17-7 析出硬化型半沃斯田鐵系不銹鋼之相分析與機械性能之探討

Abstract

本實驗使用華新麗華公司所提供之17Cr-7Ni PH不鏽鋼進行有關相辨認分析與析出強化之研究。該材料同時也被歸類於半沃斯田鐵系，它除了添加不銹鋼常見的Cr和Ni元素以外也額外添加了Al和N元素，目的是為了使AlN有著晶粒細化和NiAl能達到析出強化之效果。 首先，實驗的第一部分會將華新麗華所提供的鑄碇試樣、熱軋完後試樣與HRAP試樣(已做完Modified ConditionA熱處理)進行EBSD、KAM、IQ之相鑑定分析以期望區別此材料複雜的相組織。而第二部分則會透過熱膨脹儀模擬三種不同的固溶處理(ConditionA、Modified ConditionA、Repeatedly-modified ConditionA)來探討其是否具有晶粒細化之效果，並發現Modified ConditionA與Repeatedly-modified ConditionA熱處理能稍微地抑制混晶問題，但效果不如預期的好，其原因乃在Modified Sample中無法有效地析出奈米尺度之AlN。第三部分則是會以HRAP試樣作為起始材料，分別進行ConditionT與Repeatedly-tempered ConditionT熱處理後，並再次進行EBSD、KAM分析以釐清兩種不同參數之試樣析出前的相比例狀態，接著便分別進行565°C持溫不同時間(0~4.5h)的時效處理，期望NiAl成核於板條狀麻田散鐵基地內以產生析出強化之效果，再以OM、TEM、STEM進行觀察與統計分析，並發現NiAl僅需短時間之持溫就會廣泛地成核於麻田散鐵基地上(均質成核)，且於後續的時效會逐漸透過差排與缺陷處發生粗化，最後則進行有關於拉伸試驗的機械性能測試與破斷面之觀察，而得知該材料的破裂機制屬於延性與脆性破裂共存之混合模式。

In this study, the 17Cr-7Ni PH stainless steel provided by Walsin Lihwa Company was used to do phase identification analysis and precipitate hardening research.This material was classified as semi-austenitic stainless steel. It’s composition contains Al and N elements for the purpose of grain refinement and precipitate hardenning by AlN and NiAl respectively. In the first part, three different as-receive samples (Ingot, HR and HRAP) were analyzed by the EBSD, KAM, IQ technique to expect to distinguish mixed phase of this material. In the second part, three different solution treatments (ConditionA, Modified ConditionA, Repeatedly-modified ConditionA) are conducted by dilatometer to examine whether they have grain refinement effect, and we found Modified ConditionA and Repeatedly-modified ConditionA heat treatments can refine grain size slightly, but not very effective. This is because nano-scale AlN couldn’t precipitate in Modified Sample effectively. In third part, HRAP sample would be used as starting material and conducted the ConditionT and Repeatedly-tempered ConditionT heat treatment respectively, and then do the EBSD, KAM, IQ analysis to clarify the phase different of them. After that, 565°C aging treatment for various time(0~4.5h) was conducted to achieve the effect of precipitate hardening, as well as observed and analyzed statistically by OM, TEM, STEM, and we can conclude NiAl precipitates nucleated widely in martensite matrix within short aging time (homogeneous nucleation), and they coarsened at dislocation or defect after longer aging time. Finally, the tensile test was conducted to evaluate mechanical properties of this material ,and fractographs was taken by SEM. The SEM result show the fracture surface contained dimples, cleavage facets and microvoids, indicating mixed mode fracture.