1. 動電位(wei)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(rong)態為1050℃的(de)2507雙(shuang)相(xiang)(xiang)(xiang)不銹鋼于(yu)3.5%NaCl溶(rong)液中(zhong)(zhong)動(dong)電位(wei)極(ji)化后(hou)的(de)腐蝕形(xing)貌如(ru)圖(tu)(tu)5.4所示，圖(tu)(tu)中(zhong)(zhong)深色(se)是(shi)鐵(tie)(tie)(tie)素(su)(su)(su)體(ti)(ti)α相(xiang)(xiang)(xiang)、淺色(se)是(shi)奧氏(shi)體(ti)(ti)y相(xiang)(xiang)(xiang)、黑色(se)圓點(dian)(dian)是(shi)點(dian)(dian)蝕坑(keng)。從圖(tu)(tu)5.4可(ke)知點(dian)(dian)蝕坑(keng)主要(yao)存在(zai)(zai)于(yu)鐵(tie)(tie)(tie)素(su)(su)(su)體(ti)(ti)x相(xiang)(xiang)(xiang)上，這說明奧氏(shi)體(ti)(ti)y相(xiang)(xiang)(xiang)比(bi)鐵(tie)(tie)(tie)素(su)(su)(su)體(ti)(ti)α相(xiang)(xiang)(xiang)要(yao)穩定(ding)，有著(zhu)較(jiao)(jiao)優的(de)抗(kang)點(dian)(dian)腐蝕性能。奧氏(shi)體(ti)(ti)γ相(xiang)(xiang)(xiang)相(xiang)(xiang)(xiang)比(bi)于(yu)鐵(tie)(tie)(tie)素(su)(su)(su)體(ti)(ti)α相(xiang)(xiang)(xiang)有較(jiao)(jiao)好的(de)抗(kang)點(dian)(dian)蝕性能的(de)原因在(zai)(zai)于(yu)元(yuan)素(su)(su)(su)N的(de)作用。元(yuan)素(su)(su)(su)N是(shi)奧氏(shi)體(ti)(ti)形(xing)成元(yuan)素(su)(su)(su)，于(yu)奧氏(shi)體(ti)(ti)γ相(xiang)(xiang)(xiang)中(zhong)(zhong)的(de)溶(rong)解(jie)度(du)要(yao)比(bi)在(zai)(zai)鐵(tie)(tie)(tie)素(su)(su)(su)體(ti)(ti)α相(xiang)(xiang)(xiang)中(zhong)(zhong)的(de)大，此外N能夠讓(rang)Cr和(he)Mo元(yuan)素(su)(su)(su)從鐵(tie)(tie)(tie)素(su)(su)(su)體(ti)(ti)α相(xiang)(xiang)(xiang)遷移到奧氏(shi)體(ti)(ti)γ相(xiang)(xiang)(xiang)中(zhong)(zhong)，N顯著(zhu)影響(xiang)著(zhu)這兩種(zhong)元(yuan)素(su)(su)(su)在(zai)(zai)奧氏(shi)體(ti)(ti)γ相(xiang)(xiang)(xiang)和(he)鐵(tie)(tie)(tie)素(su)(su)(su)體(ti)(ti)α相(xiang)(xiang)(xiang)中(zhong)(zhong)的(de)分配，兩相(xiang)(xiang)(xiang)中(zhong)(zhong)合金元(yuan)素(su)(su)(su)含量的(de)差值(zhi)隨N元(yuan)素(su)(su)(su)含量的(de)增(zeng)多而降低，所以奧氏(shi)體(ti)(ti)γ相(xiang)(xiang)(xiang)的(de)點(dian)(dian)蝕電位(wei)較(jiao)(jiao)鐵(tie)(tie)(tie)素(su)(su)(su)體(ti)(ti)α相(xiang)(xiang)(xiang)要(yao)高，從而蝕坑(keng)較(jiao)(jiao)先在(zai)(zai)Eb相(xiang)(xiang)(xiang)對比(bi)較(jiao)(jiao)低的(de)鐵(tie)(tie)(tie)素(su)(su)(su)體(ti)(ti)α相(xiang)(xiang)(xiang)中(zhong)(zhong)產(chan)生。

2. 交(jiao)流阻抗測試分(fen)析

  1000℃、1050℃、1100℃、1150℃及1200℃固(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)(rong)(rong)態的(de)(de)(de)(de)(de)(de)(de)(de)2507 雙(shuang)(shuang)(shuang)相(xiang)(xiang)(xiang)不銹(xiu)(xiu)(xiu)鋼(gang)30℃下于(yu)3.5%NaCl溶(rong)(rong)(rong)(rong)(rong)(rong)液(ye)(ye)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)Nyquist 圖如圖5.5所(suo)(suo)示(shi)，從(cong)圖中(zhong)(zhong)(zhong)可(ke)以很明顯看出隨(sui)固(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)(rong)(rong)熱(re)處(chu)理(li)(li)溫(wen)(wen)度的(de)(de)(de)(de)(de)(de)(de)(de)增(zeng)(zeng)(zeng)高(gao)容(rong)(rong)抗(kang)(kang)(kang)(kang)(kang)(kang)弧半(ban)(ban)徑先(xian)(xian)增(zeng)(zeng)(zeng)大(da)后(hou)(hou)(hou)減(jian)(jian)小，1050℃時(shi)容(rong)(rong)抗(kang)(kang)(kang)(kang)(kang)(kang)弧半(ban)(ban)徑最大(da)。