圖3.7(a)~(d)為(wei)(wei)(wei)(wei)鐵(tie)(tie)素體(ti)(ti)(ti)和奧(ao)氏(shi)體(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Cr、Mo、Ni元(yuan)素含(han)(han)(han)量(liang)(liang)與固(gu)(gu)(gu)溶(rong)(rong)(rong)溫(wen)(wen)度(du)(du)(du)的(de)(de)(de)(de)關系圖。圖3.7(a)~(d)證(zheng)實了鐵(tie)(tie)素體(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Cr和Mo含(han)(han)(han)量(liang)(liang)更(geng)高(gao)(gao)，而(er)奧(ao)氏(shi)體(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Ni和Mn含(han)(han)(han)量(liang)(liang)更(geng)高(gao)(gao)。從圖中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)可(ke)(ke)看出，鐵(tie)(tie)素體(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Cr含(han)(han)(han)量(liang)(liang)為(wei)(wei)(wei)(wei)23.77%~25.16%,比(bi)(bi)奧(ao)氏(shi)體(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)Cr含(han)(han)(han)量(liang)(liang)高(gao)(gao)2%左右；鐵(tie)(tie)素體(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)Mo含(han)(han)(han)量(liang)(liang)為(wei)(wei)(wei)(wei)3.86%~4.37%,比(bi)(bi)奧(ao)氏(shi)體(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Mo含(han)(han)(han)量(liang)(liang)高(gao)(gao)1.7%左右；奧(ao)氏(shi)體(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Ni含(han)(han)(han)量(liang)(liang)為(wei)(wei)(wei)(wei)5.42%、6.7%,比(bi)(bi)鐵(tie)(tie)素體(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Ni含(han)(han)(han)量(liang)(liang)高(gao)(gao)2%;當固(gu)(gu)(gu)溶(rong)(rong)(rong)處理溫(wen)(wen)度(du)(du)(du)為(wei)(wei)(wei)(wei)1050℃時(shi)，鐵(tie)(tie)素體(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Cr、Mo和Ni含(han)(han)(han)量(liang)(liang)分別為(wei)(wei)(wei)(wei)23.77%、3.97%、4.24%,奧(ao)氏(shi)體(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Cr、Mo和Ni含(han)(han)(han)量(liang)(liang)分別為(wei)(wei)(wei)(wei)23.53%、2.63%、5.42%.可(ke)(ke)見(jian)在1050℃溫(wen)(wen)度(du)(du)(du)下(xia)進(jin)行固(gu)(gu)(gu)溶(rong)(rong)(rong)時(shi)，兩(liang)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Cr、Mo、Ni含(han)(han)(han)量(liang)(liang)差異(yi)最(zui)小，此時(shi)鐵(tie)(tie)素體(ti)(ti)(ti)含(han)(han)(han)量(liang)(liang)為(wei)(wei)(wei)(wei)51.9%,奧(ao)氏(shi)體(ti)(ti)(ti)含(han)(han)(han)量(liang)(liang)為(wei)(wei)(wei)(wei)48.1%.當固(gu)(gu)(gu)溶(rong)(rong)(rong)溫(wen)(wen)度(du)(du)(du)改(gai)變時(shi)，鐵(tie)(tie)素體(ti)(ti)(ti)／奧(ao)氏(shi)體(ti)(ti)(ti)兩(liang)相(xiang)(xiang)(xiang)(xiang)(xiang)比(bi)(bi)例相(xiang)(xiang)(xiang)(xiang)(xiang)差變大(da)(da)，且兩(liang)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Cr、Mo、Ni含(han)(han)(han)量(liang)(liang)差異(yi)也(ye)變大(da)(da)。當固(gu)(gu)(gu)溶(rong)(rong)(rong)溫(wen)(wen)度(du)(du)(du)為(wei)(wei)(wei)(wei)1000℃,兩(liang)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(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%;當固(gu)(gu)(gu)溶(rong)(rong)(rong)溫(wen)(wen)度(du)(du)(du)為(wei)(wei)(wei)(wei)1150℃時(shi)，兩(liang)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(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)(ke)見(jian)1000℃固(gu)(gu)(gu)溶(rong)(rong)(rong)試樣的(de)(de)(de)(de)兩(liang)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Cr、Mo、Ni元(yuan)素含(han)(han)(han)量(liang)(liang)差大(da)(da)于1150℃固(gu)(gu)(gu)溶(rong)(rong)(rong)試樣的(de)(de)(de)(de)兩(liang)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)Cr、Mo、Ni元(yuan)素含(han)(han)(han)量(liang)(liang)差。

