圖(tu)(tu)3.7(a)~(d)為(wei)(wei)(wei)(wei)(wei)(wei)鐵(tie)素(su)體(ti)(ti)(ti)(ti)(ti)和(he)奧(ao)氏(shi)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo、Ni元素(su)含量(liang)(liang)(liang)(liang)(liang)(liang)與固(gu)溶(rong)溫(wen)(wen)度(du)(du)(du)的(de)(de)(de)(de)(de)(de)關(guan)系圖(tu)(tu)。圖(tu)(tu)3.7(a)~(d)證實了(le)鐵(tie)素(su)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr和(he)Mo含量(liang)(liang)(liang)(liang)(liang)(liang)更(geng)高，而奧(ao)氏(shi)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Ni和(he)Mn含量(liang)(liang)(liang)(liang)(liang)(liang)更(geng)高。從圖(tu)(tu)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)可(ke)看出(chu)，鐵(tie)素(su)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr含量(liang)(liang)(liang)(liang)(liang)(liang)為(wei)(wei)(wei)(wei)(wei)(wei)23.77%~25.16%,比奧(ao)氏(shi)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)Cr含量(liang)(liang)(liang)(liang)(liang)(liang)高2%左右；鐵(tie)素(su)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)Mo含量(liang)(liang)(liang)(liang)(liang)(liang)為(wei)(wei)(wei)(wei)(wei)(wei)3.86%~4.37%,比奧(ao)氏(shi)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Mo含量(liang)(liang)(liang)(liang)(liang)(liang)高1.7%左右；奧(ao)氏(shi)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Ni含量(liang)(liang)(liang)(liang)(liang)(liang)為(wei)(wei)(wei)(wei)(wei)(wei)5.42%、6.7%,比鐵(tie)素(su)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Ni含量(liang)(liang)(liang)(liang)(liang)(liang)高2%;當(dang)固(gu)溶(rong)處理溫(wen)(wen)度(du)(du)(du)為(wei)(wei)(wei)(wei)(wei)(wei)1050℃時，鐵(tie)素(su)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo和(he)Ni含量(liang)(liang)(liang)(liang)(liang)(liang)分別為(wei)(wei)(wei)(wei)(wei)(wei)23.77%、3.97%、4.24%,奧(ao)氏(shi)體(ti)(ti)(ti)(ti)(ti)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo和(he)Ni含量(liang)(liang)(liang)(liang)(liang)(liang)分別為(wei)(wei)(wei)(wei)(wei)(wei)23.53%、2.63%、5.42%.可(ke)見在(zai)1050℃溫(wen)(wen)度(du)(du)(du)下(xia)進行(xing)固(gu)溶(rong)時，兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo、Ni含量(liang)(liang)(liang)(liang)(liang)(liang)差(cha)異最小，此(ci)時鐵(tie)素(su)體(ti)(ti)(ti)(ti)(ti)含量(liang)(liang)(liang)(liang)(liang)(liang)為(wei)(wei)(wei)(wei)(wei)(wei)51.9%,奧(ao)氏(shi)體(ti)(ti)(ti)(ti)(ti)含量(liang)(liang)(liang)(liang)(liang)(liang)為(wei)(wei)(wei)(wei)(wei)(wei)48.1%.