1. 動電(dian)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1050℃的(de)2507雙相(xiang)(xiang)(xiang)(xiang)不銹鋼于3.5%NaCl溶液中(zhong)動電(dian)位極(ji)化后的(de)腐(fu)蝕(shi)(shi)形(xing)貌如(ru)圖5.4所示，圖中(zhong)深(shen)色(se)是(shi)鐵(tie)(tie)(tie)(tie)(tie)(tie)素(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)、淺色(se)是(shi)奧(ao)(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)y相(xiang)(xiang)(xiang)(xiang)、黑(hei)色(se)圓點是(shi)點蝕(shi)(shi)坑。從(cong)圖5.4可(ke)知點蝕(shi)(shi)坑主要(yao)存(cun)在(zai)于鐵(tie)(tie)(tie)(tie)(tie)(tie)素(su)(su)(su)(su)體(ti)(ti)(ti)x相(xiang)(xiang)(xiang)(xiang)上(shang)，這說明奧(ao)(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)y相(xiang)(xiang)(xiang)(xiang)比(bi)鐵(tie)(tie)(tie)(tie)(tie)(tie)素(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)要(yao)穩定，有著較(jiao)優(you)的(de)抗(kang)(kang)點腐(fu)蝕(shi)(shi)性(xing)能(neng)。奧(ao)(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)(xiang)相(xiang)(xiang)(xiang)(xiang)比(bi)于鐵(tie)(tie)(tie)(tie)(tie)(tie)素(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)有較(jiao)好的(de)抗(kang)(kang)點蝕(shi)(shi)性(xing)能(neng)的(de)原因在(zai)于元(yuan)素(su)(su)(su)(su)N的(de)作(zuo)用。元(yuan)素(su)(su)(su)(su)N是(shi)奧(ao)(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)形(xing)成(cheng)元(yuan)素(su)(su)(su)(su)，于奧(ao)(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)(xiang)中(zhong)的(de)溶解(jie)度要(yao)比(bi)在(zai)鐵(tie)(tie)(tie)(tie)(tie)(tie)素(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)中(zhong)的(de)大，此外(wai)N能(neng)夠讓(rang)Cr和Mo元(yuan)素(su)(su)(su)(su)從(cong)鐵(tie)(tie)(tie)(tie)(tie)(tie)素(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)遷移(yi)到奧(ao)(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)(xiang)中(zhong)，N顯著影響(xiang)著這兩種(zhong)元(yuan)素(su)(su)(su)(su)在(zai)奧(ao)(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)(xiang)和鐵(tie)(tie)(tie)(tie)(tie)(tie)素(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)中(zhong)的(de)分配(pei)，兩相(xiang)(xiang)(xiang)(xiang)中(zhong)合金元(yuan)素(su)(su)(su)(su)含量的(de)差值隨N元(yuan)素(su)(su)(su)(su)含量的(de)增多而降低，所以奧(ao)(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)(xiang)的(de)點蝕(shi)(shi)電(dian)位較(jiao)鐵(tie)(tie)(tie)(tie)(tie)(tie)素(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)要(yao)高，從(cong)而蝕(shi)(shi)坑較(jiao)先(xian)在(zai)Eb相(xiang)(xiang)(xiang)(xiang)對比(bi)較(jiao)低的(de)鐵(tie)(tie)(tie)(tie)(tie)(tie)素(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)中(zhong)產生。

2. 交流阻抗測試分析

