圖(tu)3.7(a)~(d)為(wei)(wei)(wei)(wei)(wei)鐵(tie)素(su)體(ti)(ti)和奧氏體(ti)(ti)相(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Cr、Mo、Ni元(yuan)素(su)含(han)(han)(han)(han)(han)(han)量(liang)(liang)(liang)(liang)與固(gu)(gu)溶(rong)溫(wen)度的(de)(de)(de)(de)關系(xi)圖(tu)。圖(tu)3.7(a)~(d)證(zheng)實了(le)鐵(tie)素(su)體(ti)(ti)相(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Cr和Mo含(han)(han)(han)(han)(han)(han)量(liang)(liang)(liang)(liang)更(geng)(geng)高(gao)(gao)(gao),而奧氏體(ti)(ti)相(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Ni和Mn含(han)(han)(han)(han)(han)(han)量(liang)(liang)(liang)(liang)更(geng)(geng)高(gao)(gao)(gao)。從圖(tu)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)可(ke)看(kan)出,鐵(tie)素(su)體(ti)(ti)相(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Cr含(han)(han)(han)(han)(han)(han)量(liang)(liang)(liang)(liang)為(wei)(wei)(wei)(wei)(wei)23.77%~25.16%,比(bi)奧氏體(ti)(ti)相(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)Cr含(han)(han)(han)(han)(han)(han)量(liang)(liang)(liang)(liang)高(gao)(gao)(gao)2%左(zuo)右(you);鐵(tie)素(su)體(ti)(ti)相(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)Mo含(han)(han)(han)(han)(han)(han)量(liang)(liang)(liang)(liang)為(wei)(wei)(wei)(wei)(wei)3.86%~4.37%,比(bi)奧氏體(ti)(ti)相(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Mo含(han)(han)(han)(han)(han)(han)量(liang)(liang)(liang)(liang)高(gao)(gao)(gao)1.7%左(zuo)右(you);奧氏體(ti)(ti)相(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Ni含(han)(han)(han)(han)(han)(han)量(liang)(liang)(liang)(liang)為(wei)(wei)(wei)(wei)(wei)5.42%、6.7%,比(bi)鐵(tie)素(su)體(ti)(ti)相(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Ni含(han)(han)(han)(han)(han)(han)量(liang)(liang)(liang)(liang)高(gao)(gao)(gao)2%;當固(gu)(gu)溶(rong)處理溫(wen)度為(wei)(wei)(wei)(wei)(wei)1050℃時,鐵(tie)素(su)體(ti)(ti)相(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Cr、Mo和Ni含(han)(han)(han)(han)(han)(han)量(liang)(liang)(liang)(liang)分(fen)別為(wei)(wei)(wei)(wei)(wei)23.77%、3.97%、4.24%,奧氏體(ti)(ti)相(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Cr、Mo和Ni含(han)(han)(han)(han)(han)(han)量(liang)(liang)(liang)(liang)分(fen)別為(wei)(wei)(wei)(wei)(wei)23.53%、2.63%、5.42%.可(ke)見(jian)在(zai)1050℃溫(wen)度下(xia)進行固(gu)(gu)溶(rong)時,兩(liang)(liang)相(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Cr、Mo、Ni含(han)(han)(han)(han)(han)(han)量(liang)(liang)(liang)(liang)差(cha)(cha)(cha)(cha)異最小,此(ci)時鐵(tie)素(su)體(ti)(ti)含(han)(han)(han)(han)(han)(han)量(liang)(liang)(liang)(liang)為(wei)(wei)(wei)(wei)(wei)51.9%,奧氏體(ti)(ti)含(han)(han)(han)(han)(han)(han)量(liang)(liang)(liang)(liang)為(wei)(wei)(wei)(wei)(wei)48.1%.當固(gu)(gu)溶(rong)溫(wen)度改變(bian)時,鐵(tie)素(su)體(ti)(ti)/奧氏體(ti)(ti)兩(liang)(liang)相(xiang)比(bi)例相(xiang)差(cha)(cha)(cha)(cha)變(bian)大,且(qie)兩(liang)(liang)相(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Cr、Mo、Ni含(han)(han)(han)(han)(han)(han)量(liang)(liang)(liang)(liang)差(cha)(cha)(cha)(cha)異也變(bian)大。當固(gu)(gu)溶(rong)溫(wen)度為(wei)(wei)(wei)(wei)(wei)1000℃,兩(liang)(liang)相(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)Cr為(wei)(wei)(wei)(wei)(wei)3.69%、Mo為(wei)(wei)(wei)(wei)(wei)1.51%、Ni為(wei)(wei)(wei)(wei)(wei)3.37%;當固(gu)(gu)溶(rong)溫(wen)度為(wei)(wei)(wei)(wei)(wei)1150℃時,兩(liang)(liang)相(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)Cr為(wei)(wei)(wei)(wei)(wei)2.29%、Mo為(wei)(wei)(wei)(wei)(wei)1.34%、Ni為(wei)(wei)(wei)(wei)(wei)2.09%,可(ke)見(jian)1000℃固(gu)(gu)溶(rong)試樣的(de)(de)(de)(de)兩(liang)(liang)相(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)Cr、Mo、Ni元(yuan)素(su)含(han)(han)(han)(han)(han)(han)量(liang)(liang)(liang)(liang)差(cha)(cha)(cha)(cha)大于1150℃固(gu)(gu)溶(rong)試樣的(de)(de)(de)(de)兩(liang)(liang)相(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)Cr、Mo、Ni元(yuan)素(su)含(han)(han)(han)(han)(han)(han)量(liang)(liang)(liang)(liang)差(cha)(cha)(cha)(cha)。


