1. 動電位極化曲線(xian)分(fen)析
不同固溶處理后的2205雙相(xiang)不銹鋼在不同溫度的3.5%NaCl溶液中的極化曲線如圖5.7所示。
從圖5.7中可以看出，不同固溶處理的2205雙相不銹鋼在20℃、30℃、45℃的3.5%NaCI溶液中都存在一定范圍的鈍化區，且彼此的鈍化區間相差不大。但是，當3.5%NaCl溶液的溫度提升至60℃時，（950℃、1000℃、1100℃、1150℃)/30min 固溶處理的雙相不銹鋼的鈍化范圍與1050℃/30min 固溶處理的雙相不銹鋼的鈍化范圍相比，其明顯變窄。這說明隨著溶液溫度的升高，1050℃/30min固溶處理的雙相不銹鋼的鈍(dun)化膜更加穩定。
根據GB 4334.9-1984,當腐蝕電流密度達到0.1mA/c㎡時，此時曲線上所對應的電位值就是點蝕電位。結合GB 4334.9-1984和圖5.7,得到不同固溶處理的2205雙相不銹鋼在不同溫度的3.5%NaCl溶液中的點蝕電位，如圖5.8和表5.3所示。
從(cong)圖5.8中可(ke)以(yi)看出(chu)，隨著3.5%NaCl溶(rong)(rong)(rong)(rong)液(ye)的(de)(de)溫(wen)度的(de)(de)升高，不同固溶(rong)(rong)(rong)(rong)處(chu)理的(de)(de)雙(shuang)(shuang)(shuang)相(xiang)不銹(xiu)鋼的(de)(de)點(dian)(dian)蝕電(dian)位(wei)下降(jiang)。并(bing)且可(ke)以(yi)看出(chu)，當溫(wen)度從(cong)20℃升高至45℃時，不同固溶(rong)(rong)(rong)(rong)處(chu)理的(de)(de)雙(shuang)(shuang)(shuang)相(xiang)不銹(xiu)鋼的(de)(de)點(dian)(dian)蝕電(dian)位(wei)下降(jiang)的(de)(de)趨(qu)勢較(jiao)為平緩；當3.5%NaCl溶(rong)(rong)(rong)(rong)液(ye)的(de)(de)溫(wen)度進(jin)一步升高至60℃時，（950℃、1000℃、1100℃、1150℃)/30min固溶(rong)(rong)(rong)(rong)處(chu)理的(de)(de)雙(shuang)(shuang)(shuang)相(xiang)不銹(xiu)鋼的(de)(de)點(dian)(dian)蝕電(dian)位(wei)急劇(ju)下降(jiang)，而1050℃/30min固溶(rong)(rong)(rong)(rong)處(chu)理的(de)(de)雙(shuang)(shuang)(shuang)相(xiang)不銹(xiu)鋼的(de)(de)點(dian)(dian)蝕電(dian)位(wei)下降(jiang)趨(qu)勢依然平緩，這說明隨著溶(rong)(rong)(rong)(rong)液(ye)溫(wen)度的(de)(de)升高，1050℃/30min 固溶(rong)(rong)(rong)(rong)處(chu)理的(de)(de)雙(shuang)(shuang)(shuang)相(xiang)不銹(xiu)鋼的(de)(de)點(dian)(dian)蝕敏(min)感性較(jiao)低(di)，且鈍化膜更加穩(wen)定。
從(cong)(cong)表(biao)5.3中(zhong)也可以看(kan)(kan)出，對(dui)于950℃/30min固(gu)溶(rong)(rong)(rong)(rong)(rong)處(chu)(chu)(chu)(chu)理(li)的(de)(de)(de)(de)(de)(de)雙(shuang)相不銹(xiu)(xiu)鋼(gang)(gang)而(er)(er)言，當(dang)3.5%NaCl溶(rong)(rong)(rong)(rong)(rong)液(ye)(ye)的(de)(de)(de)(de)(de)(de)溫(wen)度(du)(du)從(cong)(cong)20℃升(sheng)高(gao)(gao)至(zhi)(zhi)(zhi)60℃時，其(qi)點(dian)蝕(shi)電(dian)(dian)位從(cong)(cong)1.0784V下(xia)(xia)降(jiang)(jiang)(jiang)(jiang)至(zhi)(zhi)(zhi)0.56967V,降(jiang)(jiang)(jiang)(jiang)幅(fu)為(wei)(wei)0.50873V;對(dui)于1000℃/30min固(gu)溶(rong)(rong)(rong)(rong)(rong)處(chu)(chu)(chu)(chu)理(li)的(de)(de)(de)(de)(de)(de)雙(shuang)相不銹(xiu)(xiu)鋼(gang)(gang)而(er)(er)言，當(dang)3.5%NaCl溶(rong)(rong)(rong)(rong)(rong)液(ye)(ye)的(de)(de)(de)(de)(de)(de)溫(wen)度(du)(du)從(cong)(cong)20℃升(sheng)高(gao)(gao)至(zhi)(zhi)(zhi)60℃時，其(qi)點(dian)蝕(shi)電(dian)(dian)位從(cong)(cong)1.084V下(xia)(xia)降(jiang)(jiang)(jiang)(jiang)至(zhi)(zhi)(zhi)0.57095V,降(jiang)(jiang)(jiang)(jiang)幅(fu)為(wei)(wei)0.51305V;對(dui)于1050℃/30min固(gu)溶(rong)(rong)(rong)(rong)(rong)處(chu)(chu)(chu)(chu)理(li)的(de)(de)(de)(de)(de)(de)雙(shuang)相不銹(xiu)(xiu)鋼(gang)(gang)而(er)(er)言，當(dang)3.5%NaCI溶(rong)(rong)(rong)(rong)(rong)液(ye)(ye)的(de)(de)(de)(de)(de)(de)溫(wen)度(du)(du)從(cong)(cong)20℃升(sheng)高(gao)(gao)至(zhi)(zhi)(zhi)60℃時，其(qi)點(dian)蝕(shi)電(dian)(dian)位從(cong)(cong)1.1348V下(xia)(xia)降(jiang)(jiang)(jiang)(jiang)至(zhi)(zhi)(zhi)0.89279V,降(jiang)(jiang)(jiang)(jiang)幅(fu)為(wei)(wei)0.24171V;對(dui)于1100℃/30min 固(gu)溶(rong)(rong)(rong)(rong)(rong)處(chu)(chu)(chu)(chu)理(li)的(de)(de)(de)(de)(de)(de)雙(shuang)相不銹(xiu)(xiu)鋼(gang)(gang)而(er)(er)言，當(dang)3.5%NaCl溶(rong)(rong)(rong)(rong)(rong)液(ye)(ye)的(de)(de)(de)(de)(de)(de)溫(wen)度(du)(du)從(cong)(cong)20℃升(sheng)高(gao)(gao)至(zhi)(zhi)(zhi)60℃時，其(qi)點(dian)蝕(shi)電(dian)(dian)位從(cong)(cong)1.1255V下(xia)(xia)降(jiang)(jiang)(jiang)(jiang)至(zhi)(zhi)(zhi)0.49891V,降(jiang)(jiang)(jiang)(jiang)幅(fu)為(wei)(wei)0.62659V;對(dui)于1150/30min℃固(gu)溶(rong)(rong)(rong)(rong)(rong)處(chu)(chu)(chu)(chu)理(li)的(de)(de)(de)(de)(de)(de)雙(shuang)相不銹(xiu)(xiu)鋼(gang)(gang)而(er)(er)言，當(dang)3.5%NaCl溶(rong)(rong)(rong)(rong)(rong)液(ye)(ye)的(de)(de)(de)(de)(de)(de)溫(wen)度(du)(du)從(cong)(cong)20℃升(sheng)高(gao)(gao)至(zhi)(zhi)(zhi)60℃時，其(qi)點(dian)蝕(shi)電(dian)(dian)位從(cong)(cong)1.073V下(xia)(xia)降(jiang)(jiang)(jiang)(jiang)至(zhi)(zhi)(zhi)0.65157V,降(jiang)(jiang)(jiang)(jiang)幅(fu)為(wei)(wei)0.42143V.