Low-cost shaft lever type non-conditioned steel rolling method

Abstract

The invention relates to a rolling method of low-cost shaft lever type non-conditioned steel, the shaft lever type non-conditioned steel comprises the following components in percentage by mass: 0.42-0.50% of C, 0.17-0.37% of Si, 0.50-0.80% of Mn, less than or equal to 0.035% of P, less than or equal to 0.035% of S, 0.10-0.25% of Cr, less than or equal to 0.30% of Ni, less than or equal to 0.20% of Cu, less than or equal to 0.10% of V, 0.010-0.035% of Al and the balance of matrix Fe and inevitable impurities, and the rolling method of the shaft lever type non-conditioned steel comprises the working procedures of billet heating, rough rolling, intermediate rolling, finish rolling, water cooling and cooling bed cooling. The self-tempering temperature of a rolled piece is controlled according to the specification of the rolled piece during water cooling, common materials without precious alloy elements can be adopted, the cost of small-specification shaft lever non-tempered steel with the diameter smaller than or equal to 85 mm is reduced, the production efficiency is improved, and meanwhile the performance of the steel is equivalent to the quality which can be achieved through an off-line normalizing process.

Description

Technical Field

[0001] The invention belongs to the technical field of shaft rod steel production, and in particular relates to a low-cost shaft rod non-adjustable steel rolling method. Background Art

[0002] The main functions of the shaft in the mechanical system are to transmit power, support rotating parts, maintain the correct mechanical position, and transform the form of motion. Therefore, compared with bearing steel, shaft steel needs to have better strength, toughness and wear resistance to withstand rotation and bending stress. In order to make the steel have a certain strength and hardness, as well as good plasticity and toughness, the shaft steel also needs to go through quenching and tempering heat treatment processes such as heating, quenching, and tempering. However, due to the limitations of quenched and tempered steel such as long processing cycle, high heat treatment cost, and quenching deformation, it is more desirable to obtain non-quenched and tempered steel that omits the quenching and tempering process and has better original performance. In the prior art, non-quenched and tempered steel is generally strengthened and toughened by microalloying, controlled rolling or controlled rolling forging, controlled cooling and other methods to make its comprehensive performance close to that of quenched and tempered steel. For example, patent CN114015847A discloses a method for producing a 45 steel for direct cutting by using a controlled rolling and controlled cooling process, wherein V, Nb, and Ti are added to the composition for microalloying, and the steel billet after continuous casting is successively subjected to heating, descaling, rolling, billet opening, roller table waiting air cooling, head and tail cutting, continuous rolling, alternating strong cooling and weak cooling through water cooling, and slow cooling to obtain a non-quenched and tempered 45 steel with a specification of Φ140-160mm. However, there are still the following technical difficulties in manufacturing low-cost, small-specification shaft-type non-quenched and tempered steel:

[0003] 1. In order to reduce the equipment load of the billet opening process, large-size billets need to adopt larger heating and billet opening temperatures, but high-temperature rolling has the risk of grain coarsening and loss of strength and toughness. Therefore, after billet opening, it is necessary to undergo air cooling at room temperature, slow cooling and then low-temperature rolling. At the same time, due to the influence of large specifications, strong cooling and rapid cooling are required first, and then slow cooling is required during rolling controlled cooling to reduce the risk of steel cracking. This leads to many non-quenching and tempering processes, long processes and high costs for shafts and rods. In order to improve production efficiency, the billet opening process is omitted, and the rolling temperature is relatively high, which will increase the difficulty of controlled cooling. At the same time, the cooling control of shafts and rods of different specifications is different. The heat between the cores on the same cross section will diffuse and conduct to the surface of the rolled piece. Improper controlled cooling can easily lead to increased surface hardness of the billet, high production cost, and aggravated tool wear in subsequent turning processing, which is not conducive to production, or increase the precipitation of coarse ferrite, resulting in insufficient grain size, insufficient strength and toughness of mechanical properties, and failure to meet the mechanical performance requirements.

[0004] Second, strengthening by adding precious alloys such as Nb and Ti requires the addition of N elements for bonding, and combined with process methods such as controlled rolling and controlled cooling. On the one hand, this increases the production cost. For the purpose of reducing costs, eliminating microalloys will bring about a certain loss of strength and toughness. On the other hand, more carbonitrides precipitate at the grain boundaries, which will lead to poor surface quality of continuous casting billets and small-sized round steels. Summary of the invention

[0005] The present invention aims to solve at least one of the above-mentioned technical problems to a certain extent. The present invention provides a low-cost method for rolling non-adjustable steel for shaft rods, which can reduce the cost of small-size non-adjustable steel products for shaft rods with a diameter of ≤85mm, improve production efficiency, and avoid problems such as surface cracks and insufficient strength and toughness of products.

