圖(tu)3.7(a)~(d)為(wei)(wei)(wei)(wei)鐵(tie)(tie)素(su)(su)體(ti)(ti)(ti)(ti)和(he)奧(ao)氏(shi)(shi)體(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)Cr、Mo、Ni元素(su)(su)含(han)(han)(han)(han)量(liang)與固(gu)(gu)(gu)溶(rong)溫(wen)(wen)度(du)的(de)(de)關(guan)系(xi)圖(tu)。圖(tu)3.7(a)~(d)證實了鐵(tie)(tie)素(su)(su)體(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)Cr和(he)Mo含(han)(han)(han)(han)量(liang)更高(gao)，而奧(ao)氏(shi)(shi)體(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)Ni和(he)Mn含(han)(han)(han)(han)量(liang)更高(gao)。從圖(tu)中(zhong)(zhong)(zhong)(zhong)可(ke)看出(chu)，鐵(tie)(tie)素(su)(su)體(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)Cr含(han)(han)(han)(han)量(liang)為(wei)(wei)(wei)(wei)23.77%~25.16%,比奧(ao)氏(shi)(shi)體(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)Cr含(han)(han)(han)(han)量(liang)高(gao)2%左右；鐵(tie)(tie)素(su)(su)體(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)Mo含(han)(han)(han)(han)量(liang)為(wei)(wei)(wei)(wei)3.86%~4.37%,比奧(ao)氏(shi)(shi)體(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)Mo含(han)(han)(han)(han)量(liang)高(gao)1.7%左右；奧(ao)氏(shi)(shi)體(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)Ni含(han)(han)(han)(han)量(liang)為(wei)(wei)(wei)(wei)5.42%、6.7%,比鐵(tie)(tie)素(su)(su)體(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)Ni含(han)(han)(han)(han)量(liang)高(gao)2%;當(dang)固(gu)(gu)(gu)溶(rong)處理溫(wen)(wen)度(du)為(wei)(wei)(wei)(wei)1050℃時，鐵(tie)(tie)素(su)(su)體(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)Cr、Mo和(he)Ni含(han)(han)(han)(han)量(liang)分(fen)別為(wei)(wei)(wei)(wei)23.77%、3.97%、4.24%,奧(ao)氏(shi)(shi)體(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)Cr、Mo和(he)Ni含(han)(han)(han)(han)量(liang)分(fen)別為(wei)(wei)(wei)(wei)23.53%、2.63%、5.42%.可(ke)見在1050℃溫(wen)(wen)度(du)下進(jin)行固(gu)(gu)(gu)溶(rong)時，兩相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)Cr、Mo、Ni含(han)(han)(han)(han)量(liang)差(cha)異最小，此(ci)時鐵(tie)(tie)素(su)(su)體(ti)(ti)(ti)(ti)含(han)(han)(han)(han)量(liang)為(wei)(wei)(wei)(wei)51.9%,奧(ao)氏(shi)(shi)體(ti)(ti)(ti)(ti)含(han)(han)(han)(han)量(liang)為(wei)(wei)(wei)(wei)48.1%.當(dang)固(gu)(gu)(gu)溶(rong)溫(wen)(wen)度(du)改變(bian)時，鐵(tie)(tie)素(su)(su)體(ti)(ti)(ti)(ti)／奧(ao)氏(shi)(shi)體(ti)(ti)(ti)(ti)兩相(xiang)(xiang)(xiang)(xiang)(xiang)比例相(xiang)(xiang)(xiang)(xiang)(xiang)差(cha)變(bian)大(da)，且(qie)兩相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)Cr、Mo、Ni含(han)(han)(han)(han)量(liang)差(cha)異也變(bian)大(da)。