1. 動電(dian)位(wei)極(ji)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(bu)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(xiang)不銹(xiu)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)(de)(de)(de)2507雙相(xiang)不銹(xiu)鋼(gang)于3.5%NaCl溶(rong)液中(zhong)動電位(wei)極(ji)化(hua)后的(de)(de)(de)(de)腐蝕(shi)(shi)形貌如圖(tu)5.4所示(shi)，圖(tu)中(zhong)深色是(shi)鐵素(su)(su)(su)(su)(su)(su)(su)(su)(su)體(ti)(ti)α相(xiang)、淺色是(shi)奧(ao)(ao)氏(shi)(shi)體(ti)(ti)y相(xiang)、黑色圓點(dian)(dian)(dian)(dian)是(shi)點(dian)(dian)(dian)(dian)蝕(shi)(shi)坑。從(cong)圖(tu)5.4可知點(dian)(dian)(dian)(dian)蝕(shi)(shi)坑主要(yao)存在(zai)于鐵素(su)(su)(su)(su)(su)(su)(su)(su)(su)體(ti)(ti)x相(xiang)上，這(zhe)說明(ming)奧(ao)(ao)氏(shi)(shi)體(ti)(ti)y相(xiang)比(bi)鐵素(su)(su)(su)(su)(su)(su)(su)(su)(su)體(ti)(ti)α相(xiang)要(yao)穩定，有著(zhu)較(jiao)(jiao)(jiao)優的(de)(de)(de)(de)抗點(dian)(dian)(dian)(dian)腐蝕(shi)(shi)性(xing)能(neng)(neng)。奧(ao)(ao)氏(shi)(shi)體(ti)(ti)γ相(xiang)相(xiang)比(bi)于鐵素(su)(su)(su)(su)(su)(su)(su)(su)(su)體(ti)(ti)α相(xiang)有較(jiao)(jiao)(jiao)好(hao)的(de)(de)(de)(de)抗點(dian)(dian)(dian)(dian)蝕(shi)(shi)性(xing)能(neng)(neng)的(de)(de)(de)(de)原(yuan)因在(zai)于元(yuan)素(su)(su)(su)(su)(su)(su)(su)(su)(su)N的(de)(de)(de)(de)作用。元(yuan)素(su)(su)(su)(su)(su)(su)(su)(su)(su)N是(shi)奧(ao)(ao)氏(shi)(shi)體(ti)(ti)形成元(yuan)素(su)(su)(su)(su)(su)(su)(su)(su)(su)，于奧(ao)(ao)氏(shi)(shi)體(ti)(ti)γ相(xiang)中(zhong)的(de)(de)(de)(de)溶(rong)解度要(yao)比(bi)在(zai)鐵素(su)(su)(su)(su)(su)(su)(su)(su)(su)體(ti)(ti)α相(xiang)中(zhong)的(de)(de)(de)(de)大，此外(wai)N能(neng)(neng)夠讓Cr和Mo元(yuan)素(su)(su)(su)(su)(su)(su)(su)(su)(su)從(cong)鐵素(su)(su)(su)(su)(su)(su)(su)(su)(su)體(ti)(ti)α相(xiang)遷移到奧(ao)(ao)氏(shi)(shi)體(ti)(ti)γ相(xiang)中(zhong)，N顯著(zhu)影響著(zhu)這(zhe)兩種元(yuan)素(su)(su)(su)(su)(su)(su)(su)(su)(su)在(zai)奧(ao)(ao)氏(shi)(shi)體(ti)(ti)γ相(xiang)和鐵素(su)(su)(su)(su)(su)(su)(su)(su)(su)體(ti)(ti)α相(xiang)中(zhong)的(de)(de)(de)(de)分配(pei)，兩相(xiang)中(zhong)合金元(yuan)素(su)(su)(su)(su)(su)(su)(su)(su)(su)含量的(de)(de)(de)(de)差值隨N元(yuan)素(su)(su)(su)(su)(su)(su)(su)(su)(su)含量的(de)(de)(de)(de)增多而降低，所以(yi)奧(ao)(ao)氏(shi)(shi)體(ti)(ti)γ相(xiang)的(de)(de)(de)(de)點(dian)(dian)(dian)(dian)蝕(shi)(shi)電位(wei)較(jiao)(jiao)(jiao)鐵素(su)(su)(su)(su)(su)(su)(su)(su)(su)體(ti)(ti)α相(xiang)要(yao)高，從(cong)而蝕(shi)(shi)坑較(jiao)(jiao)(jiao)先在(zai)Eb相(xiang)對比(bi)較(jiao)(jiao)(jiao)低的(de)(de)(de)(de)鐵素(su)(su)(su)(su)(su)(su)(su)(su)(su)體(ti)(ti)α相(xiang)中(zhong)產生。

2. 交流阻(zu)抗測(ce)試(shi)分析

