Experimental Study And Numerical Simulation On Grain Size In Heat Treatment Of 300M Steel

As the key components of aircraft take-off and landing system. Landing gear undertake huge load and strong impact. So it is directly related to the safety of aircraft and the crew. Nowdays most of the aircraft landing gear are forged with 300 M steel and the forming method easily appear coarse grain structure. So, heat treatment is needed to achieve the requirements of microstructure and grain size. Studying on the influence of various heat treatment factors on the grain size is particularly important.In this paper, research on heat conduction equation of temperature field, the phase transformation kinetics of organization field and thermal elastic-plastic stress-strain constitutive relation of stress field research, provides theoretical basis in heat treatment process simulation powerful support. What’s more, the selection of nonlinear of the blackness coefficient, latent heat of phase change and heat transfer coefficient are also important. Through a combination of cooling experiment data and the simulated data, approximation method is used to obtain the relationship of steel blackeness coefficient and temperature.Based on the above theoretical analysis and parameters, the process of landing gear heat treatment is simulated by the Deform finite element software. So the changes of temperature, microstructure and stress of the landing gear important nodes are got, that contribute to obtain a complete optimization of heat treatment process. By the same heat treatment process, the microstructure of the sample and the simulation results are compared to verify the correctness of the simulation results.According to the results of orthogonal experiment, the effects of the heating speed, heating temperature, holding time and cooling rate on the grain size are got. At the same time, the above four factors and heating system on the grain size are also further analyzed.