The Effects of Manganese and Processing Technology on the Aging of Low-Carbon Steels

The aging control in low-carbon steels produced in continuous annealing lines is mainly performed by the boron addition, to stabilize nitrogen in solid solution. However, during the welding procedure in continuous lines, at the moment of tempering, segregation of borocarbides in the grain boundary may result in weld fillet rupture, resulting in loss of productivity. In order to verify the effectiveness of Mn on aging resistance, four steels were processed on a completely industrial scale, with Mn ranged between 0.14 and 0.29%. Among these steels, two were used with B addition, with the percentage of 0.0010 and 0.0017%, and two with no addition of this element. Among the steels with no B addition, those with the highest %Mn showed a higher aging resistance. In the steels with B addition, the aging resistance was similar, even with the different %C and %N. In this case, a higher effectiveness of C stabilization was verified in the steel with higher %Mn. The formation of manganese sulfide was indicated as an important carbide stabilization mechanism, by field-emission gun scanning electron microscopy observation. Simultaneously to variations in chemical composition, the influences of the main aging-related process parameters were studied. The result of the present study confirms the effectiveness of the addition of Mn in aging resistance in both boron-added and non-boron steels.