圖3.7(a)~(d)為(wei)(wei)(wei)(wei)(wei)(wei)(wei)鐵(tie)(tie)(tie)素(su)(su)(su)體(ti)(ti)和(he)(he)(he)奧(ao)(ao)氏(shi)體(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo、Ni元(yuan)(yuan)素(su)(su)(su)含(han)(han)(han)(han)量與固溶(rong)溫(wen)(wen)度的(de)(de)(de)(de)(de)(de)關系圖。圖3.7(a)~(d)證實(shi)了鐵(tie)(tie)(tie)素(su)(su)(su)體(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr和(he)(he)(he)Mo含(han)(han)(han)(han)量更高(gao)，而奧(ao)(ao)氏(shi)體(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Ni和(he)(he)(he)Mn含(han)(han)(han)(han)量更高(gao)。從圖中(zhong)(zhong)(zhong)(zhong)(zhong)可看出(chu)，鐵(tie)(tie)(tie)素(su)(su)(su)體(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr含(han)(han)(han)(han)量為(wei)(wei)(wei)(wei)(wei)(wei)(wei)23.77%~25.16%,比奧(ao)(ao)氏(shi)體(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)Cr含(han)(han)(han)(han)量高(gao)2%左右；鐵(tie)(tie)(tie)素(su)(su)(su)體(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)Mo含(han)(han)(han)(han)量為(wei)(wei)(wei)(wei)(wei)(wei)(wei)3.86%~4.37%,比奧(ao)(ao)氏(shi)體(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Mo含(han)(han)(han)(han)量高(gao)1.7%左右；奧(ao)(ao)氏(shi)體(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Ni含(han)(han)(han)(han)量為(wei)(wei)(wei)(wei)(wei)(wei)(wei)5.42%、6.7%,比鐵(tie)(tie)(tie)素(su)(su)(su)體(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Ni含(han)(han)(han)(han)量高(gao)2%;當(dang)(dang)固溶(rong)處理溫(wen)(wen)度為(wei)(wei)(wei)(wei)(wei)(wei)(wei)1050℃時，鐵(tie)(tie)(tie)素(su)(su)(su)體(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo和(he)(he)(he)Ni含(han)(han)(han)(han)量分別為(wei)(wei)(wei)(wei)(wei)(wei)(wei)23.77%、3.97%、4.24%,奧(ao)(ao)氏(shi)體(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo和(he)(he)(he)Ni含(han)(han)(han)(han)量分別為(wei)(wei)(wei)(wei)(wei)(wei)(wei)23.53%、2.63%、5.42%.可見在(zai)1050℃溫(wen)(wen)度下進行(xing)固溶(rong)時，兩(liang)(liang)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo、Ni含(han)(han)(han)(han)量差(cha)(cha)異最(zui)小，此時鐵(tie)(tie)(tie)素(su)(su)(su)體(ti)(ti)含(han)(han)(han)(han)量為(wei)(wei)(wei)(wei)(wei)(wei)(wei)51.9%,奧(ao)(ao)氏(shi)體(ti)(ti)含(han)(han)(han)(han)量為(wei)(wei)(wei)(wei)(wei)(wei)(wei)48.1%.當(dang)(dang)固溶(rong)溫(wen)(wen)度改(gai)變時，鐵(tie)(tie)(tie)素(su)(su)(su)體(ti)(ti)／奧(ao)(ao)氏(shi)體(ti)(ti)兩(liang)(liang)相(xiang)(xiang)(xiang)比例相(xiang)(xiang)(xiang)差(cha)(cha)變大(da)(da)，且(qie)兩(liang)(liang)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo、Ni含(han)(han)(han)(han)量差(cha)(cha)異也變大(da)(da)。