1. 動電位極(ji)化(hua)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)(rong)態為(wei)1050℃的(de)(de)(de)2507雙(shuang)相(xiang)(xiang)(xiang)不銹鋼于(yu)(yu)3.5%NaCl溶(rong)(rong)液(ye)中(zhong)動(dong)電(dian)位極化后的(de)(de)(de)腐蝕(shi)形(xing)貌如(ru)圖5.4所示，圖中(zhong)深色是(shi)(shi)鐵(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)、淺色是(shi)(shi)奧氏(shi)(shi)(shi)體(ti)(ti)(ti)(ti)(ti)(ti)(ti)y相(xiang)(xiang)(xiang)、黑色圓點(dian)是(shi)(shi)點(dian)蝕(shi)坑(keng)。從(cong)(cong)圖5.4可知點(dian)蝕(shi)坑(keng)主要(yao)存在(zai)(zai)于(yu)(yu)鐵(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)(ti)(ti)x相(xiang)(xiang)(xiang)上，這說明(ming)奧氏(shi)(shi)(shi)體(ti)(ti)(ti)(ti)(ti)(ti)(ti)y相(xiang)(xiang)(xiang)比(bi)鐵(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)要(yao)穩定(ding)，有(you)著(zhu)較(jiao)(jiao)優的(de)(de)(de)抗點(dian)腐蝕(shi)性(xing)能(neng)。奧氏(shi)(shi)(shi)體(ti)(ti)(ti)(ti)(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)相(xiang)(xiang)(xiang)比(bi)于(yu)(yu)鐵(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)有(you)較(jiao)(jiao)好的(de)(de)(de)抗點(dian)蝕(shi)性(xing)能(neng)的(de)(de)(de)原因在(zai)(zai)于(yu)(yu)元(yuan)(yuan)素(su)(su)(su)N的(de)(de)(de)作用。元(yuan)(yuan)素(su)(su)(su)N是(shi)(shi)奧氏(shi)(shi)(shi)體(ti)(ti)(ti)(ti)(ti)(ti)(ti)形(xing)成元(yuan)(yuan)素(su)(su)(su)，于(yu)(yu)奧氏(shi)(shi)(shi)體(ti)(ti)(ti)(ti)(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)中(zhong)的(de)(de)(de)溶(rong)(rong)解度(du)要(yao)比(bi)在(zai)(zai)鐵(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)中(zhong)的(de)(de)(de)大，此外N能(neng)夠讓Cr和(he)Mo元(yuan)(yuan)素(su)(su)(su)從(cong)(cong)鐵(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)遷移到奧氏(shi)(shi)(shi)體(ti)(ti)(ti)(ti)(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)中(zhong)，N顯著(zhu)影響(xiang)著(zhu)這兩種元(yuan)(yuan)素(su)(su)(su)在(zai)(zai)奧氏(shi)(shi)(shi)體(ti)(ti)(ti)(ti)(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)和(he)鐵(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)中(zhong)的(de)(de)(de)分配，兩相(xiang)(xiang)(xiang)中(zhong)合金元(yuan)(yuan)素(su)(su)(su)含(han)量(liang)的(de)(de)(de)差值隨N元(yuan)(yuan)素(su)(su)(su)含(han)量(liang)的(de)(de)(de)增多而降低(di)(di)，所以奧氏(shi)(shi)(shi)體(ti)(ti)(ti)(ti)(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)的(de)(de)(de)點(dian)蝕(shi)電(dian)位較(jiao)(jiao)鐵(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)要(yao)高，從(cong)(cong)而蝕(shi)坑(keng)較(jiao)(jiao)先在(zai)(zai)Eb相(xiang)(xiang)(xiang)對比(bi)較(jiao)(jiao)低(di)(di)的(de)(de)(de)鐵(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)中(zhong)產生(sheng)。

