不銹鋼的爐中釬焊一般是在某種保護性(xing)氣(qi)(qi)(qi)氛下或真空中進行，保護氣(qi)(qi)(qi)氛有氫(qing)氣(qi)(qi)(qi)、分解氨和氬氣(qi)(qi)(qi)。
干燥的氫氣或分解氨常用做爐中釬焊不銹鋼時的還原性保護氣氛，它們可還原不銹鋼表面的氧化膜，并保護不銹鋼表面在釬焊時不再氧化。一般要求氫氣或分解氨的露點低于-40℃,但也要考慮保護氣體的露點要與釬焊溫度及母材的成分相適應。釬焊溫度越低、不銹鋼表面氧化膜越穩定，要求氫氣露點越低，見圖3-4。使用分解氨作保護氣氛時，必須保證NH3完全分解，避免殘余的NH3使不銹鋼表面氮化。
使(shi)用(yong)(yong)(yong)氫(qing)氣或(huo)分解(jie)氨(an)作(zuo)保護(hu)(hu)氣氛(fen)的(de)好處是(shi)：可實(shi)現釬焊爐的(de)連續工(gong)(gong)作(zuo)，便于大批(pi)量生(sheng)產；釬焊過程(cheng)中不需(xu)使(shi)用(yong)(yong)(yong)釬劑，且焊后(hou)工(gong)(gong)件(jian)光亮，無需(xu)任何焊后(hou)工(gong)(gong)件(jian)表(biao)面清理工(gong)(gong)作(zuo)；可配合選用(yong)(yong)(yong)的(de)釬料品種多；在(zai)批(pi)量生(sheng)產條件(jian)下焊接成本低。但是(shi)使(shi)用(yong)(yong)(yong)氫(qing)氣或(huo)分解(jie)氨(an)作(zuo)保護(hu)(hu)氣氛(fen)時要注意(yi)生(sheng)產安全，當空氣中混有4%~74%的(de)氫(qing)氣或(huo)12.5%~27%氨(an)氣時，會因燃燒(shao)而產生(sheng)爆炸。
作(zuo)為惰性(xing)氣(qi)(qi)(qi)體，氬(ya)(ya)氣(qi)(qi)(qi)可用作(zuo)爐中釬(han)焊(han)不(bu)銹(xiu)鋼(gang)時的保護氣(qi)(qi)(qi)氛。與(yu)氫氣(qi)(qi)(qi)和分解(jie)氨(an)不(bu)同，氬(ya)(ya)氣(qi)(qi)(qi)不(bu)具有(you)還原性(xing)，只(zhi)是利用其(qi)惰性(xing)保護不(bu)銹(xiu)鋼(gang)表(biao)面在釬(han)焊(han)過程(cheng)中不(bu)氧化，所以不(bu)銹(xiu)鋼(gang)進爐釬(han)焊(han)前(qian)必(bi)須(xu)徹底清除(chu)其(qi)表(biao)面的氧化膜，并且一般(ban)要求氬(ya)(ya)氣(qi)(qi)(qi)的露點(dian)低于(yu)-40℃。
使用氬(ya)氣作保護氣氛一(yi)般是因(yin)為以下某(mou)種或(huo)多種原因(yin)：①. 可(ke)采用含高(gao)蒸汽壓元素的釬(han)(han)，如錳基釬(han)(han)料(liao)或(huo)含錳較多的釬(han)(han)料(liao)；②. 單件或(huo)小批量釬(han)(han)焊(han)時(shi)，設(she)備(bei)成本低(di)；③. 不(bu)銹(xiu)鋼與(yu)異(yi)種材釬(han)(han)焊(han)時(shi)避免(mian)某(mou)些材料(liao)與(yu)爐內(nei)氣氛的反應(ying)，如在含氫(qing)氣氛中釬(han)(han)焊(han)連接不(bu)銹(xiu)鋼與(yu)鈦合(he)金時(shi)，鈦金吸氫(qing)并與(yu)氫(qing)反應(ying)；④. 生產過程(cheng)安全(quan)。
使用氬氣作保護氣氛時，常見的做法是將真空爐抽至高真空后（10-2~10-3Pa)充入少量氬氣，關閉爐體氣閥后升溫。或者在特制的密封容器內通人流動的氬氣，將空氣趕凈后，容器放入馬弗爐內加熱。也可在趕凈空氣后，關閉氣路，容器放人馬弗爐內加熱，但在升溫過
程(cheng)中(zhong)要(yao)隨時(shi)注(zhu)意(yi)容(rong)器內的壓力(li)，當容(rong)器內壓力(li)超過大氣(qi)壓較多時(shi)應隨時(shi)放出一(yi)些氣(qi)體(ti)(ti)(ti)，以(yi)保證容(rong)器完好和(he)生產安全。使(shi)用特制的容(rong)器還有另(ling)一(yi)個便利：當使(shi)用未(wei)經凈(jing)化的普通瓶裝氬(ya)氣(qi)時(shi)，可(ke)向(xiang)釬焊爐內通入少許(xu)BF3氣(qi)體(ti)(ti)(ti)釬劑(ji)，或加入少許(xu)氟硼酸(suan)鉀，氟硼酸(suan)鉀在800~900℃分解產生BF3.BF3可(ke)以(yi)去除金(jin)屬表面(mian)的氧(yang)化物，促(cu)進釬料的潤濕。氣(qi)體(ti)(ti)(ti)釬劑(ji)的使(shi)用濃度一(yi)般控制在0.1%~0.001%(體(ti)(ti)(ti)積(ji)分數(shu)），避免焊后形成殘渣。氟化物對人體(ti)(ti)(ti)有害，要(yao)注(zhu)意(yi)工(gong)作場地的通風(feng)。
