High Strength and Retained Ductility Achieved in a Nitrided Strip Cast Nb-Microalloyed Steel
- PDF / 989,304 Bytes
- 8 Pages / 593.972 x 792 pts Page_size
- 12 Downloads / 204 Views
TRODUCTION
THIN steel sheets with a combination of strength and ductility have applications in the construction and automotive industries. CASTRIP is a revolutionary twin-rolling method of producing steel strip directly from liquid. Thin (from ~0.8 to 1.5 mm) strip steel can be produced with significantly less energy, time, and floor space, while maintaining an increased output compared with conventional slab-casting techniques. Both plain carbon steel and Nb-microalloyed steel have been produced using this method.[1] Hot-rolled 0.084 wt pct Nb-microalloyed steel (08Nb steel) typically has a yield strength of 475 MPa with 15 pct total elongation.[2] With a combination of good mechanical properties, low-cost, and low-energy processes, steel sheets manufactured from the CASTRIP process constitute a new group of structural materials, having the potential to substitute some of the hot and cold rolled products, currently available in the market. Previous studies have shown that Nb atoms are retained in the matrix as a supersaturated solid solution with no apparent Nb-rich precipitates dispersion because of the relatively fast cooling rate of the CASTRIP process.[2–4] As the C and N contents in KELVIN Y. XIE, SACHIN L. SHRESTHA, and PETER J. FELFER, Ph.D. students, JULIE M. CAIRNEY, Associate Professor, and SIMON P. RINGER, Professor, are with the Australian Centre for Microscopy & Microanalysis, The University of Sydney, Sydney, NSW 2006, Australia and also with the School of Aeronautical, Mechanical and Mechatronics Engineering, The University of Sydney, Sydney, NSW 2006. Contact e-mail: kelvin.xie@sydney. edu.au; [email protected] CHRIS R. KILLMORE, Product Design Manager, KRISTIN R. CARPENTER, Product Development Metallurgist, and HAROLD R. KAUL, Senior Product Development Officer, are with the Metallurgical Technology, BlueScope Steel, Five Island Rd, Port Kembla, NSW 2500, Australia. Manuscript submitted May 21, 2012. Article published online October 2, 2012 848—VOLUME 44A, FEBRUARY 2013
CASTRIP steels are fairly low (i.e., 0.031 and 0.007 wt pct, respectively) and the final thickness of the as hotrolled Nb-steel sheets is between 0.8 and 1.5 mm, rapid diffusion of nitrogen into the steel is possible. This process provides the opportunity to further strengthen the Nb-microalloyed steel through nitriding via interstitial solid solution strengthening from N and dispersion strengthening from fine nitride clusters. Nitriding is commonly used to improve the surface hardness, fatigue life, tribological properties, and corrosion resistance of steels.[5] Nitrogen is an interstitial element in steel and has five times higher solubility in ferrite than carbon at room temperature.[5] This increases nitrogen solid solution strengthening potential and reduces the formation of precipitates; especially the coarse grain boundary precipitates that can contribute to brittle fracture of steels compared with carbon. Various techniques such as salt bath nitriding,[6–8] gas nitriding,[9,10] laser nitriding,[11] and plasma nitriding
Data Loading...
