1. 動電位極(ji)化曲線分析

  2507雙相不銹鋼經1000℃、1050℃、1100℃、1150℃及1200℃固溶處理后于30℃在3.5%NaCl溶液中的動電位極化曲線如圖5.3所示。從圖5.3可知各固溶溫度下2507雙相不銹鋼(gang)的極化曲線形狀大體相同，都具有明顯的鈍化區域，且鈍化區域都較寬。國標GB 4334.9-1984規定陽極極化曲線上與電流密度值為100μA/c㎡相應的電位為擊破電位（Eb),擊破電位指金屬材料最先產生點腐蝕的電位，其值越高表明材料產生孔蝕的傾向越低。當2507雙相(xiang)不銹鋼主要化學成分一定時，其表面保護膜的均勻性及穩定性跟鋼的兩相組織（α相及γ相）有著密切聯系，鋼中的α相和γ相分布均勻、相比例接近1:1時保護膜比較穩定且對鋼的點蝕行為有較好的阻礙作用；當鋼中的α相和γ相分布不均勻時易導致鋼表面保護膜遭受破壞，降低鋼的抗點蝕性能。經過不同固溶溫度處理的DSS2507的擊破電位（Eb)值如表5.1所列。從表5.1可知DSS2507于3.5%NaCl溶液中的擊破電位（Eb)隨著固溶熱處理溫度的上升呈現先變大后減小的走勢，1050℃時點蝕電位值最高，表明該固溶溫度下2507雙相鋼發生點蝕的傾向較低。固溶溫度為1000℃時2507雙相不銹鋼中鐵素體相跟奧氏體相界處有σ相析出，其附近較易形成貧鉻及貧鉬區域，造成該固溶熱處理溫度下鋼的抗點腐蝕能力較弱；1050℃時DSS2507中的兩相結構（鐵素體α相及奧氏體y相）分布較均勻，相比例約為1:1,有利于鋼表面鈍化膜的穩定，進而對點蝕具有較好的抑制作用，表現為點蝕電位Eb值較高；然而隨固溶熱處理溫度繼續上升，鐵素體α相量增多奧氏體γ相量減少，導致鐵素體形成元素Cr和Mo的濃度減小，而奧氏體形成元素N濃度升高，因此Cr、Mo和N在這兩種組織結構中的分布變得不均勻，由于Cr、Mo和N是鋼的主要耐點蝕元素，因此鋼的耐腐蝕能力降低。具體表現為點蝕電位E,值降低，所以在1050~1200℃溫度范圍內2507雙相不銹鋼的點蝕電位降低。此外從表5.1中列出的（Eb-Ecom)值可以看出其值變化趨勢跟點蝕電位（Eb)值的變化趨勢相同，都呈先升高后降低的趨勢。由于（Eb-Ecom)差值表示形核阻力的大小，因此由（Eb-Ecom)差值變化趨勢可知點蝕形核的阻力也是先增大后減小，即隨著固溶溫度的升高鋼的抗點蝕性能呈先增強后減弱的趨勢。此外從表5.1中可以看出，隨固溶熱處理溫度的上升自腐蝕電流密度（Icorr)先降低后增高，1050℃時自腐蝕電流密度較低為3.5367×10-7A/c㎡.綜上所述，固溶處理溫度為1050℃時2507雙相不銹鋼有較好的抗腐蝕能力。

  固溶態為1050℃的(de)(de)2507雙相(xiang)(xiang)(xiang)不(bu)銹鋼(gang)于(yu)(yu)3.5%NaCl溶液中(zhong)動電(dian)位(wei)極(ji)化后的(de)(de)腐蝕(shi)形(xing)貌如(ru)圖5.4所示，圖中(zhong)深(shen)色是鐵(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)、淺色是奧(ao)(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)y相(xiang)(xiang)(xiang)、黑(hei)色圓點(dian)(dian)是點(dian)(dian)蝕(shi)坑(keng)。從(cong)圖5.4可(ke)知點(dian)(dian)蝕(shi)坑(keng)主要存在(zai)(zai)于(yu)(yu)鐵(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)x相(xiang)(xiang)(xiang)上，這說明奧(ao)(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)y相(xiang)(xiang)(xiang)比(bi)(bi)鐵(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)要穩定，有(you)著(zhu)較優的(de)(de)抗(kang)點(dian)(dian)腐蝕(shi)性能(neng)(neng)(neng)。奧(ao)(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)相(xiang)(xiang)(xiang)比(bi)(bi)于(yu)(yu)鐵(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)有(you)較好(hao)的(de)(de)抗(kang)點(dian)(dian)蝕(shi)性能(neng)(neng)(neng)的(de)(de)原因在(zai)(zai)于(yu)(yu)元(yuan)素(su)(su)(su)(su)(su)N的(de)(de)作用(yong)。元(yuan)素(su)(su)(su)(su)(su)N是奧(ao)(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)形(xing)成元(yuan)素(su)(su)(su)(su)(su)，于(yu)(yu)奧(ao)(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)中(zhong)的(de)(de)溶解度要比(bi)(bi)在(zai)(zai)鐵(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)中(zhong)的(de)(de)大，此外N能(neng)(neng)(neng)夠讓(rang)Cr和Mo元(yuan)素(su)(su)(su)(su)(su)從(cong)鐵(