Effect of Sulfur and Zirconium on the Machinability and Mechanical Properties of AISI 1045 Steels
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mls11045grade steels are principally used for the manufacture of forged parts. A considerable amount of machining has also to be performed on the forged parts for finishing purposes. Improved machinability would, therefore, be of benefit to these steels if achieved without incurring a significant loss in ductility because of the forging considerations. These steels are not resulfurized (sulfur = 0.04 pct max) since although sulfur is traditionally used for improving machinability, it also decreases toughness by inclusion formation. Recently, however, a series of steels of 1045 grade but termed "resulfurized" has been introduced in Japan for making parts such as connecting rods. The sulfur content is in the range 0.04 to 0.13 pct and not ~0.30 pct used in AISI low carbon resulfurized steels. These are, therefore, similar to AISI 1117, 1137, and 1141 grades, although these grades have a higher manganese content (1.0 to 1.6 pct) and are generally fine grained. Nonetheless, much of this work can be applied to these grades as well. For the sake of distinction, however, the steels investigated here will be referred to as modified 1045 grades. Improvements in machinability due to small increases in sulfur content have been frequently studied in calcium deoxidized steel ~-3and aluminum deoxidized steel. ~,3,4The most extensive study on medium carbon steels has been undertaken by Naylor et al, 5 where most significant improvements in machinability (flank wear and tool life measurements) were obtained by sulfur additions of up to 0.10 pct. No work reported included a detailed study of the effect of small increases of sulfur on tensile and impact properties of medium carbon steels. This work was, therefore, undertaken to study the DEBANSHU BHATTACHARYA is Senior Research Engineer, Steel Products Research, Inland Steel Research Laboratories, East Chicago, IN 46312. Manuscript submitted July 25, 1980. METALLURGICAL TRANSACTIONS A
effects of small increases of sulfur on the machinability and mechanical properties of 1045 steels with the objective of improving machinability without a significant loss in ductility of these steels. Experimental Procedure Laboratory heats (136 kg) were made of modified 1045 composition with aim sulfur levels of 0.01, 0.04, 0.06, and 0.10 pct. The steel was cast in molds which simulate strand casting freezing rates since this grade of steel is usually produced in the billet caster. All the steels were processed in the laboratory hot mill in parallel with a hot reduction of 80 pct. Metallographic samples were prepared from 19 mm rolled plate and examined under the microscope. Inclusion morphology viz volume fraction, average Feret's diameter (circumference/qr), and aspect ratio were analyzed as a function of sulfur content by the Automatic Image Analysis System (OMNICON) which scans 100 fields of view within a 5 mm 2 area. Machinability was measured in terms of the cutting energy per unit volume of metal machined (specific cutting energy). The details of the test set up have been described previously
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