Holding Time Influence on the Hot Ductility Behavior of a Continuously Cast Low Alloy Steel

Abstract

Cracking during the continuous casting process is undesirable and continuous work is being carried out to find further improvements and understand the mechanisms that lead to failure. Investigations on the hot ductility behavior of a continuously cast low alloyed steel using different holding times before straining were done in the present work. Samples were heated to melting temperature in a vacuum atmosphere and then cooled to one of the three test temperatures chosen: 750, 850, and 900 °C. When the desired temperature was reached, the sample was isothermally held for either 10, 90, 300, or 3600 s before the tensile test started, with a strain rate of 10−3 s−1. The reduction of area was measured, SEM images of the fractured surfaces were taken plus LOM images for the analysis of the microstructure. The results show that there was no significant change in the ductility at any of the temperatures until 300 s, with a change in behavior at 3600 s. This was further confirmed with the images and precipitation kinetics simulations. The results are described and compared.

Comparison of Hot Ductility Behavior of microAlloyed Steels with Different B-, Cr-, Ni- and Ti-content

“…Curves are shown in Figure 1. The results for the steel number 1, which have been partially published [8], show a ductility minimum between 850 and 700 °C, which is determined by the reference value of 40%, indicated. As for the steel number 2, the ductility seen is higher at all points, with its lowest at 700 °C and no clear ductility trough formed, never reaching the minimum of 40 % of reduction of area.…”

“…The steel number 2 has more alloying elements, such as B, Cr, Ni and Ti, and also both lower sulfur content and more vanadium. The samples were machined with equal geometry for both steels, in dog-bone shape and axis parallel to the rolling directions, as shown in previous work [8]. Experiments were performed in an in-house built thermomechanical simulator, the BETA 250-5.…”

“…Samples were held by the upper tension arm of the machine, which deals with the displacement in the vertical direction. The lower part of the specimen is fixed and supported to compensate for the thermal expansion [8].…”

Effect of Austenitization Temperature on Hot Ductility of C-Mn-Al HSLA Steel

“…As can be seen in Table 2 and Figure 11 , the particles with sizes within 3.01–4.00 μm represents the biggest volume, followed by particles with size within 2.01–3.00 μm, 4.01–5.00 μm, 5.01–10.00 μm, and 1.00–2.00 μm and greater than 10 μm. Considering several types of research on fracture surfaces, there is clear evidence that poor hot ductility of investigated steels was associated with the presence of AlN and/or AlN-MnS particles [ 10 , 11 , 17 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ]. Precipitation kinetics simulations performed by the authors of [ 29 ] showed that longer holding time leads to growth of AlN at grain boundaries, a coarsening of MnS at dislocations, and a coarsening and growth of AlN at MnS.…”

“…Considering several types of research on fracture surfaces, there is clear evidence that poor hot ductility of investigated steels was associated with the presence of AlN and/or AlN-MnS particles [ 10 , 11 , 17 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ]. Precipitation kinetics simulations performed by the authors of [ 29 ] showed that longer holding time leads to growth of AlN at grain boundaries, a coarsening of MnS at dislocations, and a coarsening and growth of AlN at MnS. The authors of [ 31 ] found that in FeCrAl steel, the number of AlN particles increases with increasing cooling rate, although the volume fraction is relatively unaffected.…”