圖(tu)3.7(a)~(d)為(wei)(wei)鐵(tie)(tie)素(su)(su)體(ti)(ti)和(he)(he)奧(ao)氏體(ti)(ti)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo、Ni元素(su)(su)含(han)(han)(han)量(liang)(liang)與(yu)固(gu)溶(rong)(rong)溫(wen)度的(de)(de)(de)(de)(de)(de)關系圖(tu)。圖(tu)3.7(a)~(d)證(zheng)實了鐵(tie)(tie)素(su)(su)體(ti)(ti)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr和(he)(he)Mo含(han)(han)(han)量(liang)(liang)更(geng)高(gao)，而奧(ao)氏體(ti)(ti)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Ni和(he)(he)Mn含(han)(han)(han)量(liang)(liang)更(geng)高(gao)。從(cong)圖(tu)中(zhong)(zhong)(zhong)(zhong)可看出，鐵(tie)(tie)素(su)(su)體(ti)(ti)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr含(han)(han)(han)量(liang)(liang)為(wei)(wei)23.77%~25.16%,比奧(ao)氏體(ti)(ti)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)Cr含(han)(han)(han)量(liang)(liang)高(gao)2%左右(you)；鐵(tie)(tie)素(su)(su)體(ti)(ti)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)Mo含(han)(han)(han)量(liang)(liang)為(wei)(wei)3.86%~4.37%,比奧(ao)氏體(ti)(ti)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Mo含(han)(han)(han)量(liang)(liang)高(gao)1.7%左右(you)；奧(ao)氏體(ti)(ti)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Ni含(han)(han)(han)量(liang)(liang)為(wei)(wei)5.42%、6.7%,比鐵(tie)(tie)素(su)(su)體(ti)(ti)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Ni含(han)(han)(han)量(liang)(liang)高(gao)2%;當(dang)固(gu)溶(rong)(rong)處理溫(wen)度為(wei)(wei)1050℃時(shi)，鐵(tie)(tie)素(su)(su)體(ti)(ti)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo和(he)(he)Ni含(han)(han)(han)量(liang)(liang)分(fen)別為(wei)(wei)23.77%、3.97%、4.24%,奧(ao)氏體(ti)(ti)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo和(he)(he)Ni含(han)(han)(han)量(liang)(liang)分(fen)別為(wei)(wei)23.53%、2.63%、5.42%.可見在1050℃溫(wen)度下進(jin)行固(gu)溶(rong)(rong)時(shi)，兩(liang)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo、Ni含(han)(han)(han)量(liang)(liang)差(cha)(cha)異最小(xiao)，此時(shi)鐵(tie)(tie)素(su)(su)體(ti)(ti)含(han)(han)(han)量(liang)(liang)為(wei)(wei)51.9%,奧(ao)氏體(ti)(ti)含(han)(han)(han)量(liang)(liang)為(wei)(wei)48.1%.