1. 動電(dian)位極化曲線分(fen)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(shuang)相不銹鋼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(shuang)相不銹(xiu)鋼(gang)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(gu)溶(rong)(rong)態(tai)為1050℃的(de)(de)2507雙相(xiang)(xiang)(xiang)不銹(xiu)鋼(gang)于(yu)3.5%NaCl溶(rong)(rong)液(ye)中(zhong)(zhong)動電(dian)位極化后的(de)(de)腐蝕形(xing)貌如圖5.4所示，圖中(zhong)(zhong)深色是(shi)鐵素(su)(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)、淺(qian)色是(shi)奧(ao)氏體(ti)(ti)(ti)y相(xiang)(xiang)(xiang)、黑色圓點(dian)是(shi)點(dian)蝕坑(keng)。從(cong)圖5.4可知點(dian)蝕坑(keng)主要(yao)存在(zai)(zai)于(yu)鐵素(su)(su)(su)(su)(su)體(ti)(ti)(ti)x相(xiang)(xiang)(xiang)上，這(zhe)(zhe)說明奧(ao)氏體(ti)(ti)(ti)y相(xiang)(xiang)(xiang)比鐵素(su)(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)要(yao)穩定，有著較(jiao)優的(de)(de)抗點(dian)腐蝕性能。奧(ao)氏體(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)相(xiang)(xiang)(xiang)比于(yu)鐵素(su)(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)有較(jiao)好的(de)(de)抗點(dian)蝕性能的(de)(de)原因在(zai)(zai)于(yu)元(yuan)(yuan)素(su)(su)(su)(su)(su)N的(de)(de)作用。元(yuan)(yuan)素(su)(su)(su)(su)(su)N是(shi)奧(ao)氏體(ti)(ti)(ti)形(xing)成元(yuan)(yuan)素(su)(su)(su)(su)(su)，于(yu)奧(ao)氏體(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)中(zhong)(zhong)的(de)(de)溶(rong)(rong)解度要(yao)比在(zai)(zai)鐵素(su)(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)中(zhong)(zhong)的(de)(de)大，此外N能夠讓(rang)Cr和Mo元(yuan)(yuan)素(su)(su)(su)(su)(su)從(cong)鐵素(su)(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)遷(qian)移到奧(ao)氏體(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)中(zhong)(zhong)，N顯(xian)著影響著這(zhe)(zhe)兩種元(yuan)(yuan)素(su)(su)(su)(su)(su)在(zai)(zai)奧(ao)氏體(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)和鐵素(su)(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)中(zhong)(zhong)的(de)(de)分配，兩相(xiang)(xiang)(xiang)中(zhong)(zhong)合(he)金元(yuan)(yuan)素(su)(su)(su)(su)(su)含(han)量(liang)的(de)(de)差值隨N元(yuan)(yuan)素(su)(su)(su)(su)(su)含(han)量(liang)的(de)(de)增多(duo)而降低，所以奧(ao)氏體(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)的(de)(de)點(dian)蝕電(dian)位較(jiao)鐵素(su)(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)要(yao)高，從(cong)而蝕坑(keng)較(jiao)先在(zai)(zai)Eb相(xiang)(xiang)(xiang)對比較(jiao)低的(de)(de)鐵素(su)(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)中(zhong)(zhong)產生(sheng)。

2. 交(jiao)流阻抗測試分析

  1000℃、1050℃、1100℃、1150℃及1200℃固(gu)溶(rong)態的(de)(de)(de)(de)(de)(de)2507 雙(shuang)(shuang)相(xiang)(xiang)(xiang)不銹鋼30℃下(xia)(xia)于(yu)3.5%NaCl溶(rong)液(ye)中的(de)(de)(de)(de)(de)(de)Nyquist 圖如(ru)(ru)圖5.5所(suo)示(shi)，從圖中可(ke)以(yi)很明顯看出(chu)隨固(gu)溶(rong)熱(re)(re)處(chu)(chu)(chu)理(li)(li)溫(wen)度(du)(du)的(de)(de)(de)(de)(de)(de)增(zeng)高(gao)(gao)(gao)容(rong)(rong)(rong)(rong)抗(kang)(kang)(kang)弧半(ban)(ban)(ban)徑先增(zeng)大后(hou)減(jian)小，1050℃時(shi)(shi)容(rong)(rong)(rong)(rong)抗(kang)(kang)(kang)弧半(ban)(ban)(ban)徑最(zui)大。