水輪機配件銲接之機械性質研究
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2009
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Abstract
本研究採用水輪機配件常用材料S45C中碳鋼作為V型槽銲接母材，選用三種國產銲條（以A、B、C分別表示）及一種國外進口銲條（以D表示）來進行堆銲銲接，再取試片全銲道，依照ASTM E8M公制規範車製拉伸試棒，經銲後金相顯微組織觀察、微硬度測量、拉伸試驗、SEM破斷面觀察及EDS分析，探討銲料之機械性質和微觀結構變化情形，期望藉此研究提供選擇銲條之應用與參考。
從實驗結果顯示： A、B、C銲條成份組成為中碳鋼，銲道根部至銲道融池區由波來體組織變化為變韌體組織；冠部微硬度值為Hv 245，均稍大於中心線；降伏強度（YS）約360MPa、抗拉強度（UTS）約460MPa；拉伸破斷面經由SEM觀察，屬延性破壞。
銲條D組成除了Fe、C外，具一定比例之Cr、Ni含量，其銲後銲道切面光亮，其性質接近不銹鋼特性，其組織為沃斯田體‧肥粒體系不銹鋼（Austenitic-ferritic stainless steel）亦稱為雙相不銹鋼（Two phase stainless steel）；硬度高出A、B、C銲條約50％， 於融熔線更高出約100％；而降伏強度（YS）、抗拉強度（UTS）也分別高出A、B、C銲條約35％、60％；拉伸破斷面亦屬延性破壞，但孔洞較上述三種銲條細緻。
This research introduces S45C medium-carbon steel which commonly used as base material for V-groove welding in hydraulic turbine accessories, in which 3 domestic welding rods (specified as A, B, C, respectively) and one imported welding rod (specified as D) were selected to proceed stack welding, to take test strip on full welding bead and make tensile test bar as per ASTM E8M standard regulation, and to observe via metallographic microstructure, microhardness measurement, tensile test, observation of SEM cross-section and EDS analysis after welding, to explore the mechanical property and changes in microcosmic structure, in which this research is to be provided as a reference and application for the welding rod. According to the experiment results : the medium-carbon steel is composed by A, B and C, to change from pearlite structure and become a bainite structure from the root of welding bead to weld-pool of welding bead; with Hv 245 microhardness value for cap area that is slightly higher than middle line; around 360MPa for yield strength (YS) and 460MPa for ultimate tensile strength; and to observe tensile cross-section via SEM, which belongs to ductile fracture. In addition to Fe and C, welding rod D contains certain ratio of Cr, Ni, with shining cross-sectional welding bead after welding process, close to stainless nature and Austenitic-ferritic stainless steel structure, which is also named as two-phase stainless steel, with 50% hardness higher than welding rod A, B and C, and welding line exceeds around 100% while YS and UTS exceed 35% and 60% than welding rod A, B and C; tensile cross-section also belongs to ductile fracture with finer hole than above 3 welding rods.
This research introduces S45C medium-carbon steel which commonly used as base material for V-groove welding in hydraulic turbine accessories, in which 3 domestic welding rods (specified as A, B, C, respectively) and one imported welding rod (specified as D) were selected to proceed stack welding, to take test strip on full welding bead and make tensile test bar as per ASTM E8M standard regulation, and to observe via metallographic microstructure, microhardness measurement, tensile test, observation of SEM cross-section and EDS analysis after welding, to explore the mechanical property and changes in microcosmic structure, in which this research is to be provided as a reference and application for the welding rod. According to the experiment results : the medium-carbon steel is composed by A, B and C, to change from pearlite structure and become a bainite structure from the root of welding bead to weld-pool of welding bead; with Hv 245 microhardness value for cap area that is slightly higher than middle line; around 360MPa for yield strength (YS) and 460MPa for ultimate tensile strength; and to observe tensile cross-section via SEM, which belongs to ductile fracture. In addition to Fe and C, welding rod D contains certain ratio of Cr, Ni, with shining cross-sectional welding bead after welding process, close to stainless nature and Austenitic-ferritic stainless steel structure, which is also named as two-phase stainless steel, with 50% hardness higher than welding rod A, B and C, and welding line exceeds around 100% while YS and UTS exceed 35% and 60% than welding rod A, B and C; tensile cross-section also belongs to ductile fracture with finer hole than above 3 welding rods.
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水輪機, 砂礫沖蝕, 銲接, 機械性質, 壽命延長, hydraulic turbine, gravel erosion, welding, mechanical property, extension of service life