當(dang)固(gu)溶(rong)溫(wen)(wen)度(du)(du)(du)改變(bian)(bian)時，鐵(tie)素(su)體(ti)(ti)(ti)(ti)(ti)／奧(ao)氏(shi)體(ti)(ti)(ti)(ti)(ti)兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)(xiang)比例相(xiang)(xiang)(xiang)(xiang)差(cha)變(bian)(bian)大，且兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo、Ni含量(liang)(liang)(liang)(liang)(liang)(liang)差(cha)異也變(bian)(bian)大。當(dang)固(gu)溶(rong)溫(wen)(wen)度(du)(du)(du)為(wei)(wei)(wei)(wei)(wei)(wei)1000℃,兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)Cr為(wei)(wei)(wei)(wei)(wei)(wei)3.69%、Mo為(wei)(wei)(wei)(wei)(wei)(wei)1.51%、Ni為(wei)(wei)(wei)(wei)(wei)(wei)3.37%;當(dang)固(gu)溶(rong)溫(wen)(wen)度(du)(du)(du)為(wei)(wei)(wei)(wei)(wei)(wei)1150℃時，兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)Cr為(wei)(wei)(wei)(wei)(wei)(wei)2.29%、Mo為(wei)(wei)(wei)(wei)(wei)(wei)1.34%、Ni為(wei)(wei)(wei)(wei)(wei)(wei)2.09%,可(ke)見1000℃固(gu)溶(rong)試(shi)樣的(de)(de)(de)(de)(de)(de)兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo、Ni元素(su)含量(liang)(liang)(liang)(liang)(liang)(liang)差(cha)大于1150℃固(gu)溶(rong)試(shi)樣的(de)(de)(de)(de)(de)(de)兩(liang)(liang)(liang)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)(zhong)Cr、Mo、Ni元素(su)含量(liang)(liang)(liang)(liang)(liang)(liang)差(cha)。

  由(you)公(gong)式(shi)“PREN.=[Cr]+3.3[Mo]”計(ji)算(suan)鐵素體的(de)PREN值(zhi)，由(you)公(gong)式(shi)“PREN,=[Cr]+3.3[Mo]+16[N]-[Mn]”計(ji)算(suan)奧(ao)氏(shi)體的(de)PREN值(zhi)，可得PREN值(zhi)與固溶(rong)溫度(du)的(de)關系圖(tu)，如(ru)圖(tu)3.7(e)所(suo)(suo)示(shi)。從圖(tu)3.7(e)可看(kan)出，在不同固溶(rong)狀態(tai)下(xia)，兩相(xiang)的(de)PREN值(zhi)有所(suo)(suo)不同，但(dan)PRENa>PRENy.當(dang)固溶(rong)溫度(du)為1050℃時(shi)，PREN.最小(xiao)(xiao)、PREN,最大，分別為36.9和30.6,兩者相(xiang)差最小(xiao)(xiao)。

  圖(tu)3.8為不同固溶(rong)試(shi)樣的(de)(de)極化曲線。可見，在自(zi)腐蝕(shi)電(dian)位下(xia)，材料開始發(fa)生鈍化；當極化電(dian)位升高(gao)到一定(ding)值時，不同固溶(rong)的(de)(de)材料都發(fa)生點蝕(shi)，電(dian)流(liu)密(mi)度急劇增(zeng)大。根據(ju)GB 4334.9-1984中電(dian)流(liu)密(mi)度為0.1mA/c㎡所對(dui)應的(de)(de)電(dian)位為點蝕(shi)電(dian)位和Tafel擬(ni)合，分別得(de)到點蝕(shi)電(dian)位、自(zi)腐蝕(shi)電(dian)流(liu)密(mi)度與固溶(rong)溫度的(de)(de)關系圖(tu)，如圖(tu)3.11(a)所示。

