Influence of Ti on hot ductility of Nb containing HSLA steels

Abstract

The influence of a low Ti addition (∼0·01%) on the hot ductility of Nb containing HSLA steels has been examined. For conventional cooling conditions in which an average cooling rate from the melting point to the test temperature was used, the ductility decreased markedly with the addition of Ti. However, when cooling conditions after melting were more in accord with the thermal heat treatment undergone by the strand during continuous casting, i.e. cooling is fast to begin with, reaches a minimum and then reheats, after which the temperature falls more slowly to the test temperature, the Ti addition was found to be beneficial.

Hot ductility of TWIP steels

“…Hence, slower cooling rates of 10~15 o C/min would be recommended to give better ductility [171] as this allows more B to segregate to the boundaries as well as coarsening the TiN precipitates. In testing it is always better to use a more accurate simulation of the continuous casting conditions which includes both the primary and secondary cooling stages of casting, shown in Fig 2.8, as has been shown in some of the more recent work [169], rather than the average cooling rate for the two cooling regimes as in this work. However, it is probable that generally, it is the secondary cooling rate which controls the ductility during casting rather than the primary.…”

“…It might be expected that Ti would be beneficial to ductility even in a fine form as TiN precipitates more randomly, whereas AlN precipitates preferentially at the austenite grain surfaces. However, fine precipitation of TiN in the matrix when it occurs is very detrimental to ductility [78,79,131,169].…”

Characterization of high phosphorous containing hot rolled weather resistant structural steels

“…G22 steel exhibits reduction in area (RA) values more than 60% at all temperature while that of G32 steel are 55, 37 and 48% at 850 1C, 900 1C and 950 1C, respectively. More importantly, straightening operation of thick slab during continuous casting occurs at lower temperature range, especially, near 900 1C [29]. These results can be correlated to the investigation of Imai et al [17] and that of a number of other researchers who have found that the tendency of hot shortness or surface cracking of Cu bearing steel decreases with addition of Ni to the steel.…”

“…Before tensile test, specimens were thermally homogenized at the test temperatures for 10 s. Slow cross head speed (1 mm/min) was chosen for the test, which gives the strain rate 6.67 Â 10 À 4 s À 1 as the selected gauge length was 25 mm. The slow strain rate applied is similar to that occurring during straightening operation ( $ 10 À 3 s À 1 ) of 240 mm thick slab on continuous casting [29]. Hot ductility was realized from the % of reduction in area (RA) at failure after tensile test.…”

“…Hence, the significantly lower RA values in the case of G32 steel is attributed to the absence of Ni. Furthermore, hot tensile test has been also used for assessing the likelihood of transverse cracking occurring in the straightening operation during the continuous casting of steel [29,[46][47][48][49]. It has been found that steel should not be susceptible to this cracking problem when reduction in area (RA) value exceeds 40% [49].…”