Heat treatment process of clamp forge piece

Abstract

The invention belongs to the field of metallurgy, and particularly relates to a heat treatment process of a clamp forge piece which comprises the following chemical components in percentage by mass: 0.14%-0.17% of C, 0.20%-0.40% of Si, 1.45%-1.60% of Mn, less than or equal to 0.015% of P, less than or equal to 0.010% of S, 0.60%-0.75% of Cr, 0.60%-0.75% of Ni, 0.20%-0.30% of Mo, 0.06%-0.08% of V, less than or equal to 0.20% of Cu, 0.015%-0.025% of Nb, less than or equal to 0.02% of N and the balance of Fe and inevitable impurities. The heat treatment process of the clamp forge piece comprises normalizing, quenching and tempering. The effective thickness of the forge piece is not larger than 650 mm. The process is simple, the internal structure of the forge piece can be effectively improved, grains are refined, the comprehensive mechanical performance of the forge piece is improved, and all indexes of the mechanical performance meet acceptance requirements.

Description

Technical Field

[0001] The invention relates to the field of metallurgy, in particular to a heat treatment process for a clamp body forging. Background Art

[0002] The clamp body forging is used in the structure of the towing device in the marine industry. The mechanical performance acceptance requirements are: the yield strength R of the tensile test eL ≥620MPa, tensile strength R m 720MPa~890MPa, elongation A≥15%, section shrinkage Z≥45%; impact absorption energy A of three samples in each group in -20℃ impact test KV ≥62J (see Table 1). The tensile test is carried out in accordance with GB / T228.1-2010 (Room Temperature Tensile Test Method for Metallic Materials), and the tensile specimen is a R4 circular cross-section proportional specimen cut after 1 / 2 of the maximum thickness of the forging and prepared in accordance with GB / T228.1-2010; the impact test is carried out in accordance with GB / T229-2020 (Charpy Pendulum Impact Test Method for Metallic Materials), and the impact specimen is a standard Charpy V-notch impact specimen cut after 1 / 2 of the maximum thickness of the forging and prepared in accordance with GB / T229-2020.

[0003] Table 1 Mechanical performance index acceptance requirements for caliper forgings

[0004]

[0005] In the process of developing the structure of the tongs forgings used in the marine industry towing device, the acceptance of mechanical properties is a huge challenge. Due to the particularly high requirements for its comprehensive mechanical properties, the yield strength and the impact absorption work of each group of three specimens in the -20℃ impact test cannot meet the acceptance requirements at the same time. It is necessary to study and design an optimized heat treatment process to improve the internal structure of the forgings, refine the grains, and improve its comprehensive mechanical properties so that all mechanical performance indicators meet the acceptance requirements.

[0006] Patent No. 201910808111.8 discloses a method for processing a brake caliper body, including step one: blanking, deburring, preheating before forging, upsetting, preheating before forging, bending, preheating before forging, pre-forging, acid and alkali cleaning, grinding, preheating before forging, final forging, trimming, solution treatment, water cooling, aging treatment, vibration grinding, alkali washing, acid washing, shot blasting, and inspection. It is mainly used for brake caliper bodies. The purpose of the treatment is to improve the hardness, tensile strength and yield strength of the parts, so that the surface of the automobile brake caliper body becomes smoother after vibration grinding and shot blasting. The brake caliper body prepared by this method has a yield strength of only 315MPa and a tensile strength of only 345MPa, which is far lower than the mechanical property acceptance requirements of the forgings that need to be achieved in the present invention, and is not suitable for the production of caliper forgings in the structure of marine industry towing devices. Summary of the invention

[0007] The purpose of the present invention is to solve the above technical problems and provide a heat treatment process for the clamp body forging which has a simple process, can effectively improve the internal structure of the forging, refine the grains, and improve the comprehensive mechanical properties of the forging so that all mechanical performance indicators meet the acceptance requirements.

[0008] The heat treatment process of the caliper body forging of the present invention is as follows: the caliper body forging includes the following chemical components and mass percentages: C: 0.14% to 0.17%, Si: 0.20% to 0.40%, Mn: 1.45% to 1.60%, P≤0.015%, S≤0.010%, Cr: 0.60% to 0.75%, Ni: 0.60% to 0.75%, Mo: 0.20% to 0.30%, V: 0.06% to 0.08%, Cu≤0.20%, Nb: 0.015% to 0.025%, N≤0.02%, and the rest is Fe and unavoidable impurities;

[0009] The heat treatment process of the caliper body forging includes normalizing, quenching and tempering; the effective thickness of the forging is not greater than 650 mm.

