In this study, cracks or scabs formed during hot rolling of Bi-S-based free-machining steel wire rods were analyzed, and their formation mechanisms were clarified in relation with microstructure. Detailed microstructural analyses of large-diameter rods showed that the rod having low carbon content was cracked, whereas the rod having higher carbon content was not, because oxides formed during hot rolling were penetrated into the relatively soft surface, thereby leading to the surface cracking. While the crack-free, large-diameter rod containing high carbon content was subsequently rolled to make a small-diameter rod, a few scabs of 1 to 2 mm in size were formed on the surface as some protrusions were folded during hot rolling. Thus, in order to prevent the cracking or scab formation in wire rods, (1) the increase in hot-rolling temperature for homogeneous rolling of rods, (2) the minimization of temperature drop of rolled rods upon descaling treatment, and (3) the increase of rolling passes and the decrease of reduction ratio of each pass were suggested. Using these methods, crack-or scab-free wire rods could be successfully fabricated.

In this study, cracks formed in the edge side of Bi-S-based free-machining steel billets during hot rolling were analyzed in detail, and their formation mechanisms were clarified in relation with microstructure. Particular emphasis was placed on roles of bands of pearlites or C-and Mn-rich regions and complex iron oxides present in the edge side. Pearlite bands in the cracked region were considerably bent to the surface, while those in the noncracked region were parallel to the surface. This was because the alignment direction of pearlite bands was irregularly deviated up to 45 deg from the normal direction parallel to the surface, while the billet was rolled and rotated at 90 deg in the same direction between rolling passes. On the edge side, where pearlite bands were bent, iron oxides intruded deeply into the interior along pearlite bands, which worked as stress concentration sites during hot rolling and, consequently, main causes of the crack initiation in the rolled billet. On the surface of the wire rod rolled from the cracked billet, a few scabs were found when some protrusions were folded during hot rolling. In order to prevent the cracking in billets and scab formation in wire rods, (1) the increase of rolling passes and the decrease of reduction ratio for homogeneous rolling of billets and (2) the reduction in sulfur content for minimizing the formation and intrusion of complex iron oxides were suggested.

An established dislocation density related, one-internal variable model was used, with some modifications, as a basis for modeling the mechanical response of aluminum alloy AA6111. In addition to conventional rolling, equal channel angular pressing (ECAP) was used to produce a wide range of grain sizes, down to the submicrometer scale. The samples were heat treated before and after both processes to optimize tensile ductility. Implementation of the model to uniaxial tensile response of the conventionally rolled and the ECAP processed materials confirmed its good predictive capability. The model was further used to formulate simple relations between true uniform strain and the constitutive parameters that allow reliable prediction of the uniform elongation.

Aluminum Alloys Research SummaryThe alloy AA6111 has been chosen in many countries for automotive outerbody panels, but low ductility remains a major obstacle to competition with steel. Equal channel angular extrusion (ECAE) was used as a tool to produce fi ne-grained structures with enhanced ductility. Conventional grain sizes in the range of 9 µm to 50 µm were used to investigate the infl uence of severe plastic deformation (SPD) and heat treatment on mechanical properties of AA6111 sheet at room temperature. It has been found that SPD by ECAE followed by heat treatment leads to an increase in both strength and ductility, in addition to high r-value. The

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