綜上所(suo)述(shu)可以看(kan)(kan)出，1050℃/30min固(gu)溶(rong)(rong)(rong)(rong)(rong)處(chu)(chu)(chu)(chu)理(li)的(de)(de)(de)(de)(de)(de)雙(shuang)相不銹(xiu)(xiu)鋼(gang)(gang)的(de)(de)(de)(de)(de)(de)點(dian)蝕(shi)電(dian)(dian)位較(jiao)高(gao)(gao)，以及(ji)點(dian)蝕(shi)電(dian)(dian)位隨著溶(rong)(rong)(rong)(rong)(rong)液(ye)(ye)溫(wen)度(du)(du)升(sheng)高(gao)(gao)而(er)(er)下(xia)(xia)降(jiang)(jiang)(jiang)(jiang)的(de)(de)(de)(de)(de)(de)幅(fu)值較(jiao)低，說明其(qi)1050℃固(gu)溶(rong)(rong)(rong)(rong)(rong)處(chu)(chu)(chu)(chu)理(li)的(de)(de)(de)(de)(de)(de)雙(shuang)相不銹(xiu)(xiu)鋼(gang)(gang)的(de)(de)(de)(de)(de)(de)點(dian)蝕(shi)敏感性(xing)較(jiao)低。而(er)(er)950℃/30min、1000℃/30min、1100℃/30min、1150℃/30min 固(gu)溶(rong)(rong)(rong)(rong)(rong)處(chu)(chu)(chu)(chu)理(li)的(de)(de)(de)(de)(de)(de)不銹(xiu)(xiu)鋼(gang)(gang)的(de)(de)(de)(de)(de)(de)點(dian)蝕(shi)電(dian)(dian)位都比1050℃/30min固(gu)溶(rong)(rong)(rong)(rong)(rong)處(chu)(chu)(chu)(chu)理(li)的(de)(de)(de)(de)(de)(de)不銹(xiu)(xiu)鋼(gang)(gang)的(de)(de)(de)(de)(de)(de)點(dian)蝕(shi)電(dian)(dian)位低，耐(nai)點(dian)蝕(shi)性(xing)能有所(suo)下(xia)(xia)降(jiang)(jiang)(jiang)(jiang)。
1050℃/30min固溶(rong)處理的2205雙相(xiang)不銹鋼在20℃3.5%NaCl溶(rong)液中(zhong)極化(hua)后的點(dian)蝕形貌如圖(tu)5.9所示。圖(tu)中(zhong)淡色部分(fen)為(wei)奧氏體，深(shen)色部分(fen)為(wei)鐵素體，黑色部分(fen)為(wei)點(dian)蝕坑。
從圖5.9中可以看，點蝕易發生于鐵素體和鐵素體－奧氏體晶界處，并且點蝕易向鐵素體中發展。在雙相不銹鋼中，Cr、Mo、N是主要的耐點蝕元素，鐵素體含有更多量的Cr和Mo;而奧氏體還有更多的Ni和Mn,并且N元素富集于奧氏體相中，提高局部腐蝕抗力。雙相不銹鋼的耐點蝕當量值可由“PREN=％Cr+3.3×%Mo+16×%N”計算得到，耐點蝕當量值越高，雙相不銹鋼的耐點蝕能力越強。隨著固溶處理的溫度的升高，鐵素體的含量逐漸增加，而奧氏體的含量不斷減少，造成鐵素體中的Cr、Mo被稀釋，導致鐵素體的耐點蝕當量逐漸降低；而隨著固溶處理溫度的升高，奧氏體的含量降低，造成奧氏體中的N濃度升高，奧氏體耐點蝕當量逐漸升高。