7.jpg


  由公(gong)式(shi)“PREN.=[Cr]+3.3[Mo]”計算(suan)(suan)鐵素體的PREN值(zhi)(zhi),由公(gong)式(shi)“PREN,=[Cr]+3.3[Mo]+16[N]-[Mn]”計算(suan)(suan)奧(ao)氏體的PREN值(zhi)(zhi),可得PREN值(zhi)(zhi)與固溶(rong)溫度的關系(xi)圖(tu),如圖(tu)3.7(e)所示。從圖(tu)3.7(e)可看(kan)出,在(zai)不(bu)同固溶(rong)狀態下(xia),兩(liang)相(xiang)的PREN值(zhi)(zhi)有所不(bu)同,但PRENa>PRENy.當固溶(rong)溫度為1050℃時(shi),PREN.最小(xiao)、PREN,最大,分別為36.9和(he)30.6,兩(liang)者相(xiang)差最小(xiao)。


  圖3.8為(wei)(wei)不同(tong)固(gu)溶試樣的(de)(de)極化(hua)曲線(xian)。可(ke)見,在(zai)自(zi)(zi)腐蝕(shi)電(dian)(dian)(dian)位下,材料開始發生鈍化(hua);當極化(hua)電(dian)(dian)(dian)位升高(gao)到一定值時(shi),不同(tong)固(gu)溶的(de)(de)材料都(dou)發生點(dian)蝕(shi),電(dian)(dian)(dian)流(liu)密度(du)急劇增(zeng)大。根據GB 4334.9-1984中電(dian)(dian)(dian)流(liu)密度(du)為(wei)(wei)0.1mA/c㎡所對應的(de)(de)電(dian)(dian)(dian)位為(wei)(wei)點(dian)蝕(shi)電(dian)(dian)(dian)位和(he)Tafel擬合(he),分別(bie)得到點(dian)蝕(shi)電(dian)(dian)(dian)位、自(zi)(zi)腐蝕(shi)電(dian)(dian)(dian)流(liu)密度(du)與固(gu)溶溫度(du)的(de)(de)關系圖,如(ru)圖3.11(a)所示。