  1000℃、1050℃、1100℃、1150℃及(ji)1200℃固溶(rong)(rong)態(tai)(tai)的(de)(de)(de)(de)(de)(de)(de)(de)(de)2507 雙(shuang)(shuang)(shuang)(shuang)(shuang)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)不(bu)(bu)(bu)銹鋼(gang)30℃下于(yu)(yu)3.5%NaCl溶(rong)(rong)液(ye)(ye)中的(de)(de)(de)(de)(de)(de)(de)(de)(de)Nyquist 圖(tu)(tu)(tu)(tu)如圖(tu)(tu)(tu)(tu)5.5所(suo)示(shi)，從(cong)圖(tu)(tu)(tu)(tu)中可以(yi)很明(ming)顯看(kan)(kan)出(chu)隨固溶(rong)(rong)熱處(chu)理溫(wen)度(du)的(de)(de)(de)(de)(de)(de)(de)(de)(de)增(zeng)高(gao)(gao)(gao)容(rong)(rong)抗(kang)(kang)弧(hu)半(ban)(ban)徑(jing)(jing)先(xian)增(zeng)大(da)(da)(da)后(hou)(hou)減(jian)小(xiao)，1050℃時(shi)容(rong)(rong)抗(kang)(kang)弧(hu)半(ban)(ban)徑(jing)(jing)最大(da)(da)(da)。通(tong)常(chang)情況下界面(mian)(mian)間電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)(he)的(de)(de)(de)(de)(de)(de)(de)(de)(de)遷移(yi)(yi)促進了(le)高(gao)(gao)(gao)頻區(qu)容(rong)(rong)抗(kang)(kang)弧(hu)的(de)(de)(de)(de)(de)(de)(de)(de)(de)形成，容(rong)(rong)抗(kang)(kang)弧(hu)與(yu)雙(shuang)(shuang)(shuang)(shuang)(shuang)電(dian)(dian)(dian)(dian)(dian)(dian)層容(rong)(rong)抗(kang)(kang)及(ji)金(jin)(jin)屬材料溶(rong)(rong)解(jie)(jie)的(de)(de)(de)(de)(de)(de)(de)(de)(de)綜合作用(yong)有(you)(you)關，并且金(jin)(jin)屬－溶(rong)(rong)液(ye)(ye)界面(mian)(mian)的(de)(de)(de)(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)(zu)(zu)影響著(zhu)容(rong)(rong)抗(kang)(kang)弧(hu)半(ban)(ban)徑(jing)(jing)的(de)(de)(de)(de)(de)(de)(de)(de)(de)大(da)(da)(da)小(xiao)，電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)(he)在金(jin)(jin)屬－溶(rong)(rong)液(ye)(ye)界面(mian)(mian)轉移(yi)(yi)時(shi)受到(dao)的(de)(de)(de)(de)(de)(de)(de)(de)(de)阻(zu)(zu)(zu)(zu)力(li)越(yue)強意(yi)味(wei)(wei)著(zhu)容(rong)(rong)抗(kang)(kang)弧(hu)半(ban)(ban)徑(jing)(jing)越(yue)大(da)(da)(da)，即(ji)意(yi)味(wei)(wei)著(zhu)金(jin)(jin)屬的(de)(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)蝕性能(neng)越(yue)優。從(cong)圖(tu)(tu)(tu)(tu)5.5容(rong)(rong)抗(kang)(kang)弧(hu)半(ban)(ban)徑(jing)(jing)的(de)(de)(de)(de)(de)(de)(de)(de)(de)改(gai)變(bian)趨(qu)(qu)勢可知，固溶(rong)(rong)熱處(chu)理溫(wen)度(du)升(sheng)高(gao)(gao)(gao)使DSS2507的(de)(de)(de)(de)(de)(de)(de)(de)(de)耐蝕性能(neng)首先(xian)增(zeng)強而(er)后(hou)(hou)減(jian)弱(ruo)，1050℃時(shi)2507雙(shuang)(shuang)(shuang)(shuang)(shuang)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)不(bu)(bu)(bu)銹鋼(gang)的(de)(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)腐(fu)蝕性能(neng)最優。不(bu)(bu)(bu)同固溶(rong)(rong)態(tai)(tai)的(de)(de)(de)(de)(de)(de)(de)(de)(de)2507雙(shuang)(shuang)(shuang)(shuang)(shuang)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)不(bu)(bu)(bu)銹鋼(gang)于(yu)(yu)3.5%NaCl溶(rong)(rong)液(ye)(ye)中的(de)(de)(de)(de)(de)(de)(de)(de)(de)等效(xiao)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)如圖(tu)(tu)(tu)(tu)5.6所(suo)示(shi)，采用(yong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)是R(C(R(CR))).Rs指參比(bi)(bi)(bi)電(dian)(dian)(dian)