微合金元素Cu及等温温度对低碳硅锰钢氢扩散行为的影响

目的探究微合金及热处理工艺对氢扩散的影响。方法设计含0.4%Cu及未含Cu的两种低合金钢,采用两相区保温-淬火-配分(IQ&P)热处理工艺获得280、400℃等温温度的试验钢,通过SEM、EBSD、电化学氢渗透等方法分析其氢扩散行为。结果对于无Cu钢,当等温温度为280℃时,大角度晶界占比55%,残余奥氏体(RA)体积分数约为0.02%,氢扩散系数约为1.82×10^−7 cm^2/s;当等温温度为400℃时,大角度晶界占比51%,RA体积分数约为0.35%,氢扩散系数约为1.30×10^−7 cm^2/s。对于含0.4%Cu的低合金钢,等温温度为280℃时,大角度晶界占比46%,RA体积分数约为0.15%,氢扩散系数约为2.70×10^−7 cm^2/s;贝氏体区等温温度为400℃时,大角度晶界占比33%,RA体积分数约为3.00%,氢扩散系数约为0.40×10^−7 cm^2/s。结论微合金元素Cu的添加,导致晶粒度的细化,大角度晶界占比更低,RA含量更高,从而其氢扩散系数更低,不利于氢扩散行为的发生。当等温温度由280℃升到400℃时,虽然会导致晶粒粗化,但大角度晶界占比更低,且RA含量更高,同样会降低其氢扩散系数,不利于氢扩散行为的发生。由此可知,含0.4%Cu、等温温度为400℃时,IQ&P钢的氢扩散能力最差。

Effect of Micro-alloying Element Cu and Isothermal Temperature on Hydrogen Diffusion Behavior of Low Carbon Si-Mn Steel

The work aims to explore the effects of micro-alloys and heat treatment processes on hydrogen diffusion.Two kinds of low alloy steels containing 0.4%Cu and without Cu were designed.The test steels with isothermal temperature of 280℃and 400℃were obtained after IQ&P process.The behavior of hydrogen diffusion was analyzed by SEM,EBSD and electrochemical hydrogen permeation techniques.For steel without Cu,when the isothermal temperature was 280℃,the large angle grain boundary accounted for 55%,the volume content of residual austenite(RA)was about 0.02%,and the hydrogen diffusion coefficient was 1.82×10^−7 cm^2/s.When the isothermal temperature was 400℃,the large angle grain boundary accounted for 51%,the volume content of RA was about 0.35%,and the hydrogen diffusion coefficient was 1.30×10^−7 cm^2/s.For steel with 0.4%Cu,when the isothermal temperature was 280℃,the large angle grain boundary accounted for 46%,the volume content of RA was 0.15%,and the hydrogen diffusion coefficient was 2.70×10^−7 cm^2/s.When the isothermal temperature was 400℃,the large angle grain boundary accounted for 33%,the volume content of RA was about 3.00%and the hydrogen diffusion coefficient was about 0.40×10^−7 cm^2/s.Therefore,Cu leads to the refinement of grain size,lower proportion of high angle grain boundary and higher RA content,resulting in lower hydrogen diffusion coefficient,which is not conducive to the occurrence of hydrogen diffusion behavior.When the isothermal temperature increases from 280℃to 400℃,the grain coarsening occurs,but the hydrogen diffusion coefficient is also reduced due to the lower proportion of high angle grain boundary and higher RA content,which is not conducive to the occurrence of hydrogen diffusion behavior.Therefore,the hydrogen diffusion ability of(IQ&P)steel with 0.4%Cu and 400℃isothermal temperature is the worst.