摘要
激光淬火(相变硬化)是激光技术在工业中应用的一个重要领域，该技术与激光物理学、激光加工技术、金属学热处理等几门学科紧密相关。本文在介绍激光淬火之前，首先介绍了激光的发展、应用以及激光加工的现状。
我们研究的是激光淬火对几种典型模具钢的作用，通过对热处理后的试样的硬度分布的测定，用金相和电镜观察金相组织的变化，认为激光热处理产生高硬度的原因是晶粒细化、高的位错密度和高的马氏体含量。并且，激光交叠热处理是在生产中可能发生的问题，我们通过大量的实验发现在激光硬化区由于一定程度的回火效应而产生硬度回落现象。但在高合金钢Cr12中发现硬度回落现象并不明显，这是因为本身该钢种的激光加工硬化带硬度并不大，另外高合金含量产生的弥散强化以及残余奥氏体的减少也是硬度回落小的一个原因。这些研究工作对实际工作生产会有一定的指导意义。全文共分五章：
第一章：概述激光的特性，以及激光技术在许多领域应用的现状。
第二章：介绍了工业中的各种激光加工技术和激光加工系统，详细说明了本实验所使用的高功率激光加工系统；
第三章：详细叙述了激光淬火的机理和热传导数学模型；
第四章：通过实验，分析激光淬火后的模具钢的硬化带的硬度分布及金相组织特性，同时对激光交叠热处理的特点及形成机理都作了深入的探讨。
第五章：总结本文的工作，展望进一步的工作。
本文的研究了激光淬火以及激光交叠热处理对模具钢性能的影响，分析了激光热处理的机理，对实际工作会有一定的实际意义，激光淬火也会随着激光器的发展有更广阔的应用前景。
Laser quenching is one of the important field of using laser technology in industry, which is closely connected with several subjects, i.e. laser physics theory, laser processing technology, metal physics et, al. The history, application and present processing situation of laser are introduced at first.
We studied the effect of laser quenching (harden by phase transformation) on some representative mould steels. Through measuring the rigidity on the surface of samples treated by laser heat treatment , and through photographing microstructures of the steel surface , we find many reasons attribute to high hardness. These reasons include ultra-fine grains, high density dislocation and more content of carbon in martensite. Moreover, laser overlapping treatment is another actual problem in many places. By a lot of experiments, as be showed in many theses, we find the hardness of mould steels were lowered because of tempering. And we also discovered there is no decreasing of the hardness on the surface of Cr12 steel. It is due to Dispersion harden by plentiful of alloy carbide and decreasing of residual austcnitc .These research work should provide some useful references for technicians in practice. At last, the program was also introduced.
Five chapters were divided as follows:
In Chapter One characteristics of laser was described. Laser technology has also been introduced.
In Chapter Two, varieties of laser technology and laser processing system have been described. Next, the laser processing in our lab was introduced particularly.
In Chapter Three, the principle of laser quenching was introduced. Subsequently, the math model based on heat conducting principle has also been constructed.
In Chapter Four, in our experiments, we selected four representative mould steels as samples. After laser heat treatment, the hardness of samples was measured by special instrument, microstructure was also photographed to be analyzed carefully. Through these experiments, we also debated on the theories which explain the new phenomenon occurring in laser overlapping treatment.
In Chapter Five, our research and this thesis were summarized, and the future work was also predicted.
In this thesis, we studied the effect of laser heat treatment and overlapping treatment on mould steel, debated on the principle of laser heat treatment, and explained the new phenomenon observed in this experiment. To some degree, maybe our research is beneficial to the development of laser heat treatment technology in practice.
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