Effect of Austempering Route on Microstructural Characterization of Nanobainitic Steel

• Published in: Acta metallurgica sinica : English letters Vol. 27; no. 1; pp. 19 - 26
• Main Authors: Lan, Huifang, Du, Linxiu, Zhou, Na, Liu, Xianghua
• Format: Journal Article
• Language: English
• Published: Heidelberg The Chinese Society for Metals 01.02.2014; Springer Nature B.V
• Subjects: Austempering; Bainitic steel; Bainitic transformations; Carbon; Characterization and Evaluation of Materials; Chemistry and Materials Science; Corrosion and Coatings; Ductility; Hot rolling; Low temperature; Materials Science; Mechanical properties; Metallic Materials; Nanohardness; Nanotechnology; Organometallic Chemistry; Retained austenite; Spectroscopy/Spectrometry; Steel; Tensile strength; Tribology; X-射线衍射分析; 上贝氏体; 体积分数; 微观组织; 残余奥氏体; 残留奥氏体; 等温淬火; 线对; Nanohardness; Strength–ductility balance; Nanobainitic steel; Retained austenite; Stability
• ISSN: 1006-7191; 2194-1289
• DOI: 10.1007/s40195-013-0006-2

A low-temperature nanobainitic steel was obtained through one-step and two-step austempering. The effect of austempering temperature, time, and route on bainitic lath width, volume fraction of retained austenite, carbon concen- tration in retained austenite, and nanohardness of bainitic lath and retained austenite was studied. Results showed that the transformation kinetics was slowed down and the bainitic lath was refined as the austempering temperature decreased from 300 to 250 C. Both coarser and finer bainitic laths were obtained with the two-step austempering, which was consistent with the lath size at 300 and 250 C austempering, respectively. X-ray diffraction analysis showed that both volume fraction of retained austenite and its carbon concentration decreased with the decrease of austempering temperature for the one-step austempering, and especially the carbon concentration is obviously increased when the two-step austempering is adopted. The nanohardness of the bainitic lath in the sample after two-step austempering treated lies between that of the samples after 300 and 250 C austempering treated. The product of tensile strength and total elongation of the two-step austempered sample is the highest, which increases monotonously with the product of retained austenite fraction and its carbon concentration. Higher strengthluctility balance may be resulted by the fine bainitic lath, high volume fraction, and high stability of retained austenite in the sample after two-step austempered.