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Sheet metal vacuum carburizing process

Plates are stamped and formed parts, and are now widely used in industries such as industrial sewing machines and automobiles. Considering its stamping and processing performance, many parts are made of low carbon steel, which is treated by vacuum carburizing and quenching to improve the strength and wear resistance of the parts.

It is generally believed that the occurrence of troostite is caused by insufficient quenching cooling rate, that is to say, it is caused by the slow cooling rate in the medium temperature stage of quenching oil, that is, the vapor film stage. Therefore, we believe that the low-temperature cooling rate of quenching oil has a greater impact on the structure of quenched parts with the same carburized carbon concentration distribution. Appropriately increasing the low-temperature cooling rate of quenching oil can increase the quenching hardening layer depth of the parts, improve the quenching structure, and increase the strength of the parts.

The low-temperature cooling rate of quenching oil has a great influence on the structure of quenched parts with the same carburized carbon concentration distribution. Appropriately increasing the low-temperature cooling rate of quenching oil can increase the quenching hardening layer depth of the parts, improve the quenching structure, and increase the strength of the parts.

Sheet metal vacuum carburizing process

The vacuum carburizing and quenching process is 860 C, soaking for 30 minutes, vacuum carburizing for 60 minutes (Cp is 0.8%), and then directly quenching the oil.

The depth of vacuum carburizing and quenching hardening layer is 0.3mm. The parts go through only one polishing process. After vacuum carburizing and quenching, it is found that the metallographic structure from the surface to the center is martensite + carbide, ferrite + pearlite + martensite, lath martensite, that is, after the carburizing layer appears Abnormal structure of ferrite + pearlite + martensite. Checking the original part, it was found that the surface of the part was seriously decarburized, and the depth of the decarburization layer reached 0.4mm. Therefore, during the carburizing process, the decarburization layer was not completely infiltrated, and abnormal structures appeared in the subsequent quenching. We believe that as long as the depth of the decarburized layer on the surface of the plate does not exceed half of the depth of the carburized layer, it does not have much influence on the carburization, but attention must be paid to the deeper surface decarburized layer to prevent abnormal structures. Reduced service life of parts.

The 2mm thick thin-walled parts we deal with require a surface hardness of (700±70) HV after vacuum carburizing and quenching. Therefore, the parts were stacked in 7 layers and then loaded into the furnace. After vacuum carburizing and quenching, it was found that the parts had local soft spots and the minimum hardness was 420HV. Due to the cooling and stirring device of the quenching oil tank of the equipment used, the flow direction of the oil is from bottom to top, so after the parts are stacked in 7 layers, the flow of oil is blocked, causing the local oil in the oil tank to stand still and not flow, causing the parts to have local hardness and soft spots .

Therefore, the parts are changed to the method of hanging the furnace to keep the oil flowing smoothly. In order to reduce deformation, a special hanging clamp is designed to make the parts vertically downward into the oil, and the hardness uniformity of the parts after vacuum quenching is good, which meets the requirements.