Study of PWHT Microstructures and Mechanical Properties for Mild Steel and SA106B Pipe Material

Welding is a well-known process of steel fabrication especially in oil and gas industry. Nowadays, we all can see a lot of improvement of welding quality on steel fabrication sector. This is all involving remarkable finding about the behavior effect of steel welding especially on weld defect cases. Defect is an excessive condition and outside the acceptance limits. Weld defects include porosity, incomplete fusion, weld cracking, and undercut. In order to control the welding defect, many researches have been done including the heat treatment for weld. All of it is to avoid undesired failure that can lead to catastrophic. On a carbon steel material structure, defect usually occurs at the weld region.
Welding process involve the process of heating and cooling of material being weld together. This cyclic heat source from welding process will alter the base metal microstructure. The alteration of base metal microstructure can cause the mechanical properties at the welded structure to changes. Localized expansions also exist due to heat from welding or molten metal. When the weld cools, some areas cool and contract more than others. This contraction with the bulk metal surrounding weldment will provide residual stresses. This residual stress is often become cause a premature failure of critical component like bridge bar links and pressure vessel. One way to overcome this problem is heat treatment.
Heat treatment is a method used to modify the physical properties of a material. The use of heat treatment is to heating or chilling the material to extreme temperature to achieve a desired result such stress relieving, hardening, or softening. Base on Iron-Carbon phase diagram, we are able to see the changes in microstructure during heating and cooling.
This research is to characterize the mechanical properties and its microstructure of the weld zone in order to avoid failure due to weld defect or microstructure refinement for carbon steel material. This research is to characterize the mechanical properties by subjecting the material microstructure to post weld heat treatment (PWHT). This study will provide relationship of the steel microstructure, mechanical properties, and PWHT.