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(shuang)相(xiang)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(tai)為1050℃的2507雙相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)不銹鋼于3.5%NaCl溶液中(zhong)(zhong)(zhong)(zhong)動電位極化后的腐(fu)蝕(shi)(shi)形(xing)(xing)貌如(ru)圖(tu)5.4所(suo)示，圖(tu)中(zhong)(zhong)(zhong)(zhong)深(shen)色(se)(se)是(shi)鐵(tie)(tie)(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)、淺色(se)(se)是(shi)奧(ao)(ao)(ao)氏體(ti)(ti)(ti)(ti)y相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)、黑色(se)(se)圓點是(shi)點蝕(shi)(shi)坑。從圖(tu)5.4可知點蝕(shi)(shi)坑主要存(cun)在(zai)(zai)于鐵(tie)(tie)(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)x相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)上(shang)，這(zhe)(zhe)說明奧(ao)(ao)(ao)氏體(ti)(ti)(ti)(ti)y相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)比(bi)鐵(tie)(tie)(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)要穩定，有著較(jiao)優(you)的抗(kang)點腐(fu)蝕(shi)(shi)性能(neng)。奧(ao)(ao)(ao)氏體(ti)(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)比(bi)于鐵(tie)(tie)(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)有較(jiao)好的抗(kang)點蝕(shi)(shi)性能(neng)的原因在(zai)(zai)于元(yuan)素(su)(su)(su)N的作用。元(yuan)素(su)(su)(su)N是(shi)奧(ao)(ao)(ao)氏體(ti)(ti)(ti)(ti)形(xing)(xing)成元(yuan)素(su)(su)(su)，于奧(ao)(ao)(ao)氏體(ti)(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的溶解度要比(bi)在(zai)(zai)鐵(tie)(tie)(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的大，此外N能(neng)夠讓Cr和Mo元(yuan)素(su)(su)(su)從鐵(tie)(tie)(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)遷移(yi)到奧(ao)(ao)(ao)氏體(ti)(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)，N顯著影響著這(zhe)(zhe)兩種元(yuan)素(su)(su)(su)在(zai)(zai)奧(ao)(ao)(ao)氏體(ti)(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)和鐵(tie)(tie)(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的分配，兩相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)合金元(yuan)素(su)(su)(su)含(han)量的差值隨N元(yuan)素(su)(su)(su)含(han)量的增(zeng)多而(er)(er)降低(di)，所(suo)以(yi)奧(ao)(ao)(ao)氏體(ti)(ti)(ti)(ti)γ相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)的點蝕(shi)(shi)電位較(jiao)鐵(tie)(tie)(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)要高，從而(er)(er)蝕(shi)(shi)坑較(jiao)先在(zai)(zai)Eb相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)對比(bi)較(jiao)低(di)的鐵(tie)(tie)(tie)素(su)(su)(su)體(ti)(ti)(ti)(ti)α相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)產(chan)生(sheng)。

2. 交流阻(zu)抗測試分析

  1000℃、1050℃、1100℃、1150℃及1200℃固(gu)(gu)(gu)溶(rong)(rong)態(tai)的(de)(de)(de)(de)(de)(de)2507 雙相(xiang)(xiang)(xiang)不銹(xiu)(xiu)(xiu)鋼(gang)(gang)(gang)(gang)30℃下于(yu)(yu)3.5%NaCl溶(rong)(rong)液中(zhong)的(de)(de)(de)(de)(de)(de)Nyquist 圖(tu)如(ru)圖(tu)5.5所(suo)示，從(cong)圖(tu)中(zhong)可以很明(ming)顯(xian)看(kan)出(chu)隨(sui)固(gu)(gu)(gu)溶(rong)(rong)熱(re)處(chu)理溫(wen)度(du)的(de)(de)(de)(de)(de)(de)增(zeng)高容(rong)(rong)(rong)抗(kang)(kang)弧(hu)(hu)(hu)半(ban)徑(jing)(jing)先(xian)(xian)增(zeng)大(da)(da)(da)后(hou)(hou)(hou)減(jian)小(xiao)，1050℃時(shi)(shi)(shi)(shi)容(rong)(rong)(rong)抗(kang)(kang)弧(hu)(hu)(hu)半(ban)徑(jing)(jing)最大(da)(da)(da)。