通常(chang)情(qing)況下界面(mian)間電(dian)(dian)(dian)荷(he)(he)的(de)(de)(de)(de)(de)(de)(de)(de)遷移(yi)(yi)促進(jin)(jin)了高(gao)頻區容(rong)(rong)抗(kang)(kang)(kang)(kang)(kang)(kang)弧的(de)(de)(de)(de)(de)(de)(de)(de)形(xing)成，容(rong)(rong)抗(kang)(kang)(kang)(kang)(kang)(kang)弧與雙(shuang)(shuang)(shuang)電(dian)(dian)(dian)層(ceng)容(rong)(rong)抗(kang)(kang)(kang)(kang)(kang)(kang)及金(jin)屬(shu)(shu)材料(liao)溶(rong)(rong)(rong)(rong)(rong)(rong)解的(de)(de)(de)(de)(de)(de)(de)(de)綜(zong)合作(zuo)用有(you)關，并且(qie)金(jin)屬(shu)(shu)－溶(rong)(rong)(rong)(rong)(rong)(rong)液(ye)(ye)界面(mian)的(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)荷(he)(he)轉(zhuan)移(yi)(yi)電(dian)(dian)(dian)阻(zu)(zu)(zu)影響著(zhu)容(rong)(rong)抗(kang)(kang)(kang)(kang)(kang)(kang)弧半(ban)(ban)徑的(de)(de)(de)(de)(de)(de)(de)(de)大(da)小，電(dian)(dian)(dian)荷(he)(he)在金(jin)屬(shu)(shu)－溶(rong)(rong)(rong)(rong)(rong)(rong)液(ye)(ye)界面(mian)轉(zhuan)移(yi)(yi)時(shi)受到的(de)(de)(de)(de)(de)(de)(de)(de)阻(zu)(zu)(zu)力越(yue)(yue)強意(yi)(yi)味(wei)著(zhu)容(rong)(rong)抗(kang)(kang)(kang)(kang)(kang)(kang)弧半(ban)(ban)徑越(yue)(yue)大(da)，即意(yi)(yi)味(wei)著(zhu)金(jin)屬(shu)(shu)的(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)(kang)(kang)(kang)(kang)蝕性能(neng)(neng)(neng)越(yue)(yue)優。從(cong)圖5.5容(rong)(rong)抗(kang)(kang)(kang)(kang)(kang)(kang)弧半(ban)(ban)徑的(de)(de)(de)(de)(de)(de)(de)(de)改變趨(qu)勢可(ke)知，固(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)(rong)(rong)熱(re)處(chu)理(li)(li)溫(wen)(wen)度升(sheng)高(gao)使DSS2507的(de)(de)(de)(de)(de)(de)(de)(de)耐(nai)蝕性能(neng)(neng)(neng)首(shou)先(xian)(xian)增(zeng)(zeng)(zeng)強而(er)后(hou)(hou)(hou)減(jian)(jian)弱(ruo)(ruo)，1050℃時(shi)2507雙(shuang)(shuang)(shuang)相(xiang)(xiang)(xiang)不銹(xiu)(xiu)(xiu)鋼(gang)的(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)(kang)(kang)(kang)(kang)腐(fu)蝕性能(neng)(neng)(neng)最優。