Microstructure evolution and mechanical properties of a 690 MPa grade pressure vessel steel with low welding crack sensitivity at different quenching temperatures were studied by means of optical microscope,scanning electron microscope,high-temperature confocal microscope,electronic tensile testing machine and fully automatic impact testing machine.The results show that the microstructure of the designed tested steel is mainly composed of granular bainite,lath bainite and ferrite after rolling and quenching at 820-970 ℃.Under a high-temperature confocal microscope,it is observed that during the quenching process at 970 ℃,when the temperature drops to 520 ℃,some grains begin to undergo shear transformation and form lath bainite.After quenching and tempering,part of the quenched microstructure is retained due to the genetic effect of the microstructure.When the quenching temperature rises to above 950 ℃,the strength level of the quenched and tempered tested steel can reach 690 MPa grade.
quenching temperaturesteel for pressure vesselhigh-temperature confocal microscopebainiteproperties
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