當(dang)固(gu)溶(rong)(rong)溫(wen)度改變(bian)時(shi)，鐵(tie)(tie)素(su)(su)體(ti)(ti)／奧(ao)氏體(ti)(ti)兩(liang)相(xiang)(xiang)(xiang)(xiang)比例(li)相(xiang)(xiang)(xiang)(xiang)差(cha)(cha)變(bian)大(da)，且(qie)兩(liang)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo、Ni含(han)(han)(han)量(liang)(liang)差(cha)(cha)異也變(bian)大(da)。當(dang)固(gu)溶(rong)(rong)溫(wen)度為(wei)(wei)1000℃,兩(liang)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)Cr為(wei)(wei)3.69%、Mo為(wei)(wei)1.51%、Ni為(wei)(wei)3.37%;當(dang)固(gu)溶(rong)(rong)溫(wen)度為(wei)(wei)1150℃時(shi)，兩(liang)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)Cr為(wei)(wei)2.29%、Mo為(wei)(wei)1.34%、Ni為(wei)(wei)2.09%,可見1000℃固(gu)溶(rong)(rong)試樣的(de)(de)(de)(de)(de)(de)兩(liang)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo、Ni元素(su)(su)含(han)(han)(han)量(liang)(liang)差(cha)(cha)大(da)于1150℃固(gu)溶(rong)(rong)試樣的(de)(de)(de)(de)(de)(de)兩(liang)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)Cr、Mo、Ni元素(su)(su)含(han)(han)(han)量(liang)(liang)差(cha)(cha)。

  由公(gong)式“PREN.=[Cr]+3.3[Mo]”計(ji)算(suan)鐵素體的(de)PREN值，由公(gong)式“PREN,=[Cr]+3.3[Mo]+16[N]-[Mn]”計(ji)算(suan)奧(ao)氏體的(de)PREN值，可得(de)PREN值與固溶(rong)(rong)溫(wen)度的(de)關系圖(tu)，如(ru)圖(tu)3.7(e)所示。從圖(tu)3.7(e)可看出(chu)，在不同(tong)固溶(rong)(rong)狀態下，兩相(xiang)的(de)PREN值有所不同(tong)，但PRENa>PRENy.當(dang)固溶(rong)(rong)溫(wen)度為1050℃時，PREN.最小、PREN,最大，分別為36.9和30.6,兩者相(xiang)差最小。

  圖(tu)3.8為不(bu)同(tong)固(gu)溶試樣(yang)的極(ji)化曲(qu)線。可見，在自(zi)腐蝕(shi)電(dian)(dian)位(wei)下，材料開始發(fa)生鈍化；當極(ji)化電(dian)(dian)位(wei)升高(gao)到一定值時(shi)，不(bu)同(tong)固(gu)溶的材料都發(fa)生點蝕(shi)，電(dian)(dian)流(liu)密(mi)度急劇(ju)增(zeng)大。根據GB 4334.9-1984中電(dian)(dian)流(liu)密(mi)度為0.1mA/c㎡所對(dui)應的電(dian)(dian)位(wei)為點蝕(shi)電(dian)(dian)位(wei)和Tafel擬(ni)合，分別(bie)得到點蝕(shi)電(dian)(dian)位(wei)、自(zi)腐蝕(shi)電(dian)(dian)流(liu)密(mi)度與固(gu)溶溫度的關系圖(tu)，如圖(tu)3.11(a)所示(shi)。

