Application of Nonlinear Ultrasonic Effect for Evaluation of Characteristics of the Heat Affected Zone in Welded Ferrite-Bainite High Strength Steel

The high-strength steel is normally subjected to a welding process when used in a structure. And a heat-affected zone (HAZ) with completely different microstructures and mechanical properties from the base metal is created. The toughness of the HAZ is reduced compared to the base metal, which affects the stability of the structure. Therefore, it is need to control microstructure of HAZ and evaluate it. This study verified that the nonlinear ultrasonic technique could effectively detect the microstructural changes in the HAZ. For this purpose, 590 MPa grade ferrite���bainite high-strength steel specimens were prepared with different grain sizes by varying the heat exposure time in an electric furnace. Then, a ultrasonic velocity and a relative ultrasonic nonlinear parameter were measured in four types of specimens. The experimental results showed that the relative ultrasonic nonlinear parameter and hardness tended to decrease as the grain size increase.Maste