Study On Recrystallization Annealing Microstruture And Performance Of M42 Super-hard High Speed Steel

High speed steels are widely used as cutting tools for its high hardness,good wear resistance and excellent red-hardness.However,high-speed steel has poor plasticity and is easily broken during cold working.The traditional isothermal annealing process can improve the plasticity of high speed steel,but has the disadvantages of long production cycle and high cost.In this paper,the microstructure evolution of high-speed steel recrystallization annealing and its effect on properties were studied with M42 super-hard high-speed steel.The effects of annealing process,strain and initial microstructure on the recrystallization behavior of high-speed steel were analyzed.Theoretical guidance is provided for the development of a reasonable recrystallization annealing process in actual production.The results show that with the increase of annealing temperature,the cold-drawn M42 high speed steel wire undergoes different stages of recovery,recrystallization and grain growth,and the temperature ranges are below 700?,700? to 800? and above 800?,respectively.Among them,the optimum temperature range of recrystallization annealing of M42 high speed steel is 780~820?.When annealing at 780?,the time ranges of recovery,recrystallization and grain growth are 0~120s,120~300s and above 300 s.Among them,the optimal annealing time is 5min~30min.When the holding time exceeds 30 min,the size of grain and the carbide becomes bigger,the quantity becomes smaller,and the plasticity of the high speed steel decreases.The dislocation density of the matrix distributes inhomogeneouly after recrystallization annealing.It indicates that carbides have different abilities to hinder the recrystallization.The 800? annealing experiment of M42 cold drawn steel wire with different strains(0.074,0.151,0.207)shows that the critical strain of recrystallization is about 0.2.When the strain is less than 0.2,the recovery occurs only,and the strength and hardness decrease slowly.When the strain is over 0.2,the cold drawn steel wire occurs complete recrystallization,and the strength and hardness decrease rapidly.Compared with the recrystallization annealing process of M42 high speed steel cold drawn steel wire with different initial structure,it is found that the cold drawn steel wire is more likely to recrystallize when the carbide size is larger and the number density is smaller.The large amount of carbides present in high-speed steel strongly hinder the migration of dislocations and grain boundary during recrystallization.It is concluded that the hindrance of carbides is greater than the driving force of it.