Wed, 20 Jun 2018 02:34:45 +0000

Application of vertical vacuum oil quenching furnace in heat treatment

Vacuum heat treatment technology has no oxidation and decarburization, degassing, degreasing, good surface quality and small excellent comprehensive mechanical properties, heat treatment parts deformation, long service life, pollution-free environment, high degree of automation, a series of prominent advantages and got rapid development. The research and application of vacuum heat treatment technology have been applied in many fields such as annealing, oil (gas) quenching, high-pressure gas quenching, carburizing, nitriding, metal seeping, tempering, sintering, brazing, coating and cleaning. With the continuous improvement of the quality requirements of heat treatment for aviation products, vacuum heat treatment technology has been widely used in the aviation industry. In recent years, more and more vertical vacuum oil quenching furnaces are used, but only two domestic manufacturers can produce this equipment. Compared with the foreign equipment, the price is only 1/3 ~ 1/4 of the imported equipment, and the cost performance is relatively high. Vertical vacuum oil quenching furnace is mainly used in long axis, long pole parts, such as quenching, compared with horizontal vacuum oil quenching furnace, its deformation greatly decreases, and has been successfully applied in aircraft landing gear, aerospace manufacturing enterprises of vertical shaft, missile shell quenching. Because the quenching transfer time of three-chamber vertical vacuum quenching furnace is relatively long, there are few studies on the application of thin-walled slender rods in China. Parts made in our company, there are a lot of main mechanical parts belong to the thin wall long pole parts, such as: shell, rocker arm, shoulder axis, etc., the effective thickness of 3 ~ 10 mm, length is 700 ~ 1600 mm, material for 30 crmnsia, 30 crmnsini2a, in the existing horizontal vacuum oil quenching furnace and ordinary box type resistance furnace quenching, or deformation is large, or oxidation decarburization is serious, unable to meet the technical requirements. Therefore, our company purchased zcl-408 vertical vacuum oil quenching furnace, which suspended the parts vertically for quenching such parts. This study discusses whether the hardening of thin-walled parts can meet the technical requirements of heat treatment in vertical vacuum oil quenching furnace.
Test equipment, materials and methods

 

