不同固溶處理的2205不銹鋼在3.5%NaCl溶液中的慢應變拉伸曲線如圖4.3所示。慢應變拉伸數據得到的各相性能指標值如圖4.4和表4.2所示。

  材料的應(ying)力(li)腐(fu)蝕(shi)敏感性的強弱可以用其比值來反映：該值越大，材料的應力腐蝕敏感性越低。從圖4.4可以看出，隨著固溶處理的溫度的升高，雙相不銹鋼在空氣中的斷面收縮率先升高后下降，雙相不銹鋼(gang)在溶液中斷面收縮率先升高后下降，以及兩者之比（ψ環境／ψ空氣）的值先升高后下降，說明隨著固溶處理的溫度從950℃升高至1150℃,雙相不銹鋼的應力腐蝕敏感性先變弱后變強。

  慢(man)應(ying)(ying)變(bian)拉伸斷(duan)裂(lie)(lie)后的(de)(de)雙(shuang)相(xiang)不銹鋼(gang)的(de)(de)斷(duan)口(kou)形(xing)(xing)貌(mao)如(ru)圖(tu)4.5所示。圖(tu)4.6為1050℃/30min 固溶(rong)處理的(de)(de)雙(shuang)相(xiang)不銹鋼(gang)在(zai)3.5%NaCl溶(rong)液中(zhong)慢(man)應(ying)(ying)變(bian)拉伸后的(de)(de)斷(duan)口(kou)剖(pou)面圖(tu)。從圖(tu)4.6中(zhong)可以看(kan)出(chu)，雙(shuang)相(xiang)不銹鋼(gang)中(zhong)的(de)(de)斷(duan)口(kou)形(xing)(xing)貌(mao)中(zhong)存在(zai)由(you)裂(lie)(lie)紋，裂(lie)(lie)紋的(de)(de)源頭(tou)在(zai)雙(shuang)相(xiang)不銹鋼(gang)試(shi)樣表面，裂(lie)(lie)紋由(you)雙(shuang)相(xiang)不銹鋼(gang)表面相(xiang)試(shi)樣內部延伸，并終(zhong)止于奧(ao)氏(shi)體，說明奧(ao)氏(shi)體對(dui)應(ying)(ying)力腐(fu)蝕的(de)(de)裂(lie)(lie)紋的(de)(de)擴展有一定(ding)的(de)(de)阻礙作用。

  從表4.2中(zhong)(zhong)(zhong)可以看(kan)出(chu)，當固(gu)(gu)(gu)溶(rong)(rong)(rong)處(chu)(chu)(chu)理(li)(li)(li)(li)(li)的(de)(de)(de)溫度(du)(du)從950℃升(sheng)(sheng)高(gao)(gao)(gao)至(zhi)1000℃時(shi)(shi)(shi)(shi)，雙(shuang)相(xiang)(xiang)不銹鋼(gang)在(zai)空(kong)(kong)(kong)氣(qi)中(zhong)(zhong)(zhong)的(de)(de)(de)斷(duan)(duan)(duan)面(mian)收(shou)(shou)(shou)縮(suo)(suo)率(lv)(lv)從63.22956%升(sheng)(sheng)高(gao)(gao)(gao)至(zhi)82.92134%,升(sheng)(sheng)高(gao)(gao)(gao)幅值(zhi)約為(wei)(wei)19%;當固(gu)(gu)(gu)溶(rong)(rong)(rong)處(chu)(chu)(chu)理(li)(li)(li)(li)(li)的(de)(de)(de)溫度(du)(du)升(sheng)(sheng)高(gao)(gao)(gao)到1050℃時(shi)(shi)(shi)(shi)，雙(shuang)相(xiang)(xiang)不銹鋼(gang)在(zai)空(kong)(kong)(kong)氣(qi)中(zhong)(zhong)(zhong)斷(duan)(duan)(duan)面(mian)收(shou)(shou)(shou)縮(suo)(suo)率(lv)(lv)為(wei)(wei)82.50531%;當固(gu)(gu)(gu)溶(rong)(rong)(rong)處(chu)(chu)(chu)理(li)(li)(li)(li)(li)的(de)(de)(de)溫度(du)(du)為(wei)(wei)1100℃時(shi)(shi)(shi)(shi)，雙(shuang)相(xiang)(xiang)不銹鋼(gang)在(zai)空(kong)(kong)(kong)氣(qi)中(zhong)(zhong)(zhong)斷(duan)(duan)(duan)面(mian)收(shou)(shou)(shou)縮(suo)(suo)率(lv)(lv)為(wei)(wei)82.67233%;進一(yi)步升(sheng)(sheng)高(gao)(gao)(gao)固(gu)(gu)(gu)溶(rong)(rong)(rong)處(chu)(chu)(chu)理(li)(li)(li)(li)(li)的(de)(de)(de)溫度(du)(du)至(zhi)1150℃時(shi)(shi)(shi)(shi)，雙(shuang)相(xiang)(xiang)不銹鋼(gang)在(zai)空(kong)(kong)(kong)氣(qi)中(zhong)(zhong)(zhong)斷(duan)(duan)(duan)面(mian)收(shou)(shou)(shou)縮(suo)(suo)率(lv)(lv)為(wei)(wei)80.08303%.