1. 動電位(wei)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(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2507雙相(xiang)(xiang)不(bu)銹鋼于(yu)3.5%NaCl溶(rong)液中(zhong)動電位(wei)極(ji)化后的腐(fu)蝕形貌如(ru)圖5.4所示(shi)，圖中(zhong)深色(se)是鐵(tie)(tie)(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)、淺色(se)是奧(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)(ti)(ti)(ti)y相(xiang)(xiang)、黑色(se)圓點(dian)是點(dian)蝕坑。從圖5.4可(ke)知點(dian)蝕坑主要(yao)(yao)存(cun)在(zai)(zai)于(yu)鐵(tie)(tie)(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)(ti)x相(xiang)(xiang)上(shang)，這說明奧(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)(ti)(ti)(ti)y相(xiang)(xiang)比鐵(tie)(tie)(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)要(yao)(yao)穩(wen)定，有(you)著較(jiao)優(you)的抗(kang)點(dian)腐(fu)蝕性能(neng)。奧(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)(ti)(ti)(ti)γ相(xiang)(xiang)相(xiang)(xiang)比于(yu)鐵(tie)(tie)(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)有(you)較(jiao)好的抗(kang)點(dian)蝕性能(neng)的原因在(zai)(zai)于(yu)元素(su)(su)(su)(su)(su)N的作用。元素(su)(su)(su)(su)(su)N是奧(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)(ti)(ti)(ti)形成元素(su)(su)(su)(su)(su)，于(yu)奧(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)(ti)(ti)(ti)γ相(xiang)(xiang)中(zhong)的溶(rong)解度要(yao)(yao)比在(zai)(zai)鐵(tie)(tie)(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)中(zhong)的大，此外N能(neng)夠讓Cr和(he)Mo元素(su)(su)(su)(su)(su)從鐵(tie)(tie)(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)遷移(yi)到(dao)奧(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)(ti)(ti)(ti)γ相(xiang)(xiang)中(zhong)，N顯著影(ying)響著這兩種元素(su)(su)(su)(su)(su)在(zai)(zai)奧(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)(ti)(ti)(ti)γ相(xiang)(xiang)和(he)鐵(tie)(tie)(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)中(zhong)的分配，兩相(xiang)(xiang)中(zhong)合金(jin)元素(su)(su)(su)(su)(su)含量的差值隨(sui)N元素(su)(su)(su)(su)(su)含量的增多(duo)而(er)降低(di)，所以奧(ao)(ao)氏(shi)(shi)體(ti)(ti)(ti)(ti)(ti)(ti)γ相(xiang)(xiang)的點(dian)蝕電位(wei)較(jiao)鐵(tie)(tie)(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)要(yao)(yao)高，從而(er)蝕坑較(jiao)先在(zai)(zai)Eb相(xiang)(xiang)對比較(jiao)低(di)的鐵(tie)(tie)(tie)素(su)(su)(su)(su)(su)體(ti)(ti)(ti)(ti)(ti)(ti)α相(xiang)(xiang)中(zhong)產生。

2. 交流阻抗測試(shi)分(fen)析

