1. 動電位極化(hua)曲線分析(xi)

  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(wei)1050℃的(de)(de)(de)2507雙相(xiang)(xiang)(xiang)(xiang)(xiang)不銹(xiu)鋼(gang)于(yu)3.5%NaCl溶液中(zhong)(zhong)(zhong)動電(dian)位(wei)極化后(hou)的(de)(de)(de)腐蝕(shi)形貌(mao)如圖5.4所(suo)示，圖中(zhong)(zhong)(zhong)深色是鐵(tie)素(su)(su)體(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)(xiang)、淺色是奧氏體(ti)(ti)(ti)(ti)(ti)y相(xiang)(xiang)(xiang)(xiang)(xiang)、黑色圓點(dian)是點(dian)蝕(shi)坑(keng)。從圖5.4可知點(dian)蝕(shi)坑(keng)主要存在(zai)(zai)(zai)于(yu)鐵(tie)素(su)(su)體(ti)(ti)(ti)(ti)(ti)x相(xiang)(xiang)(xiang)(xiang)(xiang)上，這(zhe)說明奧氏體(ti)(ti)(ti)(ti)(ti)y相(xiang)(xiang)(xiang)(xiang)(xiang)比(bi)(bi)鐵(tie)素(su)(su)體(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)(xiang)要穩(wen)定，有著較(jiao)優的(de)(de)(de)抗點(dian)腐蝕(shi)性(xing)能(neng)。奧氏體(ti)(ti)(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)(xiang)(xiang)相(xiang)(xiang)(xiang)(xiang)(xiang)比(bi)(bi)于(yu)鐵(tie)素(su)(su)體(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)(xiang)有較(jiao)好的(de)(de)(de)抗點(dian)蝕(shi)性(xing)能(neng)的(de)(de)(de)原因在(zai)(zai)(zai)于(yu)元(yuan)(yuan)素(su)(su)N的(de)(de)(de)作(zuo)用。元(yuan)(yuan)素(su)(su)N是奧氏體(ti)(ti)(ti)(ti)(ti)形成元(yuan)(yuan)素(su)(su)，于(yu)奧氏體(ti)(ti)(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)的(de)(de)(de)溶解度要比(bi)(bi)在(zai)(zai)(zai)鐵(tie)素(su)(su)體(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)的(de)(de)(de)大，此外N能(neng)夠讓(rang)Cr和Mo元(yuan)(yuan)素(su)(su)從鐵(tie)素(su)(su)體(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)(xiang)遷移(yi)到奧氏體(ti)(ti)(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)，N顯著影響著這(zhe)兩種元(yuan)(yuan)素(su)(su)在(zai)(zai)(zai)奧氏體(ti)(ti)(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)(xiang)(xiang)和鐵(tie)素(su)(su)體(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)的(de)(de)(de)分配，兩相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)合金元(yuan)(yuan)素(su)(su)含(han)量(liang)的(de)(de)(de)差值隨(sui)N元(yuan)(yuan)素(su)(su)含(han)量(liang)的(de)(de)(de)增多而(er)降(jiang)低，所(suo)以奧氏體(ti)(ti)(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)(xiang)(xiang)的(de)(de)(de)點(dian)蝕(shi)電(dian)位(wei)較(jiao)鐵(tie)素(su)(su)體(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)(xiang)要高，從而(er)蝕(shi)坑(keng)較(jiao)先在(zai)(zai)(zai)Eb相(xiang)(xiang)(xiang)(xiang)(xiang)對比(bi)(bi)較(jiao)低的(de)(de)(de)鐵(tie)素(su)(su)體(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)產(chan)生(sheng)。

2. 交流阻抗測試分析