2. 交流阻抗測試分析

  1000℃、1050℃、1100℃、1150℃及(ji)1200℃固(gu)(gu)溶(rong)(rong)(rong)(rong)態的(de)(de)(de)(de)(de)(de)(de)(de)2507 雙相不(bu)銹(xiu)鋼(gang)30℃下于3.5%NaCl溶(rong)(rong)(rong)(rong)液中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)Nyquist 圖如(ru)圖5.5所(suo)(suo)示(shi)，從(cong)(cong)圖中(zhong)(zhong)(zhong)可以很明顯(xian)看(kan)出(chu)隨固(gu)(gu)溶(rong)(rong)(rong)(rong)熱處(chu)理(li)(li)溫度的(de)(de)(de)(de)(de)(de)(de)(de)增(zeng)(zeng)高(gao)(gao)(gao)容(rong)抗(kang)(kang)(kang)(kang)(kang)(kang)弧半徑先(xian)增(zeng)(zeng)大后減(jian)(jian)小，1050℃時(shi)(shi)容(rong)抗(kang)(kang)(kang)(kang)(kang)(kang)弧半徑最大。通(tong)常情況(kuang)下界面(mian)(mian)間(jian)電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)的(de)(de)(de)(de)(de)(de)(de)(de)遷(qian)移促進了(le)高(gao)(gao)(gao)頻區容(rong)抗(kang)(kang)(kang)(kang)(kang)(kang)弧的(de)(de)(de)(de)(de)(de)(de)(de)形成，容(rong)抗(kang)(kang)(kang)(kang)(kang)(kang)弧與雙電(dian)(dian)(dian)(dian)(dian)(dian)層容(rong)抗(kang)(kang)(kang)(kang)(kang)(kang)及(ji)金(jin)(jin)屬材(cai)料溶(rong)(rong)(rong)(rong)解的(de)(de)(de)(de)(de)(de)(de)(de)綜合作用有關(guan)，并(bing)且(qie)金(jin)(jin)屬－溶(rong)(rong)(rong)(rong)液界面(mian)(mian)的(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)轉移電(dian)(dian)(dian)(dian)(dian)(dian)阻影(ying)響著(zhu)(zhu)容(rong)抗(kang)(kang)(kang)(kang)(kang)(kang)弧半徑的(de)(de)(de)(de)(de)(de)(de)(de)大小，電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)在金(jin)(jin)屬－溶(rong)(rong)(rong)(rong)液界面(mian)(mian)轉移時(shi)(shi)受到(dao)(dao)的(de)(de)(de)(de)(de)(de)(de)(de)阻力(li)越(yue)強意味著(zhu)(zhu)容(rong)抗(kang)(kang)(kang)(kang)(kang)(kang)弧半徑越(yue)大，即(ji)意味著(zhu)(zhu)金(jin)(jin)屬的(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)(kang)(kang)(kang)(kang)蝕(shi)性(xing)能(neng)(neng)(neng)越(yue)優。從(cong)(cong)圖5.5容(rong)抗(kang)(kang)(kang)(kang)(kang)(kang)弧半徑的(de)(de)(de)(de)(de)(de)(de)(de)改(gai)變趨勢可知，固(gu)(gu)溶(rong)(rong)(rong)(rong)熱處(chu)理(li)(li)溫度升(sheng)(sheng)高(gao)(gao)(gao)使DSS2507的(de)(de)(de)(de)(de)(de)(de)(de)耐蝕(shi)性(xing)能(neng)(neng)(neng)首(shou)先(xian)增(zeng)(zeng)強而后減(jian)(jian)弱(ruo)(ruo)，1050℃時(shi)(shi)2507雙相不(bu)銹(xiu)鋼(gang)的(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)(kang)(kang)(kang)(kang)腐(fu)蝕(shi)性(xing)能(neng)(neng)(neng)最優。