  1000℃、1050℃、1100℃、1150℃及(ji)1200℃固(gu)(gu)(gu)溶(rong)(rong)態的(de)(de)(de)(de)(de)(de)2507 雙(shuang)相(xiang)(xiang)(xiang)(xiang)不(bu)銹(xiu)鋼(gang)(gang)30℃下(xia)于(yu)(yu)3.5%NaCl溶(rong)(rong)液(ye)(ye)中的(de)(de)(de)(de)(de)(de)Nyquist 圖如圖5.5所(suo)(suo)示，從(cong)圖中可以很(hen)明顯(xian)看出(chu)(chu)隨固(gu)(gu)(gu)溶(rong)(rong)熱(re)(re)處(chu)理(li)溫度(du)的(de)(de)(de)(de)(de)(de)增(zeng)高(gao)容(rong)(rong)抗(kang)(kang)(kang)弧(hu)(hu)半(ban)徑(jing)先(xian)(xian)增(zeng)大(da)(da)(da)后減(jian)(jian)小(xiao)(xiao)，1050℃時(shi)(shi)(shi)容(rong)(rong)抗(kang)(kang)(kang)弧(hu)(hu)半(ban)徑(jing)最(zui)大(da)(da)(da)。通常(chang)情況下(xia)界(jie)面間(jian)電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)的(de)(de)(de)(de)(de)(de)遷(qian)(qian)移(yi)(yi)(yi)(yi)促進了高(gao)頻區(qu)容(rong)(rong)抗(kang)(kang)(kang)弧(hu)(hu)的(de)(de)(de)(de)(de)(de)形成，容(rong)(rong)抗(kang)(kang)(kang)弧(hu)(hu)與雙(shuang)電(dian)(dian)(dian)(dian)(dian)(dian)層容(rong)(rong)抗(kang)(kang)(kang)及(ji)金(jin)屬(shu)材料(liao)溶(rong)(rong)解的(de)(de)(de)(de)(de)(de)綜合作(zuo)用(yong)有關，并且金(jin)屬(shu)－溶(rong)(rong)液(ye)(ye)界(jie)面的(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)轉(zhuan)(zhuan)移(yi)(yi)(yi)(yi)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)影響著容(rong)(rong)抗(kang)(kang)(kang)弧(hu)(hu)半(ban)徑(jing)的(de)(de)(de)(de)(de)(de)大(da)(da)(da)小(xiao)(xiao)，電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)在(zai)金(jin)屬(shu)－溶(rong)(rong)液(ye)(ye)界(jie)面轉(zhuan)(zhuan)移(yi)(yi)(yi)(yi)時(shi)(shi)(shi)受(shou)(shou)到的(de)(de)(de)(de)(de)(de)阻(zu)(zu)(zu)力(li)越(yue)強(qiang)(qiang)(qiang)意味(wei)著容(rong)(rong)抗(kang)(kang)(kang)弧(hu)(hu)半(ban)徑(jing)越(yue)大(da)(da)(da)，即(ji)意味(wei)著金(jin)屬(shu)的(de)(de)(de)(de)(de)(de)抗(kang)(kang)(kang)蝕(shi)(shi)性(xing)(xing)(xing)(xing)能(neng)(neng)(neng)(neng)越(yue)優。從(cong)圖5.5容(rong)(rong)抗(kang)(kang)(kang)弧(hu)(hu)半(ban)徑(jing)的(de)(de)(de)(de)(de)(de)改變趨(qu)勢(shi)(shi)可知(zhi)，固(gu)(gu)(gu)溶(rong)(rong)熱(re)(re)處(chu)理(li)溫度(du)升高(gao)使DSS2507的(de)(de)(de)(de)(de)(de)耐蝕(shi)(shi)性(xing)(xing)(xing)(xing)能(neng)(neng)(neng)(neng)首先(xian)(xian)增(zeng)強(qiang)(qiang)(qiang)而后減(jian)(jian)弱(ruo)，1050℃時(shi)(shi)(shi)2507雙(shuang)相(xiang)(xiang)(xiang)(xiang)不(bu)銹(xiu)鋼(gang)(gang)的(de)(de)(de)(de)(de)(de)抗(kang)(kang)(kang)腐蝕(shi)(shi)性(xing)(xing)(xing)(xing)能(neng)(neng)(neng)(neng)最(zui)優。不(bu)同(tong)固(gu)(gu)(gu)溶(rong)(rong)態的(de)(de)(de)(de)(de)(de)2507雙(shuang)相(xiang)(xiang)(xiang)(xiang)不(bu)銹(xiu)鋼(gang)(gang)于(yu)(yu)3.5%NaCl溶(rong)(rong)液(ye)(ye)中的(de)(de)(de)(de)(de)(de)等(deng)效電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)如圖5.6所(suo)(suo)示，采用(yong)的(de)(de)(de)(de)(de)(de)是R(C(R(CR))).Rs指參(can)比(bi)(bi)電(dian)(dian)(dian)(dian)(dian)(dian)極和工(gong