圖3.7(a)~(d)為(wei)(wei)(wei)(wei)鐵(tie)素(su)(su)體(ti)(ti)(ti)和(he)(he)奧氏(shi)(shi)(shi)體(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)Cr、Mo、Ni元(yuan)素(su)(su)含(han)(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)(liang)與固(gu)(gu)(gu)(gu)溶(rong)(rong)溫度(du)的(de)(de)(de)關系圖。圖3.7(a)~(d)證實了鐵(tie)素(su)(su)體(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)Cr和(he)(he)Mo含(han)(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)(liang)更高(gao)(gao)，而奧氏(shi)(shi)(shi)體(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)Ni和(he)(he)Mn含(han)(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)(liang)更高(gao)(gao)。從(cong)圖中(zhong)(zhong)(zhong)(zhong)(zhong)可(ke)看(kan)出，鐵(tie)素(su)(su)體(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)Cr含(han)(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)(liang)為(wei)(wei)(wei)(wei)23.77%~25.16%,比奧氏(shi)(shi)(shi)體(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)Cr含(han)(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)(liang)高(gao)(gao)2%左(zuo)右；鐵(tie)素(su)(su)體(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)Mo含(han)(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)(liang)為(wei)(wei)(wei)(wei)3.86%~4.37%,比奧氏(shi)(shi)(shi)體(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)Mo含(han)(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)(liang)高(gao)(gao)1.7%左(zuo)右；奧氏(shi)(shi)(shi)體(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)Ni含(han)(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)(liang)為(wei)(wei)(wei)(wei)5.42%、6.7%,比鐵(tie)素(su)(su)體(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)Ni含(han)(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)(liang)高(gao)(gao)2%;當(dang)(dang)固(gu)(gu)(gu)(gu)溶(rong)(rong)處(chu)理溫度(du)為(wei)(wei)(wei)(wei)1050℃時，鐵(tie)素(su)(su)體(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)Cr、Mo和(he)(he)Ni含(han)(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)(liang)分別為(wei)(wei)(wei)(wei)23.77%、3.97%、4.24%,奧氏(shi)(shi)(shi)體(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)Cr、Mo和(he)(he)Ni含(han)(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)(liang)分別為(wei)(wei)(wei)(wei)23.53%、2.63%、5.42%.