Teshugang (May 2024)
Effect of Nitrogen Content and Final Rolling Temperature on Low- temperature Impact Toughness of Titanium Microalloyed High- strength Steel CGLC700
Abstract
Aiming at the problem of poor low-temperature impact toughness of titanium microalloyed high-strength steel CGLC700， by thermodynamic calculations and high-temperature in-situ observations， as well as the use of electron back scattering diffraction， transmission electron microscopy， scanning electron microscopy， and optical microscopy have been used to investigate inclusions， second-phase particles， fracture morphology， and low-temperature impact toughness of the Ti-bearing high-strength steel. The results show that the reasons for the poor low-temperature impact toughness of Ti-bearing high-strength steel are related to the large-size brittle inclusions and the precipitation phase of Ti（C，N） and TiN in the steel. When the nitrogen content in steel is reduced from 0. 004 9% to ≤0. 003 5%， the number and size of brittle in clusions in steel can be effectively reduced， and the impact toughness of steel can be improved. Reducing the final rolling temperature from 885-895 ℃ to 875-885 °C can promote the precipitation of nanoscale TiC second phase particles and the formation of large-angle grain boundaries， and reduce the effective grain size， thereby significantly improving the low-temperature impact toughness of steel. Compared with experimental steel 1#， when the nitrogen content was reduced to ≤ 0. 003 5% and the final rolling temperature was 875-885 °C， the average grain size in titanium microalloyed high-strength steel decreased from 3. 1 μm to 2. 7 μm， the proportion of small-size effective grains was higher， the large-size inclusions and number density decreased， the proportion in the large-angle grain boundary increased by 16. 6%， and the low-temperature impact energy of steel could be increased from 14. 75 J to 37. 35 J.
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