High-carbon high-alloy grinding ball steel internal damage control rolling method

Abstract

The invention discloses a high-carbon high-alloy grinding ball steel rolling internal damage control method, and belongs to the technical field of metal material rolling machining. Comprising the following steps that high-carbon high-alloy grinding ball steel billets are subjected to high-temperature diffusion homogenization treatment and then subjected to staged temperature control rolling, the initial rolling temperature in the blooming stage is 1020-1080 DEG C, the single-pass reduction rate is 6-10%, the pass interval is larger than or equal to 20 seconds, the total reduction rate is 40-80%, and the core peak temperature is controlled to be smaller than or equal to 1150 DEG C; the finish rolling temperature is 800-850 DEG C; during rolling, atomized water is sprayed for dynamic cooling every 2-3 passes, and two-stage cooling (water cooling to 600-650 DEG C at 15-20 DEG C / s, and slow cooling to room temperature) is carried out after final rolling. According to the method, element diffusion, temperature rise inhibition and structure refinement are synergistically regulated and controlled, so that the core void ratio is reduced, the austenite grain size is larger than or equal to 8 grades, a uniform bainite and dispersed carbide composite structure is obtained, and the anti-fatigue performance of the grinding ball steel is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal material rolling processing, and specifically relates to a method for controlling internal damage of high-carbon high-alloy grinding ball steel by high-temperature heating diffusion, optimization of the start rolling temperature and suppression of the rolling temperature rise, focusing on solving the problems of central cavity defects and internal cracks in the rolling process, and compensating for the central defects of the continuous casting billet. Background Art

[0002] High carbon and high alloy grinding ball steel (such as C 0.8% to 1.5%, Cr 2% to 5%, Mo 0.5% to 1.5%) is widely used in the manufacture of mining grinding media due to its high hardness and wear resistance. However, there are the following technical bottlenecks in its rolling process:

[0003] 1. Element segregation and core voids: The alloy elements such as Cr and Mo are unevenly distributed in the cast billet. During high-temperature rolling, the core temperature rises too fast (locally exceeding 1200°C), resulting in local dissolution and re-precipitation of carbides, forming micron-sized voids.

[0004] 2. Uncontrolled rolling temperature rise: The traditional process uses high rolling temperature (≥1150℃) and multiple rapid rolling. The deformation heat accumulation causes the core temperature to rise significantly, aggravating the uneven structure and phase change stress.

[0005] 3. Hidden dangers in subsequent processing: The core cavity is easy to develop into cracks during subsequent heat treatment or service, reducing the fatigue life of the grinding balls.

[0006] Existing technologies mostly improve performance by adding post-rolling heat treatment, but cannot suppress core defects from the source of rolling. Therefore, a rolling process that takes into account element diffusion, temperature rise suppression and low stress forming is urgently needed. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a method for controlling internal damage during rolling of high-carbon and high-alloy grinding ball steel, which reduces the rolling temperature rise and eliminates core cavities and internal cracks through the synergistic effects of high-temperature diffusion homogenization, staged temperature-controlled rolling and dynamic cooling.

[0008] In order to achieve the above technical purpose, the technical solution adopted by the present invention is:

[0009] The composition of the high carbon high alloy steel billet, by mass percentage, is: C: 0.95-1.3%, Mn: 0.9-1.0%, Cr: 2.1-4.0%, Mo: 0.5-0.9%, N: 0.006-0.01%; V: 0.1-0.8%, and the balance is Fe and unavoidable impurities.

[0010] High temperature diffusion homogenization pretreatment: High carbon and high alloy steel billet is heated to 1220-1280℃ and kept warm for 3-7 hours.

[0011] Furthermore, a stepped temperature increase is adopted: the hot charging temperature of the steel billet is ≥400°C,

[0012] Stage 1: The hot charging temperature ranges from 400 to 750 - 800°C, with a heating rate of 30 - 40°C / h, holding for 1 - 2 h, and the core-surface temperature difference ≤60°C; hold for 1 - 2 h.

