1. The content of pro-eutectoid ferrite decreases with increase of cooling velocity. The precipitation of pro-eutectoid ferrite is restrained completely, when the cooling velocity gets to 100 K/min. In other words, the critical cooling velocity of ferrite is lower than 100 K/min.
A simulation example for offline heat treatment showed that there is a zone of cooling speed 78 ℃/s at 1018 mm from the surface of circular bead. The zone is just in the vicinity of critical cooling speed of bainite transformation and is easy to cause abnormal disequilibrium structure.
The simulation results show that while coiling temperature being 660～680 ℃, the average cooling speed at centre of coil is only 0.04 ℃/s, very far lower than critical cooling speed 0.1 ℃/s to occur carbides isolation eutectoid, so the deep-drawing properties of coil sharply decrease.
There are the critical melt-spinning rates, above which α-Fe can not solidify any more, but Nd2Fe14B grains themselves crystallize from liquid, respectively in Nd8Fe86B6, Nd4.5Fe77B18.5 or Nd2Fe14B alloys.
From the point view of crystal dynamics ,we discuss the ability of material forming non-crystal and introduce the method that can figure out the substance criticalcooling rate Q* by using T-T-T figure(Time-temperature-transformation curve ,also called 3-TFigure) All of these above-mentioned are of great significance for us to exploit new amorphous solids materials ,probe into the new approach to make non-crystal materials and understand the stability of materials.
Based on the equations of thermal conduction and equilibrium between the melt and the disk in the spinning production,a formula of the cooling rate is derived. The cooling rate depends not only on the physical properties of the melt and the disk, but also on parameters of the spinning technique. The maximum thickness of amorphous alloy ribbons can also be determined by this formula and the critical cooling rate.