Study On Transformation Law And Refinement Of Microstructure In 40Cr Rolling Process

40Cr medium carbon steel is widely used in shafts and gear parts of large machinery and equipment.As a typical high-strength steel material,compared with traditional steel materials,the production cost is low and the energy consumption is small.The calculation and simulation of 40 Cr medium carbon steel were carried out.Through hot rolled,warm rolled and annealed experiments.The effects of various processes on the mechanical properties of experimental steel were analyzed through microhardness and tensile experiments.The main findings are as follows:After hot rolled experiments,it is concluded that the multi-pass rolling is less than the number of passes;the higher the rolling temperature,the ferrite grain size is finer.The structure obtained by air-cooled normalizing after rolled is ferrite and pearlite,with low strength and hardness,but good plasticity and toughness;the structure obtained by water-cooled quenching after rolled is ferrite and martensite,with high strength and hardness,but poor plasticity and toughness.After warm rolled at 550°C,the average ferrite grain sizes of the four groups of samples were 1.10?m,1.45?m,and 1.14?m,respectively;the microhardness values were 39.4HRC,39.1HRC,38.7HRC,and 38.2HRC.It can be seen that the average ferrite size of the obtained ferrite is the smallest and the microhardness value is the highest after the 40 Cr medium carbon steel is subjected to 80% hot rolled deformation strengthening in five passes and the 70% warm rolled in three passes.With the increase of annealing time,the average size of ferrite grains increased from 1.02?m to 1.66?m.The carbides on the grain boundaries are larger than the carbides inside the grains.The proportion of small-angle grain boundaries is getting lower and lower,and the proportion of large-angle grain boundaries is getting higher and higher.The micro hardness decreased from 38.2HRC to 19.5HRC.The tensile strength decreased from 1234.08 MPa to 734.49MPa;and the elongation increased from 8.31% to 14%.The initial work hardening rate gradually reduced.Figure47;Table8;Reference 75...