[0006] The technical solution adopted by the present invention to solve the technical problem is:

[0007] A low-cost non-adjustable steel rolling method for shaft rods, the rolling method comprising:

[0008] (1) Billet heating: The billet is heated until the surface and core temperatures are consistent and the structure is austenitized;

[0009] (2) rolling: the steel billet heated in step (1) is subjected to rough rolling, intermediate rolling and finish rolling, and the rolling start temperature is controlled to be 950-1070° C. to obtain a rolled product;

[0010] (3) Water cooling: Cool the rolled piece obtained in step (2) through water:

[0011] For rolled products with a diameter of Ф≤40mm or with a diameter of Ф>50mm and ≤60mm, the red-return temperature of the rolled products shall be controlled to be 630~650℃;

[0012] For rolled products with diameters of Ф>40mm and ≤50mm, the red-return temperature of the rolled products shall be controlled at 640~660℃;

[0013] For rolled products with diameters of Ф>60mm and ≤70mm, the red-return temperature of the rolled products shall be controlled at 620~640℃;

[0014] For rolled products with diameters of Ф>70mm and ≤80mm, the red-return temperature of the rolled products shall be controlled at 610~630℃;

[0015] For rolled products with diameters of Ф>80mm and ≤85mm, the red-returning temperature of the rolled products shall be controlled at 600~620℃;

[0016] (4) Cooling on a cooling bed: The rolled product after step (3) is placed on a cooling bed for natural cooling to obtain non-adjustable steel for shafts and rods.

[0017] The above rolling method omits the step of opening the blank and directly rolls after heating. There is no need to wait for the temperature in the middle, which can speed up the production rhythm. At the same time, a higher rolling temperature is selected to create favorable conditions for the plastic deformation of the steel blank, reduce the wear on the rolling line, and improve the rolling efficiency. It avoids the coarse grain caused by excessively high rolling temperature. After rolling, the temperature of the rolled piece returning to red is controlled according to the specifications of the rolled piece:

[0018] On the one hand, the cooling penetration capacity of water cooling for rolled products of different specifications should be fully considered to avoid excessive cooling intensity and too low red-returning temperature of rolled products, which will increase the surface hardness of rolled products and aggravate tool wear in subsequent turning processing. It is also necessary to avoid too low cooling intensity and too high red-returning temperature of rolled products, which will cause too low surface hardness of rolled products and increase the precipitation of coarse ferrite, resulting in insufficient grain size, mechanical properties and toughness of rolled products. Grain refinement and the formation of fine pearlite structure can be promoted by controlling the red-returning temperature of rolled products.

[0019] On the other hand, full consideration is given to the performance margins of rolled products of different specifications to avoid unnecessary increase in production energy consumption due to excessive cooling intensity and too low red-returning temperature of rolled products, to avoid surface cracks on products, and to avoid loss of material strength and toughness due to too low cooling intensity and too high red-returning temperature of rolled products. The wire rod can be naturally cooled on the cooling bed after water cooling, without the need for slow cooling with a cover, and the offline speed is faster. In this way, the grain size can be refined through effective controlled cooling, the surface hardness of small-size rolled products with a diameter of ≤85mm can be controlled, the strength and toughness indicators can be improved, the non-adjustable steel requirements of shafts can be met, and the addition of precious alloys such as Nb and Ti can be avoided for strengthening, further effectively reducing manufacturing costs.

[0020] In order to further enable the steel billet to be burned through and promote the homogenization of the steel billet composition, appropriate high temperature section temperature and holding time are selected to achieve suitable plasticity, create conditions for rolling deformation after being taken out of the furnace, and avoid burning caused by excessive temperature and excessive holding time. In a preferred embodiment, in the step (1), the heating is sequentially increased according to preheating, heating stage 1, heating stage 2 and soaking stage. The heating temperatures of the heating stage 2 and soaking stage are 1080-1160°C, and the holding time of the soaking stage is 60-100min.

[0021] In order to further prevent the oxide scale generated during the heating of the steel billet from being rolled into the surface of the rolled piece and affecting the surface quality, in a preferred embodiment, in the step (2), the steel billet heated in the step (1) is descaled before rolling.