可以看(kan)出(chu)，當固(gu)(gu)(gu)溶(rong)(rong)(rong)處(chu)(chu)(chu)理(li)(li)(li)(li)(li)的(de)(de)(de)溫度(du)(du)從1000℃升(sheng)(sheng)高(gao)(gao)(gao)至(zhi)1100℃時(shi)(shi)(shi)(shi)，雙(shuang)相(xiang)(xiang)不銹鋼(gang)在(zai)空(kong)(kong)(kong)氣(qi)中(zhong)(zhong)(zhong)的(de)(de)(de)斷(duan)(duan)(duan)面(mian)收(shou)(shou)(shou)縮(suo)(suo)率(lv)(lv)幾乎(hu)沒有(you)變化(hua)，當固(gu)(gu)(gu)溶(rong)(rong)(rong)處(chu)(chu)(chu)理(li)(li)(li)(li)(li)的(de)(de)(de)溫度(du)(du)升(sheng)(sheng)高(gao)(gao)(gao)至(zhi)1150℃時(shi)(shi)(shi)(shi)，雙(shuang)相(xiang)(xiang)不銹鋼(gang)在(zai)空(kong)(kong)(kong)氣(qi)中(zhong)(zhong)(zhong)斷(duan)(duan)(duan)面(mian)收(shou)(shou)(shou)縮(suo)(suo)率(lv)(lv)開始下(xia)降(jiang)至(zhi)80.08303%,這(zhe)與1150℃/30min固(gu)(gu)(gu)溶(rong)(rong)(rong)處(chu)(chu)(chu)理(li)(li)(li)(li)(li)的(de)(de)(de)試(shi)樣中(zhong)(zhong)(zhong)的(de)(de)(de)鐵(tie)(tie)(tie)素(su)(su)體(ti)和奧(ao)氏體(ti)的(de)(de)(de)百(bai)分(fen)含量(liang)(liang)有(you)關(guan)，此(ci)時(shi)(shi)(shi)(shi)的(de)(de)(de)鐵(tie)(tie)(tie)素(su)(su)體(ti)的(de)(de)(de)百(bai)分(fen)含量(liang)(liang)為(wei)(wei)59%,而奧(ao)氏體(ti)的(de)(de)(de)百(bai)分(fen)含量(liang)(liang)為(wei)(wei)41%,即1150℃/30min 固(gu)(gu)(gu)溶(rong)(rong)(rong)處(chu)(chu)(chu)理(li)(li)(li)(li)(li)的(de)(de)(de)試(shi)樣中(zhong)(zhong)(zhong)含有(you)過量(liang)(liang)的(de)(de)(de)強度(du)(du)高(gao)(gao)(gao)的(de)(de)(de)鐵(tie)(tie)(tie)素(su)(su)體(ti)，以及不足量(liang)(liang)的(de)(de)(de)塑性優的(de)(de)(de)奧(ao)氏體(ti)，導(dao)(dao)致該(gai)固(gu)(gu)(gu)溶(rong)(rong)(rong)處(chu)(chu)(chu)理(li)(li)(li)(li)(li)狀態下(xia)的(de)(de)(de)試(shi)樣在(zai)空(kong)(kong)(kong)氣(qi)中(zhong)(zhong)(zhong)的(de)(de)(de)斷(duan)(duan)(duan)面(mian)收(shou)(shou)(shou)縮(suo)(suo)率(lv)(lv)有(you)所下(xia)降(jiang)。對于950℃固(gu)(gu)(gu)溶(rong)(rong)(rong)處(chu)(chu)(chu)理(li)(li)(li)(li)(li)的(de)(de)(de)試(shi)樣，其(qi)含有(you)6.1%的(de)(de)(de)硬而脆的(de)(de)(de)σ相(xiang)(xiang)，這(zhe)必然導(dao)(dao)致該(gai)固(gu)(gu)(gu)溶(rong)(rong)(rong)處(chu)(chu)(chu)理(li)(li)(li)(li)(li)狀態下(xia)的(de)(de)(de)試(shi)樣的(de)(de)(de)斷(duan)(duan)(duan)面(mian)收(shou)(shou)(shou)縮(suo)(suo)率(lv)(lv)明(ming)顯降(jiang)低，僅(jin)為(wei)(wei)63.22956%。

