Influence of composition on crack sensitivity of ferritic stainless steel

Abstract

The high temperature cracking of 17 wt-%Cr ferritic stainless steel during continuous casting was investigated in detail. No relationship between the high temperature internal cracking and the ductile to brittle transition temperature (DBTT) was found. The experimental results imply that the cracking is owing to a combination of factors: a high ferrite potential, a hot ductility gap, and the weaker grain boundary cohesion. The 17 wt-%Cr Ti stabilised grades were found to be the most sensitive ferritic grades for crack formation at high temperatures. The ductility was evaluated by means of hot tension tests. At 1200°C, the fracture surfaces of the Ti free ferritic steel had an intergranular character. At temperatures between 700 and 1100°C, the fracture surfaces were dimpled. Below 600°C cleavage fracture occurs. The 17 wt-%Cr Ti stabilised steel contained solidification related cracks. These cracks widen during the further cooling and could clearly be seen on the surface of a cracked specimen. The Ti stabilised grades had a ductility gap at 1100°C. The DBTT was measured by means of Charpy tests. Most grades had a DBTT higher than 200°C. Type AISI 430Ti and AISI 409 ferritic steel both had a lower DBTT of ~ 90°C.