The Role of Alloying Elements in High Speed Steel Type Cast Irons

Abstract

The solidification process and hardenability of high speed steel type cast irons were investigated using a series of hypo-eutectic alloys of Fe-% C-5% Cr-5% Mo-5.5% V-(0,5)% W-(0,5)% Co-(0,5)% Ni and a hypereutectic Fe-2.3% C-5% Cr-5% Mo-9% V-5% W-5% Co alloy. In each hypo-eutectic alloy, the crystallization proceeds in the order of primary γ, γ+MC eutectic, γ+M₂C eutectic, while the primary MC instead of y crystallizes in the hyper-eutectic alloy. Mo and W increase the amount of eutectic carbide M₂C, white Ni promotes the crystallization of graphite at eutectic cell boundary. The amount and distribution of each carbide are explained with the aid of phase diagrams and the experimental data on the distribution of alloying elements during solidification. The hardness of quenched alloy takes the maximum value at an austenitizing temperature between 1273K and 1373K since the hardness depends on both the amount and the hardness of martensite. Each alloy exhibits a temper hardening, Co in particular enhances the hardness when the alloy is tempered at around 823K.

Keywords:

• High Speed Steel
• solidification
• hardenability
• wear
• carbide
• graphite