雙(shuang)相不銹(xiu)鋼中(zhong)(zhong)含(han)(han)有較(jiao)高(gao)(gao)含(han)(han)量(liang)(liang)的(de)(de)(de)(de)(de)(de)Cr和Mo,在(zai)氧化(hua)(hua)性(xing)(xing)(xing)介質中(zhong)(zhong)其表(biao)面(mian)會生成一層鈍(dun)化(hua)(hua)膜(mo)(mo)(mo)保(bao)護基(ji)體(ti)(ti)(ti)。由(you)于CI-對鈍(dun)化(hua)(hua)膜(mo)(mo)(mo)存(cun)在(zai)破(po)壞性(xing)(xing)(xing)，甚至通過鈍(dun)化(hua)(hua)膜(mo)(mo)(mo)的(de)(de)(de)(de)(de)(de)間隙(xi)，與基(ji)體(ti)(ti)(ti)金(jin)屬(shu)接(jie)觸(chu)，使得基(ji)體(ti)(ti)(ti)發(fa)生溶(rong)解。鈍(dun)化(hua)(hua)膜(mo)(mo)(mo)的(de)(de)(de)(de)(de)(de)穩定(ding)性(xing)(xing)(xing)能(neng)夠反(fan)映其對金(jin)屬(shu)的(de)(de)(de)(de)(de)(de)保(bao)護程度(du)，而點(dian)(dian)(dian)(dian)蝕(shi)(shi)(shi)(shi)電(dian)位能(neng)夠反(fan)映鈍(dun)化(hua)(hua)膜(mo)(mo)(mo)的(de)(de)(de)(de)(de)(de)穩定(ding)性(xing)(xing)(xing)。通常情況(kuang)下，點(dian)(dian)(dian)(dian)蝕(shi)(shi)(shi)(shi)電(dian)位越(yue)高(gao)(gao)，金(jin)屬(shu)的(de)(de)(de)(de)(de)(de)耐(nai)(nai)(nai)點(dian)(dian)(dian)(dian)蝕(shi)(shi)(shi)(shi)性(xing)(xing)(xing)能(neng)越(yue)好。由(you)第(di)3章可知，當(dang)固溶(rong)處理(li)(li)的(de)(de)(de)(de)(de)(de)溫度(du)為(wei)(wei)1050℃時，2205雙(shuang)相不銹(xiu)鋼基(ji)體(ti)(ti)(ti)中(zhong)(zhong)的(de)(de)(de)(de)(de)(de)鐵(tie)素(su)體(ti)(ti)(ti)的(de)(de)(de)(de)(de)(de)含(han)(han)量(liang)(liang)與奧氏(shi)體(ti)(ti)(ti)的(de)(de)(de)(de)(de)(de)含(han)(han)量(liang)(liang)之比(bi)約為(wei)(wei)1:1,且(qie)鐵(tie)素(su)體(ti)(ti)(ti)和奧氏(shi)體(ti)(ti)(ti)的(de)(de)(de)(de)(de)(de)分布較(jiao)均勻，Cr和Mo在(zai)鐵(tie)素(su)體(ti)(ti)(ti)中(zhong)(zhong)的(de)(de)(de)(de)(de)(de)含(han)(han)量(liang)(liang)分布和N在(zai)奧氏(shi)體(ti)(ti)(ti)中(zhong)(zhong)的(de)(de)(de)(de)(de)(de)含(han)(han)量(liang)(liang)分布較(jiao)均勻，整體(ti)(ti)(ti)的(de)(de)(de)(de)(de)(de)耐(nai)(nai)(nai)點(dian)(dian)(dian)(dian)蝕(shi)(shi)(shi)(shi)當(dang)量(liang)(liang)較(jiao)高(gao)(gao)，表(biao)現出較(jiao)好的(de)(de)(de)(de)(de)(de)耐(nai)(nai)(nai)點(dian)(dian)(dian)(dian)蝕(shi)(shi)(shi)(shi)性(xing)(xing)(xing)能(neng)。