熔化焊各種方法均可用來焊接鉻系馬氏體不銹鋼管(guan),但最常用的方法是手工焊條電弧焊和鎢極氬弧焊。當采用手工焊條電弧焊時應盡可能采用低氫、超低氫焊條,焊前經過300~350℃的高溫烘烤以減少擴散氫的含量,降低冷裂紋的敏感性。鎢極氬弧焊(GTAW)主要使用于薄壁構件和管道焊件,以及重要部件的根部封底。GTAW焊的特點是焊接質量高,焊縫成型美觀,可單面焊,雙面成型,保證管子內焊縫的成型質量。焊接時為防止背面氧化,封底焊通常采取氬氣背面保護的措施。Ar+CO2或Ar+O2的富氬混合氣體保護焊也常用于焊接馬氏體不銹鋼,具有焊接效率高,焊縫質量較好以及焊縫金屬具有較高抗氫致(冷)裂紋的特點。表2-6是已標準化的Cr13型馬氏體及低碳鉻鎳系馬氏體不銹鋼管常用焊材。
鉻系馬氏(shi)(shi)體(ti)(ti)不(bu)銹鋼管,因焊(han)(han)(han)(han)接性(xing)較(jiao)差,采用(yong)(yong)(yong)與(yu)母(mu)材(cai)(cai)(cai)(cai)(cai)成分相同的焊(han)(han)(han)(han)材(cai)(cai)(cai)(cai)(cai)時(shi)(shi),通常均(jun)應(ying)采取(qu)焊(han)(han)(han)(han)前預熱,焊(han)(han)(han)(han)后熱處理。但(dan)當焊(han)(han)(han)(han)件(jian)的拘束度(du)大(da),且(qie)難于(yu)進(jin)行(xing)預熱和(he)(he)焊(han)(han)(han)(han)后熱處理時(shi)(shi),也可(ke)(ke)以(yi)采用(yong)(yong)(yong)奧(ao)氏(shi)(shi)體(ti)(ti)型焊(han)(han)(han)(han)接材(cai)(cai)(cai)(cai)(cai)料(見表2-6),以(yi)提高焊(han)(han)(han)(han)接接頭的塑韌性(xing),防止裂紋的發生(sheng)。但(dan)奧(ao)氏(shi)(shi)體(ti)(ti)或以(yi)奧(ao)氏(shi)(shi)體(ti)(ti)為(wei)主焊(han)(han)(han)(han)縫(feng)金(jin)屬(shu)的強度(du)低(di)(di)于(yu)馬氏(shi)(shi)體(ti)(ti)母(mu)材(cai)(cai)(cai)(cai)(cai),而(er)且(qie)由于(yu)焊(han)(han)(han)(han)縫(feng)金(jin)屬(shu)化(hua)學成分和(he)(he)顯微組織與(yu)母(mu)材(cai)(cai)(cai)(cai)(cai)差別(bie)較(jiao)大(da),焊(han)(han)(han)(han)接殘(can)余應(ying)力(li)(li)較(jiao)大(da),對焊(han)(han)(han)(han)接接頭的使(shi)用(yong)(yong)(yong)性(xing)能產生(sheng)不(bu)利影響(xiang),特別(bie)是(shi)對接頭的疲(pi)勞(lao)蠕(ru)變性(xing)能和(he)(he)應(ying)力(li)(li)腐蝕(shi)破裂不(bu)利。因此采用(yong)(yong)(yong)奧(ao)氏(shi)(shi)體(ti)(ti)焊(han)(han)(han)(han)材(cai)(cai)(cai)(cai)(cai)時(shi)(shi)應(ying)根據(ju)使(shi)用(yong)(yong)(yong)條件(jian)嚴格選擇和(he)(he)進(jin)行(xing)工藝評定。有時(shi)(shi)還可(ke)(ke)采用(yong)(yong)(yong)鎳(nie)基合(he)金(jin)焊(han)(han)(han)(han)材(cai)(cai)(cai)(cai)(cai),使(shi)焊(han)(han)(han)(han)縫(feng)的膨脹系數與(yu)母(mu)材(cai)(cai)(cai)(cai)(cai)接近,盡量(liang)降(jiang)低(di)(di)焊(han)(han)(han)(han)接殘(can)余應(ying)力(li)(li)和(he)(he)高溫熱應(ying)力(li)(li)。