Investigating the effect of ball milling during the deep cryogenic heat treatment of the 1.2080 tool steel

The effect of attrition milling on the structure and hardness of the 1.2080 tool steel during the deep cryogenic heat treatment was investigated via the scanning electron microscope (SEM), X-ray diffraction (XRD) and microhardness and hardness evaluation. Some newly formed defects were produced during the attrition milling of the samples as a result of the surface contact between the balls and samples. These defects affect the carbides nucleation during the cryogenic heat treatment. Moreover, the surface impact produces a residual compressive stress on the samples surface. These phenomena lead to an increase in the hardness and percentage of the carbides. It was also observed that milling the samples before the cryogenic heat treatment is not beneficial due to austenite aging. Furthermore, some newly nano-sized carbides were also produced during the cryogenic heat treatment in the structure, increasing the hardness further.

► Cryogenic treatment increases the hardness and makes a higher carbide percentage.
► Cryo-milling increases the carbide percentage and makes a homogenous distribution.
► Cryo-milling increases the hardness due to a remaining compressive stress.
► Aging decreases the hardness and destructing the carbide distribution.