Microstructures and mechanical properties of alloy tool steel castings with carbides stabilizer elements
Alloy tool steel castings, whose chemical compositions are 1.5％ C and 12％ Cr, have good wear resistance owing to continuous crystallization of M7C3 type carbides. However, the continuity of these carbides reduces the strength of the castings in comparison with that of alloy tool steels with the same hardness. This study aims to determine the optimum C and Cr contents for dispersing continuous Cr carbides and develop castings satisfying both good mechanical characteristics and wear properties. The melts were adjusted by varying the alloy compositions between 0.5 and 1.5 mass％C, and between 8 and 12 mass％Cr in a high frequency induction furnace by investment casting. The microstructures of the specimens were observed after the electrical etching with 10％ oxalic acid solution, and the area fractions of carbides were measured by using an image analysis device. The identification of carbides was performed by using an X-ray diffraction apparatus. The element distributions in microstructures were measured by using a SEM-EDX apparatus. In static mechanical property testing the tensile test, bending test, Rockwell hardness test with C scale and micro Vickers hardness test with HV0.1 were performed. The abrasion wear test was conducted by using a specimen polishing device with ＃240 alumina polishing paper. The fraction of wear loss was obtained by dividing the wear loss by the initial weight of the specimen. The amount of carbides was found to decrease with decreasing C and Cr contents. Cr carbides also dispersed in the matrix microstructure, and decreasing the C content increased the mechanical properties such as tensile strength and bending strength. Especially, samples with 0.5％ carbon content exhibit superior characteristics such as 1,300 MPa tensile strength and 2,450 MPa bending strength compared to other samples. On the other hand, decreasing the C content was found to deteriorate wear properties greatly due to reduced area fraction of crystallized carbides in the matrix microstructure. From the view points of the morphology and distribution conditions of carbides, we may conclude that a superior wear resistance can be obtained in a casting whose amount of the continuously-crystallized eutectic carbides is relatively smaller and also which has many dispersed fine carbides with high hardness. Based on these experimental results, we prepared samples adding Ti to the base melt. The results revealed improvements in the mechanical properties and wear properties of these Ti-added samples due to the fine TiC type carbides which crystallized preferentially than Cr type carbides in the matrix microstructures.
alloy tool steel mechanical properties wear properties titanium carbide
Tohru Nobuki Eiji Endo Hideki Nakayama Minoru Hatate
Department of Mechanical Engineering, Faculty of Engineering, KINKI University, Hiroshima 739-2116, Castem Co., Ltd.,Fukuyama 720-0004, Japan
国际会议
The 11th Asian Foundry Congress(第11届亚洲铸造会议 AFC-11)
广州
英文
1-7
2011-11-12（万方平台首次上网日期，不代表论文的发表时间）