The processes of reheating in the temperature range (T reheat / from 950 to 1250 ı C with the holding time (t hold / from 600 to 3600 s on the material known as high-strength low-alloy (HSLA) steel were investigated. The abnormal grain growth caused by the dissolution of Nb(C x ,N y / particles was observed after T reheat reached 1150 ı C. The influence of T reheat on average austenite grain size (AGS) was stronger than that of t hold . Two different models were applied for the description of average AGS on T reheat and t hold .
This paper presents initial results of pulsatory forming performed on a pulsator at the Department of Metal Forming, Faculty of Metallurgy, Technical University in KoSice. Pulsatory forming (stress-cycling)
Open network cracking, transverse central and transverse corner cracks, with shell like shaped fracture surfaces, are analyzed in this work. Cracked slabs were analysed, made 6 low carbon steels heats-2 heats showed high Al and N contents, 2 heats showed high N and 2 ones had high Al content. In fracture surfaces or in their close vicinity presence of Cu grains, AlN nitrides and sulphides (Mn,Fe) S was shown. The assumption, that the thermodynamic failure cause, producing shell like fractures in continuously cast slabs is of the same nature as in traditional large castings was verified. It is caused by: high Al and N content, precipitation of AlN and coarse austenite grains. In low carbon steels as a risk factor for shell like cracks, contents higher than the following limits can be assumed Al > 0,04 % and N > 0,008 % , or [Al] [N] > 3.10-4 or Al/N > 5.
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