雙相不銹鋼熱影響區的應力腐蝕破裂機構建立

Stress Corrosion Cracking Mechanism of Heat-affected Zones of Duplex Stainless Steels

本文係探討2205雙相不銹鋼（DSS）的不同銲後熱影響區（HAZ）組織在40wt%CaCl2（100℃）溶液中之應力腐蝕破裂（SCC）行為機構。其中，DSS係變化不同含氮量範圍為0.1%～0.165wt %，而銲後HAZ組織係以Gleeble 1500熱加工模擬分別控制△t8/5為5、20、60及100秒。結果發現：氮含量越低，△t8/5冷卻速度越快，SCC傳播方式傾向以沿晶方式傳播，此時材料發生SCC的敏感性也越高。反之，隨著氮含量增加，且△t8/5冷卻時間也增長，SCC傳播方式轉變為穿晶方式成長，材料整體抗SCC性能也增加。造成SCC傳播路徑的改變，與HAZ組織再生成的γ相型態有關，其中晶界沃斯田鐵（GBA）會加速SCC傳播，且以沿晶方式成長，而惠德曼沃斯田鐵（WA）、晶粒內沃斯田鐵（IGA）及部分變態沃斯田鐵（PTA）等再生成的γ相會阻礙SCC生長，使得傳播途徑轉變為穿晶應力腐蝕破裂（TGSCC）。

The effects of microstructures of heat-affected zone (HAZ) on the stress corrosion cracking (SCC) mechanism of 2205 duplex stainless steels (DSSs) in 40wt% CaCl2 solution at 100℃ were investigated in this paper. Three different nitrogen compositions varied from 0.096wt% to 0.165wt% were prepared. The Gleeble 1500 thermo-mechanical simulator was adopted to control the cooling time ( t8/5) of HAZ in the range 5~100s. The results indicated that the crack propagated in an intergranular manner when the nitrogen content was low and the cooling rate was fast. In this condition, the SCC susceptibility of DSS was high. On the other hand, when the nitrogen was increased and the cooling time was elongated, the crack propagation path transformed to transgranular manner and the SCC resistance was also increased. The change of SCC growth path was related to the reformation of austenite in the HAZ. The presence of grain boundary austenite (GBA) was found to promote the occurrence of intergranular stress corrosion cracking (IGSCC). Widmanstatten austenite (WA), intergranular austenite (IGA), and partially transformed austenite (PTA) exhibited a beneficial effect on SCC resistance by deviating the crack propagation path.