  1000℃、1050℃、1100℃、1150℃及1200℃固溶(rong)(rong)(rong)(rong)態(tai)的(de)(de)(de)(de)(de)2507 雙(shuang)(shuang)(shuang)相(xiang)(xiang)(xiang)(xiang)不(bu)(bu)銹(xiu)(xiu)(xiu)鋼(gang)(gang)30℃下于3.5%NaCl溶(rong)(rong)(rong)(rong)液(ye)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)Nyquist 圖如圖5.5所(suo)示(shi)，從圖中(zhong)(zhong)(zhong)可以很明(ming)(ming)顯看(kan)出(chu)隨(sui)固溶(rong)(rong)(rong)(rong)熱(re)處(chu)(chu)理溫(wen)度(du)的(de)(de)(de)(de)(de)增高(gao)(gao)(gao)容(rong)(rong)(rong)(rong)抗(kang)(kang)(kang)弧(hu)(hu)(hu)半(ban)徑(jing)(jing)先(xian)(xian)增大(da)(da)(da)后(hou)減小(xiao)，1050℃時(shi)容(rong)(rong)(rong)(rong)抗(kang)(kang)(kang)弧(hu)(hu)(hu)半(ban)徑(jing)(jing)最大(da)(da)(da)。通(tong)常情(qing)況(kuang)下界(jie)(jie)(jie)面(mian)間(jian)電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)的(de)(de)(de)(de)(de)遷移(yi)(yi)促進了(le)高(gao)(gao)(gao)頻區容(rong)(rong)(rong)(rong)抗(kang)(kang)(kang)弧(hu)(hu)(hu)的(de)(de)(de)(de)(de)形成(cheng)(cheng)，容(rong)(rong)(rong)(rong)抗(kang)(kang)(kang)弧(hu)(hu)(hu)與雙(shuang)(shuang)(shuang)電(dian)(dian)(dian)(dian)(dian)(dian)層容(rong)(rong)(rong)(rong)抗(kang)(kang)(kang)及金(jin)(jin)(jin)屬材料溶(rong)(rong)(rong)(rong)解的(de)(de)(de)(de)(de)綜合作(zuo)用(yong)有(you)(you)關，并且金(jin)(jin)(jin)屬－溶(rong)(rong)(rong)(rong)液(ye)界(jie)(jie)(jie)面(mian)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)轉(zhuan)(zhuan)移(yi)(yi)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)影響著(zhu)容(rong)(rong)(rong)(rong)抗(kang)(kang)(kang)弧(hu)(hu)(hu)半(ban)徑(jing)(jing)的(de)(de)(de)(de)(de)大(da)(da)(da)小(xiao)，電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)在金(jin)(jin)(jin)屬－溶(rong)(rong)(rong)(rong)液(ye)界(jie)(jie)(jie)面(mian)轉(zhuan)(zhuan)移(yi)(yi)時(shi)受(shou)到的(de)(de)(de)(de)(de)阻(zu)(zu)力(li)(li)越(yue)(yue)強意(yi)(yi)味著(zhu)容(rong)(rong)(rong)(rong)抗(kang)(kang)(kang)弧(hu)(hu)(hu)半(ban)徑(jing)(jing)越(yue)(yue)大(da)(da)(da)，即意(yi)(yi)味著(zhu)金(jin)(jin)(jin)屬的(de)(de)(de)(de)(de)抗(kang)(kang)(kang)蝕(shi)性(xing)(xing)能(neng)(neng)(neng)越(yue)(yue)優。從圖5.5容(rong)(rong)(rong)(rong)抗(kang)(kang)(kang)弧(hu)(hu)(hu)半(ban)徑(jing)(jing)的(de)(de)(de)(de)(de)改變(bian)(bian)趨勢(shi)(shi)可知(zhi)，固溶(rong)(rong)(rong)(rong)熱(re)處(chu)(chu)理溫(wen)度(du)升高(gao)(gao)(gao)使DSS2507的(de)(de)(de)(de)(de)耐(nai)蝕(shi)性(xing)(xing)能(neng)(neng)(neng)首(shou)先(xian)(xian)增強而(er)后(hou)減弱，1050℃時(shi)2507雙(shuang)(shuang)(shuang)相(xiang)(xiang)(xiang)(xiang)不(bu)(bu)銹(xiu)(xiu)(xiu)鋼(gang)(gang)的(de)(de)(de)(de)(de)抗(kang)(kang)(kang)腐(fu)蝕(shi)性(xing)(xing)能(neng)(neng)(neng)最優。