  從圖(tu)4.5(a)、（b)中可以看(kan)出(chu)，950℃/30min固(gu)溶(rong)(rong)(rong)處(chu)理(li)的(de)雙(shuang)相(xiang)不銹(xiu)(xiu)鋼(gang)(gang)(gang)在(zai)空(kong)(kong)氣(qi)中和(he)溶(rong)(rong)(rong)液中的(de)斷口(kou)(kou)均(jun)呈現準解理(li)平面；950℃/30min 固(gu)溶(rong)(rong)(rong)處(chu)理(li)的(de)雙(shuang)相(xiang)不銹(xiu)(xiu)鋼(gang)(gang)(gang)在(zai)空(kong)(kong)氣(qi)中的(de)斷口(kou)(kou)局部有少量韌(ren)窩存在(zai)，而在(zai)溶(rong)(rong)(rong)液中的(de)斷口(kou)(kou)幾乎是準解理(li)平面，二者都(dou)屬于脆性(xing)(xing)斷裂(lie)，這主要是由于大量脆性(xing)(xing)σ相(xiang)沿(yan)著(zhu)晶界析出(chu)，降低(di)了材料的(de)耐(nai)應力腐蝕性(xing)(xing)能(neng)和(he)力學性(xing)(xing)能(neng)。從圖(tu)4.5(e)、（f)中可以看(kan)出(chu)，1050℃/30min固(gu)溶(rong)(rong)(rong)處(chu)理(li)的(de)雙(shuang)相(xiang)不銹(xiu)(xiu)鋼(gang)(gang)(gang)在(zai)空(kong)(kong)氣(qi)和(he)溶(rong)(rong)(rong)液中的(de)斷口(kou)(kou)都(dou)存在(zai)大量韌(ren)窩，雙(shuang)相(xiang)不銹(xiu)(xiu)鋼(gang)(gang)(gang)在(zai)溶(rong)(rong)(rong)液中的(de)韌(ren)性(xing)(xing)損(sun)失(shi)較(jiao)小(xiao)，而（950℃、1000℃、1100℃、1150℃)/30min 固(gu)溶(rong)(rong)(rong)處(chu)理(li)的(de)雙(shuang)相(xiang)不銹(xiu)(xiu)鋼(gang)(gang)(gang)在(zai)溶(rong)(rong)(rong)液中都(dou)存在(zai)較(jiao)大的(de)韌(ren)性(xing)(xing)損(sun)失(shi)，表明(ming)1050℃/30min 固(gu)溶(rong)(rong)(rong)處(chu)理(li)的(de)雙(shuang)相(xiang)不銹(xiu)(xiu)鋼(gang)(gang)(gang)具有較(jiao)好的(de)耐(nai)應力腐蝕性(xing)(xing)能(neng)。

  從(cong)表(biao)4.2中也可以(yi)(yi)看出(chu)，950℃/30min 固(gu)(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)處理(li)(li)(li)的(de)(de)(de)(de)試(shi)樣(yang)(yang)(yang)在3.5%NaCl溶(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)液(ye)(ye)中的(de)(de)(de)(de)斷(duan)(duan)面收縮(suo)率僅(jin)為(wei)32.0158%,其(qi)ψ3.5%NaCI溶(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)液(ye)(ye)／空氣(qi)也僅(jin)為(wei)50.6342%,表(biao)現出(chu)很強(qiang)的(de)(de)(de)(de)應(ying)力(li)(li)(li)(li)腐(fu)(fu)(fu)蝕(shi)(shi)敏感性(xing)，具有(you)差(cha)的(de)(de)(de)(de)耐(nai)(nai)(nai)應(ying)力(li)(li)(li)(li)腐(fu)(fu)(fu)蝕(shi)(shi)性(xing)能(neng)(neng)。