Articles written in Sadhana
Volume 46 All articles Published: 24 May 2021 Article ID 0106
In the production of carbon-manganese hot rolled steel strips, less than 6 mm thickness, the wound coil had a shape defect associated with coil collapse. The defect was overcome by the assessment of physical simulation of the associated phase transformations in the run out table using Gleeble. It was found that when the steel strips had a lower Ar1 temperature than the coiling temperature, the occurrence of coil collapse was common. The coil collapse is due to the secondary phase transformation taking place during coiling and coilholding, where the liberation of the transformation heat softens the coil that leads to the coil collapse. Hence, by optimization of the hot rolling conditions such that the phase transformation is completed at the ROT before coiling, it is possible to avoid the coil collapse. Gleeble based physical simulation of the cooling pattern was correlated with the theoretical Ar1 temperature to enable prediction of the coil collapse possibility. Based on the physical simulation of the different cooling conditions, imposition of the correct cooling condition at the industrial ROT enabled elimination of coil collapse. In addition to avoiding coil collapse, the production loss associated with 4 to 5 min holding at the down coiler was overcome.
Volume 46 All articles Published: 14 June 2021 Article ID 0118
The effect of warm forging in the inter-critical temperature range between 705 and 844°C, in improving the impact toughness of an industrially important micro alloyed steel, 38MnSiVS6 was investigated. The impact properties were enhanced to as high as 148 J after warm forging in the inter critical range, as against19 J in the steel hot rolled from 1200°C and air cooled. In addition, the strength was enhanced by about 100 MPa after warm forging. The microstructure evolution that led to the improved toughness and strength was analyzed. The significantly enhanced toughness with moderate strength enhancement in warm deformation isattributed to the increases in the ferrite content, finer ferrite grain size, finer pearlite colonies and finer interlamellar spacing. The fractography of the impact test samples in hot deformed and air-cooled condition shows poor toughness associated with cleavage facets, while the warm forged steel, showed fine dimple rupture.