(dian)(dian)(dian)極和工作電(dian)(dian)(dian)(dian)(dian)(dian)極間的(de)(de)(de)(de)(de)(de)(de)(de)(de)溶(rong)(rong)液(ye)(ye)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)；Cd1為(wei)(wei)雙(shuang)(shuang)(shuang)(shuang)(shuang)電(dian)(dian)(dian)(dian)(dian)(dian)層電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)；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)(zu)(zu)，其值能(neng)夠反應(ying)電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)(he)在電(dian)(dian)(dian)(dian)(dian)(dian)化(hua)(hua)學反應(ying)過(guo)程中透(tou)過(guo)電(dian)(dian)(dian)(dian)(dian)(dian)極以(yi)及(ji)于(yu)(yu)電(dian)(dian)(dian)(dian)(dian)(dian)解(jie)(jie)質溶(rong)(rong)液(ye)(ye)中兩相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)界面(mian)(mian)遷移(yi)(yi)難易的(de)(de)(de)(de)(de)(de)(de)(de)(de)大(da)(da)(da)小(xiao)，也能(neng)夠反映金(jin)(jin)屬發生腐(fu)蝕反應(ying)的(de)(de)(de)(de)(de)(de)(de)(de)(de)快慢，一般情況下Rct值越(yue)高(gao)(gao)(gao)意(yi)味(wei)(wei)著(zhu)電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)(he)遷移(yi)(yi)過(guo)程中所(suo)受的(de)(de)(de)(de)(de)(de)(de)(de)(de)阻(zu)(zu)(zu)(zu)力(li)越(yue)強，即(ji)材料的(de)(de)(de)(de)(de)(de)(de)(de)(de)耐腐(fu)蝕性能(neng)越(yue)好；Cf表(biao)(biao)(biao)(biao)示(shi)鈍(dun)(dun)化(hua)(hua)膜(mo)(mo)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)，Rf表(biao)(biao)(biao)(biao)示(shi)鈍(dun)(dun)化(hua)(hua)膜(mo)(mo)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)。采用(yong)ZsimpWin軟件對等效(xiao)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)模(mo)擬計算得(de)到(dao)各元件的(de)(de)(de)(de)(de)(de)(de)(de)(de)數(shu)值如表(biao)(biao)(biao)(biao)5.2所(suo)列。從(cong)表(biao)(biao)(biao)(biao)中看(kan)(kan)出(chu)雙(shuang)(shuang)(shuang)(shuang)(shuang)電(dian)(dian)(dian)(dian)(dian)(dian)層電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)（Cdl)及(ji)鈍(dun)(dun)化(hua)(hua)膜(mo)(mo)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)（Cr)隨固溶(rong)(rong)溫(wen)度(du)的(de)(de)(de)(de)(de)(de)(de)(de)(de)升(sheng)高(gao)(gao)(gao)呈先(xian)減(jian)小(xiao)后(hou)(hou)增(zeng)大(da)(da)(da)的(de)(de)(de)(de)(de)(de)(de)(de)(de)趨(qu)(qu)勢；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)(zu)(zu)（Rct)和鈍(dun)(dun)化(hua)(hua)膜(mo)(mo)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)（Rf)呈先(xian)變(bian)大(da)(da)(da)后(hou)(hou)減(jian)小(xiao)的(de)(de)(de)(de)(de)(de)(de)(de)(de)趨(qu)(qu)勢，即(ji)電(dian)(dian)(dian)(dian)(dian)(dian)化(hua)(hua)學反應(ying)阻(zu)(zu)(zu)(zu)力(li)隨固溶(rong)(rong)熱處(chu)理溫(wen)度(du)的(de)(de)(de)(de)(de)(de)(de)(de)(de)增(zeng)高(gao)(gao)(gao)先(xian)增(zeng)強后(hou)(hou)減(jian)弱(ruo)，2507雙(shuang)(shuang)(shuang)(shuang)(shuang)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)不(bu)(bu)(bu)銹鋼(gang)的(de)(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)腐(fu)蝕性能(neng)表(biao)(biao)(biao)(biao)現(xian)(xian)(xian)為(wei)(wei)先(xian)增(zeng)強后(hou)(hou)減(jian)弱(ruo)。