而1050℃/30min 固(gu)(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)處理(li)(li)(li)的(de)(de)(de)(de)試(shi)樣(yang)(yang)(yang)在3.5%NaCl 溶(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)液(ye)(ye)中斷(duan)(duan)面收縮(suo)率達到(dao)(dao) 76.34294%,且(qie)其(qi)43.5%NaCI溶(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)液(ye)(ye)／空氣(qi)也達到(dao)(dao)92.5971%,幾乎無應(ying)力(li)(li)(li)(li)腐(fu)(fu)(fu)蝕(shi)(shi)敏感性(xing)，表(biao)現出(chu)較(jiao)好(hao)的(de)(de)(de)(de)耐(nai)(nai)(nai)應(ying)力(li)(li)(li)(li)腐(fu)(fu)(fu)蝕(shi)(shi)性(xing)能(neng)(neng)。1150℃/30min 固(gu)(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)處理(li)(li)(li)的(de)(de)(de)(de)試(shi)樣(yang)(yang)(yang)的(de)(de)(de)(de)43.5%NaCI溶(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)液(ye)(ye)／4空氣(qi)值(zhi)為(wei)69.7453%,與1050℃/30min 固(gu)(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)處理(li)(li)(li)的(de)(de)(de)(de)試(shi)樣(yang)(yang)(yang)相比(bi)較(jiao)，有(you)明顯的(de)(de)(de)(de)下降。將（950℃、1050℃、1150℃)/30min 固(gu)(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)處理(li)(li)(li)的(de)(de)(de)(de)試(shi)樣(yang)(yang)(yang)的(de)(de)(de)(de)微觀組(zu)織(zhi)進行(xing)比(bi)較(jiao)，可以(yi)(yi)看出(chu)，1150℃/30min 固(gu)(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)處理(li)(li)(li)的(de)(de)(de)(de)試(shi)樣(yang)(yang)(yang)中的(de)(de)(de)(de)鐵素(su)體百分(fen)含(han)量(liang)(liang)(liang)(liang)為(wei)59%,比(bi)1050℃/30min 固(gu)(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)處理(li)(li)(li)的(de)(de)(de)(de)試(shi)樣(yang)(yang)(yang)中的(de)(de)(de)(de)鐵素(su)體百分(fen)含(han)量(liang)(liang)(liang)(liang)（51.9%)高(gao)7.1%,并且(qie)950℃/30min 固(gu)(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)處理(li)(li)(li)的(de)(de)(de)(de)試(shi)樣(yang)(yang)(yang)中存(cun)在大量(liang)(liang)(liang)(liang)σ相；從(cong)極(ji)化曲線的(de)(de)(de)(de)分(fen)析可知，當(dang)(dang)固(gu)(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)處理(li)(li)(li)的(de)(de)(de)(de)溫度(du)過(guo)高(gao)時，鐵素(su)體百分(fen)含(han)量(liang)(liang)(liang)(liang)升高(gao)，鐵素(su)體耐(nai)(nai)(nai)點(dian)蝕(shi)(shi)當(dang)(dang)量(liang)(liang)(liang)(liang)下降，促使點(dian)蝕(shi)(shi)更易于(yu)發生；且(qie)當(dang)(dang)固(gu)(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)處理(li)(li)(li)的(de)(de)(de)(de)溫度(du)為(wei)950℃時，大量(liang)(liang)(liang)(liang)的(de)(de)(de)(de)σ相的(de)(de)(de)(de)存(cun)在顯著降低了材料的(de)(de)(de)(de)耐(nai)(nai)(nai)點(dian)蝕(shi)(shi)性(xing)能(neng)(neng)。從(cong)應(ying)力(li)(li)(li)(li)腐(fu)(fu)(fu)蝕(shi)(shi)性(xing)能(neng)(neng)分(fen)析可以(yi)(yi)看出(chu)，由于(yu)σ相的(de)(de)(de)(de)存(cun)在，950℃/30min 固(gu)(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)處理(li)(li)(li)的(de)(de)(de)(de)試(shi)樣(yang)(yang)(yang)的(de)(de)(de)(de)耐(nai)(nai)(nai)應(ying)力(li)(li)(li)(li)腐(fu)(fu)(fu)蝕(shi)(shi)性(xing)能(neng)(neng)比(bi)1050℃/30min固(gu)(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)處理(li)(li)(li)的(de)(de)(de)(de)試(shi)樣(yang)(yang)(yang)的(de)(de)(de)(de)耐(nai)(nai)(nai)應(ying)力(li)(li)(li)(li)腐(fu)(fu)(fu)蝕(shi)(shi)性(xing)能(neng)(neng)差(cha)，以(yi)(yi)及1150℃/30min固(gu)(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)處理(li)(li)(li)的(de)(de)(de)(de)試(shi)樣(yang)(yang)(yang)中的(de)(de)(de)(de)過(guo)量(liang)(liang)(liang)(liang)鐵素(su)體導致(zhi)材料的(de)(de)(de)(de)耐(nai)(nai)(nai)應(ying)力(li)(li)(li)(li)腐(fu)(fu)(fu)蝕(shi)(shi)性(xing)能(neng)(neng)比(bi)1050℃/30min固(gu)(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)處理(li)(li)(li)的(de)(de)(de)(de)試(shi)樣(yang)(yang)(yang)的(de)(de)(de)(de)耐(nai)(nai)(nai)應(ying)力(li)(li)(li)(li)腐(fu)(fu)(fu)蝕(shi)(shi)性(xing)能(neng)(neng)有(you)所下降。

   一方面(mian)，鐵素體含(han)量升高，材(cai)料(liao)耐點(dian)(dian)(dian)(dian)蝕(shi)當量下(xia)降，點(dian)(dian)(dian)(dian)蝕(shi)更易發生，導致(zhi)鈍化膜性(xing)能(neng)不(bu)穩定和易破裂，耐應力腐(fu)蝕(shi)性(xing)能(neng)變(bian)差；另一方面(mian)，σ相的產生使(shi)其周圍(wei)存在貧鉻區，降低材(cai)料(liao)耐點(dian)(dian)(dian)(dian)蝕(shi)性(xing)能(neng)，同(tong)時使(shi)得材(cai)料(liao)的耐應力腐(fu)蝕(shi)性(xing)能(neng)下(xia)降。而1050℃/30min固溶處理的雙相不(bu)銹鋼中的兩相比例接近1:1,同(tong)時具有較好的耐點(dian)(dian)(dian)(dian)蝕(shi)性(xing)能(neng)和較好的耐應力腐(fu)蝕(shi)性(xing)能(neng)。

