ASTM A992 建築結構用鋼電渣銲件之顯微組織與織構演化

Evolutions of Microstructures and Texture of ASTM A992 Construction Steels Electroslag Weldment

鋼板在高入熱量電渣銲接之影響下，會使得熱影響區範圍增大，且其晶粒粗大，產生脆性組織，嚴重影響大型結構體銲接後之機械性質。本研究針對ASTM A992 建築結構用鋼之32 mm、40 mm 及50 mm 板厚之鋼板，進行電渣銲接 （electroslag welding, ESW），並以微硬度量測、金相觀察及電子背向散射繞射 （electron backscattered diffraction, EBSD） 等實驗方法，觀察鋼板銲前與銲後板厚方向機械性質和顯微組織之變化、及銲件凝固後之織構的演化，以作為設計規範及材料規範之參考。微硬度量測結果顯示，經由高入熱量電渣銲接可提高所有板厚之整體硬度，以粗晶粒熱影響區的硬度為最高，銲道次之。EBSD 分析顯示，不同板厚之銲道中心皆具有形成擇優取向之高斯織構{110}<001>及立方織構{100}<001>晶粒取向，證明晶粒<001>方向會沿著熱流方向快速成長，抑制其他方位的晶粒成長。應用電渣銲接時，受高入熱量之影響使部分柱板之熔融線達1/2 板厚，產生大範圍之熱影響區，且銲後柱板板厚中央仍然存在非均向性的帶狀波來鐵組織，再加上粗晶區冷卻時，易形成硬度高的相，此皆對材料之韌性有不利的影響，故電熱熔渣銲接應用於A992 建築結構用鋼之銲接時，不建議使用低於32 mm 之薄板。

The evolutions of microstructures, mechanical properties and textureof ASTM A992 construction steels after electroslag welding (ESW) wereinvestigated. The experimental results show that the primary microstructuresin the steel plate can be categorized into four morphologies, allotriomorphic ferrite, Widmanstätten ferrite, acicular ferrite, and pearliteafter ESW. The coarse grain heat-affected zone (CGHAZ) has the highesthardness value. The results of electron backscattered diffraction (EBSD)analysis indicates that preferred orientation is presented not only in coarsegrain heat-affected zone (CGHAZ), but also in the center of weld metal.{123}< 634 > is the preferred orientation in CGHAZ and cubic texture{100}<001> and Goss texture {110}<001> are the texture presented in thecenter of weld metal, showing the competitive grains growth in <001>direction in the weld metal.Base on the experimental findings, it can be concluded that the highheat input generated by ESW will produce large area of coarse grains inheat affect zone and will penetrate deep into the steel plate. Both of themare adverse to toughness. It is suggested that ESW should not applied toA992 steel plate under 32 mm thick.