Microstructures and Mechanical Properties of 440C Stainless Steel Strengthened with TaC via Vacuum Sintering and Heat Treatments

摘要

In this study, different amounts of tantalum carbide (TaC) powders (10, 20 and 30 mass%) were mixed and added to 440C steel powders. The composite powders were sintered at 1270, 1280 and 1290 degrees C, respectively, for 1 h. The experimental results showed that a suitable amount of TaC particle addition was effective in improving the strength and hardness of the composite materials. Conversely, excess TaC hindered the liquid diffusion of the Fe elements. As a result, the 440C specimens with 30% TaC addition still had 1.3% porosity. The 440C specimens with 10% TaC addition sintered at 1270 degrees C possessed the highest TRS values (2260.3 MPa), while those with 20% TaC addition sintered at 1290 degrees C had the highest hardness values (HRA 85.2). The microstructural evaluation of the 440C specimens with 10% TaC addition revealed that all the rod-shaped M7C3 carbides transformed to M23C6 carbides and precipitated within the grains as a strengthening phase after heat treatment, which was advantageous to the transverse rupture strength (TRS). Consequently, the TRS value of the 440C specimens with 10% TaC addition was significantly increased (2260.3 -> 2458.4 MPa) after heat treatment, thus possessing a high hardness (HRA 83.8).