1. 動(dong)電(dian)位極化曲(qu)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(gang)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)(de)(de)(de)2507雙相(xiang)(xiang)(xiang)不銹鋼(gang)于3.5%NaCl溶(rong)液中(zhong)動(dong)電位極化后的(de)(de)(de)(de)腐(fu)蝕(shi)形(xing)貌如(ru)圖(tu)5.4所示(shi)，圖(tu)中(zhong)深色是(shi)鐵(tie)(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)、淺色是(shi)奧(ao)(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)y相(xiang)(xiang)(xiang)、黑(hei)色圓點(dian)(dian)是(shi)點(dian)(dian)蝕(shi)坑。從(cong)(cong)(cong)圖(tu)5.4可(ke)知點(dian)(dian)蝕(shi)坑主要(yao)(yao)(yao)存在(zai)于鐵(tie)(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)x相(xiang)(xiang)(xiang)上，這說明(ming)奧(ao)(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)y相(xiang)(xiang)(xiang)比(bi)鐵(tie)(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)要(yao)(yao)(yao)穩定(ding)，有著較(jiao)(jiao)(jiao)優的(de)(de)(de)(de)抗點(dian)(dian)腐(fu)蝕(shi)性能(neng)。奧(ao)(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)相(xiang)(xiang)(xiang)比(bi)于鐵(tie)(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)有較(jiao)(jiao)(jiao)好的(de)(de)(de)(de)抗點(dian)(dian)蝕(shi)性能(neng)的(de)(de)(de)(de)原(yuan)因(yin)在(zai)于元(yuan)素(su)(su)(su)(su)(su)N的(de)(de)(de)(de)作用。元(yuan)素(su)(su)(su)(su)(su)N是(shi)奧(ao)(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)形(xing)成元(yuan)素(su)(su)(su)(su)(su)，于奧(ao)(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)中(zhong)的(de)(de)(de)(de)溶(rong)解度要(yao)(yao)(yao)比(bi)在(zai)鐵(tie)(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)中(zhong)的(de)(de)(de)(de)大，此外(wai)N能(neng)夠讓Cr和Mo元(yuan)素(su)(su)(su)(su)(su)從(cong)(cong)(cong)鐵(tie)(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)遷移(yi)到奧(ao)(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)中(zhong)，N顯著影響著這兩種元(yuan)素(su)(su)(su)(su)(su)在(zai)奧(ao)(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)和鐵(tie)(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)中(zhong)的(de)(de)(de)(de)分配，兩相(xiang)(xiang)(xiang)中(zhong)合金元(yuan)素(su)(su)(su)(su)(su)含(han)量(liang)的(de)(de)(de)(de)差值隨N元(yuan)素(su)(su)(su)(su)(su)含(han)量(liang)的(de)(de)(de)(de)增多而降低，所以奧(ao)(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)的(de)(de)(de)(de)點(dian)(dian)蝕(shi)電位較(jiao)(jiao)(jiao)鐵(tie)(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)要(yao)(yao)(yao)高，從(cong)(cong)(cong)而蝕(shi)坑較(jiao)(jiao)(jiao)先在(zai)Eb相(xiang)(xiang)(xiang)對(dui)比(bi)較(jiao)(jiao)(jiao)低的(de)(de)(de)(de)鐵(tie)(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)α相(xiang)(xiang)(xiang)中(zhong)產(chan)生。

