Effect of ferrite morphology on fracture mode of stainless steel weld metal

Summary

On the basis of stereographic fractographic observations, this paper describes an investigation of the relationship between the ferrite morphology and fracture mode of Fe‐18Cr‐8Ni stainless steel weld metal at cryogenic temperature and proposes a way of improving the weld metal toughness.

A new etching technique is first used to observe the three‐dimensional ferrite morphology. This involves preferential dissolution of the austenite matrix at a specific potential using a potentiostat. The electrical potential used was ‐0.15 V vs an HgCl electrode.

The technique is then applied for fractographic observations of fracture surfaces at cryogenic temperature. The results suggest that the cleavage fracture initiated at the continuous film‐like ferrite causes loss of fracture toughness. The austenite matrix containing globular or discontinuous vermicular ferrite, however, shows a dimple fracture pattern.