Strength, Toughness, and Flaw Tolerance of 25.4-mm (1-in.) Alloy Steel Lifting Chain

The interrelationship of strength, toughness, and flaw tolerance of 25.4-mm (1-in.) alloy steel lifting chain procured from five chain manufacturers has been investigated. Both International Standards Organization (ISO) Grade 63 and Grade 80 chains were tested. The susceptibility of these chains to sudden fracture in service in the presence of flaws is of interest to producers and users, and it was anticipated that the results would be helpful in arriving at a recommended upper limit of strength consistent with safety, inspection, and economic considerations.

Small round-bar tension-test and Charpy impact-test specimens were machined from each chain to characterize the materials. Fracture-mechanics calculations of critical flaw sizes then were conducted by using a Charpy-K_Ic correlation. The results showed that the Grade 80 chain, having a Rockwell C hardness (HRC) of 40, is susceptible to brittle fracture in the presence of small flaws. Tension tests on specimens from chain samples containing machined flaws 2.54 mm (0.1 in.) deep confirmed the calculations. Grade 80 chain containing the machined flaw fractured at less than half the load required to break unnotched chain; however, Grade 63 chain, having a HRC of 33, was virtually unaffected by the presence of a 2.54-mm (0.1-in.) deep flaw.