  圖(tu)(tu)3.9(a)、（b)分別為(wei)不同固溶試樣的(de)(de)Nyquist 圖(tu)(tu)和(he)Bode圖(tu)(tu)。從圖(tu)(tu)3.9(a)可(ke)(ke)見，試樣在(zai)(zai)低頻和(he)高頻區分別存(cun)在(zai)(zai)一個(ge)容抗(kang)(kang)弧。從圖(tu)(tu)3.9(b)可(ke)(ke)見，試樣在(zai)(zai)低頻和(he)高頻處分別存(cun)在(zai)(zai)一個(ge)時間常(chang)數。根據(ju)曹楚南的(de)(de)《電(dian)(dian)化學阻(zu)抗(kang)(kang)譜導論》可(ke)(ke)知(zhi)。雙相不銹鋼在(zai)(zai)NaCl溶液中的(de)(de)阻(zu)抗(kang)(kang)譜中存(cun)在(zai)(zai)兩個(ge)時間常(chang)數，常(chang)以圖(tu)(tu)3.10所(suo)示的(de)(de)等效電(dian)(dian)路（R1為(wei)電(dian)(dian)荷(he)轉移電(dian)(dian)阻(zu)，R2為(wei)鈍(dun)化膜電(dian)(dian)阻(zu)）進行阻(zu)抗(kang)(kang)擬合(he)(he)。經阻(zu)抗(kang)(kang)擬合(he)(he)，得(de)到鈍(dun)化膜電(dian)(dian)阻(zu)、電(dian)(dian)荷(he)轉移電(dian)(dian)阻(zu)與固溶處理溫度的(de)(de)關(guan)系圖(tu)(tu)，如圖(tu)(tu)3.11(b)所(suo)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(xiang)不銹鋼(gang)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。

  通過(guo)計(ji)算得到不(bu)同(tong)相比例下的(de)(de)(de)(de)鐵素體(ti)PREN值和奧氏體(ti)PREN值，可(ke)(ke)見(jian)不(bu)同(tong)相比例下的(de)(de)(de)(de)PREN.都大(da)于PREN,.雙相不(bu)銹(xiu)鋼的(de)(de)(de)(de)耐(nai)(nai)點(dian)(dian)蝕(shi)(shi)性(xing)(xing)(xing)能可(ke)(ke)通過(guo)點(dian)(dian)蝕(shi)(shi)電(dian)位(wei)衡量。點(dian)(dian)蝕(shi)(shi)電(dian)位(wei)越(yue)高，耐(nai)(nai)點(dian)(dian)獨性(xing)(xing)(xing)能越(yue)好。前人(ren)認為(wei)雙相不(bu)銹(xiu)鋼的(de)(de)(de)(de)耐(nai)(nai)點(dian)(dian)蝕(shi)(shi)性(xing)(xing)(xing)能由(you)B能N值較區(qu)的(de)(de)(de)(de)相決定(ding)，且(qie)PEN值越(yue)高，耐(nai)(nai)點(dian)(dian)蝕(shi)(shi)性(xing)(xing)(xing)能越(yue)好，從(cong)圖(tu)3.71e)可(ke)(ke)矩，不(bu)同(tong)海溶(rong)(rong)試(shi)(shi)樣的(de)(de)(de)(de)PREN.都大(da)于PREN,,當固溶(rong)(rong)溫度(du)為(wei)1050℃時，PHEN,最(zui)(zui)大(da)，材(cai)料的(de)(de)(de)(de)耐(nai)(nai)點(dian)(dian)蝕(shi)(shi)性(xing)(xing)(xing)能應最(zui)(zui)好。從(cong)圖(tu)3.11(a)、（b)可(ke)(ke)知，1050℃固溶(rong)(rong)試(shi)(shi)樣的(de)(de)(de)(de)點(dian)(dian)蝕(shi)(shi)電(dian)位(wei)最(zui)(zui)高，鈍化(hua)膜阻抗值最(zui)(zui)大(da)，電(dian)荷轉移電(dian)阻值最(zui)(zui)商；且(qie)從(cong)圖(tu)3.12(b)可(ke)(ke)見(jian)，1050℃固溶(rong)(rong)試(shi)(shi)樣的(de)(de)(de)(de)點(dian)(dian)蝕(shi)(shi)坑尺寸最(zui)(zui)小，表現出(chu)最(zui)(zui)好的(de)(de)(de)(de)耐(nai)(nai)點(dian)(dian)蝕(shi)(shi)性(xing)(xing)(xing)能。綜(zong)上可(ke)(ke)知，雙相不(bu)銹(xiu)鋼的(de)(de)(de)(de)耐(nai)(nai)點(dian)(dian)蝕(shi)(shi)性(xing)(xing)(xing)能由(you) PREN 值較小相決定(ding)的(de)(de)(de)(de)理論是(shi)有實驗依據的(de)(de)(de)(de)。

