圖(tu)3.7(a)~(d)為(wei)(wei)(wei)(wei)鐵素(su)(su)(su)體(ti)(ti)和(he)(he)奧氏(shi)(shi)(shi)體(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)Cr、Mo、Ni元素(su)(su)(su)含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)與固溶(rong)(rong)溫(wen)度(du)(du)的(de)(de)(de)(de)(de)關系圖(tu)。圖(tu)3.7(a)~(d)證實(shi)了(le)鐵素(su)(su)(su)體(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)Cr和(he)(he)Mo含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)更高(gao)，而奧氏(shi)(shi)(shi)體(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)Ni和(he)(he)Mn含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)更高(gao)。從(cong)圖(tu)中(zhong)(zhong)(zhong)(zhong)可看出，鐵素(su)(su)(su)體(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)Cr含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)為(wei)(wei)(wei)(wei)23.77%~25.16%,比(bi)(bi)奧氏(shi)(shi)(shi)體(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)Cr含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)高(gao)2%左右；鐵素(su)(su)(su)體(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)Mo含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)為(wei)(wei)(wei)(wei)3.86%~4.37%,比(bi)(bi)奧氏(shi)(shi)(shi)體(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)Mo含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)高(gao)1.7%左右；奧氏(shi)(shi)(shi)體(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)Ni含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)為(wei)(wei)(wei)(wei)5.42%、6.7%,比(bi)(bi)鐵素(su)(su)(su)體(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)Ni含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)高(gao)2%;當固溶(rong)(rong)處理溫(wen)度(du)(du)為(wei)(wei)(wei)(wei)1050℃時(shi)，鐵素(su)(su)(su)體(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)Cr、Mo和(he)(he)Ni含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)分(fen)別為(wei)(wei)(wei)(wei)23.77%、3.97%、4.24%,奧氏(shi)(shi)(shi)體(ti)(ti)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)Cr、Mo和(he)(he)Ni含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)分(fen)別為(wei)(wei)(wei)(wei)23.53%、2.63%、5.42%.可見在1050℃溫(wen)度(du)(du)下進(jin)行固溶(rong)(rong)時(shi)，兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)Cr、Mo、Ni含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)差(cha)異最(zui)小，此(ci)時(shi)鐵素(su)(su)(su)體(ti)(ti)含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)為(wei)(wei)(wei)(wei)51.9%,奧氏(shi)(shi)(shi)體(ti)(ti)含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)為(wei)(wei)(wei)(wei)48.1%.當固溶(rong)(rong)溫(wen)度(du)(du)改變(bian)時(shi)，鐵素(su)(su)(su)體(ti)(ti)／奧氏(shi)(shi)(shi)體(ti)(ti)兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)比(bi)(bi)例相(xiang)(xiang)(xiang)差(cha)變(bian)大，且(qie)兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)Cr、Mo、Ni含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)差(cha)異也(ye)變(bian)大。當固溶(rong)(rong)溫(wen)度(du)(du)為(wei)(wei)(wei)(wei)1000℃,兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)中(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%;當固溶(rong)(rong)溫(wen)度(du)(du)為(wei)(wei)(wei)(wei)1150℃時(shi)，兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)中(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%,可見1000℃固溶(rong)(rong)試樣的(de)(de)(de)(de)(de)兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)Cr、Mo、Ni元素(su)(su)(su)含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)差(cha)大于1150℃固溶(rong)(rong)試樣的(de)(de)(de)(de)(de)兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)Cr、Mo、Ni元素(su)(su)(su)含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)差(cha)。


7.jpg


  由公式“PREN.=[Cr]+3.3[Mo]”計算(suan)鐵素體的(de)PREN值(zhi)(zhi)，由公式“PREN,=[Cr]+3.3[Mo]+16[N]-[Mn]”計算(suan)奧(ao)氏體的(de)PREN值(zhi)(zhi)，可得PREN值(zhi)(zhi)與固(gu)溶溫度的(de)關(guan)系(xi)圖(tu)，如圖(tu)3.7(e)所示。從圖(tu)3.7(e)可看出(chu)，在不(bu)(bu)同固(gu)溶狀態下，兩(liang)相的(de)PREN值(zhi)(zhi)有(you)所不(bu)(bu)同，但PRENa>PRENy.當固(gu)溶溫度為1050℃時，PREN.最(zui)小、PREN,最(zui)大(da)，分別為36.9和30.6,兩(liang)者相差最(zui)小。