[0010] In the normalizing step, the clamp body forging is first heated to 600°C-650°C and kept warm for 2-5 hours, then heated to 920°C-970°C and kept warm again, and after being taken out of the furnace, it is cooled to room temperature by a blower.

[0011] In the quenching step, the normalized clamp body forging is heated to 600°C-650°C and kept warm for 2-5 hours, then heated to 860°C-900°C and kept warm again, and then water-cooled to below 250°C after being taken out of the furnace.

[0012] In the tempering step, the quenched clamp body forging is heated to 300°C-350°C and kept warm for 2-5 hours, then heated to 590°C-650°C for even temperature, kept warm again, and then oil-cooled to below 250°C after being taken out of the furnace.

[0013] In the water cooling step in the quenching step:

[0014] For the clamp body forgings with effective thickness less than 300mm, full water cooling is adopted;

[0015] For the clamp body forgings with effective thickness of 300mm to 500mm, intermittent cooling of water cooling + air cooling + water cooling is adopted;

[0016] For the clamp body forgings with an effective thickness greater than 500 mm and not greater than 650 mm, intermittent cooling of water cooling + air cooling + water cooling + air cooling + water cooling is adopted.

[0017] In the water cooling step: for the clamp body forging with an effective thickness of less than 300 mm, full water cooling is adopted, and the water cooling time is 10 to 35 minutes;

[0018] For the clamp body forgings with effective thickness of 300mm to 500mm, intermittent cooling of water cooling for 25 to 40 minutes + air cooling for 2 to 5 minutes + water cooling for 10 to 20 minutes is adopted;

[0019] For the clamp body forgings with an effective thickness greater than 500 mm and not greater than 650 mm, intermittent cooling is adopted: water cooling for 35 to 45 minutes + air cooling for 4 to 6 minutes + water cooling for 12 to 15 minutes + air cooling for 2 to 3 minutes + water cooling for 7 to 10 minutes.

[0020] In the normalizing step, the time for holding the material again is calculated as 1h / 100mm, and the temperature equalization time is 1 / 2 of the holding time.

[0021] In the quenching step, the time for holding the material again is calculated as 1h / 100mm, and the temperature equalization time is 1 / 2 of the holding time.

[0022] In the tempering step, the time for holding the material again is calculated as 2h / 100mm, and the equalization time is 1 / 2 of the holding time.

[0023] The caliper forging of the present invention is made of raw materials with the above chemical composition through steelmaking, forging, machining (rough machining), heat treatment, and machining (finishing machining). Except for the heat treatment, other processes are existing technologies and will not be described in detail.

[0024] The clamp body forging of the present invention is used in the manufacture of the towing device structure of the marine industry, and the comprehensive mechanical performance requirements of the clamp body forging are very high. The specific acceptance indicators are: the yield strength R of the tensile test eL ≥620MPa, tensile strength R m 720MPa~890MPa, elongation A≥15%, section shrinkage Z≥45%; impact absorption energy A of three samples in each group in -20℃ impact testKV ≥62J, the yield strength and the impact absorption energy of the -20℃ impact test cannot meet the acceptance requirements at the same time.

[0025] In order to meet the above performance indicators, the inventors conducted in-depth research, including:

[0026] 1) Improve the forging material by adding specific alloy elements to improve the internal structure of the forging, improve the comprehensive mechanical properties of the forging, and solve the problem that the yield strength of the clamp forging and the impact absorption work of the -20℃ impact test cannot meet the acceptance requirements at the same time. Research has found that elements such as Cr and Mo can enhance the corrosion resistance of forgings by forming a dense oxide film; the addition of elements such as Cr and V can significantly improve the hardenability of forgings, so that forgings can obtain a deeper hardened layer during quenching, thereby improving the mechanical properties of forgings; Cr, Mo, V and other elements can also form special carbides with carbon, which have high hardness, high wear resistance and high temperature stability; the addition of Ni can improve the strength of forgings without reducing the plasticity of forgings, so that forgings maintain good comprehensive mechanical properties, and Ni can improve the low-temperature toughness of forgings, so that forgings still maintain excellent mechanical properties under low temperature conditions; Mo, Nb and other elements can improve the high-temperature performance of forgings, so that forgings can still maintain excellent mechanical properties and chemical stability under high temperature conditions, and Nb can also improve the welding performance of forgings; Cu can improve the strength and toughness of forgings and resist atmospheric corrosion. The proportion of Cr, Ni, Mo, V, Cu, Nb and other elements added makes the clamp body forgings improve strength, hardness, high temperature performance, corrosion resistance and other properties, while obtaining excellent welding performance and low temperature toughness, so that the forgings have more superior comprehensive performance and meet the special needs of the shipbuilding industry and marine towing device structural engineering. On the other hand, the addition amount of the above elements should also be strictly limited. Too little can not significantly improve the hardenability of the forgings, and it is impossible to ensure that the forgings maintain excellent corrosion resistance to acids and alkalis, heat resistance, and rust resistance at high temperatures while improving strength and toughness. But it cannot be too much, especially Cr: 0.60% ~ 0.75%, too much will lead to reduced plasticity and toughness of the forgings. In addition, Cr, Ni, Mo, V elements have a significant promoting effect on the inheritance of forging tissues, reducing the grain refinement effect of re-austenitization, so the content of each element must be strictly controlled and cannot be adjusted at will.

