How to solve the oxidation in gear by vacuum carburizing technology

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Vacuum carburizing technology solves the internal oxidation principle
Because vacuum carburizing is far below atmospheric pressure of 10kPa (760Torr) under the completion of the pressure, the typical pressure range of low-pressure vacuum carburizing is 400 ~ 666 (3 ~ 5Torr), vacuum conditions make carbon atoms more easily transferred to the steel surface; At the same time because there is no gas carburizing process of water gas reaction, so there is no internal oxidation phenomenon.

Examples of application

Automobile transmission gear and shaft teeth, the original use of conventional carburizing quenching process, due to the presence of oxygen and oxide in carburizing atmosphere carrier gas, internal oxidation phenomenon can not be avoided, and heat treatment distortion is greater.

Example 1, output shaft, material 20MnCr5, heat treatment technical requirements: surface and core hardness of 680 ~ 780HV30 and 350 ~ 480HV30 respectively, effective hardening layer depth (hardness 550HV1) of 0.7 ~ 1.0mm.

1) process. Carburizing temperature 950℃, heating and uniform-temperature time 50min; Carburizing time 10.13min; Diffusion time: 78.87min. The quenching medium is high purity nitrogen. Quenching pressure: 2MPa; Quenching time: 10min; The enrichment rate was 13.81mg/h·cm. Tempering temperature 150℃; Tempering time: 2.5h.

2) Inspection results. The hardness of surface and core is 725 ~ 727HV30 and 434 ~ 442HV30 respectively. The depth of the effective hardened layer on the tooth surface is 0.788mm (550HV1); The microstructure of the tooth surface was carbide (grade 1) + residual austenite (grade 2) + Martensite (grade 2), without obvious non-Martensite microstructure. The three axial diameter deformations (radial runout) are respectively 0.021 ~ 0.045mm, 0.029 ~ 0.089mm and 0.041 ~ 0.054mm.

Example 2, driven bevel gear, material 16MnCr5, heat treatment technical requirements: surface and heart hardness of 680 ~ 780HV30 and 320 ~ 480HV30 respectively, effective hardening layer depth (hardness 510HV1) of 0.5 ~ 0.8mm.

1) process. Carburizing temperature 950℃, heating and uniform-temperature time 50min; Carburizing time 9.25min; The diffusion time is 49.75min. The quenching medium is high purity nitrogen. Quenching pressure 1.5mpa; Quenching time: 15min; Tempering temperature 150℃; Tempering time 3h.

2) Inspection results. The hardness of surface and core is 720 ~ 729HV30 and 350 ~ 356HV30 respectively. The depth of the effective hardened layer on the tooth surface is 0.64mm (550HVl). The microstructure of the tooth surface was carbide (grade 1) + residual austenite (grade 2) + Martensite (grade 2), without obvious non-Martensite microstructure. Heat treatment deformation: flatness of outer plane <0.05mm, flatness of inner plane <0.10mm, roundness of inner hole <0.05mm.

Example 3, using low pressure vacuum carburizing not only completely solve the problem of internal oxidation, and the application of the low pressure carburizing equipment temperature of 1050 ℃, the crystallite size increased obviously can not make the steel, will not affect the mechanical properties of parts condition, increase the speed of carburizing, thus greatly improve the speed of carburizing, shorten the production cycle, improve the production efficiency, save the energy.

1) Carburizing equipment for low-pressure vacuum carburizing equipment, materials 20CrMnMo, 20Cr, 20Ni4A, carburizing process conditions and requirements: carburizing temperature 980℃; Depth of carburizing layer 0.80mm; Surface carbon concentration 0.84%.

2) Test results. The depth of carburizing layer is 0.82mm. Surface carbon concentration 0.85%; The gradient distribution of carbon concentration is basically consistent with the simulation curve. After carburizing and quenching gear, the surface of the metal primary color, no oxidation inside the layer, fine and uniform structure, to achieve the ideal state.