[0022] In order to further improve the grain refinement effect, the selection of a suitable finishing rolling temperature can promote grain refinement and strengthen the matrix, while creating favorable conditions for subsequent water cooling to form a large degree of undercooling, refine the pearlite structure after phase transformation, and improve the strength and toughness of the steel. In a preferred embodiment, in the step (2), the finishing rolling temperature of the rolled piece is controlled to be 890-950°C, and the final rolling temperature is ≥870°C.

[0023] In order to further control the red-return temperature of the rolled piece, appropriate water volume and water pressure in the water tank are selected to avoid excessive cooling intensity, low red-return temperature of the rolled piece or surface cracks of the rolled piece due to excessive water volume or water pressure in the water tank, and to avoid insufficient cooling intensity, excessive red-return temperature of the rolled piece and coarsening of the structure due to insufficient water volume or water pressure in the water tank. In a preferred embodiment, in step (3), the water volume of the water tank for water-through cooling is controlled to be 100-430 L / min, and the water pressure is 2.3-9.5 MPa.

[0024] In order to further control the cooling accuracy of water-through cooling, the water volume fluctuation and water pressure fluctuation of the water tank can be further controlled. In a preferred embodiment, in step (3), the water volume fluctuation of the water tank for water-through cooling is controlled to be ≤20L / min, and the water pressure fluctuation is ≤1.7MPa.

[0025] In a preferred embodiment, in the step (3), the rolled piece is subjected to a first water cooling, a second water cooling and a third water cooling in sequence;

[0026] The water volume of the first water-cooling water tank is 250-430 L / min, and the water pressure is 5-9.5 MPa;

[0027] The water volume of the second water-cooling water tank is 200-430 L / min, and the water pressure is 3-9.5 MPa;

[0028] The water volume of the third water-penetrating cooling water tank is 100-415 L / min, and the water pressure is 2.3-9.5 MPa.

[0029] The three water cooling processes are all carried out after rolling. The water volume and water pressure of the water tank for the first water cooling process are relatively large, which can improve the strong cooling effect, increase the degree of supercooling, and achieve the purpose of fine grain. By further controlling the water volume and water pressure of the water tank for the second and third water cooling processes, the red-returning temperature of the rolled piece and the organizational state during the cooling process can be further controlled, the surface hardness of the rolled piece can be controlled, and the strength and toughness indicators can be improved.

[0030] For rolled products with smaller diameters, appropriately reducing the water volume in the water tank for the third water cooling can adapt to the performance margin of the rolled products and further reduce production energy consumption. In a preferred embodiment, for rolled products with a diameter specification of Ф>40mm and ≤50mm and a diameter specification of Ф>70 and ≤80mm, the water volume in the water tank for the third water cooling is 0 to 50L / min less than the water volume in the water tank for the second water cooling.

[0031] For rolled products with larger diameters, significantly reducing the water volume in the cooling water tank for the third water-penetration can avoid a surge in the surface hardness of the rolled products. In a preferred embodiment, for rolled products with a diameter of Ф≤40mm, a diameter of Ф>50mm and ≤70mm, and a diameter of Ф>80mm and ≤85mm, the water volume in the cooling water tank for the third water-penetration is 50 to 160 L / min less than that in the cooling water tank for the second water-penetration.

[0032] A low-cost non-adjustable steel for axles, wherein the non-adjustable steel for axles is manufactured by any of the above-mentioned low-cost non-adjustable steel rolling methods for axles. For non-adjustable steel for axles with a diameter of ≤85 mm, the steel finally produced can meet the quality requirements that can be achieved by using an offline normalizing process, and meet the user's requirements for material strength, hardness and grain size.

[0033] The non-adjustable steel for shaft rods eliminates precious alloy elements such as Nb and Ti, reduces costs, avoids deterioration of the surface quality of steel billets and round steels, and appropriately adds Cr components to appropriately improve strength. In a preferred embodiment, the components of the non-adjustable steel for shaft rods include, by mass percentage: C: 0.42~0.50%, Si: 0.17~0.37%, Mn: 0.50~0.80%, P≤0.035%, S≤0.035%, Cr: 0.10~0.25%, Ni≤0.30%, Cu≤0.20%, V≤0.10%, Al: 0.010~0.035%, and the rest are matrix Fe and unavoidable impurities.

