Microstructure control of ferrous martensite by defects inherited from austenite

(1)基体位错和析出物进入马氏体的遗传在Fe-20%Ni-5.5%Mn的板条马氏体中，奥氏体中引入的位错以Bain对应的方式继承到马氏体中。在Fe-31%Ni-10Co-3Ti奥氏体中析出的γ‘-Ni3Al继承形成薄片马氏体相。γ‘因时效时间短而尺寸细小，通过相变剪切改变其组织，在冷却过程中形成热弹性马氏体。当γ‘尺寸随时效时间延长而变大时，γ’不发生结构变化，冷却过程中形成非热马氏体。(2)沉淀细化板条马氏体通过减小奥氏体晶尺寸来细化Fe-(1.5，2)Mn-0.2C合金中的板条马氏体包/块。在晶粒度约为2μm的奥氏体中，采用合金碳化物钉扎，可获得块状尺寸为1μm的奥氏体。淬火马氏体的强度随块体尺寸的变化遵循Hall-Petch关系。细小弥散的V(C，N)粒子能够细化板条马氏体组织。(3)马氏体/贝氏体亚结构随位错的变化在透镜状马氏体中，亚结构由孪生转变为位错。在马氏体/奥氏体界面附近，由于相变应变的塑性调节，奥氏体位错缠绕。在马氏体中也观察到类似的纠缠位错，导致界面附近的局部晶格取向。结果表明，这些位错是从周围的奥氏体中继承而来的。在Fe-Ni合金中，奥氏体形变细化板条马氏体组织，但导致上贝氏体组织粗化。

(1)Inheritance of matrix dislocation and precipitate into martensiteIn ausformed lath martensite in Fe-20%Ni-5.5%Mn, dislocations introduced in the austenite are inherited into martensite with the Bain correspondence. γ'-Ni3Al precipitated in the austenite of Fe-31%Ni-10Co-3Ti is inherited into thin-plate martensite. When γ', which has a finer size due to a short aging, changes its structure by transformation shear, thermally elastic martensite is formed in the cooling. When the γ' size gets larger by prolonged aging, no structure change occurs for γ' and athermal martensite is formed in the cooling.(2)Refinement of lath martensite by precipitationLath martensite packets/blocks are refined by decreasing austenite grain size in Fe-(1.5,2)Mn-0.2C alloys. In the austenite of which grain size is about 2μm with pinning by alloy carbide, a block size of 1μm was obtained. The strength of the as-quenched martensite increases by following a Hall-Petch type relation against the block size. Finely dispersed V(C,N) particles are capable of refining the lath martensite structure.(3)The change of martensite/bainite substructure with inherited dislocationsIn lenticular martensite, substructure changes from twinning to dislocations. Near the martensite/austenite interface, the austenite contains tangled dislocations due to plastic accommodation of transformation strain. Similar tangled dislocations are also observed in the martensite, resulting in local lattice orientation near the interface. It is concluded that those dislocations are inherited from the surrounding austenite. It is observed that the deformation of austenite prior to transformation (ausforming) refines lath martensite structures but results in the coarsening of upper bainite structures in Fe-Ni alloys.