Paper Title:
Effect of Prior Heat Treatment on Hardness Profile after Nitrocarburization in Medium Carbon Steel
  Abstract

Gaseous ferritic nitrocarburization is one of the major surface hardening methods to improve the fatigue strength of machinery parts made of medium carbon steels. The fatigue strength of nitrocarburized steel parts depends on the hardness profile below the surface; however, the mechanism of its evolution during nitrocarburization has not been fully understood. Recently, as-forged steels, in which thermal refining process like normalizing is omitted from the viewpoints of environmental considerations, energy savings and manufacturing cost reductions, have been widely used in the machinery parts industry. Therefore, it is important to understand the mechanism of hardness increase below the surface of the nitrocarburized steels with respect to the effect of prior refining heat treatment. In the present study, the hardness increase at the subsurface region of nitrocarburized steels containing 0.4mass%C was characterized, and the influence of prior normalizing treatment was investigated. Microstructure of both the as-forged and the normalized specimens was the ferrite/perlite mixture, while the ferrite volume fraction in the as-forged steel was smaller than the latter. These as-forged and normalized steels were gaseous nitrocarburized at 853K for 2 hours under the atmosphere of RX gas and NH3 gas mixture, and then they were oil-quenched to 373K. Overall hardness below the surface after nitrocarburization was higher for the specimen without prior normalizing treatment, although both specimens had the similar nitrogen concentration profiles and precipitation behaviors of the nitrides. However, it was found that the individual ferrite grains in the as-forged steel were more hardened than those in the normalized steel. These indicate that the most likely cause of the hardness increase near the surface after nitrocarburization is the solid solution hardening by dissolved nitrogen and that the ferrite grains of the as-forged steel were likely to soak up more nitrogen and were hardened to the higher degree since the similar amount of nitrogen were incorporated mainly within ferrite grains. Thus, the prior heat treatment strongly affects the amount of hardening through the ferrite fraction.

  Info
Periodical
Materials Science Forum (Volumes 638-642)
Main Theme
Edited by
T. Chandra, N. Wanderka, W. Reimers , M. Ionescu
Pages
3200-3205
DOI
10.4028/www.scientific.net/MSF.638-642.3200
Citation
M. Egashira, S. Nishitani, M. Yuya, N. Sano, "Effect of Prior Heat Treatment on Hardness Profile after Nitrocarburization in Medium Carbon Steel", Materials Science Forum, Vols. 638-642, pp. 3200-3205, 2010
Online since
January 2010
Export
Price
$32.00
Share

In order to see related information, you need to Login.

In order to see related information, you need to Login.

Authors: Wee Do Yoo, Jong Hoon Lee, Kuk Tae Youn, Young Mok Rhyim
Abstract:The microstructures and mechanical properties of 17-4 PH stainless steel at each steps of heat treatment, such as homogenizing, solid...
15
Authors: M.S. Koo, Ping Guang Xu, J.H. Li, Yo Tomota, O. Muransky, Petr Lukáš, Yoshitaka Adachi
Abstract:A challenge was made to examine the micro-structural evolution during thermomechanically controlled processing (TMCP) by in situ neutron...
419
Authors: Guo Bin Li, Zheng Zhi Zhao, Di Tang
Abstract:The microstructure evolution of 780 MPa hot dip galvanized dual-phase (DP) steel at heating stages of the annealing process was analyzed...
1331
Authors: Mahmoud M. Tash
Chapter 2: Materials Science and Engineering
Abstract:The present study was undertaken to investigate the effect of thermo-mechanical treatment (TMT) on the microstructure and mechanical...
838
Authors: Jin Ming Liu, Jie Liu, Guang Wei Fan, Dong Fang Du, Guo Ping Li, Cheng Jun Chai
A. Environment Related Materials and Photocatalysts
Abstract:Effect of solution treated temperature at 5001100°C on ferrite/austenite ratio and σ phase precipitation has been studied in this paper, and...
3