  圖3.8為(wei)不同(tong)固(gu)溶(rong)試(shi)樣的極化(hua)(hua)曲線。可見，在(zai)自腐(fu)(fu)蝕(shi)電(dian)(dian)(dian)位(wei)(wei)下(xia)，材(cai)料開(kai)始發生鈍化(hua)(hua)；當極化(hua)(hua)電(dian)(dian)(dian)位(wei)(wei)升(sheng)高到一定值時(shi)，不同(tong)固(gu)溶(rong)的材(cai)料都(dou)發生點(dian)蝕(shi)，電(dian)(dian)(dian)流密度(du)(du)急劇增大。根據GB 4334.9-1984中(zhong)電(dian)(dian)(dian)流密度(du)(du)為(wei)0.1mA/c㎡所對應的電(dian)(dian)(dian)位(wei)(wei)為(wei)點(dian)蝕(shi)電(dian)(dian)(dian)位(wei)(wei)和Tafel擬合，分別(bie)得到點(dian)蝕(shi)電(dian)(dian)(dian)位(wei)(wei)、自腐(fu)(fu)蝕(shi)電(dian)(dian)(dian)流密度(du)(du)與固(gu)溶(rong)溫度(du)(du)的關系(xi)圖，如圖3.11(a)所示。


8.jpg


  圖(tu)3.9(a)、（b)分別(bie)為不同(tong)固(gu)溶試(shi)樣的(de)Nyquist 圖(tu)和Bode圖(tu)。從圖(tu)3.9(a)可(ke)見，試(shi)樣在(zai)低頻(pin)(pin)和高(gao)頻(pin)(pin)區(qu)分別(bie)存在(zai)一個(ge)容(rong)抗(kang)弧。從圖(tu)3.9(b)可(ke)見，試(shi)樣在(zai)低頻(pin)(pin)和高(gao)頻(pin)(pin)處分別(bie)存在(zai)一個(ge)時間(jian)常(chang)數。根據(ju)曹楚南的(de)《電(dian)(dian)(dian)化學阻抗(kang)譜導論》可(ke)知。雙相不銹鋼在(zai)NaCl溶液中的(de)阻抗(kang)譜中存在(zai)兩個(ge)時間(jian)常(chang)數，常(chang)以(yi)圖(tu)3.10所示的(de)等效電(dian)(dian)(dian)路（R1為電(dian)(dian)(dian)荷轉移電(dian)(dian)(dian)阻，R2為鈍(dun)化膜電(dian)(dian)(dian)阻）進行阻抗(kang)擬合(he)。經阻抗(kang)擬合(he)，得到鈍(dun)化膜電(dian)(dian)(dian)阻、電(dian)(dian)(dian)荷轉移電(dian)(dian)(dian)阻與固(gu)溶處理(li)溫度的(de)關系圖(tu)，如圖(tu)3.11(b)所示。


9.jpg


 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(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。


12.jpg


  通(tong)過(guo)計算得到不(bu)同(tong)(tong)相(xiang)比(bi)例下的(de)鐵素體PREN值(zhi)和奧氏體PREN值(zhi)，可(ke)見不(bu)同(tong)(tong)相(xiang)比(bi)例下的(de)PREN.都大于(yu)PREN,.雙相(xiang)不(bu)銹(xiu)鋼(gang)的(de)耐(nai)(nai)(nai)點(dian)(dian)(dian)(dian)蝕(shi)(shi)性(xing)(xing)能(neng)(neng)可(ke)通(tong)過(guo)點(dian)(dian)(dian)(dian)蝕(shi)(shi)電(dian)(dian)位衡量(liang)。點(dian)(dian)(dian)(dian)蝕(shi)(shi)電(dian)(dian)位越(yue)(yue)高(gao)(gao)，耐(nai)(nai)(nai)點(dian)(dian)(dian)(dian)獨性(xing)(xing)能(neng)(neng)越(yue)(yue)好(hao)。前人認為(wei)雙相(xiang)不(bu)銹(xiu)鋼(gang)的(de)耐(nai)(nai)(nai)點(dian)(dian)(dian)(dian)蝕(shi)(shi)性(xing)(xing)能(neng)(neng)由(you)B能(neng)(neng)N值(zhi)較區的(de)相(xiang)決(jue)定，且PEN值(zhi)越(yue)(yue)高(gao)(gao)，耐(nai)(nai)(nai)點(dian)(dian)(dian)(dian)蝕(shi)(shi)性(xing)(xing)能(neng)(neng)越(yue)(yue)好(hao)，從(cong)圖3.71e)可(ke)矩，不(bu)同(tong)(tong)海溶試樣的(de)PREN.都大于(yu)PREN,,當(dang)固溶溫度為(wei)1050℃時，PHEN,最(zui)大，材料(liao)的(de)耐(nai)(nai)(nai)點(dian)(dian)(dian)(dian)蝕(shi)(shi)性(xing)(xing)能(neng)(neng)應最(zui)好(hao)。從(cong)圖3.11(a)、（b)可(ke)知，1050℃固溶試樣的(de)點(dian)(dian)(dian)(dian)蝕(shi)(shi)電(dian)(dian)位最(zui)高(gao)(gao)，鈍化膜阻抗值(zhi)最(zui)大，電(dian)(dian)荷轉移(yi)電(dian)(dian)阻值(zhi)最(zui)商；且從(cong)圖3.12(b)可(ke)見，1050℃固溶試樣的(de)點(dian)(dian)(dian)(dian)蝕(shi)(shi)坑尺寸最(zui)小，表(biao)現出最(zui)好(hao)的(de)耐(nai)(nai)(nai)點(dian)(dian)(dian)(dian)蝕(shi)(shi)性(xing)(xing)能(neng)(neng)。綜上可(ke)知，雙相(xiang)不(bu)銹(xiu)鋼(gang)的(de)耐(nai)(nai)(nai)點(dian)(dian)(dian)(dian)蝕(shi)(shi)性(xing)(xing)能(neng)(neng)由(you) PREN 值(zhi)較小相(xiang)決(jue)定的(de)理論是有實(shi)驗依據(ju)的(de)。


