Numerical Simulation Of The Heat Treatment Process For The Main Shaft Of The A668 Steel Turbine

The A668 steel turbine main shaft is an important component of the water motor.It bears the direct impact of water flow and bending and torsion during work,and requires high enough performance to avoid vibration and deformation.In actual production,the heat treatment process of the A668 steel turbine main shaft usually uses empirical methods to formulate problems such as uneven distribution of strength and toughness.The empirical method requires a lot of experiments and production practices,and there are huge time,energy and material costs.This paper explored the relationship between the heat treatment process and organization of the A668 steel turbine main shaft through a combination of experiment and numerical simulation.The following main conclusions were obtained:(1)By modifying the first terms of the index positions of FC,PC,and BC in the phase change calculation model to 1.401,-4.8,and-8.53 respectively,and drawing a CCT curve of A668 steel using a new method of drawing CCT curves.According to the CCT curve,the critical cooling rate was 118?/s and Ms was 350.2?.(2)The simulation results of the end-quenching experiment showed that martensite,bainite,pearlite and ferrite appear at positions 0mm,10 mm,32mm and 100 mm from the end face,respectively.The verification of the numerical simulation results by the actual end-quenching experiment showed that the metallographic structure and hardness test results of the actual end-quenching experiment were consistent with the numerical simulation results,indicating the correctness of the numerical simulation phase transformation model and the hardness calculation model.(3)The numerical simulation of the temperature and grain size distribution of the A668 steel hydraulic turbine main shaft under two different heating methods,rapid heating and step heating,showed that the maximum temperature difference between the high temperature zone and the low temperature zone of the workpiece reached 200? in the rapid heating mode.In the step heating mode,the maximum temperature difference between the high temperature area and the low temperature area of the workpiece was 60?.At the end of the rapid heating,the grain size in the middle of the spindle was 28 ?m,while at the end of the step heating,the grain size at the same position is 111 ?m.In the rapid heating process,the grain size at the center of the flange section was 16 ?m,while in the step heating process,the grain size at the same position was 29 ?m.(4)The numerical simulation of the temperature change and microstructure distribution of the A668 steel turbine main shaft in air-cooled and water-cooled modes showed that the temperature change rate of the main shaft inside and outside during the cooling process caused the temperature difference to increase first and then decrease.The maximum temperature difference was 166? at 77 minutes,and the temperature difference basically disappeared at 800 minutes.After air cooling,the structure of the main shaft was ferrite and pearlite,and the uniform hardness was 14.6HRC.The maximum temperature difference was 760? at 30 minutes of water cooling,and 100? at 200 minutes of water cooling.After water cooling,the outer layer of the main shaft obtained bainite and martensite with a certain thickness,the outer surface hardness was 49 HRC,the subsurface temperature was 35 HRC,and the core portion was 14.6HRC.