摘要：用固体渗硼技术对40Cr、40CrNi和45Cr钢分别在850℃、880℃、910℃和940℃保温3、5、7、9个小时进行渗硼。通过光学显微镜观察了三种钢在不同加热温度和保温时间下，钢渗层的形貌和显微组织，同时得到渗层厚度的范围为11~124μm。测量得到的不同含碳量钢渗层的硬度比较接近。渗硼层的生长动力学是通过测量不同温度和保温时间下渗层的厚度来分析的。

    结果表明：生长速率常数K随着温度和保温时间的增加而增加。40Cr、40CrNi和45Cr的扩散激活能分别为234、256和269 kJ/mol。可以发现，不同钢种的渗硼扩散激活能随着含碳量和Cr元素的升高近似呈线性增长。同时也画出了三个钢种渗硼层的等厚度图,通过等厚度图可以将渗硼的工艺参数和渗层厚度联系起来。68055

毕业论文关键词：碳钢；Cr元素；固体渗硼；渗硼层；动力学；扩散激活能

毕业设计说明书（论文）外文摘要

Title   Research on the Boriding Kinetics of Carbon Steels with Different Carbon or Cr Contents

Abstract

In this study, the 40Cr,40CrNi and 45Cr steels substrates were pack-borided at 850, 880, 910and 940℃ for 3, 5, 7, and 9 h. The morphology formed on the surface of steel substrates were confirmed by optical microscopy analysis. Boride layer thickness formed on the borided steels ranged from 11 to 124 μm depending on process temperature, treatment time and carbon contents of the substrates. The hardness of borides of different carbon-contents steels was very similar. Layer growth kinetics were analyzed by measuring the extent of penetration of  borided layers as a function of boronizing time and temperature in the range of 850-940℃. The kinetics of the reaction have also been determined by varying the boriding temperature and time.

The results show that K increase with boriding temperature and time. Activation energies (Q) of borided 40Cr、40CrNi and 45Cr steels at present study were respectively determined as 234, 256 and 269 kJ/mol, which were increased with carbon contents or Cr contents. Moreover, an attempt was made to investigate the possibility of predicting the contour diagrams of boride layers variation and to establish some empirical relationships between process parameters and boride layer thicknesses.

Key word: Carbon steels; Cr contents; Solid boronizing; Borides; Kinetics; Activation energy

目   次

1 绪论 1

2 实验方法 4

  2.1  实验材料与设备4

  2.2  实验过程与方案5

3 实验结果与讨论 6

  3.1渗硼层金相组织分析6

  3.2渗硼层显微硬度分析9

  3.3渗硼层生长动力学分析12

结论 22

致谢  23

参考文献24

1 绪论

1.1 渗硼动力学研究的意义和方法

渗硼是一种材料表面强化的化学热处理技术，通过高温时硼的扩散，与基体材料在相应温度下可形成由一个或多个金属间化合物相组成的渗硼层，显著地提高基体的表面硬度和耐磨性。钢铁材料经渗硼后得到的渗硼层由Fe2B或者FeB+Fe2B组成，Fe2B相的硬度一般为1300-1800HV，而FeB相一般达到1600-2200HV，具有较高的耐磨性，并具有良好的减摩作用，尤其抗磨粒磨损性能要优于渗碳和渗氮[1]。但FeB相的脆性比较大，所以两相硼化层的脆性和剥落倾向比较大[2]，使渗硼工艺的应用受到一定限制。

要得到性能优异的渗硼层，与很多因素有关。如渗硼层过厚，也会增加其脆性和剥落倾向。决定渗硼层厚度的主要工艺参数是渗硼温度和时间，而含碳量和合金元素含量不同的钢，经不同温度和保温时间渗硼后的渗硼层厚度、硬度都有所不同。通过研究做出不同钢种的渗硼层生长动力学曲线（渗硼层厚度与时间、温度的关系）以及渗硼层等厚度图，就可以通过设定的渗硼时间和温度可预测渗硼层的厚度，反之也可以根据确定的渗硼厚度调整渗硼时间和温度，这是对工业生产具有非常好的指导意义。