  1000℃、1050℃、1100℃、1150℃及(ji)(ji)1200℃固(gu)溶(rong)(rong)態(tai)的(de)(de)(de)(de)(de)(de)(de)(de)2507 雙(shuang)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)不銹(xiu)(xiu)鋼(gang)30℃下(xia)于3.5%NaCl溶(rong)(rong)液中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)Nyquist 圖(tu)如圖(tu)5.5所(suo)示(shi)，從(cong)圖(tu)中(zhong)(zhong)(zhong)(zhong)可以很明顯看出(chu)隨(sui)固(gu)溶(rong)(rong)熱處理(li)溫(wen)(wen)(wen)度的(de)(de)(de)(de)(de)(de)(de)(de)增(zeng)高(gao)容(rong)(rong)(rong)抗(kang)(kang)弧半徑(jing)先(xian)增(zeng)大(da)后(hou)(hou)減小(xiao)(xiao)，1050℃時容(rong)(rong)(rong)抗(kang)(kang)弧半徑(jing)最大(da)。通常(chang)情況下(xia)界(jie)面(mian)(mian)間電(dian)(dian)(dian)(dian)(dian)荷(he)(he)(he)(he)的(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)弧的(de)(de)(de)(de)(de)(de)(de)(de)形成(cheng)，容(rong)(rong)(rong)抗(kang)(kang)弧與(yu)雙(shuang)電(dian)(dian)(dian)(dian)(dian)層(ceng)容(rong)(rong)(rong)抗(kang)(kang)及(ji)(ji)金屬(shu)(shu)材(cai)料(liao)溶(rong)(rong)解的(de)(de)(de)(de)(de)(de)(de)(de)綜合作用有關，并且金屬(shu)(shu)－溶(rong)(rong)液界(jie)面(mian)(mian)的(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)荷(he)(he)(he)(he)轉(zhuan)移(yi)電(dian)(dian)(dian)(dian)(dian)阻(zu)影響著(zhu)容(rong)(rong)(rong)抗(kang)(kang)弧半徑(jing)的(de)(de)(de)(de)(de)(de)(de)(de)大(da)小(xiao)(xiao)，電(dian)(dian)(dian)(dian)(dian)荷(he)(he)(he)(he)在(zai)金屬(shu)(shu)－溶(rong)(rong)液界(jie)面(mian)(mian)轉(zhuan)移(yi)時受(shou)到的(de)(de)(de)(de)(de)(de)(de)(de)阻(zu)力(li)(li)(li)越(yue)強(qiang)意(yi)味(wei)著(zhu)容(rong)(rong)(rong)抗(kang)(kang)弧半徑(jing)越(yue)大(da)，即(ji)意(yi)味(wei)著(zhu)金屬(shu)(shu)的(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)蝕(shi)性能(neng)越(yue)優。從(cong)圖(tu)5.5容(rong)(rong)(rong)抗(kang)(kang)弧半徑(jing)的(de)(de)(de)(de)(de)(de)(de)(de)改(gai)變趨(qu)(qu)勢(shi)可知，固(gu)溶(rong)(rong)熱處理(li)溫(wen)(wen)(wen)度升(sheng)高(gao)使DSS2507的(de)(de)(de)(de)(de)(de)(de)(de)耐蝕(shi)性能(neng)首先(xian)增(zeng)強(qiang)而后(hou)(hou)減弱，1050℃時2507雙(shuang)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)不銹(xiu)(xiu)鋼(gang)的(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)腐(fu)蝕(shi)性能(neng)最優。不同固(gu)溶(rong)(rong)態(tai)的(de)(de)(de)(de)(de)(de)(de)(de)2507雙(shuang)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)不銹(xiu)(xiu)鋼(gang)于3.5%NaCl溶(rong)(rong)液中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)等效電(dian)(dian)(dian)(dian)(dian)路如圖(tu)5.6所(suo)示(shi)，采(cai)用的(de)(de)(de)(de)(de)(de)(de)(de)是R(C(R(CR))).Rs指參比(bi)電(dian)(dian)(dian)(dian)(dian)極(ji)和工作電(dian)(dian)(dian)(dian)(dian)極(ji)間的(de)(de)(de)(de)(de)(de)(de)