Research Of Proeutectoid Ferrite Growh Process Of Fe-C-X(Cr, Mn) Alloy

In this paper, pure iron, carbon dust, electrolysis manganese as the raw material, meltingand pouring the low-carbon steel ingot of C content is0.08%, Cr content was0.37%,1.12%,1.68%, Mn content was0.67%,1.16%,1.6%, respectively. The growth regularity ofproeutectoid ferrite during the cooling process of carbon steel has been observed in-situ byusing HTCSLM, meanwhile, using the thermal dilatometer,optical microscopy, scanningelectron microscopy, Vickers hardness, EBSD and other equipment to respectively researchthe effect of Cr,Mn content on eutectoid ferrite transformation in low carbon. The results aresummarized as follows:Under the circumstances of continuous cooling, the relative vessel percentage content ofpolygonal ferrite decrease as the Cr content increase. With the increase of Mn content, thegrain size of polygonal ferrite in the low carbon steel after normalizing enlarges. Theproeutectoid ferrite can be divided into polygonal ferrite, plank ferrite and acicular ferrite. Therelative vessel percentage of polygonal ferrite decreases with the Mn content increase whilethe relative vessel percentage of plank ferrite and acicular ferrite increases.With the Crcontent rise, the sample micro hardness under normalization and continuous cooling increasesgradually.Adding Cr or Mn into carton steel will make the phase diagram change and influent theinitial and end temperature and the transformation interval of austenite transforming to ferrite.As the Mn content increases, the initial transition temperature reduceses, the end transitiontemperature increases, the transformation interval is reduced while as the Cr content increases,the initial transition temperature increases, the end transition temperature mainly unchange,the transformation interval enlarges.The proeutectoid ferrite plates will develop in prior direction but not very strictly, itsgrowth direction waves and changes in a small scope. The growth rate also changes as thegrowth fashion and direction changing. In the process of continuous cooling, proeutectoidferrite nucleates, grows along the austenite grain boundary, and cross the austenite grainboundary, then form77°included angle, the proeutectoid ferrite plate grows in the style ofstraight line, deflexion, parabola, the included angle between deflecting direction and primarydirection is8°or25°, Widmannstatten ferrite can be formed when grow in the straight linefashion.The proeutectoid ferrite exposure crystallographic orientation relationship has beenobserved by EBSD, the result show that the distinction of proeutectoid ferrite exposurecrystallographic orientation relationship is not obvious, primarily contralize the scope of 001-101-111; and the angle distribution of most proeutectoid ferrite grains is not large and inthe scope of3~8°.