[0013] Stage 2: The temperature ranges from 750 - 800°C to 950 - 1000°C, with a heating rate of 40 - 50°C / h, holding for 1.5 - 2.5 h, and the core-surface temperature difference ≤30°C; hold for 2 - 3 h.

[0014] Stage 3: The temperature ranges from 950 - 1000°C to 1220 - 1280°C, with a heating rate of 25 - 30°C / h, and the core-surface temperature difference ≤15°C; hold for 3 - 5 h.

[0015] Controlled rolling with staged temperature control:

[0016] Initial rolling stage: The starting rolling temperature is reduced to 1020 - 1080°C, and multi-pass small reduction amounts are adopted (the reduction rate per pass is 6 - 10%), the peak temperature at the core ≤1150°C, the interval time between passes ≥20 seconds, and the temperature rise is suppressed by extending the heat dissipation time; the total thickness reduction rate is 40% - 80%.

[0017] The rolling speed is regulated in sections. The speed in the first 5 - 7 passes is 1.0 - 1.5 m / s, and the speed in the subsequent passes is reduced to 0.6 - 1.0 m / s.

[0018] Final rolling stage: The final rolling temperature is controlled at 800 - 850°C.

[0019] Dynamic cooling to suppress temperature rise: During rolling, atomized water is sprayed on the surface of the steel billet every 2 - 3 passes (the water temperature is 30 - 50°C, and the spraying time ≤5 seconds) to reduce the surface temperature by 50 - 80°C, forming a gradient heat dissipation condition; the surface temperature after spraying ≤700°C, and the core-surface temperature difference expands to 70 - 90°C (accelerating the heat dissipation at the core).

[0020] After final rolling, two-stage cooling is adopted: First, water-cool at a rate of 15 - 20°C / s to 600 - 650°C, and then slow-cool at a rate ≤5°C / s to room temperature to avoid the martensite transformation stress at the core.

[0021] Furthermore, slow cooling is carried out by air cooling or stacking cooling.

[0022] Furthermore, as an optimization, the interval time between passes is 25 - 30 seconds.

[0023] Furthermore, as an optimization, the peak temperature at the core in the initial rolling stage is controlled at 1100 - 1140°C.

[0024] Key innovation points:

[0025] (1) Element segregation elimination and tissue homogenization: Through high-temperature diffusion at 1220 - 1280 °C and stepwise heating (core-surface temperature difference ≤ 30 °C), promote the full diffusion of Cr and Mo carbide-forming elements, reduce micro-segregation by ≥ 70%, and avoid the central cavity caused by abnormal dissolution of carbides during rolling.

[0026] (2) Lower the starting rolling temperature to 1020 - 1080 °C, combine with multi-pass small reduction (6 - 10% per pass) and pass interval ≥ 20 seconds, cooperate with dynamic spray cooling (surface temperature reduction 50 - 80 °C per time), the peak temperature at the core ≤ 1150 °C, 80 - 100 °C lower than the traditional process, effectively inhibit the micro-cavities caused by the carbide dissolution-reprecipitation cycle.

[0027] (3) Finish rolling temperature 800 - 850 °C and two-stage cooling process, avoid martensite transformation at the core, release residual stress during the slow cooling stage (≤ 5 °C / s), and form a uniform and fine bainite (grain size ≥ 8) and dispersed carbides in the tissue.

[0028] (4) After optimization, the central cavity rate is reduced from 50% of the traditional process to ≤ 0.02%, the risk of crack propagation during subsequent processing and service is reduced by more than 90%, and the life of grinding balls is extended by 40%. Description of the Drawings

[0029] Figure 1 : Central tissue of the rolled material prepared by the traditional process;

[0030] Figure 2 : Central tissue of the rolled material prepared by the process of Example 1 of the present invention;

[0031] Figure 3 : Simulation results of the temperature field during rolling, showing the core-surface temperature difference and the temperature rise inhibition effect. Detailed Embodiments

[0032] Example 1:

[0033] Steel grade composition: 1.0% C, 0.93% Mn, 3.2% Cr, 0.8% Mo, 0.3% V, 0.007% N, the rest is Fe;

[0034] Roll a steel billet of 300 * 320 mm into Φ80 mm.

