氫擴散行為對高強度鋼材氫誘發延遲破裂之影響研究

Effect of Hydrogen Diffusion Behavior on Hydrogen-Induced Delayed Fracture of High Strength Steels

對9254高強度彈簧鋼材而言，於550oC回火溫度下、不含釩之鋼材（9254-85）反較含釩鋼材（9254V-85）具有更高的延遲破裂臨界氫含量值。為解釋此一現象，本研究利用氫滲透試驗法（hydrogen permeation test），探討氫擴散行為對高強度鋼材氫誘發延遲破裂之影響。試驗結果顯示，對9254V-85而言，氫由充氫端表面通過試片擴散至氧化端表面之時間（tb）遠大於9524-85，而飽和充氫電流密度（iH,∞）遠小於9254-85。亦即在無施力、可排除材料強度之因素下，9254V-85中生成之VC析出物阻礙氫的擴散，導致氫的擴散速度較慢，且具有明顯之吸氫能力，使飽和充氫濃度降低，由此確認了VC析出物擁有額外之吸氫能力，而提升發生延遲破裂之臨界氫含量。然相較於不含釩的9254鋼材，前者因具有較高之抗拉強度，差排密度較高，拉伸過程中於差排附近聚集之氫原子隨差排移到至晶界處，而使延遲破裂發生所需之臨界氫含量降低，而上述兩者之因素之能力強弱，決定了9254高強度彈簧鋼材之氫誘發破裂敏感性優劣。

For 9254 high strength spring steels temper treated at 550oC, the steel without V-addition (9254-85) owns higher hydrogen threshold of delayed fracture than that with V-addition (9254V-85). In order to explain the above result, the effect of hydrogen diffusion behavior on hydrogen-induced delayed fracture of high strength steel was evaluated by hydrogen permeation test. The experimental results show that 9254V-85 owns longer tb, which is the time passing through the thickness of the steel, demonstrating a lower hydrogen diffusion rate. 9254V-85 also has a lower maximum hydrogen current density (iH,∞) than 9254 8585. Both of the above were resulted in the effect of the formation of VC precipitation. VC precipitation owns extra hydrogen-trapped ability therefore promoting the threshold is thus confirmed. For 9254V-85, the threshold can also be lower due to its higher tensile strength. Higher strength makes more hydrogen move to the grain boundary because of a high dislocation density. The susceptibility of delayed fracture was determined to the competition of the positive effect on the increase of threshold from the hydrogen trap ability due to VC precipitation and the negative effect from higher strength stress of the vanadium containing steels with 550oC tempering temperature.