[0034] Compared with the prior art, the beneficial effects of the present invention are at least:

[0035] (1) The present invention adopts a reasonable controlled rolling and controlled cooling process, which can save the process of opening the blank and waiting for the temperature in the middle, reduce the production process, shorten the production cycle, and improve production efficiency. At the same time, it fully considers the cooling penetration capacity and performance margin of the water-penetrating cooling capacity for rolled pieces of different specifications, and controls the red-returning temperature of the rolled pieces according to the specifications of the rolled pieces to improve the strength and toughness indicators. It can effectively reduce the cost of small-sized shaft rods with a diameter of ≤85mm, so that the steel finally produced can meet the quality requirements that can be achieved by the offline normalizing process, and meet the user's requirements for material strength, hardness and grain size.

[0036] (2) The present invention can use common materials without precious alloy elements, which reduces production costs while reducing the generation of surface cracks, achieving a tensile strength of ≥740MPa, a yield strength of ≥450MPa, an elongation after fracture of ≥15%, a cross-sectional shrinkage of ≥30%, a surface hardness of 220-280HBW, and a grain size of ≥6.0. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0038] Figure 1 This is a grain size photograph of Example 5 of the present invention.

[0039] Figure 2 It is a grain size photograph of comparative example 4 of the present invention. DETAILED DESCRIPTION

[0040] Embodiments of the present invention are described in detail below. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0041] Embodiment 1:

[0042] A preferred embodiment of the low-cost non-adjustable steel rolling method for shaft rods of the present invention is produced according to the process flow of steel billet heating → descaling → rough rolling → intermediate rolling → finishing rolling → first water cooling → second water cooling → third water cooling → cooling on a cooling bed, and specifically includes the following steps:

[0043] (1) Billet heating: The billet is heated until the surface and core temperatures are consistent and the structure is austenitized. The temperature is raised in sequence according to preheating, heating stage 1, heating stage 2 and soaking stage. The heating temperature of the heating stage 2 and soaking stage is 1100°C, and the holding time of the soaking stage is 65 minutes. This allows the billet to reach rollable plasticity and create conditions for rolling deformation after being taken out of the furnace.

[0044] (2) Rolling: The steel billet heated in step (1) is descaled with high-pressure water to remove the oxide scale on the surface of the steel billet, and then the steel billet is sent to a rolling line for rough rolling, intermediate rolling and finishing rolling in sequence. During the rough rolling, the starting rolling temperature is controlled to be 1005-1025°C, the finishing rolling temperature of the rolled piece entering the finishing mill of the rolling line is 920-940°C, and the final rolling temperature is 910-925°C. The finishing rolling process is controlled to refine the grains, and after finishing rolling, a rolled piece with a diameter specification of 30 mm is obtained.

[0045] (3) Water cooling: The rolled piece obtained in step (2) is subjected to first water cooling, second water cooling and third water cooling in sequence, and the red-return temperature of the rolled piece is controlled to be 635±5°C, so as to promote grain refinement, form fine pearlite structure, control the surface hardness of the rolled piece, and improve the strength and toughness indexes. Specifically:

[0046] The water volume of the first water-cooling water tank is 250-270 L / min, and the water pressure is 6.5-8 MPa;

[0047] The water volume of the second water-cooling water tank is 240-260 L / min, and the water pressure is 7-8.5 MPa;

[0048] The water volume of the third water-penetrating cooling water tank is 100-130 L / min, and the water pressure is 3-4.5 MPa.

[0049] (4) The rolled piece after step (3) is placed on a cooling bed for natural cooling without the need for a cover for slow cooling, thereby obtaining non-adjustable steel for shafts and rods.

[0050] Example 2: The difference from Example 1 is that the composition of the shaft rod non-adjustable steel is different from that of Example 1.

[0051] Comparative Example 1: The difference from Example 1 is that the parameter control of the water-through cooling is different from that of Example 1.

[0052] Comparative Example 2: The difference from Example 1 is that the parameter control of the water-through cooling is different from that of Example 1.

[0053] Embodiment 3:

[0054] A preferred embodiment of the low-cost non-adjustable steel rolling method for shaft rods of the present invention is produced according to the process flow of steel billet heating → descaling → rough rolling → intermediate rolling → finishing rolling → first water cooling → second water cooling → third water cooling → cooling on a cooling bed, and specifically includes the following steps:

[0055] (1) Billet heating: The billet is heated until the surface and core temperatures are consistent and the structure is austenitized. The temperature is raised in sequence according to preheating, heating stage 1, heating stage 2 and soaking stage. The heating temperature of the heating stage 2 and soaking stage is 1095°C, and the holding time of the soaking stage is 65 minutes. The billet reaches rollable plasticity and creates conditions for rolling deformation after being taken out of the furnace.