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)遷移到奧(ao)(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)中(zhong)，N顯著(zhu)影響著(zhu)這兩(liang)種元(yuan)素(su)(su)(su)(su)(su)在(zai)(zai)奧(ao)(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)和鐵(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)中(zhong)的(de)(de)分(fen)配，兩(liang)相(xiang)(xiang)(xiang)中(zhong)合金(jin)元(yuan)素(su)(su)(su)(su)(su)含量(liang)的(de)(de)差(cha)值隨N元(yuan)素(su)(su)(su)(su)(su)含量(liang)的(de)(de)增多而(er)降低(di)，所以(yi)奧(ao)(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)的(de)(de)點(dian)(dian)蝕(shi)電(dian)位(wei)較鐵(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)要高，從(cong)而(er)蝕(shi)坑(keng)較先在(zai)(zai)Eb相(xiang)(xiang)(xiang)對比(bi)(bi)較低(di)的(de)(de)鐵(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)中(zhong)產生。

2. 交流阻抗測(ce)試分(fen)析

  1000℃、1050℃、1100℃、1150℃及(ji)1200℃固(gu)(gu)溶(rong)(rong)態(tai)的(de)(de)(de)(de)2507 雙(shuang)相(xiang)(xiang)(xiang)(xiang)不銹(xiu)(xiu)(xiu)鋼(gang)(gang)30℃下于3.5%NaCl溶(rong)(rong)液(ye)(ye)(ye)中(zhong)(zhong)的(de)(de)(de)(de)Nyquist 圖如圖5.5所示(shi)(shi)，從圖中(zhong)(zhong)可以(yi)很(hen)明顯看出(chu)隨固(gu)(gu)溶(rong)(rong)熱(re)(re)處(chu)理(li)溫(wen)度(du)的(de)(de)(de)(de)增(zeng)高(gao)(gao)(gao)容(rong)抗(kang)弧半(ban)徑(jing)先(xian)(xian)(xian)增(zeng)大(da)(da)后(hou)(hou)(hou)減(jian)小(xiao)(xiao)(xiao)，1050℃時容(rong)抗(kang)弧半(ban)徑(jing)最大(da)(da)。通常情況下界(jie)面間(jian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)的(de)(de)(de)(de)遷移促進(jin)(jin)了高(gao)(gao)(gao)頻區容(rong)抗(kang)弧的(de)(de)(de)(de)形成(cheng)，容(rong)抗(kang)弧與雙(shuang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)層容(rong)抗(kang)及(ji)金屬(shu)材料溶(rong)(rong)解的(de)(de)(de)(de)綜合(he)作用有關，并且(qie)金屬(shu)－溶(rong)(rong)液(ye)(ye)(ye)界(jie)面的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)轉移電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)影響著(zhu)容(rong)抗(kang)弧半(ban)徑(jing)的(de)(de)(de)(de)大(da)(da)小(xiao)(xiao)(xiao)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)在(zai)金屬(shu)－溶(rong)(rong)液(ye)(ye)(ye)界(jie)面轉移時受到(dao)(dao)的(de)(de)(de)(de)阻(zu)(zu)(zu)力(li)(li)越(yue)(yue)強(qiang)意(yi)(yi)味(wei)著(zhu)容(rong)抗(kang)弧半(ban)徑(jing)越(yue)(yue)大(da)(da)，即(ji)意(yi)(yi)味(wei)著(zhu)金屬(shu)的(de)(de)(de)(de)抗(kang)蝕(shi)(shi)(shi)(shi)性能(neng)(neng)越(yue)(yue)優。從圖5.5容(rong)抗(kang)弧半(ban)徑(jing)的(de)(de)(de)(de)改變趨(qu)勢(shi)(shi)可知(zhi)，固(gu)(gu)溶(rong)(rong)熱(re)(re)處(chu)理(li)溫(wen)度(du)升高(gao)(gao)(gao)使DSS2507的(de)(de)(de)(de)耐蝕(shi)(shi)(shi)(shi)性能(neng)(neng)首先(xian)(xian)(xian)增(zeng)強(qiang)而后(hou)(hou)(hou)減(jian)弱(ruo)，1050℃時2507雙(shuang)相(xiang)(xiang)(xiang)(xiang)不銹(xiu)(xiu)(xiu)鋼(gang)(gang)的(de)(de)(de)(de)抗(kang)腐(fu)蝕(shi)(shi)(shi)(shi)性能(neng)(neng)最優。