通(tong)常情況下界(jie)面(mian)間電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷的(de)(de)(de)(de)(de)(de)遷(qian)移(yi)(yi)(yi)促(cu)進了高頻區(qu)容(rong)(rong)(rong)抗(kang)(kang)弧(hu)(hu)(hu)的(de)(de)(de)(de)(de)(de)形成，容(rong)(rong)(rong)抗(kang)(kang)弧(hu)(hu)(hu)與(yu)雙電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)層(ceng)(ceng)容(rong)(rong)(rong)抗(kang)(kang)及金(jin)屬(shu)材料(liao)溶(rong)(rong)解的(de)(de)(de)(de)(de)(de)綜合作用(yong)有關，并(bing)且(qie)金(jin)屬(shu)－溶(rong)(rong)液界(jie)面(mian)的(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷轉(zhuan)(zhuan)移(yi)(yi)(yi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)影響著容(rong)(rong)(rong)抗(kang)(kang)弧(hu)(hu)(hu)半(ban)徑(jing)(jing)的(de)(de)(de)(de)(de)(de)大(da)(da)(da)小(xiao)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷在金(jin)屬(shu)－溶(rong)(rong)液界(jie)面(mian)轉(zhuan)(zhuan)移(yi)(yi)(yi)時(shi)(shi)(shi)(shi)受(shou)到(dao)(dao)的(de)(de)(de)(de)(de)(de)阻(zu)(zu)(zu)(zu)(zu)力(li)(li)越(yue)(yue)強(qiang)意(yi)(yi)味(wei)著容(rong)(rong)(rong)抗(kang)(kang)弧(hu)(hu)(hu)半(ban)徑(jing)(jing)越(yue)(yue)大(da)(da)(da)，即(ji)意(yi)(yi)味(wei)著金(jin)屬(shu)的(de)(de)(de)(de)(de)(de)抗(kang)(kang)蝕性(xing)能(neng)越(yue)(yue)優。從(cong)圖(tu)5.5容(rong)(rong)(rong)抗(kang)(kang)弧(hu)(hu)(hu)半(ban)徑(jing)(jing)的(de)(de)(de)(de)(de)(de)改變趨(qu)(qu)勢可知，固(gu)(gu)(gu)溶(rong)(rong)熱(re)處(chu)理溫(wen)度(du)升(sheng)(sheng)高使DSS2507的(de)(de)(de)(de)(de)(de)耐(nai)蝕性(xing)能(neng)首先(xian)(xian)增(zeng)強(qiang)而(er)(er)(er)后(hou)(hou)(hou)減(jian)弱，1050℃時(shi)(shi)(shi)(shi)2507雙相(xiang)(xiang)(xiang)不銹(xiu)(xiu)(xiu)鋼(gang)(gang)(gang)(gang)的(de)(de)(de)(de)(de)(de)抗(kang)(kang)腐蝕性(xing)能(neng)最優。不同固(gu)(gu)(gu)溶(rong)(rong)態(tai)的(de)(de)(de)(de)(de)(de)2507雙相(xiang)(xiang)(xiang)不銹(xiu)(xiu)(xiu)鋼(gang)(gang)(gang)(gang)于(yu)(yu)3.5%NaCl溶(rong)(rong)液中(zhong)的(de)(de)(de)(de)(de)(de)等效電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路如(ru)圖(tu)5.6所(suo)示，采用(yong)的(de)(de)(de)(de)(de)(de)是(shi)R(C(R(CR))).Rs指(zhi)參比電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)和(he)工作電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)間的(de)(de)(de)(de)(de)(de)溶(rong)(rong)液電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)；Cd1為雙電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)層(ceng)(ceng)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)；Rct為電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷轉(zhuan)(zhuan)移(yi)(yi)(yi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)，其值(zhi)能(neng)夠(gou)反(fan)(fan)應電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷在電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)化(hua)學反(fan)(fan)應過程(cheng)中(zhong)透(tou)過電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)以及于(yu)(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)解質溶(rong)(rong)液中(zhong)兩相(xiang)(xiang)(xiang)界(jie)面(mian)遷(qian)移(yi)(yi)(yi)難(nan)易的(de)(de)(de)(de)(de)(de)大(da)(da)(da)小(xiao)，也能(neng)夠(gou)反(fan)(fan)映金(jin)屬(shu)發生腐蝕反(fan)(fan)應的(de)(de)(de)(de)(de)(de)快慢，一般情況下Rct值(zhi)越(yue)(yue)高意(yi)(yi)味(wei)著電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷遷(qian)移(yi)(yi)(yi)過程(cheng)中(zhong)所(suo)受(shou)的(de)(de)(de)(de)(de)(de)阻(zu)(zu)(zu)(zu)(zu)力(li)(li)越(yue)(yue)強(qiang)，即(ji)材料(liao)的(de)(de)(de)(de)(de)(de)耐(nai)腐蝕性(xing)能(neng)越(yue)(yue)好；Cf表(biao)(biao)示鈍化(hua)膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)，Rf表(biao)(biao)示鈍化(hua)膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)。