[0027] 2) The heat treatment process was improved, including: a. Adding a normalizing process as a preliminary heat treatment to prepare the organization for the subsequent tempering heat treatment. Here, normalizing adopts two-stage heating, first heating to 600℃~650℃ to reduce the thermal stress caused by the excessive temperature difference between the inside and outside of the forging during the heating process, and then heating to 920℃~970℃ for uniform temperature and then heat preservation, austenitizing at this temperature to eliminate tissue inheritance and prepare tissue conditions for subsequent cooling transformation; b. In the quenching step, two-stage heating is also adopted, and the clamp body forging is finally heated to 860℃~900℃, which is slightly lower than the normalizing step. By controlling the heating temperature at 860℃~900℃, austenitizing is performed again to further refine the grains and obtain a uniform austenite structure. Too high a temperature will make the grains coarser, and too low austenitizing will be insufficient; c. In the tempering step, the quenched forging is heated to 300℃~350℃ and kept for 2-5 hours, and then heated To 590℃~650℃ uniform temperature, in order to facilitate the decomposition of lower bainite and the transformation of residual austenite, to obtain a stable tempered structure, so that the forgings finally obtain excellent comprehensive mechanical properties; d, adopt a variety of cooling methods, blast cooling to room temperature after normalizing to eliminate network carbides, refine grains, and prepare the organization for the subsequent quenching and tempering heat treatment. During quenching, water cooling is used to below 250℃ to transform the re-austenitized organization into a fine and uniform lower bainite organization. After tempering, oil cooling is used instead of conventional air cooling to below 250℃. Considering that the cooling capacity of oil is stronger than that of air, using oil cooling after tempering can avoid the occurrence of the second type of temper brittleness. Although the cooling capacity of oil is smaller than that of water, it is more stable than water. After tempering, oil cooling can relieve the internal stress of forgings and prevent product deformation. By applying different cooling methods at different stages in the heat treatment steps to achieve the purpose of eliminating organizational inheritance, refining grains, and reducing stress concentration, both excellent comprehensive mechanical properties can be obtained and deformation or cracking can be avoided.

[0028] 3) In the quenching step, in order to enhance the cooling effect and ensure that the forgings complete the structural transformation to the maximum extent during quenching, water with better cooling effect is selected as the quenching medium to obtain higher strength and toughness. However, due to the strong cooling capacity of water, forgings are prone to deformation and cracking due to large thermal stress and structural stress during quenching. If the cooling rate is still very high within the temperature range of 300℃ to 200℃, the workpiece will be severely deformed and even cracked. Therefore, different water cooling methods are used for forgings of different thicknesses. For smaller forgings with an effective thickness of less than 300mm, full water cooling is used; for large forgings with an effective thickness of 300㎜ to 500mm, intermittent cooling of water cooling + air cooling + water cooling is used; and for extra-large forgings with an effective thickness greater than 500㎜ and not greater than 650mm, intermittent cooling of water cooling + air cooling + water cooling + air cooling + water cooling is used. Different water cooling methods are used for forgings of different thicknesses to ensure that the forgings undergo full structural transformation within the temperature range of 650℃ to 550℃, while reducing the phase change stress caused by the rapid structural transformation within the temperature range of 300℃ to 200℃, especially near the Ms line. This can achieve higher strength and toughness while avoiding deformation or cracking.

[0029] Beneficial effects:

[0030] The comprehensive mechanical properties of the caliper forgings subjected to heat treatment according to the present invention are significantly improved: the yield strength R eL ≥620MPa, tensile strength R m 720MPa~890MPa, elongation A≥15%, section shrinkage Z≥45%; impact absorption energy A of three samples in each group in -20℃ impact test KV ≥62J. All indicators of mechanical properties of forgings meet the acceptance requirements, solving the problem that the yield strength of the pliers forgings and the impact absorption work of the -20℃ impact test cannot meet the acceptance requirements at the same time. It is suitable for pliers forgings with an effective thickness of ≤650mm, with simple process and strong controllability. DETAILED DESCRIPTION

[0031] Embodiment 1:

[0032] The clamp body forging has an effective thickness of 100 mm, and its chemical composition (%, wt, smelting analysis) is as follows: C: 0.14%, Si: 0.28%, Mn: 1.54%, P: 0.007%, S: 0.005%, Cr: 0.72%, Ni: 0.64%, Mo: 0.22%, V: 0.06%, Cu: 0.20%, Nb: 0.018%, N: 0.02%.

