1. 動電位極化曲線分析

  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(shuang)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)2507雙相(xiang)(xiang)不(bu)銹鋼于(yu)3.5%NaCl溶液中動電位極化后的(de)(de)腐蝕(shi)形(xing)(xing)貌如圖5.4所示(shi)，圖中深色(se)是(shi)(shi)鐵(tie)(tie)素(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)、淺(qian)色(se)是(shi)(shi)奧(ao)(ao)氏(shi)(shi)(shi)體(ti)(ti)(ti)y相(xiang)(xiang)、黑色(se)圓點(dian)(dian)是(shi)(shi)點(dian)(dian)蝕(shi)坑。從圖5.4可知點(dian)(dian)蝕(shi)坑主(zhu)要存在(zai)(zai)于(yu)鐵(tie)(tie)素(su)(su)體(ti)(ti)(ti)x相(xiang)(xiang)上，這說明奧(ao)(ao)氏(shi)(shi)(shi)體(ti)(ti)(ti)y相(xiang)(xiang)比鐵(tie)(tie)素(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)要穩(wen)定，有(you)著(zhu)較(jiao)(jiao)優(you)的(de)(de)抗(kang)點(dian)(dian)腐蝕(shi)性能(neng)。奧(ao)(ao)氏(shi)(shi)(shi)體(ti)(ti)(ti)γ相(xiang)(xiang)相(xiang)(xiang)比于(yu)鐵(tie)(tie)素(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)有(you)較(jiao)(jiao)好(hao)的(de)(de)抗(kang)點(dian)(dian)蝕(shi)性能(neng)的(de)(de)原因(yin)在(zai)(zai)于(yu)元(yuan)(yuan)素(su)(su)N的(de)(de)作用。元(yuan)(yuan)素(su)(su)N是(shi)(shi)奧(ao)(ao)氏(shi)(shi)(shi)體(ti)(ti)(ti)形(xing)(xing)成元(yuan)(yuan)素(su)(su)，于(yu)奧(ao)(ao)氏(shi)(shi)(shi)體(ti)(ti)(ti)γ相(xiang)(xiang)中的(de)(de)溶解度要比在(zai)(zai)鐵(tie)(tie)素(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)中的(de)(de)大，此外N能(neng)夠讓(rang)Cr和(he)(he)Mo元(yuan)(yuan)素(su)(su)從鐵(tie)(tie)素(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)遷移到奧(ao)(ao)氏(shi)(shi)(shi)體(ti)(ti)(ti)γ相(xiang)(xiang)中，N顯著(zhu)影響(xiang)著(zhu)這兩種(zhong)元(yuan)(yuan)素(su)(su)在(zai)(zai)奧(ao)(ao)氏(shi)(shi)(shi)體(ti)(ti)(ti)γ相(xiang)(xiang)和(he)(he)鐵(tie)(tie)素(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)中的(de)(de)分配，兩相(xiang)(xiang)中合金元(yuan)(yuan)素(su)(su)含(han)量的(de)(de)差值隨N元(yuan)(yuan)素(su)(su)含(han)量的(de)(de)增多而(er)降低，所以奧(ao)(ao)氏(shi)(shi)(shi)體(ti)(ti)(ti)γ相(xiang)(xiang)的(de)(de)點(dian)(dian)蝕(shi)電位較(jiao)(jiao)鐵(tie)(tie)素(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)要高，從而(er)蝕(shi)坑較(jiao)(jiao)先在(zai)(zai)Eb相(xiang)(xiang)對比較(jiao)(jiao)低的(de)(de)鐵(tie)(tie)素(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)中產生。

2. 交流阻抗測試分(fen)析