[0035] Process parameters:

[0036] a. Stepwise heating:

[0037] Stage 1: Hot delivery of the steel billet from 400 → 800 °C, heating rate 35 °C / h, core-surface temperature difference ≤ 50 °C (holding for 1 h);

[0038] Stage 2: 800 → 1000 °C, heating rate 45 °C / h, core-surface temperature difference ≤ 30 °C (holding for 2 h);

[0039] Stage 3: 1000 → 1270 °C, heating rate 30 °C / h, core-surface temperature difference ≤ 15 °C (holding for 3.5 h);

[0040] The final core-surface temperature difference ≤ 10 °C.

[0041] b. Rolling in stages:

[0042] The starting rolling temperature is 1050 °C, and it is rolled in 15 passes:

[0043] For the first 7 passes: reduction rate 9%, rolling speed 1.0 m / s, pass interval 25 s (core temperature rise ≤ 15 °C /

[0044] pass); for the last 3 passes: reduction rate 7%, rolling speed 0.6 m / s, pass interval 30 s (core temperature rise ≤ 8 °C / pass), the peak core temperature is 1100 °C; the remaining specifications are allocated for the last 5 passes.

[0045] c. Dynamic cooling:

[0046] Spray atomized water at 40 °C for 4 s every 2 passes (surface temperature drop 60 °C), the surface temperature after spraying ≤ 700 °C, and the core-surface temperature difference expands to 80 °C (accelerating core heat dissipation).

[0047] d. Cooling after final rolling:

[0048] The final rolling temperature is 800 °C, and it is immediately water-cooled to 630 °C at 18 °C / s (cooling time 9.5 s);

[0049] Transfer to a slow cooling pit and cool to room temperature at 1 °C / s.

[0050] Test results:

[0051] Flaw detection defects: Ultrasonic testing is carried out through GE ultrasonic equipment (testing standard GB / T

[0052] 31211.1 - 2024) ≥ φ1 mm equivalent core defects (void ratio) is 0%. (Traditional process defect rate 20%). Core defects (void ratio): It is the ratio of the number of bars with voids and pores in the core to the total number of flaw-detected bars.

[0053] The average impact energy (testing standard ASTM A370 - 2021) of Example 1 is 30 J, and the average impact energy of the traditional process is 21 J; the average life of Example 1 is 150 g / ton of material (the detection method of life is the weight of steel balls consumed by steel balls grinding ores and other materials), and the life of the traditional process is 108 g / ton.

[0054] In Example 1, the grain size of the structure after rolling is Grade 9.0.

[0055] Example 2:

[0056] A steel billet of 300*320mm is rolled into Φ80mm.

[0057] Steel grade composition: 1.0% C, Mn: 0.95%, 3.2% Cr, 0.8% Mo, 0.3% V, 0.008% N, and the rest is Fe;

[0058] Process parameters: A steel billet of 300*320mm is rolled into Φ80mm;

[0059] a. Stepwise heating:

[0060] Stage 1: The hot-rolled steel billet is heated from 400 to 800°C at a heating rate of 35°C / h, and the core-surface temperature difference ≤ 50°C (holding for 1h);

[0061] Stage 2: From 800 to 1000°C at a heating rate of 45°C / h, and the core-surface temperature difference ≤ 30°C (holding for 2h);

[0062] Stage 3: From 1000 to 1270°C at a heating rate of 30°C / h, and the core-surface temperature difference ≤ 15°C (holding for 3.5h);

[0063] The final core-surface temperature difference ≤ 10°C.

