Microstructure control of ferrous martensite by defects inherited from austenite

(1)在Fe-20%Ni-5.5%Mn中，基体位错继承并析出为马氏体，形成条状马氏体，奥氏体中引入的位错继承为符合贝恩对应的马氏体。Fe-31%Ni-10Co-3Ti奥氏体中析出的γ′-Ni3Al继承为薄板马氏体。由于时效时间短，γ′具有较细的尺寸，当γ′通过转变剪切改变其组织时，在冷却过程中形成热弹性马氏体。随着时效时间的延长，γ′尺寸变大，γ′组织没有发生变化，在冷却过程中形成非热马氏体。(2)通过析出细化板条马氏体通过降低Fe-(1.5,2)Mn-0.2C合金中的奥氏体晶粒尺寸细化板条马氏体包块。在晶粒尺寸约为2μm的奥氏体中，通过硬质合金的钉钉，得到了1μm的块体尺寸。淬火马氏体强度随块体尺寸的增大呈Hall-Petch型关系。分散的V（C，N）颗粒细化了板条马氏体组织。(3)继承位错的马氏体/贝氏体亚结构的变化在透镜状马氏体中，亚结构由孪晶转变为位错。在马氏体/奥氏体界面附近，由于相变应变的塑性调节，奥氏体包含缠结位错。在马氏体中也观察到类似的缠结位错，导致界面附近的局部晶格取向。这些位错是由周围的奥氏体遗传而来的。结果表明，在Fe-Ni合金中，奥氏体相变前的形变使板条马氏体组织细化，但使上部贝氏体组织粗化。

(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.