The Impact Of Heat Treatment On The Performance Of X80 Pipeline Steel

This paper systematically studied quenching and tempering process to X80 pipeline steel hardness, strength, elongation, area reduction rate, the impact of corrosion behavior, and analyzed the corresponding microstructure, which is produced by Maanshan Iron & Steel (Group) Holding Co., Ltd. The result shows that:There is a common law that when the heating temperature is 930℃and the quenching medium are Water and salt water, after quenching the microstructure are based as martensite, and the grain is small, hardness are maximum. The hardness decreased when the temperature is increased.Salt water makes the cooling capacity of quenching media increased, the bainite and carbon residue are less in the microstructure and the hardness is higher. So the salt water is better as a quenching medium if you want to get higher hardness and more martensite.The ferrite dispersion can be observed in the martensite after a secondary quenching, and the metallurgical structure is more uniform the hardness is lower when the secondary quenching's temperature is 875℃. Normalizing pretreated samples then quenching and tempering the grain is not small. And the Changes in the strength and toughness have the same trend compared with t after tempering. And the strength and toughness is higher without normalizing pretreatment.The microstructure is tempered sorbite by tempering after quenching, as the tempering temperature is higher the hardness and strength reduces, while the elongation and area reduction rates rising, especially when the tempering temperature is 625℃to 635℃, the changes in hardness and tensile properties is obvious. But the hardness and tensile properties changes relatively flat when the tempering temperature is 635℃to 655℃. The relationship between the hardness and tensile strength meet a linear, and the linear Proportional coefficient a value should be 3.5678.Heat treatment did not significantly change the X80 pipeline steel's corrosion resistance; it means that the corrosion resistance of the material depends on its internal components. When the material is in sodium chloride solution the corrosion rate is faster than that is in the tap water. And the corrosion rate, corrosion current density increased with the increases of concentration of sodium chloride solution. And the corrosion potential moved to the negative direction with increasing concentration of sodium chloride solution.