Study On The Heat Treat Process Experiment Of 17CrNiMo6 Steel Used For Heavy-duty Gear

In this paper,the heat treatment process test of heavy-duty gear material17CrNiMo6 steel is studied.The structure and properties of the preparation heat treatment test,high temperature carburizing quenching test and rapid carburizing test under different process conditions are analyzed respectively.The metallographic structure of 17CrNiMo6 steel with diameter of 90 mm is bainite after heating at 940 ? for 100 min,and normal normalizing heat treatment after air cooling.The hardness of surface and 1/2R is similar to that of center,ranging from 275 HB to 278 HB.The 20CrNi2 Mo steel with a diameter of 90 mm was heated at 940 ? for 120 min,and the metallographic structure obtained after air cooling was“bainite + a small amount of ferrite”.The surface hardness was about 277 HB,the hardness at 1/2R and the center was about 256 HB,and the internal hardness was about 20 HB lower.Isothermal normalizing heat treatment tests were carried out on 17CrNiMo6 steel and 20CrNi2 Mo steel respectively.The results show that the hardness of both steels decreases from 275~278 HB to 210 HB and 20CrNi2 Mo steel from 256~277 HB by heating for 30 min at 940 ?,furnace cooling to 650 ? and air cooling after holding for 2 h.Conventional normalizing and high temperature tempering heat treatment experiments were carried out on 17CrNiMo6 steel and 20CrNi2 Mo steel respectively.The experimental parameters were as follows: air cooling to room temperature after holding at 940 ? for 30 min,then air cooling after tempering at 650 ? for 2 h.The metallographic structure of the samples of the two materials was tempered sorbite.The hardness of 17CrNiMo6 steel was reduced to about 203 HB,and that of20CrNi2 Mo steel was reduced to about 223 HB.17CrNiMo6 steel will not be brittle after being heated for a long time at 930~980 ? for 24 h,quenched at 820 ? and tempered at low temperature.However,when 17CrNiMo6 steel is heated for a long time at 1050? for 24 h,the grain coarsening and impact toughness decrease.Rapid deep carburization of 17CrNiMo6 gear steel was carried out using nano-diamond powder hot infiltration technology.The experimental results show that the depth of carburizing layer is about 4 mm.After carburizing 17CrNiMo6 steel,oil quenching was heated at 820 ?,840 ?,860 ?,880 ? and 900 ?,respectively,and then tempered at 180 ? for 2 h.The results show that the hardness of carburizinglayer is the highest when the quenching temperature is 820 ? and the hardness can reach 63.4 HRC.With the increase of quenching temperature,the hardness of carburized layer begins to decrease.The metallographic structure of carburized layer is “lath tempered martensite + a small amount of bainite + fine dispersed carbide”when quenching temperature is 820 ?,and “lath tempered martensite + acicular” or“concealed acicular tempered martensite + a small amount of bainite + fine dispersed carbide” when quenching temperature is 860 ?.For the core,the metallographic structure is “lath tempered martensite + a small amount of bainite + a small amount of ferrite” at quenching temperatures of 820 ?,840 ? and 860 ?,and with the increase of quenching temperature,the structure of the core gradually becomes larger;while at quenching temperatures of 880 ? and 900 ?,the structure of the core is“lath tempered martensite + a small amount of bainite”.