40CrNiMo钢棱角位交流电场辅助粉末渗硼层的组织与性能

Microstructure and properties of 40CrNiMo steel corner area boronized layer prepared by alternating current electric field assisted pack boriding

以Al_(2)O_(3)为填充剂和活性炭为添加剂的改性粉末为渗硼剂,采用40CrNiMo钢为基体,在75 V/100 Hz交流电场作用下于630、650、700、750和850℃进行电场增强辅助固体渗硼。采用X射线衍射仪、扫描电镜和硬度计对渗硼后的样品进行显微分析及性能测试。结果表明:交流电场对渗硼过程有明显的促进作用,即便在较低的渗硼温度(750、700和650℃)下也可以在40CrNiMo钢试样的平面及棱角区域形成单一的Fe_(2)B相渗硼层;850℃时,渗硼层的棱角部位出现了少量的FeB相。温度过高(如850℃)及过高的电场辅助渗硼电流(如700℃渗硼时的2.38 A电流),会使渗硼层表面形成疏松表层,不利于致密渗硼层的形成;750℃渗硼4 h后的渗硼层具有最高的致密性和渗层硬度,其渗层厚度和表层区域硬度分别为120μm和1700 HV0.05。

A modified powder with Al_(2)O_(3) as the filler and activated carbon as the additive was used as the boronizing agent,40CrNiMo steel was used as the matrix,and electric field enhancement assisted solid boriding was carried out at 630,650,700,750 and 850℃under the action of a 75 V/100 Hz alternating current(AC)electric field.Microscopic analysis and performance testing were conducted on the boronized samples using X-ray diffraction,scanning electron microscopy and hardness tester.The results show that the AC electric field has a significant promoting effect on the boriding process,and even at lower boriding temperatures(750℃,700℃and 650℃),a single Fe_(2)B phase boriding layer can be formed in the planar and corner areas of the 40CrNiMo steel sample.At 850℃,a small amount of FeB phase appears at the corners of the boronized layer.Excessive temperature(such as 850℃)and electric field assisted boriding current(such as 2.38 A current at 700℃)can cause the formation of a loose surface layer on the surface of the boronized layer,which is not conducive to the formation of a dense boronized layer.The boronized layer after 4 h of boriding at 750℃has the highest compactness and hardness,with the boronized layer thickness and surface hardness of 120μm and 1700 HV0.05,respectively.