A production process of round steel for low-speed and heavy-load large bearing rings

Abstract

The present invention discloses a production process of round steel for low-speed heavy-load large bearing rings, comprising the following steps: (1) continuous casting billet heating: adopting hot charging process, hot charging temperature is controlled to be ≥550℃; (2) rough rolling: reciprocating rolling, reducing rolling speed; (3) intermediate rolling: the rolled piece realizes austenite recrystallization zone deformation and grain refinement in the continuous rolling unit; (4) finishing rolling: controlling cooling before finishing rolling, controlling the final rolling speed within 1.2m / s, and water cooling to below Ar1 after rolling; (5) slow cooling: the round steel is cooled in a heat preservation cover on a cooling bed. The present invention optimizes and adjusts the heating and rolling processes to reduce the carbide network and band levels, and effectively improves the comprehensive mechanical properties of large bearing rings during processing and use.

Description

Technical Field

[0001] The invention relates to a production process of round steel, in particular to a production process of round steel for low-speed, heavy-load and large-scale bearing rings. Background Art

[0002] The main shaft bearings of large equipment such as railway transportation, mining machinery, metallurgical machinery, chemical machinery, and general machinery are mostly large or extra-large bearings with thick walls (usually more than 35mm). After assembly and commissioning, they enter the service state. Once started, if there is a problem during operation, it is almost impossible to disassemble and replace them. Their fatigue life and stability are directly related to site safety. The service environment of this large bearing ring is basically low-speed and heavy-load. During the operation, it needs to withstand large axial forces and overturning moments, as well as certain radial forces. The load-bearing conditions are complex, so high requirements are placed on its hardness, fatigue strength, good hardenability, impact toughness, and dimensional stability.

[0003] In the manufacture of the above-mentioned rings, the proportion of high-carbon chromium bearing steel used accounts for more than 80% of the total. However, it is necessary to go through stable and advanced smelting, heating, rolling and other processes to obtain raw materials with ideal purity and uniformity of structure. After subsequent forging, heat treatment and machining processes, bearing rings with high contact fatigue limit, high wear resistance and good dimensional stability are manufactured.

[0004] The basic process of processing large bearing rings includes round steel segmentation → heating → forging → ring rolling → spheroidizing annealing → rough machining of inner and outer surfaces of the ring blank → quenching + tempering heat treatment → finishing. The key requirements are that the end surface of large-sized bearing round steel is flat, the internal residual stress is small and can adapt to medium-frequency induction heating conditions (fast heating rate), the spheroidizing annealing structure is uniformly dispersed, the raceway surface of the finished part has high hardness and the core has certain toughness, the core area has refined grains, the carbide band and mesh level is reduced, it has high fatigue limit and elastic limit, and prevents excessive plastic deformation of the bearing under heavy load service environment. It is still difficult to solve the above technical problems in the existing technology. Summary of the invention

[0005] Purpose of the invention: The present invention aims to provide a production process of round steel for low-speed, heavy-load, large-scale bearing rings with high dimensional accuracy and core grain size.

[0006] Technical solution: The production process of round steel for low-speed, heavy-load, large-scale bearing rings of the present invention comprises the following steps:

[0007] (1) Continuous casting billet heating: adopt hot charging process, and the hot charging temperature is controlled to be ≥550℃; by increasing the billet entering the furnace temperature, the temperature of each heating section is reasonably controlled and distributed to avoid overheating and overburning defects in the core;

[0008] (2) Rough rolling: reciprocating rolling, reducing the rolling speed;

[0009] (3) Intermediate rolling: The rolled piece is deformed and the grains are refined in the austenite recrystallization zone in the continuous rolling mill;

[0010] (4) Finishing rolling: Taking advantage of the process layout, cooling is controlled before finishing rolling, the final rolling speed is controlled within 1.2 m / s, and water-cooling is performed to below Ar1 after rolling;

[0011] (5) Slow cooling: The round steel is cooled in an insulating cover on the cooling bed.