[0064] b. Staged rolling:

[0065] The starting rolling temperature is 1030°C, and it is rolled in 15 passes:

[0066] The first 7 passes: The reduction rate is 9%, the rolling speed is 1.4m / s, and the pass interval is 25 seconds (the core temperature rise ≤ 15°C /

[0067] pass);

[0068] The last 3 passes: The reduction rate is 7%, the rolling speed is 0.7m / s, and the pass interval is 30 seconds (the core temperature rise ≤ 8°C /

[0069] pass). The peak temperature of the core is 1140°C, and the remaining specifications are distributed for the last 5 passes.

[0070] c. Dynamic cooling:

[0071] Spray atomized water at 40°C for 3 seconds every 2 passes (the surface temperature drops by 60°C). After spraying, the surface temperature ≤ 700°C, and the core-surface temperature difference expands to 80°C (accelerating the heat dissipation of the core).

[0072] d. Cooling after final rolling:

[0073] The final rolling temperature is 815°C, and it is immediately water-cooled to 630°C at a rate of 18°C / s (cooling time 12 seconds);

[0074] Transfer to the slow cooling pit and cool to room temperature at 1 °C / s.

[0075] Test results:

[0076] Flaw detection defect: Ultrasonic testing (testing standard GB / T 31211.1-2024) ≥ equivalent defect rate (void rate) of φ1mm is 5%.

[0077] The average impact energy (testing standard ASTMA370-2021) is 29 J, and the average life is 130 g / ton of material. The grain size of the structure is 8.5 grades.

[0078] Example 3

[0079] Steel grade composition: 0.9% C, 0.92% Mn, 2.8% Cr, 0.6% Mo, 0.4% V, 0.007% N, and the rest is Fe;

[0080] Process parameters:

[0081] Roll a steel billet of 300*320mm into Φ80mm.

[0082] a. Stepwise temperature rise:

[0083] Stage 1: Hot delivery from 400 to 750 °C, temperature rise rate of 30 °C / h (holding for 1.5 h, core-surface temperature difference ≤ 60 °C); Stage 2: From 750 to 950 °C, temperature rise rate of 40 °C / h (holding for 2.5 h, core-surface temperature difference ≤ 25 °C);

[0084] Stage 3: From 950 to 1230 °C, temperature rise rate of 25 °C / h (holding for 5 h, core-surface temperature difference ≤ 10 °C).

[0085] The final core-surface temperature difference ≤ 10 °C.

[0086] b. Segmented control of rolling speed:

[0087] The rolling start temperature is 1070 °C, and it is rolled in 15 passes:

[0088] Rough rolling stage (the first 5 passes): Reduction ratio of 10%, rolling speed of 1.0 m / s, pass interval of 22 seconds;

[0089] Finish rolling stage (the last 5 passes): Reduction ratio of 8%, rolling speed of 0.6 m / s, pass interval of 35 seconds, and the remaining specifications are distributed for the last 5 passes;

[0090] The peak temperature in the core during the rolling process is 1120 °C (1250 °C for the traditional process).

[0091] c. Dynamic cooling:

[0092] Spray atomized water at 45°C for 4 seconds every 3 passes, the surface temperature drops by 70°C, and the temperature difference between the core and the surface after spraying reaches 90°C.

[0093] d. Cooling after finish rolling:

[0094] The finish rolling temperature is 845°C, water-cooled to 600°C at a rate of 16°C / s (cooling time 15 seconds);

[0095] Stack and slow cool (covered with heat insulation cotton) to room temperature at a rate of 4°C / s.

[0096] Test results:

[0097] Flaw detection defects: Ultrasonic testing (testing standard GB / T 31211.1 - 2024) ≥ equivalent defect rate of φ1mm, that is, the cavity rate is 1%.

[0098] The impact energy of the grinding ball (testing standard ASTMA370 - 2021) is 25J, and the average life is 140g / ton of material. The grain size of the structure is 8.0 grade.