采用(yong)ZsimpWin軟(ruan)件對(dui)等效電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路模擬計(ji)算得到(dao)(dao)各元件的(de)(de)(de)(de)(de)(de)數值(zhi)如(ru)表(biao)(biao)5.2所(suo)列。從(cong)表(biao)(biao)中(zhong)看(kan)出(chu)雙電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)層(ceng)(ceng)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)（Cdl)及鈍化(hua)膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)（Cr)隨(sui)固(gu)(gu)(gu)溶(rong)(rong)溫(wen)度(du)的(de)(de)(de)(de)(de)(de)升(sheng)(sheng)高呈先(xian)(xian)減(jian)小(xiao)后(hou)(hou)(hou)增(zeng)大(da)(da)(da)的(de)(de)(de)(de)(de)(de)趨(qu)(qu)勢；電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷轉(zhuan)(zhuan)移(yi)(yi)(yi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)（Rct)和(he)鈍化(hua)膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)（Rf)呈先(xian)(xian)變大(da)(da)(da)后(hou)(hou)(hou)減(jian)小(xiao)的(de)(de)(de)(de)(de)(de)趨(qu)(qu)勢，即(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)化(hua)學反(fan)(fan)應阻(zu)(zu)(zu)(zu)(zu)力(li)(li)隨(sui)固(gu)(gu)(gu)溶(rong)(rong)熱(re)處(chu)理溫(wen)度(du)的(de)(de)(de)(de)(de)(de)增(zeng)高先(xian)(xian)增(zeng)強(qiang)后(hou)(hou)(hou)減(jian)弱，2507雙相(xiang)(xiang)(xiang)不銹(xiu)(xiu)(xiu)鋼(gang)(gang)(gang)(gang)的(de)(de)(de)(de)(de)(de)抗(kang)(kang)腐蝕性(xing)能(neng)表(biao)(biao)現(xian)為先(xian)(xian)增(zeng)強(qiang)后(hou)(hou)(hou)減(jian)弱。1000℃時(shi)(shi)(shi)(shi)鋼(gang)(gang)(gang)(gang)的(de)(de)(de)(de)(de)(de)相(xiang)(xiang)(xiang)界(jie)處(chu)有σ相(xiang)(xiang)(xiang)析(xi)出(chu)，σ相(xiang)(xiang)(xiang)硬而(er)(er)(er)脆降低(di)了鋼(gang)(gang)(gang)(gang)表(biao)(biao)面(mian)鈍化(hua)膜(mo)的(de)(de)(de)(de)(de)(de)穩(wen)定(ding)(ding)，表(biao)(biao)現(xian)為具有較(jiao)低(di)的(de)(de)(de)(de)(de)(de)鈍化(hua)膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)（Rf);1050℃時(shi)(shi)(shi)(shi)鋼(gang)(gang)(gang)(gang)中(zhong)的(de)(de)(de)(de)(de)(de)兩相(xiang)(xiang)(xiang)比例(li)(li)約為1:1,兩相(xiang)(xiang)(xiang)分布較(jiao)均(jun)勻(yun)且(qie)成分穩(wen)定(ding)(ding)有利于(yu)(yu)鈍化(hua)膜(mo)的(de)(de)(de)(de)(de)(de)穩(wen)定(ding)(ding)，具體表(biao)(biao)現(xian)為鈍化(hua)膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)（Rf)值(zhi)較(jiao)高，表(biao)(biao)明(ming)此(ci)刻(ke)離子遷(qian)移(yi)(yi)(yi)時(shi)(shi)(shi)(shi)所(suo)受(shou)阻(zu)(zu)(zu)(zu)(zu)力(li)(li)較(jiao)大(da)(da)(da)，進而(er)(er)(er)2507雙相(xiang)(xiang)(xiang)不銹(xiu)(xiu)(xiu)鋼(gang)(gang)(gang)(gang)的(de)(de)(de)(de)(de)(de)抗(kang)(kang)腐蝕能(neng)力(li)(li)最佳；固(gu)(gu)(gu)溶(rong)(rong)熱(re)處(chu)理溫(wen)度(du)的(de)(de)(de)(de)(de)(de)進一步升(sheng)(sheng)高使鋼(gang)(gang)(gang)(gang)中(zhong)的(de)(de)(de)(de)(de)(de)兩相(xiang)(xiang)(xiang)比例(li)(li)失調，表(biao)(biao)現(xian)為鐵(tie)素體相(xiang)(xiang)(xiang)含量大(da)(da)(da)幅升(sheng)(sheng)高，奧氏體相(xiang)(xiang)(xiang)含量減(jian)小(xiao)，不利于(yu)(yu)鋼(gang)(gang)(gang)(gang)表(biao)(biao)面(mian)鈍化(hua)膜(mo)的(de)(de)(de)(de)(de)(de)穩(wen)定(ding)(ding)，導致鈍化(hua)膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)（Rf)減(jian)小(xiao)，實際表(biao)(biao)現(xian)為鋼(gang)(gang)(gang)(gang)的(de)(de)(de)(de)(de)(de)抗(kang)(kang)蝕性(xing)能(neng)下降，這與(yu)動電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)位掃描獲得的(de)(de)(de)(de)(de)(de)結(jie)論相(xiang)(xiang)(xiang)同。