1. 動電(dian)位極化(hua)曲線(xian)分(fen)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(gang)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(bu)銹(xiu)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(gu)溶態為1050℃的(de)2507雙相(xiang)(xiang)(xiang)(xiang)不銹(xiu)鋼于(yu)3.5%NaCl溶液中(zhong)(zhong)動電(dian)(dian)位極化后的(de)腐蝕形貌如圖(tu)(tu)5.4所(suo)示，圖(tu)(tu)中(zhong)(zhong)深色(se)是(shi)鐵(tie)(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)、淺色(se)是(shi)奧(ao)(ao)氏(shi)(shi)(shi)體(ti)(ti)(ti)(ti)(ti)y相(xiang)(xiang)(xiang)(xiang)、黑色(se)圓點(dian)是(shi)點(dian)蝕坑。從圖(tu)(tu)5.4可(ke)知點(dian)蝕坑主要(yao)存在于(yu)鐵(tie)(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)x相(xiang)(xiang)(xiang)(xiang)上，這(zhe)說明奧(ao)(ao)氏(shi)(shi)(shi)體(ti)(ti)(ti)(ti)(ti)y相(xiang)(xiang)(xiang)(xiang)比鐵(tie)(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)要(yao)穩定，有著(zhu)(zhu)較(jiao)(jiao)優的(de)抗點(dian)腐蝕性(xing)能。奧(ao)(ao)氏(shi)(shi)(shi)體(ti)(ti)(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)(xiang)相(xiang)(xiang)(xiang)(xiang)比于(yu)鐵(tie)(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)有較(jiao)(jiao)好的(de)抗點(dian)蝕性(xing)能的(de)原因在于(yu)元素(su)(su)(su)N的(de)作用。元素(su)(su)(su)N是(shi)奧(ao)(ao)氏(shi)(shi)(shi)體(ti)(ti)(ti)(ti)(ti)形成元素(su)(su)(su)，于(yu)奧(ao)(ao)氏(shi)(shi)(shi)體(ti)(ti)(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)的(de)溶解度要(yao)比在鐵(tie)(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)的(de)大，此外N能夠讓Cr和Mo元素(su)(su)(su)從鐵(tie)(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)遷(qian)移到(dao)奧(ao)(ao)氏(shi)(shi)(shi)體(ti)(ti)(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)，N顯著(zhu)(zhu)影響著(zhu)(zhu)這(zhe)兩(liang)種元素(su)(su)(su)在奧(ao)(ao)氏(shi)(shi)(shi)體(ti)(ti)(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)(xiang)和鐵(tie)(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)的(de)分配(pei)，兩(liang)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)合金元素(su)(su)(su)含量的(de)差值隨N元素(su)(su)(su)含量的(de)增多而降低，所(suo)以奧(ao)(ao)氏(shi)(shi)(shi)體(ti)(ti)(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)(xiang)的(de)點(dian)蝕電(dian)(dian)位較(jiao)(jiao)鐵(tie)(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)要(yao)高，從而蝕坑較(jiao)(jiao)先在Eb相(xiang)(xiang)(xiang)(xiang)對(dui)比較(jiao)(jiao)低的(de)鐵(tie)(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)產(chan)生。

2. 交流阻抗測試分析(xi)

  1000℃、1050℃、1100℃、1150℃及(ji)(ji)1200℃固(gu)溶(rong)(rong)(rong)(rong)態(tai)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)2507 雙(shuang)相(xiang)不(bu)(bu)銹(xiu)鋼(gang)(gang)30℃下(xia)于3.5%NaCl溶(rong)(rong)(rong)(rong)液(ye)中(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)Nyquist 圖(tu)(tu)如圖(tu)(tu)5.5所示，從圖(tu)(tu)中(zhong)可以很明(ming)顯看出隨(sui)固(gu)溶(rong)(rong)(rong)(rong)熱(re)處理(li)溫(wen)度(du)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)增(zeng)(zeng)高(gao)容(rong)抗(kang)(kang)(kang)弧(hu)(hu)半(ban)徑(jing)先(xian)(xian)(xian)增(zeng)(zeng)大(da)后減小(xiao)(xiao)，1050℃時(shi)(shi)(shi)容(rong)抗(kang)(kang)(kang)弧(hu)(hu)半(ban)徑(jing)最(zui)大(da)。