可(ke)見在(zai)1050℃溫度(du)下進行固(gu)(gu)(gu)(gu)溶(rong)(rong)時，兩(liang)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)Cr、Mo、Ni含(han)(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)(liang)差(cha)(cha)異最小，此時鐵(tie)素(su)(su)體(ti)(ti)(ti)含(han)(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)(liang)為(wei)(wei)(wei)(wei)51.9%,奧氏(shi)(shi)(shi)體(ti)(ti)(ti)含(han)(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)(liang)為(wei)(wei)(wei)(wei)48.1%.當(dang)(dang)固(gu)(gu)(gu)(gu)溶(rong)(rong)溫度(du)改變(bian)時，鐵(tie)素(su)(su)體(ti)(ti)(ti)／奧氏(shi)(shi)(shi)體(ti)(ti)(ti)兩(liang)相(xiang)(xiang)(xiang)(xiang)(xiang)比例相(xiang)(xiang)(xiang)(xiang)(xiang)差(cha)(cha)變(bian)大，且兩(liang)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)Cr、Mo、Ni含(han)(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)(liang)差(cha)(cha)異也變(bian)大。當(dang)(dang)固(gu)(gu)(gu)(gu)溶(rong)(rong)溫度(du)為(wei)(wei)(wei)(wei)1000℃,兩(liang)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)Cr為(wei)(wei)(wei)(wei)3.69%、Mo為(wei)(wei)(wei)(wei)1.51%、Ni為(wei)(wei)(wei)(wei)3.37%;當(dang)(dang)固(gu)(gu)(gu)(gu)溶(rong)(rong)溫度(du)為(wei)(wei)(wei)(wei)1150℃時，兩(liang)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)Cr為(wei)(wei)(wei)(wei)2.29%、Mo為(wei)(wei)(wei)(wei)1.34%、Ni為(wei)(wei)(wei)(wei)2.09%,可(ke)見1000℃固(gu)(gu)(gu)(gu)溶(rong)(rong)試(shi)樣的(de)(de)(de)兩(liang)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)Cr、Mo、Ni元(yuan)素(su)(su)含(han)(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)(liang)差(cha)(cha)大于1150℃固(gu)(gu)(gu)(gu)溶(rong)(rong)試(shi)樣的(de)(de)(de)兩(liang)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)Cr、Mo、Ni元(yuan)素(su)(su)含(han)(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)(liang)差(cha)(cha)。

  由公式“PREN.=[Cr]+3.3[Mo]”計(ji)算鐵素體的(de)PREN值(zhi)，由公式“PREN,=[Cr]+3.3[Mo]+16[N]-[Mn]”計(ji)算奧氏體的(de)PREN值(zhi)，可得(de)PREN值(zhi)與固溶(rong)(rong)溫度(du)的(de)關系圖(tu)(tu)，如圖(tu)(tu)3.7(e)所(suo)示。從圖(tu)(tu)3.7(e)可看出，在不同(tong)固溶(rong)(rong)狀(zhuang)態下，兩(liang)相的(de)PREN值(zhi)有所(suo)不同(tong)，但(dan)PRENa>PRENy.當固溶(rong)(rong)溫度(du)為1050℃時，PREN.最(zui)小(xiao)、PREN,最(zui)大，分別(bie)為36.9和(he)30.6,兩(liang)者相差最(zui)小(xiao)。