  圖(tu)3.9(a)、（b)分(fen)(fen)別(bie)為不(bu)同固(gu)(gu)溶(rong)試樣(yang)(yang)的Nyquist 圖(tu)和Bode圖(tu)。從(cong)圖(tu)3.9(a)可(ke)見，試樣(yang)(yang)在(zai)低頻和高(gao)頻區分(fen)(fen)別(bie)存(cun)在(zai)一個(ge)(ge)(ge)容抗(kang)弧。從(cong)圖(tu)3.9(b)可(ke)見，試樣(yang)(yang)在(zai)低頻和高(gao)頻處分(fen)(fen)別(bie)存(cun)在(zai)一個(ge)(ge)(ge)時間常數(shu)。根據曹(cao)楚(chu)南的《電(dian)化(hua)(hua)學阻抗(kang)譜(pu)導論》可(ke)知(zhi)。雙相不(bu)銹鋼在(zai)NaCl溶(rong)液(ye)中(zhong)的阻抗(kang)譜(pu)中(zhong)存(cun)在(zai)兩個(ge)(ge)(ge)時間常數(shu)，常以圖(tu)3.10所(suo)(suo)示的等效電(dian)路（R1為電(dian)荷轉移電(dian)阻，R2為鈍(dun)化(hua)(hua)膜電(dian)阻）進行阻抗(kang)擬合(he)。經阻抗(kang)擬合(he)，得到鈍(dun)化(hua)(hua)膜電(dian)阻、電(dian)荷轉移電(dian)阻與固(gu)(gu)溶(rong)處理溫度的關系圖(tu)，如圖(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(shuang)相不(bu)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)過計算(suan)得(de)到不(bu)同(tong)(tong)相(xiang)(xiang)比例下(xia)的(de)(de)(de)(de)(de)鐵素體PREN值(zhi)和奧氏體PREN值(zhi)，可(ke)(ke)(ke)見(jian)不(bu)同(tong)(tong)相(xiang)(xiang)比例下(xia)的(de)(de)(de)(de)(de)PREN.都(dou)大(da)于PREN,.雙相(xiang)(xiang)不(bu)銹鋼的(de)(de)(de)(de)(de)耐(nai)點(dian)(dian)蝕(shi)(shi)(shi)性(xing)能(neng)(neng)(neng)可(ke)(ke)(ke)通(tong)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)(yue)高(gao)，耐(nai)點(dian)(dian)獨性(xing)能(neng)(neng)(neng)越(yue)(yue)好。前人(ren)認為雙相(xiang)(xiang)不(bu)銹鋼的(de)(de)(de)(de)(de)耐(nai)點(dian)(dian)蝕(shi)(shi)(shi)性(xing)能(neng)(neng)(neng)由(you)B能(neng)(neng)(neng)N值(zhi)較區的(de)(de)(de)(de)(de)相(xiang)(xiang)決(jue)定，且(qie)PEN值(zhi)越(yue)(yue)高(gao)，耐(nai)點(dian)(dian)蝕(shi)(shi)(shi)性(xing)能(neng)(neng)(neng)越(yue)(yue)好，從圖3.71e)可(ke)(ke)(ke)矩，不(bu)同(tong)(tong)海溶(rong)(rong)試(shi)樣的(de)(de)(de)(de)(de)PREN.都(dou)大(da)于PREN,,當(dang)固溶(rong)(rong)溫度(du)為1050℃時，PHEN,最(zui)(zui)(zui)大(da)，材(cai)料(liao)的(de)(de)(de)(de)(de)耐(nai)點(dian)(dian)蝕(shi)(shi)(shi)性(xing)能(neng)(neng)(neng)應最(zui)(zui)(zui)好。從圖3.11(a)、（b)可(ke)(ke)(ke)知(zhi)，1050℃固溶(rong)(rong)試(shi)樣的(de)(de)(de)(de)(de)點(dian)(dian)蝕(shi)(shi)(shi)電(dian)位(wei)最(zui)(zui)(zui)高(gao)，鈍化膜阻(zu)抗值(zhi)最(zui)(zui)(zui)大(da)，電(dian)荷轉移(yi)電(dian)阻(zu)值(zhi)最(zui)(zui)(zui)商；且(qie)從圖3.12(b)可(ke)(ke)(ke)見(jian)，1050℃固溶(rong)(rong)試(shi)樣的(de)(de)(de)(de)(de)點(dian)(dian)蝕(shi)(shi)(shi)坑尺寸最(zui)(zui)(zui)小，表現出最(zui)(zui)(zui)好的(de)(de)(de)(de)(de)耐(nai)點(dian)(dian)蝕(shi)(shi)(shi)性(xing)能(neng)(neng)(neng)。