Si-Mn high strength structural steel has been developed in Japan these few years, being supported by the recent tendency of lightening the weight of structure. In this report, the effect of addition of V and other elements such as Zr, Cr, Ti, Si, on Si-Mn structural steel were studied. In the case of laboratory test, there were 13 grades of samples. In the first group, containing 6 grades steel, the effect of V on Si-Mn structural steel were researched. In the second group, containing 4 samples, the effect of V and Zr or Cr or Ti were tested. In the third group, the effect of V addition on lower C-higher Si-Mn steel were studied. All samples were melted with a high frequency electric furnace and cast into 5kg ingots, then rolled to bars (9mmφ).
Specimens were tested under three conditions such as rolled, heated and as air-cooled or furnace-cooled after heating and as-quenched and-tempered. Tensile strength, yield strength, elongation, and reduction of area were determined by tensile test. Hardness test, V-noched Charpy impact test, and microstructure test were also made. It was concluded as follows:
(1) Tensile strength and yield strength rose, and elongation and impact value were decreased, with increasing V content. V also unified the microstructure and made ferrite grainsize refined. V behaved as anti-softening by tempering, which was seemed to depend on carbide formation.
(2) Adding Cr or Ti in Si-Mn-V steel resulted in increasing tensile strength, but gave no effect on elongation and low-temperature impact value. Ti and Zr made ferrite grain-size refined, but Cr did not do so.
(3) Even if C content was decreased from 0.2% to 0.1%C, the tensile strength was invariable when the Si was increased from 0.4% to 0.65%. The second, angle shape steel was made by Si-Mn-V steel, and special shape steel for the use of mine props was made by Si-Mn-Cr steel on production line. Si-Mn-V steel angle was determined by mechanical tensile test and by welding maximum hardness test. In the case of Si-Mn-Cr mine props steel, the effect of C content on heat-treated tensile properties were studied.