[0033] The heat treatment process of normalizing + quenching + tempering is adopted.

[0034] 1) Normalizing: First heat the forging to 600℃~650℃ and keep it for 2 hours, then heat it to 920℃ and keep it for 0.5 hours and keep it for 1 hour. After it comes out of the furnace, use a blower to cool it to room temperature;

[0035] 2) Quenching: Heat the forgings after normalizing to 600℃~650℃ and keep it at this temperature for 2 hours, then heat it to 880℃ and keep it at this temperature for 0.5 hours and keep it at this temperature for another hour. After it comes out of the furnace, water cool it to below 250℃ (water cooling time is 10~35min);

[0036] 3) Tempering: Heat the quenched forgings to 300℃~350℃ and keep them warm for 2 hours, then heat them to 600℃ and keep them warm for 1 hour, then keep them warm for another 2 hours. After taking them out of the furnace, oil cool them to below 250℃.

[0037] The mechanical properties test results of the heat-treated clamp body forgings in this embodiment are as follows: the yield strength R eL =657MPa, tensile strength R m =763MPa, elongation A=20%, section shrinkage Z=62%; impact absorption energy A of three samples in the same group in the -20℃ impact test KV They are 64J, 68J and 74J respectively.

[0038] Embodiment 2:

[0039] The clamp body forging has an effective thickness of 200 mm, and its chemical composition (%, wt, smelting analysis) is as follows: C: 0.16%, Si: 0.26%, Mn: 1.58%, P: 0.008%, S: 0.005%, Cr: 0.74%, Ni: 0.66%, Mo: 0.27%, V: 0.06%, Cu: 0.18%, Nb: 0.019%, N: 0.02%.

[0040] The heat treatment process of normalizing + quenching + tempering is adopted.

[0041] 1) Normalizing: First heat the forging to 600℃~650℃ and keep it for 2 hours, then heat it to 940℃ and keep it for 1 hour and then keep it for 2 hours. After it comes out of the furnace, use a blower to cool it to room temperature;

[0042] 2) Quenching: Heat the forgings after normalizing to 600℃~650℃ and keep it at this temperature for 2 hours, then heat it to 900℃ and keep it at this temperature for 1 hour and then keep it at this temperature for 2 hours. After it comes out of the furnace, water cool it to below 250℃ (water cooling time is 10~35min);

[0043] 3) Tempering: Heat the quenched forgings to 300℃~350℃ and keep them warm for 2 hours, then heat them to 590℃ and keep them warm for 2 hours, then keep them warm for 4 hours again. After taking them out of the furnace, oil cool them to below 250℃.

[0044] The mechanical properties test results of the heat-treated clamp body forgings in this embodiment are as follows: the yield strength R eL =653MPa, tensile strength R m =759MPa, elongation A=19%, section shrinkage Z=59%; the impact absorption energy A of the three samples in the same group in the -20℃ impact test KV They are 67J, 71J and 77J respectively.

[0045] Embodiment three:

[0046] The clamp body forging has an effective thickness of 300 mm, and its chemical composition (%, wt, smelting analysis) is as follows: C: 0.17%, Si: 0.29%, Mn: 1.52%, P: 0.008%, S: 0.006%, Cr: 0.72%, Ni: 0.68%, Mo: 0.22%, V: 0.07%, Cu: 0.20%, Nb: 0.017%, N: 0.01%.

[0047] The heat treatment process of normalizing + quenching + tempering is adopted.

[0048] 1) Normalizing: First heat the forging to 600℃~650℃ and keep it at this temperature for 3 hours, then heat it to 950℃ and keep it at this temperature for 1.5 hours and then keep it at this temperature for 3 hours. After it comes out of the furnace, use a blower to cool it to room temperature;

[0049] 2) Quenching: Heat the forgings after normalizing to 600℃~650℃ and keep them warm for 3 hours, then heat them to 870℃ and keep them warm for 1.5 hours and then keep them warm for 3 hours. After taking them out of the furnace, water cool them to below 250℃ (water cooling for 25~40min + air cooling for 2~5min + water cooling for 10~20min);

[0050] 3) Tempering: Heat the quenched forgings to 300℃~350℃ and keep them warm for 3 hours, then heat them to 630℃ and keep them warm for 3 hours, then keep them warm for 6 hours again. After taking them out of the furnace, oil cool them to below 250℃.