  1000℃、1050℃、1100℃、1150℃及(ji)1200℃固(gu)溶(rong)(rong)(rong)態的(de)(de)(de)(de)(de)(de)2507 雙(shuang)(shuang)相(xiang)(xiang)(xiang)不(bu)(bu)(bu)銹(xiu)(xiu)(xiu)鋼(gang)(gang)30℃下(xia)于3.5%NaCl溶(rong)(rong)(rong)液(ye)(ye)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Nyquist 圖如圖5.5所(suo)示(shi)，從圖中(zhong)(zhong)(zhong)可(ke)以(yi)很明顯(xian)看出(chu)隨(sui)固(gu)溶(rong)(rong)(rong)熱處(chu)(chu)(chu)理(li)溫(wen)度(du)的(de)(de)(de)(de)(de)(de)增高容抗(kang)弧半徑(jing)(jing)先(xian)(xian)增大(da)(da)后(hou)減(jian)小(xiao)(xiao)，1050℃時(shi)(shi)容抗(kang)弧半徑(jing)(jing)最(zui)大(da)(da)。通常情況(kuang)下(xia)界(jie)面間(jian)電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)(he)的(de)(de)(de)(de)(de)(de)遷(qian)移(yi)(yi)促進(jin)了高頻(pin)區容抗(kang)弧的(de)(de)(de)(de)(de)(de)形(xing)成，容抗(kang)弧與雙(shuang)(shuang)電(dian)(dian)(dian)(dian)(dian)(dian)層(ceng)容抗(kang)及(ji)金(jin)(jin)屬材料(liao)溶(rong)(rong)(rong)解(jie)的(de)(de)(de)(de)(de)(de)綜合作用有關，并(bing)且(qie)金(jin)(jin)屬－溶(rong)(rong)(rong)液(ye)(ye)界(jie)面的(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)(he)轉移(yi)(yi)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)影響(xiang)著容抗(kang)弧半徑(jing)(jing)的(de)(de)(de)(de)(de)(de)大(da)(da)小(xiao)(xiao)，電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)(he)在(zai)金(jin)(jin)屬－溶(rong)(rong)(rong)液(ye)(ye)界(jie)面轉移(yi)(yi)時(shi)(shi)受到(dao)的(de)(de)(de)(de)(de)(de)阻(zu)(zu)力(li)(li)越(yue)(yue)強意(yi)味(wei)著容抗(kang)弧半徑(jing)(jing)越(yue)(yue)大(da)(da)，即(ji)意(yi)味(wei)著金(jin)(jin)屬的(de)(de)(de)(de)(de)(de)抗(kang)蝕(shi)性能(neng)(neng)(neng)越(yue)(yue)優。從圖5.5容抗(kang)弧半徑(jing)(jing)的(de)(de)(de)(de)(de)(de)改變(bian)趨(qu)勢(shi)可(ke)知，固(gu)溶(rong)(rong)(rong)熱處(chu)(chu)(chu)理(li)溫(wen)度(du)升高使DSS2507的(de)(de)(de)(de)(de)(de)耐蝕(shi)性能(neng)(neng)(neng)首先(xian)(xian)增強而后(hou)減(jian)弱(ruo)，1050℃時(shi)(shi)2507雙(shuang)(shuang)相(xiang)(xiang)(xiang)不(bu)(bu)(bu)銹(xiu)(xiu)(xiu)鋼(gang)(gang)的(de)(de)(de)(de)(de)(de)抗(kang)腐(fu)蝕(shi)性能(neng)(neng)(neng)最(zui)優。不(bu)(bu)(bu)同固(gu)溶(rong)(rong)(rong)態的(de)(de)(de)(de)(de)(de)2507雙(shuang)(shuang)相(xiang)(xiang)(xiang)不(bu)(bu)(bu)銹(xiu)(xiu)(xiu)鋼(gang)(gang)于3.5%NaCl溶(rong)(rong)(rong)液(ye)(ye)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)等效電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)如圖5.6所(suo)示(shi)，采用的(de)(de)(de)(de)(de)(de)是R(C(R(CR))).Rs指參比電(dian)(dian)(dian)(dian)(dian)(dian)極(ji)和工(gong)作電(dian)(dian)(dian)(dian)(dian)(dian)極(ji)間(jian)的(de)(de)(de)(de)(de)(de)溶(rong)(rong)(rong)液(ye)(ye)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)；Cd1為(wei)(wei)雙(shuang)(shuang)電(dian)(dian)(dian)(dian)(dian)(dian)層(ceng)電(dian)(dian)(dian)(dian)(dian)(dian)容；Rct為(wei)(wei)電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