Abstract
The initial austenite grain size of boron microalloyed steel with three different amounts of boron (20, 40, and 60 ppm) was investigated under different heating temperatures (1150, 1100, and 1050 °C), and hot compression tests of samples in a wide range of temperature (900–1100 °C) and strain rate (0.1–10 s−1) were conducted. It was found that the initial austenite grain size increases with increasing temperature and boron content. The flow stress decreased with increasing boron content at lower strain rates. The flow stress constitutive equation of hot deformation was developed for the experimental steels; results showed that boron addition has the trend to reduce the hot deformation activation energy. The characteristic points of the flow curves were analyzed. Results revealed that the peak and critical stress decreased in response to an increase of boron content. The work-hardening behavior of both steels was investigated, and it was found that boron addition can decrease the work-hardening rate when strained at lower strain rates. On the contrary, peak and critical strains increased as boron content increased, indicating that boron has the ability to delay the onset of dynamic recrystallization.
Highlights
High strength low alloy steels (HSLA) are attracting a strong interest from various industrial sectors, in the automotive industry [1,2]
It is well known that the refinement of the initial austenite grain size and thermo-mechanical processing (TMP) are the most common method to refine the microstructural for hot-rolled steel
Various phenomena have been shown to occur during the high temperature deformation process of austenitic steel: (1) work hardening (WH), (2) dynamic recovery (DRV) and (3) dynamic recrystallization (DRX) depending on tunable process conditions such as deformation temperature and strain rate
Summary
High strength low alloy steels (HSLA) are attracting a strong interest from various industrial sectors, in the automotive industry [1,2]. Many investigations have reported the effect of boron on hot stamped [8], hot ductility [9], phase transformation [10], hardenability [11] and boundary segregation behavior [12], systematic work of boron content on initial austenite grain size and hot deformation behavior is lacking. Kim [16], Banks [17] and Stumpf [18] observed that boron had a delayed effect of the onset of DRX In these studies [13,14,15,16,17,18], the effect of boron content on initial austenite grain size and activation energy for hot deformation was not discussed. The flow curves at different deformation and critical parameters as a function of boron composition are presented
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