[0056] (2) Rolling: The steel billet heated in step (1) is descaled with high-pressure water to remove the oxide scale on the surface of the steel billet, and then the steel billet is sent to a rolling line for rough rolling, intermediate rolling and finishing rolling in sequence. During rough rolling, the starting rolling temperature is controlled to be 950-970°C, the finishing rolling temperature of the rolled piece entering the finishing mill of the rolling line is 890-910°C, and the final rolling temperature is 870-890°C. The finishing rolling process is controlled to refine the grains, and after finishing rolling, a rolled piece with a diameter specification of 41 mm is obtained.

[0057] (3) Water cooling: The rolled piece obtained in step (2) is subjected to first water cooling, second water cooling and third water cooling in sequence, and the red-returning temperature of the rolled piece is controlled to be 650±5°C, so as to promote grain refinement, form fine pearlite structure, control the surface hardness of the rolled piece, and improve the strength and toughness indexes. Specifically:

[0058] The water volume of the first water-penetrating cooling water tank is 300-320 L / min, and the water pressure is 6-7.5 MPa;

[0059] The water volume of the second water-cooling water tank is 300-320 L / min, and the water pressure is 3.5-5 MPa;

[0060] The water volume of the third water-penetrating cooling water tank is 285-305 L / min, and the water pressure is 5-6.5 MPa.

[0061] (4) The rolled piece after step (3) is placed on a cooling bed for natural cooling without the need for a cover for slow cooling, thereby obtaining a non-adjustable steel for a shaft rod, the grain diagram of which is as follows: Figure 1 shown.

[0062] Example 4: The difference from Example 3 is that the composition of the shaft rod non-adjustable steel is different from that of Example 3.

[0063] Comparative Example 3: The difference from Example 3 is that the parameter control of the water-through cooling is different from that of Example 3.

[0064] Embodiment 5:

[0065] A preferred embodiment of the low-cost non-adjustable steel rolling method for shaft rods of the present invention is produced according to the process flow of steel billet heating → descaling → rough rolling → intermediate rolling → finishing rolling → first water cooling → second water cooling → third water cooling → cooling on a cooling bed, and specifically includes the following steps:

[0066] (1) Billet heating: The billet is heated until the surface and core temperatures are consistent and the structure is austenitized. The temperature is raised in sequence according to preheating, heating stage 1, heating stage 2 and soaking stage. The heating temperature of the heating stage 2 and soaking stage is 1080°C, and the holding time of the soaking stage is 60 minutes. The billet reaches rollable plasticity and creates conditions for rolling deformation after being taken out of the furnace.

[0067] (2) Rolling: The steel billet heated in step (1) is descaled by high-pressure water to remove the oxide scale on the surface of the steel billet, and then the steel billet is sent to a rolling line for rough rolling, intermediate rolling and finishing rolling in sequence. During the rough rolling, the starting rolling temperature is controlled to be 955-975°C, the finishing rolling temperature of the rolled piece entering the finishing mill of the rolling line is 890-910°C, and the final rolling temperature is 870-885°C. The finishing rolling process is controlled to refine the grains, and after finishing rolling, a rolled piece with a diameter specification of 46 mm is obtained.

[0068] (3) Water cooling: The rolled piece obtained in step (2) is subjected to first water cooling, second water cooling and third water cooling in sequence, and the red-return temperature of the rolled piece is controlled to be 645±5°C, so as to promote grain refinement, form fine pearlite structure, control the surface hardness of the rolled piece, and improve the strength and toughness indexes. Specifically:

[0069] The water volume of the first water-cooling water tank is 300-340 L / min, and the water pressure is 8-9.5 MPa;

[0070] The water volume of the second water-cooling water tank is 320-340L / min, and the water pressure is 6-7.5MPa;

[0071] The water volume of the third water-penetrating cooling water tank is 250-370 L / min, and the water pressure is 6.5-8 MPa.

[0072] (4) The rolled piece after step (3) is placed on a cooling bed for natural cooling without the need for a cover for slow cooling, thereby obtaining a non-adjustable steel for a shaft rod, the grain diagram of which is as follows: Figure 1 shown.

[0073] Example 6: The difference from Example 5 is that the composition of the shaft rod non-adjustable steel is different from that of Example 5.