綜上(shang)可(ke)(ke)(ke)知(zhi)，雙相(xiang)(xiang)不(bu)銹鋼的(de)(de)(de)(de)(de)耐(nai)點(dian)(dian)蝕(shi)(shi)(shi)性(xing)能(neng)(neng)(neng)由(you) PREN 值(zhi)較小相(xiang)(xiang)決(jue)定的(de)(de)(de)(de)(de)理論是有實(shi)驗依據的(de)(de)(de)(de)(de)。

  從圖(tu)3.12(a)~(d)可(ke)見(jian)，在(zai)不(bu)同(tong)固溶狀態(tai)下，鐵(tie)素體(ti)相都更(geng)易(yi)發(fa)生(sheng)點蝕；而從圖(tu)3.7(e)可(ke)見(jian)，在(zai)不(bu)同(tong)固溶狀態(tai)下，PREN.都大于PREN,,鐵(tie)素體(ti)的耐點蝕性(xing)能應優于奧(ao)氏體(ti)相，可(ke)見(jian)兩者(zhe)存(cun)在(zai)矛盾。

  隨固(gu)(gu)(gu)(gu)溶(rong)(rong)溫(wen)度變(bian)化(hua)(hua)，雙相(xiang)(xiang)不(bu)(bu)銹鋼中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)鐵(tie)(tie)素(su)(su)(su)(su)(su)體和(he)奧氏體相(xiang)(xiang)的(de)(de)(de)(de)(de)(de)比(bi)例改變(bian)，且(qie)(qie)兩相(xiang)(xiang)形(xing)態(tai)(tai)也發(fa)生變(bian)化(hua)(hua)。Cr是鐵(tie)(tie)素(su)(su)(su)(su)(su)體形(xing)成(cheng)(cheng)元(yuan)素(su)(su)(su)(su)(su)，可提高材(cai)(cai)(cai)料(liao)(liao)的(de)(de)(de)(de)(de)(de)耐(nai)蝕(shi)性(xing)(xing)能；Mo是鐵(tie)(tie)素(su)(su)(su)(su)(su)體形(xing)成(cheng)(cheng)元(yuan)素(su)(su)(su)(su)(su)，可提高點(dian)蝕(shi)電(dian)位，降低腐(fu)(fu)蝕(shi)速率；Ni是奧氏體形(xing)成(cheng)(cheng)元(yuan)素(su)(su)(su)(su)(su)，可維持兩相(xiang)(xiang)平衡(heng)，提高耐(nai)蝕(shi)性(xing)(xing)能。并且(qie)(qie)材(cai)(cai)(cai)料(liao)(liao)中(zhong)(zhong)(zhong)存在(zai)一定量的(de)(de)(de)(de)(de)(de)N,其為奧氏體形(xing)成(cheng)(cheng)元(yuan)素(su)(su)(su)(su)(su)，提高局部(bu)腐(fu)(fu)蝕(shi)抗力。從(cong)圖3.7(a)~(c)可見(jian)，隨固(gu)(gu)(gu)(gu)溶(rong)(rong)溫(wen)度變(bian)化(hua)(hua)，兩相(xiang)(xiang)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo、Ni元(yuan)素(su)(su)(su)(su)(su)含量發(fa)生變(bian)化(hua)(hua)。由(you)于(yu)(yu)Cr、Mo、Ni元(yuan)素(su)(su)(su)(su)(su)之(zhi)間(jian)的(de)(de)(de)(de)(de)(de)腐(fu)(fu)蝕(shi)電(dian)位存在(zai)差(cha)異，勢必造成(cheng)(cheng)兩相(xiang)(xiang)之(zhi)間(jian)存在(zai)電(dian)化(hua)(hua)學差(cha)異，使腐(fu)(fu)蝕(shi)更易發(fa)生。從(cong)圖3.7(e)可知(zhi)，不(bu)(bu)同(tong)固(gu)(gu)(gu)(gu)溶(rong)(rong)狀態(tai)(tai)下材(cai)(cai)(cai)料(liao)(liao)的(de)(de)(de)(de)(de)(de)PREN,大(da)小(xiao)關(guan)系為1050℃>1000℃>1150℃>1100℃,因(yin)此根據前人的(de)(de)(de)(de)(de)(de)研究(jiu)，不(bu)(bu)同(tong)固(gu)(gu)(gu)(gu)溶(rong)(rong)態(tai)(tai)材(cai)(cai)(cai)料(liao)(liao)的(de)(de)(de)(de)(de)(de)耐(nai)點(dian)蝕(shi)性(xing)(xing)能優(you)劣關(guan)系應為：1050℃優(you)于(yu)(yu)1000℃優(you)于(yu)(yu)1150℃.