改良型9Cr-1Mo鋼材之氬銲銲接研究

Gas Tungsten Arc Welding of the Modified 9Cr-1Mo Steel

10.6409/JMSE.200001.0159

藍恭治(K. C. Lan)；薛人愷(R. K. Shiue)；陳鈞(C. Chen)

改良型9Cr-1Mo鋼 ； 氬銲 ； 回火 ； 衛擊韌性 ； 顯微組織 ； Modified 9Cr-lMo Steel ； GTAW ； tempering ； impact toughness ； microstructure

材料科學與工程

32卷4期（2000 / 01 / 01）

159 - 169

繁體中文

改良性9Cr-lMo(T91)鋼材因具有優良的高溫機械性質及抗腐能力，近年來被廣泛的使用於火力電廠內之各式高溫、高壓爐管中。研究結果顯示：若銲件銲後回火溫度介於540至600℃間，銲道之衝擊值最差。而當回火溫度700℃超過時，衝擊值才開始急速回昇。使用此類鋼材之銲接時，若回火溫度不足且長時間運轉於540℃的環境下，銲道及熱影響區會産生嚴重的脆化問題，進而可能發生脆性破壞。T91-T91銲道主要是板條狀麻田散鐵所構成，在麻田散鐵板條邊界上發現有殘留沃斯田鐵。當銲道回火到540℃/1hr後，原存在的殘留沃斯田鐵，在冷卻過程中變態爲麻田散鐵（未經回火）且有部份生成雙晶，故對衝擊韌性有不良的影響。而當回火溫度超過700℃時，麻田散鐵內之差排密度大幅下降，且可見肥粒鐵M23C6碳化物生成於回火麻田散鐵的基地內，而使韌性大幅增加。

The modified 9Cr-lMo steel has been widely used in high temperature/pressure tubes in fossil power plants due to its good creep strength and corrosion resistance. The experimental results indicated that the welds exhibited inferior impact toughness if tempering temperatures were between 540 and 600CC. The impact energy increase remarkably if the welds tempered above 700CC. Both the weld metal and the heat-affected zone (HAZ) could be serious embrittled and resulted in brittle fracture due to improper tempering treatments and long-term operation at 540℃. The microstructure of T91-T91 welds was comprised of lath martensite and interlath retained austenite. The retained austenite was transformed to untempered lath and twinned martensites for welds tempered at 540℃/1hr. As tempering temperature exceeded 700CC, the dislocation density in lath martensite was greatly reduced and the formation of ferrites and M23C6 carbides was found in the tempered martensite matrix, resulting in an improved toughness of the welds.