圖3.7(a)~(d)為(wei)鐵(tie)(tie)素(su)體(ti)(ti)(ti)(ti)(ti)和(he)奧(ao)(ao)氏(shi)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo、Ni元素(su)含(han)(han)(han)(han)量(liang)(liang)與固(gu)(gu)溶(rong)溫(wen)度(du)的(de)(de)(de)(de)(de)(de)關(guan)系圖。圖3.7(a)~(d)證實(shi)了鐵(tie)(tie)素(su)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr和(he)Mo含(han)(han)(han)(han)量(liang)(liang)更高(gao)，而奧(ao)(ao)氏(shi)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Ni和(he)Mn含(han)(han)(han)(han)量(liang)(liang)更高(gao)。從圖中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)可(ke)看出(chu)，鐵(tie)(tie)素(su)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr含(han)(han)(han)(han)量(liang)(liang)為(wei)23.77%~25.16%,比(bi)奧(ao)(ao)氏(shi)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)Cr含(han)(han)(han)(han)量(liang)(liang)高(gao)2%左右；鐵(tie)(tie)素(su)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)Mo含(han)(han)(han)(han)量(liang)(liang)為(wei)3.86%~4.37%,比(bi)奧(ao)(ao)氏(shi)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Mo含(han)(han)(han)(han)量(liang)(liang)高(gao)1.7%左右；奧(ao)(ao)氏(shi)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Ni含(han)(han)(han)(han)量(liang)(liang)為(wei)5.42%、6.7%,比(bi)鐵(tie)(tie)素(su)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Ni含(han)(han)(han)(han)量(liang)(liang)高(gao)2%;當固(gu)(gu)溶(rong)處理溫(wen)度(du)為(wei)1050℃時，鐵(tie)(tie)素(su)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo和(he)Ni含(han)(han)(han)(han)量(liang)(liang)分(fen)別為(wei)23.77%、3.97%、4.24%,奧(ao)(ao)氏(shi)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo和(he)Ni含(han)(han)(han)(han)量(liang)(liang)分(fen)別為(wei)23.53%、2.63%、5.42%.可(ke)見在1050℃溫(wen)度(du)下進行固(gu)(gu)溶(rong)時，兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo、Ni含(han)(han)(han)(han)量(liang)(liang)差(cha)異(yi)最小，此時鐵(tie)(tie)素(su)體(ti)(ti)(ti)(ti)(ti)含(han)(han)(han)(han)量(liang)(liang)為(wei)51.9%,奧(ao)(ao)氏(shi)體(ti)(ti)(ti)(ti)(ti)含(han)(han)(han)(han)量(liang)(liang)為(wei)48.1%.當固(gu)(gu)溶(rong)溫(wen)度(du)改(gai)變(bian)時，鐵(tie)(tie)素(su)體(ti)(ti)(ti)(ti)(ti)／奧(ao)(ao)氏(shi)體(ti)(ti)(ti)(ti)(ti)兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)比(bi)例(li)相(xiang)(xiang)(xiang)差(cha)變(bian)大，且兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo、Ni含(han)(han)(han)(han)量(liang)(liang)差(cha)異(yi)也變(bian)大。當固(gu)(gu)溶(rong)溫(wen)度(du)為(wei)1000℃,兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)Cr為(wei)3.69%、Mo為(wei)1.51%、Ni為(wei)3.37%;當固(gu)(gu)溶(rong)溫(wen)度(du)為(wei)1150℃時，兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)Cr為(wei)2.29%、Mo為(wei)1.34%、Ni為(wei)2.09%,可(ke)見1000℃固(gu)(gu)溶(rong)試(shi)樣的(de)(de)(de)(de)(de)(de)兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo、Ni元素(su)含(han)(han)(han)(han)量(liang)(liang)差(cha)大于1150℃固(gu)(gu)溶(rong)試(shi)樣的(de)(de)(de)(de)(de)(de)兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)Cr、Mo、Ni元素(su)含(han)(han)(han)(han)量(liang)(liang)差(cha)。

