Study On The Induce Heating Nigtriding Under Vacuum

Vacuum nitriding, as a new nitriding technique, is getting more and more attention because of its advantages such as high nitriding speed, deep nitriding case and clean nitriding surface. It has made great progress in theory and application. However, there still exist some problems requiring researching and solving, for example, the heating of the specimen in the vacuum stove. In low vacuum condition, convection takes little effect and the heating of specimens is mostly completed by radiation. So for a traditional stove to heat specimen, the heating process is long and the temperature rising is slow. It not only wastes the energy but also leads to the deteriorism of the specimen in the center part because of the long-time heating. In addition, the temperature rising of the specimens are not uniform because those close to the heater are heated faster than others. Compared with conventional heating in vacuum condition, inductive heating has some superior characteristics such as heating the specimen to the required temperature in a few second, heating the specimen surface only to spare the energy, and promoting the decomposing of NH3 to provide multitudinous choices for nitriding parameters.Based on the above considerations, the research mainly concern on the characteristics of the combination of vacuum nitriding and high-frequency inductive nitriding. Through the experiments in different nitriding conditions, the characteristics of vacuum nitriding were studied in inductive heating condition. The attention of the research work is paid to the choice of nitriding parameters and the influence of the parameters on the thickness and the structure of nitriding case. The main results are stated as below:1. The research on the nitriding of 45# steel shows that vacuum nitriding with inductive heating has some characteristics different from other vacuum nitriding. It requires more flow rate of NH3 to support its fast nitriding. A thick nitriding case up to 0.35mm can be obtained in a short nitriding time (2-4h). After that, the thickness increasing of nitriding case with nitriding time became unremarkable.2. The 45# steel treated in vacuum inductive nitriding has a different structure as that in other nitriding. It consists of e-phase and a little γ-phase, and lots of pores exist in thenitriding case, which severely decreases the compaction of the layer. Abnormal organizations of different thickness can be observed in some specimens. These abnormal organizations may be the nitric-ferrite or nitride (carbide) that is separated out through the cooling of austenitized substrate resulted from the overheating in the nitriding process due to the inaccurate temperature control3. Compared to specimens in vacuum inductive nitriding, those in ion nitriding have less disfigurement in the compound case as a result of splutter effect in ion nitriding. Of three specimens in vacuum inductive nitriding, the specimen most close to the inductive loop has the best nitriding result, which may result from the different nitriding temperature in different places.