不同固(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)(rong)(rong)態的(de)(de)(de)(de)(de)(de)(de)(de)2507雙(shuang)(shuang)(shuang)相(xiang)(xiang)(xiang)不銹(xiu)(xiu)(xiu)鋼(gang)于(yu)3.5%NaCl溶(rong)(rong)(rong)(rong)(rong)(rong)液(ye)(ye)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)等(deng)效電(dian)(dian)(dian)路(lu)(lu)如圖5.6所(suo)(suo)示(shi)，采用的(de)(de)(de)(de)(de)(de)(de)(de)是R(C(R(CR))).Rs指(zhi)參比(bi)電(dian)(dian)(dian)極和工(gong)作(zuo)電(dian)(dian)(dian)極間的(de)(de)(de)(de)(de)(de)(de)(de)溶(rong)(rong)(rong)(rong)(rong)(rong)液(ye)(ye)電(dian)(dian)(dian)阻(zu)(zu)(zu)；Cd1為(wei)雙(shuang)(shuang)(shuang)電(dian)(dian)(dian)層(ceng)電(dian)(dian)(dian)容(rong)(rong)；Rct為(wei)電(dian)(dian)(dian)荷(he)(he)轉(zhuan)移(yi)(yi)電(dian)(dian)(dian)阻(zu)(zu)(zu)，其值能(neng)(neng)(neng)夠(gou)反(fan)應(ying)電(dian)(dian)(dian)荷(he)(he)在電(dian)(dian)(dian)化(hua)(hua)(hua)學反(fan)應(ying)過(guo)程中(zhong)(zhong)(zhong)透(tou)過(guo)電(dian)(dian)(dian)極以及于(yu)電(dian)(dian)(dian)解質溶(rong)(rong)(rong)(rong)(rong)(rong)液(ye)(ye)中(zhong)(zhong)(zhong)兩(liang)(liang)相(xiang)(xiang)(xiang)界面(mian)遷移(yi)(yi)難(nan)易的(de)(de)(de)(de)(de)(de)(de)(de)大(da)小，也能(neng)(neng)(neng)夠(gou)反(fan)映金(jin)屬(shu)(shu)發生腐(fu)蝕反(fan)應(ying)的(de)(de)(de)(de)(de)(de)(de)(de)快慢，一(yi)般情(qing)況下Rct值越(yue)(yue)高(gao)意(yi)(yi)味(wei)著(zhu)電(dian)(dian)(dian)荷(he)(he)遷移(yi)(yi)過(guo)程中(zhong)(zhong)(zhong)所(suo)(suo)受的(de)(de)(de)(de)(de)(de)(de)(de)阻(zu)(zu)(zu)力越(yue)(yue)強，即材料(liao)的(de)(de)(de)(de)(de)(de)(de)(de)耐(nai)腐(fu)蝕性能(neng)(neng)(neng)越(yue)(yue)好；Cf表(biao)(biao)(biao)示(shi)鈍化(hua)(hua)(hua)膜(mo)(mo)(mo)(mo)(mo)電(dian)(dian)(dian)容(rong)(rong)，Rf表(biao)(biao)(biao)示(shi)鈍化(hua)(hua)(hua)膜(mo)(mo)(mo)(mo)(mo)電(dian)(dian)(dian)阻(zu)(zu)(zu)。采用ZsimpWin軟(ruan)件對等(deng)效電(dian)(dian)(dian)路(lu)(lu)模擬(ni)計算(suan)得到各元(yuan)件的(de)(de)(de)(de)(de)(de)(de)(de)數值如表(biao)(biao)(biao)5.2所(suo)(suo)列。從(cong)表(biao)(biao)(biao)中(zhong)(zhong)(zhong)看出雙(shuang)(shuang)(shuang)電(dian)(dian)(dian)層(ceng)電(dian)(dian)(dian)容(rong)(rong)（Cdl)及鈍化(hua)(hua)(hua)膜(mo)(mo)(mo)(mo)(mo)電(dian)(dian)(dian)容(rong)(rong)（Cr)隨(sui)固(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)(rong)(rong)溫(wen)(wen)度的(de)(de)(de)(de)(de)(de)(de)(de)升(sheng)高(gao)呈先(xian)(xian)減(jian)(jian)小后(hou)(hou)(hou)增(zeng)(zeng)(zeng)大(da)的(de)(de)(de)(de)(de)(de)(de)(de)趨(qu)勢；電(dian)(dian)(dian)荷(he)(he)轉(zhuan)移(yi)(yi)電(dian)(dian)(dian)阻(zu)(zu)(zu)（Rct)和鈍化(hua)(hua)(hua)膜(mo)(mo)(mo)(mo)(mo)電(dian)(dian)(dian)阻(zu)(zu)(zu)（Rf)呈先(xian)(xian)變大(da)后(hou)(hou)(hou)減(jian)(jian)小的(de)(de)(de)(de)(de)(de)(de)(de)趨(qu)勢，即電(dian)(dian)(dian)化(hua)(hua)(hua)學反(fan)應(ying)阻(zu)(zu)(zu)力隨(sui)固(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)(rong)(rong)熱(re)處(chu)理(li)(li)溫(wen)(wen)