通常情況下(xia)界(jie)面(mian)間電(dian)(dian)(dian)(dian)荷(he)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)遷移(yi)(yi)促進了高(gao)頻區容(rong)抗(kang)(kang)(kang)弧(hu)(hu)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)形成，容(rong)抗(kang)(kang)(kang)弧(hu)(hu)與(yu)雙(shuang)電(dian)(dian)(dian)(dian)層(ceng)(ceng)(ceng)容(rong)抗(kang)(kang)(kang)及(ji)(ji)金屬(shu)材料溶(rong)(rong)(rong)(rong)解的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)綜合作(zuo)用(yong)有關，并且金屬(shu)－溶(rong)(rong)(rong)(rong)液(ye)界(jie)面(mian)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)荷(he)轉(zhuan)(zhuan)移(yi)(yi)電(dian)(dian)(dian)(dian)阻(zu)(zu)影(ying)響著(zhu)容(rong)抗(kang)(kang)(kang)弧(hu)(hu)半(ban)徑(jing)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)大(da)小(xiao)(xiao)，電(dian)(dian)(dian)(dian)荷(he)在金屬(shu)－溶(rong)(rong)(rong)(rong)液(ye)界(jie)面(mian)轉(zhuan)(zhuan)移(yi)(yi)時(shi)(shi)(shi)受(shou)到的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)阻(zu)(zu)力(li)(li)(li)越(yue)(yue)(yue)強(qiang)意味著(zhu)容(rong)抗(kang)(kang)(kang)弧(hu)(hu)半(ban)徑(jing)越(yue)(yue)(yue)大(da)，即意味著(zhu)金屬(shu)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)(kang)蝕(shi)性能(neng)(neng)越(yue)(yue)(yue)優(you)。從圖(tu)(tu)5.5容(rong)抗(kang)(kang)(kang)弧(hu)(hu)半(ban)徑(jing)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)改變趨勢(shi)可知(zhi)，固(gu)溶(rong)(rong)(rong)(rong)熱(re)處理(li)溫(wen)度(du)升高(gao)使DSS2507的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)耐蝕(shi)性能(neng)(neng)首先(xian)(xian)(xian)增(zeng)(zeng)強(qiang)而后減弱，1050℃時(shi)(shi)(shi)2507雙(shuang)相(xiang)不(bu)(bu)銹(xiu)鋼(gang)(gang)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)(kang)腐(fu)(fu)蝕(shi)性能(neng)(neng)最(zui)優(you)。不(bu)(bu)同固(gu)溶(rong)(rong)(rong)(rong)態(tai)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)2507雙(shuang)相(xiang)不(bu)(bu)銹(xiu)鋼(gang)(gang)于3.5%NaCl溶(rong)(rong)(rong)(rong)液(ye)中(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)等效電(dian)(dian)(dian)(dian)路如圖(tu)(tu)5.6所示，采用(yong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)是R(C(R(CR))).Rs指(zhi)參比電(dian)(dian)(dian)(dian)極(ji)和(he)工作(zuo)電(dian)(dian)(dian)(dian)極(ji)間的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)溶(rong)(rong)(rong)(rong)液(ye)電(dian)(dian)(dian)(dian)阻(zu)(zu)；Cd1為(wei)雙(shuang)電(dian)(dian)(dian)(dian)層(ceng)(ceng)(ceng)電(dian)(dian)(dian)(dian)容(rong)；Rct為(wei)電(dian)(dian)(dian)(dian)荷(he)轉(zhuan)(zhuan)移(yi)(yi)電(dian)(dian)(dian)(dian)阻(zu)(zu)，其值能(neng)(neng)夠反(fan)(fan)應(ying)電(dian)(dian)(dian)(dian)荷(he)在電(dian)(dian)(dian)(dian)化(hua)(hua)(hua)(hua)學(xue)(xue)反(fan)(fan)應(ying)過程(cheng)中(zhong)透過電(dian)(dian)(dian)(dian)極(ji)以及(ji)(ji)于電(dian)(dian)(dian)(dian)解質溶(rong)(rong)(rong)(rong)液(ye)中(zhong)兩相(xiang)界(jie)面(mian)遷移(yi)(yi)難易的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)大(da)小(xiao)(xiao)，也能(neng)(neng)夠反(fan)(fan)映(ying)金屬(shu)發(fa)生腐(fu)(fu)蝕(shi)反(fan)(fan)應(ying)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)快慢(man)，一(yi)般情況下(xia)Rct值越(yue)(yue)(yue)高(gao)意味著(zhu)電(dian)(dian)(dian)(dian)荷(he)遷移(yi)(yi)過程(cheng)中(zhong)所受(shou)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)阻(zu)(zu)力(li)(li)(li)越(yue)(yue)(yue)強(qiang)，即材料的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)耐腐(fu)(fu)蝕(shi)性能(neng)(neng)越(yue)(yue)(yue)好；Cf表(biao)(biao)(biao)(biao)示鈍(dun)(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)電(dian)(dian)(dian)(dian)容(rong)，Rf表(biao)(biao)(biao)(biao)示鈍(dun)(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)電(dian)(dian)(dian)(dian)阻(zu)(zu)。