Lamellar Phase Transformations in Fe-C-X Alloys

小行星9628936 这是对铁碳钢中珠光体形成的基本研究。 珠光体是共析分解的层状产物，是所有金相结构中最常见的一种。 它可以在钢中形成，也可以在一系列有色金属合金中形成，在等温、连续冷却和强制速度生长条件下转变。 这个项目的目的是扩展有关珠光体生长的晶体学概念，并研究三元替代合金元素在珠光体发展中的作用。 讨论的主要问题：是珠光体铁素体/奥氏体或珠光体铁素体/奥氏体界面处的合金元素原子扩散路径。 这些边界真的是人们所认为的快速扩散路径吗？ 替代元素的分配如何影响珠光体的发展？ 进行了大量的热力学计算，并与实验观察元素分配和lamenoid发展。 主要的实验方法包括在内部制造所有三元钢合金，并在铅浴中进行等温热处理。 通过高分辨率透射电子显微镜检查结构。 化学分配研究在场发射枪透射电子显微镜中进行，该显微镜能够从直径小于1纳米的区域收集化学数据。 %替代合金元素在钢生产中很重要，因为它们可以部分地通过延迟珠光体反应而大大增加合金的硬化性，珠光体反应导致产生马氏体的能力更大。 此外，少量添加作为强碳化物形成剂的元素，如钒和钛，可以通过沉淀硬化铁素体薄片与间隔约10纳米的平行碳化物薄片，在中碳钢合金中产生超高强度珠光体结构。 ***

9628936 Shiflet This is a fundamental examination of pearlite formation in iron-carbon steels. Pearlite is a lamellar product of eutectoid decomposition and is one of the most familiar of all metallographic structures. It can form in steels and also in a range of non-ferrous alloys during transformation under isothermal, continuous cooling and forced-velocity growth conditions. The aim of this project is to extend crystallographic concepts concerning the growth of pearlite and examine the role of ternary substitutional alloying elements in pearlite development. Key questions addressed: Is the alloying element atomic diffusion path at the pearlitic cementite/austenite or pearlitic ferrite/austenite interphase boundaries. Are these boundaries really the rapid diffusion paths they are perceived to be? How does the partitioning of substitutional elements affect pearlite development? Extensive thermodynamic calculations are performed and correlated with experimental observations as to element partitioning and lamellae development. The primary experimental approach includes making all ternary steel alloys in-house and performing heat treatments isothermally in lead baths. Examination of the structure is by high-resolution transmission electron microscopy. Chemical partitioning studies are performed in a Field Emission Gun transmission electron microscope that is capable of collecting chemical data from areas less than 1 nanometer in diameter. %%% Substitutional alloying elements are important in steel production because they can greatly increase the hardenability of the alloy, in part, by delaying the pearlite reaction which leads to a greater ability to produce martensite. Also, small additions of elements that are strong carbide formers, such as vanadium and titanium, can lead to ultra-high strength pearlite structures in medium carbon steel alloys through precipitation hardening the ferrite lamellae with parallel sheets of carbides roughly 10 nanome ters apart. ***