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The microstructures and mechanical properties of a series of direct-quenched steels containing,in weight percent,from 0.05 to 0.20 carbon,0.20 to 0.40 silicon,1.10 to 1.70 manganese and at least one microalloying element of vanadium,niobium,titanium and boron have been investigated.After controlled rolling,these steels were cooled in spray water to 400,300 and 200℃,respectively and then cooled in still air.Comparison of the Charpy V-notch impact toughness of direct-quenched steels without subsequent tempering was made with that of direct-quenched steels tempered at 600℃.It is found that an attractive combination of strength and toughness is achived by means of direct-quenching.There exists two types of microstructures in accordance with carbon equivalent.Lath martensitic microstructure is obtained for C_(eq)>0.4%,granular bainitic microstructures for C_(eq).< 0.35%and mixtures of martensite and bainite for C_(eq),.in the range of 0.35— 0.40%.The effect of interrupted quenching temperature on microstructure is not significant for low C_(eq).steel,but interrupted quenching temperature has a strong effect on microstructure for high C_(eq),.steel.
The microstructures and mechanical properties of a series of direct-quenched steels containing, in weight percent, from 0.05 to 0.20 carbon, 0.20 to 0.40 silicon, 1.10 to 1.70 manganese and at least one microalloying element of vanadium, niobium, titanium and boron have been investigated. After controlled rolling, these steels were cooled in spray water to 400,300 and 200 ° C, respectively and then cooled in still air. Comparison of the Charpy V-notch impact toughness of direct-quenched steels without subsequent tempering was made with that of direct It is found that an anomaly combination of strength and toughness is achived by means of direct-quenching. There exists two types of microstructures in accordance with carbon equivalent. Lath martensitic microstructure is obtained for C_ (eq) > 0.4%, granular bainitic microstructures for C_ (eq). <0.35% and mixtures of martensite and bainite for C_ (eq), in the range of 0.35 - 0.40%. The effect of interrupted quenching te mperature on microstructure is not significant for low C_ (eq) .steel, but interrupted quenching temperature has a strong effect on microstructure for high C_ (eq) ,. steel.