The Development of High Hard and 
Tough Matrix Type High Speed Tool Steels  
By SHUN-SUKE NAKAHAMA*1, YUKINORI MATSUDA*2, KUNIO NAMIKI*3, KOZO OZAKI*4

3. The concept of the development (continued)

3.2 Conventional matrix type high speed tool steels

MHS steels have the chemistry corresponding to the matrix chemistry as quenched. The fundamental concept of MHS steel is shown in Fig.6 (below). Due to fine carbides they show higher toughness and fatigue strength than conventional steels. Originally, they were developed in the US and VASCO still has the US patent of matrix type steels.3~'4~ Table 1 shows the examples of principal chemistries of MHS steel. Compared to the most popular high speed steel AISI M2, MI-IS steels contain lower carbon and carbides former such as W, Mo and V. The microphotograph of conventional MHS steel is shown in Fig.7 (below). To observe coarse primary carbides spheroidized annealed materials were electrically distinction etched by using 1% Cr203 solution. Primary crystallization carbides from melt, MC and M2C, can be distinction etched. Even MHS steels show coarse carbides which are determined as VC by Energy Dispersive X-ray analysis.