  由(you)公式“PREN.=[Cr]+3.3[Mo]”計算鐵素(su)體的PREN值(zhi)(zhi)，由(you)公式“PREN,=[Cr]+3.3[Mo]+16[N]-[Mn]”計算奧氏體的PREN值(zhi)(zhi)，可(ke)得PREN值(zhi)(zhi)與固溶溫(wen)度(du)的關系(xi)圖(tu)，如圖(tu)3.7(e)所示。從圖(tu)3.7(e)可(ke)看出，在不同固溶狀態下，兩(liang)相(xiang)的PREN值(zhi)(zhi)有所不同，但(dan)PRENa>PRENy.當固溶溫(wen)度(du)為(wei)1050℃時，PREN.最小、PREN,最大，分(fen)別(bie)為(wei)36.9和30.6,兩(liang)者(zhe)相(xiang)差最小。

  圖(tu)(tu)3.8為不同固溶(rong)試樣(yang)的(de)(de)(de)(de)極(ji)(ji)化曲(qu)線(xian)。可(ke)見，在(zai)自(zi)腐(fu)蝕(shi)(shi)電(dian)(dian)位(wei)(wei)下，材(cai)料開始(shi)發生鈍(dun)化；當極(ji)(ji)化電(dian)(dian)位(wei)(wei)升高到一定值(zhi)時，不同固溶(rong)的(de)(de)(de)(de)材(cai)料都發生點(dian)(dian)蝕(shi)(shi)，電(dian)(dian)流密度(du)急劇增大(da)。根(gen)據GB 4334.9-1984中電(dian)(dian)流密度(du)為0.1mA/c㎡所對應(ying)的(de)(de)(de)(de)電(dian)(dian)位(wei)(wei)為點(dian)(dian)蝕(shi)(shi)電(dian)(dian)位(wei)(wei)和Tafel擬合，分別得(de)到點(dian)(dian)蝕(shi)(shi)電(dian)(dian)位(wei)(wei)、自(zi)腐(fu)蝕(shi)(shi)電(dian)(dian)流密度(du)與固溶(rong)溫度(du)的(de)(de)(de)(de)關系圖(tu)(tu)，如圖(tu)(tu)3.11(a)所示。

  圖(tu)(tu)3.9(a)、（b)分別(bie)為不同固溶試(shi)樣的(de)Nyquist 圖(tu)(tu)和Bode圖(tu)(tu)。從圖(tu)(tu)3.9(a)可見，試(shi)樣在低頻(pin)和高頻(pin)區分別(bie)存(cun)(cun)在一個容抗弧。從圖(tu)(tu)3.9(b)可見，試(shi)樣在低頻(pin)和高頻(pin)處(chu)分別(bie)存(cun)(cun)在一個時間(jian)(jian)常(chang)數。根據曹楚南(nan)的(de)《電(dian)(dian)化學阻(zu)(zu)抗譜導(dao)論》可知(zhi)。雙相不銹鋼在NaCl溶液中(zhong)的(de)阻(zu)(zu)抗譜中(zhong)存(cun)(cun)在兩個時間(jian)(jian)常(chang)數，常(chang)以圖(tu)(tu)3.10所(suo)示(shi)的(de)等效電(dian)(dian)路（R1為電(dian)(dian)荷(he)轉移電(dian)(dian)阻(zu)(zu)，R2為鈍化膜電(dian)(dian)阻(zu)(zu)）進行阻(zu)(zu)抗擬(ni)(ni)合。經阻(zu)(zu)抗擬(ni)(ni)合，得到鈍化膜電(dian)(dian)阻(zu)(zu)、電(dian)(dian)荷(he)轉移電(dian)(dian)阻(zu)(zu)與固溶處(chu)理溫度的(de)關系圖(tu)(tu)，如圖(tu)(tu)3.11(b)所(suo)示(shi)。