)(he)轉移(yi)(yi)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)，其值(zhi)能(neng)(neng)(neng)夠反(fan)應(ying)電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)(he)在(zai)電(dian)(dian)(dian)(dian)(dian)(dian)化(hua)(hua)(hua)(hua)學反(fan)應(ying)過(guo)程中(zhong)(zhong)(zhong)透過(guo)電(dian)(dian)(dian)(dian)(dian)(dian)極(ji)以(yi)及(ji)于電(dian)(dian)(dian)(dian)(dian)(dian)解(jie)質溶(rong)(rong)(rong)液(ye)(ye)中(zhong)(zhong)(zhong)兩(liang)(liang)相(xiang)(xiang)(xiang)界(jie)面遷(qian)移(yi)(yi)難易的(de)(de)(de)(de)(de)(de)大(da)(da)小(xiao)(xiao)，也能(neng)(neng)(neng)夠反(fan)映金(jin)(jin)屬發生腐(fu)蝕(shi)反(fan)應(ying)的(de)(de)(de)(de)(de)(de)快慢，一般情況(kuang)下(xia)Rct值(zhi)越(yue)(yue)高意(yi)味(wei)著電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)(he)遷(qian)移(yi)(yi)過(guo)程中(zhong)(zhong)(zhong)所(suo)受的(de)(de)(de)(de)(de)(de)阻(zu)(zu)力(li)(li)越(yue)(yue)強，即(ji)材料(liao)的(de)(de)(de)(de)(de)(de)耐腐(fu)蝕(shi)性能(neng)(neng)(neng)越(yue)(yue)好(hao)；Cf表(biao)(biao)(biao)示(shi)鈍(dun)(dun)(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)(mo)電(dian)(dian)(dian)(dian)(dian)(dian)容，Rf表(biao)(biao)(biao)示(shi)鈍(dun)(dun)(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)(mo)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)。采用ZsimpWin軟件對等效電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)模(mo)擬計(ji)算得到(dao)各元件的(de)(de)(de)(de)(de)(de)數值(zhi)如表(biao)(biao)(biao)5.2所(suo)列(lie)。從表(biao)(biao)(biao)中(zhong)(zhong)(zhong)看出(chu)雙(shuang)(shuang)電(dian)(dian)(dian)(dian)(dian)(dian)層(ceng)電(dian)(dian)(dian)(dian)(dian)(dian)容（Cdl)及(ji)鈍(dun)(dun)(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)(mo)電(dian)(dian)(dian)(dian)(dian)(dian)容（Cr)隨(sui)固(gu)溶(rong)(rong)(rong)溫(wen)度(du)的(de)(de)(de)(de)(de)(de)升高呈(cheng)(cheng)先(xian)(xian)減(jian)小(xiao)(xiao)后(hou)增大(da)(da)的(de)(de)(de)(de)(de)(de)趨(qu)勢(shi)；電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)(he)轉移(yi)(yi)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)（Rct)和鈍(dun)(dun)(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)(mo)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)（Rf)呈(cheng)(cheng)先(xian)(xian)變(bian)大(da)(da)后(hou)減(jian)小(xiao)(xiao)的(de)(de)(de)(de)(de)(de)趨(qu)勢(shi)，即(ji)電(dian)(dian)(dian)(dian)(dian)(dian)化(hua)(hua)(hua)(hua)學反(fan)應(ying)阻(zu)(zu)力(li)(li)隨(sui)固(gu)溶(rong)(rong)(rong)熱處(chu)(chu)(chu)理(li)溫(wen)度(du)的(de)(de)(de)(de)(de)(de)增高先(xian)(xian)增強后(hou)減(jian)弱(ruo)，2507雙(shuang)(shuang)相(xiang)(xiang)(xiang)不(bu)(bu)(bu)銹(xiu)(xiu)(xiu)鋼(gang)(gang)的(de)(de)(de)(de)(de)(de)抗(kang)腐(fu)蝕(shi)性能(neng)(neng)(neng)表(biao)(biao)(biao)現為(wei)(wei)先(xian)(xian)增強后(hou)減(jian)弱(ruo)。