Research Of Fatigue Performance On Ultrasonic Impact Treated Q345Steel Welded Joint In High Temperature

This paper makes study on influence of high temperature on fatigue performanceimprovement experienced ultrasonic impact treatment（UIT）of Q345steel butt joint.Firstly, contrast different temperature heat treatment of ultrasonic impact treatmentwelding joint fatigue performance, then execute UIT again on experienced heattreatment of welding joint and estimate fatigue performance to achieve the purpose ofrepair; In addition also compared high temperature UIT with room temperature UITeffect.The results show that UIT can obviously improve Q345butt joint fatiguestrength, but the fatigue strength of experienced heat treatment will reduce. Fatiguestrength of UITed weld joint improved39.8%compared to as-welded. Fatigueperformance of endured350℃-1h heat treatment UITed specimen fell22.5%compared to UITed. Fatigue performance of endured450℃-1h heat treatment UITedspecimen reduced by38.7%compared to UITed, and14.4%compared to as-welded.Fatigue strength of heat treatment UITed decreased obviously UITed welding jointfatigue strength is because: surface residual compression stress elimination; hardness,yield strength reduce; and the impact process surface roughness increases, the crackinitiation and expand easily.After heat treatment and impact again, fatigue performance can be recoveredalmost; its fatigue strength improved37.8%than impact+450℃-1h heat treatment,18.1%compared with as-welded.Effect of high temperature ultrasonic impact to improve Q345butt joint fatigueperformance is less than room temperature; the higher the temperature of the impact,the lower fatigue performance.350℃ultrasonic impact fatigue strength is0.92timesof the room temperature impact;450℃ultrasonic impact fatigue strength is0.76times of the room temperature impact. When UIT temperature is higher, the formationof surface residual compressive stress is larger, depth of near surface plasticdeformation layer is shallow, but the influence of hardness is no obvious. The impactof high temperature ultrasonic impact surface roughness is higher than the roomtemperature impact. Main reason of higher temperature lower fatigue property is: hightemperature impact surface roughness is higher, in addition it is influenced by hardness, yield strength.