Study Of Technological Test On The Plasma Arc Surface Hardening Technology

The characteristics and advantages of surface quenching by plasma arc are introduced in this paper. Based on arc column physics of plasma arc, the process of thermal conduction is analyzed theoretically, the distribution curve of temperature field is established and the shape of hardened area is predicted. By researching the parameters that influence the quenching technology, the experimental plan which focuses on the changes of arc power, scanning velocity and gas flow is made for the stability and controllability of quenching, the available quenching equipments are improved and a set of manipulating methods of quenching technology is summarized.With the typical materials including 45 steel, 45Mn, 38CrSi, 35CrMo and 40Cr, the experimental study is performed, the tissue appearance, the surface wave before and after quenching, the hardened area and the surface hardness are analyzed, the influencing laws of arc power, scanning speed, gas flow and chemical components of material to the quenching results are found out.The results of the experimental study shows: because of the very high heating speed of plasma arc, the small influencing area and the extremely high cooling speed (>10~4oc/s), the overheating and undercooling are very great in the process of phase transition. After being quenched by plasma arc, trivial and compact quenching component that is the high hardness tissue of martensite with lath and needle shape is generated in the sample. It can enhance the surface wear ability of the sample substantially. The surface hardness of the sample is 780-889 HV0.1 which is 250 HV0.1 higher than common thermal treatment, the depth of hardened layer is 0.2~0.4mm while the width is 2~4mm. The hardened layers are distributed from the surface to the depth with the gradient changing gently and rationally. The hardened area presents crescent looks just like prediction. The quenching sample deformed very little because the small heating area, theshallow hardened layer and the short quenching time. It can be assembled directly after hardening without the subsequent processes of rectifying deformation and making finish cut.The technology of surface quenching with plasma arc needs a few equipments and low processing cost, possesses high working efficiency, has no special requirements for environment and needs simple maintenance. It is a new technology that is suitable for broad application in industry. With the works done in this paper, a basis for the development of an expert system in the future that is used for the optimal control of technological parameters of surface quenching with plasma arc is established.