt%, Alt is 0.0354%, and the rest are Fe and unavoidable impurities.

[0108] Compared with Comparative Example 1, the preparation method of this comparative example has the following differences:

[0109] The converter end point [O] is 940ppm, [N] is 58ppm, and the tapping adopts the double-gear control method. During LF refining, the ladle is not allowed to drain, the soft blowing time is 8min, the calming time is 12min, and the [N] at the time of leaving the station is 55ppm. Protective casting is adopted, the constant pulling speed is 1.05m / min, and the ratio is ≥98.5%.

[0110] The continuous casting billet is heated in the furnace, and the temperature out of the furnace is 1205℃; the finishing rolling inlet temperature is 967℃, the finishing rolling outlet temperature is 890℃, and the coiling temperature is controlled at 580℃. The reduction rate of the final stand of the finishing rolling is 18%. The laminar cooling mode is front-end centralized cooling. When producing 16mm, the second and seventh groups of ultra-fast cooling headers are properly opened, and the small flow intervals are separated; after coiling, it is slowly cooled to room temperature.

[0111] The 16mm high fatigue and high strength drive axle housing steel produced in this comparative example has a yield strength of 584MPa, a tensile strength of 670MPa, an elongation after fracture of 22%, and a low temperature impact energy of -20℃ of 97J after transverse mechanical property testing. The number of cyclic loadings that can be withstood in the fatigue performance test is 640,000 times.

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

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

[0114] The above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A steel for a bridge shell, characterized in that: The invention 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 are Fe and trace elements.

2. The steel for axle housing according to claim 1, characterized in that: The microstructure of the steel for the bridge housing includes 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%; the average grain size of the steel for the bridge housing is ≤6μm.

3. The bridge shell steel according to claim 1, characterized in that: The steel for the bridge shell has D-type inclusions ≤1.0 level, Ds-type inclusion size ≤13 μm, and B-type inclusions ≤0.5 level.

4. The steel for axle housing according to any one of claims 1 to 3, characterized in that: The steel used for the bridge housing has a yield strength of ≥460MPa, an elongation after fracture of ≥24%, a low-temperature impact toughness of -20°C of ≥80J, and can withstand cyclic loading times of ≥800,000 times in a fatigue performance test.

5. A method for preparing axle housing steel according to any one of claims 1 to 4, characterized in that: include: Converter smelting: smelting the molten iron in a converter, controlling the end point [O] content ≤ 800ppm and [N] content ≤ 45ppm at the converter smelting to obtain molten steel; LF refining: The molten steel is subjected to LF refining, and the soft blowing time of the inert gas is controlled ≥8min, the calming time of molten steel is ≥10min, and the [N] content is ≤40ppm to obtain refined molten steel; Casting: Casting the refined molten steel at a pulling speed of 1.1m / min to 1.4m / min to obtain a cast billet, wherein the cast billet 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; Rolling and cooling: the ingot is rolled and cooled to obtain the axle housing steel.

6. The method for preparing axle housing steel according to claim 5, characterized in that: In the casting step, the pulling speed is 1.2 m / min, and the constant ratio at this pulling speed is ≥98%.

7. The method for preparing axle housing steel according to claim 5, characterized in that: In the rolling and cooling steps, the ingot obtained by casting is sent to a heating furnace, and the furnace outlet temperature is controlled to be 1180°C to 1250°C, and then rolled. The rolling includes finish rolling, and the inlet temperature of the finish rolling is 950°C to 1080°C, and the outlet temperature of the finish rolling is 820°C to 900°C.

8. The method for preparing axle housing steel according to claim 5, characterized in that: In the rolling and cooling steps, the cumulative reduction rate in the ferrite region is controlled to be ≥18%.

9. The method for preparing axle housing steel according to claim 5, characterized in that: In the rolling and cooling steps, the ingot is heated and rolled before being coiled, and the coiling temperature is 550°C to 630°C.

10. The method for preparing axle housing steel according to any one of claims 5 to 9, characterized in that: In the rolling and cooling steps, the cooling is a front-end concentrated laminar layer cooling mode, and the cooling rate is controlled at ≤30°C / s.

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