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  圖(tu)(tu)(tu)3.9(a)、(b)分別(bie)為(wei)(wei)不同固溶(rong)(rong)試(shi)樣(yang)的(de)(de)Nyquist 圖(tu)(tu)(tu)和Bode圖(tu)(tu)(tu)。從圖(tu)(tu)(tu)3.9(a)可(ke)見,試(shi)樣(yang)在(zai)低頻(pin)(pin)和高頻(pin)(pin)區分別(bie)存(cun)(cun)在(zai)一個(ge)容抗弧。從圖(tu)(tu)(tu)3.9(b)可(ke)見,試(shi)樣(yang)在(zai)低頻(pin)(pin)和高頻(pin)(pin)處分別(bie)存(cun)(cun)在(zai)一個(ge)時(shi)間(jian)常數。根據曹楚南的(de)(de)《電(dian)(dian)化(hua)學阻(zu)抗譜(pu)導論》可(ke)知(zhi)。雙相不銹鋼在(zai)NaCl溶(rong)(rong)液中的(de)(de)阻(zu)抗譜(pu)中存(cun)(cun)在(zai)兩(liang)個(ge)時(shi)間(jian)常數,常以圖(tu)(tu)(tu)3.10所示(shi)的(de)(de)等效電(dian)(dian)路(R1為(wei)(wei)電(dian)(dian)荷轉移電(dian)(dian)阻(zu),R2為(wei)(wei)鈍化(hua)膜電(dian)(dian)阻(zu))進(jin)行阻(zu)抗擬合。經阻(zu)抗擬合,得到鈍化(hua)膜電(dian)(dian)阻(zu)、電(dian)(dian)荷轉移電(dian)(dian)阻(zu)與固溶(rong)(rong)處理溫度的(de)(de)關系(xi)圖(tu)(tu)(tu),如圖(tu)(tu)(tu)3.11(b)所示(shi)。


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 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。


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  通過計算得(de)到不同相(xiang)(xiang)比例下的(de)鐵(tie)素體(ti)PREN值和奧氏體(ti)PREN值,可見不同相(xiang)(xiang)比例下的(de)PREN.都(dou)大(da)(da)于(yu)(yu)PREN,.雙相(xiang)(xiang)不銹鋼(gang)的(de)耐(nai)點(dian)(dian)(dian)蝕(shi)(shi)(shi)(shi)性能(neng)可通過點(dian)(dian)(dian)蝕(shi)(shi)(shi)(shi)電(dian)位衡量。點(dian)(dian)(dian)蝕(shi)(shi)(shi)(shi)電(dian)位越(yue)(yue)高,耐(nai)點(dian)(dian)(dian)獨性能(neng)越(yue)(yue)好(hao)。前人認(ren)為雙相(xiang)(xiang)不銹鋼(gang)的(de)耐(nai)點(dian)(dian)(dian)蝕(shi)(shi)(shi)(shi)性能(neng)由(you)B能(neng)N值較(jiao)區(qu)的(de)相(xiang)(xiang)決(jue)定,且(qie)PEN值越(yue)(yue)高,耐(nai)點(dian)(dian)(dian)蝕(shi)(shi)(shi)(shi)性能(neng)越(yue)(yue)好(hao),從圖(tu)3.71e)可矩,不同海溶(rong)試(shi)(shi)樣(yang)的(de)PREN.都(dou)大(da)(da)于(yu)(yu)PREN,,當固溶(rong)溫度為1050℃時,PHEN,最(zui)(zui)大(da)(da),材(cai)料的(de)耐(nai)點(dian)(dian)(dian)蝕(shi)(shi)(shi)(shi)性能(neng)應最(zui)(zui)好(hao)。從圖(tu)3.11(a)、(b)可知,1050℃固溶(rong)試(shi)(shi)樣(yang)的(de)點(dian)(dian)(dian)蝕(shi)(shi)(shi)(shi)電(dian)位最(zui)(zui)高,鈍化膜(mo)阻抗值最(zui)(zui)大(da)(da),電(dian)荷轉移電(dian)阻值最(zui)(zui)商;且(qie)從圖(tu)3.12(b)可見,1050℃固溶(rong)試(shi)(shi)樣(yang)的(de)點(dian)(dian)(dian)蝕(shi)(shi)(shi)(shi)坑(keng)尺(chi)寸最(zui)(zui)小,表現出最(zui)(zui)好(hao)的(de)耐(nai)點(dian)(dian)(dian)蝕(shi)(shi)(shi)(shi)性能(neng)。綜上可知,雙相(xiang)(xiang)不銹鋼(gang)的(de)耐(nai)點(dian)(dian)(dian)蝕(shi)(shi)(shi)(shi)性能(neng)由(you) PREN 值較(jiao)小相(xiang)(xiang)決(jue)定的(de)理論是(shi)有實(shi)驗依據的(de)。