當(dang)(dang)固溶(rong)溫(wen)(wen)度為(wei)(wei)(wei)(wei)(wei)(wei)(wei)1000℃,兩(liang)(liang)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)Cr為(wei)(wei)(wei)(wei)(wei)(wei)(wei)3.69%、Mo為(wei)(wei)(wei)(wei)(wei)(wei)(wei)1.51%、Ni為(wei)(wei)(wei)(wei)(wei)(wei)(wei)3.37%;當(dang)(dang)固溶(rong)溫(wen)(wen)度為(wei)(wei)(wei)(wei)(wei)(wei)(wei)1150℃時，兩(liang)(liang)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)Cr為(wei)(wei)(wei)(wei)(wei)(wei)(wei)2.29%、Mo為(wei)(wei)(wei)(wei)(wei)(wei)(wei)1.34%、Ni為(wei)(wei)(wei)(wei)(wei)(wei)(wei)2.09%,可見1000℃固溶(rong)試樣(yang)的(de)(de)(de)(de)(de)(de)兩(liang)(liang)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo、Ni元(yuan)(yuan)素(su)(su)(su)含(han)(han)(han)(han)量差(cha)(cha)大(da)(da)于1150℃固溶(rong)試樣(yang)的(de)(de)(de)(de)(de)(de)兩(liang)(liang)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)Cr、Mo、Ni元(yuan)(yuan)素(su)(su)(su)含(han)(han)(han)(han)量差(cha)(cha)。

  由公(gong)式(shi)“PREN.=[Cr]+3.3[Mo]”計(ji)算鐵(tie)素體(ti)(ti)的PREN值(zhi)，由公(gong)式(shi)“PREN,=[Cr]+3.3[Mo]+16[N]-[Mn]”計(ji)算奧(ao)氏體(ti)(ti)的PREN值(zhi)，可得PREN值(zhi)與固(gu)(gu)溶(rong)(rong)溫(wen)度的關(guan)系圖，如圖3.7(e)所示。從(cong)圖3.7(e)可看出，在(zai)不(bu)同固(gu)(gu)溶(rong)(rong)狀態(tai)下，兩相的PREN值(zhi)有所不(bu)同，但PRENa>PRENy.當固(gu)(gu)溶(rong)(rong)溫(wen)度為1050℃時，PREN.最(zui)小、PREN,最(zui)大，分別(bie)為36.9和(he)30.6,兩者(zhe)相差最(zui)小。

  圖(tu)3.8為不(bu)同固溶(rong)(rong)試樣的(de)(de)極化(hua)曲線。可(ke)見，在自(zi)腐蝕電(dian)(dian)位(wei)下，材(cai)料開(kai)始發生鈍化(hua)；當極化(hua)電(dian)(dian)位(wei)升高到一定值(zhi)時，不(bu)同固溶(rong)(rong)的(de)(de)材(cai)料都(dou)發生點(dian)蝕，電(dian)(dian)流(liu)密度(du)(du)(du)急劇(ju)增大。根據GB 4334.9-1984中(zhong)電(dian)(dian)流(liu)密度(du)(du)(du)為0.1mA/c㎡所對應(ying)的(de)(de)電(dian)(dian)位(wei)為點(dian)蝕電(dian)(dian)位(wei)和Tafel擬合，分別得到點(dian)蝕電(dian)(dian)位(wei)、自(zi)腐蝕電(dian)(dian)流(liu)密度(du)(du)(du)與固溶(rong)(rong)溫度(du)(du)(du)的(de)(de)關系圖(tu)，如圖(tu)3.11(a)所示。

  圖3.9(a)、（b)分別為不(bu)(bu)同固(gu)溶試樣的(de)(de)Nyquist 圖和Bode圖。從圖3.9(a)可見(jian)，試樣在低頻(pin)和高(gao)頻(pin)區分別存在一個容抗弧。從圖3.9(b)可見(jian)，試樣在低頻(pin)和高(gao)頻(pin)處分別存在一個時(shi)間(jian)常數(shu)。根據曹楚南(nan)的(de)(de)《電(dian)(dian)化學阻抗譜導論(lun)》可知。雙相不(bu)(bu)銹(xiu)鋼在NaCl溶液中(zhong)的(de)(de)阻抗譜中(zhong)存在兩個時(shi)間(jian)常數(shu)，常以圖3.10所示(shi)的(de)(de)等效電(dian)(dian)路（R1為電(dian)(dian)荷轉移電(dian)(dian)阻，R2為鈍化膜電(dian)(dian)阻）進行阻抗擬(ni)合。經阻抗擬(ni)合，得到鈍化膜電(dian)(dian)阻、電(dian)(dian)荷轉移電(dian)(dian)阻與固(gu)溶處理溫度的(de)(de)關系圖，如圖3.11(b)所示(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(shuang)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(guo)計算得到不同(tong)相(xiang)比(bi)(bi)例(li)下的(de)鐵素體PREN值(zhi)(zhi)和奧氏(shi)體PREN值(zhi)(zhi)，可(ke)見不同(tong)相(xiang)比(bi)(bi)例(li)下的(de)PREN.都(dou)大(da)于PREN,.雙(shuang)(shuang)相(xiang)不銹鋼(gang)的(de)耐點(dian)(dian)蝕(shi)(shi)(shi)性(xing)(xing)能(neng)(neng)可(ke)通(tong)過(guo)點(dian)(dian)蝕(shi)(shi)(shi)電位衡(heng)量。