 從圖3.11(a)可見，1050℃固溶試樣的點蝕電位最高，約為0.89V,且1050℃固溶試樣的自腐蝕電流密度最低，約為2.34×10^-6A/c㎡,說明該狀態下試樣的耐點蝕性能最好。由圖3.11(b)可知，1050℃固溶試樣的鈍化膜電阻值最高，約為1300Ω,且其電荷轉移電阻值也最高，約為9500Ω,說明該狀態下試樣的鈍化膜較穩定，耐點蝕性能較好。

  圖3.12為不同固溶的2205雙相不銹鋼極化后的點蝕形貌圖，圖中黑色為蝕坑，深色為鐵素體，淡色為奧氏體。從圖3.12可見，四種固溶試樣的點蝕都發生于鐵素體與奧氏體相界面處，且易向鐵素體相中長大。當固溶溫度為1050℃時，試樣的點蝕尺寸最小，點蝕敏感性最低。

  通(tong)過計算得到(dao)不(bu)同(tong)相(xiang)(xiang)比例下的(de)(de)(de)(de)鐵素(su)體(ti)PREN值(zhi)和奧氏體(ti)PREN值(zhi)，可(ke)見(jian)不(bu)同(tong)相(xiang)(xiang)比例下的(de)(de)(de)(de)PREN.都大(da)于(yu)(yu)PREN,.雙相(xiang)(xiang)不(bu)銹鋼(gang)(gang)的(de)(de)(de)(de)耐(nai)點蝕(shi)性能可(ke)通(tong)過點蝕(shi)電(dian)位(wei)衡量。點蝕(shi)電(dian)位(wei)越(yue)高(gao)(gao)，耐(nai)點獨性能越(yue)好(hao)。前人認為雙相(xiang)(xiang)不(bu)銹鋼(gang)(gang)的(de)(de)(de)(de)耐(nai)點蝕(shi)性能由B能N值(zhi)較區的(de)(de)(de)(de)相(xiang)(xiang)決定(ding)，且PEN值(zhi)越(yue)高(gao)(gao)，耐(nai)點蝕(shi)性能越(yue)好(hao)，從圖3.71e)可(ke)矩(ju)，不(bu)同(tong)海溶試(shi)(shi)樣的(de)(de)(de)(de)PREN.都大(da)于(yu)(yu)PREN,,當固(gu)溶溫度為1050℃時(shi)，PHEN,最大(da)，材料(liao)的(de)(de)(de)(de)耐(nai)點蝕(shi)性能應最好(hao)。從圖3.11(a)、（b)可(ke)知，1050℃固(gu)溶試(shi)(shi)樣的(de)(de)(de)(de)點蝕(shi)電(dian)位(wei)最高(gao)(gao)，鈍化膜阻抗(kang)值(zhi)最大(da)，電(dian)荷(he)轉移電(dian)阻值(zhi)最商；且從圖3.12(b)可(ke)見(jian)，1050℃固(gu)溶試(shi)(shi)樣的(de)(de)(de)(de)點蝕(shi)坑(keng)尺(chi)寸最小，表現出最好(hao)的(de)(de)(de)(de)耐(nai)點蝕(shi)性能。綜上可(ke)知，雙相(xiang)(xiang)不(bu)銹鋼(gang)(gang)的(de)(de)(de)(de)耐(nai)點蝕(shi)性能由 PREN 值(zhi)較小相(xiang)(xiang)決定(ding)的(de)(de)(de)(de)理論(lun)是有實(shi)驗依據的(de)(de)(de)(de)。

  從(cong)圖(tu)3.12(a)~(d)可(ke)見，在(zai)不(bu)同固(gu)溶(rong)狀態下，鐵素體相都更易發(fa)生點(dian)蝕(shi)；而從(cong)圖(tu)3.7(e)可(ke)見，在(zai)不(bu)同固(gu)溶(rong)狀態下，PREN.都大于(yu)PREN,,鐵素體的(de)耐點(dian)蝕(shi)性(xing)能(neng)應優于(yu)奧氏(shi)體相，可(ke)見兩者存(cun)在(zai)矛盾。