  圖3.8為(wei)不同(tong)固(gu)溶(rong)試樣的極化(hua)曲線。可見，在(zai)自腐蝕(shi)電(dian)(dian)(dian)(dian)位(wei)下，材料開始發生鈍化(hua)；當極化(hua)電(dian)(dian)(dian)(dian)位(wei)升高到(dao)一定(ding)值時，不同(tong)固(gu)溶(rong)的材料都發生點(dian)蝕(shi)，電(dian)(dian)(dian)(dian)流(liu)密(mi)度急劇增大(da)。根據GB 4334.9-1984中電(dian)(dian)(dian)(dian)流(liu)密(mi)度為(wei)0.1mA/c㎡所對應的電(dian)(dian)(dian)(dian)位(wei)為(wei)點(dian)蝕(shi)電(dian)(dian)(dian)(dian)位(wei)和Tafel擬合，分別得到(dao)點(dian)蝕(shi)電(dian)(dian)(dian)(dian)位(wei)、自腐蝕(shi)電(dian)(dian)(dian)(dian)流(liu)密(mi)度與固(gu)溶(rong)溫度的關系圖，如圖3.11(a)所示。

  圖(tu)(tu)3.9(a)、（b)分別(bie)(bie)為不同固溶試(shi)樣(yang)的(de)Nyquist 圖(tu)(tu)和Bode圖(tu)(tu)。從圖(tu)(tu)3.9(a)可見，試(shi)樣(yang)在低頻和高頻區分別(bie)(bie)存(cun)在一個(ge)容抗弧。從圖(tu)(tu)3.9(b)可見，試(shi)樣(yang)在低頻和高頻處(chu)分別(bie)(bie)存(cun)在一個(ge)時間常(chang)數。根據(ju)曹楚南的(de)《電(dian)(dian)(dian)化學(xue)阻(zu)抗譜導(dao)論》可知。雙相不銹鋼在NaCl溶液(ye)中的(de)阻(zu)抗譜中存(cun)在兩個(ge)時間常(chang)數，常(chang)以(yi)圖(tu)(tu)3.10所示的(de)等效(xiao)電(dian)(dian)(dian)路（R1為電(dian)(dian)(dian)荷(he)轉(zhuan)移電(dian)(dian)(dian)阻(zu)，R2為鈍(dun)化膜電(dian)(dian)(dian)阻(zu)）進行阻(zu)抗擬合。經阻(zu)抗擬合，得到(dao)鈍(dun)化膜電(dian)(dian)(dian)阻(zu)、電(dian)(dian)(dian)荷(he)轉(zhuan)移電(dian)(dian)(dian)阻(zu)與固溶處(chu)理溫(wen)度的(de)關系圖(tu)(tu)，如圖(tu)(tu)3.11(b)所示。

 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(xiu)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(ji)算得(de)到不(bu)同相比例(li)下的(de)(de)(de)(de)鐵素(su)體(ti)PREN值(zhi)(zhi)(zhi)和奧氏體(ti)PREN值(zhi)(zhi)(zhi)，可(ke)見不(bu)同相比例(li)下的(de)(de)(de)(de)PREN.都(dou)大于PREN,.雙(shuang)相不(bu)銹(xiu)鋼的(de)(de)(de)(de)耐(nai)點蝕(shi)(shi)性(xing)(xing)能(neng)(neng)(neng)可(ke)通(tong)過點蝕(shi)(shi)電(dian)位(wei)衡(heng)量。點蝕(shi)(shi)電(dian)位(wei)越高，耐(nai)點獨性(xing)(xing)能(neng)(neng)(neng)越好。前人認為雙(shuang)相不(bu)銹(xiu)鋼的(de)(de)(de)(de)耐(nai)點蝕(shi)(shi)性(xing)(xing)能(neng)(neng)(neng)由B能(neng)(neng)(neng)N值(zhi)(zhi)(zhi)較區的(de)(de)(de)(de)相決定，且(qie)PEN值(zhi)(zhi)(zhi)越高，耐(nai)點蝕(shi)(shi)性(xing)(xing)能(neng)(neng)(neng)越好，從(cong)(cong)圖3.71e)可(ke)矩，不(bu)同海溶試樣(yang)的(de)(de)(de)(de)PREN.都(dou)大于PREN,,當固溶溫度(du)為1050℃時，PHEN,最(zui)大，材料的(de)(de)(de)(de)耐(nai)點蝕(shi)(shi)性(xing)(xing)能(neng)(neng)(neng)應最(zui)好。