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渗硼层较大的脆性和剥落,是使渗硼工艺迄今不能普遍应用的重要原因。本文用声发射技术结合抗弯试验、金相及宏观分析,对双相(FeB+Fe_2B)渗硼层的脆性和剥落及渗硼对抗弯强度的影响,进行了研究。实验表明,用声发射技术结合抗弯试验,是研究渗硼层脆性的好方法。声发射计数率的高低与裂纹数量和扩展情况有关,渗硼层的大量剥落,使声发射计数率降低。剥落主要是由平行表面裂纹造成的。双相渗硼层的脆性很大,均在大大低于心部材料弹性极限以下的应力下产生裂纹,而且其脆性因渗硼配方,温度,冷速和热处理工艺不同而别。渗硼使 Cr12钢断裂强度降低二倍以上,使低温回火的中碳钢断裂强度降低近一倍左右,但对高温回火的中碳钢无明显影响。
Boronizing layer larger brittleness and spalling, boronizing process is so far can not be an important reason for universal application. In this paper, the effects of the brittleness and exfoliation of bimetallic (FeB + Fe_2B) boronizing layer on boronizing and the flexural strength of boronizing were studied by using acoustic emission technique combined with bending test, metallography and macroscopic analysis. Experiments show that the combination of acoustic emission technology and bending test is a good way to study the brittleness of boronizing layer. Acoustic emission count rate of the level and the number of cracks and the extension of the case, a large number of peeling boride layer, the acoustic emission count rate decreased. Spalling is mainly caused by parallel surface cracks. Biphasic boronizing layers are highly brittle and both crack under stress substantially below the elastic limit of the core material, and the brittleness is due to the different boronizing recipe, temperature, cooling rate and heat treatment process. Boronizing reduces the fracture strength of Cr12 steel by more than twice, so that the fracture strength of medium carbon steel reduced by about one time is nearly doubled, but has no obvious effect on medium carbon steel tempered at high temperature.