[0051] The mechanical properties test results of the heat-treated clamp body forgings in this embodiment are as follows: the yield strength R eL =647MPa, tensile strength R m =758MPa, elongation A=19%, section shrinkage Z=60%; the impact absorption energy A of the three samples in the same group in the -20℃ impact test KV They are 68J, 73J and 79J respectively.

[0052] Embodiment 4:

[0053] The clamp body forging has an effective thickness of 450 mm, and its chemical composition (%, wt, smelting analysis) is as follows: C: 0.15%, Si: 0.38%, Mn: 1.58%, P: 0.008%, S: 0.007%, Cr: 0.70%, Ni: 0.60%, Mo: 0.20%, V: 0.08%, Cu: 0.18%, Nb: 0.019%, N: 0.02%.

[0054] The heat treatment process of normalizing + quenching + tempering is adopted.

[0055] 1) Normalizing: First heat the forging to 600℃~650℃ and keep it for 4 hours, then heat it to 940℃ and keep it for 2.25 hours and then keep it for 4.5 hours. After it comes out of the furnace, use a blower to cool it to room temperature;

[0056] 2) Quenching: Heat the forgings after normalizing to 600℃~650℃ and keep them warm for 4 hours, then heat them to 860℃ and keep them warm for 2.25 hours and then keep them warm for 4.5 hours. After taking them out of the furnace, water cool them to below 250℃ (water cooling for 25~40min + air cooling for 2~5min + water cooling for 10~20min);

[0057] 3) Tempering: Heat the quenched forgings to 300℃~350℃ and keep them warm for 4 hours, then heat them to 620℃ and keep them warm for 4.5 hours and keep them warm again for 9 hours. After taking them out of the furnace, oil cool them to below 250℃.

[0058] The mechanical properties test results of the heat-treated clamp body forgings in this embodiment are as follows: the yield strength R eL =649MPa, tensile strength R m =761MPa, elongation A=18%, section shrinkage Z=57%; the impact absorption energy A of the three samples in the same group in the -20℃ impact test KV They are 73J, 83J and 87J respectively.

[0059] Embodiment five:

[0060] The clamp body forging has an effective thickness of 500 mm, and its chemical composition (%, wt, smelting analysis) is as follows: C: 0.14%, Si: 0.30%, Mn: 1.45%, P: 0.010%, S: 0.007%, Cr: 0.75%, Ni: 0.60%, Mo: 0.29%, V: 0.08%, Cu: 0.18%, Nb: 0.020%, N: 0.02%.

[0061] The heat treatment process of normalizing + quenching + tempering is adopted.

[0062] 1) Normalizing: First heat the forging to 600℃~650℃ and keep it for 4 hours, then heat it to 970℃ and keep it for 2.5 hours and then keep it for 5 hours. After it comes out of the furnace, use a blower to cool it to room temperature;

[0063] 2) Quenching: Heat the forgings after normalizing to 600℃~650℃ and keep them warm for 4 hours, then heat them to 900℃ and keep them warm for 2.5 hours and then keep them warm for 5 hours. After taking them out of the furnace, water cool them to below 250℃ (water cooling for 25~40min + air cooling for 2~5min + water cooling for 10~20min);

[0064] 3) Tempering: Heat the quenched forgings to 300℃~350℃ and keep them warm for 4 hours, then heat them to 590℃ and keep them warm for 5 hours and keep them warm for 10 hours again. After taking them out of the furnace, oil cool them to below 250℃.

[0065] The mechanical properties test results of the heat-treated clamp body forgings in this embodiment are as follows: the yield strength R eL =639MPa, tensile strength R m =752MPa, elongation A=18%, section shrinkage Z=58%; the impact absorption energy A of the three samples in the same group in the -20℃ impact test KV They are 66J, 78J and 82J respectively.

[0066] Embodiment six:

[0067] The clamp body forging has an effective thickness of 650 mm, and its chemical composition (%, wt, smelting analysis) is as follows: C: 0.17%, Si: 0.20%, Mn: 1.60%, P: 0.008%, S: 0.007%, Cr: 0.60%, Ni: 0.60%, Mo: 0.28%, V: 0.08%, Cu: 0.20%, Nb: 0.015%, N: 0.02%.

[0068] The heat treatment process of normalizing + quenching + tempering is adopted.

