3.5%鎳(nie)鋼(gang)(gang)通過降低(di)(di)(di)碳、硫(liu)、磷(lin)含(han)量(liang)，加入(ru)鎳(nie)等合金成分(fen)，并通過熱(re)處(chu)理(li)(li)(li)細化(hua)晶粒，使其(qi)具(ju)有優良的低(di)(di)(di)溫性(xing)能，被(bei)廣泛應(ying)(ying)用(yong)(yong)(yong)于(yu)乙(yi)烯、化(hua)肥、液化(hua)石(shi)油氣及(ji)煤(mei)氣工(gong)程(cheng)中低(di)(di)(di)溫設(she)備的制(zhi)造。3.5%鎳(nie)鋼(gang)(gang)一(yi)般(ban)為正火(huo)(huo)(huo)或正火(huo)(huo)(huo)＋回火(huo)(huo)(huo)狀態使用(yong)(yong)(yong)，其(qi)低(di)(di)(di)溫韌(ren)性(xing)較穩定(ding)，顯微組織(zhi)為鐵素體(ti)和珠光體(ti)，使用(yong)(yong)(yong)溫度(du)達-101℃.經調(diao)質處(chu)理(li)(li)(li)，其(qi)組織(zhi)和低(di)(di)(di)溫韌(ren)性(xing)得到進一(yi)步改(gai)善，最(zui)低(di)(di)(di)使用(yong)(yong)(yong)溫度(du)為-110℃.為避(bi)(bi)免由(you)于(yu)過熱(re)而使焊(han)(han)(han)縫(feng)及(ji)熱(re)影響區的韌(ren)性(xing)惡化(hua)，焊(han)(han)(han)接時(shi)(shi)焊(han)(han)(han)條盡量(liang)不擺動，采陽焊(han)(han)(han)道(dao)(dao)、多(duo)道(dao)(dao)多(duo)層焊(han)(han)(han)，并嚴格控制(zhi)焊(han)(han)(han)接預(yu)(yu)熱(re)溫度(du)及(ji)焊(han)(han)(han)道(dao)(dao)間溫度(du)，一(yi)般(ban)控制(zhi)在(zai)50~100℃范圍(wei)內，同時(shi)(shi)應(ying)(ying)采用(yong)(yong)(yong)小的熱(re)輸入(ru)施(shi)焊(han)(han)(han)，焊(han)(han)(han)條電弧焊(han)(han)(han)的熱(re)輸人應(ying)(ying)控制(zhi)在(zai)2.0kJ/mm以(yi)下(xia)，熔化(hua)極氣體(ti)保護焊(han)(han)(han)的熱(re)輸入(ru)應(ying)(ying)控制(zhi)在(zai)2.5kJ/mm以(yi)下(xia)。由(you)于(yu)3.5%鎳(nie)鋼(gang)(gang)中的含(han)碳量(liang)較低(di)(di)(di)，所以(yi)其(qi)淬(cui)硬傾向(xiang)不大(da)，一(yi)般(ban)可以(yi)不預(yu)(yu)熱(re)，但板厚(hou)在(zai)25mm以(yi)上(shang)，焊(han)(han)(han)件剛性(xing)較大(da)時(shi)(shi)，焊(han)(han)(han)前要預(yu)(yu)熱(re)到150℃左右，道(dao)(dao)間溫度(du)與預(yu)(yu)熱(re)溫度(du)相同，鋼(gang)(gang)有應(ying)(ying)變時(shi)(shi)效(xiao)傾向(xiang)，當冷加工(gong)變形量(liang)在(zai)5%以(yi)上(shang)時(shi)(shi)，要進行消除應(ying)(ying)力熱(re)處(chu)理(li)(li)(li)改(gai)善韌(ren)性(xing)。該(gai)類(lei)鋼(gang)(gang)在(zai)焊(han)(han)(han)后消除應(ying)(ying)力退火(huo)(huo)(huo)處(chu)理(li)(li)(li)過程(cheng)中，易產生回火(huo)(huo)(huo)脆性(xing)。為避(bi)(bi)免回火(huo)(huo)(huo)脆性(xing)，建議(yi)采用(yong)(yong)(yong)4.5%Ni-0.2%Mo系焊(han)(han)(han)絲，用(yong)(yong)(yong)NB-3N焊(han)(han)(han)條焊(han)(han)(han)接時(shi)(shi)，建議(yi)采用(yong)(yong)(yong)表5-58規定(ding)的焊(han)(han)(han)接電流(liu)，焊(han)(han)(han)后進行600~625℃熱(re)處(chu)理(li)(li)(li)，有利于(yu)收善焊(han)(han)(han)接接頭的低(di)(di)(di)溫韌(ren)性(xing)。