在真空爐中釬焊不銹鋼是一種常用且理想的方法。釬焊不銹鋼時一般要求真空度達到10-2～10-3Pa,并且要求真空爐的氣體泄漏率小于10-2Pa/s.使用真空爐釬焊不銹鋼的好處是：可避免不銹鋼的氧化；可避免釬焊爐內氣氛對母材的不良影響；真空爐升、降溫速度慢，工件不變形或變形量很小；無論以何種方式添加釬料均不會在接頭內形成氣孔；無需消耗保護氣體；無需氣體凈化裝置；無安全隱患；帶有充氣及快冷風扇置的真空爐同樣具有較高的生產率，并可實現釬焊與焊后工件熱處理的結合。
在氫氣或分解氨氣氛爐中釬焊不銹鋼可使用紫銅、銅基、銀基、錳基、鎳基和金基釬料。在氬氣氛爐中釬焊不銹鋼可使用銅基、銀基、錳基、金基釬料。在真空爐中釬焊不銹鋼可采用紫銅、不含易蒸發元素（Zn、Cd)或僅含少量高蒸汽壓元素（Mn)的銅基和銀基釬料、鎳基釬料和金基釬料。使用鎳基釬料釬焊不銹鋼薄件時，要選擇對母材溶蝕傾向小的釬料。
爐中(zhong)(zhong)(zhong)釬(han)(han)(han)(han)(han)(han)焊(han)(han)(han)(han)時(shi)(shi)(shi)(shi)影響釬(han)(han)(han)(han)(han)(han)焊(han)(han)(han)(han)接頭(tou)性(xing)(xing)(xing)能，特別是(shi)力學性(xing)(xing)(xing)能的(de)(de)(de)(de)主要工藝參數包釬(han)(han)(han)(han)(han)(han)焊(han)(han)(han)(han)溫(wen)(wen)度(du)(du)(du)(du)(du)(du)、保(bao)溫(wen)(wen)時(shi)(shi)(shi)(shi)間(jian)(jian)。釬(han)(han)(han)(han)(han)(han)焊(han)(han)(han)(han)溫(wen)(wen)度(du)(du)(du)(du)(du)(du)一(yi)般選(xuan)擇(ze)在釬(han)(han)(han)(han)(han)(han)料液相(xiang)線溫(wen)(wen)度(du)(du)(du)(du)(du)(du)以上50~100℃,保(bao)溫(wen)(wen)時(shi)(shi)(shi)(shi)間(jian)(jian)在5~10min.當(dang)工件較大(da)時(shi)(shi)(shi)(shi)，可在升(sheng)溫(wen)(wen)過(guo)(guo)程中(zhong)(zhong)(zhong)釬(han)(han)(han)(han)(han)(han)料固(gu)相(xiang)線溫(wen)(wen)度(du)(du)(du)(du)(du)(du)以下(xia)某(mou)(mou)溫(wen)(wen)度(du)(du)(du)(du)(du)(du)保(bao)溫(wen)(wen)一(yi)段時(shi)(shi)(shi)(shi)間(jian)(jian)，確(que)保(bao)工件溫(wen)(wen)度(du)(du)(du)(du)(du)(du)均勻。使用鎳基(ji)釬(han)(han)(han)(han)(han)(han)料時(shi)(shi)(shi)(shi)，除了釬(han)(han)(han)(han)(han)(han)焊(han)(han)(han)(han)溫(wen)(wen)度(du)(du)(du)(du)(du)(du)和保(bao)溫(wen)(wen)時(shi)(shi)(shi)(shi)間(jian)(jian)外(wai)，釬(han)(han)(han)(han)(han)(han)縫(feng)(feng)間(jian)(jian)隙(xi)(xi)也(ye)是(shi)接頭(tou)強(qiang)度(du)(du)(du)(du)(du)(du)和塑性(xing)(xing)(xing)的(de)(de)(de)(de)決定因素之一(yi)。圖(tu)3-5、圖(tu)3-6顯(xian)示(shi)了三種(zhong)鎳基(ji)釬(han)(han)(han)(han)(han)(han)料釬(han)(han)(han)(han)(han)(han)焊(han)(han)(han)(han)不銹鋼時(shi)(shi)(shi)(shi)釬(han)(han)(han)(han)(han)(han)焊(han)(han)(han)(han)接頭(tou)強(qiang)度(du)(du)(du)(du)(du)(du)與釬(han)(han)(han)(han)(han)(han)縫(feng)(feng)間(jian)(jian)隙(xi)(xi)的(de)(de)(de)(de)關系。為(wei)降低(di)(di)釬(han)(han)(han)(han)(han)(han)料的(de)(de)(de)(de)熔點，鎳基(ji)釬(han)(han)(han)(han)(han)(han)料中(zhong)(zhong)(zhong)含有較多的(de)(de)(de)(de)硼(peng)、硅(gui)(gui)、磷(lin)(lin)，它們在釬(han)(han)(han)(han)(han)(han)料組(zu)織中(zhong)(zhong)(zhong)以脆(cui)性(xing)(xing)(xing)的(de)(de)(de)(de)硼(peng)化物、硅(gui)(gui)化物、磷(lin)(lin)化物形式存在。