Internal Intensive Quenching: Optimal Heat Treatment for inaccessible component areas

在本课题的研究过程中，提出了一种提高液压元件在内部高压载荷作用下寿命的方法。这些部件在现代燃油喷射系统中被大量使用，并且必须承受高达4000巴的循环压力。为了进一步提高这些部件的效率，在未来的系统中有一种更高压力的趋势，同时由于整体车辆质量的减少，部件将向越来越多的细丝结构发展。为了在相同的组件寿命时间内维持这些施加压力的变化，必须在生产过程中对基础材料的性能进行调整，以达到最佳的微观结构。最近的钻孔壁局部应变硬化方法，如漂移或自强化，是基于引入压缩残余应力，如果适用，在钻孔壁上产生小的应变硬化效应。与热方法相比，这些机制对组件寿命的影响非常有限。另一方面，由于目标区域的可及性有限，大多数已建立的热方法（如壳体硬化）在小孔径时存在困难。因此，在本项目中，重点是在基于马氏体硬化的改进强化淬火工艺中控制和修改显微组织、残余应力和应变硬化。该工艺的发展包括将零件有效地感应加热到奥氏体化温度，然后用高压水-空气混合物局部淬火，以达到钻孔的最佳近表面状态。新开发的工艺应首先在简单的通孔上进行试验，然后再转移到更多面向应用的钻孔交叉点上。

In the course of this project a method to increase the life time of hydraulic components under an interior high pressure loading is developed. Such components find intensive usage in modern fuel-injection systems and have to withstand a cyclic pressure up to 4000 bar. To further increase the efficiency of such components there is a trend towards higher pressures in future systems while at the same time the components advance to more and more filigree structures due to the overall vehicle mass reduction. To sustain those changes in applied pressure with an equal component life time the properties of the base material have to be tailored during the production process towards an optimal microstructure. Recent methods for the local strain hardening of bore walls like drifting or autofrettage are based on the introduction of compressive residual stresses and if applicable small strain hardening effects in the bore hole wall. Compared to thermal methods the impact of these mechanisms on the component lifetime is very limited. On the other side most of the established thermal methods, e. g. case hardening, have difficulties with small bore diameters due to the restricted accessibility of the targeted areas. Therefore in this project the focus is directed towards the control and modification of the microstructure, residual stresses and strain hardening in a modified intensive quenching process based on martensitic hardening. The development of this process includes the efficient inductive heating of the part to austenization temperature followed by a local quenching with a high pressure water-air mixture to achieve an optimal near surface state of the bore hole. The newly developed process should first be tested on simple through-holes and then be transferred on more application oriented drilling intersections.