[0069] 1) Normalizing: First heat the forging to 600℃~650℃ and keep it for 5 hours, then heat it to 930℃ and keep it for 3.25 hours and then keep it for 6.5 hours. After it comes out of the furnace, use a blower to cool it to room temperature;

[0070] 2) Quenching: Heat the forgings after normalizing to 600℃~650℃ and keep it at this temperature for 5 hours, then heat it to 870℃ and keep it at this temperature for 3.25 hours and keep it at this temperature for 6.5 hours. After it comes out of the furnace, water cool it to below 250℃ (water cooling for 35~45min + air cooling for 4~6min + water cooling for 12~15min + air cooling for 2~3min + water cooling for 7~10min);

[0071] 3) Tempering: Heat the quenched forgings to 300℃~350℃ and keep them warm for 5 hours, then heat them to 650℃ and keep them warm for 6.5 hours and keep them warm for 13 hours again. After taking them out of the furnace, oil cool them to below 250℃.

[0072] The mechanical properties test results of the heat-treated clamp body forgings in this embodiment are as follows: the yield strength R eL =646MPa, tensile strength R m =749MPa, elongation A=19%, section shrinkage Z=56%; the impact absorption energy A of the three samples in the same group in the -20℃ impact test KV They are 67J, 88J and 92J respectively.

[0073] Comparative Example 1:

[0074] Cancel step 1), and the rest is the same as in embodiment 6.

[0075] The clamp body forging has an effective thickness of 650 mm, and its chemical composition (%, wt, smelting analysis) is as follows: C: 0.17%, Si: 0.20%, Mn: 1.60%, P: 0.008%, S: 0.007%, Cr: 0.60%, Ni: 0.60%, Mo: 0.28%, V: 0.08%, Cu: 0.20%, Nb: 0.015%, N: 0.02%.

[0076] The heat treatment process of quenching + tempering is adopted.

[0077] 1) Quenching: Heat the forging to 600℃~650℃ and keep it for 5 hours, then heat it to 870℃ and keep it for 3.25 hours and keep it for 6.5 hours. After it comes out of the furnace, water cool it to below 250℃ (water cooling 35~45min + air cooling 4~6min + water cooling 12~15min + air cooling 2~3min + water cooling 7~10min);

[0078] 2) Tempering: Heat the quenched forgings to 300℃~350℃ and keep them warm for 5 hours, then heat them to 650℃ and keep them warm for 6.5 hours and keep them warm for 13 hours again. After taking them out of the furnace, oil cool them to below 250℃.

[0079] The mechanical properties test results of the heat-treated clamp forgings in this comparative example are as follows: the yield strength R eL =625MPa, tensile strength R m =737MPa, elongation A = 19%, section shrinkage Z = 69%; the impact absorption energy A of the three samples in the same group in the -20℃ impact test KV They are 45J, 58J and 83J respectively.

[0080] Comparative Example 2:

[0081] Cancel step 2), and the rest is the same as in embodiment 6.

[0082] The clamp body forging has an effective thickness of 650 mm, and its chemical composition (%, wt, smelting analysis) is as follows: C: 0.17%, Si: 0.20%, Mn: 1.60%, P: 0.008%, S: 0.007%, Cr: 0.60%, Ni: 0.60%, Mo: 0.28%, V: 0.08%, Cu: 0.20%, Nb: 0.015%, N: 0.02%.

[0083] The normalizing + tempering heat treatment process is adopted.

[0084] 1) Normalizing: First heat the forging to 600℃~650℃ and keep it for 5 hours, then heat it to 930℃ and keep it for 3.25 hours and then keep it for 6.5 hours. After it comes out of the furnace, use a blower to cool it to room temperature;

[0085] 2) Tempering: Heat the forgings after normalizing to 300℃~350℃ and keep it at this temperature for 5 hours, then heat it to 650℃ and keep it at this temperature for 6.5 hours and keep it at this temperature for another 13 hours. After taking it out of the furnace, oil cool it to below 250℃.

[0086] The mechanical properties test results of the heat-treated clamp forgings in this comparative example are as follows: the yield strength R eL =602MPa, tensile strength R m =728MPa, elongation A=22%, section shrinkage Z=71%; the impact absorption energy A of the three samples in the same group in the -20℃ impact test KV They are 10J, 28J and 32J respectively.

[0087] Comparative Example 3:

[0088] The step 1) and the step 2) are swapped, that is, the original step 2) is changed into the step 1), and the original step 1) is changed into the step 2), and the rest is the same as in the sixth embodiment.

[0089] The clamp body forging has an effective thickness of 650 mm, and its chemical composition (%, wt, smelting analysis) is as follows: C: 0.17%, Si: 0.20%, Mn: 1.60%, P: 0.008%, S: 0.007%, Cr: 0.60%, Ni: 0.60%, Mo: 0.28%, V: 0.08%, Cu: 0.20%, Nb: 0.015%, N: 0.02%.