通常情況下(xia)(xia)界面間電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)(he)(he)的(de)(de)(de)(de)(de)(de)遷(qian)移(yi)促進了(le)高(gao)(gao)(gao)頻區(qu)容(rong)(rong)(rong)(rong)抗(kang)(kang)(kang)弧的(de)(de)(de)(de)(de)(de)形成，容(rong)(rong)(rong)(rong)抗(kang)(kang)(kang)弧與雙(shuang)(shuang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)層容(rong)(rong)(rong)(rong)抗(kang)(kang)(kang)及金屬材料(liao)溶(rong)解的(de)(de)(de)(de)(de)(de)綜合作(zuo)用有關，并(bing)且金屬－溶(rong)液(ye)界面的(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)(he)(he)轉移(yi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)影響著(zhu)(zhu)容(rong)(rong)(rong)(rong)抗(kang)(kang)(kang)弧半(ban)(ban)(ban)徑的(de)(de)(de)(de)(de)(de)大小，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)(he)(he)在金屬－溶(rong)液(ye)界面轉移(yi)時(shi)(shi)受到的(de)(de)(de)(de)(de)(de)阻(zu)(zu)(zu)(zu)力(li)(li)越(yue)強意(yi)味著(zhu)(zhu)容(rong)(rong)(rong)(rong)抗(kang)(kang)(kang)弧半(ban)(ban)(ban)徑越(yue)大，即意(yi)味著(zhu)(zhu)金屬的(de)(de)(de)(de)(de)(de)抗(kang)(kang)(kang)蝕(shi)(shi)性(xing)能(neng)越(yue)優。從圖5.5容(rong)(rong)(rong)(rong)抗(kang)(kang)(kang)弧半(ban)(ban)(ban)徑的(de)(de)(de)(de)(de)(de)改變(bian)趨勢可(ke)知，固(gu)溶(rong)熱(re)(re)處(chu)(chu)(chu)理(li)(li)溫(wen)度(du)(du)升(sheng)(sheng)高(gao)(gao)(gao)使DSS2507的(de)(de)(de)(de)(de)(de)耐蝕(shi)(shi)性(xing)能(neng)首先增(zeng)強而(er)后(hou)減(jian)弱(ruo)，1050℃時(shi)(shi)2507雙(shuang)(shuang)相(xiang)(xiang)(xiang)不銹鋼的(de)(de)(de)(de)(de)(de)抗(kang)(kang)(kang)腐(fu)蝕(shi)(shi)性(xing)能(neng)最(zui)優。不同固(gu)溶(rong)態的(de)(de)(de)(de)(de)(de)2507雙(shuang)(shuang)相(xiang)(xiang)(xiang)不銹鋼于(yu)3.5%NaCl溶(rong)液(ye)中的(de)(de)(de)(de)(de)(de)等效(xiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)如(ru)(ru)圖5.6所(suo)示(shi)，采用的(de)(de)(de)(de)(de)(de)是R(C(R(CR))).Rs指參比(bi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)和工作(zuo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)間的(de)(de)(de)(de)(de)(de)溶(rong)液(ye)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)；Cd1為(wei)(wei)雙(shuang)(shuang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)層電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)；Rct為(wei)(wei)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)(he)(he)轉移(yi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)，其值(zhi)(zhi)能(neng)夠(gou)(gou)反(fan)(fan)應(ying)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)(he)(he)在電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)化(hua)學(xue)反(fan)(fan)應(ying)過(guo)程中透過(guo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)以(yi)及于(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)解質(zhi)溶(rong)液(ye)中兩相(xiang)(xiang)(xiang)界面遷(qian)移(yi)難易的(de)(de)(de)(de)(de)(de)大小，也能(neng)夠(gou)(gou)反(fan)(fan)映金屬發生(sheng)腐(fu)蝕(shi)(shi)反(fan)(fan)應(ying)的(de)(de)(de)(de)(de)(de)快慢，一般(ban)情況下(xia)(xia)Rct值(zhi)(zhi)越(yue)高(gao)(gao)(gao)意(yi)味著(zhu)(zhu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)(he)(he)遷(qian)移(yi)過(guo)程中所(suo)受的(de)(de)(de)(de)(de)(de)阻(zu)(zu)(zu)(zu)力(li)(li)越(yue)強，即材料(liao)的(de)(de)(de)(de)(de)(de)耐腐(fu)蝕(shi)(shi)性(xing)能(neng)越(yue)好；Cf表(biao)(biao)示(shi)鈍(dun)(dun)化(hua)膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)，Rf表(biao)(biao)示(shi)鈍(dun)(dun)化(hua)膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)。