Studying the Influence of Nickel Content on the Microstructure, Hardness and Defects of Submerged Arc AISI 5147 Steel Welds

Abstract

Low alloy steel types are remarkably utilized in manufacturing a variety of products such as oil and gas pipelines, fuel storage tanks, industrial equipment and tools in addition to several construction and farm machinery parts. These products may undergo duty failure, and consequently may need a repair by means of welding processes. Submerged arc welding of AISI 5147 low alloy steel was performed, firstly with no Ni additives, followed by adding Ni to flux with a range of (10, 20, 30, 40 and 50 wt. %).Microscopy examination and Vickers micro hardness test were then used to evaluate the resulted welds. Results revealed that the microstructure of the welds was predominantly acicular ferrite (AF). Increasing the wt. % of Ni powder added to the flux refines to some extent the AF structure, and thus increasing the average hardness value of the weld. More increase in the wt. % of Ni definitely increases the ductility of the weld and thus decreases the hardness values. On the other hand, increasing the welding speed usedcoarsens the structure of the AF, which in turn reduces the average hardness value of the weld.Microscopy also showed that the greater the wt.% of Ni powder added to the flux, the more gaseousporosity defects.