  隨固(gu)(gu)(gu)(gu)(gu)溶(rong)溫(wen)度(du)變化，雙(shuang)相(xiang)(xiang)不(bu)銹鋼中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)鐵素(su)體(ti)(ti)和(he)奧(ao)氏(shi)體(ti)(ti)相(xiang)(xiang)的(de)(de)(de)(de)(de)(de)比例改(gai)變，且(qie)(qie)(qie)兩(liang)相(xiang)(xiang)形態也發生變化。Cr是(shi)鐵素(su)體(ti)(ti)形成(cheng)(cheng)元(yuan)素(su)，可(ke)提高材(cai)料(liao)(liao)(liao)的(de)(de)(de)(de)(de)(de)耐蝕(shi)(shi)性能(neng)(neng)(neng)(neng)；Mo是(shi)鐵素(su)體(ti)(ti)形成(cheng)(cheng)元(yuan)素(su)，可(ke)提高點蝕(shi)(shi)電位(wei)，降低腐(fu)蝕(shi)(shi)速率；Ni是(shi)奧(ao)氏(shi)體(ti)(ti)形成(cheng)(cheng)元(yuan)素(su)，可(ke)維(wei)持兩(liang)相(xiang)(xiang)平衡，提高耐蝕(shi)(shi)性能(neng)(neng)(neng)(neng)。并且(qie)(qie)(qie)材(cai)料(liao)(liao)(liao)中(zhong)(zhong)(zhong)(zhong)存(cun)在一定量的(de)(de)(de)(de)(de)(de)N,其為奧(ao)氏(shi)體(ti)(ti)形成(cheng)(cheng)元(yuan)素(su)，提高局部(bu)腐(fu)蝕(shi)(shi)抗力。從圖(tu)3.7(a)~(c)可(ke)見(jian)，隨固(gu)(gu)(gu)(gu)(gu)溶(rong)溫(wen)度(du)變化，兩(liang)相(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo、Ni元(yuan)素(su)含(han)量發生變化。由(you)于(yu)Cr、Mo、Ni元(yuan)素(su)之間(jian)的(de)(de)(de)(de)(de)(de)腐(fu)蝕(shi)(shi)電位(wei)存(cun)在差(cha)異(yi)，勢必造成(cheng)(cheng)兩(liang)相(xiang)(xiang)之間(jian)存(cun)在電化學(xue)差(cha)異(yi)，使(shi)腐(fu)蝕(shi)(shi)更易發生。從圖(tu)3.7(e)可(ke)知，不(bu)同固(gu)(gu)(gu)(gu)(gu)溶(rong)狀態下材(cai)料(liao)(liao)(liao)的(de)(de)(de)(de)(de)(de)PREN,大(da)(da)小關系為1050℃>1000℃>1150℃>1100℃,因此(ci)(ci)根據前人的(de)(de)(de)(de)(de)(de)研究，不(bu)同固(gu)(gu)(gu)(gu)(gu)溶(rong)態材(cai)料(liao)(liao)(liao)的(de)(de)(de)(de)(de)(de)耐點蝕(shi)(shi)性能(neng)(neng)(neng)(neng)優劣關系應為：1050℃優于(yu)1000℃優于(yu)1150℃.當固(gu)(gu)(gu)(gu)(gu)溶(rong)溫(wen)度(du)為1050℃時，PREN,值較大(da)(da)，兩(liang)相(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo、Ni元(yuan)素(su)含(han)量差(cha)異(yi)最小，材(cai)料(liao)(liao)(liao)的(de)(de)(de)(de)(de)(de)點蝕(shi)(shi)坑(keng)較小，材(cai)料(liao)(liao)(liao)的(de)(de)(de)(de)(de)(de)耐點蝕(shi)(shi)性能(neng)(neng)(neng)(neng)最優。1000℃固(gu)(gu)(gu)(gu)(gu)溶(rong)試(shi)樣(yang)的(de)(de)(de)(de)(de)(de)點蝕(shi)(shi)坑(keng)尺寸(cun)大(da)(da)于(yu)1150℃固(gu)(gu)(gu)(gu)(gu)溶(rong)試(shi)樣(yang)的(de)(de)(de)(de)(de)(de)點蝕(shi)(shi)坑(keng)尺寸(cun)，因此(ci)(ci)，前者的(de)(de)(de)(de)(de)(de)耐點蝕(shi)(shi)性能(neng)(neng)(neng)(neng)劣于(yu)后者的(de)(de)(de)(de)(de)(de)耐點蝕(shi)(shi)性能(neng)(neng)(neng)(neng)。由(you)此(ci)(ci)可(ke)見(jian)，雙(shuang)相(xiang)(xiang)不(bu)銹鋼中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)相(xiang)(xiang)腐(fu)蝕(shi)(shi)不(bu)能(neng)(neng)(neng)(neng)僅僅由(you)PREN值來解釋。由(you)圖(tu)3.7(a)~(c)可(ke)知，1000℃固(gu)(gu)(gu)(gu)(gu)溶(rong)試(shi)樣(yang)的(de)(de)(de)(de)(de)(de)兩(liang)相(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo、Ni元(yuan)素(su)含(han)量差(cha)大(da)(da)于(yu)1150℃固(gu)(gu)(gu)(gu)(gu)溶(rong)試(shi)樣(yang)的(de)(de)(de)(de)(de)(de)兩(liang)相(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Gr、Mo、Ni元(yuan)素(su)含(han)量差(cha)，因此(ci)(ci)，雙(shuang)相(xiang)(xiang)不(bu)銹鋼中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)相(xiang)(xiang)腐(fu)蝕(shi)(shi)還與兩(liang)相(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)元(yuan)素(su)分布有關，并且(qie)(qie)(qie)還需考慮到材(cai)料(liao)(liao)(liao)中(zhong)(zhong)(zhong)(zhong)點蝕(shi)(shi)敏感性較強的(de)(de)(de)(de)(de)(de)區域，如晶界和(he)相(xiang)(xiang)界。