點(dian)(dian)蝕(shi)(shi)(shi)電位越(yue)高，耐點(dian)(dian)獨(du)性(xing)(xing)能(neng)(neng)越(yue)好(hao)(hao)。前人認為雙(shuang)(shuang)相(xiang)不銹鋼(gang)的(de)耐點(dian)(dian)蝕(shi)(shi)(shi)性(xing)(xing)能(neng)(neng)由B能(neng)(neng)N值(zhi)(zhi)較區的(de)相(xiang)決(jue)定，且(qie)PEN值(zhi)(zhi)越(yue)高，耐點(dian)(dian)蝕(shi)(shi)(shi)性(xing)(xing)能(neng)(neng)越(yue)好(hao)(hao)，從圖3.71e)可(ke)矩(ju)，不同(tong)海溶(rong)試樣(yang)的(de)PREN.都(dou)大(da)于PREN,,當固溶(rong)溫度為1050℃時，PHEN,最(zui)(zui)大(da)，材料的(de)耐點(dian)(dian)蝕(shi)(shi)(shi)性(xing)(xing)能(neng)(neng)應(ying)最(zui)(zui)好(hao)(hao)。從圖3.11(a)、（b)可(ke)知(zhi)(zhi)，1050℃固溶(rong)試樣(yang)的(de)點(dian)(dian)蝕(shi)(shi)(shi)電位最(zui)(zui)高，鈍化膜阻抗值(zhi)(zhi)最(zui)(zui)大(da)，電荷轉移電阻值(zhi)(zhi)最(zui)(zui)商(shang)；且(qie)從圖3.12(b)可(ke)見，1050℃固溶(rong)試樣(yang)的(de)點(dian)(dian)蝕(shi)(shi)(shi)坑(keng)尺寸最(zui)(zui)小，表(biao)現出(chu)最(zui)(zui)好(hao)(hao)的(de)耐點(dian)(dian)蝕(shi)(shi)(shi)性(xing)(xing)能(neng)(neng)。綜上可(ke)知(zhi)(zhi)，雙(shuang)(shuang)相(xiang)不銹鋼(gang)的(de)耐點(dian)(dian)蝕(shi)(shi)(shi)性(xing)(xing)能(neng)(neng)由 PREN 值(zhi)(zhi)較小相(xiang)決(jue)定的(de)理論是有實(shi)驗依據的(de)。

  從圖3.12(a)~(d)可(ke)見，在(zai)不(bu)同(tong)固溶(rong)狀態下(xia)，鐵(tie)素體相都(dou)更易(yi)發生點(dian)蝕；而(er)從圖3.7(e)可(ke)見，在(zai)不(bu)同(tong)固溶(rong)狀態下(xia)，PREN.都(dou)大于(yu)PREN,,鐵(tie)素體的耐點(dian)蝕性能應優(you)于(yu)奧氏體相，可(ke)見兩(liang)者存在(zai)矛盾。

  隨(sui)(sui)固(gu)(gu)(gu)溶(rong)溫(wen)(wen)度(du)變化(hua)，雙相(xiang)不銹(xiu)鋼中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)鐵(tie)素(su)(su)體(ti)和奧(ao)(ao)氏體(ti)相(xiang)的(de)(de)(de)(de)(de)(de)比例(li)改變，且兩(liang)(liang)(liang)相(xiang)形態也發(fa)生變化(hua)。Cr是(shi)鐵(tie)素(su)(su)體(ti)形成元(yuan)(yuan)素(su)(su)，可(ke)(ke)提(ti)高材(cai)料(liao)(liao)的(de)(de)(de)(de)(de)(de)耐(nai)蝕(shi)(shi)(shi)性能(neng)(neng)；Mo是(shi)鐵(tie)素(su)(su)體(ti)形成元(yuan)(yuan)素(su)(su)，可(ke)(ke)提(ti)高點(dian)(dian)(dian)蝕(shi)(shi)(shi)電位，降低腐(fu)(fu)(fu)蝕(shi)(shi)(shi)速率；Ni是(shi)奧(ao)(ao)氏體(ti)形成元(yuan)(yuan)素(su)(su)，可(ke)(ke)維(wei)持兩(liang)(liang)(liang)相(xiang)平衡(heng)，提(ti)高耐(nai)蝕(shi)(shi)(shi)性能(neng)(neng)。并(bing)且材(cai)料(liao)(liao)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)存在(zai)(zai)一定(ding)量的(de)(de)(de)(de)(de)(de)N,其為(wei)(wei)(wei)(wei)奧(ao)(ao)氏體(ti)形成元(yuan)(yuan)素(su)(su)，提(ti)高局部腐(fu)(fu)(fu)蝕(shi)(shi)(shi)抗力。從圖3.7(a)~(c)可(ke)(ke)見，隨(sui)(sui)固(gu)(gu)(gu)溶(rong)溫(wen)(wen)度(du)變化(hua)，兩(liang)(liang)(liang)相(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo、Ni元(yuan)(yuan)素(su)(su)含(han)量發(fa)生變化(hua)。由(you)于(yu)Cr、Mo、Ni元(yuan)(yuan)素(su)(su)之間(jian)的(de)(de)(de)(de)(de)(de)腐(fu)(fu)(fu)蝕(shi)(shi)(shi)電位存在(zai)(zai)差異，勢必(bi)造成兩(liang)(liang)(liang)相(xiang)之間(jian)存在(zai)(zai)電化(hua)學(xue)差異，使(shi)腐(fu)(fu)(fu)蝕(shi)(shi)(shi)更易發(fa)生。