從(cong)(cong)圖3.11(a)、（b)可(ke)知，1050℃固溶試樣(yang)的(de)(de)(de)(de)點蝕(shi)(shi)電(dian)位(wei)最(zui)高，鈍化膜阻抗值(zhi)(zhi)(zhi)最(zui)大，電(dian)荷轉移電(dian)阻值(zhi)(zhi)(zhi)最(zui)商(shang)；且(qie)從(cong)(cong)圖3.12(b)可(ke)見，1050℃固溶試樣(yang)的(de)(de)(de)(de)點蝕(shi)(shi)坑尺寸最(zui)小，表現出最(zui)好的(de)(de)(de)(de)耐(nai)點蝕(shi)(shi)性(xing)(xing)能(neng)(neng)(neng)。綜上可(ke)知，雙(shuang)相不(bu)銹(xiu)鋼的(de)(de)(de)(de)耐(nai)點蝕(shi)(shi)性(xing)(xing)能(neng)(neng)(neng)由 PREN 值(zhi)(zhi)(zhi)較小相決定的(de)(de)(de)(de)理論(lun)是(shi)有實驗(yan)依據(ju)的(de)(de)(de)(de)。

  從圖(tu)3.12(a)~(d)可見，在(zai)(zai)不同固(gu)溶(rong)(rong)狀態下，鐵素(su)體(ti)相(xiang)都更易(yi)發生點蝕(shi)；而從圖(tu)3.7(e)可見，在(zai)(zai)不同固(gu)溶(rong)(rong)狀態下，PREN.都大于PREN,,鐵素(su)體(ti)的耐點蝕(shi)性能應優于奧氏體(ti)相(xiang)，可見兩者存(cun)在(zai)(zai)矛盾。

  隨固(gu)(gu)(gu)(gu)溶(rong)溫度變(bian)(bian)化(hua)(hua)，雙相(xiang)(xiang)不銹鋼(gang)中(zhong)(zhong)(zhong)的(de)(de)鐵素(su)(su)體和奧(ao)氏(shi)(shi)體相(xiang)(xiang)的(de)(de)比例改變(bian)(bian)，且(qie)兩(liang)相(xiang)(xiang)形(xing)(xing)態(tai)也發生變(bian)(bian)化(hua)(hua)。Cr是(shi)鐵素(su)(su)體形(xing)(xing)成(cheng)元(yuan)(yuan)(yuan)素(su)(su)，可(ke)(ke)提(ti)高材(cai)(cai)料(liao)(liao)的(de)(de)耐(nai)(nai)(nai)蝕(shi)(shi)(shi)性(xing)(xing)能(neng)(neng)；Mo是(shi)鐵素(su)(su)體形(xing)(xing)成(cheng)元(yuan)(yuan)(yuan)素(su)(su)，可(ke)(ke)提(ti)高點(dian)(dian)蝕(shi)(shi)(shi)電位，降低腐蝕(shi)(shi)(shi)速(su)率；Ni是(shi)奧(ao)氏(shi)(shi)體形(xing)(xing)成(cheng)元(yuan)(yuan)(yuan)素(su)(su)，可(ke)(ke)維持兩(liang)相(xiang)(xiang)平衡(heng)，提(ti)高耐(nai)(nai)(nai)蝕(shi)(shi)(shi)性(xing)(xing)能(neng)(neng)。并(bing)且(qie)材(cai)(cai)料(liao)(liao)中(zhong)(zhong)(zhong)存(cun)在一定量(liang)的(de)(de)N,其為奧(ao)氏(shi)(shi)體形(xing)(xing)成(cheng)元(yuan)(yuan)(yuan)素(su)(su)，提(ti)高局部腐蝕(shi)(shi)(shi)抗力。從圖(tu)3.7(a)~(c)可(ke)(ke)見(jian)，隨固(gu)(gu)(gu)(gu)溶(rong)溫度變(bian)(bian)化(hua)(hua)，兩(liang)相(xiang)(xiang)中(zhong)(zhong)(zhong)的(de)(de)Cr、Mo、Ni元(yuan)(yuan)(yuan)素(su)(su)含(han)量(liang)發生變(bian)(bian)化(hua)(hua)。由(you)于(yu)Cr、Mo、Ni元(yuan)(yuan)(yuan)素(su)(su)之間(jian)的(de)(de)腐蝕(shi)(shi)(shi)電位存(cun)在差異，勢(shi)必(bi)造成(cheng)兩(liang)相(xiang)(xiang)之間(jian)存(cun)在電化(hua)(hua)學差異，使腐蝕(shi)(shi)(shi)更易發生。