Effect of yttrium hydride addition on microstructure and properties of powder metallurgy CM2 high speed steel

Abstract

In this paper, carbide powder, carbonyl iron powder and yttrium hydride (YH2) were used as raw materials, through ball milling, vacuum drying, cold pressing and vacuum sintering to prepare high-carbon CM2 high-speed steels (HSS). The effect of YH2 addition on the microstructure and mechanical properties of sintered and heat-treated HSS was studied. The results show that due to the addition of YH2, submicron spherical Y2O3 particles dissolved with a certain amount of sulfur and other alloying elements are formed at the grain boundaries and inside the grains. Compared with the samples without YH2 addition, the bending strength of the samples with 0.1 wt.% YH2 is increased by 6.7%, reaching 3425 MPa. However, excessive addition of YH2 results in the formation of large-sized Y2O3 particles at the grain boundaries, resulting in decreased mechanical properties. With the increase of YH2 addition, the hardness, tempering softening resistance and in-situ hot hardness gradually increase.

Keywords

• Yttrium hydride
• Powder metallurgy
• High speed steel
• Carbide
• Tempering softening resistance