INVESTIGATING THE RESIDUAL STRESSES THAT FORMED AFTER THE HARDENING HEAT TREATMENT OF AISI/SAE 4140 STEEL BY ULTRASONIC TESTING METHOD

Authors : Aziz Barış Başyiğit, Necip Camuşcu

Pages : 32-43

View : 27 | Download : 10

Publication Date : 2021-06-30

Article Type : Research

Abstract :Residual stresses may form after various machining and heat treating applications. Some applications include; thermo-mechanical methods, unsuitable usage of machining tools and cutting parameters. Residual stresses may also increase up to very high levels in consequence of hardening and surface treatment of metallic materials. Residual stresses can form after the production of structural and mechanical components and deteriorate the fatique and service life, dimension stability, technical security requirements. Hence, the residual stress level of such parts should be decreased to reasonable values to increase the service life and reduce costs. In this work; the effects of tempering temperature on residual stresses of AISI/SAE 4140 steel alloy that widely used in mechanical part industries after hardening heat treatment is investigated. 40x40x120 mm in dimensions of 15 samples is heat treated as normalized owing to ensure uniform beginning microstructures. Then, hardening heat treatment is applied with 6 different tempering temperatures besides 2 untempered samples. After hardness surveys of all samples are tested with ultrasonic flow detector. Longitudinal and surface waves are used in ultrasonic examinations. Whether the residual stress in test materials increase the sound velocity of the ultrasonic wave decreases. The relationship between travel speeds of ultrasonic waves and residual stresses are estimated by mathematical equations.
Keywords : Residual stresses, Ultrasonic testing, Heat treating of steels