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Anisotropic Distortion of Tool Steels D2 and M3 during Gas Quenching and Tempering

Heat treatment of forged high alloyed tool steels produces anisotropic dimensional change. In the present work, the distortion behaviour of tool steels D2 and M3 during gas quenching and tempering was investigated. The influences of material manufacturing processes including casting, forging and powder metallurgy on anisotropic distortion were investigated. Rectangular samples were quenched in a vacuum furnace with high pressure gas cooling. The sample distortion was measured by a coordinate measuring machine. By means of dilatometry and metallography, the possible mechanism of anisotropic distortion was investigated. Experimental results showed that the distortion of cast and powder metallurgical steels was nearly isotropic because of an isotropic carbide arrangement, but the distortion of ingot cast and forged steels was apparently anisotropic during gas quenching and tempering. The carbide bands are the main cause of anisotropic distortion in the investigated steels. Dilatometric experiments showed that phase transformation plays an important role in the mechanism of anisotropic distortion. First simulations of the dimensional change during quenching indicated that transformation induced plasticity is the main mechanism by which anisotropic distortion occurs in this type of steels.