當(dang)固(gu)(gu)(gu)溶(rong)溫(wen)(wen)度(du)為(wei)(wei)(wei)(wei)1000℃,兩相(xiang)(xiang)(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(dang)固(gu)(gu)(gu)溶(rong)溫(wen)(wen)度(du)為(wei)(wei)(wei)(wei)1150℃時，兩相(xiang)(xiang)(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(ke)見1000℃固(gu)(gu)(gu)溶(rong)試樣(yang)(yang)的(de)(de)兩相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)的(de)(de)Cr、Mo、Ni元素(su)(su)含(han)(han)(han)(han)量(liang)差(cha)大(da)于(yu)1150℃固(gu)(gu)(gu)溶(rong)試樣(yang)(yang)的(de)(de)兩相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)Cr、Mo、Ni元素(su)(su)含(han)(han)(han)(han)量(liang)差(cha)。

  由(you)公(gong)式“PREN.=[Cr]+3.3[Mo]”計算鐵素體的PREN值(zhi)，由(you)公(gong)式“PREN,=[Cr]+3.3[Mo]+16[N]-[Mn]”計算奧氏體的PREN值(zhi)，可(ke)得PREN值(zhi)與(yu)固(gu)溶(rong)(rong)溫度的關系圖(tu)，如圖(tu)3.7(e)所示。從圖(tu)3.7(e)可(ke)看出，在不同(tong)固(gu)溶(rong)(rong)狀態下，兩相的PREN值(zhi)有所不同(tong)，但PRENa>PRENy.當固(gu)溶(rong)(rong)溫度為1050℃時，PREN.最小、PREN,最大，分別為36.9和(he)30.6,兩者相差(cha)最小。

  圖3.8為不同(tong)固溶(rong)(rong)試樣的極化曲線。可(ke)見(jian)，在自腐蝕(shi)電(dian)位(wei)下，材料(liao)開始發(fa)生鈍化；當極化電(dian)位(wei)升高到一定值時，不同(tong)固溶(rong)(rong)的材料(liao)都發(fa)生點(dian)蝕(shi)，電(dian)流(liu)密度急劇增大(da)。根(gen)據(ju)GB 4334.9-1984中電(dian)流(liu)密度為0.1mA/c㎡所(suo)對應(ying)的電(dian)位(wei)為點(dian)蝕(shi)電(dian)位(wei)和Tafel擬(ni)合，分別得到點(dian)蝕(shi)電(dian)位(wei)、自腐蝕(shi)電(dian)流(liu)密度與固溶(rong)(rong)溫度的關系圖，如圖3.11(a)所(suo)示。

  圖(tu)(tu)3.9(a)、（b)分別為不(bu)同固溶試(shi)樣(yang)的(de)Nyquist 圖(tu)(tu)和(he)Bode圖(tu)(tu)。從圖(tu)(tu)3.9(a)可(ke)見，試(shi)樣(yang)在(zai)低頻和(he)高頻區分別存(cun)(cun)在(zai)一個(ge)(ge)容(rong)抗(kang)(kang)弧(hu)。從圖(tu)(tu)3.9(b)可(ke)見，試(shi)樣(yang)在(zai)低頻和(he)高頻處分別存(cun)(cun)在(zai)一個(ge)(ge)時間常數。根據曹楚南的(de)《電(dian)(dian)(dian)(dian)(dian)化(hua)學(xue)阻(zu)(zu)抗(kang)(kang)譜導論(lun)》可(ke)知(zhi)。雙相不(bu)銹鋼在(zai)NaCl溶液中(zhong)的(de)阻(zu)(zu)抗(kang)(kang)譜中(zhong)存(cun)(cun)在(zai)兩個(ge)(ge)時間常數，常以圖(tu)(tu)3.10所(suo)(suo)示的(de)等(deng)效電(dian)(dian)(dian)(dian)(dian)路（R1為電(dian)(dian)(dian)(dian)(dian)荷(he)轉移(yi)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)，R2為鈍(dun)化(hua)膜電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)）進行阻(zu)(zu)抗(kang)(kang)擬合。經阻(zu)(zu)抗(kang)(kang)擬合，得到鈍(dun)化(hua)膜電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)、電(dian)(dian)(dian)(dian)(dian)荷(he)轉移(yi)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)與固溶處理溫度的(de)關系圖(tu)(tu)，如圖(tu)(tu)3.11(b)所(suo)(suo)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(xiu)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(ji)算得(de)到不同(tong)相(xiang)比例下的鐵素體PREN值和(he)奧(ao)氏體PREN值，可(ke)見不同(tong)相(xiang)比例下的PREN.都大(da)于(yu)PREN,.雙(shuang)相(xiang)不銹(xiu)鋼的耐點(dian)(dian)蝕(shi)(shi)(shi)性(xing)能(neng)可(ke)通過點(dian)(dian)蝕(shi)(shi)(shi)電(dian)位(wei)衡量。