)作(zuo)電(dian)(dian)(dian)(dian)(dian)(dian)極間(jian)的(de)(de)(de)(de)(de)(de)溶(rong)(rong)液(ye)(ye)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)；Cd1為(wei)(wei)雙(shuang)電(dian)(dian)(dian)(dian)(dian)(dian)層電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)；Rct為(wei)(wei)電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)轉(zhuan)(zhuan)移(yi)(yi)(yi)(yi)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)，其值(zhi)能(neng)(neng)(neng)(neng)夠(gou)(gou)反(fan)(fan)應(ying)電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)在(zai)電(dian)(dian)(dian)(dian)(dian)(dian)化(hua)學反(fan)(fan)應(ying)過程(cheng)中透(tou)過電(dian)(dian)(dian)(dian)(dian)(dian)極以及(ji)于(yu)(yu)電(dian)(dian)(dian)(dian)(dian)(dian)解質溶(rong)(rong)液(ye)(ye)中兩(liang)相(xiang)(xiang)(xiang)(xiang)界(jie)面遷(qian)(qian)移(yi)(yi)(yi)(yi)難(nan)易的(de)(de)(de)(de)(de)(de)大(da)(da)(da)小(xiao)(xiao)，也能(neng)(neng)(neng)(neng)夠(gou)(gou)反(fan)(fan)映(ying)金(jin)屬(shu)發(fa)生腐蝕(shi)(shi)反(fan)(fan)應(ying)的(de)(de)(de)(de)(de)(de)快慢，一(yi)般情況下(xia)Rct值(zhi)越(yue)高(gao)意味(wei)著電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)遷(qian)(qian)移(yi)(yi)(yi)(yi)過程(cheng)中所(suo)(suo)受(shou)(shou)的(de)(de)(de)(de)(de)(de)阻(zu)(zu)(zu)力(li)越(yue)強(qiang)(qiang)(qiang)，即(ji)材料(liao)的(de)(de)(de)(de)(de)(de)耐腐蝕(shi)(shi)性(xing)(xing)(xing)(xing)能(neng)(neng)(neng)(neng)越(yue)好；Cf表(biao)(biao)示鈍(dun)(dun)(dun)化(hua)膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)，Rf表(biao)(biao)示鈍(dun)(dun)(dun)化(hua)膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)。采用(yong)ZsimpWin軟(ruan)件(jian)對等(deng)效電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)模擬計(ji)算得到各元件(jian)的(de)(de)(de)(de)(de)(de)數值(zhi)如表(biao)(biao)5.2所(suo)(suo)列。從(cong)表(biao)(biao)中看出(chu)(chu)雙(shuang)電(dian)(dian)(dian)(dian)(dian)(dian)層電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)（Cdl)及(ji)鈍(dun)(dun)(dun)化(hua)膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)（Cr)隨固(gu)(gu)(gu)溶(rong)(rong)溫度(du)的(de)(de)(de)(de)(de)(de)升高(gao)呈(cheng)先(xian)(xian)減(jian)(jian)小(xiao)(xiao)后增(zeng)大(da)(da)(da)的(de)(de)(de)(de)(de)(de)趨(qu)勢(shi)(shi)；電(dian)(dian)(dian)(dian)(dian)(dian)荷(he)轉(zhuan)(zhuan)移(yi)(yi)(yi)(yi)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)（Rct)和鈍(dun)(dun)(dun)化(hua)膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)（Rf)呈(cheng)先(xian)(xian)變大(da)(da)(da)后減(jian)(jian)小(xiao)(xiao)的(de)(de)(de)(de)(de)(de)趨(qu)勢(shi)(shi)，即(ji)電(dian)(dian)(dian)(dian)(dian