Application of vertical vacuum oil quenching furnace in heat treatment

1.1 test equipment.
1.2 structure introduction zcl-408 vertical vacuum oil quenching furnace is a vertical three-chamber structure, one is a quenching oil groove, one is an intermediate transition chamber, and the top one is a heating chamber. It is composed of furnace body, furnace drum, heat insulation, elevator, feeding tank, oil tank, oil circulation mixing mechanism, vacuum system, air charging system, water cooling system and hydraulic system.
1.3 test material test qualified materials into the factory all the reinspection, choose commonly used 30 crmnsia low alloy structural steel and low alloy high strength steel 30 crmnsini2a, processed into 3, 10 mm thickness hardness test specimens with (20 mm long and 20 mm) wide and 5 mm short rate tensile test bar. 1.4 test technical requirements and plans
1.5 both the process test piece and the tensile test bar are bound in the effective heating zone by three layers: upper, middle and lower; 3 hardness test pieces are placed in each layer; and 2 tensile test bars are placed. Quenching with vertical vacuum oil quenching furnace, vacuum degree of work 1 ~ 10 pa, adopt B244 vacuum quenching oil quenching oil, the oil temperature heating to 50 ℃; The tempering is carried out by a jh-36 well return furnace. Stepwise warming is adopted for quenching, preheating first and then warming up to quenching temperature.
1.6 mechanical properties require mechanical properties of two types of steel.
2. Results and analysis
The samples 2.1 first 30 crmnsia test data to 900 ℃ quenching, processing results. Can see 3 mm thick and 10 mm thick thin-walled 30 crmnsia in heating zone in next three layers, which tie after 900 ℃ quenching hardness value acuity after 49 HRC, 10 mm in the middle of thin-walled package has the highest hardness can reach 51.5 HRC. All of them meet the requirements of mechanical properties of 30CrMnSiA (greater than or equal to 47HRC), indicating that the quenching transfer time of 40s in the vacuum state can meet the rigid requirements for quenching of thin wall parts made of 30CrMnSiA from 3 to 10mm. The samples were then compacted with tensile strength. Showed that 30 crmnsia sample in heating zone in next three layers, which samples at 500 ℃ tempering after binding the tensile strength of the overall reached 30 crmnsia mechanical performance requirements (1080 mpa) or higher. For the yield strength, the sample reached the maximum of 1025MPa in the lower layer, the upper layer was relatively uniform to 1000MPa, the middle layer had the minimum yield strength of 957MPa, and the three layers generally met the requirements of 30CrMnSiA mechanical performance (> 835MPa). The elongation reached a maximum of 20% in the middle layer, and was relatively uniform in the upper layer. The overall elongation also reached the requirement of 30CrMnSiA mechanical performance (10%). All three layers meet the requirement of 30CrMnSiA mechanical performance (45%). Hardness after tempering. As you can see, the sample after 500 ℃ tempering, 10 mm thin wall parts in the middle of a maximum 40.5 HRC hardness, and 3 mm thin wall parts of hardness in the lower reaches the minimum 37.5 HRC. The hardness of all three layers of samples reached the requirement of 30CrMnSiA (> 35HRC).
2.2 due to the test data of 30 crmnsini2a 30 crmnsini2a test data after quenching and tempering hardness, tensile strength after 250 ℃ tempering. Can see: 30 crmnsini2a the tensile strength of the sample in the lower reach a maximum 1722 mpa, in the middle, the tensile strength of the minimum value of 1700 mpa, conform to the mechanics performance of 30 crmnsini2a p 1570 HRC), elongation and basically meet the mechanical property requirements of 30 crmnsini2a (8%), reduction of area in the middle reaches a maximum 68%, reach the minimum value in the lower 48%, and can meet the requirements of the reduction of area of 30 crmnsini2a (45%). 30 crmnsini2a samples, 3 mm, 10 mm thin wall parts after 250 ℃ tempering hardness values are meet the requirements of mechanical properties (35 HRC) or higher. All in all, from the hardness and strength after quenching and tempering hardness data after data can be seen that the vertical vacuum oil quenching furnace quenching can satisfy the demand of the thin-walled parts quenching, quenching hardness and strength in accordance with 30 crmnsia and 30 crmnsini2a technical requirements. After the test, we have been on the rocker arm, shoulder axis, such as shell thin wall parts was carried out in the vertical vacuum oil quenching furnace heat treatment, hardness, mechanical properties, deformation and surface brightness all met the technical requirements, has been successfully used in the product, use effect is good. HB/Z191 stipulates that the transfer time of quenching should generally not exceed 25s, while the vertical vacuum oil quenching furnace is divided into three Chambers with a large size, which is difficult to meet such requirements. We use of vertical vacuum oil quenching furnace quenching transfer time is 40 s (starting from the open interval of popular open time, all parts to sink groove end timing), all the parts began to leave the heating chamber parts in oil tank for only 20 s, in a vacuum heating speed is slower than the salt bath and controlled atmosphere furnace, so the temperature of the vacuum parts reduce speed is slower than under atmospheric conditions, therefore, the 40 s of the vertical vacuum oil quenching furnace quenching transfer time is can satisfy the requirements of the alloy steel vacuum heat treatment.
3. Conclusion vertical vacuum oil quenching furnace can be used for long shaft rod parts heat treatment, can effectively solve the problem of quenching deformation of such parts, can be widely used, therefore, we through the three specimens, 10 mm thick, experimental study on heat treatment of the vertical vacuum oil quenching furnace quenching transfer time can satisfy my company alloy steel slender thin-walled bar heat treatment technical requirements.