不同固(gu)(gu)溶(rong)(rong)態(tai)的(de)(de)(de)(de)2507雙(shuang)相(xiang)(xiang)(xiang)(xiang)不銹(xiu)(xiu)(xiu)鋼(gang)(gang)于3.5%NaCl溶(rong)(rong)液(ye)(ye)(ye)中(zhong)(zhong)的(de)(de)(de)(de)等效電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)如圖5.6所示(shi)(shi)，采用的(de)(de)(de)(de)是R(C(R(CR))).Rs指參比(bi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)極和(he)工(gong)作電(dian)(dian)(dian)(dian)(dian)(dian)(dian)極間(jian)的(de)(de)(de)(de)溶(rong)(rong)液(ye)(ye)(ye)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)；Cd1為(wei)(wei)(wei)(wei)雙(shuang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)層電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)；Rct為(wei)(wei)(wei)(wei)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)轉移電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)，其值(zhi)能(neng)(neng)夠反應(ying)(ying)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)在(zai)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)化學反應(ying)(ying)過程(cheng)中(zhong)(zhong)透過電(dian)(dian)(dian)(dian)(dian)(dian)(dian)極以(yi)及(ji)于電(dian)(dian)(dian)(dian)(dian)(dian)(dian)解質(zhi)溶(rong)(rong)液(ye)(ye)(ye)中(zhong)(zhong)兩(liang)相(xiang)(xiang)(xiang)(xiang)界(jie)面遷移難(nan)易的(de)(de)(de)(de)大(da)(da)小(xiao)(xiao)(xiao)，也能(neng)(neng)夠反映金屬(shu)發生腐(fu)蝕(shi)(shi)(shi)(shi)反應(ying)(ying)的(de)(de)(de)(de)快慢，一般情況下Rct值(zhi)越(yue)(yue)高(gao)(gao)(gao)意(yi)(yi)味(wei)著(zhu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)遷移過程(cheng)中(zhong)(zhong)所受的(de)(de)(de)(de)阻(zu)(zu)(zu)力(li)(li)越(yue)(yue)強(qiang)，即(ji)材料的(de)(de)(de)(de)耐腐(fu)蝕(shi)(shi)(shi)(shi)性能(neng)(neng)越(yue)(yue)好；Cf表(biao)(biao)示(shi)(shi)鈍(dun)(dun)(dun)化膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)，Rf表(biao)(biao)示(shi)(shi)鈍(dun)(dun)(dun)化膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)。采用ZsimpWin軟件對等效電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)模擬計算得到(dao)(dao)各元(yuan)件的(de)(de)(de)(de)數值(zhi)如表(biao)(biao)5.2所列。從表(biao)(biao)中(zhong)(zhong)看出(chu)雙(shuang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)層電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)（Cdl)及(ji)鈍(dun)(dun)(dun)化膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)（Cr)隨固(gu)(gu)溶(rong)(rong)溫(wen)度(du)的(de)(de)(de)(de)升高(gao)(gao)(gao)呈先(xian)(xian)(xian)減(jian)小(xiao)(xiao)(xiao)后(hou)(hou)(hou)增(zeng)大(da)(da)的(de)(de)(de)(de)趨(qu)勢(shi)(shi)；電(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)轉