)(dian)化(hua)學反(fan)(fan)應(ying)阻(zu)(zu)(zu)力(li)隨固(gu)(gu)(gu)溶(rong)(rong)熱(re)(re)處(chu)理(li)溫度(du)的(de)(de)(de)(de)(de)(de)增(zeng)高(gao)先(xian)(xian)增(zeng)強(qiang)(qiang)(qiang)后減(jian)(jian)弱(ruo)，2507雙(shuang)相(xiang)(xiang)(xiang)(xiang)不(bu)銹(xiu)鋼(gang)(gang)的(de)(de)(de)(de)(de)(de)抗(kang)(kang)(kang)腐蝕(shi)(shi)性(xing)(xing)(xing)(xing)能(neng)(neng)(neng)(neng)表(biao)(biao)現(xian)(xian)為(wei)(wei)先(xian)(xian)增(zeng)強(qiang)(qiang)(qiang)后減(jian)(jian)弱(ruo)。1000℃時(shi)(shi)(shi)鋼(gang)(gang)的(de)(de)(de)(de)(de)(de)相(xiang)(xiang)(xiang)(xiang)界(jie)處(chu)有σ相(xiang)(xiang)(xiang)(xiang)析出(chu)(chu)，σ相(xiang)(xiang)(xiang)(xiang)硬而脆降(jiang)低了鋼(gang)(gang)表(biao)(biao)面鈍(dun)(dun)(dun)化(hua)膜(mo)的(de)(de)(de)(de)(de)(de)穩(wen)定，表(biao)(biao)現(xian)(xian)為(wei)(wei)具(ju)有較低的(de)(de)(de)(de)(de)(de)鈍(dun)(dun)(dun)化(hua)膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)（Rf);1050℃時(shi)(shi)(shi)鋼(gang)(gang)中的(de)(de)(de)(de)(de)(de)兩(liang)相(xiang)(xiang)(xiang)(xiang)比(bi)(bi)例約為(wei)(wei)1:1,兩(liang)相(xiang)(xiang)(xiang)(xiang)分布(bu)較均勻且成分穩(wen)定有利(li)于(yu)(yu)鈍(dun)(dun)(dun)化(hua)膜(mo)的(de)(de)(de)(de)(de)(de)穩(wen)定，具(ju)體(ti)表(biao)(biao)現(xian)(xian)為(wei)(wei)鈍(dun)(dun)(dun)化(hua)膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)（Rf)值(zhi)較高(gao)，表(biao)(biao)明此刻離子(zi)遷(qian)(qian)移(yi)(yi)(yi)(yi)時(shi)(shi)(shi)所(suo)(suo)受(shou)(shou)阻(zu)(zu)(zu)力(li)較大(da)(da)(da)，進而2507雙(shuang)相(xiang)(xiang)(xiang)(xiang)不(bu)銹(xiu)鋼(gang)(gang)的(de)(de)(de)(de)(de)(de)抗(kang)(kang)(kang)腐蝕(shi)(shi)能(neng)(neng)(neng)(neng)力(li)最(zui)佳；固(gu)(gu)(gu)溶(rong)(rong)熱(re)(re)處(chu)理(li)溫度(du)的(de)(de)(de)(de)(de)(de)進一(yi)步升高(gao)使鋼(gang)(gang)中的(de)(de)(de)(de)(de)(de)兩(liang)相(xiang)(xiang)(xiang)(xiang)比(bi)(bi)例失調，表(biao)(biao)現(xian)(xian)為(wei)(wei)鐵素體(ti)相(xiang)(xiang)(xiang)(xiang)含(han)量大(da)(da)(da)幅升高(gao)，奧氏(shi)體(ti)相(xiang)(xiang)(xiang)(xiang)含(han)量減(jian)(jian)小(xiao)(xiao)，不(bu)利(li)于(yu)(yu)鋼(gang)(gang)表(biao)(biao)面鈍(dun)(dun)(dun)化(hua)膜(mo)的(de)(de)(de)(de)(de)(de)穩(wen)定，導致鈍(dun)(dun)(dun)化(hua)膜(mo)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)（Rf)減(jian)(jian)小(xiao)(xiao)，實際表(biao)(biao)現(xian)(xian)為(wei)(wei)鋼(gang)(gang)的(de)(de)(de)(de)(de)(de)抗(kang)(kang)(kang)蝕(shi)(shi)性(xing)(xing)(xing)(xing)能(neng)(neng)(neng)(neng)下(xia)降(jiang)，這(zhe)與動(dong)電(dian)(dian)(dian)(dian)(dian)(dian)位掃描獲(huo)得的(de)(de)(de)(de)(de)(de)結論(lun)相(xiang)(xiang)(xiang)(xiang)同(tong)。