[0012] Furthermore, when the hot charging process described in step (1) is loaded into the furnace, the burner of the preheating section is turned on, and the temperature of the preheating section is controlled at 850-1160°C to ensure that the billet exceeds 800°C in the non-heating section, creating conditions for subsequent rapid heating. The heating section is controlled at 1170-1230°C to fully utilize the heating capacity of the heating section so that the core of the continuous casting billet reaches 1200°C to achieve the effect of full cross-section heat penetration of the billet. The upper limit temperature of the heating section 2 and the soaking section is appropriately lowered to 1200-1220°C to ensure that the high-temperature diffusion time of the billet is ≥420 minutes while reducing the risk of overheating in the core area.

[0013] Furthermore, in step (2), the reduction amount of each of the first four passes of rough rolling is ≥70mm, ensuring that the shape parameter of the rolled piece in a single pass is ≥0.80. By increasing the reduction amount of the first few passes, the stress-strain state of the core area is improved, and the temperature rise of the core during the plastic processing process is reduced. The roller speed is reduced by 1 / 3 compared with other product processes, from the original 60-90r / min to 40-60r / min, which increases the deformation degree of the core of the steel billet and further improves the core density and the uniformity of the structure on the cross section. In addition, the double-drum tendency of the intermediate billet produced by this reduction system is greatly reduced, which can improve the bite conditions in the subsequent continuous rolling stage, reduce the non-contact area, and reduce the risk of surface wrinkles and cracks.

[0014] Furthermore, before entering the intermediate rolling mill described in step (3), a roller protection cover is used to control the temperature drop at the corners of the rolled piece and reduce the risk of corner defects; twist-free rolling is achieved by alternately setting the horizontal and vertical continuous rolling mills. From the real-time rolling force monitoring, when the next pass bites in, the rolling force of the previous pass decreases slightly, but the trend is gentle. The entire stage is in micro-tension rolling, and the stable production process is conducive to surface size control and surface quality improvement; the intermediate rolling outlet temperature is controlled at 930-960°C.

[0015] Furthermore, in step (4), the rolled piece starts to move when the temperature of the rolled piece on the marshaling stand reaches ≤860°C, and is cooled to ≤810°C in the water tank before entering the KOCKS finishing mill. The final rolling speed is controlled within 1.2m / s, and the KOCKS rear water tank is opened to cool the rolled piece. The characteristic of this step is that there are air cooling + water tank cooling equipment in front of the finishing mill, and water tank + long conveyor roller (total length of about 200 meters) in the rear, which can ensure that the large-size rolling process can be evenly cooled in sections to the control temperature range, avoiding large internal stress and reducing the risk of surface chilled structure formation. Ensure that the rolled piece is austenitic in the KOCKS unit.

[0016] Furthermore, in step (5), the round steel passes through the cooling bed on the long conveyor roller. During the cooling process, the round steel returns to a red temperature of ≤630°C, at which time the phase change has been completed. The round steel enters the heat preservation cover for simple temperature treatment, and the temperature out of the cover is ≤400°C, further reducing the residual stress inside the rolled piece. Preferably, the diameter of the round steel is 80-120mm.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The dimensional accuracy and grain size of the round steel produced by the process are greatly improved. The present invention adjusts the hot charging temperature of the bearing steel continuous casting billet, fully utilizes the heating capacity of the additional stage to achieve rapid heating of the core, and reasonably reduces the insulation temperature of the last two stages. Combined with the rough rolling with low speed and large pressure, medium rolling with temperature control and continuous rolling, process air cooling + water cooling, KOCKS finishing rolling and temperature uniformity in the insulation cover, the Φ80-120mm specification round steel produced has an allowable diameter deviation of no more than 1 / 2GB / T 702-2017 Table 1: 1 / 2 of the accuracy of Group 1, the curvature is controlled within 2.5‰ of the length of the round steel, the actual grain size of the core area is ≥ Grade 4, and the carbide bands and nets in the core of the longitudinal sample are not more than Grade 3.0; (2) After the round steel is plasma segmented, the end face is flat, and no cracking of the core is found during the medium-frequency induction rapid heating process; the improvement of carbide inhomogeneity is conducive to the stability of spheroidizing annealing + quenching + tempering heat treatment, improves the organizational uniformity of the finished product, and thus ensures the fatigue limit and toughness of the finished ring, and reduces the risk of uneven deformation. The present invention optimizes and adjusts the heating and rolling processes to reduce the carbide net and band levels, and effectively improves the comprehensive mechanical properties of large bearing rings during processing and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is the hot-rolled structure (grain size) diagram of the core of Φ80mm round steel;

