Problems with Steel Welds
Martensite formation - transformation to ??coupled with fast cooling can lead to high strength but brittle regions in the HAZ - keep carbon content low to reduce this.
Austenite grain growth - large ? grains have lower strength and higher hardenability than small grains - keep carbon content low to reduce this.
Other problems include hydrogen embrittlement, porosity, slag inclusions, weld-decay (stainless steels)
Good control of the welding process is essential to prevent these