2. 交流阻抗(kang)測試分(fen)析

  1000℃、1050℃、1100℃、1150℃及1200℃固(gu)溶(rong)(rong)態的(de)(de)(de)(de)(de)(de)(de)(de)(de)2507 雙(shuang)(shuang)(shuang)(shuang)相(xiang)(xiang)(xiang)(xiang)(xiang)不(bu)(bu)銹(xiu)鋼(gang)(gang)30℃下于(yu)3.5%NaCl溶(rong)(rong)液(ye)中(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)Nyquist 圖如(ru)圖5.5所(suo)(suo)示(shi)(shi)，從(cong)圖中(zhong)可(ke)以(yi)(yi)很(hen)明顯(xian)看出隨固(gu)溶(rong)(rong)熱(re)處(chu)(chu)(chu)理溫(wen)(wen)(wen)度(du)的(de)(de)(de)(de)(de)(de)(de)(de)(de)增(zeng)高(gao)容(rong)(rong)(rong)抗(kang)(kang)弧(hu)半(ban)(ban)徑(jing)(jing)先(xian)(xian)增(zeng)大(da)(da)后(hou)(hou)(hou)減小，1050℃時(shi)容(rong)(rong)(rong)抗(kang)(kang)弧(hu)半(ban)(ban)徑(jing)(jing)最大(da)(da)。通常(chang)情況(kuang)下界面(mian)(mian)間(jian)電(dian)(dian)(dian)(dian)(dian)荷的(de)(de)(de)(de)(de)(de)(de)(de)(de)遷(qian)(qian)移(yi)促進了(le)高(gao)頻區容(rong)(rong)(rong)抗(kang)(kang)弧(hu)的(de)(de)(de)(de)(de)(de)(de)(de)(de)形(xing)成，容(rong)(rong)(rong)抗(kang)(kang)弧(hu)與雙(shuang)(shuang)(shuang)(shuang)電(dian)(dian)(dian)(dian)(dian)層容(rong)(rong)(rong)抗(kang)(kang)及金屬(shu)材料(liao)溶(rong)(rong)解(jie)的(de)(de)(de)(de)(de)(de)(de)(de)(de)綜合作用(yong)(yong)有(you)關，并且金屬(shu)－溶(rong)(rong)液(ye)界面(mian)(mian)的(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)荷轉移(yi)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)影響著(zhu)(zhu)容(rong)(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)小，電(dian)(dian)(dian)(dian)(dian)荷在金屬(shu)－溶(rong)(rong)液(ye)界面(mian)(mian)轉移(yi)時(shi)受到的(de)(de)(de)(de)(de)(de)(de)(de)(de)阻(zu)(zu)力越強意味著(zhu)(zhu)容(rong)(rong)(rong)抗(kang)(kang)弧(hu)半(ban)(ban)徑(jing)(jing)越大(da)(da)，即(ji)意味著(zhu)(zhu)金屬(shu)的(de)(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)蝕(shi)(shi)性(xing)能(neng)越優(you)。從(cong)圖5.5容(rong)(rong)(rong)抗(kang)(kang)弧(hu)半(ban)(ban)徑(jing)(jing)的(de)(de)(de)(de)(de)(de)(de)(de)(de)改變趨勢(shi)可(ke)知，固(gu)溶(rong)(rong)熱(re)處(chu)(chu)(chu)理溫(wen)(wen)(wen)度(du)升(sheng)(sheng)高(gao)使(shi)DSS2507的(de)(de)(de)(de)(de)(de)(de)(de)(de)耐蝕(shi)(shi)性(xing)能(neng)首(shou)先(xian)(xian)增(zeng)強而后(hou)(hou)(hou)減弱(ruo)(ruo)，1050℃時(shi)2507雙(shuang)(shuang)(shuang)(shuang)相(xiang)(xiang)(xiang)(xiang)(xiang)不(bu)(bu)銹(xiu)鋼(gang)(gang)的(de)(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)腐(fu)蝕(shi)(shi)性(xing)能(neng)最優(you)。