不□鋼銲件變形與殘留應力之研究

Abstract

本研究目的主要在探討脈衝參數與氮氣含量對沃斯田鐵不□鋼銲件角變形與殘留應力之影響。在實驗上，實驗材料選用SUS 304與310兩種沃斯田鐵型不□鋼，銲接方法採用自生氣護鎢極電弧銲，以肥粒相測定儀來量測不□鋼銲道殘留肥粒相含量，以平均垂直位移法來量測不□鋼銲件角變形量，以鑽孔應變計法來量測不□鋼銲件殘留應力值。為觀察銲接溫度場的分佈狀況與分析銲接熱應力的作用行為，在銲接過程中以熱電偶來記錄不□鋼銲件熱循環曲線。實驗結果顯示較高的脈衝頻率、較小的脈衝間距、較高的振幅比及較高的持續時間比等脈衝特性參數，皆可降低沃斯田鐵不□鋼銲件角變形量與殘留應力值。在保護氣體中添加少許的氮氣含量比例時，將會導致304不□鋼銲道殘留肥粒相含量的急遽降低。保護氣體中之氮氣含量比例愈高時，將會提高銲接熱輸入量，進而提高不□鋼銲件角變形量與殘留應力值。本實驗發現當沃斯田鐵不□鋼銲道內存在有肥粒相組織時將可降低銲接角變形與殘留應力，至於其影響行為與作用機制可能與肥粒相組織具有較低的熱膨脹係數與較佳的高溫延性有關。本實驗亦發現在同一銲接條件下，310不□鋼比304不□鋼有較高的銲接角變形與殘留應力，推究其原因可能與310不□鋼銲件具有較高的降伏應力及較低的熱傳導性與熱擴散性有關。

The objective of this study was to investigate the effect of pulse parameters and nitrogen contents on the angular distortion and residual stress in austenitic stainless steel weldments. An autogenous gas tungsten arc welding was conducted on austenitic stainless steels 304 and 310 to produce a bead-on-plate weld. The retained delta-ferrite content of welds was measured by using the Ferritscope. The welding angular distortion was determined by using the mean vertical displacement method. The welding residual stress was determined by using the hole-drilling strain-gage method of ASTM standard E837. The thermal cycles of weldment were recorded during welding process to investigate the influence of thermal stresses. The experimental results indicate that the higher pulse frequency, smaller pulse spacing, greater amplitude ratio, and greater duration ratio can reduce the angular distortion and residual stress in stainless steel weldments. The retained delta-ferrite content in 304 stainless steel weld metals was rapidly reduced as the nitrogen addition in argon shielding gas was increased. The welding angular distortion and residual stress were raised with the increase of the amount of nitrogen gas added in the shielding gas. This experiment result found that the existence of retained ferrite microstructure within the austenitic matrix has a beneficial effect in reducing angular distortion and residual stress tendency in stainless steel weldments. The angular distortion and residual stress of 310 stainless steels are greater than that of 304 stainless steels under the same welding conditions because its higher yield stress, lower thermal conductivity and thermal diffusivity.