  從圖(tu)3.12(a)~(d)可見，在(zai)不同固溶狀(zhuang)態下，鐵(tie)素體相都更易發生(sheng)點蝕；而從圖(tu)3.7(e)可見，在(zai)不同固溶狀(zhuang)態下，PREN.都大于PREN,,鐵(tie)素體的耐(nai)點蝕性能應(ying)優于奧(ao)氏體相，可見兩者存(cun)在(zai)矛盾(dun)。


  隨(sui)固(gu)(gu)溶溫(wen)(wen)(wen)度(du)(du)(du)變(bian)(bian)化，雙相(xiang)(xiang)(xiang)不銹鋼(gang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)鐵素(su)(su)體(ti)和奧氏體(ti)相(xiang)(xiang)(xiang)的(de)(de)(de)(de)(de)比例改(gai)變(bian)(bian)，且兩(liang)相(xiang)(xiang)(xiang)形(xing)(xing)態(tai)也發生變(bian)(bian)化。Cr是(shi)鐵素(su)(su)體(ti)形(xing)(xing)成元(yuan)(yuan)(yuan)素(su)(su)，可(ke)提(ti)高材(cai)(cai)料(liao)的(de)(de)(de)(de)(de)耐(nai)蝕(shi)(shi)(shi)性能(neng)；Mo是(shi)鐵素(su)(su)體(ti)形(xing)(xing)成元(yuan)(yuan)(yuan)素(su)(su)，可(ke)提(ti)高點(dian)(dian)(dian)蝕(shi)(shi)(shi)電位，降低腐(fu)(fu)蝕(shi)(shi)(shi)速率；Ni是(shi)奧氏體(ti)形(xing)(xing)成元(yuan)(yuan)(yuan)素(su)(su)，可(ke)維持兩(liang)相(xiang)(xiang)(xiang)平衡，提(ti)高耐(nai)蝕(shi)(shi)(shi)性能(neng)。并(bing)且材(cai)(cai)料(liao)中(zhong)(zhong)(zhong)(zhong)存在(zai)(zai)一定量(liang)的(de)(de)(de)(de)(de)N,其為奧氏體(ti)形(xing)(xing)成元(yuan)(yuan)(yuan)素(su)(su)，提(ti)高局部腐(fu)(fu)蝕(shi)(shi)(shi)抗力。從圖3.7(a)~(c)可(ke)見，隨(sui)固(gu)(gu)溶溫(wen)(wen)(wen)度(du)(du)(du)變(bian)(bian)化，兩(liang)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)Cr、Mo、Ni元(yuan)(yuan)(yuan)素(su)(su)含(han)量(liang)發生變(bian)(bian)化。由(you)(you)于(yu)Cr、Mo、Ni元(yuan)(yuan)(yuan)素(su)(su)之間(jian)的(de)(de)(de)(de)(de)腐(fu)(fu)蝕(shi)(shi)(shi)電位存在(zai)(zai)差(cha)異，勢必造成兩(liang)相(xiang)(xiang)(xiang)之間(jian)存在(zai)(zai)電化學(xue)差(cha)異，使(shi)腐(fu)(fu)蝕(shi)(shi)(shi)更易發生。從圖3.7(e)可(ke)知，不同(tong)固(gu)(gu)溶狀態(tai)下材(cai)(cai)料(liao)的(de)(de)(de)(de)(de)PREN,大(da)小關(guan)系為1050℃>1000℃>1150℃>1100℃,因此(ci)根(gen)據前(qian)(qian)人的(de)(de)(de)(de)(de)研究，不同(tong)固(gu)(gu)溶態(tai)材(cai)(cai)料(liao)的(de)(de)(de)(de)(de)耐(nai)點(dian)(dian)(dian)蝕(shi)(shi)(shi)性能(neng)優(you)劣關(guan)系應為：1050℃優(you)于(yu)1000℃優(you)于(yu)1150℃.