The Effects Of RE On Performance And Microstructure Of M35 High Speed Steel

High-speed steel (HSS) is widely used for making tools, dies etc. for its'high hardness, high red-hardness and good wear-resistanting property. Fracture often occurs in process of HSS strand drawing.The morphology of drawing fractures were investigated and classified. Statistical results showed that the reasons for drawing fractures were caused by inappropriate drawing process (no orientation-equipment and heavy wear between mould and strand) and strands'defects. The drawing fractures frequency decreased after equipment improved. Defects of strands could be eliminated by optimizing heat treatment process and adding of rare earth element (RE).The effects of heat treatment parameters on structure and mechanical property of M35 steels were studied. The results showed that the optimum parameters are as follows, at 880℃for 2h and cooling in furnace, at 760℃for 5h, then quenching in water.The influences of RE on structure and performance of high-speed steel were also studied. RE was added to metallic molten pool during electroslag remelting process. The results showed that the remainder of RE was about14%. Compared with non-RE treatment high-speed steel, the content of [O] decreased from 61×10-6 to 41×10-6and [S] decreased from 0.02% to 0.008% in RE treatment HSS. With RE additional, the structure and performence of HSS changed as follows: (1) The ledeburite network as cast structure had been broken. (2) The grain of austenite was small and homogeneous in forged structure. (3) The size of the carbides in strands was smaller than that of non-RE strands. (4)The tensile strength of strands decreased from 855 MPa to 815 MPa and the reduction of area increased from 15% to 20%.