Simulation of Cooling Behavior and Microstructure Development of PM Steels
Examensarbete för masterexamen
In recent years, growing demand for greater mechanical properties of PM steel components with competitive fabrication cost has led to enormous innovation in different aspects of PM industry. Recent research has focused on introducing new alloying systems, different furnace atmospheres and combining sintering and post sintering processes for more hardenable powder metallurgy (PM) steels. By elimination of any secondary operation such as quench-hardening and instead by introducing the hardening treatment right after sintering, fabrication cost is reduced by far. Sinter-hardening is a result of research conducted along this line. In this process, it is possible to manufacture sintered parts with a martensitic-bainitic microstructure by applying sufficient cooling rates (1-10°C/s depending on composition) directly after sintering. In addition, alloying elements such as Cr, Mo and Mn are usually added to the Fe-based powder to enhance the hardenability of the material. In this thesis, the cooling response of prealloyed steel powder during the sinter-hardening process has been investigated by means of Finite Element Method (FEM). An axi-symmetric FE model has been developed using MATLAB to predict the cooling response, considering the effects of nonlinear boundary conditions, latent heat of phase transformation and nonlinear thermal properties. The code was verified in two steps, firstly, by means of ANSYS commercial code and later by making a comparison between the results of the present FE simulation and the works done by previous researchers. Finally, the method was applied to simulate the cooling response and microstructural development of two prealloyed Cr-Mo steel powder grades; Astaloy CrL+0.6%C and Astaloy CrL+0.8%C.
Övrig bearbetning/sammanfogning , Other processing/assembly