[0074] Comparative Example 4 is different from Example 5 in that the parameter control of the water-through cooling is different from that of Example 5.

[0075] Embodiment 7:

[0076] A preferred embodiment of the low-cost non-adjustable steel rolling method for shaft rods of the present invention is produced according to the process flow of steel billet heating → descaling → rough rolling → intermediate rolling → finishing rolling → first water cooling → second water cooling → third water cooling → cooling on a cooling bed, and specifically includes the following steps:

[0077] (1) Billet heating: The billet is heated until the surface and core temperatures are consistent and the structure is austenitized. The temperature is raised in sequence according to preheating, heating stage 1, heating stage 2 and soaking stage. The heating temperature of the heating stage 2 and soaking stage is 1090°C, and the holding time of the soaking stage is 70 minutes. This allows the billet to reach rollable plasticity and create conditions for rolling deformation after being taken out of the furnace.

[0078] (2) Rolling: The steel billet heated in step (1) is descaled with high-pressure water to remove the oxide scale on the surface of the steel billet, and then the steel billet is sent to a rolling line for rough rolling, intermediate rolling and finishing rolling in sequence. During rough rolling, the starting rolling temperature is controlled to be 960-980°C, the finishing rolling temperature of the rolled piece entering the finishing mill of the rolling line is 895-910°C, and the final rolling temperature is 875-890°C. The finishing rolling process is controlled to refine the grains, and after finishing rolling, a rolled piece with a diameter specification of 51 mm is obtained.

[0079] (3) Water cooling: The rolled piece obtained in step (2) is subjected to first water cooling, second water cooling and third water cooling in sequence, and the red-return temperature of the rolled piece is controlled to be 635±5°C, so as to promote grain refinement, form fine pearlite structure, control the surface hardness of the rolled piece, and improve the strength and toughness indexes. Specifically:

[0080] The water volume of the first water-cooling water tank is 250-270 L / min, and the water pressure is 6.5-8 MPa;

[0081] The water volume of the second water-cooling water tank is 240-260 L / min, and the water pressure is 7-8.5 MPa;

[0082] The water volume of the third water-penetrating cooling water tank is 100-130 L / min, and the water pressure is 3-4.5 MPa.

[0083] (4) The rolled piece after step (3) is placed on a cooling bed for natural cooling without the need for a cover for slow cooling, thereby obtaining non-adjustable steel for shafts and rods.

[0084] Example 8: The difference from Example 7 is that the composition of the shaft rod non-adjustable steel is different from that of Example 7.

[0085] Comparative Example 5: The difference from Example 7 is that the parameter control of the water-through cooling is different from that of Example 7.

[0086] Comparative Example 6: The difference from Example 7 is that the parameter control of the water-through cooling is different from that of Example 7.

[0087] Example 9: The difference from Example 7 is that the composition, diameter specification, and water cooling parameter control of the shaft rod non-adjustable steel are different from those of Example 7.

[0088] Comparative Example 7: The difference from Example 9 is that the parameter control of the water-through cooling is different from that of Example 9.

[0089] Comparative Example 8: The difference from Example 9 is that the parameter control of the water-through cooling is different from that of Example 9.

[0090] Example 10: The difference from Example 7 is that the composition, diameter specification, and water cooling parameter control of the shaft rod non-adjustable steel are different from those of Example 7.

[0091] Comparative Example 9: The difference from Example 10 is that the parameter control of the water-through cooling is different from that of Example 10.

[0092] Comparative Example 10: The difference from Example 10 is that the parameter control of the water-through cooling is different from that of Example 10.

[0093] Example 11: The difference from Example 7 is that the composition, diameter specification, and water cooling parameter control of the shaft rod non-adjustable steel are different from those of Example 7.

[0094] Comparative Example 11: The difference from Example 11 is that the parameter control of the water-through cooling is different from that of Example 11.

[0095] Comparative Example 12 is different from Example 11 in that the parameter control of the water-through cooling is different from that of Example 11.