[0099] Comparative Example 1 (traditional process)

[0100] The traditional process steel billet of 300*320mm is rolled into Φ80mm, hot delivered at 400→1200°C, and the heating rate is 160°C / h (holding for 1.5h, temperature difference between core and surface ≤ 150°C)

[0101] Rolled by continuous rolling for 13 passes, the single-pass reduction ratio is 25%, no temperature control in the middle, the starting rolling temperature is 1100°C, the finish rolling temperature is 1000°C, and it is cooled to room temperature by walking air cooling on the cooling bed.

[0102] Specifically: The speed of the first pass is 0.5m / s, continuous rolling of the first 7 rolling mills, the maximum temperature rise in the core is 1250°C, continuous rolling of the last 6 rolling mills, the speed of the 8th rolling mill is 0.8m / s, no cooling in the middle, and the surface temperature after finish rolling is 1000°C. After splitting and sizing, it is sent to the cooling bed for air cooling to room temperature.

[0103] Flaw detection defects: Ultrasonic testing (testing standard GB / T 31211.1 - 2024) ≥ equivalent defect rate of φ1mm is 20%.

[0104] Comparative Example 2

[0105] The main difference between Comparative Example 2 and Example 1 is that: the rolling speed in the staged rolling Experimental Example 1 is set to 1.8m / s, the rolling speed exceeds the required speed, and the peak temperature in the core reaches 1300°C.

[0106] Specifically:

[0107] Steel grade composition: The same as that in Example 1;

[0108] Process parameters:

[0109] a. Step - by - step heating: The same as in Example 1:

[0110] b. Staged rolling:

[0111] The starting rolling temperature is 1050 °C, and it is rolled in 15 passes:

[0112] For the first 7 passes: The reduction ratio is 9%, the rolling speed is 1.8 m / s, and the pass interval is 25 seconds (the core temperature rise ≤ 15 °C /

[0113] pass); For the last 3 passes: The reduction ratio is 7%, the rolling speed is 1.8 m / s, and the pass interval is 30 seconds (the core temperature rise ≤ 8 °C / pass). The peak core temperature is 1300 °C; For the last 5 passes, the remaining gauge distribution is rolled, and the rolling speed is 1.5 m / s.

[0114] c. Dynamic cooling:

[0115] Spray atomized water at 40 °C for 4 seconds every 2 passes (the surface temperature drops by 60 °C), and the surface temperature after spraying ≤ 700 °C, and the core - surface temperature difference expands to 120 °C.

[0116] d. Post - finishing cooling:

[0117] The finishing temperature is 800 °C, and it is immediately water - cooled to 630 °C at a rate of 18 °C / s (cooling time 9.5 seconds);

[0118] It is transferred to a slow - cooling pit and cooled to room temperature at a rate of 1 °C / s.

[0119] In Comparative Example 2, the core structure is over - burned, resulting in core defects, and the equivalent defect rate of ≥φ1mm is 50%.

[0120] Comparative Example 3

[0121] Steel grade composition: The same as in Example 1

[0122] Process parameters:

[0123] a. Step - by - step heating:

[0124] Stage 1: The hot - delivered billet is heated from 400 to 800 °C at a heating rate of 60 °C / h, and the core - surface temperature difference ≤ 50 °C (holding for 1 h);

[0125] Stage 2: From 800 to 1270 °C at a heating rate of 50 °C / h, (holding for 5.5 h);

[0126] The final core - surface temperature difference ≤ 60 °C.

[0127] Subsequent rolling and cooling: The same as in Example 1.

[0128] The defect rate of Comparative Example 3 is 50%, inducing thermal stress cracks

[0129] Comparative Example 4

[0130] The difference between Comparative Example 4 and Example 1 lies in that: the starting rolling temperature is 1100°C; other operations are the same as those in Example 1.