當(dang)固溶(rong)處理(li)(li)的(de)(de)(de)(de)(de)(de)溫度(du)為(wei)(wei)950℃時，大量(liang)(liang)的(de)(de)(de)(de)(de)(de)σ相會沿著鐵(tie)素(su)體(ti)(ti)(ti)－奧氏(shi)體(ti)(ti)(ti)晶界(jie)析出，而σ相是一種硬(ying)脆相，其周(zhou)圍(wei)會存(cun)在(zai)貧鉻(ge)區，它的(de)(de)(de)(de)(de)(de)存(cun)在(zai)顯著降低(di)材料(liao)的(de)(de)(de)(de)(de)(de)力學性(xing)(xing)(xing)能(neng)和耐(nai)(nai)(nai)蝕(shi)(shi)(shi)(shi)性(xing)(xing)(xing)能(neng)，且(qie)σ相的(de)(de)(de)(de)(de)(de)析出使其存(cun)在(zai)區域(yu)的(de)(de)(de)(de)(de)(de)鈍(dun)化(hua)(hua)膜(mo)(mo)(mo)薄弱(ruo)，使得點(dian)(dian)(dian)(dian)蝕(shi)(shi)(shi)(shi)電(dian)位較(jiao)低(di)，點(dian)(dian)(dian)(dian)蝕(shi)(shi)(shi)(shi)更容易發(fa)生。當(dang)固溶(rong)處理(li)(li)的(de)(de)(de)(de)(de)(de)溫度(du)升高(gao)(gao)至1150℃時，基(ji)體(ti)(ti)(ti)中(zhong)(zhong)的(de)(de)(de)(de)(de)(de)鐵(tie)素(su)體(ti)(ti)(ti)的(de)(de)(de)(de)(de)(de)含(han)(han)量(liang)(liang)百分比(bi)為(wei)(wei)59%,而奧氏(shi)體(ti)(ti)(ti)的(de)(de)(de)(de)(de)(de)含(han)(han)量(liang)(liang)百分比(bi)為(wei)(wei)41%,鐵(tie)素(su)體(ti)(ti)(ti)含(han)(han)量(liang)(liang)過多(duo)，導致鐵(tie)素(su)體(ti)(ti)(ti)的(de)(de)(de)(de)(de)(de)耐(nai)(nai)(nai)點(dian)(dian)(dian)(dian)蝕(shi)(shi)(shi)(shi)當(dang)量(liang)(liang)下降，造成耐(nai)(nai)(nai)點(dian)(dian)(dian)(dian)蝕(shi)(shi)(shi)(shi)性(xing)(xing)(xing)能(neng)下降。
2. 交流阻抗測試(shi)分析
不同固溶處理的2205雙相不銹鋼在不同溫度的3.5%NaCl溶液中的Nyquist圖如圖5.10所示。從圖5.10中可以看出，在不同溫度的3.5%NaCl溶液中的不同固溶處理的雙相不銹鋼的Nyquist圖中的高頻和低頻處，都存在一個容抗弧，說明雙相不銹鋼表面存在一層鈍化膜。所以該電化學過程中，存在兩個時間常數。并且，曹楚南的電化學阻抗譜分析也認為，不銹鋼鈍化過程存在兩個時間常數，這與本實驗所測數據是一致的。而本實驗的電化學阻抗測試是在雙相不銹鋼自鈍化狀態下進行的，而雙相不銹鋼在自腐蝕電位下形成的表面鈍化膜是存在缺陷的，材料表面由于缺陷的存在而暴露于電解質溶液中，所以采用如圖5.11所示的等效電路（其中，R1為溶液電阻；R2為電荷轉移電阻；R3為鈍化膜電阻；Cdl為雙電層電容；Cf為鈍化膜膜電容）。
根據圖(tu)(tu)5.11的等效(xiao)電(dian)(dian)路，利用軟(ruan)件ZSimpWin進(jin)行阻(zu)(zu)抗(kang)的擬合，得到如圖(tu)(tu)5.12所(suo)示(shi)的電(dian)(dian)荷轉(zhuan)移(yi)電(dian)(dian)阻(zu)(zu)曲線(xian)圖(tu)(tu)和如圖(tu)(tu)5.13所(suo)示(shi)的鈍化膜阻(zu)(zu)抗(kang)值(zhi)曲線(xian)圖(tu)(tu)。電(dian)(dian)荷轉(zhuan)移(yi)電(dian)(dian)阻(zu)(zu)阻(zu)(zu)抗(kang)值(zhi)和鈍化膜阻(zu)(zu)抗(kang)值(zhi)如表5.4所(suo)列。
