Effect Of Electropulsing Treatment On Microstructure And Properties Of Manganese Series Alloy Steels

With the development of society, energy saving, low carbon, environmental protection has become the theme of modern time. As the most widely used structural materials, steel materials bear an important mission. Under the premise of meeting the safety requirements, We always save material as much as possible. Improving the strength of steel is the key to achieve energy saving and emission reduction. Pulse current treatment is a new material processing method, which is different from the traditional heat treatment method. It has the advantages of short action time, fast response, high energy utilization rate. Pulse current flowing through the metal material will form a thermal, electrical, force integrated field in the interior of the material. A series of complex changes occur when the material is in an extremely unbalanced state. The research of the laws behind these complex changes is of great significance to the study of the mechanism of electropulsing treatment. In this paper, the effects of electropulsing treatment on the microstructure and properties of three manganese alloy steel with different manganese contents were studied by means of pulse current processing method.The experimental materials used in this paper are three steel alloys with different man. contents ZG60Mn8, ZG60Mn12 and ZG60Mn23. They were treated by pulse current, and the research contents are as follows:1. As-cast ZG60Mn8 contained residual austenite and carbides. After 480 ms pulse current quenching, the content of residual austenite is reduced), the size of martensite being refined, carbide being dissolved. After as-cast ZG60Mn8 were soluted under 1050℃,the carbide in the microstructure was dissolved, and the grain size was refined. Moreover, the amount of retained austenite and the defects in the microstructure both decreased. The solid solution treated samples were processed by 480 ms pulse current quenching. The size of martensite was refined. The microstructure was more uniform. The tensile strength and elongation of the samples were improved. Liquid nitrogen cryogenic treatment was executed on the soluted ZG60Mn8.As a result, part of the residual austenite further transformed to martensite. Carbide precipitated at grain boundaries, and microstructure embrittled. After 480 ms pulse current quenching, the grain boundary carbides were dissolved, martensite obtained from liquid nitrogen cryogenic transformed into martensite again via austenization. In this inverse transformation process, the size of martensite was refined, and the structure was more uniform, then the comprehensive mechanical properties were promoted.2. After 20% and 30% reduction of the amount of cold rolling processing, the microstructure of ZG60Mn12 was still austenite, and the phenomenon of processing hardening occured. The greater the amount of deformation, the more significant processing hardening. With the increase of the time of electropulsing treatment, the samples showed different degrees of recovery and recrystallization.The hardness and tensile strength of the sample decreased slightly.Elongation rate firstly increased and then decreased, reaching the maximum at 520 ms.When 560 ms, the recrystallization grains grew further, the organization coarsening, while the extension rate was reduced. And the products of strength and elongation reached maximum at 520 ms pulse current processing time.3. After 30% cold rolling reduction and deformation treatment, the microstructure of ZG60Mn12 and ZG60Mn23 were austenite. The strength and hardness of the samples all increased, and the elongation rate decreased. With the increase of Mn content, the stability of austenite increased. Work hardening ability decreased, and the deformation capacity became greater. As the time of pulse current increased, the internal cold-rolled steel TWIP generated varying degrees of recovery and recrystallization, the hardness and strength of the sample reduced gradually. Grain size first decreased and then increased, reaching the minimum at 520 ms. With the increase of the pulse current action time, the elongation rate of ZG60Mn12 increasesd first and then decreased, reaching the maximum at 520 ms. The extension rate of ZG60Mn23 increased continuously with the increase of the duration of the pulse current. This is because in the 560 ms annealing twins appeared inside ZG60Mn23 sample, which can effectively promote the generation of slip. Therefore, the extension rate continued to increase.