不(bu)(bu)同固(gu)溶(rong)(rong)態的(de)(de)(de)(de)(de)(de)(de)(de)(de)2507雙(shuang)(shuang)(shuang)(shuang)相(xiang)(xiang)(xiang)(xiang)(xiang)不(bu)(bu)銹(xiu)鋼(gang)(gang)于(yu)3.5%NaCl溶(rong)(rong)液(ye)中(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)等效電(dian)(dian)(dian)(dian)(dian)路如(ru)圖5.6所(suo)(suo)示(shi)(shi)，采(cai)用(yong)(yong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)是R(C(R(CR))).Rs指(zhi)參(can)比電(dian)(dian)(dian)(dian)(dian)極和工作電(dian)(dian)(dian)(dian)(dian)極間(jian)的(de)(de)(de)(de)(de)(de)(de)(de)(de)溶(rong)(rong)液(ye)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)；Cd1為(wei)雙(shuang)(shuang)(shuang)(shuang)電(dian)(dian)(dian)(dian)(dian)層電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)；Rct為(wei)電(dian)(dian)(dian)(dian)(dian)荷轉移(yi)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)，其值能(neng)夠反應(ying)電(dian)(dian)(dian)(dian)(dian)荷在電(dian)(dian)(dian)(dian)(dian)化(hua)(hua)學(xue)反應(ying)過(guo)程中(zhong)透過(guo)電(dian)(dian)(dian)(dian)(dian)極以(yi)(yi)及于(yu)電(dian)(dian)(dian)(dian)(dian)解(jie)質溶(rong)(rong)液(ye)中(zhong)兩(liang)相(xiang)(xiang)(xiang)(xiang)(xiang)界面(mian)(mian)遷(qian)(qian)移(yi)難易的(de)(de)(de)(de)(de)(de)(de)(de)(de)大(da)(da)小，也能(neng)夠反映(ying)金屬(shu)發生腐(fu)蝕(shi)(shi)反應(ying)的(de)(de)(de)(de)(de)(de)(de)(de)(de)快(kuai)慢，一般情況(kuang)下Rct值越高(gao)意味著(zhu)(zhu)電(dian)(dian)(dian)(dian)(dian)荷遷(qian)(qian)移(yi)過(guo)程中(zhong)所(suo)(suo)受的(de)(de)(de)(de)(de)(de)(de)(de)(de)阻(zu)(zu)力越強，即(ji)材料(liao)的(de)(de)(de)(de)(de)(de)(de)(de)(de)耐腐(fu)蝕(shi)(shi)性(xing)能(neng)越好；Cf表(biao)(biao)示(shi)(shi)鈍(dun)化(hua)(hua)膜(mo)(mo)(mo)(mo)(mo)電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)，Rf表(biao)(biao)示(shi)(shi)鈍(dun)化(hua)(hua)膜(mo)(mo)(mo)(mo)(mo)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)。采(cai)用(yong)(yong)ZsimpWin軟件對等效電(dian)(dian)(dian)(dian)(dian)路模擬計算得到各元(yuan)件的(de)(de)(de)(de)(de)(de)(de)(de)(de)數(shu)值如(ru)表(biao)(biao)5.2所(suo)(suo)列。從(cong)表(biao)(biao)中(zhong)看出雙(shuang)(shuang)(shuang)(shuang)電(dian)(dian)(dian)(dian)(dian)層電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)（Cdl)及鈍(dun)化(hua)(hua)膜(mo)(mo)(mo)(mo)(mo)電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)（Cr)隨固(gu)溶(rong)(rong)溫(wen)(wen)(wen)度(du)的(de)(de)(de)(de)(de)(de)(de)(de)(de)升(sheng)(sheng)高(gao)呈先(xian)(xian)減小后(hou)(hou)(hou)增(zeng)大(da)(da)的(de)(de)(de)(de)(de)(de)(de)(de)(de)趨勢(shi)；電(dian)(dian)(dian)(dian)(dian)荷轉移(yi)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)（Rct)和鈍(dun)化(hua)(hua)膜(mo)(mo)(mo)(mo)(mo)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)（Rf)呈先(xian)(xian)變大(da)(da)后(hou)(hou)(hou)減小的(de)(de)(de)(de)(de)(de)(de)(de)(de)趨勢(shi)，即(ji)電(dian)(dian)(dian)(dian)(dian)化(hua)(hua)學(xue)反應(ying)阻(zu)(zu)力隨固(gu)溶(rong)(rong)熱(re)處(chu)(