The Influence Of Heat Treatment On The Decarburization Behavior And Microstructure Of The60Si2MnA Spring Steel

ABSTRACT:60Si2MnA spring steel was investigated by making effective use of heat treatment process to improve the structures and properties of experimental steel as great as possible and exploring its potential. The structures and properties of60Si2MnA spring steel was systematicly analysed and the ferrite decarburized layer formation mechanism of experimental steel was investigated; The appropriate heat treatment process was obtained to improve the microstructure and mechanical properties of spring steel. There are following conclusions:(1) The yield and tensile strength is888and1024MPa, respectively.The elongation is9.37%. The microstructure is mainly made up of pearlite and ferrite. Simultaneously, C、Mn and P contribute to segregation in some regions, forming the ferrite banding.The rating of nonmetallic inclusions in the experimental steel was7. The main component of nonmetallic inclusions of the experimental steel were spherical CaO (MgO)-Al2O3-SiO2ternary complex inclusions, irregular distribution of spherical inclusions CaO-MgO, and small amount of the strip sulfide.(2) The ferrite decarburization organization appears when experimental steel exposed in the temperature range of725℃～925℃The maximum thickness of decarburization layer appears when the temperature was850℃. The ferrite decarburization layer thickness and holding time showed a parabolic relationship, the relationship equation was df=2.34×10-6t1/2. When the cooling rate was0.05℃/s, it was possible to observe the thicker decarburized tissue, when the cooling rate was equal to or more than0.2℃/s, the sample substantially does not occur decarburization.(3) The optimized heat treatment process was obtained with considering the best match between strength and toughness and the economic benefit. The experimental steel was heated until the temperature reached600℃with holding for25mins, then heated up to 950℃quickly and keep for25mins followed by oil quenched, Subsequently, the experimental steel was tempered at460℃for50mins. The mechanical property of the experimental steel can make a significant improvement and the optimized match between strength and toughness was acquired. The yield strength Rp0.2, tensile strength Rm and elongation reach1578Mpa,1736Mpa and10.7%, respectively.