不(bu)同(tong)(tong)固(gu)(gu)溶(rong)(rong)(rong)(rong)態的(de)(de)(de)(de)(de)(de)(de)(de)2507雙相不(bu)銹(xiu)鋼(gang)于3.5%NaCl溶(rong)(rong)(rong)(rong)液中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)等(deng)效電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)如(ru)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(can)比(bi)電(dian)(dian)(dian)(dian)(dian)(dian)極和工作電(dian)(dian)(dian)(dian)(dian)(dian)極間(jian)的(de)(de)(de)(de)(de)(de)(de)(de)溶(rong)(rong)(rong)(rong)液電(dian)(dian)(dian)(dian)(dian)(dian)阻；Cd1為雙電(dian)(dian)(dian)(dian)(dian)(dian)層電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)；Rct為電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)轉移電(dian)(dian)(dian)(dian)(dian)(dian)阻，其值(zhi)能(neng)(neng)(neng)夠反(fan)應(ying)(ying)電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)在電(dian)(dian)(dian)(dian)(dian)(dian)化(hua)(hua)(hua)(hua)學(xue)反(fan)應(ying)(ying)過(guo)程中(zhong)(zhong)(zhong)透(tou)過(guo)電(dian)(dian)(dian)(dian)(dian)(dian)極以及(ji)于電(dian)(dian)(dian)(dian)(dian)(dian)解質(zhi)溶(rong)(rong)(rong)(rong)液中(zhong)(zhong)(zhong)兩相界面(mian)(mian)遷(qian)移難(nan)易的(de)(de)(de)(de)(de)(de)(de)(de)大小，也能(neng)(neng)(neng)夠反(fan)映金(jin)(jin)屬發生腐(fu)蝕(shi)反(fan)應(ying)(ying)的(de)(de)(de)(de)(de)(de)(de)(de)快慢，一(yi)般情況(kuang)下Rct值(zhi)越(yue)高(gao)(gao)(gao)意味著(zhu)(zhu)電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)遷(qian)移過(guo)程中(zhong)(zhong)(zhong)所(suo)(suo)受的(de)(de)(de)(de)(de)(de)(de)(de)阻力(li)越(yue)強，即(ji)材(cai)料的(de)(de)(de)(de)(de)(de)(de)(de)耐腐(fu)蝕(shi)性(xing)能(neng)(neng)(neng)越(yue)好；Cf表(biao)(biao)(biao)(biao)示(shi)鈍(dun)(dun)化(hua)(hua)(hua)(hua)膜電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)，Rf表(biao)(biao)(biao)(biao)示(shi)鈍(dun)(dun)化(hua)(hua)(hua)(hua)膜電(dian)(dian)(dian)(dian)(dian)(dian)阻。采用ZsimpWin軟件對等(deng)效電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)模擬計算得(de)到(dao)(dao)各元件的(de)(de)(de)(de)(de)(de)(de)(de)數值(zhi)如(ru)表(biao)(biao)(biao)(biao)5.2所(suo)(suo)列。從(cong)(cong)表(biao)(biao)(biao)(biao)中(zhong)(zhong)(zhong)看(kan)出(chu)雙電(dian)(dian)(dian)(dian)(dian)(dian)層電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)（Cdl)及(ji)鈍(dun)(dun)化(hua)(hua)(hua)(hua)膜電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)（Cr)隨固(gu)(gu)溶(rong)(rong)(rong)(rong)溫度的(de)(de)(de)(de)(de)(de)(de)(de)升(sheng)(sheng)高(gao)(gao)(gao)呈先(xian)減(jian)(jian)小后增(zeng)(zeng)大的(de)(de)(de)(de)(de)(de)(de)(de)趨勢；電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)轉移電(dian)(dian)(dian)(dian)(dian)(dian)阻（Rct)