不(bu)(bu)同(tong)固溶(rong)(rong)(rong)(rong)態(tai)的(de)(de)(de)(de)(de)2507雙(shuang)(shuang)(shuang)相(xiang)(xiang)(xiang)(xiang)不(bu)(bu)銹(xiu)(xiu)(xiu)鋼(gang)(gang)于3.5%NaCl溶(rong)(rong)(rong)(rong)液(ye)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)等(deng)效電(dian)(dian)(dian)(dian)(dian)(dian)路如圖5.6所(suo)示(shi)，采用(yong)的(de)(de)(de)(de)(de)是R(C(R(CR))).Rs指(zhi)參(can)比(bi)電(dian)(dian)(dian)(dian)(dian)(dian)極和工(gong)作(zuo)電(dian)(dian)(dian)(dian)(dian)(dian)極間(jian)的(de)(de)(de)(de)(de)溶(rong)(rong)(rong)(rong)液(ye)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)；Cd1為(wei)(wei)(wei)(wei)雙(shuang)(shuang)(shuang)電(dian)(dian)(dian)(dian)(dian)(dian)層電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)；Rct為(wei)(wei)(wei)(wei)電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)轉(zhuan)(zhuan)移(yi)(yi)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)，其值能(neng)(neng)(neng)夠反(fan)(fan)應電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)在電(dian)(dian)(dian)(dian)(dian)(dian)化(hua)(hua)學反(fan)(fan)應過(guo)(guo)程中(zhong)(zhong)(zhong)透過(guo)(guo)電(dian)(dian)(dian)(dian)(dian)(dian)極以及于電(dian)(dian)(dian)(dian)(dian)(dian)解質溶(rong)(rong)(rong)(rong)液(ye)中(zhong)(zhong)(zhong)兩相(xiang)(xiang)(xiang)(xiang)界(jie)(jie)(jie)面(mian)遷移(yi)(yi)難易的(de)(de)(de)(de)(de)大(da)(da)(da)小(xiao)，也能(neng)(neng)(neng)夠反(fan)(fan)映金(jin)(jin)(jin)屬發生腐(fu)蝕(shi)反(fan)(fan)應的(de)(de)(de)(de)(de)快慢，一般情(qing)況(kuang)下Rct值越(yue)(yue)高(gao)(gao)(gao)意(yi)(yi)味著(zhu)電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)遷移(yi)(yi)過(guo)(guo)程中(zhong)(zhong)(zhong)所(suo)受(shou)的(de)(de)(de)(de)(de)阻(zu)(zu)力(li)(li)越(yue)(yue)強，即材料的(de)(de)(de)(de)(de)耐(nai)腐(fu)蝕(shi)性(xing)(xing)能(neng)(neng)(neng)越(yue)(yue)好；Cf表(biao)(biao)(biao)(biao)示(shi)鈍(dun)(dun)化(hua)(hua)膜(mo)(mo)(mo)(mo)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)，Rf表(biao)(biao)(biao)(biao)示(shi)鈍(dun)(dun)化(hua)(hua)膜(mo)(mo)(mo)(mo)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)。采用(yong)ZsimpWin軟(ruan)件對等(deng)效電(dian)(dian)(dian)(dian)(dian)(dian)路模擬計(ji)算得到各元件的(de)(de)(de)(de)(de)數值如表(biao)(biao)(biao)(biao)5.2所(suo)列。從表(biao)(biao)(biao)(biao)中(zhong)(zhong)(zhong)看(kan)出(chu)雙(shuang)(shuang)(shuang)電(dian)(dian)(dian)(dian)(dian)(dian)層電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)（Cdl)及鈍(dun)(dun)化(hua)(hua)膜(mo)(mo)(mo)(mo)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)（Cr)隨(sui)固溶(rong)(rong)(rong)(rong)溫(wen)度(du)的(de)(de)(de)(de)(de)升高(gao)(gao)(gao)呈(cheng)先(xian)(xian)減小(xiao)后(hou)增大(da)(da)(da)的(de)(de)(de)(de)(de)趨勢(shi)(shi)；電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)轉(zhuan)(zhuan)移(yi)(yi)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)（Rct)和鈍(dun)(dun)化(hua)(hua)膜(mo)(mo)(mo)(mo)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)（Rf)呈(cheng)先(xian)(xian)變(bian)(bian)大(da)(da)(da)后(hou)減小(xiao)的(de)(de)(de)(de)(de)趨勢(shi)(shi)，即電(dian)(dian)(