  從圖3.12(a)~(d)可見,在(zai)(zai)不同固(gu)溶狀態(tai)下,鐵(tie)素(su)體(ti)相都(dou)更易發生點蝕;而從圖3.7(e)可見,在(zai)(zai)不同固(gu)溶狀態(tai)下,PREN.都(dou)大于PREN,,鐵(tie)素(su)體(ti)的耐點蝕性能應優于奧氏體(ti)相,可見兩者(zhe)存在(zai)(zai)矛(mao)盾。


  隨固(gu)溶(rong)(rong)(rong)溫度(du)變(bian)(bian)(bian)(bian)化(hua)(hua),雙相(xiang)(xiang)(xiang)不(bu)銹(xiu)(xiu)鋼中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)鐵(tie)(tie)素(su)(su)(su)(su)(su)(su)體(ti)和奧(ao)氏(shi)體(ti)相(xiang)(xiang)(xiang)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)比例改變(bian)(bian)(bian)(bian),且兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)形(xing)(xing)態(tai)也(ye)發生變(bian)(bian)(bian)(bian)化(hua)(hua)。Cr是鐵(tie)(tie)素(su)(su)(su)(su)(su)(su)體(ti)形(xing)(xing)成元(yuan)(yuan)(yuan)素(su)(su)(su)(su)(su)(su),可(ke)(ke)(ke)(ke)提高(gao)材料(liao)(liao)(liao)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)耐(nai)(nai)(nai)蝕(shi)(shi)性(xing)(xing)能(neng)(neng);Mo是鐵(tie)(tie)素(su)(su)(su)(su)(su)(su)體(ti)形(xing)(xing)成元(yuan)(yuan)(yuan)素(su)(su)(su)(su)(su)(su),可(ke)(ke)(ke)(ke)提高(gao)點(dian)(dian)蝕(shi)(shi)電位,降低(di)腐(fu)(fu)蝕(shi)(shi)速率;Ni是奧(ao)氏(shi)體(ti)形(xing)(xing)成元(yuan)(yuan)(yuan)素(su)(su)(su)(su)(su)(su),可(ke)(ke)(ke)(ke)維持兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)平衡(heng),提高(gao)耐(nai)(nai)(nai)蝕(shi)(shi)性(xing)(xing)能(neng)(neng)。并且材料(liao)(liao)(liao)中(zhong)(zhong)(zhong)存(cun)在(zai)一定量(liang)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)N,其為(wei)奧(ao)氏(shi)體(ti)形(xing)(xing)成元(yuan)(yuan)(yuan)素(su)(su)(su)(su)(su)(su),提高(gao)局部腐(fu)(fu)蝕(shi)(shi)抗力。從圖3.7(a)~(c)可(ke)(ke)(ke)(ke)見,隨固(gu)溶(rong)(rong)(rong)溫度(du)變(bian)(bian)(bian)(bian)化(hua)(hua),兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)Cr、Mo、Ni元(yuan)(yuan)(yuan)素(su)(su)(su)(su)(su)(su)含(han)量(liang)發生變(bian)(bian)(bian)(bian)化(hua)(hua)。由于(yu)Cr、Mo、Ni元(yuan)(yuan)(yuan)素(su)(su)(su)(su)(su)(su)之間(jian)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)腐(fu)(fu)蝕(shi)(shi)電位存(cun)在(zai)差(cha)異,勢必造成兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)之間(jian)存(cun)在(zai)電化(hua)(hua)學差(cha)異,使(shi)腐(fu)(fu)蝕(shi)(shi)更易發生。從圖3.7(e)可(ke)(ke)(ke)(ke)知,不(bu)同(tong)固(gu)溶(rong)(rong)(rong)狀態(tai)下材料(liao)(liao)(liao)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)PREN,大(da)(da)小(xiao)關(guan)系(xi)為(wei)1050℃>1000℃>1150℃>1100℃,因(yin)此(ci)根據前人的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)研究,不(bu)同(tong)固(gu)溶(rong)(rong)(rong)態(tai)材料(liao)(liao)(liao)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)耐(nai)(nai)(nai)點(dian)(dian)蝕(shi)(shi)性(xing)(xing)能(neng)(neng)優(you)(you)劣關(guan)系(xi)應為(wei):1050℃優(you)(you)于(yu)1000℃優(you)(you)于(yu)1150℃.