  由公式“PREN.=[Cr]+3.3[Mo]”計算鐵素體(ti)的PREN值，由公式“PREN,=[Cr]+3.3[Mo]+16[N]-[Mn]”計算奧(ao)氏(shi)體(ti)的PREN值，可(ke)得(de)PREN值與固溶溫(wen)(wen)度的關系圖，如圖3.7(e)所示(shi)。從圖3.7(e)可(ke)看出，在(zai)不同固溶狀態(tai)下，兩相(xiang)的PREN值有所不同，但PRENa>PRENy.當固溶溫(wen)(wen)度為1050℃時，PREN.最(zui)小(xiao)、PREN,最(zui)大，分別(bie)為36.9和30.6,兩者相(xiang)差(cha)最(zui)小(xiao)。

  圖3.8為(wei)不(bu)同固(gu)溶試樣的(de)(de)極化(hua)曲線(xian)。可(ke)見，在自(zi)腐蝕(shi)電(dian)(dian)(dian)位(wei)下，材料(liao)開始發生鈍化(hua)；當極化(hua)電(dian)(dian)(dian)位(wei)升高到一(yi)定值時，不(bu)同固(gu)溶的(de)(de)材料(liao)都(dou)發生點(dian)(dian)(dian)蝕(shi)，電(dian)(dian)(dian)流(liu)(liu)密(mi)度急劇(ju)增大。根(gen)據GB 4334.9-1984中(zhong)電(dian)(dian)(dian)流(liu)(liu)密(mi)度為(wei)0.1mA/c㎡所(suo)(suo)對應的(de)(de)電(dian)(dian)(dian)位(wei)為(wei)點(dian)(dian)(dian)蝕(shi)電(dian)(dian)(dian)位(wei)和Tafel擬合，分別得到點(dian)(dian)(dian)蝕(shi)電(dian)(dian)(dian)位(wei)、自(zi)腐蝕(shi)電(dian)(dian)(dian)流(liu)(liu)密(mi)度與固(gu)溶溫度的(de)(de)關系(xi)圖，如圖3.11(a)所(suo)(suo)示。

  圖(tu)3.9(a)、（b)分(fen)別為不同固溶(rong)(rong)試(shi)樣的Nyquist 圖(tu)和(he)Bode圖(tu)。從圖(tu)3.9(a)可見，試(shi)樣在(zai)低(di)頻(pin)和(he)高(gao)頻(pin)區分(fen)別存(cun)在(zai)一(yi)個(ge)容抗(kang)(kang)弧。從圖(tu)3.9(b)可見，試(shi)樣在(zai)低(di)頻(pin)和(he)高(gao)頻(pin)處分(fen)別存(cun)在(zai)一(yi)個(ge)時(shi)間常(chang)數(shu)。根(gen)據曹楚南(nan)的《電化學阻抗(kang)(kang)譜導(dao)論》可知。雙(shuang)相不銹鋼在(zai)NaCl溶(rong)(rong)液(ye)中(zhong)的阻抗(kang)(kang)譜中(zhong)存(cun)在(zai)兩個(ge)時(shi)間常(chang)數(shu)，常(chang)以圖(tu)3.10所示的等效電路（R1為電荷(he)轉移(yi)電阻，R2為鈍化膜電阻）進行阻抗(kang)(kang)擬(ni)合(he)。經阻抗(kang)(kang)擬(ni)合(he)，得到鈍化膜電阻、電荷(he)轉移(yi)電阻與固溶(rong)(rong)處理溫(wen)度的關系圖(tu)，如(ru)圖(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(bu)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)(tong)過(guo)計算得到不(bu)(bu)(bu)同(tong)相(xiang)比(bi)例(li)下的鐵(tie)素(su)體PREN值(zhi)(zhi)(zhi)(zhi)和奧氏(shi)體PREN值(zhi)(zhi)(zhi)(zhi)，可(ke)(ke)見(jian)不(bu)(bu)(bu)同(tong)相(xiang)比(bi)例(li)下的PREN.都大于PREN,.雙相(xiang)不(bu)(bu)(bu)銹鋼(gang)(gang)的耐(nai)點(dian)(dian)蝕(shi)(shi)性(xing)(xing)能(neng)可(ke)(ke)通(tong)(tong)過(guo)點(dian)(dian)蝕(shi)(shi)電(dian)位衡量。點(dian)(dian)蝕(shi)(shi)電(dian)位越(yue)(yue)(yue)高(gao)，耐(nai)點(dian)(dian)獨性(xing)(xing)能(neng)越(yue)(yue)(yue)好(hao)。前(qian)人認為(wei)雙相(xiang)不(bu)(bu)(bu)銹鋼(gang)(gang)的耐(nai)點(dian)(dian)蝕(shi)(shi)性(xing)(xing)能(neng)由B能(neng)N值(zhi)(zhi)(zhi)(zhi)較區(qu)的相(xiang)決定，且PEN值(zhi)(zhi)(zhi)(zhi)越(yue)(yue)(yue)高(gao)，耐(nai)點(dian)(dian)蝕(shi)(shi)性(xing)(xing)能(neng)越(yue)(yue)(yue)好(hao)，從(cong)圖3.71e)可(ke)(ke)矩，不(bu)(bu)(bu)同(tong)海溶試(shi)樣的PREN.都大于PREN,,當固(gu)溶溫度為(wei)1050℃時，PHEN,最大，材料的耐(nai)點(dian)(dian)蝕(shi)(shi)性(xing)(xing)能(neng)應最好(hao)。從(cong)圖3.11(a)、（b)可(ke)(ke)知(zhi)，1050℃固(gu)溶試(shi)樣的點(dian)(dian)蝕(shi)(shi)電(dian)位最高(gao)，鈍化膜阻抗值(zhi)(zhi)(zhi)(zhi)最大，電(dian)荷(he)轉移(yi)電(dian)阻值(zhi)(zhi)(zhi)(zhi)最商；且從(cong)圖3.12(b)可(ke)(ke)見(jian)，1050℃固(gu)溶試(shi)樣的點(dian)(dian)蝕(shi)(shi)坑尺寸最小，表(biao)現出最好(hao)的耐(nai)點(dian)(dian)蝕(shi)(shi)性(xing)(xing)能(neng)。綜上(shang)可(ke)(ke)知(zhi)，雙相(xiang)不(bu)(bu)(bu)銹鋼(gang)(gang)的耐(nai)點(dian)(dian)蝕(shi)(shi)性(xing)(xing)能(neng)由 PREN 值(zhi)(zhi)(zhi)(zhi)較小相(xiang)決定的理論是(shi)有實(shi)驗依據的。

