Welding Cracking Analysis and Cracking Mechanism of 347 Stainless Steel Catalyst Beam

347 stainless steel possesses excellent properties and is widely used in large reactors. Through detailed analysis, this work identifies the cracking mode of the welded joint in the thick‐walled support beam of the 347 stainless steel catalyst in the slurry bed reactor. Experiment results show that the crack exists in the coarse‐grained heat‐affected zone close to the fusion line, and the fracture surface exhibits typical intergranular cracking and a significant amount of secondary cracking. Initial fracture exhibits significant oxidation, with no dimples or cleavage microstructures observed. Base metal exhibits excellent resistance to intergranular corrosion, with the presence of low‐melting‐point Nb/Cr/Mo eutectic phases near the crack tip. Under the influence of the welding thermal cycle, the low‐melting‐point eutectic phase induces grain boundary liquefaction. With the expansion of the liquefied zone and the action of thermal stress, the melting of low‐melting‐point eutectics leads to the formation of intergranular cracks. The generated microcracks rapidly propagate along the grain boundaries, coalesce with other microcracks, and form larger main cracks, leading to fracture.