Which of the following is harmful to the mechanical and chemical properties of a completed weld?

Slag is the correct answer because it is a byproduct that forms during the welding process, particularly in processes such as shielded metal arc welding (SMAW). While the purpose of slag can be to protect the molten weld pool from oxidation and contamination, if not properly removed, it can lead to several detrimental effects on the quality of the weld.

If slag is trapped within the weld, it can cause inclusions, which are imperfections that weaken the integrity of the weld joint. These inclusions can act as points of stress concentration, leading to a reduction in mechanical strength and ductility. Additionally, residual slag can create a barrier to proper intermetallic bonding, resulting in poorer overall chemical properties and weld performance.

Understanding the role of slag emphasizes the importance of proper cleaning and inspection practices in welding procedures, as this ensures the weld’s mechanical and chemical properties remain intact after the welding process is complete.