Mao Weimin

INFLUENCE OF COLUMNAR GRAINS ON THE COLD ROLLING TEXTURE EVOLUTION IN Fe-3%Si\ ELECTRICAL STEEL

Fe-3%Si电工钢铸锭中普遍存在柱状晶,其晶体学及形状各向异性对随后的热轧、冷轧及退火织构产生很大的影响.利用xRD与EBSD技术对长轴分别平行于轧面法向（ND）,轧制方向（RD）和横向（TD）的柱状晶冷轧样品的织构及组织进行了研究,并对晶界的特殊作用进行了分析.结果表明,中等压下量下,3种柱状晶样品具有不同程度的{001}织构遗传性,即3种样品均不同程度的摆脱了{111}线织构的形成;柱状晶长轴平行于ND和TD时,{001}取向在冷轧时得到大的保留;柱状晶长轴平行于RD时,得到最强的{111}〈112〉织构;柱状晶长轴平行于TD时,冷轧组织中旋转立方织构及{111}〈110〉织构较强.此外,3种样品的织构均表现出由立方→{001}〈130〉→{113}〈251〉的过渡路径,与等轴多晶样品沿α线和γ线转动的路径不同.不同方向的柱状晶晶界对冷轧变形过程中晶粒转动的作用不同,但因晶粒尺寸大而作用有限,且与初始取向相关.

Influence of structure transition on plastic behaviors of iron based ordered alloys

The influence of ordered structure on the dislocation configuration, structure of anti-phase domain boundary, partial dislocation slips, etc. are analyzed in the background of promoting the plasticity of iron based ordered solid solutions with second-order phase transformation. The principles of deformation softening and annealing hardening in ordered solid solutions are discussed because of deformation induced structure disordering. It is concluded that the independent slip ability of the partial dislocations and the corresponding low temperature plasticity of ordered solid solutions could be promoted obviously by proper alloying effects, which reduces the anti-phase domain boundary energy, or by maintaining the disordering state into the low temperature range. The similar principles could be also used to modify the low temperature plasticity of other metal based ordered solid solutions.

BEHAVIORS OF BRASS TEXTURE AND ITS INFLUENCE ON GOSS TEXTURE IN GRAIN ORIENTED ELECTRICAL STEELS

In comparison with the conventional grain-oriented electrical steels(the so-called CGO steels),the high permeability electrical steels(the so-called Hi-B steels) including those of nitrided steels possess higher magnetic properties,but their processing window is narrow.In particular,a near brass-oriented texture which rotated around the normal direction of sheets from Goss orientation is often observed in improperly processed sheets of Hi-B steels,i.e,this type of sheet possesses a correct morphological structure of well abnormally grown grains,but a poor crystallographic texture with low magnetic properties.The underlying mechanism is less dealt with in literature in comparison with the formation of Goss texture.Thus,the objective of this work is to analyze the formation mechanism of this texture component.For this purpose,XRD and EBSD technique were applied to reveal both macro- and micro-textures from the shear texture of hot rolled plate surface to primarily and secondarily annealed sheets paying particular attention to the origin and relationship of Brass-oriented grains with their surrounding grains.It is demonstrated that Brass-oriented grains are formed by the rotation of Goss-oriented grains around the normal direction in the sheared surface layer of hot rolled plate when the shearing around transverse direction is restrained.Compared with the close relation between Goss and {111}(112) oriented grains, similar behaviors during cold rolling and annealing occur between brass- and {lll}(110)-oriented grains,namely,the latter are also inclined to be adjacently related and mutual transformation could occur between those deformation grains and recrystallization grains.In particular,a higher rolling reduction reduces Goss grain number much significantly,whereas it favors the retention of brass- and {111}〈110〉-oriented grains leading to preferred growth of brass-oriented grains.In the condition of easy growth of Brass grains with their {110} being parallel to rolling plane like Goss grains in the thinner sheets,the much fewer Goss grains could not swallow the brass-oriented grains.Thus,this technical issue of producing grain oriented electrical steels with high magnetic properties can be understood in terms of fundamentals of texture evolution during deformation and recrystallization of bcc metals.

Migration behaviors of boundaries in polycrystalline metals during grain growth process

New equations for grain growth process induced by migration of boundary ligaments and corners were deduced, in order to overcome the shortcoming of the conventional basic theory for normal grain growth in three dimensional polycrystals. The Kelvins 14-sided polyhedron was assumed as basic shape of the grains. The evolutions of ligament density and corner density during grain growth as well as their influences on grain growth rate and migration activation enthalpy were analyzed. The grain growth process of an experimental Fe-3%Si alloy was simulated based on the new equations. It was indicated that the boundary migration driven by motion of ligaments and corners, especially the latter one, comes closer to the real grain growth process, and the shortcoming in conventional equation has been modified obviously. The evolution tendency of activation enthalpy for boundary migration calculated agrees with the actual observations. The new equations did not yet include the effects of second phase particles and solute atoms in three dimensional polycrystalline metals, and therefore could not describe the real process perfectly, which needs to be improved further.