Investigation of Worn Chain Links

Three links of a chain showing unusually strong wear were examined. Corresponding to the stress, the wear was strongest in the bends of the links, but it was especially pronounced in the bend in which the butt weld seam was located. Investigation showed the links were manufactured from an unkilled carbon-deficient steel, and were case hardened to a depth of 0.8 to 0.9 mm. The peripheral structure at the places not showing wear consisted of coarse acicular martensite with a high percentage of retained austenite. The links therefore were strongly overheated, probably directly heated during case hardening. The butt weld seams were not tight and were covered with oxide inclusions. Given that wear occurred preferentially at the welds it may be concluded that this weld defect contributed to the substantial wear. This leaves unanswered whether these chains could have withstood the high operating stress if they had been welded satisfactorily and hardened correctly, and whether it made any sense to case harden highly stressed chains of this type.