This study aims to research and develop applications of alloy tool steel (SKD11) castings with high C and high Cr, manufactured by the investment casting process. We systematically investigated the influence of amount, morphology, and distribution of M
7C
3 and/or MC type carbides on mechanical properties such as tensile and bending strength, elongation, and hardness. The steel castings were melted in a high frequency induction furnace, and melts varying from 0.3mass% V to 10mass% V were cast into an alumina mould 14mm in thickness, heated to 1,373K. With increasing V content, crystallized carbides in the castings were found to increase and change from plate-like eutectic M
7C
3 type to granular MC type, crystallizing randomly owing to stronger stabilization of the carbide of V than Cr. The hardness of quenched and subsequent tempered castings with 10mass% V was lower than that with less than 5mass% V. Because most of the C in castings with more than 5mass% V is used to form MC type carbide, there is a lack of C content in the matrix to maintain good hardening ability as a result of martensite transformation during quenching. The castings with 1.8mass% C and 5mass% V modified by increasing the C content according to amount of V added was found to exhibit higher strength and hardness than those with the SKD11 composition. Fracture crack was observed to propagate continuously along the M
7C
3 type carbide, suggesting that higher strength can be obtained by dispersing or separating continuous carbide.
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