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

• Published in: Journal of alloys and compounds Vol. 712; pp. 760 - 767
• Main Authors: Huang, Kuo-Tsung, Chang, Shih-Hsien, Hsieh, Pei-Chung
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 25.07.2017; Elsevier BV
• Subjects: 440C stainless steel; Carbides; Corrosion; Corrosion resistance; Creep rupture strength; Dispersions; Grain boundaries; Heat treating; Heat treatment; Martensitic stainless steels; Mechanical properties; Metal matrix composites; Microstructure; Niobium carbide; Particulate composites; Polarization resistance; Secondary hardening; Transverse rupture strength; Vacuum sintering; Transverse rupture strength; Polarization resistance; Niobium carbide; Heat treatment; 440C stainless steel
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2017.04.125

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 °C for 1 h, respectively. The experimental results show that the optimal sintering temperature for the 440C-NbC composites is 1270 °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 × 102 Ω cm2. While the 440C specimens contain or with 15 wt% NbC show the highest hardness value of HRA 80.9 after sintering at 1280 °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. •The properties obviously improved after adding 5% NbC powder to 440C stainless steel.•N5 specimen had the highest TRS value (1985.2 MPa) after sintered at 1270 °C for 1 h.•The polarization resistance (Rp) of the N5 specimens increased to 1.01 × 102 Ω cm2.•M7C3 carbides decomposed and re-precipitated as M23C6 carbides after heat treatments.•The highest hardness (HRA 86.2) was obtained via sintering and heat treatment.