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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 1200degreesC, the fracture surfaces of the Ti free ferritic steel had an intergranular character. At temperatures between 700 and 1100degreesC, the fracture surfaces were dimpled. Below 600degreesC 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 1100degreesC. The DBTT was measured by means of Charpy tests. Most grades had a DBTT higher than 200degreesC. Type AISI 430Ti and AISI 409 ferritic steel both had a lower DBTT of similar to90degreesC

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The present work provides an overview of the work on the interaction between hydrogen (H) and the steel’s microstructure. Different techniques are used to evaluate the H-induced damage phenomena. The impact of H charging on multiphase high-strength steels, i.e., high-strength low-alloy (HSLA), transformation-induced plasticity (TRIP) and dual phase (DP) is first studied. The highest hydrogen embrittlement resistance is obtained for HSLA steel due to the presence of Ti- and Nb-based precipitates. Generic Fe-C lab-cast alloys consisting of a single phase, i.e., ferrite, bainite, pearlite or martensite, and with carbon contents of approximately 0, 0.2 and 0.4 wt %, are further considered to simplify the microstructure. Finally, the addition of carbides is investigated in lab-cast Fe-C-X alloys by adding a ternary carbide forming element to the Fe-C alloys. To understand the H/material interaction, a comparison of the available H trapping sites, the H pick-up level and the H diffusivity with the H-induced mechanical degradation or H-induced cracking is correlated with a thorough microstructural analysis.