當(dang)固(gu)(gu)溶溫(wen)(wen)(wen)度(du)(du)(du)為1050℃時，PREN,值較(jiao)大(da)，兩(liang)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)Cr、Mo、Ni元(yuan)(yuan)(yuan)素(su)(su)含(han)量(liang)差(cha)異最(zui)小，材(cai)(cai)料(liao)的(de)(de)(de)(de)(de)點(dian)(dian)(dian)蝕(shi)(shi)(shi)坑(keng)較(jiao)小，材(cai)(cai)料(liao)的(de)(de)(de)(de)(de)耐(nai)點(dian)(dian)(dian)蝕(shi)(shi)(shi)性能(neng)最(zui)優(you)。1000℃固(gu)(gu)溶試(shi)樣(yang)的(de)(de)(de)(de)(de)點(dian)(dian)(dian)蝕(shi)(shi)(shi)坑(keng)尺(chi)寸(cun)(cun)大(da)于(yu)1150℃固(gu)(gu)溶試(shi)樣(yang)的(de)(de)(de)(de)(de)點(dian)(dian)(dian)蝕(shi)(shi)(shi)坑(keng)尺(chi)寸(cun)(cun)，因此(ci)，前(qian)(qian)者的(de)(de)(de)(de)(de)耐(nai)點(dian)(dian)(dian)蝕(shi)(shi)(shi)性能(neng)劣于(yu)后者的(de)(de)(de)(de)(de)耐(nai)點(dian)(dian)(dian)蝕(shi)(shi)(shi)性能(neng)。由(you)(you)此(ci)可(ke)見，雙相(xiang)(xiang)(xiang)不銹鋼(gang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)相(xiang)(xiang)(xiang)腐(fu)(fu)蝕(shi)(shi)(shi)不能(neng)僅(jin)僅(jin)由(you)(you)PREN值來解釋。由(you)(you)圖3.7(a)~(c)可(ke)知，1000℃固(gu)(gu)溶試(shi)樣(yang)的(de)(de)(de)(de)(de)兩(liang)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)Cr、Mo、Ni元(yuan)(yuan)(yuan)素(su)(su)含(han)量(liang)差(cha)大(da)于(yu)1150℃固(gu)(gu)溶試(shi)樣(yang)的(de)(de)(de)(de)(de)兩(liang)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)Gr、Mo、Ni元(yuan)(yuan)(yuan)素(su)(su)含(han)量(liang)差(cha)，因此(ci)，雙相(xiang)(xiang)(xiang)不銹鋼(gang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)相(xiang)(xiang)(xiang)腐(fu)(fu)蝕(shi)(shi)(shi)還(huan)與兩(liang)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)元(yuan)(yuan)(yuan)素(su)(su)分布有關(guan)，并(bing)且還(huan)需考(kao)慮到材(cai)(cai)料(liao)中(zhong)(zhong)(zhong)(zhong)點(dian)(dian)(dian)蝕(shi)(shi)(shi)敏(min)感性較(jiao)強的(de)(de)(de)(de)(de)區域，如晶界和相(xiang)(xiang)(xiang)界。


  點蝕是一種局部腐蝕(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(ying)響(xiang)(xiang)雙(shuang)相不銹(xiu)鋼相腐蝕的因素不僅(jin)包(bao)括(kuo)PREN值，還包(bao)括(kuo)各(ge)相中的元素分布和兩(liang)相比(bi)例，并(bing)且(qie)三(san)者互相影(ying)響(xiang)(xiang)、關系復雜。因此，不能(neng)僅(jin)憑PREN值的大(da)小來判(pan)斷耐點蝕能(neng)力，應(ying)該(gai)綜合考慮(lv)各(ge)因素的影(ying)響(xiang)(xiang)。