Microstructure and Mechanical Properties of Cooled and Tempered Cu and Nb-Bearing Ultra-Low Carbon Steels

Abstract:

To improve the toughness and weldability, the carbon content of the steels has to be deduced, and more and more attention has been attracted to the low carbon and ultra-low carbon steels. To strengthen the microstructure Cu and Nb-bearing steels are developed. However, the knowledge on influence of combined addition of Cu and Nb is still in lack. The microstructure and mechanical properties are studied in the 6-mm thick as-rolled and tempered ultra-low carbon steel plates with varied copper and niobium content. The microstructure and mechanical properties are studied in the 6-mm thick as-rolled and tempered ultra-low carbon steel plates with varied copper and niobium content. The experimental results show that if niobium is added without copper, the increase of niobium addition does not have a significant influence on the phase transformation and mechanical properties before tempering. The strength and toughness of those copper-free niobium steels do not vary significantly after tempered at different temperatures, while the strength of niobium steels with 1.8% copper added increases after tempered in the range of 450-650°C and reaches a peak at 500-550°C. If combined with 1.8% copper, the increase of niobium addition from 0.08% to 0.16% improves the hardenabililty and strength significantly, and the strength peak after tempering moves to a lower temperature. The strength of air-cooled niobium steels with 1.8% copper added is usually higher than those water-cooled, while after tempered at a proper temperature, the strength of the latter becomes higher than the former.

• Periodical: Materials Science Forum (Volumes 638-642)
• Pages: 3242-3247
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.638-642.3242
• Online since: January 2010
• Authors: Hui Guo, Zhi Qiang Yao, Shan Wu Yang, Xin Lai He
• Keywords: Cooled, Cu-Bearing, Mechanical Property, Nb-Bearing, Tempered, Ultra-Low Carbon Steel

References

[1] A. Ghosh, B. Mishra, S. Das and S. Chatterjee: Met. Mater. Trans., Vol. 36A (2005), p.703.

[2] F. Perrard, A. Deschamps, F. Bley, P. Donnadieu and P. Maugis: J. Appl. Cryst., Vol. 39 (2006), p.473.

[3] M.S. Gagliano and M.E. Fine: Calphad, Vol. 25 (2001), p.207.

[4] A.J. DeArdo, International Symposium on Niobium 2001, Orlando, FL, USA; 2-5 Dec. 2001, p.427 Fig. 5 Variation of impact energy of Steel 4, 5, and 6 with tempering temperature after tempered for 1hour.