氢对含(Ti,Mo)C析出相的调质钢的超高周疲劳性能的影响

Effect of Hydrogen on the Very High Cycle Fatigue Properties of Quenched and Tempered Steels Containing(Ti,Mo)C Precipitates

研究了未溶和回火析出的(Ti,Mo)C析出相的氢陷阱作用对调质铬钼钢的超高周疲劳性能的影响。结果表明:球形未溶(Ti,Mo)C析出相的氢解吸附激活能为142.6 kJ/mol,这种强氢陷阱在电化学充氢条件下不会捕获氢;细小的回火(Ti,Mo)C析出相是有效的氢陷阱,其捕获的氢的解吸附激活能为17.0 kJ/mol,这部分氢的扩散系数较小,室温放置336 h仍不能扩散出试样,但在循环载荷下能够从氢陷阱处解吸附并且向裂纹尖端或应力集中处扩散,仍能在一定程度上降低钢的超高周疲劳强度;位错和晶界处的可逆氢的解吸附激活能为16.9 kJ/mol,这部分氢扩散系数较大,室温放置96 h就能全部扩散出试样,在循环载荷下这部分氢能够迅速向裂纹尖端或应力集中处扩散,显著降低疲劳裂纹扩展应力强度因子门槛值,最终显著降低超高周疲劳强度;考虑到两者捕获的氢含量相当,被细小的回火(Ti,Mo)C析出相捕获的氢对超高周疲强度的有害作用要远小于位错、晶界处的可扩散氢对超高周疲劳强度的有害作用。非金属夹杂物的氢解吸附激活能为70.9 kJ/mol,这种强氢陷阱在电化学充氢条件下同样不会捕获氢。

The effects of hydrogen trapping behavior of undissolved and temper-induced(Ti,Mo)C precipitates on the very high cycle fatigue properties of quenched and tempered Cr-Mo steel were investigated. Results reveal that spherical undissolved(Ti,Mo)C precipitates with a hydrogen desorption activation energy of 142.6 kJ/mol cannot trap hydrogen through electrochemical charging;fine, temper-induced(Ti,Mo)C precipitates are effective hydrogen trap sites. Hydrogen trapped by fine, temper-induced(Ti,Mo)C precipitates with a desorption activation energy of 17.0 kJ/mol cannot diffuse out from the sample even if exposed to atmosphere for 336 h, while it may desorb from the trap site under cyclic loading and then diffuse to the crack tip or stress concentration field, resulting in a decrease in fatigue strength. Diffusible hydrogen trapped by dislocations and grain boundaries with a desorption activation energy of 16.9 kJ/mol can rapidly diffuse to crack tip or stress concentration field and then reduce the threshold value of stress intensity factor(SIF) of crack growth remarkably, resulting in a decrease of fatigue strength;this portion of hydrogen can diffuse out from the sample after atmosphere exposure for 96 h;Considering that the hydrogen content in both hydrogen trapping site is equivalent, the deleterious effect of hydrogen trapped by fine, temper-induced(Ti,Mo)C precipitates on fatigue strength is relatively smaller than that of the diffusible hydrogen trapped by dislocations and grain boundaries. Non-metallic inclusions(Al2 O3) with a hydrogen desorption activation energy of 70.9 kJ/mol also cannot trap hydrogen through electrochemical charging.