  從(cong)以上分析可以看出(chu)，點(dian)蝕(shi)(shi)和應(ying)(ying)力(li)腐(fu)蝕(shi)(shi)的(de)(de)發(fa)(fa)生(sheng)存在某種關(guan)系，即點(dian)蝕(shi)(shi)會促(cu)進應(ying)(ying)力(li)腐(fu)蝕(shi)(shi)的(de)(de)發(fa)(fa)生(sheng)，而提(ti)高材(cai)料的(de)(de)耐點(dian)蝕(shi)(shi)性能也能夠(gou)提(ti)高材(cai)料的(de)(de)耐應(ying)(ying)力(li)腐(fu)蝕(shi)(shi)性能。應(ying)(ying)力(li)腐(fu)蝕(shi)(shi)的(de)(de)陽極溶(rong)解理(li)論認為，應(ying)(ying)力(li)腐(fu)蝕(shi)(shi)的(de)(de)發(fa)(fa)生(sheng)與材(cai)料表面氧化膜的(de)(de)形(xing)成一破裂(lie)有關(guan)。點(dian)蝕(shi)(shi)破壞鈍化膜的(de)(de)完整性，促(cu)進了應(ying)(ying)力(li)腐(fu)蝕(shi)(shi)的(de)(de)發(fa)(fa)生(sheng)。

  1000℃、1050℃、1100℃、1150℃及1200℃固溶態的2507雙相不(bu)銹鋼室溫下在3.5%NaCl溶液中的SSRT結果如圖4.7和表4.3所示。從整體能夠獲得隨固溶處理溫度的增高DSS2507的抗拉強度表現為先降低后上升的變化趨勢，1000℃時抗拉強度是888.36MPa,1100℃時抗拉強度減小成875.886MPa,隨固溶熱處理溫度繼續增高到1200℃抗拉強度又上升至905.562MPa.從應變量（試樣標距部分的拉伸量）的角度看隨固溶熱處理溫度的上升應變量呈先變大后減小的趨勢，固溶溫度為1000℃時斷裂應變為11.0487mm,當固溶溫度升高到1050℃時斷裂應變升高到11.1307mm,而固溶熱處理溫度的繼續上升又導致斷裂應變開始減小，1200℃時減小到10.0628mm.導致以上現象出現的原因在于固溶熱處理溫度處于1000~1050℃之間時，抗拉強度受材料組織再結晶完全程度的影響，在該溫度范圍內2507雙相不銹鋼的組織再結晶完全程度提高，并且在該溫度范圍內起著主導作用所以剛的強度下降韌性升高；1050~1200℃之間材料的兩相組織轉變發揮著核心影響作用，鐵素體α相量隨固溶熱處理溫度增高漲幅較大而奧氏體γ相量卻降低，又由于鐵素體α相是bcc結構奧氏體γ相是fcc結構，在室溫條件下前者強度高于后者，所以1050~1200℃范圍內鋼的強度變高而韌性減小。

  雙相鋼在線亞洲日產一區二區:應力腐蝕開裂敏(min)(min)感(gan)性(xing)(xing)的(de)(de)(de)(de)(de)強弱能(neng)(neng)(neng)(neng)夠通過(guo)斷(duan)裂(lie)時間（tb)來(lai)反映：該值(zhi)越大，表(biao)明雙相(xiang)鋼的(de)(de)(de)(de)(de)SCC敏(min)(min)感(gan)性(xing)(xing)越低(di)，抵抗(kang)SCC的(de)(de)(de)(de)(de)性(xing)(xing)能(neng)(neng)(neng)(neng)更強。從(cong)表(biao)4.3可(ke)(ke)以(yi)看(kan)出(chu) DSS2507的(de)(de)(de)(de)(de)斷(duan)裂(lie)時間（tb)隨固(gu)溶(rong)(rong)(rong)熱處理溫度的(de)(de)(de)(de)(de)上升(sheng)(sheng)呈先變大后(hou)減(jian)小的(de)(de)(de)(de)(de)變化走勢。當(dang)固(gu)溶(rong)(rong)(rong)溫度為(wei)1000℃時，DSS2507中的(de)(de)(de)(de)(de)鐵素體(ti)跟(gen)奧氏體(ti)這兩相(xiang)相(xiang)界處有(you)σ相(xiang)析出(chu)，由(you)于σ相(xiang)硬而(er)脆(cui)，且其周圍存在(zai)貧(pin)鉻(ge)區，σ相(xiang)的(de)(de)(de)(de)(de)存在(zai)能(neng)(neng)(neng)(neng)夠顯著(zhu)降低(di)材(cai)料的(de)(de)(de)(de)(de)力(li)學(xue)性(xing)(xing)能(neng)(neng)(neng)(neng)和耐蝕(shi)性(xing)(xing)能(neng)(neng)(neng)(neng)，根據應力(li)腐蝕(shi)的(de)(de)(de)(de)(de)陽極溶(rong)(rong)(rong)解機理可(ke)(ke)知(zhi)，SCC的(de)(de)(de)(de)(de)發生跟(gen)鈍化膜(mo)(mo)的(de)(de)(de)(de)(de)“破裂(lie)－修復－破裂(lie)”過(guo)程有(you)關聯。