Investigation Of Heat Treatment Process And Properties Of Large-scale Forged 20MnMoNb

20MnMoNb steel widely used in a variety of ultra-high pressure test containers.With the increase in wall thickness,a higher requirement is put forward to the heat treatment process for the forging.In the actual production process,some standards can be as the reference for forging heat treatment within a certain size range(300mm~ 500mm).However,there is no standard reference for 530 mm thick 20 MnMoNb forging material.In this work,the simulation model of heat treatment temperature field of 20 MnMoNb large temperature forgings was established.The model was validated according to the thermocouple temperature measurement curve in different heat treatment process.The model was proved to be reliable.And then,this model was used to simulate the temperature field during heat treatment,the factors impacting the temperature difference between the surface and inner part were analyzed.In the heat treatment process,extending the holding time during low temperature stage has little influence on temperature rise curve,but extending the holding time during high temperature,the temperature rise cure changes obviously.When the furnace peak temperature increased to 910?,and increased holding time to 18 h,the quenching technology was better.The maximum temperature of the workpiece is 897.7?,the minimum temperature is 895.3?.This can meet the 20 MnMoNb quenching temperature requirements.When the furnace peak temperature raised to 680?,and extended the holding time to 14 h,the tempering technology is better.The maximum temperature of the workpiece is 663.1?,the minimum temperature is 656.5?,which can meet the quenching temperature requirement of 20 MnMoNb.A large forged 550 x 550 x 650 mm 20 MnMoNb plate was heat treated according to the parameters commanded by the simulation work,and the microstructure and mechanical properties of different region in forging were evaluated.The microstructure varies from inner to external of forging no matter in central area(CG,Center Group)or boundary area(BG,Boundary Group).The microstructure of CG varies as follow: massive ferrite + pearlite + granular bainite ? massive ferrite + lath bainite + a small amount of martensite ? tempering troostite ? tempered sorbate.The microstructure of BG varies as follow: ferrite + pearlite + bainite + a small amount of martensite ? lath martensite + tempering mixed structure ? tempering Sorbite.The area where consists of more martensite,the higher hardness is.The tensile properties of CG and BG regions also change with the evolution of microstructure.The variation trend of the two groups in tensile property is almost the same.CG obtains a peak of intensity from the center ~ 150 mm,while BG reaches the peak value at ~ 120 mm from the center.According to the comparison of organization and tensile property,it can be deduced that the hardening range of 20 MnMoNb in 550 mm thick is about 155 mm * 2,and the complete tempering area is about 95 mm * 2...