移電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)（Rct)和(he)鈍(dun)(dun)(dun)化膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)（Rf)呈先(xian)(xian)(xian)變大(da)(da)后(hou)(hou)(hou)減(jian)小(xiao)(xiao)(xiao)的(de)(de)(de)(de)趨(qu)勢(shi)(shi)，即(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)化學反應(ying)(ying)阻(zu)(zu)(zu)力(li)(li)隨固(gu)(gu)溶(rong)(rong)熱(re)(re)處(chu)理(li)溫(wen)度(du)的(de)(de)(de)(de)增(zeng)高(gao)(gao)(gao)先(xian)(xian)(xian)增(zeng)強(qiang)后(hou)(hou)(hou)減(jian)弱(ruo)，2507雙(shuang)相(xiang)(xiang)(xiang)(xiang)不銹(xiu)(xiu)(xiu)鋼(gang)(gang)的(de)(de)(de)(de)抗(kang)腐(fu)蝕(shi)(shi)(shi)(shi)性能(neng)(neng)表(biao)(biao)現(xian)為(wei)(wei)(wei)(wei)先(xian)(xian)(xian)增(zeng)強(qiang)后(hou)(hou)(hou)減(jian)弱(ruo)。1000℃時鋼(gang)(gang)的(de)(de)(de)(de)相(xiang)(xiang)(xiang)(xiang)界(jie)處(chu)有σ相(xiang)(xiang)(xiang)(xiang)析出(chu)，σ相(xiang)(xiang)(xiang)(xiang)硬而脆降低了鋼(gang)(gang)表(biao)(biao)面鈍(dun)(dun)(dun)化膜(mo)的(de)(de)(de)(de)穩(wen)定，表(biao)(biao)現(xian)為(wei)(wei)(wei)(wei)具(ju)有較(jiao)低的(de)(de)(de)(de)鈍(dun)(dun)(dun)化膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)（Rf);1050℃時鋼(gang)(gang)中(zhong)(zhong)的(de)(de)(de)(de)兩(liang)相(xiang)(xiang)(xiang)(xiang)比(bi)例(li)約為(wei)(wei)(wei)(wei)1:1,兩(liang)相(xiang)(xiang)(xiang)(xiang)分(fen)布較(jiao)均勻且(qie)成(cheng)分(fen)穩(wen)定有利于鈍(dun)(dun)(dun)化膜(mo)的(de)(de)(de)(de)穩(wen)定，具(ju)體表(biao)(biao)現(xian)為(wei)(wei)(wei)(wei)鈍(dun)(dun)(dun)化膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)（Rf)值(zhi)較(jiao)高(gao)(gao)(gao)，表(biao)(biao)明此刻離子(zi)遷移時所受阻(zu)(zu)(zu)力(li)(li)較(jiao)大(da)(da)，進(jin)(jin)而2507雙(shuang)相(xiang)(xiang)(xiang)(xiang)不銹(xiu)(xiu)(xiu)鋼(gang)(gang)的(de)(de)(de)(de)抗(kang)腐(fu)蝕(shi)(shi)(shi)(shi)能(neng)(neng)力(li)(li)最佳(jia)；固(gu)(gu)溶(rong)(rong)熱(re)(re)處(chu)理(li)溫(wen)度(du)的(de)(de)(de)(de)進(jin)(jin)一步升高(gao)(gao)(gao)使鋼(gang)(gang)中(zhong)(zhong)的(de)(de)(de)(de)兩(liang)相(xiang)(xiang)(xiang)(xiang)比(bi)例(li)失調(diao)，表(biao)(biao)現(xian)為(wei)(wei)(wei)(wei)鐵素體相(xiang)(xiang)(xiang)(xiang)含量大(da)(da)幅升高(gao)(gao)(gao)，奧氏(shi)體相(xiang)(xiang)(xiang)(xiang)含量減(jian)小(xiao)(xiao)(xiao)，不利于鋼(gang)(gang)表(biao)(biao)面鈍(dun)(dun)(dun)化膜(mo)的(de)(de)(de)(de)穩(wen)定，導(dao)致鈍(dun)(dun)(dun)化膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)（Rf)減(jian)小(xiao)(xiao)(xiao)，實(shi)際表(biao)(biao)現(xian)為(wei)(wei)(wei)(wei)鋼(gang)(gang)的(de)(de)(de)(de)抗(kang)蝕(shi)(shi)(shi)(shi)性能(neng)(neng)下降，這與動電(dian)(dian)(dian)(dian)(dian)(dian)(dian)位掃(sao)描獲(huo)得的(de)(de)(de)(de)結論(lun)相(xiang)(xiang)(xiang)(xiang)同。