[0131] The peak temperature at the core reaches 1180°C (≤1150°C in the original process), abnormal dissolution of carbides occurs, and the defect rate is 30%.

[0132] Comparative Example 5

[0133] The difference between Comparative Example 5 and Example 1 lies in that: the finishing rolling temperature is 900°C; other operations are the same as those in Example 1.

[0134] High-temperature finishing rolling leads to coarsening of austenite grains (grain size of 6.0), precipitation of network carbides, and the impact energy is 25 J. The defect rate is 10%.

[0135] Comparative Example 6

[0136] The difference between Comparative Example 6 and Example 1 lies in that: spray cooling between passes is cancelled. Other operations are the same as those in Example 1.

[0137] The defect rate at the core of Comparative Example 6 is 35%.

[0138] Comparative Example 7

[0139] The difference between Comparative Example 7 and Example 1 is only that: the water cooling rate is 30°C / s. Other operations are the same as those in Example 1.

[0140] The defect rate at the core of Comparative Example 7 is 10%.

[0141] Comparative Example 8

[0142] The difference between Comparative Example 8 and Example 1 is only that: the reduction ratio in the first rolling is increased to 15%. Other operations are the same as those in Example 1.

[0143] The defect rate at the core of Comparative Example 8 is 20%.

[0144] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for controlling internal damage during rolling of high-carbon high-alloy grinding ball steel, characterized in that: The following steps are involved: (1) Billet composition control: In terms of mass percentage, the billet composition is C: 0.95-1.3%, Mn: 0.9-1.0%, Cr: 2.1-4.0%, Mo: 0.5-0.9%, N: 0.006-0.01%; V: 0.1-0.8%, and the balance is Fe and unavoidable impurities; (2) High temperature diffusion homogenization pretreatment: heat the steel billet to 1220-1280°C and keep it warm for 3-7 hours; (3) Temperature controlled rolling in stages: Initial rolling stage: rolling temperature 1020-1080℃, single pass reduction rate 6-10%, pass interval ≥20 seconds, core peak temperature ≤1150℃; rolling speed is controlled in stages, the first 5-7 passes are 1.0-1.5m / s, and the subsequent passes are reduced to 0.6-1.0m / s; Final rolling stage: final rolling temperature 800-850℃; (4) Dynamic cooling: spray 30-50℃ atomized water on the surface of the billet after every 2-3 rolling passes, and the spraying time is ≤5 seconds; (5) Two-stage cooling after final rolling: first water cool to 600-650℃ at 15-20℃ / s, then slowly cool to room temperature at ≤5℃ / s.

2. The method according to claim 1, characterized in that Step (2) uses a step-by-step heating method: Stage 1: hot delivery 400→750~800℃, heating rate 30~40℃ / h, heat preservation 1~2h, core surface temperature difference ≤60℃; Keep warm for 1 to 2 hours; Stage 2: 750-800℃→950-1000℃, heating rate 40-50℃ / h, heat preservation 1.5-2.5h, core surface temperature difference ≤30℃; heat preservation 2-3h; Stage 3: 950-1000℃→1220-1280℃, heating rate 25-30℃ / h, core surface temperature difference ≤15℃; keep warm for 3-5h.

3. The method according to claim 1, characterized in that The reduction rate of a single pass in the initial rolling stage is 8-10%, and the interval time between passes is 25-30 seconds.

4. The method according to claim 1, characterized in that The total reduction rate of rolling thickness in step (3) is 40%-80%.

5. The method according to claim 1, characterized in that After spray cooling in step (4), the surface temperature of the steel billet is reduced by 50-80°C.

6. The method according to claim 1, characterized in that In step (5), the slow cooling is carried out by air cooling or pile cooling.

7. The high carbon high alloy grinding ball steel is obtained by rolling according to the method according to any one of claims 1 to 6, characterized in that: The core void ratio is ≤0.02% and the grain size is ≥grade 8.

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