圖(tu)3.7(a)~(d)為(wei)(wei)鐵(tie)素(su)(su)體(ti)(ti)(ti)(ti)(ti)和奧(ao)(ao)(ao)氏(shi)(shi)(shi)(shi)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Cr、Mo、Ni元素(su)(su)含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)與固(gu)(gu)(gu)溶(rong)(rong)溫(wen)度(du)的(de)(de)(de)(de)關系圖(tu)。圖(tu)3.7(a)~(d)證實了鐵(tie)素(su)(su)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Cr和Mo含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)更高(gao)(gao)(gao)，而(er)奧(ao)(ao)(ao)氏(shi)(shi)(shi)(shi)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Ni和Mn含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)更高(gao)(gao)(gao)。從(cong)圖(tu)中(zhong)(zhong)(zhong)(zhong)可看出(chu)，鐵(tie)素(su)(su)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Cr含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)為(wei)(wei)23.77%~25.16%,比奧(ao)(ao)(ao)氏(shi)(shi)(shi)(shi)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)Cr含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)高(gao)(gao)(gao)2%左右(you)；鐵(tie)素(su)(su)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)Mo含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)為(wei)(wei)3.86%~4.37%,比奧(ao)(ao)(ao)氏(shi)(shi)(shi)(shi)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Mo含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)高(gao)(gao)(gao)1.7%左右(you)；奧(ao)(ao)(ao)氏(shi)(shi)(shi)(shi)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Ni含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)為(wei)(wei)5.42%、6.7%,比鐵(tie)素(su)(su)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Ni含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)高(gao)(gao)(gao)2%;當(dang)固(gu)(gu)(gu)溶(rong)(rong)處理溫(wen)度(du)為(wei)(wei)1050℃時(shi)(shi)，鐵(tie)素(su)(su)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Cr、Mo和Ni含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)分別為(wei)(wei)23.77%、3.97%、4.24%,奧(ao)(ao)(ao)氏(shi)(shi)(shi)(shi)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Cr、Mo和Ni含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)分別為(wei)(wei)23.53%、2.63%、5.42%.可見(jian)在1050℃溫(wen)度(du)下進行固(gu)(gu)(gu)溶(rong)(rong)時(shi)(shi)，兩相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Cr、Mo、Ni含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)差(cha)(cha)(cha)異最(zui)小，此時(shi)(shi)鐵(tie)素(su)(su)體(ti)(ti)(ti)(ti)(ti)含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)為(wei)(wei)51.9%,奧(ao)(ao)(ao)氏(shi)(shi)(shi)(shi)體(ti)(ti)(ti)(ti)(ti)含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)為(wei)(wei)48.1%.當(dang)固(gu)(gu)(gu)溶(rong)(rong)溫(wen)度(du)改變(bian)時(shi)(shi)，鐵(tie)素(su)(su)體(ti)(ti)(ti)(ti)(ti)／奧(ao)(ao)(ao)氏(shi)(shi)(shi)(shi)體(ti)(ti)(ti)(ti)(ti)兩相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)比例相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)差(cha)(cha)(cha)變(bian)大，且兩相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Cr、Mo、Ni含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)差(cha)(cha)(cha)異也變(bian)大。當(dang)固(gu)(gu)(gu)溶(rong)(rong)溫(wen)度(du)為(wei)(wei)1000℃,兩相(xiang)(xiang)(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)(gu)(gu)溶(rong)(rong)溫(wen)度(du)為(wei)(wei)1150℃時(shi)(shi)，兩相(xiang)(xiang)(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(jian)1000℃固(gu)(gu)(gu)溶(rong)(rong)試樣的(de)(de)(de)(de)兩相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Cr、Mo、Ni元素(su)(su)含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)差(cha)(cha)(cha)大于1150℃固(gu)(gu)(gu)溶(rong)(rong)試樣的(de)(de)(de)(de)兩相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)Cr、Mo、Ni元素(su)(su)含(han)(han)(han)量(liang)(liang)(liang)(liang)(liang)差(cha)(cha)(cha)。