從圖(tu)5.12中可以看出，隨著3.5%NaCl溶(rong)液(ye)溫度的升高，不同固溶(rong)處理的雙(shuang)相不銹鋼的電(dian)(dian)化(hua)(hua)學(xue)(xue)反(fan)(fan)(fan)應的電(dian)(dian)荷轉移電(dian)(dian)阻降(jiang)低，電(dian)(dian)化(hua)(hua)學(xue)(xue)反(fan)(fan)(fan)應的阻力(li)下降(jiang)，電(dian)(dian)化(hua)(hua)學(xue)(xue)反(fan)(fan)(fan)應變快。耐蝕性(xing)能下降(jiang)。
從圖5.13中可以看出，隨著3.5%NaCl溶液溫度的升高，不同固溶處理的雙相不銹鋼的鈍化膜阻抗值下降，鈍化膜穩定性變差，雙相不銹鋼的耐點蝕性能下降。一方面，O2在溶液中的溶解度隨著溫度的升高而降低，當NaCI溶液的溫度升高時，溶液中含氧量降低，導致雙相不銹鋼表面鈍化膜形成所需的O元素下降，降低鈍化膜形成的可能性；另一方面，隨著溶液溫度的升高，鈍化膜的溶解速度升高，導致雙相不銹鋼的耐點蝕性能下降。
從表5.4中(zhong)可以(yi)看出；不銹(xiu)鋼的(de)電化學反應的(de)電荷轉(zhuan)移電阻(zu)阻(zu)抗(kang)值遠小(xiao)于(yu)不銹(xiu)鋼的(de)鈍(dun)化膜阻(zu)抗(kang)值，說明雙相不銹(xiu)鋼在0.5mol/L 3.5%NaCl溶(rong)液中(zhong)的(de)耐蝕性主要是由其表面的(de)鈍(dun)化膜的(de)穩定性決定。
從圖(tu)5.12和圖(tu)5.13中(zhong)可(ke)以看出，1050℃/30min固溶(rong)處(chu)(chu)(chu)理(li)的雙相(xiang)不(bu)銹鋼(gang)的鈍化(hua)(hua)膜(mo)阻(zu)(zu)(zu)抗值和電荷轉移電阻(zu)(zu)(zu)阻(zu)(zu)(zu)抗值較(jiao)(jiao)(jiao)(jiao)高，說明1050℃/30min固溶(rong)處(chu)(chu)(chu)理(li)的試(shi)樣的鈍化(hua)(hua)膜(mo)較(jiao)(jiao)(jiao)(jiao)穩定(ding)(ding)，電化(hua)(hua)學反應阻(zu)(zu)(zu)力(li)較(jiao)(jiao)(jiao)(jiao)高，腐(fu)蝕(shi)速(su)(su)率(lv)較(jiao)(jiao)(jiao)(jiao)慢(man)，耐蝕(shi)性能較(jiao)(jiao)(jiao)(jiao)好。而950℃固溶(rong)處(chu)(chu)(chu)理(li)的試(shi)樣中(zhong)存(cun)在(zai)較(jiao)(jiao)(jiao)(jiao)多σ相(xiang)，降低(di)了(le)表(biao)(biao)面的鈍化(hua)(hua)膜(mo)的穩定(ding)(ding)性，表(biao)(biao)現(xian)出較(jiao)(jiao)(jiao)(jiao)低(di)的鈍化(hua)(hua)膜(mo)阻(zu)(zu)(zu)抗值；同(tong)時在(zai)其(qi)周圍存(cun)在(zai)貧鉻區，加速(su)(su)了(le)腐(fu)蝕(shi)，表(biao)(biao)現(xian)出較(jiao)(jiao)(jiao)(jiao)低(di)的電荷轉移電阻(zu)(zu)(zu)值。對于1150℃/30min 固溶(rong)處(chu)(chu)(chu)理(li)的試(shi)樣，其(qi)組(zu)織中(zhong)含有過量的鐵素體，導致耐點(dian)蝕(shi)當(dang)量降低(di)，點(dian)蝕(shi)電位較(jiao)(jiao)(jiao)(jiao)1050℃/30min固溶(rong)處(chu)(chu)(chu)理(li)的雙相(xiang)不(bu)銹鋼(gang)的點(dian)蝕(shi)電位低(di)。
以上結果表明，阻抗測試結果與(yu)極(ji)化曲(qu)線(xian)測試得(de)到的(de)(de)結果是一致的(de)(de)，二者都說明1050℃/30min固(gu)溶(rong)處(chu)理(li)的(de)(de)試樣的(de)(de)耐點蝕(shi)性(xing)能較(jiao)好。