[0019] Figure 2 This is the carbide band diagram of the core of Φ80mm round steel after heat treatment;

[0020] Figure 3 This is the carbide network diagram of the core of Φ80mm round steel after heat treatment;

[0021] Figure 4 This is the hot-rolled structure (grain size) diagram of the core of Φ100mm round steel;

[0022] Figure 5 This is the carbide band diagram of the core of Φ100mm round steel after heat treatment;

[0023] Figure 6 This is the carbide network diagram of the core of Φ100mm round steel after heat treatment;

[0024] Figure 7 This is the hot-rolled structure (grain size) diagram of the core of Φ120mm round steel;

[0025] Figure 8 This is the carbide band diagram of the core of Φ120mm round steel after heat treatment;

[0026] Fig. 9 This is the carbide network diagram of the core of Φ120mm round steel after heat treatment. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0028] Example 1

[0029] A high carbon chromium bearing steel continuous casting billet of 320 (thickness) × 480 (width) × 5400 mm (length) was selected, and its chemical composition and mass percentage were: C: 0.97%, Si: 0.24%, Mn: 0.31%, Cr: 1.46%, Mo: 0.002%, P: 0.006%, S: 0.001%, Al: 0.011%, and the remainder was iron, and Φ80 mm round steel was rolled.

[0030] This embodiment includes the following steps:

[0031] (1) The billet is transported to the rolling mill by an insulated car, and the surface temperature of the billet on the furnace side is detected to be 580-600℃; when the billet enters the furnace, all 6 burners in the preheating section are turned on, and the temperature of the preheating section is controlled in the range of 850-1160℃. The core temperature of the billet at the outlet of the non-heating section is 810℃ according to the model calculation, the furnace temperature of the first heating section is controlled at 1170-1230℃, the furnace temperature of the second heating section and the soaking section is controlled at 1200-1220℃, and the high temperature section time is 420min;

[0032] (2) The reductions of the first four passes of rough rolling were 80 mm, 75 mm, 72 mm and 70 mm respectively, and the roll speeds were reduced to 30 r / min, 30 r / min, 50 r / min and 50 r / min respectively, and the single pass shape parameter was ≥ 0.80;

[0033] (3) The actual temperature at the intermediate rolling outlet is 940-955°C;

[0034] (4) The marshaling stand starts to move after the temperature reaches 860℃. After passing through water, the temperature of the KOCKS is 810℃ and the exit speed of the KOCKS is 1.2m / s. After passing through water, it slowly passes through a long conveyor roller to return to temperature.

[0035] (5) The upper cooling bed temperature is ≤630℃ and the outlet temperature of the insulation cover is ≤400℃.

[0036] The metallographic inspection of the large-size high-carbon chromium bearing round steel with a diameter of 80mm produced by the above manufacturing process shows that the actual grain size is level 5, the carbide bands and meshes are not more than level 2.5, the ultrasonic flaw detection meets GB / T 37566 level 3, and the high-frequency water immersion flaw detection shows that there are no defects inside the round steel.

[0037] Figure 1-3 This is the metallographic structure diagram (core area) of the 80mm diameter high carbon chromium bearing round steel in Example 1 along the rolling direction. The actual grain size is 5, the carbide bands are at level 2.0, and the carbide network is at level 2.0.

