Effects Of Microstructure And Drill Geometry Of High-speed Steel Drill's Using Life

Jiang Su TianGong Co.Ltd is the largest production base of high-speed steel(HSS) and twist drills. The HSS drills produced by Jiang Su TianGong Co.Ltd have low longevity and reliability. By analysis comparison of microstructure and geometrical dimension of the drill ,It found that the effect of drills life was microstructure and drill's geometrical dimension . With the help of optical microscope and SEM, the microstructure. was studied. Tensile test and hardness-testing was used to appraisal the mechanical property. Rare-earth treatment and heat treating technology's was studied. By using mathematical statistics,geometrical dimension's effect to the drill life was studied.Rare-earth treatment's effect to the high-speed steel was studied. The experiment result showed that rare-earth can purify high speed steel. It reduced [O] content 33% in M2 and 27% in M42. It reduced [S] 43% in M2 and 27% in M42. Addition 0.2% rare-earth can improve the cast structure. It made the closed and continuous reticular eutectic carbide in M2 steel change into semi-enclosed and discontinuous reticular. It made the rods carbide in ledeburite change into fishbone carbide. It also made the ledeburite reticular more thin and loose. It can make the carbide in morphology after striking and rolling smaller and more dispersion and make the grain smaller than usual. Addition 0.2% rare-earth improved contraction of cross sectional area of M2 hot-finished rod from 15.4% to 18.8. It improved contraction of cross sectional area of M42 hot-finished rod from 9.1% to 16.4%.Heat treatment's(including heating-up temperature,holding time,C-curve holding time,fast cooling technology,quenching temperature) effect to the high-speed steel was studied. The results showed that the optimum parameters of M2 are as follows, at 880℃for 2h and cooling in furnace, at 760℃for 5h, then quenching in water,quenching at 1200℃. The optimum parameters of M42 ware as follows, at 890℃for 3h and cooling in furnace,at 700℃for 6h and cooling in furnace. the optimum parameters of M42 is that at 890℃for 3h and cooling in furnace,at 700℃for 5h,then cooling in furnace,quenching at 1190℃.The mathematical statistics result of the drill geometrical dimension and drill life showed that the drill heart thickness,drill heart taper,diametral taper have grate effect to drill life,so they should be strictly controlled. From the mathematical statistics model,if drill's diameter was 5mm,the heart thickness between 0.84~0.97mm,the heart taper between 0.8~1.9(mm/100mm),the diametral taper between 0.3~5.6(mm/100mm),the drills would have longer life . the experiment showed that the long life drill's percentage can be improved from 56% to 79%.Experiment result showed rare-earth treatment,optimization heat treatment technology and pertinent...