The Microstrucure and Properties of Low Carbon Niobium steels after Controlled-Rolling and Rapid cooling

The relationship between the manganese and niobium contents, the proce ssing parameters （heating temperature, rolling schedual, cooling and aging after rolling）, the microstructures, the mechanical properties and the fract-uve behalior of 06MnNb steels were investigated.By employing the procedure of lower heating temperature. optimizing rolling schedual and interrupted cooling with a cooling rate of 17℃ per second between 780°-600℃ a complex microstructure containing fine acicular ferrite and small amount of fine M/A inlands and granular bainite can be obtained.This complex microstructure is superior to ferrite pearlite structure is both yield strength and low temperatare toughness. The main factor defermining streugth and toughness-of steol is the mean diameter of acicular ferrite.The toughness of bainite dependsopon its parketsije.The amount and parket sije of gaunlar banite is affected by heating temperatare and amount of deetormation.