Effects of phosphorus impurity on the microstructure and impact toughness of weld joint for the 12Cr2Mo1R heat resistant steel

•The 12Cr2Mo1R heat-resistant steel was welded by shielded metal arc welding process, a sound butt joint was obtained without.•The effects of phosphorus impurity on the microstructure and impact toughness were studied.•The impact toughness decreases with the increase of phosphorus content, and the phosphorus elements can change the fracture mode.