Effect of high cooling rates on the structurization and mechanical properties of tool materials

Abstract

The paper studies the structure and mechanical properties of Kh12 and R2AM5F2NYu tool steels and ZChKh25 cast iron produced by gas spray forming. It is shown that rapid solidification during spray forming changes not only the structural type but also the class of materials and substantially improves deformability and mechanical properties. Billets from wear-resistant cast iron formed by spraying can be deformed by hot forging, stamping, and rolling with strain to 30%.The processes of producing a new class of materials based on oversaturated metastable solid solutions are currently of great interest. The metastable structure forms due to the overheating of the liquid metal and the high cooling rates during solidification and crystallization [1][2][3]. Hence, difficult-to-deform materials, such as highspeed steels and high-alloy wear-resistant white cast iron, hold much promise. They combine high deformability, strength, and fracture toughness and possess such functional characteristics as thermal stability and wear resistance produced by conventional processes [4][5][6].Conventional die and high-speed cast steels have poor structure because a eutectic forms and the ingots show lower plasticity and poor deformability [4,5].Unlike cast steels, powder high-speed steels have practically no carbide inhomogeneity or total and dendritic segregation. They have equiaxial grain structure, isotropic properties, and, thus, better plasticity and deformability.Alloying elements for high-strength tool steels with high performance are usually selected for their carbide inhomogeneity, hardness after quenching and tempering, heat resistance, and specific purpose of high-speed tool steel.Our objective is to show how the structurization and properties of high-alloy steels and alloys can be controlled by rapid melt cooling to produce ingots by spray forming (SF).Spray forming combines two processes: (i) gas atomization of metal melt and (ii) deposition of sprayed droplets onto a base where they combine again in semi-solid state into a high-density ingot (Fig. 1).