Nonequilibrium Reversion of Low Alloy Steels by Rapid Heating

利用试样自身电阻加热的方法，如高频感应加热，对钢进行了有效加热。因此，可以合理地预期，在非平衡状态下，通过相当快的加热发生相变。本工作的目的是获得与快速加热非平衡逆转过程有关的基本信息。研究了合金元素和优先组织的影响。一种合金(A)含有0.2%的碳，另一种合金(B)含有低合金，如钼和镍。优选的组织为热轧、冷轧、再结晶马氏体。结果表明：(1)加热时，未变形组织未析出碳化物，变形组织有细小碳化物形成。(2)马氏体直接逆转为奥氏体，不发生马氏体再结晶；形成铁氧体，呈非变形结构。变形组织中有再结晶马氏体的形成。(3)加热时检测碳化物析出和再结晶马氏体的临界变形量为10%左右。(4)合金（B钢）中的析出碳化物比游离合金（A钢）中的析出碳化物要细。(5)再结晶马氏体的晶粒尺寸与反相奥氏体的晶粒尺寸有很好的相对关系。再结晶马氏体晶粒尺寸减小，反相奥氏体晶粒尺寸减小。表明再结晶马氏体晶界是奥氏体重要的成核部位之一。

Under heating method by electric resistance of sample itself such as high-frequency induction, a steel is heated efficiently.It is,therefore,reasonable to expect that the transformation occurs under noneqilibrium state by considerable rapid heating. The present work was carried out,aiming to obtain fundamental information relevant to process of nonequilibrium reversion with rapid heating. The effect of alloying elements and prior structure have been investigated. One alloy (A) contains 0.2% carbon and the other alloy (B) contains low alloy such as molybdenum and nickel. The prior structure was selected as a thermal, cold rolled, and recrystallized martensite. The results are as follows:(1) On heating no carbide precipitation was detected in non-deformed structure,whereas the formation of fine carbide was detected in deformed structure. (2) Martensite is directly reversed to austenite without occurrence of martensite recrystallization,i.e. formation of ferrite, in non-deformed structure. But formation of recrystallized martensite was detected in deformed structure. (3) The critical deformation to detect carbide precipitation and recrystallized martensite on heating is about 10%. (4) Precipitated carbide is finer in alloy (B steel) as comparison with that in free alloy(A steel). (5) There is excellent relative relation between the grain size of recrystallized martensite and that of reversed austenite.Decreasing the grain size of recrystallized martensite,does that of reversed austenite decreases. It suggests that grain boundary of recrystallized martensite is one of important nucleation site of austenite.