1000℃時(shi)鋼(gang)的(de)(de)(de)(de)(de)(de)(de)(de)(de)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)界處(chu)有(you)(you)σ相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)析出(chu)，σ相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)硬而(er)脆降(jiang)低了(le)鋼(gang)表(biao)(biao)(biao)(biao)面(mian)(mian)鈍(dun)(dun)化(hua)(hua)膜(mo)(mo)的(de)(de)(de)(de)(de)(de)(de)(de)(de)穩(wen)(wen)(wen)定(ding)，表(biao)(biao)(biao)(biao)現(xian)(xian)(xian)為(wei)(wei)具有(you)(you)較低的(de)(de)(de)(de)(de)(de)(de)(de)(de)鈍(dun)(dun)化(hua)(hua)膜(mo)(mo)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)（Rf);1050℃時(shi)鋼(gang)中的(de)(de)(de)(de)(de)(de)(de)(de)(de)兩相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)比(bi)(bi)(bi)例約為(wei)(wei)1:1,兩相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)分布較均勻且成分穩(wen)(wen)(wen)定(ding)有(you)(you)利于(yu)(yu)鈍(dun)(dun)化(hua)(hua)膜(mo)(mo)的(de)(de)(de)(de)(de)(de)(de)(de)(de)穩(wen)(wen)(wen)定(ding)，具體(ti)表(biao)(biao)(biao)(biao)現(xian)(xian)(xian)為(wei)(wei)鈍(dun)(dun)化(hua)(hua)膜(mo)(mo)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)（Rf)值較高(gao)(gao)(gao)，表(biao)(biao)(biao)(biao)明(ming)此刻離子遷移(yi)(yi)時(shi)所(suo)受阻(zu)(zu)(zu)(zu)力(li)較大(da)(da)(da)，進而(er)2507雙(shuang)(shuang)(shuang)(shuang)(shuang)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)不(bu)(bu)(bu)銹鋼(gang)的(de)(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)腐(fu)蝕能(neng)力(li)最佳；固溶(rong)(rong)熱處(chu)理溫(wen)度(du)的(de)(de)(de)(de)(de)(de)(de)(de)(de)進一步升(sheng)高(gao)(gao)(gao)使鋼(gang)中的(de)(de)(de)(de)(de)(de)(de)(de)(de)兩相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)比(bi)(bi)(bi)例失調，表(biao)(biao)(biao)(biao)現(xian)(xian)(xian)為(wei)(wei)鐵(tie)素體(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)含(han)量(liang)大(da)(da)(da)幅(fu)升(sheng)高(gao)(gao)(gao)，奧氏體(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)含(han)量(liang)減(jian)小(xiao)，不(bu)(bu)(bu)利于(yu)(yu)鋼(gang)表(biao)(biao)(biao)(biao)面(mian)(mian)鈍(dun)(dun)化(hua)(hua)膜(mo)(mo)的(de)(de)(de)(de)(de)(de)(de)(de)(de)穩(wen)(wen)(wen)定(ding)，導致鈍(dun)(dun)化(hua)(hua)膜(mo)(mo)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)（Rf)減(jian)小(xiao)，實際表(biao)(biao)(biao)(biao)現(xian)(xian)(xian)為(wei)(wei)鋼(gang)的(de)(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)蝕性能(neng)下降(jiang)，這與(yu)動電(dian)(dian)(dian)(dian)(dian)(dian)位掃描獲得(de)的(de)(de)(de)(de)(de)(de)(de)(de)(de)結(jie)論(lun)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)同。