(de)溶(rong)(rong)液電(dian)(dian)(dian)(dian)(dian)阻(zu)；Cd1為(wei)雙(shuang)電(dian)(dian)(dian)(dian)(dian)層(ceng)電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)；Rct為(wei)電(dian)(dian)(dian)(dian)(dian)荷(he)(he)(he)(he)轉(zhuan)移(yi)電(dian)(dian)(dian)(dian)(dian)阻(zu)，其(qi)值能(neng)夠(gou)反(fan)(fan)應電(dian)(dian)(dian)(dian)(dian)荷(he)(he)(he)(he)在(zai)電(dian)(dian)(dian)(dian)(dian)化(hua)(hua)(hua)(hua)學反(fan)(fan)應過程中(zhong)(zhong)(zhong)(zhong)透過電(dian)(dian)(dian)(dian)(dian)極(ji)以及(ji)(ji)于電(dian)(dian)(dian)(dian)(dian)解質溶(rong)(rong)液中(zhong)(zhong)(zhong)(zhong)兩相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)界(jie)面(mian)(mian)遷(qian)(qian)移(yi)難易的(de)(de)(de)(de)(de)(de)(de)(de)大(da)小(xiao)(xiao)，也能(neng)夠(gou)反(fan)(fan)映金屬(shu)(shu)發生腐(fu)蝕(shi)反(fan)(fan)應的(de)(de)(de)(de)(de)(de)(de)(de)快慢，一般情況下(xia)Rct值越(yue)高(gao)意(yi)味(wei)著(zhu)電(dian)(dian)(dian)(dian)(dian)荷(he)(he)(he)(he)遷(qian)(qian)移(yi)過程中(zhong)(zhong)(zhong)(zhong)所(suo)受(shou)的(de)(de)(de)(de)(de)(de)(de)(de)阻(zu)力(li)(li)(li)越(yue)強(qiang)，即(ji)材(cai)料(liao)的(de)(de)(de)(de)(de)(de)(de)(de)耐腐(fu)蝕(shi)性能(neng)越(yue)好；Cf表(biao)(biao)(biao)示(shi)鈍(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)，Rf表(biao)(biao)(biao)示(shi)鈍(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)電(dian)(dian)(dian)(dian)(dian)阻(zu)。采(cai)用ZsimpWin軟件(jian)對等效電(dian)(dian)(dian)(dian)(dian)路模擬計算得(de)到各元件(jian)的(de)(de)(de)(de)(de)(de)(de)(de)數值如表(biao)(biao)(biao)5.2所(suo)列。從(cong)表(biao)(biao)(biao)中(zhong)(zhong)(zhong)(zhong)看出(chu)雙(shuang)電(dian)(dian)(dian)(dian)(dian)層(ceng)電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)（Cdl)及(ji)(ji)鈍(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)（Cr)隨(sui)固(gu)溶(rong)(rong)溫(wen)(wen)(wen)度的(de)(de)(de)(de)(de)(de)(de)(de)升(sheng)高(gao)呈(cheng)先(xian)減小(xiao)(xiao)后(hou)(hou)增(zeng)大(da)的(de)(de)(de)(de)(de)(de)(de)(de)趨(qu)(qu)勢(shi)；電(dian)(dian)(dian)(dian)(dian)荷(he)(he)(he)(he)轉(zhuan)移(yi)電(dian)(dian)(dian)(dian)(dian)阻(zu)（Rct)和鈍(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)電(dian)(dian)(dian)(dian)(dian)阻(zu)（Rf)呈(cheng)先(xian)變大(da)后(hou)(hou)減小(xiao)(xiao)的(de)(de)(de)(de)(de)(de)(de)(de)趨(qu)(qu)勢(shi)，即(ji)電(dian)(dian)(dian)(dian)(dian)化(hua)(hua)(hua)(hua)學反(fan)(fan)應阻(zu)力(li)(li)(li)隨(sui)固(gu)溶(rong)(rong)熱處理(li)溫(wen)(wen)(wen)度的(de)(de)(de)(de)(de)(de)(de)(de)增(zeng)高(gao)先(xian)增(zeng)強(qiang)后(hou)(hou)減弱，2507雙(shuang)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)不銹(xiu)(xiu)鋼(gang)的(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)腐(fu)蝕(shi)性能(neng)表(biao)(biao)(biao)現(xian)為(wei)先(xian)增(zeng)強(qiang)后(hou)(hou)減弱。