釬(han)(han)(han)(han)(han)(han)焊(han)(han)(han)(han)時(shi)(shi)(shi)(shi)在一(yi)定的(de)(de)(de)(de)釬(han)(han)(han)(han)(han)(han)焊(han)(han)(han)(han)溫(wen)(wen)度(du)(du)(du)(du)(du)(du)和保(bao)溫(wen)(wen)時(shi)(shi)(shi)(shi)間(jian)(jian)下(xia)，當(dang)釬(han)(han)(han)(han)(han)(han)縫(feng)(feng)間(jian)(jian)隙(xi)(xi)小于某(mou)(mou)一(yi)數值(zhi)，硼(peng)、硅(gui)(gui)、磷(lin)(lin)向(xiang)母材擴(kuo)散(san)充分，凝(ning)固(gu)后釬(han)(han)(han)(han)(han)(han)縫(feng)(feng)組(zu)織為(wei)鎳基(ji)固(gu)溶體(ti)，釬(han)(han)(han)(han)(han)(han)縫(feng)(feng)強(qiang)度(du)(du)(du)(du)(du)(du)高、塑性(xing)(xing)(xing)好，此數值(zhi)稱(cheng)作該釬(han)(han)(han)(han)(han)(han)料在此釬(han)(han)(han)(han)(han)(han)焊(han)(han)(han)(han)溫(wen)(wen)度(du)(du)(du)(du)(du)(du)和保(bao)溫(wen)(wen)時(shi)(shi)(shi)(shi)間(jian)(jian)下(xia)的(de)(de)(de)(de)最大(da)釬(han)(han)(han)(han)(han)(han)焊(han)(han)(han)(han)間(jian)(jian)隙(xi)(xi)。當(dang)釬(han)(han)(han)(han)(han)(han)縫(feng)(feng)間(jian)(jian)隙(xi)(xi)超過(guo)(guo)最大(da)間(jian)(jian)隙(xi)(xi)，釬(han)(han)(han)(han)(han)(han)縫(feng)(feng)中(zhong)(zhong)(zhong)硼(peng)、硅(gui)(gui)、磷(lin)(lin)向(xiang)母材擴(kuo)散(san)不充分，釬(han)(han)(han)(han)(han)(han)縫(feng)(feng)中(zhong)(zhong)(zhong)會存在脆(cui)性(xing)(xing)(xing)化合物，釬(han)(han)(han)(han)(han)(han)縫(feng)(feng)的(de)(de)(de)(de)強(qiang)度(du)(du)(du)(du)(du)(du)和塑性(xing)(xing)(xing)都會下(xia)降。而且在一(yi)定范圍內，釬(han)(han)(han)(han)(han)(han)縫(feng)(feng)越寬，釬(han)(han)(han)(han)(han)(han)縫(feng)(feng)中(zhong)(zhong)(zhong)脆(cui)性(xing)(xing)(xing)相(xiang)越多，接頭(tou)的(de)(de)(de)(de)強(qiang)度(du)(du)(du)(du)(du)(du)和塑性(xing)(xing)(xing)越低(di)(di)。
在釬焊(han)(han)實際部件(jian)時，有(you)時部件(jian)加(jia)工精度(du)或裝配精度(du)很難保證釬縫間隙(xi)很小，適(shi)當地提高(gao)(gao)釬焊(han)(han)溫度(du)或延長(chang)保溫時間可(ke)增大(da)(da)最大(da)(da)釬焊(han)(han)間隙(xi)，見圖(tu)3-7。當在高(gao)(gao)溫下(xia)長(chang)時間保溫造成母(mu)材晶粒過(guo)分長(chang)大(da)(da)或釬料(liao)對母(mu)材溶(rong)蝕(shi)過(guo)度(du)時，也可(ke)在焊(han)(han)后接頭冷卻(que)到某一較低溫度(du)保溫，通過(guo)擴散消除釬縫中的脆性(xing)相而增大(da)(da)最大(da)(da)釬焊(han)(han)間隙(xi)，見圖(tu)3-8。但(dan)由于磷(lin)原子(zi)較大(da)(da)，向母(mu)材中擴散困難，這些措施對Ni-Cr-P和(he)Ni-P這類釬料(liao)作用不大(da)(da)。
爐中釬焊時為控制釬料不流到接頭外其他部位或造成工件與卡具的粘連，可在防止釬料潤濕處涂止焊劑。釬焊不銹鋼時可以用TiO2、Y2O3或云母粉與乙醇混和后做止焊劑。
