定向凝固高硼高速钢取向析出机制及抗高温磨损机理

The Microstructural distribution and size/laminar spacing regulation of hard phase/metal matrix in the directional solidified high-temperature wear-resistant materials are the key factors to result in directional precipitation carbides of the alloys during tempering process. The interaction behaviors of constitutes including the aforementioned matrix plus hard phase in directional solidified alloys are the significantly fatal effects to generate the directional precipitation and synergism of the microstructural phase damage under elevated temperature wear condition. Based on the texture and controllably regulated microstructure of the directional solidified low carbon high boron high-speed steel, the object of this project aims to the directional precipitation mechanism and high-temperature abrasive wear resistant mechanism so as to enhance the matrix/hard phase synergistic effect as the research targets. It can completely focus on the directional precipitation effect induced by the textured controlled microstructures as a new researching breakthrough point. Therefore, this project thoroughly investigates the interaction mechanism of the original directional structures of the alloys on directional precipitation, and essentially discloses the mechanism of the directional precipitation on the high-temperature abrasive wear resistance of the directional solidified alloy. The main research subjects of this program are included as follows. First, the regulation mechanism on the unidirectional M2B hard-phase size/laminar spacing of the directionally solidified high boron high-speed steel and the phase selecting competition as well as the dynamics of the orientation growth M2B boride can be obtained by experimental techniques and simulation method. Second, the orientation precipitation mechanism and the evolution of the orientation-precipitation microstructure under the interaction of the directional M2B and matrix in directional solidified alloy are established in detail based on the unique texture induced effect, thus modeling the precipitation-coarsening quantitative relationship between orientation secondary carbide and orientation growth M2B boride during precipitation process. Third, the influence of the dual-orientation effect of precipitation orientation and original eutectic M2B orientation on the mechanical and thermal damage laws and mechanisms of precipitation-hardening high boron high-speed steel are in-depth discussed and completely analyzed base on the consistent arrangement direction of eutectic M2B phase and secondary precipitation distributed on the matrix. Forth, the high-temperature abrasion wear damage synergism of the constitutes between matrix and hard phase and their M2B/matrix interaction mechanism of the directional solidified high boron high-speed steel under dual-orientation effect are put forward and uncovered systematically and deeply in the basis of the wear resistant behavior of the constitutes in the directional solidified alloy. The above-mentioned research results are of significant importance for understanding the microstructural regulation and discovering abrasive wear resistant mechanism of the directionally solidified high boron high-speed steel applied to the elevated condition. Meanwhile, it can also provide a new idea and method for effectively adjusting the cooperative damage control of the matrix and hard phase of the directionally solidified high boron high-speed steel during high-temperature abrasive wear process.

定向凝固高温耐磨材料中硬质相/基体的结构分布与尺度调控是导致基体产生取向析出的关键因素，其交互作用行为对诱发基体取向析出和高温磨损下的组相损伤协同性至关重要。本项目以定向凝固高硼高速钢的取向析出机制及高温磨损机理为研究目标，以控制织构诱导下的取向效应为新切入点，通过探索原始定向结构对取向析出的影响机制，揭示取向析出对定向合金抗高温磨损的作用机理。主要研究内容包括：（1）定向M2B硬质相的间距/尺度调控机理及相竞争与择优生长动力学；（2）定向M2B/基体交互作用下的织构诱发相间取向析出的微观机制与取向结构演化规律；（3）双取向效应对沉淀硬化定向凝固高硼高速钢力/热损伤的影响规律及机制；（4）定向合金在双取向效应下的高温磨损组相损伤协同性及其交互作用机理。研究结果对揭示定向凝固高硼高速钢的结构调控与抗高温磨损机制具有重要意义，并为有效调节取向析出下基体与硬质相的协同损伤控制提供新的途径与方法。

本项目基于定向凝固技术，通过控制高硼高速钢凝固过程使硬质相首先呈取向排列，随后在热处理过程中促使基体取向性的析出微纳米二次相，系统研究了取向析出机制及其对高温氧化磨损的影响及作用机理。.研究了合金化元素V、Cr、Al对定向凝固高硼高速钢的取向性的影响。结果表明，V、Al均可显著促进高硼高速钢硬质相的取向性，V既促进高取向生长，还细化柱晶间距，显著提升合金的抗弯强度和硬度；而Al则主要促进高硼高速钢基体内的纳米粒子析出，提高强韧化；Cr在定向凝固过程中主要偏聚且固溶于硬质相硼化物中，高温氧化过程中Cr容易发生相间析出，不利于定向M2B/相界处抗氧化性。.高硼高速TEM结果表明，高硼高速钢内部具有约2.5m宽的柱状板条状马氏体，随Al含量增加，基体中形成大量位错网及位错墙，并在硼化物周围出现许多岛状铁素体区，抑制硼化物的开裂。沉淀硬化过程中，Al有效促使M6(C,B)沉淀相在晶内析出，减少了M23(C,B)6的数量。取向关系表明，在原位析出中的α'//M23(B,C)6界面会有M6(B,C)沉淀析出相，发生原位转变，其取向关系为(112)M23(C,B)6 //(112)M6(C,B)。除常规链状0.2~0.4m尺度的二次相在晶界析出外，Al促使基体内部产生弥散的纳米粒子，尺度主要在30-80nm，分布沿定向生长方向，这可能是取向诱导作用下发生基体脱溶析出，并伴随亚结构形成。此外，基体内部还发现立方结构的M(B,C) 纳米粒子析出相，尺度为宽度20nm、长度40nm的近长方形，与基体具有完全共格关系，这种析出发生在位错胞核心区。.Cr和Al显著提升了高硼高速钢的高温氧化磨损性能。随温度和载荷增加，高硼高速钢的高温抗氧化磨损性能逐渐下降，但Cr、Al含量的增加促进了高温氧化磨损抗力的提升。同时，高硼高速钢中温度和载荷表现出强的协同损伤效应。纳米划痕结果表明，氧化膜的粘附力对氧化磨损影响显著，这不仅与Cr、Al含量有关，更与硬质相取向及其在高温磨损界面前沿的损伤和外部载荷大小相关。