Microstructure, mechanical properties and corrosion behavior of NbC modified AISI 440C stainless steel by vacuum sintering and heat treatments

摘要

Different amounts of niobium carbide (NbC) powder (5, 10 and 15 wt%) are mixed and added to 440C stainless steel powder. The composite powders are sintered at 1260, 1270, 1280 and 1290 degrees C for 1 h, respectively. The experimental results show that the optimal sintering temperature for the 440C-NbC composites is 1270 degrees C. Meanwhile, the 440C specimens with 5% NbC addition possess the optimal transverse rupture strength (TRS) value of 1985.2 MPa, as well as the highest polarization resistance of 1.01 x 10(2) Omega cm(2). While the 440C specimens contain or with 15 wt% NbC show the highest hardness value of HRA 80.9 after sintering at 1280 degrees C. Furthermore, the microstructural evaluation reveals that the rod-shaped M7C3 carbides located on the grain boundaries are gradually reduced after NbC particles are added, and the spherical-shaped M7C3 carbides are precipitated and dispersed in the matrix. After heat treatment, the primary M7C3 carbides are converted to M23C6 carbides, which results in a secondary hardening. The results clearly show that heat treatment effectively improves the particle size of the carbides and strengthens the matrix of the 440C-NbC composites. (C) 2017 Elsevier B.V. All rights reserved.