[0096] The components of the non-adjustable steel for the shaft rods of the above-mentioned embodiments are shown in Table 1 by mass percentage:

[0097] Table 1. Composition of non-adjustable steel for shafts of different embodiments

[0098] Serial number C Si Mn P S Cr Ni Cu V Al Example 1 0.47 0.23 0.75 0.019 0.006 0.15 0.02 0.02 0.003 0.012 Example 2 0.47 0.23 0.74 0.014 0.003 0.16 0.01 0.02 0.003 0.008 Example 3 0.46 0.21 0.74 0.015 0.006 0.15 0.02 0.02 0.003 0.011 Example 4 0.47 0.24 0.73 0.023 0.005 0.15 0.02 0.02 0.005 0.01 Example 5 0.47 0.24 0.76 0.016 0.004 0.16 0.01 0.01 0.004 0.011 Example 6 0.46 0.23 0.76 0.018 0.002 0.15 0.01 0.01 0.003 0.013 Example 7 0.47 0.22 0.74 0.015 0.004 0.16 0.01 0.01 0.003 0.011 Example 8 0.46 0.24 0.74 0.014 0.003 0.15 0.01 0.01 0.003 0.013 Example 9 0.49 0.22 0.73 0.014 0.003 0.15 0.01 0.01 0.003 0.011 Example 10 0.47 0.24 0.74 0.014 0.004 0.15 0.01 0.01 0.003 0.012 Embodiment 11 0.47 0.25 0.73 0.018 0.005 0.15 0.01 0.02 0.003 0.012

[0099] The water-through cooling parameters of the above-mentioned embodiments and comparative examples are shown in Table 2 below:

[0100] Table 2. Water cooling parameters of different embodiments and comparative examples

[0101]

[0102] The properties of the non-adjustable steels for shafts obtained in the above-mentioned embodiments and comparative examples are shown in Table 3 below:

[0103] Table 3. Non-adjustable steel properties of shafts of different embodiments and comparative examples

[0104]

[0105] It can be seen from the results of Examples 1 to 11 that the present invention adopts a reasonable controlled rolling and controlled cooling process, which can save the process of blanking and intermediate waiting for temperature, reduce the production process, shorten the production cycle, and improve production efficiency. Ordinary materials that do not contain precious alloy elements can be used to reduce production costs while reducing the occurrence of surface cracks, achieving a tensile strength of ≥740MPa, a yield strength of ≥450MPa, an elongation after fracture of ≥15%, a cross-sectional shrinkage of ≥30%, a surface hardness of 220 to 280HBW, and a grain size of ≥6.0. It can effectively reduce the cost of small-sized shaft rods and non-adjustable steel products with a diameter of ≤85mm, so that the final steel produced meets the quality requirements that can be achieved by the offline normalizing process, and meets the user's requirements for material strength, hardness and grain size.

[0106] From the comparison results of Example 1 with Comparative Examples 1 and 2, and the comparison results of Example 7 with Comparative Examples 5 and 6, it can be seen that for rolled products with a diameter specification of Ф≤40mm or a diameter specification of Ф>50mm and ≤60mm, it is preferred to control the red-return temperature of the rolled products to 630-650°C, which can refine the grain size, control the surface hardness of the rolled products, and improve the strength and toughness indicators.

[0107] From the comparison results of Example 3 and Comparative Example 3, and the comparison results of Example 5 and Comparative Example 4, it can be seen that for rolled products with a diameter specification of Ф>40mm and ≤50mm, it is preferred to control the red-return temperature of the rolled products to 640-660°C, which can refine the grain size, control the surface hardness of the rolled products, and improve the strength and toughness indicators.

[0108] From the comparison results of Example 9 with Comparative Examples 7 and 8, it can be seen that for rolled products with a diameter specification of Ф>60mm and ≤70mm, it is preferred to control the red-return temperature of the rolled products to 620-640°C, which can refine the grain size, control the surface hardness of the rolled products, and improve the strength and toughness indicators.

[0109] From the comparison results of Example 10 with Comparative Examples 9 and 10, it can be seen that for rolled products with a diameter specification of Ф>70mm and ≤80mm, it is preferred to control the red-return temperature of the rolled products to 610-630°C, which can refine the grain size, control the surface hardness of the rolled products, and improve the strength and toughness indicators.

[0110] From the comparison results of Example 11 with Comparative Examples 11 and 12, it can be seen that for rolled products with a diameter specification of Ф>80mm and ≤85mm, it is preferred to control the red-return temperature of the rolled products to 600-620°C, which can refine the grain size, control the surface hardness of the rolled products, and improve the strength and toughness indicators.

