Abstract
In this work, hot compression experiments of 300M steel were performed at 900–1150 °C and 0.01–10 s−1. The relation of flow stress and microstructure evolution was analyzed. The intriguing finding was that at a lower strain rate (0.01 s−1), the flow stress curves were single-peaked, while at a higher strain rate (10 s−1), no peak occurred. Metallographic observation results revealed the phenomenon was because dynamic recrystallization was more complete at a lower strain rate. In situ compression tests were carried out to compare with the results by ex situ compression tests. Hot working maps representing the influences of strains, strain rates, and temperatures were established. It was found that the power dissipation coefficient was not only related to the recrystallized grain size but was also related to the volume fraction of recrystallized grains. The optimal hot working parameters were suggested. This work provides comprehensive understanding of the hot workability of 300M steel in thermal compression.
Highlights
The 300M steel, an ultra-high strength steel which is a modification of AISI 4340 steel, is often used in high performance auto parts, aircraft landing gear, airframe parts, and many other high strength applications because of the outstanding mechanical properties
The selection of hot working parameters has been a major concern in isothermal compression of 300M steel, because it affects the microstructure at high temperatures, and affects the microstructures after cooling and service performance
Based on a constitutive model coupling average grain size, a processing map of 300M steel was calibrated by Sun et al [8], and a broader hot working parameter range was determined at 900–1140 ◦ C and 0.1–1.91 s−1
Summary
The 300M steel, an ultra-high strength steel (the ultimate tensile strength ≥1800 MPa) which is a modification of AISI 4340 steel, is often used in high performance auto parts, aircraft landing gear, airframe parts, and many other high strength applications because of the outstanding mechanical properties. Based on a constitutive model coupling average grain size, a processing map of 300M steel was calibrated by Sun et al [8], and a broader hot working parameter range was determined at 900–1140 ◦ C and 0.1–1.91 s−1. These researches have laid a solid foundation for the present investigation. Problems about the processing map of 300M steel still exist, and systematic research on the microstructure evolution and hot workability in thermal compression of 300M steel is in need. This work provides comprehensive understanding of the hot workability of 300M steel in thermal compression
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