σ相(xiang)的(de)(de)(de)(de)(de)析出(chu)使其所在(zai)區域的(de)(de)(de)(de)(de)鈍化膜(mo)(mo)變得薄弱，因(yin)此(ci)經過(guo)1000℃固(gu)溶(rong)(rong)(rong)的(de)(de)(de)(de)(de)試樣易發生應力(li)腐蝕(shi)斷(duan)裂(lie)，并且從(cong)表(biao)4.3也可(ke)(ke)以(yi)看(kan)出(chu)1000℃時斷(duan)裂(lie)時間（tb)較低(di)為(wei)30.42h;1050℃時斷(duan)裂(lie)時間（tb)值(zhi)最(zui)大為(wei)31.33h,這說明經過(guo)1050℃固(gu)溶(rong)(rong)(rong)處理30min的(de)(de)(de)(de)(de)DSS2507的(de)(de)(de)(de)(de)SCC敏(min)(min)感(gan)性(xing)(xing)較低(di)，有(you)較優的(de)(de)(de)(de)(de)耐SCC能(neng)(neng)(neng)(neng)力(li)，這跟(gen)其有(you)較優的(de)(de)(de)(de)(de)抗(kang)點(dian)蝕(shi)能(neng)(neng)(neng)(neng)力(li)以(yi)及鋼中兩相(xiang)均(jun)勻(yun)分布有(you)關；隨著(zhu)固(gu)溶(rong)(rong)(rong)溫度繼(ji)(ji)續升(sheng)(sheng)高(gao)至1200℃,斷(duan)裂(lie)時間（tb)又(you)(you)逐漸減(jian)小，1200℃時斷(duan)裂(lie)時間（tb)降低(di)到28.47h,這說明材(cai)料的(de)(de)(de)(de)(de)耐應力(li)腐蝕(shi)斷(duan)裂(lie)性(xing)(xing)能(neng)(neng)(neng)(neng)降低(di)。這是因(yin)為(wei)當(dang)固(gu)溶(rong)(rong)(rong)熱處理溫度繼(ji)(ji)續上升(sheng)(sheng)至1200℃時鋼中的(de)(de)(de)(de)(de)鐵素體(ti)相(xiang)量(liang)逐漸增(zeng)高(gao)而(er)奧氏體(ti)相(xiang)量(liang)逐漸減(jian)少，又(you)(you)因(yin)為(wei)鐵素體(ti)的(de)(de)(de)(de)(de)塑性(xing)(xing)比奧氏體(ti)差，進而(er)導(dao)致在(zai)高(gao)固(gu)溶(rong)(rong)(rong)溫度下DSS2507的(de)(de)(de)(de)(de)應力(li)腐蝕(shi)破裂(lie)敏(min)(min)感(gan)性(xing)(xing)增(zeng)強，具體(ti)變現為(wei)斷(duan)裂(lie)時間（tb)降低(di)。

  1000℃、1050℃、1100℃、1150℃及1200℃固(gu)(gu)溶(rong)態(tai)的(de)(de)(de)2507雙(shuang)相不銹(xiu)鋼室溫(wen)下于3.5%NaCl溶(rong)液介質中的(de)(de)(de)SSRT斷口形貌如(ru)圖(tu)4.8所示(shi)(shi)。從圖(tu)4.8中能夠較(jiao)為(wei)清晰地獲(huo)得五種(zhong)固(gu)(gu)溶(rong)態(tai)下的(de)(de)(de)DSS2507拉伸斷口都(dou)具有(you)明顯(xian)的(de)(de)(de)韌(ren)窩(wo)，都(dou)表現(xian)為(wei)韌(ren)性(xing)(xing)斷裂(lie)(lie)。圖(tu)4.8(a)雖然表現(xian)為(wei)韌(ren)性(xing)(xing)斷裂(lie)(lie)，但是有(you)明顯(xian)的(de)(de)(de)準(zhun)解理斷裂(lie)(lie)面的(de)(de)(de)出(chu)現(xian)，有(you)脆(cui)性(xing)(xing)斷裂(lie)(lie)的(de)(de)(de)傾向，這(zhe)說(shuo)明1000℃下DSS2507的(de)(de)(de)抗SCC能力較(jiao)弱(ruo)，容易發(fa)生(sheng)SCC;隨(sui)著(zhu)(zhu)固(gu)(gu)溶(rong)溫(wen)度升高(gao)至1050℃,如(ru)圖(tu)4.8(b)所示(shi)(shi)，鋼斷面上的(de)(de)(de)韌(ren)窩(wo)