點(dian)(dian)蝕(shi)(shi)(shi)電(dian)位(wei)越(yue)高(gao)，耐點(dian)(dian)獨性(xing)能(neng)越(yue)好(hao)(hao)。前人認為(wei)雙(shuang)相(xiang)不銹(xiu)鋼的耐點(dian)(dian)蝕(shi)(shi)(shi)性(xing)能(neng)由B能(neng)N值較區的相(xiang)決定，且PEN值越(yue)高(gao)，耐點(dian)(dian)蝕(shi)(shi)(shi)性(xing)能(neng)越(yue)好(hao)(hao)，從圖(tu)3.71e)可(ke)矩，不同(tong)海(hai)溶試樣的PREN.都大(da)于(yu)PREN,,當(dang)固溶溫(wen)度為(wei)1050℃時(shi)，PHEN,最(zui)(zui)(zui)大(da)，材(cai)料的耐點(dian)(dian)蝕(shi)(shi)(shi)性(xing)能(neng)應最(zui)(zui)(zui)好(hao)(hao)。從圖(tu)3.11(a)、（b)可(ke)知，1050℃固溶試樣的點(dian)(dian)蝕(shi)(shi)(shi)電(dian)位(wei)最(zui)(zui)(zui)高(gao)，鈍化(hua)膜阻抗(kang)值最(zui)(zui)(zui)大(da)，電(dian)荷轉移電(dian)阻值最(zui)(zui)(zui)商；且從圖(tu)3.12(b)可(ke)見，1050℃固溶試樣的點(dian)(dian)蝕(shi)(shi)(shi)坑(keng)尺寸(cun)最(zui)(zui)(zui)小(xiao)，表現出(chu)最(zui)(zui)(zui)好(hao)(hao)的耐點(dian)(dian)蝕(shi)(shi)(shi)性(xing)能(neng)。綜(zong)上可(ke)知，雙(shuang)相(xiang)不銹(xiu)鋼的耐點(dian)(dian)蝕(shi)(shi)(shi)性(xing)能(neng)由 PREN 值較小(xiao)相(xiang)決定的理論(lun)是有實驗依據的。

  從圖(tu)3.12(a)~(d)可見(jian)，在不(bu)同固(gu)(gu)溶狀態(tai)下，鐵(tie)素體相都更易(yi)發生點(dian)蝕；而(er)從圖(tu)3.7(e)可見(jian)，在不(bu)同固(gu)(gu)溶狀態(tai)下，PREN.都大于PREN,,鐵(tie)素體的耐點(dian)蝕性能應(ying)優(you)于奧氏體相，可見(jian)兩者存在矛(mao)盾。

  隨固(gu)溶(rong)(rong)(rong)(rong)溫(wen)度變(bian)化，雙(shuang)相(xiang)(xiang)不(bu)銹鋼中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)鐵素(su)(su)(su)體(ti)和(he)奧(ao)氏(shi)體(ti)相(xiang)(xiang)的(de)(de)(de)(de)(de)(de)(de)比例改變(bian)，且兩(liang)相(xiang)(xiang)形(xing)(xing)態也(ye)發(fa)生變(bian)化。Cr是鐵素(su)(su)(su)體(ti)形(xing)(xing)成(cheng)元(yuan)素(su)(su)(su)，可(ke)提高(gao)材料的(de)(de)(de)(de)(de)(de)(de)耐(nai)(nai)蝕(shi)(shi)(shi)性能(neng)(neng)(neng)(neng)；Mo是鐵素(su)(su)(su)體(ti)形(xing)(xing)成(cheng)元(yuan)素(su)(su)(su)，可(ke)提高(gao)點(dian)(dian)蝕(shi)(shi)(shi)電位，降低腐(fu)蝕(shi)(shi)(shi)速率；Ni是奧(ao)氏(shi)體(ti)形(xing)(xing)成(cheng)元(yuan)素(su)(su)(su)，可(ke)維持兩(liang)相(xiang)(xiang)平衡，提高(gao)耐(nai)(nai)蝕(shi)(shi)(shi)性能(neng)(neng)(neng)(neng)。并且材料中(zhong)(zhong)(zhong)存在一定(ding)量(liang)的(de)(de)(de)(de)(de)(de)(de)N,其為奧(ao)氏(shi)體(ti)形(xing)(xing)成(cheng)元(yuan)素(su)(su)(su)，提高(gao)局部腐(fu)蝕(shi)(shi)(shi)抗力。從圖3.7(a)~(c)可(ke)見(jian)，隨固(gu)溶(rong)(rong)(rong)(rong)溫(wen)度變(bian)化，兩(liang)相(xiang)(xiang)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)Cr、Mo、Ni元(yuan)素(su)(su)(su)含(han)量(liang)發(fa)生變(bian)化。由于Cr、Mo、Ni元(yuan)素(su)(su)(su)之間(jian)(jian)的(de)(de)(de)(de)(de)(de)(de)腐(fu)蝕(shi)(shi)(shi)電位存在差(cha)異(yi)，勢必造(zao)成(cheng)兩(liang)相(xiang)(xiang)之間(jian)(jian)存在電化學(xue)差(cha)異(yi)，使腐(fu)蝕(shi)(shi)(shi)更易發(fa)生。