[0090] The heat treatment process of quenching + normalizing + tempering is adopted.

[0091] 1) Quenching: Heat the forging to 600℃~650℃ and keep it at this temperature for 5 hours, then heat it to 870℃ and keep it at this temperature for 3.25 hours and then keep it at this temperature for 6.5 hours. After it comes out of the furnace, water cool it to below 250℃;

[0092] 2) Normalizing: Heat the quenched forgings to 600℃~650℃ and keep them at that temperature for 5 hours, then heat them to 930℃ and keep them at that temperature for 3.25 hours and keep them at that temperature for 6.5 hours. After they are taken out of the furnace, use a blower to cool them to room temperature.

[0093] 3) Tempering: Heat the forgings after normalizing to 300℃~350℃ and keep it warm for 5 hours, then heat it to 650℃ and keep it warm for 6.5 hours and keep it warm for 13 hours again. After taking it out of the furnace, oil cool it to below 250℃.

[0094] The mechanical properties test results of the heat-treated clamp forgings in this comparative example are as follows: the yield strength R eL =642MPa, tensile strength R m =723MPa, elongation A=16%, section shrinkage Z=50%; impact absorption energy A of three samples in the same group in the -20℃ impact test KV They are 43J, 47J and 61J respectively.

[0095] Comparative Example 4:

[0096] Except that in 2) the intermittent cooling is replaced by direct water cooling for 60 min in the quenching step, the rest is the same as in Example 6.

[0097] The clamp body forging has an effective thickness of 650 mm, and its chemical composition (%, wt, smelting analysis) is as follows: C: 0.17%, Si: 0.20%, Mn: 1.60%, P: 0.008%, S: 0.007%, Cr: 0.60%, Ni: 0.60%, Mo: 0.28%, V: 0.08%, Cu: 0.20%, Nb: 0.015%, N: 0.02%.

[0098] The heat treatment process of normalizing + quenching + tempering is adopted.

[0099] 1) Normalizing: First heat the forging to 600℃~650℃ and keep it for 5 hours, then heat it to 930℃ and keep it for 3.25 hours and then keep it for 6.5 hours. After it comes out of the furnace, use a blower to cool it to room temperature;

[0100] 2) Quenching: Heat the normalized forgings to 600℃~650℃ and keep them at this temperature for 5 hours, then heat them to 870℃ and keep them at this temperature for 3.25 hours and then keep them at this temperature for 6.5 hours. After they are taken out of the furnace, water cool them for 60 minutes to below 250℃.

[0101] 3) Tempering: Heat the quenched forgings to 300℃~350℃ and keep them warm for 5 hours, then heat to 650℃ and keep them warm for 6.5 hours and keep them warm again for 13 hours. After taking them out of the furnace, oil cool them to below 250℃.

[0102] The mechanical properties test results of the heat-treated clamp forgings in this comparative example are as follows: the yield strength R eL =649MPa, tensile strength R m =755MPa, elongation A=21%, section shrinkage Z=58%; impact absorption energy A of three samples in the same group in the -20℃ impact test KV They are 91J, 93J and 96J respectively.

[0103] The mechanical property test results of the caliper body forgings in Examples 1 to 6 and Comparative Examples 1 to 4 are shown in Table 2. The mechanical property indicators of the forgings in each Example and Comparative Example 4 meet the acceptance requirements; the impact absorption work A of each group of three samples in the -20°C impact test of the forgings in Comparative Example 1 and Comparative Example 3 is KV It cannot meet the acceptance requirements, while the other mechanical properties meet the acceptance requirements; while the yield strength of the forgings in comparative example 2 and the impact absorption work A of each group of three specimens in the -20℃ impact test KV None of them can meet the acceptance requirements.

[0104] The forgings in Examples 1 to 6 and Comparative Examples 1 to 3 had good surface quality after heat treatment, and no cracks were found. However, the forgings in Comparative Example 4 did not use intermittent cooling during quenching, but directly water-cooled, which was more intense and had a better cooling effect, and obtained better comprehensive mechanical properties than Example 6, but the forgings had multiple cracks after heat treatment, resulting in scrapping.

[0105] In order to further prove the necessity of intermittent cooling of large forgings during quenching, we used the same heat treatment process as that of Comparative Example 4 to heat treat 20 forgings with the same chemical composition and effective thickness as in Comparative Example 4. As a result, all mechanical properties met the acceptance requirements, but 12 of the forgings were scrapped due to quenching cracks, with a scrap rate of 12 / 20*100%=60%. However, the forgings heat treated using the embodiment and Comparative Examples 1 to 3 did not show quenching cracks and had intact surface quality.