數量最(zui)(zui)多(duo)且(qie)密集(ji)表明其應力腐(fu)蝕(shi)敏感(gan)性(xing)(xing)最(zui)(zui)弱(ruo)，即該固(gu)(gu)溶(rong)溫(wen)度下鋼的(de)(de)(de)應力腐(fu)蝕(shi)破裂(lie)(lie)敏感(gan)性(xing)(xing)較(jiao)弱(ruo)；隨(sui)著(zhu)(zhu)固(gu)(gu)溶(rong)溫(wen)度的(de)(de)(de)繼續升高(gao)，如(ru)圖(tu)4.8(c)~(e)所示(shi)(shi)，鋼的(de)(de)(de)韌(ren)性(xing)(xing)損失變大，韌(ren)窩(wo)數量減小且(qie)密集(ji)度減弱(ruo)，表明雙(shuang)相不銹(xiu)鋼的(de)(de)(de)應力腐(fu)蝕(shi)破裂(lie)(lie)敏感(gan)性(xing)(xing)又(you)增強。

  這與表4.3中斷(duan)裂(lie)時(shi)的(de)(de)(de)應變測(ce)試結果是相(xiang)對應的(de)(de)(de)。雙相(xiang)不銹鋼(gang)(gang)的(de)(de)(de)應力(li)腐蝕(shi)類型是陽極(ji)(ji)溶解型，跟其耐孔蝕(shi)能(neng)力(li)有(you)著較為(wei)(wei)密切的(de)(de)(de)聯系。當鋼(gang)(gang)表面(mian)(mian)的(de)(de)(de)氧化(hua)(hua)膜(mo)被破壞形(xing)成(cheng)(cheng)(cheng)蝕(shi)孔裸露出新鮮(xian)表面(mian)(mian)，該表面(mian)(mian)與其他(ta)覆(fu)蓋有(you)氧化(hua)(hua)膜(mo)的(de)(de)(de)表面(mian)(mian)形(xing)成(cheng)(cheng)(cheng)大(da)陰(yin)極(ji)(ji)小陽極(ji)(ji)的(de)(de)(de)腐蝕(shi)電池（裸露出的(de)(de)(de)新鮮(xian)表面(mian)(mian)為(wei)(wei)陽極(ji)(ji)，鋼(gang)(gang)表面(mian)(mian)覆(fu)蓋有(you)氧化(hua)(hua)膜(mo)的(de)(de)(de)表面(mian)(mian)為(wei)(wei)陰(yin)極(ji)(ji)），金(jin)屬(shu)發生陽極(ji)(ji)反應，金(jin)屬(shu)原(yuan)子溶解成(cheng)(cheng)(cheng)為(wei)(wei)離子，形(xing)成(cheng)(cheng)(cheng)裂(lie)紋(wen)(wen)。裂(lie)紋(wen)(wen)朝著縱深(shen)方向(xiang)處(chu)發展同時(shi)又因為(wei)(wei)應力(li)主要分(fen)布在裂(lie)紋(wen)(wen)尖(jian)端處(chu)，進而導(dao)致(zhi)裂(lie)紋(wen)(wen)周圍區域(yu)產生塑性形(xing)變，陽極(ji)(ji)電位(wei)下降提高(gao)了陽極(ji)(ji)溶解速度(du)，最終導(dao)致(zhi)裂(lie)紋(wen)(wen)的(de)(de)(de)擴(kuo)大(da)。

 根據第3章對2507雙相不銹鋼電化學性能的研究結果可知，隨固溶熱處理度的增高2507雙(shuang)相不銹鋼(gang)抗點蝕能力呈先增強后下降的變化趨勢，1050℃時鋼中的鐵素體相跟奧氏體相這兩相分布較均勻且兩相比例約為1:1,鋼表面保護膜穩定性較好，產生點腐蝕的電位較高，不利于促進裂紋的發展，進而該固溶溫度下2507雙相不銹鋼有較好的抗應力腐蝕開裂性能，這跟SSRT所得結果是相同的。總之，固溶熱處理溫度為1050℃時 DSS2507的抗SCC能力較強。

  固溶態為1050℃的2507雙相不銹鋼在3.5%NaCl溶液中的拉伸斷口腐蝕形貌如圖4.9所示，圖中深色組織是鐵素體α相、淺色是奧氏體γ相。從圖4.9中可以看出裂紋優先在鐵素體α相上傳播，終止于奧氏體γ相，且裂紋迂回過奧氏體γ相后繼續會在鐵素體α相中繼續傳播，這表明奧氏體γ相對鐵素體α相中裂紋的傳播有一定的抑制作用，這種現象稱為致鎖（Keying)效應。這主要是由于首先鐵素體α相為陽極，優先在腐蝕介質中發生腐蝕因而裂紋優先在鐵素體α相上發生和傳播；其次奧氏體γ相相對于鐵素體α相來說硬度及屈服強度都偏低、延展性能較好，奧氏體γ相比鐵素體α相更易發生形變且形變能較大，所以在鐵素體α相中發展的裂紋遇到奧氏體γ相時其尖端形變帶的應力會受到一定的緩和，進而對鐵素體α相中裂紋的傳播有一定的抑制作用。因此，應力腐蝕破裂裂紋優先在鐵素體α相上傳播，終止于奧氏體γ相。