Effects of isothermal transformation conditions on the microstructure and hardness values of a high-carbon Al–Si alloyed steel. (5th December 2015)

• Record Type: Journal Article
• Authors: Baradari, Sadjad; Boutorabi, Seyed Mohammad-Ali
• Is Part Of: Materials & design. Volume 86(2016:Oct.)
• Page Start: 603
• Page End: 609
• Publication Date: 2015-12-05
• Subjects: Carbide-free bainitic steel -- Austempering conditions -- Hardness -- Retained austenite; Materials -- Periodicals; Engineering design -- Periodicals; Matériaux -- Périodiques; Conception technique -- Périodiques; Electronic journals; 620.11
• DOI: 10.1016/j.matdes.2015.07.151
• Languages: English
• ISSNs: 0264-1275

Abstract

Abstract: In this investigation, the microstructure and hardness of a high-strength high-carbon steel containing 0.80 wt.% silicon and 0.84 wt.% aluminum have been evaluated under different austempering conditions. Austempering was performed at temperatures of 300, 330 and, 360 °C for different times from 1 to 8 h. Observations carried out by light optical microscopy (LOM) and scanning electron microscopy (SEM) revealed that the austempered samples have a microstructure consisting mostly of bainitic ferrite and retained austenite, and this was confirmed by X-ray diffraction (XRD) analysis and microhardness measurements. This simply indicates that it is possible to partially substitute aluminum for silicon and still retard the formation of carbides. There were no significant changes in ferrite plate thickness with increasing transformation temperature. The fraction of retained austenite, however, increased with temperature. A yield strength of 1170 MPa, an ultimate tensile strength of 1370 MPa, and a total elongation of 9.1% were obtained after isothermal transformation at 360 °C for 4 h. Depending on the transformation conditions, hardness values of about 500–660 HV30 were obtained. The hardness increased as the transformation temperature decreased. Graphical abstract: Highlights: Carbide precipitation was retarded during austempering of a low-alloy high-carbon steel with 0.80 wt.% Si and 0.84 wt.% Al A yield strength of 1170 MPa and an ultimate strength of 1370 MPa were obtained by austempering at 360°C for 4 h An extraordinary high hardness of about 660HV30 was achieved after austempering at 300°C