Bainite transformation affected by predeformation and stress in G55SiMoV steel
- PDF / 836,405 Bytes
- 8 Pages / 584.957 x 782.986 pts Page_size
- 83 Downloads / 284 Views
The influence of predeformation and stress on the isothermal bainite transformation has been investigated in G55SiMoV steel via microstructure observation and kinetic analysis. It was found that the bainite transformation became faster and at the end of isothermal holding the bainite fraction increased under the applied stress condition. When the stress increased to 150 MPa, the bainite distribution became to be nonrandom in G55SiMoV steel. Different deformation conditions, in which both promotion and inhibition occurred in the same steel, were created. The promoting and inhibiting factors affected bainite transformation comprehensively. 20% deformation could promote the bainite transformation when it deformed at 900 °C, but prevent bainite transformation when it deformed at 750 °C. Increase of ferrite nucleation rate caused by distortion and dislocation, would suppress the growth of bainite carbides and make most carbides without full growth be finer and shorter.
I. INTRODUCTION
The thermomechanical treatment has been used successfully in the past 30 years for steels containing allotriomorphic ferrite and pearlite, but recently adopted for the new bainite steels.1–3 The accumulated strain and stress in the deformed austenite should have a great effect on the subsequent bainite transformation, i.e., the state of austenite was one of the main factors on the transformation. Therefore, the related researches have been studied. The effect of stress on bainite transformation in alloy steels has been studied in some researches.4–7 The external tensile stress below the yield strength of the austenite has been confirmed to accelerate the bainite transformation and favor for the development of certain crystallographic variants of bainite.4 Kang et al.5 studied the effect of external stress on the orientation distribution of ferrite grains, and showed that the deviation angle of the ferrite orientation from the K-S relationship increased when the transformation took place under an external stress. The increase in the deviation angle of ferrite grains from the K-S relationship was considered to make the coalescence of ferrite grains difficult during growth. The influence of deformation on bainite transformation was different with various experimental conditions since the bainite transformation mechanism was complicated. In some researches, predeformation was generally presumed to promote the rate of bainite reaction.8,9 On the other hand, the different trend had been claimed. Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.325 J. Mater. Res., Vol. 29, No. 24, Dec 28, 2014
http://journals.cambridge.org
II. EXPERIMENTAL PROCEDURES
G55SiMoV steel is a new commercial medium carbon impact-resistant bearing steel whose main chemical composition is shown in Table I. Comparing with the
a)
2994
For example, Davenport et al.10 used hot-rolled samples, which demonstrated that the austenite which was deformed to a larger extent tended to transform to bainite at a lower temperature during con
Data Loading...
