| Crankshaft is widely used in locomotives and ship engines and is a key component in the engine.Its main role is to aggregate the reversed-work of the cylinders of the engine and then transmit it in a rotary motion.In addition,the crankshaft is also responsible for driving fuel pumps,oil pumps,pumps,gas distribution agencies and other auxiliary devices.Marine crankshaft is an important component of marine diesel engine,which plays a very important role in ship safety and is regarded as the "heart" of marine diesel engine.The working environment of the crankshaft is extremely complex,and it needs to bear various alternating loads,such as torsion,bending,compression and so on.Therefore,it needs strict requirements for the hardness,strength,residual stress and internal microstructure of the material.In this paper,a database of thermophysical parameters(specific heat capacity,density,thermal conductivity,thermal expansion coefficient and latent heat of phase transformation)of annealed and austenitic structure of 42 CrMo steel has been established by means of experimental measurements and software calculation,and the functional relationship between these parameters and temperature has been obtained.The specific heat capacity of 42 CrMo steel at different temperatures was measured by STA 449 F3 synchronous thermal analyzer developed,and the density,thermal diffusivity,latent heat and thermal expansion coefficient of phase change were calculated by using JMatPro material calculation software.Based on a comprehensive analysis of the heat transfer behavior of 42 CrMo steel during the heat treatment of marine crankshaft,the characteristics of various thermophysical parameters changing with the change of structure and temperature are comprehensively considered.According to these characteristics,the subroutines of temperature field and structure field are compiled in Fortran language.The three-dimensional geometric model of marine cranks was established by Pro/E software and the three-dimensional unsteady heat transfer model of temperature field,tissue field and temperature field of heating and quenching process was established and coupled with ABAQUS finite element simulation software.The variation of temperature,microstructure and stress of different parts of 42 CrMo steel marine crankshaft during heating and quenching were studied.Through the analysis of the results of temperature field simulation,it can be found that the lower warming rate is adopted for the first temperature rise,which can significantly reduce the maximum temperature difference and maximum thermal stress of the surface and heart,so that the possibility of marine crankshaft curved crutches during the heating process is greatly reduced.The first heat preservation can significantly shorten the maximum temperature difference and make the temperature distribution more uniform.The second temperature increase mainly affects the austenitization degree of the marine crankshaft,the heating rate increases,the surface appears austenitizing,but the heart tissue is basically unaffected,the temperature difference between the surface and the heart is still large,but at this time,the temperature of the core of the ship's crank is high and in an elastic state,which can alleviate the thermal stress caused by the temperature difference.As the second heat preservation increases with time,the temperature difference between the surface and the core gradually decreases until the temperature is reached,and the degree of austenitization gradually increases.Finally,the component is all austenite.Through the analysis of the results of the simulation of the structure field,it can be seen that after quenching,the surface of the crankshaft is mainly martensite with a maximum content of 96%.The subsurface of the crankshaft is mainly bainite;and the pearlite is mainly concentrated in the center.It can meet the performance requirements of high hardness,high wear resistance and high toughness of the core of the marine crankshaft. |
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