[0106] Table 2 Mechanical properties test results of forgings of examples and comparative examples

[0107]

[0108]

[0109] The original grain size (i.e., the grain size after forging and before final heat treatment), the grain size after normalizing, and the grain size after normalizing + quenching and tempering of the forgings of each embodiment are shown in Table 3, and the grain size of the forgings of each comparative example after heat treatment is shown in Table 4.

[0110] Table 3 Grain size of forgings in the example

[0111] Serial number Original grain size Grain size after normalizing Grain size after normalizing + quenching and tempering Embodiment 1 Level 2.5 Level 4.5 7.5 Embodiment 2 Level 3 Level 4.5 Level 7 Embodiment 3 Level 3 Level 5 7.5 Embodiment 4 Level 3 Level 5 Level 7 Embodiment 5 Level 2.5 Level 5 7.5 Embodiment 6 Level 3 Level 4.5 7.5

[0112] Table 4 Grain size of comparative forgings

[0113] Serial number Original grain size Grain size after heat treatment Comparative Example 1 Level 3 Level 5.5 Comparative Example 2 Level 3 Level 5 Comparative Example 3 Level 3 Level 5.5 Comparative Example 4 Level 3 Level 8

Claims

1. A heat treatment process for a caliper forging, characterized in that: The caliper body forging comprises the following chemical components and mass percentages: C: 0.14% to 0.17%, Si: 0.20% to 0.40%, Mn: 1.45% to 1.60%, P≤0.015%, S≤0.010%, Cr: 0.60% to 0.75%, Ni: 0.60% to 0.75%, Mo: 0.20% to 0.30%, V: 0.06% to 0.08%, Cu≤0.20%, Nb: 0.015% to 0.025%, N≤0.02%, and the rest is Fe and unavoidable impurities; The heat treatment process of the caliper body forging is normalizing, quenching and tempering in sequence; the effective thickness of the forging is not more than 650mm.

2. The heat treatment process of the caliper body forging according to claim 1, characterized in that: In the normalizing step, the clamp body forging is first heated to 600°C-650°C and kept warm for 2-5 hours, then heated to 920°C-970°C and kept warm again, and after being taken out of the furnace, it is cooled to room temperature by a blower.

3. The heat treatment process of the caliper body forging according to claim 1, characterized in that: In the quenching step, the normalized clamp body forging is heated to 600°C-650°C and kept warm for 2-5 hours, then heated to 860°C-900°C and kept warm again, and then water-cooled to below 250°C after being taken out of the furnace.

4. The heat treatment process of the caliper body forging according to claim 1, characterized in that: In the tempering step, the quenched clamp body forging is heated to 300°C-350°C and kept warm for 2-5 hours, then heated to 590°C-650°C for even temperature, kept warm again, and then oil-cooled to below 250°C after being taken out of the furnace.

5. The heat treatment process of the caliper body forging according to claim 3, characterized in that: In the water cooling step in the quenching step: For the clamp body forgings with effective thickness less than 300mm, full water cooling is adopted; For the clamp body forgings with effective thickness of 300mm to 500mm, intermittent cooling of water cooling + air cooling + water cooling is adopted; For the clamp body forgings with an effective thickness greater than 500 mm and not greater than 650 mm, intermittent cooling of water cooling + air cooling + water cooling + air cooling + water cooling is adopted.

6. The heat treatment process of the caliper body forging according to claim 5, characterized in that: In the water cooling step: For the clamp body forgings with effective thickness less than 300mm, full water cooling is adopted, and the water cooling time is 10 to 35 minutes; For the clamp body forgings with effective thickness of 300mm to 500mm, intermittent cooling of water cooling for 25 to 40min + air cooling for 2 to 5min + water cooling for 10 to 20min is adopted; For the clamp body forgings with an effective thickness greater than 500 mm and not greater than 650 mm, intermittent cooling is adopted: water cooling for 35 to 45 minutes + air cooling for 4 to 6 minutes + water cooling for 12 to 15 minutes + air cooling for 2 to 3 minutes + water cooling for 7 to 10 minutes.

7. The heat treatment process of the caliper body forging according to claim 2, characterized in that: In the normalizing step, the time for holding the material again is calculated as 1h / 100mm, and the temperature equalization time is 1 / 2 of the holding time.

8. The heat treatment process of the caliper body forging according to claim 3, characterized in that: In the quenching step, the time for holding the material again is calculated as 1h / 100mm, and the temperature equalization time is 1 / 2 of the holding time.

9. The heat treatment process of the caliper body forging according to claim 4, characterized in that: In the tempering step, the time for holding the material again is calculated as 2h / 100mm, and the equalization time is 1 / 2 of the holding time.

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