1 American Society For Metals,Metals Handbook,,(10th ed.,ASM,Ohio,USA,1990) p.909. 2 T.Q.Lei and J.Q.Fu,500 Technolodes for Metch Heat Treatment(China Machine Press,Beijing,1998) p.10(in Chinese). 3 M.L.Cai and H.L.Ding,Heat Treatment of Tool Steel and Die Steel(China Machine Press,Beijing,1998) p.9(in Chinese).