Formation Analysis And Control Technology Research Of Banded Structure For 17CrNiMo6 Gear Steel

In today’s world,with the shortage of energy and the intensification of the greenhouse effect,the demand for clean energy is also increasing.As a green energy,wind energy has been widely concerned around the world,so the installed capacity of wind power continues to increase.As one of the key components of wind power equipment,17 CrNiMo6 wind power gear has extremely strict performance requirements.However,during the hot working of 17 CrNiMo6 gear steel,a banded structure will be formed,which seriously restricts its processing performance and service performance.Therefore,this paper studies and analyzes the reasons for the formation of the banded structure of 17 CrNiMo6 wind power gear steel,adopts heat treatment processes with different parameters,and explores effective methods to reduce or eliminate the banded structure.It provides reference suggestions for eliminating banded structure,mixed crystal structure and non-equilibrium structure.The main findings obtained are as follows:(1)Using optical microscope,scanning electron microscope and energy dispersive spectrometer to study the forged samples of 17 CrNiMo6 wind power gears,the results show that the forged samples of 17 CrNiMo6 wind power gears have different degrees banded structure,and the banded structure composed of ferrite band and pearlite + bainite band,the enrichment of alloy elements in the pearlite + bainite region is the root cause of the banded structure,and the insufficient and uneven cooling rate after forging is caused by the banded structure direct cause.(2)Using the high temperature diffusion annealing process,it is found that this process can homogenize the alloy elements and fundamentally eliminate the banded structure.The higher the heating temperature and the longer the holding time,the more uniform the distribution of alloying elements,the smaller the difference in grain size,and the structure changes from irregular bulk ferrite and pearlite + bainite to reticulated iron along the grain boundaries.Element body and bainite;17CrNiMo6 gear steel as-forged specimens disappear when the heating temperature is 1100℃,the holding time is 11 h,and the heating temperature is1250℃,and the holding time is 2h,but the grain size difference is relatively small.When the heating temperature is 1250℃ and the holding time is 4h,the distribution of alloy elements is uniform.(3)The cooling rate after austenitization has an obvious effect on weakening the banded structure.Accelerating the cooling rate inhibits the nucleation and growth of pro-eutectoid ferrite,thereby inhibiting the generation of the banded structure,but it cannot be fundamentally Eliminate the segregation of alloying elements;and 17 CrNiMo6 gear steel as-forged samples have a large amount of bainite structure during furnace cooling,air cooling and wind cooling.(4)Combined with the existing technology,the holding time should be appropriately extended for 3～5h in the middle of different forging times,and then through reasonable uniform and rapid cooling after forging and isothermal normalizing,the phenomenon of banded structure and mixed crystals can be eliminated,and the structure can be cut off.Inherited,and got a balanced organization of ferrite and pearlite.