[0038] Example 2

[0039] A high carbon chromium bearing steel continuous casting billet of 320 (thickness) × 480 (width) × 5400 mm (length) was selected, and its chemical composition and mass percentage were: C: 0.98%, Si: 0.23%, Mn: 0.32%, Cr: 1.45%, Mo: 0.001%, P: 0.009%, S: 0.001%, Al: 0.012%, and the remainder was iron, and Φ100 mm round steel was rolled.

[0040] This embodiment includes the following steps:

[0041] (1) The billet is transported to the rolling mill by an insulated car, and the surface temperature of the billet on the furnace side is detected to be 570-590℃; when the billet enters the furnace, all 6 burners in the preheating section are turned on, and the temperature of the preheating section is controlled in the range of 870-1160℃. The core temperature of the billet at the outlet of the non-heating section is 816℃ according to the model calculation, the furnace temperature of the first heating section is controlled at 1170-1230℃, the furnace temperature of the second heating section and the soaking section is controlled at 1200-1220℃, and the high temperature section time is 430min;

[0042] (2) The reductions of the first four passes of rough rolling were 79 mm, 72 mm, 75 mm and 70 mm respectively, and the roll speeds were reduced to 30 r / min, 30 r / min, 50 r / min and 50 r / min respectively, and the shape parameter of a single pass was ≥ 0.80;

[0043] (3) The actual temperature at the intermediate rolling outlet is 930-950°C;

[0044] (4) The marshaling stand starts to move when the temperature reaches 850℃. After passing through water, the temperature of the KOCKS is 800℃ and the exit speed of the KOCKS is 1.0m / s. After passing through water, it slowly passes through a long conveying roller to return to temperature.

[0045] (5) The upper cooling bed temperature is ≤620℃, and the temperature out of the insulation cover is ≤380℃.

[0046] The metallographic inspection of the large-size high-carbon chromium bearing round steel with a diameter of 100mm produced by the above manufacturing process shows that the actual grain size is level 4, the carbide bands and meshes are not more than level 2.5, the ultrasonic flaw detection meets GB / T 37566 level 3, and the high-frequency water immersion flaw detection shows that there are no defects inside the round steel.

[0047] Figure 4-6 This is the metallographic structure diagram (core area) of the 100mm diameter high carbon chromium bearing round steel in the rolling direction of Example 2. The actual grain size is 4, the carbide band is 2.5, and the carbide network is 2.5.

[0048] Example 3

[0049] A high carbon chromium bearing steel continuous casting billet of 320 (thickness) × 480 (width) × 5400 mm (length) was selected, and its chemical composition and mass percentage were: C: 0.97%, Si: 0.23%, Mn: 0.35%, Cr: 1.50%, Mo: 0.003%, P: 0.005%, S: 0.001%, Al: 0.015%, and the remainder was iron, and Φ120 mm round steel was rolled.

[0050] This embodiment includes the following steps:

[0051] (1) The billet is transported to the rolling mill by an insulated car, and the surface temperature of the billet on the furnace side is detected to be 590-610℃; when the billet enters the furnace, all 6 burners in the preheating section are turned on, and the temperature of the preheating section is controlled in the range of 880-1160℃. The core temperature of the billet at the outlet of the non-heating section is 825℃ according to the model calculation, the furnace temperature of the first heating section is controlled at 1170-1230℃, the furnace temperature of the second heating section and the soaking section is controlled at 1200-1220℃, and the high temperature section time is 450min;

[0052] (2) The reductions of the first four passes of rough rolling were 80 mm, 76 mm, 73 mm and 71 mm respectively, and the roll speeds were reduced to 30 r / min, 30 r / min, 50 r / min and 50 r / min respectively, and the shape parameter of a single pass was ≥ 0.80;

[0053] (3) The actual temperature at the intermediate rolling outlet is 930-940°C;

[0054] (4) The marshaling stand starts to move after the temperature reaches 840℃. After passing through water, the temperature of the KOCKS is 790℃ and the exit speed of the KOCKS is 0.8m / s. After passing through water, it slowly passes through a long conveyor roller to return to temperature.

