AISI 430不銹鋼退火處理對氫擴散的影響

Annealing Effects on the Hydrogen Diffusion of AISI 430 Stainless Steels

本研究以AISI 430不銹鋼為材料，探討在不同溫度退火處理下，其微結構的變化對氫擴散（hydrogen diffusion）的影響。材料以陰極充氫方式進行氫擴散試驗，可觀察在不同高溫熱處理下，微觀結構的變化及其對氫擴散之影響，並可進行擴散遲滯時間（time-lag）、穿越時間（breakthrough time）、擴散係數和表面次層氫濃度（sublayer hydrogen concentration）的量測。同時並以掃描式電子顯微鏡（SEM）、光學顯微鏡（OM）、X-ray繞射儀來分析微結構變化。結果發現430不銹鋼之高溫熱處理在600℃~700℃時，因為熱處理後的晶粒成長，晶界比例變小，使擴散路徑減少而造成擴散速率的降低（由1.7變成1.4 × 10-8cm2/sec），此階段氫擴散係數之減小被認為是原以晶界間為主要擴散途徑者逐漸由晶格擴散效應所取代。然而800℃的熱處理發現晶格擴散的效應又逐漸被更快速的（110）擇優取向之晶格擴散所取代，所以氫擴散速率逐漸增快（3.8 × 10-8cm/sec）。在900℃熱處理下晶粒相當大，且（110）擇優取向的趨勢十分顯著，氫擴散速率則更快（4.7 × 10-8cm2/sec），因此可以認定在900 ℃熱處理下，晶格間會因擇優取向而產生一快速擴散捷徑供氫通過，而此時的晶界反而成為快速擴散捷徑的阻礙，且又因為900℃的晶粒比800℃大，故晶界比例更小，所以氫擴散速率大幅提升。

Annealing effects on the hydrogen diffusion of AISI 430 stainless steel were investigated at temperature of 873K ~ 1173K. Through hydrogen diffusion tests, the time-lag (tl), breakthrough time (tb), diffusivity and sub-surface concentration CHS were derived. Microstructure variations were analyzed by scanning electron microscopy (SEM), optical microscopy (OM), and X-ray diffractometry (XRD). It was found that the diffusivity was a little reduced to a factor of about 0.8 at 873 ~ 973K, as compared with the as-received material. It was considered that hydrogen diffusion path of grain boundaries was partly replaced by that of lattice because the grain growth reduce the ratio of grain boundary to lattice At 1073 ~ 1173K, the diffusivity was increased to a surface of 2~3, on the contrary. XRD showed a high ratio of (110) preferred orientation and SEM showed a further grain growth, especially at 1173K. It was suggested that a more quick diffusion path such as the lattice diffusion of (110) preferred orientation replaced the lattice diffusion of random orientation and the grain boundary which was possibly a barrier for a quick diffusion path was further reduced