采用(yong)ZsimpWin軟件對等效電(dian)(dian)(dian)(dian)路模擬計(ji)算得(de)(de)到各元件的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)數(shu)值如表(biao)(biao)(biao)(biao)5.2所列。從表(biao)(biao)(biao)(biao)中(zhong)看出雙(shuang)電(dian)(dian)(dian)(dian)層(ceng)(ceng)(ceng)電(dian)(dian)(dian)(dian)容(rong)（Cdl)及(ji)(ji)鈍(dun)(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)電(dian)(dian)(dian)(dian)容(rong)（Cr)隨(sui)固(gu)溶(rong)(rong)(rong)(rong)溫(wen)度(du)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)升高(gao)呈先(xian)(xian)(xian)減小(xiao)(xiao)后增(zeng)(zeng)大(da)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)趨勢(shi)；電(dian)(dian)(dian)(dian)荷(he)轉(zhuan)(zhuan)移(yi)(yi)電(dian)(dian)(dian)(dian)阻(zu)(zu)（Rct)和(he)鈍(dun)(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)電(dian)(dian)(dian)(dian)阻(zu)(zu)（Rf)呈先(xian)(xian)(xian)變大(da)后減小(xiao)(xiao)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)趨勢(shi)，即電(dian)(dian)(dian)(dian)化(hua)(hua)(hua)(hua)學(xue)(xue)反(fan)(fan)應(ying)阻(zu)(zu)力(li)(li)(li)隨(sui)固(gu)溶(rong)(rong)(rong)(rong)熱(re)處理(li)溫(wen)度(du)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)增(zeng)(zeng)高(gao)先(xian)(xian)(xian)增(zeng)(zeng)強(qiang)后減弱，2507雙(shuang)相(xiang)不(bu)(bu)銹(xiu)鋼(gang)(gang)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)(kang)腐(fu)(fu)蝕(shi)性能(neng)(neng)表(biao)(biao)(biao)(biao)現(xian)(xian)為(wei)先(xian)(xian)(xian)增(zeng)(zeng)強(qiang)后減弱。1000℃時(shi)(shi)(shi)鋼(gang)(gang)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)相(xiang)界(jie)處有σ相(xiang)析出，σ相(xiang)硬而脆降低了鋼(gang)(gang)表(biao)(biao)(biao)(biao)面(mian)鈍(dun)(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)穩定(ding)，表(biao)(biao)(biao)(biao)現(xian)(xian)為(wei)具有較(jiao)低的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)鈍(dun)(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)電(dian)(dian)(dian)(dian)阻(zu)(zu)（Rf);1050℃時(shi)(shi)(shi)鋼(gang)(gang)中(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)兩相(xiang)比例約(yue)為(wei)1:1,兩相(xiang)分布較(jiao)均勻且成分穩定(ding)有利(li)于鈍(dun)(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)穩定(ding)，具體(ti)表(biao)(biao)(biao)(biao)現(xian)(xian)為(wei)鈍(dun)(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)電(dian)(dian)(dian)(dian)阻(zu)(zu)（Rf)值較(jiao)高(gao)，表(biao)(biao)(biao)(biao)明(ming)此刻離子遷移(yi)(yi)時(shi)(shi)(shi)所受(shou)阻(zu)(zu)力(li)(li)(li)較(jiao)大(da)，進而2507雙(shuang)相(xiang)不(bu)(bu)銹(xiu)鋼(gang)(gang)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)(kang)腐(fu)(fu)蝕(shi)能(neng)(neng)力(li)(li)(li)最(zui)佳；固(gu)溶(rong)(rong)(rong)(rong)熱(re)處理(li)溫(wen)度(du)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)進一(yi)步(bu)升高(gao)使鋼(gang)(gang)中(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)兩相(xiang)比例失調，表(biao)(biao)(biao)(biao)現(xian)(xian)為(wei)鐵素(su)體(ti)相(xiang)含量大(da)幅升高(gao)，奧氏體(ti)相(xiang)含量減小(xiao)(xiao)，不(bu)(bu)利(li)于鋼(gang)(gang)表(biao)(biao)(biao)(biao)面(mian)鈍(dun)(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)穩定(ding)，導(dao)致(zhi)鈍(dun)(dun)化(hua)(hua)(hua)(hua)膜(mo)(mo)電(dian)(dian)(dian)(dian)阻(zu)(zu)（Rf)減小(xiao)(xiao)，實際表(biao)(biao)(biao)(biao)現(xian)(xian)為(wei)鋼(gang)(gang)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)抗(kang)(kang)(kang)蝕(shi)性能(neng)(neng)下(xia)降，這與(yu)動電(dian)(dian)(dian)(dian)位掃描獲得(de)(de)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)結論相(xiang)同。