Microstructure authentication on mechanical property of medium carbon Low alloy duplex steels

Abstract

The present study emphasizes on the mechanical characterization of medium carbon AISI 1040 and 4140 duplex steels. AISI 1040 and 4140 steels are generally used as structural steels for varying applications, ranging from construction field material to heat resistant parts for moderate temperatures applications. The objective of the present work is to corroborate microstructure and mechanical properties by varying the intercritical temperature in duplex steels. The normalized specimens of as bought steel are heated to a different intercritical temperatures (750, 770, and 790 °C), followed by isothermal holding for 2 h and quenching to room temperature develops duplex phase structure. This treatment grows microstructure with a variable quantity of martensite embedded in a fine ferrite matrix. For the same carbon content in the duplex alloy steels, the addition of Cr, Mo, Si, and Mn, increases the tensile strength and hardness of the material but decreases the toughness and ductility. As the intercritical temperature varies, the amount of martensite and ferrite phases present in the duplex steel also varies, which intern alters the strength and hardness of the material. Duplex steels have higher strength and hardness than as bought, even though the impact strength and ductility are poor. Microhardness is used to identify the micro phases present in the material viz., ferrite and martensite. Microstructure shows the evidence of the formation of a duplex structure with a variation in the amount of aforesaid phases. The result obtained validates the influence of microstructure on mechanical properties of AISI 1040 and 4140 steels.

Keywords

• Duplex steel
• Ferrite
• Martensite
• Bainite
• Microstructure