Study on heat treatment process of Q550D low carbon bainitic steel heavy-gauge plate
The traditional heat treatment method for heavy-gauge plates is quenching and tempering treatment in China,the plates with sorbite structure on the surface and sorbite and bainite structure at the center,which can achieve relatively ideal strength.However,due to the increase in plate thickness,the even microstructure in the thickness direction cannot be achieved,and excel-lent toughness cannot be obtained.Based on the chemical composition design of Q550D low carbon bainitic steel and applied the new heat treatment process QLT(Quenching+dual-phase zone Lamellarizing+Tempering),the undissolved ferrite phase is led into microstructure,a uniform mixed structure of bainite and ferrite of heavy-gauge plate was obtained,its toughness was further improved on the basis of ensuring strength,and the excellent comprehensive properties were obtained.The microstructure and properties of samples at different single-phase zone quenching temperatures,dual-phase zone lamellarizing temperatures and tem-pering temperatures were studied to obtain the optimal heat treatment process.Through observation of microstructure and frac-ture morphology and comparison of mechanical properties,the optimal heat treatment process is obtained as 925 ℃ quenching+830 ℃ dual-phase zone lamellarizing+640 ℃ tempering.
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