  由公式(shi)“PREN.=[Cr]+3.3[Mo]”計算(suan)鐵(tie)素體(ti)的PREN值(zhi)，由公式(shi)“PREN,=[Cr]+3.3[Mo]+16[N]-[Mn]”計算(suan)奧氏體(ti)的PREN值(zhi)，可得PREN值(zhi)與固溶(rong)溫度(du)的關系圖，如圖3.7(e)所示(shi)。從圖3.7(e)可看出(chu)，在不同(tong)固溶(rong)狀態下，兩相的PREN值(zhi)有所不同(tong)，但PRENa>PRENy.當固溶(rong)溫度(du)為(wei)1050℃時(shi)，PREN.最(zui)小(xiao)、PREN,最(zui)大，分(fen)別為(wei)36.9和(he)30.6,兩者相差最(zui)小(xiao)。

  圖3.8為不同(tong)固(gu)溶(rong)(rong)試樣的(de)(de)極化曲(qu)線。可見，在自腐蝕(shi)(shi)電(dian)(dian)位下(xia)，材料(liao)開(kai)始發(fa)生鈍化；當極化電(dian)(dian)位升(sheng)高到一定值時，不同(tong)固(gu)溶(rong)(rong)的(de)(de)材料(liao)都發(fa)生點(dian)蝕(shi)(shi)，電(dian)(dian)流密(mi)度急劇(ju)增大(da)。根(gen)據GB 4334.9-1984中(zhong)電(dian)(dian)流密(mi)度為0.1mA/c㎡所對應的(de)(de)電(dian)(dian)位為點(dian)蝕(shi)(shi)電(dian)(dian)位和Tafel擬合，分別得(de)到點(dian)蝕(shi)(shi)電(dian)(dian)位、自腐蝕(shi)(shi)電(dian)(dian)流密(mi)度與(yu)固(gu)溶(rong)(rong)溫度的(de)(de)關系圖，如圖3.11(a)所示(shi)。

  圖(tu)(tu)3.9(a)、（b)分別為不同固溶試樣(yang)的(de)(de)Nyquist 圖(tu)(tu)和(he)Bode圖(tu)(tu)。從圖(tu)(tu)3.9(a)可(ke)見，試樣(yang)在(zai)(zai)低頻和(he)高(gao)頻區分別存在(zai)(zai)一個(ge)容抗(kang)弧。從圖(tu)(tu)3.9(b)可(ke)見，試樣(yang)在(zai)(zai)低頻和(he)高(gao)頻處分別存在(zai)(zai)一個(ge)時(shi)間(jian)常數。根據(ju)曹(cao)楚南的(de)(de)《電(dian)(dian)化學(xue)阻抗(kang)譜導論》可(ke)知。雙相不銹鋼在(zai)(zai)NaCl溶液中(zhong)的(de)(de)阻抗(kang)譜中(zhong)存在(zai)(zai)兩個(ge)時(shi)間(jian)常數，常以圖(tu)(tu)3.10所示的(de)(de)等效電(dian)(dian)路（R1為電(dian)(dian)荷(he)轉(zhuan)移電(dian)(dian)阻，R2為鈍化膜電(dian)(dian)阻）進行阻抗(kang)擬合。經阻抗(kang)擬合，得(de)到(dao)鈍化膜電(dian)(dian)阻、電(dian)(dian)荷(he)轉(zhuan)移電(dian)(dian)阻與(yu)固溶處理溫(wen)度(du)的(de)(de)關系圖(tu)(tu)，如(ru)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。