dian)(dian)(dian)(dian)化(hua)(hua)學反(fan)(fan)應阻(zu)(zu)力(li)(li)隨(sui)固溶(rong)(rong)(rong)(rong)熱(re)處(chu)(chu)理溫(wen)度(du)的(de)(de)(de)(de)(de)增高(gao)(gao)(gao)先(xian)(xian)增強后(hou)減弱，2507雙(shuang)(shuang)(shuang)相(xiang)(xiang)(xiang)(xiang)不(bu)(bu)銹(xiu)(xiu)(xiu)鋼(gang)(gang)的(de)(de)(de)(de)(de)抗(kang)(kang)(kang)腐(fu)蝕(shi)性(xing)(xing)能(neng)(neng)(neng)表(biao)(biao)(biao)(biao)現(xian)為(wei)(wei)(wei)(wei)先(xian)(xian)增強后(hou)減弱。1000℃時(shi)鋼(gang)(gang)的(de)(de)(de)(de)(de)相(xiang)(xiang)(xiang)(xiang)界(jie)(jie)(jie)處(chu)(chu)有(you)(you)σ相(xiang)(xiang)(xiang)(xiang)析(xi)出(chu)，σ相(xiang)(xiang)(xiang)(xiang)硬而(er)脆(cui)降低了(le)鋼(gang)(gang)表(biao)(biao)(biao)(biao)面(mian)鈍(dun)(dun)化(hua)(hua)膜(mo)(mo)(mo)(mo)的(de)(de)(de)(de)(de)穩定，表(biao)(biao)(biao)(biao)現(xian)為(wei)(wei)(wei)(wei)具有(you)(you)較(jiao)(jiao)低的(de)(de)(de)(de)(de)鈍(dun)(dun)化(hua)(hua)膜(mo)(mo)(mo)(mo)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)（Rf);1050℃時(shi)鋼(gang)(gang)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)兩相(xiang)(xiang)(xiang)(xiang)比(bi)例(li)約為(wei)(wei)(wei)(wei)1:1,兩相(xiang)(xiang)(xiang)(xiang)分(fen)布較(jiao)(jiao)均(jun)勻且成(cheng)(cheng)分(fen)穩定有(you)(you)利于鈍(dun)(dun)化(hua)(hua)膜(mo)(mo)(mo)(mo)的(de)(de)(de)(de)(de)穩定，具體表(biao)(biao)(biao)(biao)現(xian)為(wei)(wei)(wei)(wei)鈍(dun)(dun)化(hua)(hua)膜(mo)(mo)(mo)(mo)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)（Rf)值較(jiao)(jiao)高(gao)(gao)(gao)，表(biao)(biao)(biao)(biao)明(ming)(ming)此刻(ke)離子遷移(yi)(yi)時(shi)所(suo)受(shou)阻(zu)(zu)力(li)(li)較(jiao)(jiao)大(da)(da)(da)，進而(er)2507雙(shuang)(shuang)(shuang)相(xiang)(xiang)(xiang)(xiang)不(bu)(bu)銹(xiu)(xiu)(xiu)鋼(gang)(gang)的(de)(de)(de)(de)(de)抗(kang)(kang)(kang)腐(fu)蝕(shi)能(neng)(neng)(neng)力(li)(li)最佳；固溶(rong)(rong)(rong)(rong)熱(re)處(chu)(chu)理溫(wen)度(du)的(de)(de)(de)(de)(de)進一步升高(gao)(gao)(gao)使鋼(gang)(gang)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)兩相(xiang)(xiang)(xiang)(xiang)比(bi)例(li)失調，表(biao)(biao)(biao)(biao)現(xian)為(wei)(wei)(wei)(wei)鐵(tie)素體相(xiang)(xiang)(xiang)(xiang)含(han)量大(da)(da)(da)幅升高(gao)(gao)(gao)，奧氏體相(xiang)(xiang)(xiang)(xiang)含(han)量減小(xiao)，不(bu)(bu)利于鋼(gang)(gang)表(biao)(biao)(biao)(biao)面(mian)鈍(dun)(dun)化(hua)(hua)膜(mo)(mo)(mo)(mo)的(de)(de)(de)(de)(de)穩定，導(dao)致(zhi)鈍(dun)(dun)化(hua)(hua)膜(mo)(mo)(mo)(mo)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)（Rf)減小(xiao)，實際表(biao)(biao)(biao)(biao)現(xian)為(wei)(wei)(wei)(wei)鋼(gang)(gang)的(de)(de)(de)(de)(de)抗(kang)(kang)(kang)蝕(shi)性(xing)(xing)能(neng)(neng)(neng)下降，這與動電(dian)(dian)(dian)(dian)(dian)(dian)位掃描獲得的(de)(de)(de)(de)(de)結(jie)論相(xiang)(xiang)(xiang)(xiang)同(tong)。