Effect of Quenching Process on Microstructures and Mechanical Properties of Fe-0.9Mn-0.5Cr-2.4Ni-0.5Mo-C Steel
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JMEPEG https://doi.org/10.1007/s11665-018-3163-7
Effect of Quenching Process on Microstructures and Mechanical Properties of Fe-0.9Mn-0.5Cr-2.4Ni-0.5Mo-C Steel Jie Chen, Changsheng Li, Xin Jin, Liqing Chen, and Lei Fang (Submitted June 8, 2017; in revised form September 30, 2017) To develop an appropriate quenching process to produce Fe-0.9Mn-0.5Cr-2.4Ni-0.5Mo-C steel, the microstructures and mechanical properties of this steel were investigated under the direct quenching and tempering (DQT) and the direct quenching, reheated quenching and tempering (DQQT) heat treatment processes. The microstructure of the DQQT specimen was basically tempered sorbite with spherical precipitates, while quite a bit of tempered martensite was in the DQT specimen with dispersive nanoscaled precipitates. The yield strengths of the DQT and DQQT specimens were 1154 and 955 MPa, respectively. The yield strength of the DQT specimen was higher than that of the DQQT specimen because of its finer grain size, higher density of dislocations and dispersed precipitates. The DQQT specimen had spherical precipitates, which hindered the propagation of the crack. Moreover, the high-angle grain boundaries in the DQQT specimen took a higher proportion. Therefore, the Charpy impact values of DQT and DQQT specimens at 2 60 °C were 38 and 75 J, respectively. Consequently, the mechanical properties of the Fe0.9Mn-0.5Cr-2.4Ni-0.5Mo-C steel, which met the standard of 1000 MPa grade steel plate for hydropower station, were acquired by the DQQT process. Keywords
60 C Charpy impact, microstructures, quenching process, steels for hydropower station, yield strength
1. Introduction The steel plate for hydropower station is used in penstocks of hydropower station, spiral case of hydroturbine and other ancillary facilities. Presently, the steels for penstock and spiral case mainly use three strength levels: 500, 600 and 800 MPa grade. However, hydropower units gradually develop into high head, high speed, high efficiency and high capacity. To support this development, the steels for penstock and spiral case should have a higher strength. Therefore, the thickness of steels should effectively decrease, and the welding performance and flexibility of components should be better. Consequently, the 1000MPa grade steel plate for penstock and spiral case would be adopted more and more in the future (Ref 1). Fe-0.9Mn-0.5Cr2.4Ni-0.5Mo-C steel has excellent ductility and toughness compared to conventional high-strength steels, and this lowcarbon and low-alloy steel was designed as a 1000-MPa grade steel plate for hydropower station. Fe-0.9Mn-0.5Cr-2.4Ni-0.5Mo-C steel cannot be used without a quenching and tempering. Therefore, many studies were conducted on the reheated quenching and tempering (RQT) and DQT processes for high-strength steel with excellent lowtemperature Charpy impact properties. Xiao et al. compared the
effects of DQT and RQT processes on the microstructures and mechanical properties of steel plate for large oil storage tanks. It was stated that the DQT st
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