1000℃時鋼(gang)的(de)(de)(de)(de)(de)(de)(de)(de)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)界(jie)處有σ相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)析出(chu)，σ相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)硬而脆降(jiang)低了(le)鋼(gang)表(biao)(biao)(biao)面(mian)(mian)鈍(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)的(de)(de)(de)(de)(de)(de)(de)(de)穩定(ding)，表(biao)(biao)(biao)現(xian)為(wei)具有較(jiao)低的(de)(de)(de)(de)(de)(de)(de)(de)鈍(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)電(dian)(dian)(dian)(dian)(dian)阻(zu)（Rf);1050℃時鋼(gang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)兩相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)比(bi)例(li)約為(wei)1:1,兩相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)分(fen)(fen)布較(jiao)均勻且成(cheng)分(fen)(fen)穩定(ding)有利于鈍(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)的(de)(de)(de)(de)(de)(de)(de)(de)穩定(ding)，具體表(biao)(biao)(biao)現(xian)為(wei)鈍(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)電(dian)(dian)(dian)(dian)(dian)阻(zu)（Rf)值較(jiao)高(gao)，表(biao)(biao)(biao)明此刻離子遷(qian)(qian)移(yi)時所(suo)受(shou)阻(zu)力(li)(li)(li)較(jiao)大(da)，進而2507雙(shuang)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)不銹(xiu)(xiu)鋼(gang)的(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)腐(fu)蝕(shi)能(neng)力(li)(li)(li)最佳；固(gu)溶(rong)(rong)熱處理(li)溫(wen)(wen)(wen)度的(de)(de)(de)(de)(de)(de)(de)(de)進一步升(sheng)高(gao)使鋼(gang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)兩相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)比(bi)例(li)失調，表(biao)(biao)(biao)現(xian)為(wei)鐵素體相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)含量大(da)幅升(sheng)高(gao)，奧氏體相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)含量減小(xiao)(xiao)，不利于鋼(gang)表(biao)(biao)(biao)面(mian)(mian)鈍(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)的(de)(de)(de)(de)(de)(de)(de)(de)穩定(ding)，導致(zhi)鈍(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)電(dian)(dian)(dian)(dian)(dian)阻(zu)（Rf)減小(xiao)(xiao)，實(shi)際表(biao)(biao)(biao)現(xian)為(wei)鋼(gang)的(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)蝕(shi)性能(neng)下(xia)降(jiang)，這與(yu)動電(dian)(dian)(dian)(dian)(dian)位(wei)掃(sao)描(miao)獲得(de)的(de)(de)(de)(de)(de)(de)(de)(de)結(jie)論相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)同。