和鈍(dun)(dun)化(hua)(hua)(hua)(hua)膜電(dian)(dian)(dian)(dian)(dian)(dian)阻（Rf)呈先(xian)變大后減(jian)(jian)小的(de)(de)(de)(de)(de)(de)(de)(de)趨勢，即(ji)電(dian)(dian)(dian)(dian)(dian)(dian)化(hua)(hua)(hua)(hua)學(xue)反(fan)應(ying)(ying)阻力(li)隨固(gu)(gu)溶(rong)(rong)(rong)(rong)熱處(chu)理(li)(li)溫度的(de)(de)(de)(de)(de)(de)(de)(de)增(zeng)(zeng)高(gao)(gao)(gao)先(xian)增(zeng)(zeng)強后減(jian)(jian)弱(ruo)(ruo)，2507雙相不(bu)銹(xiu)鋼(gang)的(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)(kang)(kang)(kang)(kang)腐(fu)蝕(shi)性(xing)能(neng)(neng)(neng)表(biao)(biao)(biao)(biao)現(xian)(xian)為先(xian)增(zeng)(zeng)強后減(jian)(jian)弱(ruo)(ruo)。1000℃時(shi)(shi)鋼(gang)的(de)(de)(de)(de)(de)(de)(de)(de)相界處(chu)有σ相析出(chu)，σ相硬而脆降低了(le)鋼(gang)表(biao)(biao)(biao)(biao)面(mian)(mian)鈍(dun)(dun)化(hua)(hua)(hua)(hua)膜的(de)(de)(de)(de)(de)(de)(de)(de)穩(wen)定(ding)，表(biao)(biao)(biao)(biao)現(xian)(xian)為具(ju)有較(jiao)低的(de)(de)(de)(de)(de)(de)(de)(de)鈍(dun)(dun)化(hua)(hua)(hua)(hua)膜電(dian)(dian)(dian)(dian)(dian)(dian)阻（Rf);1050℃時(shi)(shi)鋼(gang)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)兩相比(bi)例(li)約為1:1,兩相分布較(jiao)均勻且(qie)成分穩(wen)定(ding)有利于鈍(dun)(dun)化(hua)(hua)(hua)(hua)膜的(de)(de)(de)(de)(de)(de)(de)(de)穩(wen)定(ding)，具(ju)體(ti)表(biao)(biao)(biao)(biao)現(xian)(xian)為鈍(dun)(dun)化(hua)(hua)(hua)(hua)膜電(dian)(dian)(dian)(dian)(dian)(dian)阻（Rf)值(zhi)較(jiao)高(gao)(gao)(gao)，表(biao)(biao)(biao)(biao)明此(ci)刻(ke)離子(zi)遷(qian)移時(shi)(shi)所(suo)(suo)受阻力(li)較(jiao)大，進而2507雙相不(bu)銹(xiu)鋼(gang)的(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)(kang)(kang)(kang)(kang)腐(fu)蝕(shi)能(neng)(neng)(neng)力(li)最佳；固(gu)(gu)溶(rong)(rong)(rong)(rong)熱處(chu)理(li)(li)溫度的(de)(de)(de)(de)(de)(de)(de)(de)進一(yi)步升(sheng)(sheng)高(gao)(gao)(gao)使鋼(gang)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)兩相比(bi)例(li)失調(diao)，表(biao)(biao)(biao)(biao)現(xian)(xian)為鐵素體(ti)相含量大幅(fu)升(sheng)(sheng)高(gao)(gao)(gao)，奧氏體(ti)相含量減(jian)(jian)小，不(bu)利于鋼(gang)表(biao)(biao)(biao)(biao)面(mian)(mian)鈍(dun)(dun)化(hua)(hua)(hua)(hua)膜的(de)(de)(de)(de)(de)(de)(de)(de)穩(wen)定(ding)，導致鈍(dun)(dun)化(hua)(hua)(hua)(hua)膜電(dian)(dian)(dian)(dian)(dian)(dian)阻（Rf)減(jian)(jian)小，實(shi)際表(biao)(biao)(biao)(biao)現(xian)(xian)為鋼(gang)的(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)(kang)(kang)(kang)(kang)蝕(shi)性(xing)能(neng)(neng)(neng)下降，這與動電(dian)(dian)(dian)(dian)(dian)(dian)位掃描(miao)獲得(de)的(de)(de)(de)(de)(de)(de)(de)(de)結論相同(tong)(tong)。