[0111] The series of detailed descriptions listed above are only specific descriptions of feasible embodiments of the present invention, and they are not intended to limit the scope of protection of the present invention. For example, after cooling on the cooling bed, the production is carried out according to the process flow of segmentation → collection → finishing → packaging → weighing → warehousing. Any equivalent embodiments or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A low-cost non-adjustable steel rolling method for shaft rods, characterized in that: The rolling method includes: (1) Billet heating: The billet is heated until the surface and core temperatures are consistent and the structure is austenitized; (2) rolling: the steel billet heated in step (1) is subjected to rough rolling, intermediate rolling and finish rolling, and the rolling start temperature is controlled to be 950-1070° C. to obtain a rolled product; (3) Water cooling: Cool the rolled piece obtained in step (2) through water: For rolled products with a diameter of Ф≤40mm or with a diameter of Ф>50mm and ≤60mm, the red-return temperature of the rolled products shall be controlled to be 630~650℃; For rolled products with diameters of Ф>40mm and ≤50mm, the red-return temperature of the rolled products shall be controlled to be 640~660℃; For rolled products with diameters of Ф>60mm and ≤70mm, the red-return temperature of the rolled products shall be controlled to be 620~640℃; For rolled products with diameters of Ф>70mm and ≤80mm, the red-return temperature of the rolled products shall be controlled at 610~630℃; For rolled products with diameters of Ф>80mm and ≤85mm, the red-returning temperature of the rolled products shall be controlled at 600~620℃; (4) Cooling on a cooling bed: The rolled product after step (3) is placed on a cooling bed for natural cooling to obtain non-adjustable steel for shafts and rods.

2. The low-cost non-adjustable steel rolling method for shaft rods according to claim 1, characterized in that: In the step (1), the heating is sequentially increased according to preheating, heating stage 1, heating stage 2 and soaking stage, the heating temperature of heating stage 2 and soaking stage 3 is 1080-1160° C., and the insulation time of soaking stage 3 is 60-100 min.

3. The low-cost non-adjustable steel rolling method for shaft rods according to claim 1, characterized in that: In the step (2), the temperature of the finished rolling piece is controlled to be 890-950°C, and the final rolling temperature is ≥870°C.

4. The low-cost non-adjustable steel rolling method for shaft rods according to claim 1, characterized in that: In the step (3), the water volume of the water tank for water cooling is controlled to be 100-430 L / min, and the water pressure is controlled to be 2.3-9.5 MPa.

5. The low-cost non-adjustable steel rolling method for shaft rods according to claim 4, characterized in that: In the step (3), the water volume fluctuation of the water tank for water-through cooling is controlled to be ≤20L / min, and the water pressure fluctuation is controlled to be ≤1.7MPa.

6. The low-cost non-adjustable steel rolling method for shaft rods according to claim 4, characterized in that: In the step (3), the rolled piece is subjected to a first water cooling, a second water cooling and a third water cooling in sequence; The water volume of the first water-cooling water tank is 250-430 L / min, and the water pressure is 5-9.5 MPa; The water volume of the second water-cooling water tank is 200-430 L / min, and the water pressure is 3-9.5 MPa; The water volume of the third water-penetrating cooling water tank is 100-415 L / min, and the water pressure is 2.3-9.5 MPa.

7. The low-cost non-adjustable steel rolling method for shaft rods according to claim 6, characterized in that: For rolled products with diameter specifications of Ф>40mm and ≤50mm and rolled products with diameter specifications of Ф>70 and ≤80mm, the water volume of the third water-penetrating cooling water tank is 0 to 50 L / min less than the water volume of the second water-penetrating cooling water tank.

8. The low-cost non-adjustable steel rolling method for shaft rods according to claim 6, characterized in that: For rolled products with diameter specifications of Ф≤40mm, rolled products with diameter specifications of Ф>50mm and ≤70mm, and rolled products with diameter specifications of Ф>80mm and ≤85mm, the water volume of the third water-penetrating cooling water tank is 50 to 160 L / min less than the water volume of the second water-penetrating cooling water tank.

9. A low-cost non-adjustable steel for shafts, characterized in that: The shaft rod type non-adjustable steel is manufactured by the low-cost shaft rod type non-adjustable steel rolling method according to any one of claims 1 to 8.

10. The low-cost non-adjustable steel for shaft rods according to claim 9, characterized in that: The components of the shaft rod non-adjustable steel include, by mass percentage: C: 0.42-0.50%, Si: 0.17-0.37%, Mn: 0.50-0.80%, P≤0.035%, S≤0.035%, Cr: 0.10-0.25%, Ni≤0.30%, Cu≤0.20%, V≤0.10%, Al: 0.010-0.035%, and the rest are matrix Fe and unavoidable impurities.

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