  通過計算(suan)得到不同相比(bi)例下的(de)(de)鐵素體PREN值(zhi)和奧氏體PREN值(zhi)，可見不同相比(bi)例下的(de)(de)PREN.都大(da)(da)于(yu)PREN,.雙相不銹鋼(gang)(gang)(gang)的(de)(de)耐(nai)點(dian)蝕(shi)性(xing)(xing)能(neng)可通過點(dian)蝕(shi)電位(wei)衡量。點(dian)蝕(shi)電位(wei)越高(gao)，耐(nai)點(dian)獨性(xing)(xing)能(neng)越好(hao)。前人認為雙相不銹鋼(gang)(gang)(gang)的(de)(de)耐(nai)點(dian)蝕(shi)性(xing)(xing)能(neng)由(you)B能(neng)N值(zhi)較區的(de)(de)相決定(ding)，且PEN值(zhi)越高(gao)，耐(nai)點(dian)蝕(shi)性(xing)(xing)能(neng)越好(hao)，從(cong)圖3.71e)可矩，不同海溶試樣的(de)(de)PREN.都大(da)(da)于(yu)PREN,,當(dang)固溶溫度為1050℃時，PHEN,最(zui)(zui)大(da)(da)，材料的(de)(de)耐(nai)點(dian)蝕(shi)性(xing)(xing)能(neng)應最(zui)(zui)好(hao)。從(cong)圖3.11(a)、（b)可知(zhi)，1050℃固溶試樣的(de)(de)點(dian)蝕(shi)電位(wei)最(zui)(zui)高(gao)，鈍化(hua)膜阻抗值(zhi)最(zui)(zui)大(da)(da)，電荷轉移電阻值(zhi)最(zui)(zui)商；且從(cong)圖3.12(b)可見，1050℃固溶試樣的(de)(de)點(dian)蝕(shi)坑尺寸最(zui)(zui)小，表(biao)現出(chu)最(zui)(zui)好(hao)的(de)(de)耐(nai)點(dian)蝕(shi)性(xing)(xing)能(neng)。綜上(shang)可知(zhi)，雙相不銹鋼(gang)(gang)(gang)的(de)(de)耐(nai)點(dian)蝕(shi)性(xing)(xing)能(neng)由(you) PREN 值(zhi)較小相決定(ding)的(de)(de)理論(lun)是有實(shi)驗依據的(de)(de)。

  從(cong)圖3.12(a)~(d)可(ke)(ke)見，在(zai)不(bu)同固溶狀態下(xia)(xia)，鐵素(su)(su)體相都(dou)更(geng)易(yi)發生點蝕；而從(cong)圖3.7(e)可(ke)(ke)見，在(zai)不(bu)同固溶狀態下(xia)(xia)，PREN.都(dou)大于PREN,,鐵素(su)(su)體的耐點蝕性(xing)能(neng)應優于奧氏體相，可(ke)(ke)見兩者存在(zai)矛盾。