chu)(chu)理溫(wen)(wen)(wen)度(du)的(de)(de)(de)(de)(de)(de)(de)(de)(de)增(zeng)高(gao)先(xian)(xian)增(zeng)強后(hou)(hou)(hou)減弱(ruo)(ruo)，2507雙(shuang)(shuang)(shuang)(shuang)相(xiang)(xiang)(xiang)(xiang)(xiang)不(bu)(bu)銹(xiu)鋼(gang)(gang)的(de)(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)腐(fu)蝕(shi)(shi)性(xing)能(neng)表(biao)(biao)現(xian)為(wei)先(xian)(xian)增(zeng)強后(hou)(hou)(hou)減弱(ruo)(ruo)。1000℃時(shi)鋼(gang)(gang)的(de)(de)(de)(de)(de)(de)(de)(de)(de)相(xiang)(xiang)(xiang)(xiang)(xiang)界處(chu)(chu)(chu)有(you)σ相(xiang)(xiang)(xiang)(xiang)(xiang)析出，σ相(xiang)(xiang)(xiang)(xiang)(xiang)硬而脆降(jiang)低了(le)鋼(gang)(gang)表(biao)(biao)面(mian)(mian)鈍(dun)化(hua)(hua)膜(mo)(mo)(mo)(mo)(mo)的(de)(de)(de)(de)(de)(de)(de)(de)(de)穩定(ding)(ding)，表(biao)(biao)現(xian)為(wei)具有(you)較低的(de)(de)(de)(de)(de)(de)(de)(de)(de)鈍(dun)化(hua)(hua)膜(mo)(mo)(mo)(mo)(mo)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)（Rf);1050℃時(shi)鋼(gang)(gang)中(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)兩(liang)相(xiang)(xiang)(xiang)(xiang)(xiang)比例約(yue)為(wei)1:1,兩(liang)相(xiang)(xiang)(xiang)(xiang)(xiang)分布較均勻(yun)且成分穩定(ding)(ding)有(you)利于(yu)鈍(dun)化(hua)(hua)膜(mo)(mo)(mo)(mo)(mo)的(de)(de)(de)(de)(de)(de)(de)(de)(de)穩定(ding)(ding)，具體表(biao)(biao)現(xian)為(wei)鈍(dun)化(hua)(hua)膜(mo)(mo)(mo)(mo)(mo)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)（Rf)值較高(gao)，表(biao)(biao)明此刻(ke)離子遷(qian)(qian)移(yi)時(shi)所(suo)(suo)受阻(zu)(zu)力較大(da)(da)，進而2507雙(shuang)(shuang)(shuang)(shuang)相(xiang)(xiang)(xiang)(xiang)(xiang)不(bu)(bu)銹(xiu)鋼(gang)(gang)的(de)(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)腐(fu)蝕(shi)(shi)能(neng)力最佳；固(gu)溶(rong)(rong)熱(re)處(chu)(chu)(chu)理溫(wen)(wen)(wen)度(du)的(de)(de)(de)(de)(de)(de)(de)(de)(de)進一步升(sheng)(sheng)高(gao)使(shi)鋼(gang)(gang)中(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)兩(liang)相(xiang)(xiang)(xiang)(xiang)(xiang)比例失調，表(biao)(biao)現(xian)為(wei)鐵素體相(xiang)(xiang)(xiang)(xiang)(xiang)含(han)量大(da)(da)幅升(sheng)(sheng)高(gao)，奧氏體相(xiang)(xiang)(xiang)(xiang)(xiang)含(han)量減小，不(bu)(bu)利于(yu)鋼(gang)(gang)表(biao)(biao)面(mian)(mian)鈍(dun)化(hua)(hua)膜(mo)(mo)(mo)(mo)(mo)的(de)(de)(de)(de)(de)(de)(de)(de)(de)穩定(ding)(ding)，導致鈍(dun)化(hua)(hua)膜(mo)(mo)(mo)(mo)(mo)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)（Rf)減小，實(shi)際(ji)表(biao)(biao)現(xian)為(wei)鋼(gang)(gang)的(de)(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)蝕(shi)(shi)性(xing)能(neng)下降(jiang)，這與動電(dian)(dian)(dian)(dian)(dian)位掃描獲得的(de)(de)(de)(de)(de)(de)(de)(de)(de)結論相(xiang)(xiang)(xiang)(xiang)(xiang)同。