Abstract
M.Ing. (Mechanical Engineering)
Post Weld Heat Treatment (PWHT) in the form of stress relieving consists of heating the steel to a temperature below the critical range to relieve the stresses resulting from welding. The mechanical and microscopic properties may also be affected during this process. The study of the effects of Post-Weld Heat Treatment on the evolving properties of the fine-grain carbon alloy steel P355NL1 was conducted, and presented in this report.
The study focused on the mechanical and metallurgical properties of the material. The plates used were 6 mm thick with a length of 350 mm and a width of 150 mm; and they were welded using the Gas Metal Arc Welding (GMAW) method. After the welding; PWHT was performed on the plates, using a furnace with the specified temperature and time. A total of four plates were studied; where three plates underwent the same PWHT method, apart from the cooling methods. There was a control sample wherein the plate did not undergo any PWHT; the second plate was furnace-cooled; the third was air-cooled; while the fourth plate was water-cooled.
A comparative study was done on the P355NL1 plates, using three testing methods, namely: the tensile test; the microstructure examination; and the microhardness test to investigate how the different cooling methods had affected the properties of the steel, compared to the control as the basis point of comparison.
The hardness properties of air and furnace cooled P355NL1 steel decreased compared to the without sample. The tensile strength properties of the sample had shown some improvement for the water-cooled plate; the furnace and air-cooled samples had, however, decreased in terms of their tensile strength. The yield strength properties of the samples revealed similar findings. Although the metallurgical structures revealed different concentrations of darker (pearlite) and lighter (ferrite) grains in the base metal, the overall study showed that there were no significant changes in the microstructure, however, the cooling media employed can be recommended as required for tailored applications.