1000℃時(shi)(shi)鋼(gang)(gang)的(de)(de)(de)(de)(de)(de)相(xiang)(xiang)(xiang)界(jie)處(chu)(chu)(chu)有σ相(xiang)(xiang)(xiang)析出(chu)，σ相(xiang)(xiang)(xiang)硬而脆降低(di)了鋼(gang)(gang)表(biao)(biao)(biao)面鈍(dun)(dun)(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)(mo)的(de)(de)(de)(de)(de)(de)穩(wen)(wen)定(ding)(ding)，表(biao)(biao)(biao)現為(wei)(wei)具有較(jiao)低(di)的(de)(de)(de)(de)(de)(de)鈍(dun)(dun)(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)(mo)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)（Rf);1050℃時(shi)(shi)鋼(gang)(gang)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)兩(liang)(liang)相(xiang)(xiang)(xiang)比例(li)約為(wei)(wei)1:1,兩(liang)(liang)相(xiang)(xiang)(xiang)分布較(jiao)均勻且(qie)成分穩(wen)(wen)定(ding)(ding)有利(li)于鈍(dun)(dun)(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)(mo)的(de)(de)(de)(de)(de)(de)穩(wen)(wen)定(ding)(ding)，具體(ti)表(biao)(biao)(biao)現為(wei)(wei)鈍(dun)(dun)(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)(mo)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)（Rf)值(zhi)較(jiao)高，表(biao)(biao)(biao)明此刻離子遷(qian)移(yi)(yi)時(shi)(shi)所(suo)受阻(zu)(zu)力(li)(li)較(jiao)大(da)(da)，進(jin)而2507雙(shuang)(shuang)相(xiang)(xiang)(xiang)不(bu)(bu)(bu)銹(xiu)(xiu)(xiu)鋼(gang)(gang)的(de)(de)(de)(de)(de)(de)抗(kang)腐(fu)蝕(shi)能(neng)(neng)(neng)力(li)(li)最(zui)佳；固(gu)溶(rong)(rong)(rong)熱處(chu)(chu)(chu)理(li)溫(wen)度(du)的(de)(de)(de)(de)(de)(de)進(jin)一步升高使鋼(gang)(gang)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)兩(liang)(liang)相(xiang)(xiang)(xiang)比例(li)失調，表(biao)(biao)(biao)現為(wei)(wei)鐵素體(ti)相(xiang)(xiang)(xiang)含(han)量大(da)(da)幅升高，奧(ao)氏體(ti)相(xiang)(xiang)(xiang)含(han)量減(jian)小(xiao)(xiao)，不(bu)(bu)(bu)利(li)于鋼(gang)(gang)表(biao)(biao)(biao)面鈍(dun)(dun)(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)(mo)的(de)(de)(de)(de)(de)(de)穩(wen)(wen)定(ding)(ding)，導致鈍(dun)(dun)(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)(mo)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)（Rf)減(jian)小(xiao)(xiao)，實際表(biao)(biao)(biao)現為(wei)(wei)鋼(gang)(gang)的(de)(de)(de)(de)(de)(de)抗(kang)蝕(shi)性能(neng)(neng)(neng)下(xia)降，這(zhe)與動電(dian)(dian)(dian)(dian)(dian)(dian)位掃(sao)描(miao)獲得的(de)(de)(de)(de)(de)(de)結論相(xiang)(xiang)(xiang)同。