|Abstract: ||本研究乃利用氣體鎢極電弧銲接法針對欲研究之兩種來源的鎳基合金與相同316L不鏽鋼板材進行異種接合，其中，填料選用美國銲接協會(AWS)建議用之309 Mo 、Inconel 82與Inconel 625，而兩種來源之鎳基合金板材分別來自商購的Alloy 800H (以下簡稱Alloy 800H(A))及中鋼精材生產的Alloy 800H (以下簡稱Alloy 800H(B))。銲接完成後之試樣再分別進行金相觀察、硬度試驗、拉伸試驗以及SEM、TEM顯微組織、成分變化與微結構分析。探討兩種鎳合金板材經由不同銲料與316L不銹鋼進行異種接合後機械性質與顯微組織及成分變化間之關係，評估最佳異種接合之參數。 經由SEM觀察發現，在氬銲實驗的參數範圍內，熱輸入量達12.2 kJ/cm。不論在對Alloy 800H(A)或Alloy 800H(B)與316L板材異種接合中中分別填入309 Mo、Inconel 82或Inconel 625並無觀察到銲件之銲接熱裂缺陷。這些銲件橫截面SEM影像均呈現在愈接近熔融區因其所接受的熱輸出量越多而有晶界粗大化的現象，而Alloy 800H(A)與(B)在靠近銲道方向，在此二鎳基合金銲材之晶界上可以觀察到明顯的析出物。經由TEM分析，析出物為TiC, Ti(C, N)與M23C6。再者，對這些銲件進行平板拉伸試驗，當填料為309 Mo時，不管是Alloy 800H(A)或Alloy 800H(B)與316L進行異種接合，拉伸破斷均斷在填料309 Mo處；當填料為Inconel 82或Inconel 625時，Alloy 800H(A)與316L異種接合，其拉伸破斷均則斷在Alloy 800H(A)銲材中間位置，而Alloy 800H(B)與316L異種接合，其拉伸破斷則皆斷在316L板材中間位置。另外，檢視平板拉伸試驗的結果，發現其銲件之平板拉伸強度結果對應了板材本身的拉伸強度，且破斷面形貌顯現延性破裂之表徵，而呈現材料原本之機械性質。最後，為了估算在晶界上析出物之量的差異，在對應Alloy 800H(A)銲件在平板拉伸試驗之斷裂位置，對此二鎳基合金銲材分別切片並進行SEM金相觀察而擷取SEI影像，爾後利用SEM Image Analysis，估算析出物之Volume Ratio (%)，結果得到，Alloy 800H(A)析出物明顯地多於Alloy 800H(B)的量。由於這些析出物不利於鎳基合金銲材之機械性質，推測此為造成Alloy 800H(A)與Alloy 800H(B)拉伸結果不同的因素之一。|
The research is mainly concerned with the investigation on microstructural and mechanical properties for dissimilar welds between 316L stainless steel and alloy 800H. The Ni-based alloy base metals (alloy 800H) were received from two separate sources, overseas purchase and China Steel company, and hereafter designated as alloy 800H(A) and 800H(B), respectively. The two Ni-based alloy base metals were welded together with 316L stainless steel, respectively, by gas tungsten-arc welding using three types of filler materials, 309 Mo, Inconel 82 and Inconel 625 according to the AWS recommendation. These welds are sequentially carried out metallographic inspections, Vicker’s hardness determinations and tensile tests. Also, SEM, EPMA and TEM were performed to examine the variances of microstructure and chemical composition. All these are doing is studying the relationship among microstructure, mechanical properties and the variation of chemical composition. Meanwhile, evaluate the optimum parameters for dissimilar welds between 316L stainless steel and alloy 800H. Under tungsten inert gas-shielded welding with input heat up to 12.2 kJ/cm, there is no hot cracking of welding in all welds observed by means of SEM examination. These cross-section SEM micrographs of these welds all show the appearance that the closer to the weld fusion zone, the more obvious is grain boundary coarsening due to the received heat output increased. Besides, there are visible precipitates appeared on the grain boundary of the Ni-based base metals (alloy 800H(A) and alloy 800H(B)) near the side of the weld fusion zone. The precipitates are TiC, Ti(C, N) and M23C6 identified by TEM examination. Moreover, when 309 Mo was utilized to be the filler material in the dissimilar weld between 316L and alloy 800H, the welds fractured at the weld fusion zone after plate tensile test, regardless of alloy 800H(A) and alloy 800H(B); while Inconel 82 or Inconel 625 were utilized to be the filler material in the dissimilar weld between 316L and alloy 800H(A), the welds fractured at the middle of alloy 800H(A) base metal after plate tensile test. The welds, however, fractured at the middle of 316L base metal after plate tensile test while 316L and alloy 800H(B) were welded together similarly using Inconel 82 or Inconel 625 filler materials. In addition, scrutinize the results of plate tensile test, it appears that the ultimate tensile strength (UTS) of the welds nearly correspond to the UTS of the individual base metals except the welds using 309 Mo filler material, and SEM fractographs all show a ductile fracture feature. These suggest that the welds exhibit the original mechanical property of the base metals since 316L and alloy 800H both are ductile materials. Finally, to assess the amount difference of precipitates on the grain boundary in the welded alloy 800H(A) and alloy 800H(B), SEM image analysis was undertaken to evaluate the volume ratio of the precipitates on the grain boundary in the alloy 800H(A) and alloy 800H(B) base metals near the side of weld fusion zone. In contrast to the fracture site of the welds with alloy 800H(A), the SEM images were taken from the slices located at the same site in the alloy 800H(A) and alloy 800H(B) base metals. Consequently, it shows that the amount of precipitates in the alloy 800H(A) welds is more than that in the alloy 800H(B) welds. Since these precipitates are unfavorable to mechanical properties of the welds, presumably, the amount difference of the precipitates on the grain boundary in the alloy 800H base materials is one of the factors caused distinct fracture sites after plate tensile test for the alloy 800H(A) welds and 800H(B) welds using Inconel 82 or Inconel 625 filler materials.