Effect of rare earth addition on continuous heating transformation of a high speed steel for rolls

The effect of rare earth（RE） on continuous heating transformation of a high speed steel for rolls was investigated by using differ-ential scanning calorimetry（DSC） with combination of microstructure analysis.Determination of the Ac1 and Ac3,the starting temperature of carbide dissolution and melting upon heating,the enthalpy change for the α→γ transformation and overall carbide dissolution were also es-tablished.It was found that RE could reduce the volume fraction of large eutectic carbides and the chrysanthemum-like eutectic colonies but could not change the phase composition.RE made a little change to Ac1,but the variation in Ac3 and enthalpy for the α→γ followed an in-creasing pattern as the RE addition increased.The start temperatures of carbides dissolution increased with increase of RE addition,which may be associated with the influences of RE on the morphology of carbides,but the overall enthalpy change of carbides dissolution decreases as the RE addition increased.Moreover,the start temperature of melting also increased with increasing RE addition.

Precipitation kinetics of NZ30K-Mg alloys based on electrical resistivity measurement

The electrical resistivity of NZ30K-Mg alloy was measured at different heating rates during continuous heating to stud the precipitation kinetics.Two kinds of metastable phases,β＂ and β＇,formed during the heating.Kissinger method and differentia isoconversional method were employed to assess the precipitation kinetic parameters of NZ30K-Mg alloy,activation energy Eα an pre-exponential factor A＇α.The fraction of transformation（α） and the precipitation sequence in NZ30K-Mg alloy were determinec Continuous heating transformation（CHT） and isothermal heating transformation（IHT） diagrams were further obtained for guidin the aging of NZ30K-Mg alloy.The analysis shows that the precipitation kinetic parameters of NZ30K-Mg alloy can be obtaine accurately using isoconversional method.

Computer Simulation of the Continuous Annealing Recrystallization for Cold-Rolled Strip in Galvanizing Line

The continuous heating transformation program is developed to investigate the influence of continuous annealing technological parameters on recrystalization for cold-rolled strip in galvanizing line.This program can be used for the calculation of the continuous annealing temperature field of strip steel,determination of the start and end time of recrystallization in continuous heating process,and procurement of the continuous heating transformation diagram.The temperature field for continuous annealing is simulated by means of finite difference method.Based on the Scheil superposition principle,the continuous heating transformation curve is obtained by using time temperature transformation(TTT)curve which is measured experimentally.The developed program has been used in practice,and the strip speed on production line increases bv more than 10%.