3.5%鎳(nie)鋼(gang)(gang)通(tong)過降低(di)(di)(di)碳(tan)、硫(liu)、磷含量(liang)，加(jia)入(ru)鎳(nie)等合金成分，并通(tong)過熱(re)(re)(re)處理(li)(li)細化(hua)(hua)晶粒，使(shi)其具有(you)優良的(de)(de)低(di)(di)(di)溫(wen)(wen)性(xing)(xing)(xing)能(neng)，被廣泛應(ying)(ying)用(yong)(yong)于乙烯、化(hua)(hua)肥、液化(hua)(hua)石(shi)油(you)氣及(ji)煤氣工程(cheng)(cheng)中(zhong)(zhong)低(di)(di)(di)溫(wen)(wen)設備的(de)(de)制(zhi)(zhi)造。3.5%鎳(nie)鋼(gang)(gang)一般(ban)(ban)為(wei)(wei)正火(huo)(huo)或正火(huo)(huo)＋回火(huo)(huo)狀態使(shi)用(yong)(yong)，其低(di)(di)(di)溫(wen)(wen)韌(ren)性(xing)(xing)(xing)較穩定，顯微(wei)組織為(wei)(wei)鐵素體(ti)和珠光體(ti)，使(shi)用(yong)(yong)溫(wen)(wen)度達-101℃.經調質處理(li)(li)，其組織和低(di)(di)(di)溫(wen)(wen)韌(ren)性(xing)(xing)(xing)得到進(jin)一步改善，最低(di)(di)(di)使(shi)用(yong)(yong)溫(wen)(wen)度為(wei)(wei)-110℃.為(wei)(wei)避免(mian)由(you)于過熱(re)(re)(re)而使(shi)焊(han)(han)(han)(han)(han)(han)縫(feng)及(ji)熱(re)(re)(re)影響(xiang)區的(de)(de)韌(ren)性(xing)(xing)(xing)惡化(hua)(hua)，焊(han)(han)(han)(han)(han)(han)接時焊(han)(han)(han)(han)(han)(han)條(tiao)盡量(liang)不擺(bai)動，采陽焊(han)(han)(han)(han)(han)(han)道(dao)、多道(dao)多層焊(han)(han)(han)(han)(han)(han)，并嚴格控(kong)制(zhi)(zhi)焊(han)(han)(han)(han)(han)(han)接預(yu)(yu)熱(re)(re)(re)溫(wen)(wen)度及(ji)焊(han)(han)(han)(han)(han)(han)道(dao)間(jian)溫(wen)(wen)度，一般(ban)(ban)控(kong)制(zhi)(zhi)在(zai)50~100℃范圍內，同時應(ying)(ying)采用(yong)(yong)小的(de)(de)熱(re)(re)(re)輸(shu)入(ru)施焊(han)(han)(han)(han)(han)(han)，焊(han)(han)(han)(han)(han)(han)條(tiao)電弧焊(han)(han)(han)(han)(han)(han)的(de)(de)熱(re)(re)(re)輸(shu)人(ren)應(ying)(ying)控(kong)制(zhi)(zhi)在(zai)2.0kJ/mm以(yi)下，熔(rong)化(hua)(hua)極(ji)氣體(ti)保護(hu)焊(han)(han)(han)(han)(han)(han)的(de)(de)熱(re)(re)(re)輸(shu)入(ru)應(ying)(ying)控(kong)制(zhi)(zhi)在(zai)2.5kJ/mm以(yi)下。由(you)于3.5%鎳(nie)鋼(gang)(gang)中(zhong)(zhong)的(de)(de)含碳(tan)量(liang)較低(di)(di)(di)，所以(yi)其淬硬傾向(xiang)不大，一般(ban)(ban)可以(yi)不預(yu)(yu)熱(re)(re)(re)，但板(ban)厚在(zai)25mm以(yi)上，焊(han)(han)(han)(han)(han)(han)件剛性(xing)(xing)(xing)較大時，焊(han)(han)(han)(han)(han)(han)前要預(yu)(yu)熱(re)(re)(re)到150℃左右，道(dao)間(jian)溫(wen)(wen)度與預(yu)(yu)熱(re)(re)(re)溫(wen)(wen)度相(xiang)同，鋼(gang)(gang)有(you)應(ying)(ying)變時效(xiao)傾向(xiang)，當(dang)冷加(jia)工變形量(liang)在(zai)5%以(yi)上時，要進(jin)行消除應(ying)(ying)力熱(re)(re)(re)處理(li)(li)改善韌(ren)性(xing)(xing)(xing)。該類鋼(gang)(gang)在(zai)焊(han)(han)(han)(han)(han)(han)后(hou)消除應(ying)(ying)力退火(huo)(huo)處理(li)(li)過程(cheng)(cheng)中(zhong)(zhong)，易產生回火(huo)(huo)脆性(xing)(xing)(xing)。為(wei)(wei)避免(mian)回火(huo)(huo)脆性(xing)(xing)(xing)，建議(yi)采用(yong)(yong)4.5%Ni-0.2%Mo系焊(han)(han)(han)(han)(han)(han)絲(si)，用(yong)(yong)NB-3N焊(han)(han)(han)(han)(han)(han)條(tiao)焊(han)(han)(han)(han)(han)(han)接時，建議(yi)采用(yong)(yong)表5-58規定的(de)(de)焊(han)(han)(han)(han)(han)(han)接電流，焊(han)(han)(han)(han)(han)(han)后(hou)進(jin)行600~625℃熱(re)(re)(re)處理(li)(li)，有(you)利于收善焊(han)(han)(han)(han)(han)(han)接接頭(tou)的(de)(de)低(di)(di)(di)溫(wen)(wen)韌(ren)性(xing)(xing)(xing)。