Research on Nucleation Site of Martensitic Transformation by High Magnetic Field Application

研究了在强磁场和非强磁场作用下，固溶处理温度下的冷却速度、深冷前的预应变和深冷前的再加热对SUS 304L钢α '马氏体形成的影响。从固溶处理温度快速冷却增加α '马氏体的形成。在室温下的小预应变归因于在零度以下温度下的马氏体的形成。超过1%的预应变减少了α马氏体的量，3%的预应变几乎完全抑制了α马氏体的形成。施加高达26特斯拉的强磁场可以使预应变钢中α '马氏体的形成增加3%以上。从磁驱动能与加工硬化抑制能的比较中可以看出，这种抑制不是由于加工硬化抑制了马氏体核的长大，而是由于形核位数的减少。在冷却前在500摄氏度左右重新加热会抑制马氏体的形成。这一现象是通过时间相关过程发生的，表明了替代元素的扩散激活能。这种抑郁症是由于从固溶处理温度淬火诱导的成核位点的故障。再加热温度超过500摄氏度的水淬火会增加α马氏体的数量，但从这些温度进行空气冷却不会增加。根据这些结果，人们认为，从固溶处理和再加热温度超过500 ℃的淬火诱导应变通过热应力在试样中，这样的应变作为成核位点发挥重要作用。

Effects of cooling rate from solution treatment temperature, pre-strain before sub-zero cooling and reheating before sub-zero cooling on formation of alpha'martensite in SUS 304L steel with and without an application of high magnetic fields were examined. Rapid cooling from solution treatment temperature increases the formation of alpha'martensite. Small pre-strain at room temperature is attributable to a formation of epsilon martensite at the sub-zero temperature. Pre-strains over around 1% decrease the amount of alpha'martensite and 3% pre-strain depresses the formation almost completely. Application of high magnetic fields up to 26 tesla can enhances the formation of alpha'martensite in the steel pre-strained by over 3%. It is conseived from the compairing the magnetic driving energy and depression energy by work-hardening that this depression cannot attributes to the suppression of the growth of nuclei of martensite due to work-hardening but to the reduction of the number of the nucleation site. Re-heating at around 500ﾟC before cooling suppresses the formation of the martensite. This phenomena occurs through time dependent process showing activation energy of diffusion of substitutional elements. This depression is attributable to break-down of the nucleation sites induced by quenching from solution treatment temperature. Water quenching from re-heating temperatures over 500ﾟC increases the amount of alpha' martensite but air cooling from those temperatures does not increase. From these results, it was thought that quenching from solution treatment and re-heating temperatures over 500ﾟC induces strains through thermal stress in the specimens and such strains play an important role as nucleation sites.