采用ZsimpWin軟件(jian)對等效(xiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)模擬計(ji)算(suan)得到各元件(jian)的(de)(de)(de)(de)(de)(de)數值(zhi)(zhi)如(ru)(ru)表(biao)(biao)5.2所(suo)列。從表(biao)(biao)中看出(chu)雙(shuang)(shuang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)層電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)（Cdl)及鈍(dun)(dun)化(hua)膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)（Cr)隨固(gu)溶(rong)溫(wen)度(du)(du)的(de)(de)(de)(de)(de)(de)升(sheng)(sheng)高(gao)(gao)(gao)呈先減(jian)小后(hou)增(zeng)大的(de)(de)(de)(de)(de)(de)趨勢；電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)(he)(he)轉移(yi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)（Rct)和鈍(dun)(dun)化(hua)膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)（Rf)呈先變(bian)大后(hou)減(jian)小的(de)(de)(de)(de)(de)(de)趨勢，即電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)化(hua)學(xue)反(fan)(fan)應(ying)阻(zu)(zu)(zu)(zu)力(li)(li)隨固(gu)溶(rong)熱(re)(re)處(chu)(chu)(chu)理(li)(li)溫(wen)度(du)(du)的(de)(de)(de)(de)(de)(de)增(zeng)高(gao)(gao)(gao)先增(zeng)強后(hou)減(jian)弱(ruo)，2507雙(shuang)(shuang)相(xiang)(xiang)(xiang)不銹鋼的(de)(de)(de)(de)(de)(de)抗(kang)(kang)(kang)腐(fu)蝕(shi)(shi)性(xing)能(neng)表(biao)(biao)現為(wei)(wei)先增(zeng)強后(hou)減(jian)弱(ruo)。1000℃時(shi)(shi)鋼的(de)(de)(de)(de)(de)(de)相(xiang)(xiang)(xiang)界處(chu)(chu)(chu)有σ相(xiang)(xiang)(xiang)析出(chu)，σ相(xiang)(xiang)(xiang)硬而(er)脆(cui)降低(di)了(le)鋼表(biao)(biao)面鈍(dun)(dun)化(hua)膜(mo)的(de)(de)(de)(de)(de)(de)穩定(ding)(ding)，表(biao)(biao)現為(wei)(wei)具有較(jiao)(jiao)低(di)的(de)(de)(de)(de)(de)(de)鈍(dun)(dun)化(hua)膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)（Rf);1050℃時(shi)(shi)鋼中的(de)(de)(de)(de)(de)(de)兩相(xiang)(xiang)(xiang)比(bi)例約為(wei)(wei)1:1,兩相(xiang)(xiang)(xiang)分(fen)布較(jiao)(jiao)均勻且成分(fen)穩定(ding)(ding)有利于(yu)鈍(dun)(dun)化(hua)膜(mo)的(de)(de)(de)(de)(de)(de)穩定(ding)(ding)，具體表(biao)(biao)現為(wei)(wei)鈍(dun)(dun)化(hua)膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)（Rf)值(zhi)(zhi)較(jiao)(jiao)高(gao)(gao)(gao)，表(biao)(biao)明此(ci)刻離子遷(qian)移(yi)時(shi)(shi)所(suo)受阻(zu)(zu)(zu)(zu)力(li)(li)較(jiao)(jiao)大，進而(er)2507雙(shuang)(shuang)相(xiang)(xiang)(xiang)不銹鋼的(de)(de)(de)(de)(de)(de)抗(kang)(kang)(kang)腐(fu)蝕(shi)(shi)能(neng)力(li)(li)最(zui)佳；固(gu)溶(rong)熱(re)(re)處(chu)(chu)(chu)理(li)(li)溫(wen)度(du)(du)的(de)(de)(de)(de)(de)(de)進一步升(sheng)(sheng)高(gao)(gao)(gao)使鋼中的(de)(de)(de)(de)(de)(de)兩相(xiang)(xiang)(xiang)比(bi)例失調，表(biao)(biao)現為(wei)(wei)鐵素體相(xiang)(xiang)(xiang)含量(liang)大幅升(sheng)(sheng)高(gao)(gao)(gao)，奧氏體相(xiang)(xiang)(xiang)含量(liang)減(jian)小，不利于(yu)鋼表(biao)(biao)面鈍(dun)(dun)化(hua)膜(mo)的(de)(de)(de)(de)(de)(de)穩定(ding)(ding)，導致(zhi)鈍(dun)(dun)化(hua)膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)（Rf)減(jian)小，實際(ji)表(biao)(biao)現為(wei)(wei)鋼的(de)(de)(de)(de)(de)(de)抗(kang)(kang)(kang)蝕(shi)(shi)性(xing)能(neng)下(xia)(xia)降，這與動電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)位掃描獲得的(de)(de)(de)(de)(de)(de)結論相(xiang)(xiang)(xiang)同。