從圖3.7(e)可(ke)(ke)知，不同固(gu)(gu)(gu)溶(rong)狀態下材(cai)料(liao)(liao)的(de)(de)(de)(de)(de)(de)PREN,大小關(guan)系為(wei)(wei)(wei)(wei)1050℃>1000℃>1150℃>1100℃,因此(ci)(ci)根據前人的(de)(de)(de)(de)(de)(de)研(yan)究，不同固(gu)(gu)(gu)溶(rong)態材(cai)料(liao)(liao)的(de)(de)(de)(de)(de)(de)耐(nai)點(dian)(dian)(dian)蝕(shi)(shi)(shi)性能(neng)(neng)優(you)(you)劣關(guan)系應為(wei)(wei)(wei)(wei)：1050℃優(you)(you)于(yu)1000℃優(you)(you)于(yu)1150℃.當固(gu)(gu)(gu)溶(rong)溫(wen)(wen)度(du)為(wei)(wei)(wei)(wei)1050℃時，PREN,值較大，兩(liang)(liang)(liang)相(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo、Ni元(yuan)(yuan)素(su)(su)含(han)量差異最小，材(cai)料(liao)(liao)的(de)(de)(de)(de)(de)(de)點(dian)(dian)(dian)蝕(shi)(shi)(shi)坑較小，材(cai)料(liao)(liao)的(de)(de)(de)(de)(de)(de)耐(nai)點(dian)(dian)(dian)蝕(shi)(shi)(shi)性能(neng)(neng)最優(you)(you)。1000℃固(gu)(gu)(gu)溶(rong)試(shi)(shi)(shi)樣的(de)(de)(de)(de)(de)(de)點(dian)(dian)(dian)蝕(shi)(shi)(shi)坑尺寸大于(yu)1150℃固(gu)(gu)(gu)溶(rong)試(shi)(shi)(shi)樣的(de)(de)(de)(de)(de)(de)點(dian)(dian)(dian)蝕(shi)(shi)(shi)坑尺寸，因此(ci)(ci)，前者的(de)(de)(de)(de)(de)(de)耐(nai)點(dian)(dian)(dian)蝕(shi)(shi)(shi)性能(neng)(neng)劣于(yu)后者的(de)(de)(de)(de)(de)(de)耐(nai)點(dian)(dian)(dian)蝕(shi)(shi)(shi)性能(neng)(neng)。由(you)此(ci)(ci)可(ke)(ke)見，雙相(xiang)不銹(xiu)鋼中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)相(xiang)腐(fu)(fu)(fu)蝕(shi)(shi)(shi)不能(neng)(neng)僅僅由(you)PREN值來解釋。由(you)圖3.7(a)~(c)可(ke)(ke)知，1000℃固(gu)(gu)(gu)溶(rong)試(shi)(shi)(shi)樣的(de)(de)(de)(de)(de)(de)兩(liang)(liang)(liang)相(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo、Ni元(yuan)(yuan)素(su)(su)含(han)量差大于(yu)1150℃固(gu)(gu)(gu)溶(rong)試(shi)(shi)(shi)樣的(de)(de)(de)(de)(de)(de)兩(liang)(liang)(liang)相(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Gr、Mo、Ni元(yuan)(yuan)素(su)(su)含(han)量差，因此(ci)(ci)，雙相(xiang)不銹(xiu)鋼中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)相(xiang)腐(fu)(fu)(fu)蝕(shi)(shi)(shi)還與兩(liang)(liang)(liang)相(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)元(yuan)(yuan)素(su)(su)分布有關(guan)，并(bing)且還需考慮到材(cai)料(liao)(liao)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)點(dian)(dian)(dian)蝕(shi)(shi)(shi)敏感(gan)性較強的(de)(de)(de)(de)(de)(de)區域(yu)，如晶(jing)界和相(xiang)界。

  點蝕是一種局部(bu)腐(fu)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(ying)響雙相(xiang)不(bu)銹鋼相(xiang)腐蝕的(de)(de)因素不(bu)僅包(bao)括PREN值(zhi)，還包(bao)括各(ge)相(xiang)中(zhong)的(de)(de)元素分(fen)布和兩(liang)相(xiang)比例(li)，并且三者互(hu)相(xiang)影(ying)響、關(guan)系(xi)復雜(za)。因此(ci)，不(bu)能僅憑PREN值(zhi)的(de)(de)大小來判斷耐點蝕能力，應該(gai)綜合考慮各(ge)因素的(de)(de)影(ying)響。