度的(de)(de)(de)(de)(de)(de)(de)(de)增(zeng)(zeng)(zeng)高(gao)先(xian)(xian)增(zeng)(zeng)(zeng)強后(hou)(hou)(hou)減(jian)(jian)弱(ruo)(ruo)，2507雙(shuang)(shuang)(shuang)相(xiang)(xiang)(xiang)不銹(xiu)(xiu)(xiu)鋼(gang)的(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)(kang)(kang)(kang)(kang)腐(fu)蝕性能(neng)(neng)(neng)表(biao)(biao)(biao)現(xian)(xian)為(wei)先(xian)(xian)增(zeng)(zeng)(zeng)強后(hou)(hou)(hou)減(jian)(jian)弱(ruo)(ruo)。1000℃時(shi)鋼(gang)的(de)(de)(de)(de)(de)(de)(de)(de)相(xiang)(xiang)(xiang)界處(chu)有(you)σ相(xiang)(xiang)(xiang)析出，σ相(xiang)(xiang)(xiang)硬(ying)而(er)脆(cui)降低了鋼(gang)表(biao)(biao)(biao)面(mian)鈍化(hua)(hua)(hua)膜(mo)(mo)(mo)(mo)(mo)的(de)(de)(de)(de)(de)(de)(de)(de)穩定(ding)，表(biao)(biao)(biao)現(xian)(xian)為(wei)具有(you)較低的(de)(de)(de)(de)(de)(de)(de)(de)鈍化(hua)(hua)(hua)膜(mo)(mo)(mo)(mo)(mo)電(dian)(dian)(dian)阻(zu)(zu)(zu)（Rf);1050℃時(shi)鋼(gang)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)兩(liang)(liang)相(xiang)(xiang)(xiang)比(bi)例約(yue)為(wei)1:1,兩(liang)(liang)相(xiang)(xiang)(xiang)分布較均勻且(qie)成分穩定(ding)有(you)利(li)于(yu)鈍化(hua)(hua)(hua)膜(mo)(mo)(mo)(mo)(mo)的(de)(de)(de)(de)(de)(de)(de)(de)穩定(ding)，具體表(biao)(biao)(biao)現(xian)(xian)為(wei)鈍化(hua)(hua)(hua)膜(mo)(mo)(mo)(mo)(mo)電(dian)(dian)(dian)阻(zu)(zu)(zu)（Rf)值較高(gao)，表(biao)(biao)(biao)明此刻離子遷移(yi)(yi)時(shi)所(suo)(suo)受阻(zu)(zu)(zu)力較大(da)，進(jin)(jin)而(er)2507雙(shuang)(shuang)(shuang)相(xiang)(xiang)(xiang)不銹(xiu)(xiu)(xiu)鋼(gang)的(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)(kang)(kang)(kang)(kang)腐(fu)蝕能(neng)(neng)(neng)力最佳(jia)；固(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)(rong)(rong)熱(re)處(chu)理(li)(li)溫(wen)(wen)度的(de)(de)(de)(de)(de)(de)(de)(de)進(jin)(jin)一(yi)步(bu)升(sheng)高(gao)使鋼(gang)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)兩(liang)(liang)相(xiang)(xiang)(xiang)比(bi)例失調，表(biao)(biao)(biao)現(xian)(xian)為(wei)鐵素體相(xiang)(xiang)(xiang)含量(liang)(liang)大(da)幅(fu)升(sheng)高(gao)，奧氏體相(xiang)(xiang)(xiang)含量(liang)(liang)減(jian)(jian)小，不利(li)于(yu)鋼(gang)表(biao)(biao)(biao)面(mian)鈍化(hua)(hua)(hua)膜(mo)(mo)(mo)(mo)(mo)的(de)(de)(de)(de)(de)(de)(de)(de)穩定(ding)，導(dao)致鈍化(hua)(hua)(hua)膜(mo)(mo)(mo)(mo)(mo)電(dian)(dian)(dian)阻(zu)(zu)(zu)（Rf)減(jian)(jian)小，實際(ji)表(biao)(biao)(biao)現(xian)(xian)為(wei)鋼(gang)的(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)(kang)(kang)(kang)(kang)蝕性能(neng)(neng)(neng)下降，這(zhe)與動電(dian)(dian)(dian)位(wei)掃描獲得的(de)(de)(de)(de)(de)(de)(de)(de)結(jie)論相(xiang)(xiang)(xiang)同。