Abstract

In this study, tempering temperature influence on low-temperature impact toughness of carbon steels was investigated. Two sets of steel samples were machined to standard Charpy V-notched impact test dimension. The first and second sets were heated to an austenitizing temperature of 800°C and 900°C respectively for 1 hour and then water quenched. All the as-quenched specimens in each set were further tempered at 200, 300, 400 and 500 degrees Celsius for 1 hour and then air cooled. Next, impact test was carried out on the tempered samples in the temperature range of -30°C, -20°C, -10°C, 0°C, 10°C using liquid nitrogen and also at room temperature (25°C). The result indicated that all the samples austenitized at 800°C and 900°C and then tempered in the temperature range of 200°C-500°C revealed a general decrease in impact energy with the reduction in test temperature. Further, it was observed that the specimens austenitized at 800°C and tempered at 200°C have higher impact toughness values at all the testing temperatures when compared to the samples austenitized at 900°C. Both samples austenitized at 800°C and 900°C and then tempered at 300°C demonstrated linear decrease in impact energy with reduction in temperature due to temper embrittlement phenomenon. It is therefore clear that tempering temperature applied in this investigation has significant influence on the impact energy of low carbon steel under low-temperature conditions.

Key words: tempering, low-temperature impact toughness, low carbon steel