  從(cong)圖3.12(a)~(d)可(ke)見(jian)，在不同固溶(rong)狀態(tai)下(xia)，鐵(tie)素(su)體相都(dou)(dou)更易發生點蝕；而從(cong)圖3.7(e)可(ke)見(jian)，在不同固溶(rong)狀態(tai)下(xia)，PREN.都(dou)(dou)大于PREN,,鐵(tie)素(su)體的(de)耐點蝕性能應優于奧氏體相，可(ke)見(jian)兩者(zhe)存(cun)在矛盾。

  隨固(gu)(gu)溶(rong)(rong)溫度(du)變(bian)(bian)化(hua)(hua)，雙相(xiang)(xiang)(xiang)不(bu)銹(xiu)(xiu)鋼(gang)中(zhong)的(de)(de)(de)鐵(tie)(tie)素(su)(su)體(ti)和奧(ao)(ao)氏體(ti)相(xiang)(xiang)(xiang)的(de)(de)(de)比例改變(bian)(bian)，且兩(liang)相(xiang)(xiang)(xiang)形(xing)態也(ye)發(fa)生(sheng)(sheng)變(bian)(bian)化(hua)(hua)。Cr是鐵(tie)(tie)素(su)(su)體(ti)形(xing)成(cheng)(cheng)元(yuan)(yuan)(yuan)素(su)(su)，可(ke)(ke)(ke)提高(gao)材(cai)料(liao)的(de)(de)(de)耐(nai)蝕(shi)(shi)(shi)(shi)性(xing)(xing)能(neng)(neng)；Mo是鐵(tie)(tie)素(su)(su)體(ti)形(xing)成(cheng)(cheng)元(yuan)(yuan)(yuan)素(su)(su)，可(ke)(ke)(ke)提高(gao)點蝕(shi)(shi)(shi)(shi)電位，降低腐(fu)蝕(shi)(shi)(shi)(shi)速率；Ni是奧(ao)(ao)氏體(ti)形(xing)成(cheng)(cheng)元(yuan)(yuan)(yuan)素(su)(su)，可(ke)(ke)(ke)維持兩(liang)相(xiang)(xiang)(xiang)平(ping)衡，提高(gao)耐(nai)蝕(shi)(shi)(shi)(shi)性(xing)(xing)能(neng)(neng)。并(bing)且材(cai)料(liao)中(zhong)存(cun)(cun)在(zai)一定量(liang)的(de)(de)(de)N,其為(wei)奧(ao)(ao)氏體(ti)形(xing)成(cheng)(cheng)元(yuan)(yuan)(yuan)素(su)(su)，提高(gao)局部(bu)腐(fu)蝕(shi)(shi)(shi)(shi)抗力。從圖3.7(a)~(c)可(ke)(ke)(ke)見，隨固(gu)(gu)溶(rong)(rong)溫度(du)變(bian)(bian)化(hua)(hua)，兩(liang)相(xiang)(xiang)(xiang)中(zhong)的(de)(de)(de)Cr、Mo、Ni元(yuan)(yuan)(yuan)素(su)(su)含(han)量(liang)發(fa)生(sheng)(sheng)變(bian)(bian)化(hua)(hua)。由(you)于(yu)Cr、Mo、Ni元(yuan)(yuan)(yuan)素(su)(su)之(zhi)(zhi)間的(de)(de)(de)腐(fu)蝕(shi)(shi)(shi)(shi)電位存(cun)(cun)在(zai)差異，勢必造成(cheng)(cheng)兩(liang)相(xiang)(xiang)(xiang)之(zhi)(zhi)間存(cun)(cun)在(zai)電化(hua)(hua)學差異，使腐(fu)蝕(shi)(shi)(shi)(shi)更易發(fa)生(sheng)(sheng)。