Tool Steels of New Generation

摘要

Some requirements are formulated for tool steels used to make tools with their durability being limited by strength and impact resistance rather than by wear resistance. It is shown that the high-speed steel belonging to a new hypereutectoid class is optimal for the above-mentioned application. The fracture mechanisms are considered for ledeburitic (R6M5) and hypereutectoid (11M5F) classes of tool steels. It is demonstrated that critical length crack formation in hypereutectoid steels takes place not only by means of elastic but also by means of considerable plastic deformation; on this account, the work of crack initiation in 11M5F considerably exceeds that of R6M5. The above-mentioned fact is due to the peculiarities of 11M5F steel microstructure characterized by extremely fine grain and the absence of eutectic carbides. Correlation between fracture work and deformation is established under static bending (on one hand) and impact strength (on the other hand) conditions.