  隨固(gu)(gu)(gu)(gu)(gu)溶(rong)(rong)溫度(du)(du)變(bian)(bian)化，雙(shuang)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)不銹(xiu)鋼中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)鐵(tie)素(su)(su)體(ti)和奧(ao)氏(shi)體(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)的(de)(de)(de)比例改變(bian)(bian)，且(qie)兩(liang)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)形(xing)(xing)態也發(fa)生(sheng)變(bian)(bian)化。Cr是(shi)鐵(tie)素(su)(su)體(ti)形(xing)(xing)成(cheng)元(yuan)(yuan)素(su)(su)，可提(ti)高(gao)材(cai)料(liao)的(de)(de)(de)耐(nai)蝕(shi)(shi)(shi)性(xing)能；Mo是(shi)鐵(tie)素(su)(su)體(ti)形(xing)(xing)成(cheng)元(yuan)(yuan)素(su)(su)，可提(ti)高(gao)點(dian)(dian)(dian)蝕(shi)(shi)(shi)電(dian)位(wei)，降低腐蝕(shi)(shi)(shi)速率(lv)；Ni是(shi)奧(ao)氏(shi)體(ti)形(xing)(xing)成(cheng)元(yuan)(yuan)素(su)(su)，可維持(chi)兩(liang)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)平(ping)衡，提(ti)高(gao)耐(nai)蝕(shi)(shi)(shi)性(xing)能。并(bing)且(qie)材(cai)料(liao)中(zhong)(zhong)(zhong)(zhong)存(cun)(cun)在一定量(liang)的(de)(de)(de)N,其為奧(ao)氏(shi)體(ti)形(xing)(xing)成(cheng)元(yuan)(yuan)素(su)(su)，提(ti)高(gao)局部腐蝕(shi)(shi)(shi)抗力。從(cong)圖(tu)3.7(a)~(c)可見，隨固(gu)(gu)(gu)(gu)(gu)溶(rong)(rong)溫度(du)(du)變(bian)(bian)化，兩(liang)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)Cr、Mo、Ni元(yuan)(yuan)素(su)(su)含(han)量(liang)發(fa)生(sheng)變(bian)(bian)化。由(you)(you)于Cr、Mo、Ni元(yuan)(yuan)素(su)(su)之(zhi)(zhi)間的(de)(de)(de)腐蝕(shi)(shi)(shi)電(dian)位(wei)存(cun)(cun)在差(cha)異(yi)，勢必造成(cheng)兩(liang)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)之(zhi)(zhi)間存(cun)(cun)在電(dian)化學(xue)差(cha)異(yi)，使腐蝕(shi)(shi)(shi)更(geng)易發(fa)生(sheng)。從(cong)圖(tu)3.7(e)可知，不同固(gu)(gu)(gu)(gu)(gu)溶(rong)(rong)狀態下材(cai)料(liao)的(de)(de)(de)PREN,大小(xiao)關(guan)系為1050℃>1000℃>1150℃>1100℃,因此(ci)根據前人的(de)(de)(de)研究，不同固(gu)(gu)(gu)(gu)(gu)溶(rong)(rong)態材(cai)料(liao)的(de)(de)(de)耐(nai)點(dian)(dian)(dian)蝕(shi)(shi)(shi)性(xing)能優劣(lie)關(guan)系應為：1050℃優于1000℃優于1150℃.當固(gu)(gu)(gu)(gu)(gu)溶(rong)(rong)溫度(du)(du)為1050℃時，PREN,值(zhi)較大，兩(liang)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)Cr、Mo、Ni元(yuan)(yuan)素(su)(su)含(han)量(liang)差(cha)異(yi)最小(xiao)，材(cai)料(liao)的(de)(de)(de)點(dian)(dian)(dian)蝕(shi)(shi)(shi)坑較小(xiao)，材(cai)料(liao)的(de)(de)(de)耐(nai)點(dian)(dian)(dian)蝕(shi)(shi)(shi)性(xing)能最優。1000℃固(gu)(gu)(gu)(gu)(gu)溶(rong)(rong)試(shi)樣(yang)的(de)(de)(de)點(dian)(dian)(dian)蝕(shi)(shi)(shi)坑尺寸大于1150℃固(gu)(gu)(gu)(gu)(gu)溶(rong)(rong)試(shi)樣(yang)的(de)(de)(de)點(dian)(dian)(dian)蝕(shi)(shi)(shi)坑尺寸，因此(ci)，前者(zhe)(zhe)的(de)(de)(de)耐(nai)點(dian)(dian)(dian)蝕(shi)(shi)(shi)性(xing)能劣(lie)于后者(zhe)(zhe)的(de)(de)(de)耐(nai)點(dian)(dian)(dian)蝕(shi)(shi)(shi)性(xing)能。由(you)(you)此(ci)可見，雙(shuang)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)不銹(xiu)鋼中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)腐蝕(shi)(shi)(shi)不能僅僅由(you)(you)PREN值(zhi)來解釋(shi)。由(you)(you)圖(tu)3.7(a)~(c)可知，1000℃固(gu)(gu)(gu)(gu)(gu)溶(rong)(rong)試(shi)樣(yang)的(de)(de)(de)兩(liang)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)Cr、Mo、Ni元(yuan)(yuan)素(su)(su)含(han)量(liang)差(cha)大于1150℃固(gu)(gu)(gu)(gu)(gu)溶(rong)(rong)試(shi)樣(yang)的(de)(de)(de)兩(liang)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)Gr、Mo、Ni元(yuan)(yuan)素(su)(su)含(han)量(liang)差(cha)，因此(ci)，雙(shuang)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)不銹(xiu)鋼中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)腐蝕(shi)(shi)(shi)還與兩(liang)相(xiang)(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)元(yuan)(yuan)素(su)(su)分(fen)布有關(guan)，并(bing)且(qie)還需考慮到(dao)材(cai)料(liao)中(zhong)(zhong)(zhong)(zhong)點(dian)(dian)(dian)蝕(shi)(shi)(shi)敏(min)感性(xing)較強(qiang)的(de)(de)(de)區域，如晶界和相(xiang)(xiang)(xiang)(xiang)(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。

  影響雙相不銹鋼相腐蝕的(de)因素不僅包(bao)括PREN值(zhi)，還包(bao)括各(ge)相中的(de)元素分布(bu)和兩(liang)相比例，并且三(san)者互相影響、關系復雜。因此，不能僅憑PREN值(zhi)的(de)大小來判(pan)斷耐點蝕能力，應該綜合考慮各(ge)因素的(de)影響。