Effect of Heat Treatments on the Mechanical and Microstructure Properties of Welded API X70 Steel

The world race in scientific research in the fields of petroleum and how petroleum is transported to another place has inspired our scientific curiosity to research the welding bead of petroleum pipelines. This paper is an experimental examination of the response to the effect of heat treatments on the mechanical and microstructure properties of welded API X70 steel. Our study investigates how heat treatments altered the microstructure and mechanical properties of the fusion zone (FZ) in welded pipe steel of grade API X70. It shows microstructures ach ieved after one heat treatment at 550 degrees C for 1h, 2h, 3h, 4h and 5h. A metallographic test by the optical microscope and the scanning electron microscope (SEM) as well as the analysis of the samples by X-ray diffraction (XRD) and the measurement of the hardness test was applied to all the samples prepared. The results revealed that the isothermal heat treatment caused grain growth and coarsening reactions in the weld zone and the hardness of weld joints decreased were the main transformations after increasing the temperature of the heat treatment.