Alloy Design Of High-Toughness Die Steels And Study Of DM9 Die Steel

In order to develop the new die steel DM9, which is worked in heavy load conditions, this paper has studied the theoretical basis of die steel alloy design and metallography theory, and put forward the procedures of alloy design for engineering application. And melting, forging, heat treatment, micro-structure and properties of DM9 die steel have also been studied. The following results are achieved: (1) in accordance with the empirical electron theory of solids and molecules, considering the number of covalent bond pairs on the strongest bond in a segregation structure nA, the elements for matrix- strengthening can be chosen. (2) on the basis of the available phase-equilibrium thermodynamics calculation of alloy system and phase diagrams, which have been worked out, the contents of alloy elements can be identified with reference to the types, quantity and phase-transformation of carbides. (3) both the values relating to toughness (including bending strength, yield strength, impact value of unnotched samples ) and hardness of new DM9 die steel are higher than those of Crl2MoV die steel. (4) in comparison with those of 6CrW2Si, 7Cr2WMoVSi(DM7), H13 and Crl2MoV die steels, the results of experiments on DM9 have further testified the alloy design procedure, which has been referred above, are rational. The study has brought forward the theoretical basis and engineering application prospect for die steel alloy design including composition design, micro-structure design, technics design and property forecasting.