Effect of Coiling Temperature on Microstructure and Tensile Behavior of a Hot-Rolled Ferritic Lightweight Steel
- PDF / 4,259,271 Bytes
- 14 Pages / 593.972 x 792 pts Page_size
- 10 Downloads / 238 Views
TRODUCTION
FERRITE-BASED lightweight steels, usually containing 3 to 6 wt pct Al, have attracted increasing attention nowadays because of their lower densities, excellent combinations of strength and ductility, and appreciable producibility.[1–8] Due to those favorable attributes, they have great potential to be used for fabricating automotive parts for further weight savings. The density reduction of ferritic lightweight steels is originated from lattice expansion and lowering of average molar mass of steels when Al is added.[9,10] Their superior mechanical property arises from a ferrite-bainite microstructure with a significant amount of metastable retained austenite which brings the transformation-induced plasticity (TRIP) effect into play under straining.[11–14] It has been reported that ferritic lightweight steels could be more ductile than conventional TRIP steels of the same strength grades.[15,16] JUNFENG WANG, Doctoral Candidate, and XIAODONG WANG, Associate Professor, are with the School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, P.R. China. QI YANG, Senior Researcher, and LI WANG, Professor and Chief Researcher, are with Baoshan Iron & Steel Co., Ltd. and the State Key Lab of Development and Application Technology of Automotive Steels (Baosteel), Shanghai 201900, P.R. China. Contact e-mails: [email protected]; [email protected] Manuscript submitted April 8, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
In ferritic lightweight steels, a major characteristic constituent phase of d-ferrite is formed during solidification and remains in the subsequent thermal and mechanical processes without experiencing a solid-state phase transformation.[6,17,18] Hot rolling of carbon-rich ferritic lightweight steels often results in a banded microstructure, consisting of d-ferrite bands and carbide bands.[19,20] Carbide bands are composed of a-ferrite and carbides originated from the decomposition of high-temperature austenite (here we differentiate between a-ferrite and d-ferrite). Increasing C and Al contents deteriorates the stability of cementite and facilitates the formation of j-carbide, (Fe,Mn)3AlC, which has an ordered face-centered cubic crystal structure.[21–24] It has been observed that carbides could be located (i) at d-ferrite grain boundaries within ferrite bands, (ii) at boundaries between ferrite bands and carbide bands, and (iii) within carbide bands.[20–22] Increasing Al and C contents causes an increase in volume fractions of carbide colony within carbide bands and overall carbides in the matrix. However, it also affects the size, morphology, and distribution of carbides which may dominate deformation and fracture behavior of carbon-rich ferritic lightweight steels. According to Sohn et al.[24] and Shin et al.,[19] an increase in the Al content leads to coarsening of lamellar carbides within carbide bands and a denser distribution
of carbides along d-ferrite grain boundaries and band boundaries. Han et al.[21] found in a Fe-C-5Mn-6Al (in wt pct) ferritic lig
Data Loading...
