Effect of austempering time on the microstructure and carbon partitioning of ultrahigh strength steel 56NiCrMoV7

LUO, Quanshun, KITCHEN, Matthew and ABUBAKRI, Shahriar (2017). Effect of austempering time on the microstructure and carbon partitioning of ultrahigh strength steel 56NiCrMoV7. Metals, 7 (7), p. 258.

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Official URL: http://www.mdpi.com/2075-4701/7/7/258
Link to published version:: 10.3390/met7070258

Abstract

Ultrahigh strength steel 56NiCrMoV7 was austempered at 270 °C for different durations in order to investigate the microstructure evolution, carbon partitioning behaviour and hardness property. Detailed microstructure has been characterised using optical microscopy and field emission gun scanning electron microscopy. A newly developed X-ray diffraction method has been employed to dissolve the bainitic/martensitic ferrite phase as two sub-phases of different tetragonal ratios, which provides quantitative analyses of the carbon partitioning between the resultant ferrites and the retained austenite. The results show that, a short-term austempering treatment was in the incubation period of the bainite transformation, which resulted in maximum hardness being equivalent to the oil-quenching treatment. The associated microstructure comprises fine carbide-free martensitic and bainitic ferrites of supersaturated carbon contents as well as carbon-rich retained austenite. In particular, the short-term austempering treatment helped prevent the formation of lengthy martensitic laths as those being found in the microstructure of oil-quenched sample. When the austempering time was increased from 20 to 80 min, progressive decrease of the hardness was associated with the evolution of the microstructure, including progressive coarsening of bainitic ferrite, carbide precipitating inside high-carbon bainitic ferrite and its subsequent decarbonisation.

Item Type: Article
Uncontrolled Keywords: ultrahigh strength steel; austempering; carbon partitioning; carbide precipitation; bainitic/martensitic ferrite
Research Institute, Centre or Group: Materials and Engineering Research Institute > Materials Analysis and Research Services
Identification Number: 10.3390/met7070258
Related URLs:
Depositing User: Quanshun Luo
Date Deposited: 13 Jul 2017 13:58
Last Modified: 14 Jul 2017 19:43
URI: http://shura.shu.ac.uk/id/eprint/16143

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