當固(gu)溶(rong)(rong)(rong)溫度(du)為(wei)1050℃時(shi),PREN,值(zhi)較大(da)(da),兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)Cr、Mo、Ni元(yuan)(yuan)(yuan)素(su)(su)(su)(su)(su)(su)含(han)量(liang)差(cha)異最(zui)小(xiao),材料(liao)(liao)(liao)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)點(dian)(dian)蝕(shi)(shi)坑(keng)較小(xiao),材料(liao)(liao)(liao)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)耐(nai)(nai)(nai)點(dian)(dian)蝕(shi)(shi)性(xing)(xing)能(neng)(neng)最(zui)優(you)(you)。1000℃固(gu)溶(rong)(rong)(rong)試(shi)樣的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)點(dian)(dian)蝕(shi)(shi)坑(keng)尺寸大(da)(da)于(yu)1150℃固(gu)溶(rong)(rong)(rong)試(shi)樣的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)點(dian)(dian)蝕(shi)(shi)坑(keng)尺寸,因(yin)此(ci),前者(zhe)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)耐(nai)(nai)(nai)點(dian)(dian)蝕(shi)(shi)性(xing)(xing)能(neng)(neng)劣于(yu)后者(zhe)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)耐(nai)(nai)(nai)點(dian)(dian)蝕(shi)(shi)性(xing)(xing)能(neng)(neng)。由此(ci)可(ke)(ke)(ke)(ke)見,雙相(xiang)(xiang)(xiang)不(bu)銹(xiu)(xiu)鋼中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)相(xiang)(xiang)(xiang)腐(fu)(fu)蝕(shi)(shi)不(bu)能(neng)(neng)僅(jin)僅(jin)由PREN值(zhi)來解釋(shi)。由圖3.7(a)~(c)可(ke)(ke)(ke)(ke)知,1000℃固(gu)溶(rong)(rong)(rong)試(shi)樣的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)Cr、Mo、Ni元(yuan)(yuan)(yuan)素(su)(su)(su)(su)(su)(su)含(han)量(liang)差(cha)大(da)(da)于(yu)1150℃固(gu)溶(rong)(rong)(rong)試(shi)樣的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)Gr、Mo、Ni元(yuan)(yuan)(yuan)素(su)(su)(su)(su)(su)(su)含(han)量(liang)差(cha),因(yin)此(ci),雙相(xiang)(xiang)(xiang)不(bu)銹(xiu)(xiu)鋼中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)相(xiang)(xiang)(xiang)腐(fu)(fu)蝕(shi)(shi)還(huan)與(yu)兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)元(yuan)(yuan)(yuan)素(su)(su)(su)(su)(su)(su)分布有關(guan),并且還(huan)需考慮到材料(liao)(liao)(liao)中(zhong)(zhong)(zhong)點(dian)(dian)蝕(shi)(shi)敏(min)感性(xing)(xing)較強的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)區域,如晶界(jie)(jie)和相(xiang)(xiang)(xiang)界(jie)(jie)。


  點蝕是一種局部(bu)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(ying)響雙相不(bu)銹鋼相腐蝕(shi)的(de)因素不(bu)僅包括(kuo)PREN值,還包括(kuo)各(ge)相中的(de)元(yuan)素分(fen)布和兩(liang)相比例(li),并且三者互相影(ying)響、關系復(fu)雜。因此,不(bu)能僅憑PREN值的(de)大小來判斷耐點蝕(shi)能力,應該綜合考慮各(ge)因素的(de)影(ying)響。