INFLUENCE OF TITANIUM CONTENT AND GRAIN-SIZE ON HYDROGEN CRACKING BEHAVIOR OF HOT-ROLLED STEELS

Hydrogen induced cracking was investigated for hot-rolled titanium ste els. Aim of the present work was to observe the influence of titanium content and grain size on the cracking behaviour. Three titanium steel s (0.12-0.30% Ti; 0.0057-0.0480% C) and one non-titanium steel (0.0056 % C) were used for the investigation. Various grain sizes were generat ed by heat treatment at 950, 1050 and 1150-degrees-C; furnace cooling was applied. The specimens were electrolytically charged with hydrogen at various current densities. It was found that cracks are generated at low charging current densities for the investigated steels. The tit anium steels showed better performance than the non-titanium steel. It was shown that the charging current density does not correspond to th e hydrogen concentration in a steel; the hydrogen concentration in ste el B was 3.8 ppm at 1 mA/cm2, in steel D it was found to be 15.5 ppm a t 0.5 mA/cm2. The total hydrogen concentration was found to be influen ced by content of precipitates and grain size. It was shown that the p ercentage of cracked grain boundary area increases with increasing gra in size. This increase is linear for the non-titanium steel whilst for the titanium steels a plateau was observed at a grain size diameter o f 50 mum.