  從(cong)圖(tu)(tu)3.12(a)~(d)可(ke)見(jian)，在不同(tong)固溶狀態下，鐵(tie)素體相(xiang)都(dou)更易發生點(dian)蝕(shi)；而從(cong)圖(tu)(tu)3.7(e)可(ke)見(jian)，在不同(tong)固溶狀態下，PREN.都(dou)大(da)于PREN,,鐵(tie)素體的耐(nai)點(dian)蝕(shi)性能應優(you)于奧(ao)氏(shi)體相(xiang)，可(ke)見(jian)兩者存在矛(mao)盾。

  隨(sui)固(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)溫度(du)變(bian)化(hua)，雙相(xiang)(xiang)(xiang)(xiang)不銹(xiu)鋼(gang)中(zhong)的(de)(de)(de)鐵(tie)素(su)(su)體(ti)(ti)(ti)和奧氏體(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)的(de)(de)(de)比例改變(bian)，且(qie)兩(liang)(liang)相(xiang)(xiang)(xiang)(xiang)形態也發(fa)(fa)生變(bian)化(hua)。Cr是鐵(tie)素(su)(su)體(ti)(ti)(ti)形成(cheng)(cheng)元素(su)(su)，可(ke)(ke)(ke)提高材(cai)(cai)(cai)料(liao)(liao)的(de)(de)(de)耐(nai)蝕(shi)(shi)性(xing)(xing)能(neng)；Mo是鐵(tie)素(su)(su)體(ti)(ti)(ti)形成(cheng)(cheng)元素(su)(su)，可(ke)(ke)(ke)提高點(dian)蝕(shi)(shi)電(dian)位，降低腐(fu)(fu)蝕(shi)(shi)速率；Ni是奧氏體(ti)(ti)(ti)形成(cheng)(cheng)元素(su)(su)，可(ke)(ke)(ke)維持兩(liang)(liang)相(xiang)(xiang)(xiang)(xiang)平衡(heng)，提高耐(nai)蝕(shi)(shi)性(xing)(xing)能(neng)。并(bing)且(qie)材(cai)(cai)(cai)料(liao)(liao)中(zhong)存(cun)在一定量的(de)(de)(de)N,其為(wei)奧氏體(ti)(ti)(ti)形成(cheng)(cheng)元素(su)(su)，提高局(ju)部腐(fu)(fu)蝕(shi)(shi)抗力。從圖(tu)3.7(a)~(c)可(ke)(ke)(ke)見，隨(sui)固(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)溫度(du)變(bian)化(hua)，兩(liang)(liang)相(xiang)(xiang)(xiang)(xiang)中(zhong)的(de)(de)(de)Cr、Mo、Ni元素(su)(su)含(han)量發(fa)(fa)生變(bian)化(hua)。由(you)于(yu)(yu)Cr、Mo、Ni元素(su)(su)之間(jian)的(de)(de)(de)腐(fu)(fu)蝕(shi)(shi)電(dian)位存(cun)在差(cha)異，勢必造成(cheng)(cheng)兩(liang)(liang)相(xiang)(xiang)(xiang)(xiang)之間(jian)存(cun)在電(dian)化(hua)學差(cha)異，使腐(fu)(fu)蝕(shi)(shi)更易發(fa)(fa)生。從圖(tu)3.7(e)可(ke)(ke)(ke)知，不同固(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)狀(zhuang)態下材(cai)(cai)(cai)料(liao)(liao)的(de)(de)(de)PREN,大小關系為(wei)1050℃>1000℃>1150℃>1100℃,因(yin)此(ci)(ci)(ci)根據前人的(de)(de)(de)研究(jiu)，不同固(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)態材(cai)(cai)(cai)料(liao)(liao)的(de)(de)(de)耐(nai)點(dian)蝕(shi)(shi)性(xing)(xing)能(neng)優劣關系應為(wei)：1050℃優于(yu)(yu)1000℃優于(yu)(yu)1150℃.