從圖3.7(e)可(ke)知，不(bu)同固(gu)溶(rong)(rong)(rong)(rong)狀態下材料的(de)(de)(de)(de)(de)(de)(de)PREN,大(da)小(xiao)關(guan)(guan)系為1050℃>1000℃>1150℃>1100℃,因此根(gen)據前(qian)人的(de)(de)(de)(de)(de)(de)(de)研究，不(bu)同固(gu)溶(rong)(rong)(rong)(rong)態材料的(de)(de)(de)(de)(de)(de)(de)耐(nai)(nai)點(dian)(dian)蝕(shi)(shi)(shi)性能(neng)(neng)(neng)(neng)優(you)(you)劣關(guan)(guan)系應(ying)為：1050℃優(you)(you)于1000℃優(you)(you)于1150℃.當固(gu)溶(rong)(rong)(rong)(rong)溫(wen)度為1050℃時，PREN,值(zhi)較(jiao)大(da)，兩(liang)相(xiang)(xiang)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)Cr、Mo、Ni元(yuan)素(su)(su)(su)含(han)量(liang)差(cha)異(yi)最(zui)小(xiao)，材料的(de)(de)(de)(de)(de)(de)(de)點(dian)(dian)蝕(shi)(shi)(shi)坑(keng)較(jiao)小(xiao)，材料的(de)(de)(de)(de)(de)(de)(de)耐(nai)(nai)點(dian)(dian)蝕(shi)(shi)(shi)性能(neng)(neng)(neng)(neng)最(zui)優(you)(you)。1000℃固(gu)溶(rong)(rong)(rong)(rong)試(shi)樣的(de)(de)(de)(de)(de)(de)(de)點(dian)(dian)蝕(shi)(shi)(shi)坑(keng)尺(chi)寸大(da)于1150℃固(gu)溶(rong)(rong)(rong)(rong)試(shi)樣的(de)(de)(de)(de)(de)(de)(de)點(dian)(dian)蝕(shi)(shi)(shi)坑(keng)尺(chi)寸，因此，前(qian)者(zhe)的(de)(de)(de)(de)(de)(de)(de)耐(nai)(nai)點(dian)(dian)蝕(shi)(shi)(shi)性能(neng)(neng)(neng)(neng)劣于后者(zhe)的(de)(de)(de)(de)(de)(de)(de)耐(nai)(nai)點(dian)(dian)蝕(shi)(shi)(shi)性能(neng)(neng)(neng)(neng)。由此可(ke)見(jian)，雙(shuang)相(xiang)(xiang)不(bu)銹鋼中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)相(xiang)(xiang)腐(fu)蝕(shi)(shi)(shi)不(bu)能(neng)(neng)(neng)(neng)僅僅由PREN值(zhi)來(lai)解釋。由圖3.7(a)~(c)可(ke)知，1000℃固(gu)溶(rong)(rong)(rong)(rong)試(shi)樣的(de)(de)(de)(de)(de)(de)(de)兩(liang)相(xiang)(xiang)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)Cr、Mo、Ni元(yuan)素(su)(su)(su)含(han)量(liang)差(cha)大(da)于1150℃固(gu)溶(rong)(rong)(rong)(rong)試(shi)樣的(de)(de)(de)(de)(de)(de)(de)兩(liang)相(xiang)(xiang)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)Gr、Mo、Ni元(yuan)素(su)(su)(su)含(han)量(liang)差(cha)，因此，雙(shuang)相(xiang)(xiang)不(bu)銹鋼中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)相(xiang)(xiang)腐(fu)蝕(shi)(shi)(shi)還與兩(liang)相(xiang)(xiang)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)元(yuan)素(su)(su)(su)分布有關(guan)(guan)，并且還需考(kao)慮到材料中(zhong)(zhong)(zhong)點(dian)(dian)蝕(shi)(shi)(shi)敏(min)感性較(jiao)強的(de)(de)(de)(de)(de)(de)(de)區域，如晶界和(he)相(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。

  影響(xiang)雙(shuang)相(xiang)不銹鋼相(xiang)腐蝕的(de)因(yin)素不僅包括PREN值(zhi)，還(huan)包括各相(xiang)中的(de)元素分布(bu)和兩相(xiang)比例，并(bing)且三者互相(xiang)影響(xiang)、關系復雜。因(yin)此，不能僅憑PREN值(zhi)的(de)大小(xiao)來判斷耐點蝕能力，應該(gai)綜合考慮各因(yin)素的(de)影響(xiang)。