摘要
研究了表面喷丸纳米化预处理对气体渗氮行为的影响。利用低碳钢试样单面表面超声喷丸纳米化处理 ,另一面保持原始晶粒 ,在 46 0℃、5 0 0℃、5 6 0℃、6 40℃四种温度不同时间气体渗氮 ,通过金相观察和X射线衍射法测定渗氮层的厚度和种类。对比发现在 5 6 0℃以下渗氮时 ,经过表面喷丸纳米化预处理 :可以提高扩散系数D和气 -固传递系数 β,降低氮势门槛值 ;使常规渗氮温度降低 5 0℃左右或者渗氮时间缩短 5 0 % ;使渗氮层厚度随渗氮时间增长在初期就符合抛物线规律x =At0 5。 6 40℃短时间渗氮时 ,表面纳米化预处理仍然可以起到一定的加速作用 ,但是随着渗氮时间的延长 ,表面纳米化预处理优势消失 。
The effects of surface ultrasonic shot peening (SUSSP) nanocrystallization on gas nitriding were studied. The mild steel plates were SUSSP nanocrystallized on one side but the original coarse\|grained condition on the opposite side. The relationship between the compound layer growth and nitriding time for two types of surface condition was obtained by gas nitriding at 460℃,500℃,560℃,640℃ respectively with different nitriding times. The thickness of compound layer was determined by metallographic observation and the phases appeared on the top surface were identified by x\|ray diffraction. When gas nitriding below 560℃, SUSSP nanocrystallization treatment could not only enhance both diffusion coefficient D and mass transfer coefficient β dramatically during the gaseous nitriding process but also reduce the threshold nitriding potential. With SUSSP pre\|treatment, the nitriding rate can be accelerated so dramatically that nitriding time can be reduced to the half, or the conventional nitriding temperature could be reduced approximately 50℃. The growth of compound layer with nitriding time assumed parabolic relationship from the start of nitriding process as long as the sample surface was pre\|treated by SUSSP. In the case of gaseous nitriding at 640℃, SUSSP pretreatment is still of some advantages to accelerating nitriding rate when nitriding time is shorter than 3 hours. With the further progress of nitriding, the advantage of SUSSP pretreatment wiel disappears and even on the contrary might slow nitride growth.
出处
《材料热处理学报》
EI
CAS
CSCD
北大核心
2002年第1期19-24,共6页
Transactions of Materials and Heat Treatment
关键词
低碳钢
超声喷丸表面纳米化
气体渗氮
生长动力学
surface ultrasonic shot peening (sussp), nanocrystallization
gas nitriding
growth kinetic