當固(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)溫度(du)為(wei)1050℃時，PREN,值(zhi)較大，兩(liang)(liang)相(xiang)(xiang)(xiang)(xiang)中(zhong)的(de)(de)(de)Cr、Mo、Ni元素(su)(su)含(han)量差(cha)異最(zui)小，材(cai)(cai)(cai)料(liao)(liao)的(de)(de)(de)點(dian)蝕(shi)(shi)坑(keng)較小，材(cai)(cai)(cai)料(liao)(liao)的(de)(de)(de)耐(nai)點(dian)蝕(shi)(shi)性(xing)(xing)能(neng)最(zui)優。1000℃固(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)試樣的(de)(de)(de)點(dian)蝕(shi)(shi)坑(keng)尺寸(cun)大于(yu)(yu)1150℃固(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)試樣的(de)(de)(de)點(dian)蝕(shi)(shi)坑(keng)尺寸(cun)，因(yin)此(ci)(ci)(ci)，前者(zhe)的(de)(de)(de)耐(nai)點(dian)蝕(shi)(shi)性(xing)(xing)能(neng)劣于(yu)(yu)后者(zhe)的(de)(de)(de)耐(nai)點(dian)蝕(shi)(shi)性(xing)(xing)能(neng)。由(you)此(ci)(ci)(ci)可(ke)(ke)(ke)見，雙相(xiang)(xiang)(xiang)(xiang)不銹(xiu)鋼(gang)中(zhong)的(de)(de)(de)相(xiang)(xiang)(xiang)(xiang)腐(fu)(fu)蝕(shi)(shi)不能(neng)僅僅由(you)PREN值(zhi)來解釋。由(you)圖(tu)3.7(a)~(c)可(ke)(ke)(ke)知，1000℃固(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)試樣的(de)(de)(de)兩(liang)(liang)相(xiang)(xiang)(xiang)(xiang)中(zhong)的(de)(de)(de)Cr、Mo、Ni元素(su)(su)含(han)量差(cha)大于(yu)(yu)1150℃固(gu)(gu)(gu)溶(rong)(rong)(rong)(rong)試樣的(de)(de)(de)兩(liang)(liang)相(xiang)(xiang)(xiang)(xiang)中(zhong)的(de)(de)(de)Gr、Mo、Ni元素(su)(su)含(han)量差(cha)，因(yin)此(ci)(ci)(ci)，雙相(xiang)(xiang)(xiang)(xiang)不銹(xiu)鋼(gang)中(zhong)的(de)(de)(de)相(xiang)(xiang)(xiang)(xiang)腐(fu)(fu)蝕(shi)(shi)還(huan)與(yu)兩(liang)(liang)相(xiang)(xiang)(xiang)(xiang)中(zhong)的(de)(de)(de)元素(su)(su)分布有關，并(bing)且(qie)還(huan)需考慮到(dao)材(cai)(cai)(cai)料(liao)(liao)中(zhong)點(dian)蝕(shi)(shi)敏感性(xing)(xing)較強的(de)(de)(de)區域(yu)，如晶界和相(xiang)(xiang)(xiang)(xiang)界。

  點蝕是一種局(ju)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。

  影響雙(shuang)相(xiang)(xiang)不(bu)銹鋼相(xiang)(xiang)腐蝕的(de)因(yin)素不(bu)僅包(bao)括PREN值(zhi)，還包(bao)括各(ge)相(xiang)(xiang)中的(de)元素分布(bu)和兩相(xiang)(xiang)比例(li)，并且三者互相(xiang)(xiang)影響、關系(xi)復雜。因(yin)此，不(bu)能(neng)僅憑(ping)PREN值(zhi)的(de)大小來判斷(duan)耐點蝕能(neng)力(li)，應該綜合考慮(lv)各(ge)因(yin)素的(de)影響。