從圖3.7(e)可(ke)(ke)(ke)知，不(bu)同(tong)固(gu)(gu)溶(rong)(rong)狀態下(xia)材(cai)料(liao)的(de)(de)(de)PREN,大小關(guan)系為(wei)1050℃>1000℃>1150℃>1100℃,因(yin)此根據前人的(de)(de)(de)研究，不(bu)同(tong)固(gu)(gu)溶(rong)(rong)態材(cai)料(liao)的(de)(de)(de)耐(nai)點蝕(shi)(shi)(shi)(shi)性(xing)(xing)能(neng)(neng)優(you)劣關(guan)系應(ying)為(wei)：1050℃優(you)于(yu)1000℃優(you)于(yu)1150℃.當固(gu)(gu)溶(rong)(rong)溫度(du)為(wei)1050℃時(shi)，PREN,值較大，兩(liang)相(xiang)(xiang)(xiang)中(zhong)的(de)(de)(de)Cr、Mo、Ni元(yuan)(yuan)(yuan)素(su)(su)含(han)量(liang)差異最(zui)小，材(cai)料(liao)的(de)(de)(de)點蝕(shi)(shi)(shi)(shi)坑(keng)較小，材(cai)料(liao)的(de)(de)(de)耐(nai)點蝕(shi)(shi)(shi)(shi)性(xing)(xing)能(neng)(neng)最(zui)優(you)。1000℃固(gu)(gu)溶(rong)(rong)試(shi)樣的(de)(de)(de)點蝕(shi)(shi)(shi)(shi)坑(keng)尺寸大于(yu)1150℃固(gu)(gu)溶(rong)(rong)試(shi)樣的(de)(de)(de)點蝕(shi)(shi)(shi)(shi)坑(keng)尺寸，因(yin)此，前者(zhe)的(de)(de)(de)耐(nai)點蝕(shi)(shi)(shi)(shi)性(xing)(xing)能(neng)(neng)劣于(yu)后者(zhe)的(de)(de)(de)耐(nai)點蝕(shi)(shi)(shi)(shi)性(xing)(xing)能(neng)(neng)。由(you)此可(ke)(ke)(ke)見，雙相(xiang)(xiang)(xiang)不(bu)銹(xiu)(xiu)鋼(gang)中(zhong)的(de)(de)(de)相(xiang)(xiang)(xiang)腐(fu)蝕(shi)(shi)(shi)(shi)不(bu)能(neng)(neng)僅(jin)僅(jin)由(you)PREN值來解釋。由(you)圖3.7(a)~(c)可(ke)(ke)(ke)知，1000℃固(gu)(gu)溶(rong)(rong)試(shi)樣的(de)(de)(de)兩(liang)相(xiang)(xiang)(xiang)中(zhong)的(de)(de)(de)Cr、Mo、Ni元(yuan)(yuan)(yuan)素(su)(su)含(han)量(liang)差大于(yu)1150℃固(gu)(gu)溶(rong)(rong)試(shi)樣的(de)(de)(de)兩(liang)相(xiang)(xiang)(xiang)中(zhong)的(de)(de)(de)Gr、Mo、Ni元(yuan)(yuan)(yuan)素(su)(su)含(han)量(liang)差，因(yin)此，雙相(xiang)(xiang)(xiang)不(bu)銹(xiu)(xiu)鋼(gang)中(zhong)的(de)(de)(de)相(xiang)(xiang)(xiang)腐(fu)蝕(shi)(shi)(shi)(shi)還與(yu)兩(liang)相(xiang)(xiang)(xiang)中(zhong)的(de)(de)(de)元(yuan)(yuan)(yuan)素(su)(su)分布(bu)有關(guan)，并(bing)且還需考(kao)慮到材(cai)料(liao)中(zhong)點蝕(shi)(shi)(shi)(shi)敏感性(xing)(xing)較強的(de)(de)(de)區(qu)域(yu)，如晶(jing)界和相(xiang)(xiang)(xiang)界。

  點蝕(shi)是一種局部腐蝕(shi)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)腐蝕的(de)因素不僅包(bao)括PREN值，還包(bao)括各相(xiang)(xiang)中的(de)元素分布和(he)兩相(xiang)(xiang)比例，并且三者(zhe)互相(xiang)(xiang)影響(xiang)、關(guan)系復雜。因此，不能僅憑(ping)PREN值的(de)大(da)小來判斷耐點(dian)蝕能力，應該綜(zong)合考(kao)慮各因素的(de)影響(xiang)。