從圖(tu)3.7(e)可(ke)(ke)知(zhi)，不同固(gu)(gu)(gu)(gu)溶(rong)狀態(tai)下材(cai)(cai)料(liao)(liao)的(de)(de)PREN,大(da)(da)(da)小關系為1050℃>1000℃>1150℃>1100℃,因此根據(ju)前人的(de)(de)研究，不同固(gu)(gu)(gu)(gu)溶(rong)態(tai)材(cai)(cai)料(liao)(liao)的(de)(de)耐(nai)(nai)(nai)點(dian)(dian)蝕(shi)(shi)(shi)性(xing)(xing)能(neng)(neng)優(you)劣(lie)關系應為：1050℃優(you)于(yu)1000℃優(you)于(yu)1150℃.當固(gu)(gu)(gu)(gu)溶(rong)溫度為1050℃時(shi)，PREN,值(zhi)較大(da)(da)(da)，兩(liang)相(xiang)(xiang)中(zhong)(zhong)(zhong)的(de)(de)Cr、Mo、Ni元(yuan)(yuan)(yuan)素(su)(su)含(han)量(liang)差異最(zui)(zui)小，材(cai)(cai)料(liao)(liao)的(de)(de)點(dian)(dian)蝕(shi)(shi)(shi)坑(keng)(keng)較小，材(cai)(cai)料(liao)(liao)的(de)(de)耐(nai)(nai)(nai)點(dian)(dian)蝕(shi)(shi)(shi)性(xing)(xing)能(neng)(neng)最(zui)(zui)優(you)。1000℃固(gu)(gu)(gu)(gu)溶(rong)試(shi)(shi)樣(yang)的(de)(de)點(dian)(dian)蝕(shi)(shi)(shi)坑(keng)(keng)尺寸大(da)(da)(da)于(yu)1150℃固(gu)(gu)(gu)(gu)溶(rong)試(shi)(shi)樣(yang)的(de)(de)點(dian)(dian)蝕(shi)(shi)(shi)坑(keng)(keng)尺寸，因此，前者的(de)(de)耐(nai)(nai)(nai)點(dian)(dian)蝕(shi)(shi)(shi)性(xing)(xing)能(neng)(neng)劣(lie)于(yu)后者的(de)(de)耐(nai)(nai)(nai)點(dian)(dian)蝕(shi)(shi)(shi)性(xing)(xing)能(neng)(neng)。由(you)此可(ke)(ke)見(jian)，雙相(xiang)(xiang)不銹鋼(gang)中(zhong)(zhong)(zhong)的(de)(de)相(xiang)(xiang)腐蝕(shi)(shi)(shi)不能(neng)(neng)僅(jin)僅(jin)由(you)PREN值(zhi)來解釋。由(you)圖(tu)3.7(a)~(c)可(ke)(ke)知(zhi)，1000℃固(gu)(gu)(gu)(gu)溶(rong)試(shi)(shi)樣(yang)的(de)(de)兩(liang)相(xiang)(xiang)中(zhong)(zhong)(zhong)的(de)(de)Cr、Mo、Ni元(yuan)(yuan)(yuan)素(su)(su)含(han)量(liang)差大(da)(da)(da)于(yu)1150℃固(gu)(gu)(gu)(gu)溶(rong)試(shi)(shi)樣(yang)的(de)(de)兩(liang)相(xiang)(xiang)中(zhong)(zhong)(zhong)的(de)(de)Gr、Mo、Ni元(yuan)(yuan)(yuan)素(su)(su)含(han)量(liang)差，因此，雙相(xiang)(xiang)不銹鋼(gang)中(zhong)(zhong)(zhong)的(de)(de)相(xiang)(xiang)腐蝕(shi)(shi)(shi)還與兩(liang)相(xiang)(xiang)中(zhong)(zhong)(zhong)的(de)(de)元(yuan)(yuan)(yuan)素(su)(su)分布(bu)有關，并(bing)且(qie)還需(xu)考慮到材(cai)(cai)料(liao)(liao)中(zhong)(zhong)(zhong)點(dian)(dian)蝕(shi)(shi)(shi)敏感性(xing)(xing)較強的(de)(de)區域，如晶(jing)界和相(xiang)(xiang)界。

  點蝕是一種局部腐(fu)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(ying)(ying)響雙相(xiang)不(bu)銹鋼相(xiang)腐蝕的(de)(de)因(yin)素不(bu)僅包(bao)括PREN值，還包(bao)括各相(xiang)中(zhong)的(de)(de)元素分布和(he)兩相(xiang)比例，并且三者互相(xiang)影(ying)(ying)響、關系(xi)復(fu)雜。因(yin)此，不(bu)能僅憑PREN值的(de)(de)大小來判斷耐(nai)點蝕能力(li)，應該(gai)綜合考慮各因(yin)素的(de)(de)影(ying)(ying)響。