  點蝕是一種局部腐蝕現象，是由氯離子破壞鈍化膜而導致的。點蝕產生后，蝕坑處的基體被暴露在溶液中，導致材料進一步發生腐蝕，蝕坑長大。蝕坑前長大速率由材料的均勻溶解速率決定，溶解越快，蝕坑長大速度越大。因此，雙相不銹鋼的耐點蝕性能由兩部分構成：控制點蝕萌生和控制蝕坑長大的能力。本書中的點蝕電位意味著點蝕已長大。影響點蝕萌生的因素不僅包括PREN 值，還包括兩相中的元素分布和兩相的比例。從本書的分析可見，點蝕的長大與元素分布有關，兩相中的元素分布越均勻，蝕坑的長大速度越慢。因此在1050℃固溶狀態下，兩相中的元素分布最均勻，PREN,最高，合金的點蝕電位最高，材料的耐點蝕性能最好。而1000℃固溶試樣兩相中的元素分布不均勻，導致點蝕電位較低，點蝕坑尺寸較大，降低材料的耐點蝕性能。

  影響(xiang)雙相(xiang)(xiang)不銹鋼相(xiang)(xiang)腐蝕(shi)的因素(su)不僅包(bao)括(kuo)PREN值，還包(bao)括(kuo)各(ge)相(xiang)(xiang)中的元(yuan)素(su)分布(bu)和兩相(xiang)(xiang)比例，并(bing)且三者互相(xiang)(xiang)影響(xiang)、關系復雜(za)。因此，不能(neng)僅憑PREN值的大小來判(pan)斷耐點蝕(shi)能(neng)力，應該綜合考慮(lv)各(ge)因素(su)的影響(xiang)。