當固(gu)(gu)(gu)(gu)溶(rong)(rong)溫(wen)度為1050℃時，PREN,值較大(da)，兩相(xiang)(xiang)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo、Ni元(yuan)素(su)(su)(su)(su)(su)含量差(cha)異最小(xiao)，材(cai)(cai)(cai)料(liao)(liao)的(de)(de)(de)(de)(de)(de)點(dian)蝕(shi)坑(keng)較小(xiao)，材(cai)(cai)(cai)料(liao)(liao)的(de)(de)(de)(de)(de)(de)耐(nai)點(dian)蝕(shi)性(xing)(xing)能最優(you)。1000℃固(gu)(gu)(gu)(gu)溶(rong)(rong)試(shi)樣的(de)(de)(de)(de)(de)(de)點(dian)蝕(shi)坑(keng)尺(chi)寸大(da)于(yu)(yu)1150℃固(gu)(gu)(gu)(gu)溶(rong)(rong)試(shi)樣的(de)(de)(de)(de)(de)(de)點(dian)蝕(shi)坑(keng)尺(chi)寸，因(yin)此，前者的(de)(de)(de)(de)(de)(de)耐(nai)點(dian)蝕(shi)性(xing)(xing)能劣于(yu)(yu)后者的(de)(de)(de)(de)(de)(de)耐(nai)點(dian)蝕(shi)性(xing)(xing)能。由(you)此可見(jian)，雙相(xiang)(xiang)不(bu)(bu)銹鋼中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)相(xiang)(xiang)腐(fu)(fu)蝕(shi)不(bu)(bu)能僅僅由(you)PREN值來解釋。由(you)圖3.7(a)~(c)可知(zhi)，1000℃固(gu)(gu)(gu)(gu)溶(rong)(rong)試(shi)樣的(de)(de)(de)(de)(de)(de)兩相(xiang)(xiang)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Cr、Mo、Ni元(yuan)素(su)(su)(su)(su)(su)含量差(cha)大(da)于(yu)(yu)1150℃固(gu)(gu)(gu)(gu)溶(rong)(rong)試(shi)樣的(de)(de)(de)(de)(de)(de)兩相(xiang)(xiang)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)Gr、Mo、Ni元(yuan)素(su)(su)(su)(su)(su)含量差(cha)，因(yin)此，雙相(xiang)(xiang)不(bu)(bu)銹鋼中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)相(xiang)(xiang)腐(fu)(fu)蝕(shi)還與兩相(xiang)(xiang)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)(de)元(yuan)素(su)(su)(su)(su)(su)分布有關(guan)，并且(qie)(qie)還需考(kao)慮到材(cai)(cai)(cai)料(liao)(liao)中(zhong)(zhong)(zhong)點(dian)蝕(shi)敏(min)感性(xing)(xing)較強的(de)(de)(de)(de)(de)(de)區域，如晶(jing)界和(he)相(xiang)(xiang)界。

  點蝕是一種局部腐蝕現象，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。

  影響雙相(xiang)不銹鋼相(xiang)腐蝕(shi)的(de)(de)因素(su)不僅包(bao)括PREN值(zhi)，還包(bao)括各相(xiang)中的(de)(de)元素(su)分(fen)布和兩相(xiang)比例，并且三者互(hu)相(xiang)影響、關系(xi)復雜(za)。因此，不能僅憑(ping)PREN值(zhi)的(de)(de)大(da)小來判(pan)斷耐點蝕(shi)能力，應(ying)該綜合考慮各因素(su)的(de)(de)影響。