[POSTECH] Computational Metallurgy Laboratory
Graduate Institute of Ferrous Technology (GIFT)
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Cold Deformation of Martensite in Steels

H. F. Lan, W. J. Liu and X. H. Liu

Abstract

Ultrafine grains, as small as a few hundred nanometers were obtained, without severe plastic deformation, by tempering cold-rolled martensite in a low carbon and microalloyed steel. A multilevel subdivision mechanism responsible for the formation of ultrafine ferrite grains in cold-rolled martensite was discussed. It involves subdividing firstly a prior austenite grain into several martensite packets by phase transformation and then further subdividing the martensite structure into ultrafine cell blocks by plastic deformation. The relatively large misorientation between the ultrafine cell blocks achieved at a moderate strain level in martensite may be attributed to the interaction between the transformation induced and the deformation induced dislocations. Ultrafine ferrite grains were developed from the cell blocks during tempering at temperatures in the ragne 500-600oC for 60 minutes. It was also demonstrated that the microalloying precipitates can effectively pin down the movement of dislocations and grain boundaries and thus, can increase the thermal stability of the fine grained microstructure.

Download paper, Ultrafine ferrite grains produced by tempering cold-rolled martensite in low carbon and microalloyed steels, H. F. Lan, W. J. Liu and X. H. Liu

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Additional Information

cold mill
Reversing cold-mill, with electro-hydraulic screwdown system and hydraulic bending roll system, which is developed for processing research during cold rollingin the State key Laboratory of Rolling and automation, Northeastern University, China
cold mill1
Reversing cold-mill, with electro-hydraulic screwdown system and hydraulic bending roll system, which is developed for processing research during cold rollingin the State key Laboratory of Rolling and automation, Northeastern University, China
cold mill2
Reversing cold-mill, with electro-hydraulic screwdown system and hydraulic bending roll system, which is developed for processing research during cold rollingin the State key Laboratory of Rolling and automation, Northeastern University, China
hot mill
Reversing hot flat-mill with accelerated cooling and high rate device cooling system in the State key Laboratory of Rolling and automation, Northeastern University, China
Detailed martensite lath structure of as-quenched hot-rolled sheets-No.1 steel
ensite lath structure of as-quenched hot-rolled sheets - Steel 1
Detailed martensite lath structure of as-quenched hot-rolled sheets-No.2 steel
Detailed martensite lath structure of as-quenched hot-rolled sheets - Steel 2
detailed morphology of cold rolled martensite
Morphology of cold-rolled martensite. (a) along rolling direction, (b) severely bent, (c) perpendicular to the rolling direciton.
ultrafine grained microstructure of No.1 steel
Ultrafine grained microstructure of Steel 1
ultrafine grained microstructure of No.2 steel
Ultrafine-grained microstructure of Steel 2.
550C No.1 steel
Electron backscattered diffraction image of Steel 1, heat treated at 550 C
600C No.1 steel
Electron backscattered diffraction image of Steel 1, heat treated at 600 C
650C No.1 steel
Electron backscattered diffraction image of Steel 1, heat treated at 650 C
550C No.2 steel
Electron backscattered diffraction image of Steel 2, heat treated at 550 C
600C No.2 steel
Electron backscattered diffraction image of Steel 2, heat treated at 600 C
650C No.2 steel
Electron backscattered diffraction image of Steel 2, heat treated at 550 C.

It is evident from these results that the steel with microalloying elements (Steel 1) has finer grain size than that without microalloying elements (Steel 2). Microalloying precipitates retard recrystallization process by pinning grain boundary movement.



Superalloys Titanium Bainite Martensite Widmanstätten ferrite
Cast iron Welding Allotriomorphic ferrite Movies Slides
Neural Networks Creep Mechanicallly Alloyed Theses Retained Austenite
Stainless Steels Nanostructured Hydroforming Diffusion Bonding TRIP



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