The hot working and transformation to ferrite of V-Mo, Nb and Nb-V steels

Two HSLA steels with V-Mo and Nb additions were deformed to 25 or 50% reduction in a single pass at either 950 or 850 degrees C subsequent to austenitization at 1100 degrees C. The specimens were allowed to transform to ferrite isothermally at 700, 650 or 600 degrees C. The rate of transformation was determined by changes in magnetic properties. The specimens were also rolled isothermally at 850 degrees C in five passes to 60% reduction and cooled at rates of 1, 3 and 10 degrees C/s to determine the progress of transformation. The microstructures after transformation with 0 and 60% strain were examined. The acceleration caused by deformation compared to zero strain is greater for higher strain, for lower deformation but higher transformation temperatures and for the V-Mo steel. The flow stresses were measured by torsion testing to give an indication of the strain energy introduced. The above steels and a Nb-V type were rolled either to 49% in three passes or to 67% in five passes in the range 780-720 degrees C, which is near or below the Ar-3 temperature. In microscopic examination, the ferrite formed during the rolling schedule, appeared elongated and was harder than equiaxed ferrite formed during cooling. Copyright (C) 1996 Canadian Institute of Mining and Metallurgy.