Effects of niobium additions on the structure, depth, and austenite grain size of the case of carburized 0.07% C steels

Journal Article · Tue Oct 01 00:00:00 EDT 1996 · Journal of Materials Engineering and Performance

DOI:https://doi.org/10.1007/BF02646087· OSTI ID:415450

Islam, M A; Bepari, M M.A. ^[1]

---

1. Bangladesh Univ. of Engineering and Technology, Dhaka (Bangladesh). Dept. of Metallurgical Engineering

Carbon (0.07%) steel samples containing about 0.04% Nb singly and in combination with nitrogen were carburized in a natural Titas gas atmosphere at a temperature of 1,223 K (950 C) and a pressure of about 0.10 MPa for 1/2 to 4 h, followed by slow cooling in the furnace. Their microstructures were studied by optical microscopy. The austenite grain size of the case and the case depths were determined on baseline samples of low-carbon steels and also on niobium and (Nb + N) microalloyed steel samples. It was found that, when compared to the baseline steel, niobium alone or in combination with nitrogen decreased the thickness of cementite network near the surface of the carburized case of the steels. However, niobium in combination with nitrogen was more effective than niobium in reducing the thickness of cementite network. Niobium with or without nitrogen inhibited the formation of Widmanstatten cementite plates at grain boundaries and within the grains near the surface in the hypereutectoid zone of the case. It was also revealed that, when compared to the baseline steel, niobium decreased the case depth of the carburized steels, but that niobium with nitrogen is more effective than niobium along in reducing the case depth. Niobium as niobium carbide (NbC) and niobium in the presence of nitrogen as niobium carbonitride, [Nb(C,N)] particles refined the austenite grain size of the carburized case, but Nb(C,N) was more effective than NbC in inhibiting austenite grain growth.

• Sponsoring Organization: USDOE
• OSTI ID: 415450
• Journal Information: Journal of Materials Engineering and Performance, Journal Name: Journal of Materials Engineering and Performance Journal Issue: 5 Vol. 5; ISSN 1059-9495; ISSN JMEPEG
• Country of Publication: United States
• Language: English

Related Subjects

33 ADVANCED PROPULSION SYSTEMS
36 MATERIALS SCIENCE
AIRCRAFT
CARBON STEELS
CARBONITRIDES
CARBURIZATION
CEMENTITE
CHEMICAL COMPOSITION
GAS FLOW
GRAIN BOUNDARIES
GRAIN GROWTH
MATERIALS
METALLURGICAL EFFECTS
MICROSTRUCTURE
NIOBIUM
NIOBIUM CARBIDES
NITROGEN
OPTICAL MICROSCOPY
SAMPLE PREPARATION
VEHICLES