The effect of tempering parameters on the hardness and precipitation characteristics of quenched and tempered RQT701 steel plate.

Driscoll, Jonathan Richard (2018). The effect of tempering parameters on the hardness and precipitation characteristics of quenched and tempered RQT701 steel plate. University of Birmingham. M.Sc.

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Abstract

Reheated quenched and tempered 701 steel (RQT701) is a high strength low alloy martensitic grade commonly used in the earth moving and construction industries. The aim of this project was to investigate the tempering response of RQT701 steel at 580, 600 and 620 °C for between 1 and 100 hours.

Steel plate, of composition 0.17C, 0.29Cr and 0.53Mo (all wt. %) and 15 mm thickness, was supplied in the as-quenched condition. It was found that the as-quenched condition (water cooled from 925 °C at 60 °C-s, surface measurement) consisted of autotempered martensite with a hardness of 430 HV. Ice water quenching was tested and did not have any effect on the tempering response past 30 minutes.

Hardness measurements on samples tempered between 1 and 4 hours showed an increase of approximately 10 HV between 2 and 3 hours. Particle analysis using SEM images revealed the average precipitate equivalent circle diameter to increase from 45 to 71 nm, the number density to decrease from 63 to 52 per μm2, and the volume fraction of precipitates to increase from 0.017 to 0.022 %. The results suggest that the formation of very fine M2C, in combination with cementite, cause the secondary hardening peak.

Type of Work:

Thesis (Masters by Research > M.Sc.)

Award Type:

Masters by Research > M.Sc.

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