[0055] (5) The upper cooling bed temperature is ≤610℃, and the temperature out of the insulation cover is ≤360℃.

[0056] The metallographic inspection of the large-size high-carbon chromium bearing round steel with a diameter of 100mm produced by the above manufacturing process shows that the actual grain size is level 4, the carbide bands and meshes are not more than level 2.5, the ultrasonic flaw detection meets GB / T 37566 level 3, and the high-frequency water immersion flaw detection shows that there are no defects inside the round steel.

[0057] Figure 7-9 This is the metallographic structure diagram (core area) of the 120 mm diameter high carbon chromium bearing round steel in Example 3 along the rolling direction. The actual grain size is level 4, the carbide bands are at level 2.5, and the carbide network is at level 2.5.

[0058] The actual measured dimensions and shape of round steel off the production line, the allowable diameter deviation shall not exceed half of Group 1 in Table 1 of GB / T 702 (standard requirements: the dimensional tolerance of the 80mm diameter specification is ±0.6mm, the dimensional tolerance of the 100mm and 120mm diameter specifications is ±1.2mm), and the curvature is controlled at 2.5‰.

[0059] Table 1

[0060] Actual diameter range Curvature Example 1 80.10-80.32 2.5‰ Example 2 100.16-100.58 2.5‰ Example 3 120.36-120.62 2.5‰

Claims

1. A production process of round steel for low-speed, heavy-load, large-scale bearing rings, characterized in that: The steps include: (1) Continuous casting billet heating: hot charging process is adopted, and the hot charging temperature is controlled at ≥550℃; (2) Rough rolling: reciprocating rolling, reducing the rolling speed; (3) Intermediate rolling: The rolled piece is deformed and the grains are refined in the austenite recrystallization zone in the continuous rolling mill; (4) Finishing rolling: Control cooling before finishing rolling, control the final rolling speed within 1.2m / s, and water cool to below Ar1 after rolling; (5) Slow cooling: The round steel is cooled in a heat preservation cover on the cooling bed; When the hot charging process described in step (1) is used for charging the furnace, the burner of the preheating section is turned on, the temperature of the preheating section is controlled at 850-1160°C, the temperature of the first heating section is controlled at 1170-1230°C, the temperature of the second heating section and the soaking section is controlled at 1200-1220°C, and the high-temperature diffusion time of the continuous casting billet is ensured to be ≥420 minutes; In step (2), the first four rough rolling passes have a reduction of ≥70 mm per pass, ensuring that the shape parameter of the rolled piece per pass is ≥0.80, and the roller speed is 40-60 r / min; In step (3), before the rolled piece enters the tandem rolling mill, it also passes through a roller protection cover to control the temperature drop at the corner of the rolled piece and reduce the risk of corner defects; the tandem rolling mills are alternately arranged horizontally and vertically to achieve torsion-free rolling; the outlet temperature of the intermediate rolling mill is controlled at 930-960°C; During the cooling process of the round steel in the heat preservation cover on the cooling bed in step (5), the round steel returns to red temperature ≤630°C, enters the heat preservation cover for temperature equalization treatment, and the temperature out of the cover is ≤400°C.

2. The production process of round steel for low-speed, heavy-load, large-scale bearing rings according to claim 1 is characterized in that: The controlled cooling method before finishing rolling in step (4) is air cooling + water tank equipment cooling.

3. The production process of round steel for low-speed, heavy-load, large-scale bearing rings according to claim 1 is characterized in that: The temperature after water cooling in step (4) is ≤810°C.

4. The production process of round steel for low-speed, heavy-load, large-scale bearing rings according to claim 1 is characterized in that: The diameter of the round steel is 80-120 mm.

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