根據相(xiang)(xiang)(xiang)(xiang)圖，多數(shu)合金(jin)(jin)(jin)(jin)元(yuan)(yuan)素(su)在(zai)固(gu)(gu)(gu)相(xiang)(xiang)(xiang)(xiang)中的溶(rong)(rong)解(jie)度要低(di)于液(ye)(ye)相(xiang)(xiang)(xiang)(xiang)，因(yin)(yin)此在(zai)凝固(gu)(gu)(gu)過程(cheng)中溶(rong)(rong)質原子不(bu)(bu)斷被排出到液(ye)(ye)相(xiang)(xiang)(xiang)(xiang)，這種固(gu)(gu)(gu)液(ye)(ye)界面兩側溶(rong)(rong)質濃度的差(cha)異導(dao)致(zhi)合金(jin)(jin)(jin)(jin)凝固(gu)(gu)(gu)后溶(rong)(rong)質元(yuan)(yuan)素(su)成(cheng)(cheng)(cheng)分(fen)(fen)不(bu)(bu)均(jun)勻性(xing)，稱作偏(pian)(pian)(pian)析(xi)。溶(rong)(rong)質元(yuan)(yuan)素(su)分(fen)(fen)布不(bu)(bu)均(jun)勻性(xing)發生在(zai)微觀(guan)(guan)結(jie)構形(xing)成(cheng)(cheng)(cheng)范圍(wei)內（有(you)10~100μm的樹狀枝晶），此時為(wei)微觀(guan)(guan)偏(pian)(pian)(pian)析(xi)。溶(rong)(rong)質元(yuan)(yuan)素(su)通(tong)過對(dui)流傳質等質量傳輸，將導(dao)致(zhi)大(da)范圍(wei)內成(cheng)(cheng)(cheng)分(fen)(fen)不(bu)(bu)均(jun)勻性(xing)，即形(xing)成(cheng)(cheng)(cheng)了宏(hong)觀(guan)(guan)偏(pian)(pian)(pian)析(xi)。宏(hong)觀(guan)(guan)偏(pian)(pian)(pian)析(xi)可(ke)以認(ren)為(wei)是(shi)由(you)凝固(gu)(gu)(gu)過程(cheng)中液(ye)(ye)體和固(gu)(gu)(gu)體相(xiang)(xiang)(xiang)(xiang)對(dui)運動和溶(rong)(rong)質再(zai)分(fen)(fen)配過程(cheng)共同導(dao)致(zhi)的。此外，在(zai)凝固(gu)(gu)(gu)早期所形(xing)成(cheng)(cheng)(cheng)的固(gu)(gu)(gu)體相(xiang)(xiang)(xiang)(xiang)或非金(jin)(jin)(jin)(jin)屬夾雜的漂浮和下沉也會造成(cheng)(cheng)(cheng)宏(hong)觀(guan)(guan)偏(pian)(pian)(pian)析(xi)。一般認(ren)為(wei)在(zai)合金(jin)(jin)(jin)(jin)鑄(zhu)件或鑄(zhu)錠(ding)內，從幾(ji)毫米到幾(ji)厘米甚(shen)至(zhi)幾(ji)米范圍(wei)內濃度變(bian)化為(wei)宏(hong)觀(guan)(guan)偏(pian)(pian)(pian)析(xi)。因(yin)(yin)為(wei)溶(rong)(rong)質在(zai)固(gu)(gu)(gu)態中的擴(kuo)散(san)系數(shu)很(hen)低(di)，而成(cheng)(cheng)(cheng)分(fen)(fen)不(bu)(bu)均(jun)勻性(xing)范圍(wei)又很(hen)大(da)，所以在(zai)凝固(gu)(gu)(gu)完成(cheng)(cheng)(cheng)后，宏(hong)觀(guan)(guan)偏(pian)(pian)(pian)析(xi)很(hen)難通(tong)過加(jia)工(gong)處(chu)理來消除，因(yin)(yin)此抑制宏(hong)觀(guan)(guan)偏(pian)(pian)(pian)析(xi)的產生主要是(shi)對(dui)工(gong)藝參數(shu)進行優化，如控制合金(jin)(jin)(jin)(jin)成(cheng)(cheng)(cheng)分(fen)(fen)、施加(jia)外力場(chang)（磁場(chang)等）、優化鑄(zhu)錠(ding)幾(ji)何形(xing)狀、適當加(jia)大(da)冷卻(que)速率等。

  宏觀(guan)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)(xi)是(shi)大(da)范(fan)圍內的(de)(de)(de)(de)(de)成分(fen)不均(jun)勻現象，按其(qi)(qi)(qi)表現形式可分(fen)為(wei)正(zheng)(zheng)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)(xi)、反偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)(xi)和(he)(he)比(bi)重偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)(xi)等(deng)。①. 正(zheng)(zheng)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)(xi)：對(dui)(dui)平衡分(fen)配(pei)系(xi)數o<1的(de)(de)(de)(de)(de)合金系(xi)鑄(zhu)(zhu)錠(ding)(ding)(ding)先凝固的(de)(de)(de)(de)(de)部分(fen)，其(qi)(qi)(qi)溶(rong)(rong)質(zhi)(zhi)含量低于(yu)(yu)(yu)后(hou)凝固的(de)(de)(de)(de)(de)部分(fen)。對(dui)(dui)ko>1的(de)(de)(de)(de)(de)合金系(xi)則(ze)(ze)正(zheng)(zheng)好相反，其(qi)(qi)(qi)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)(xi)程度與凝固速率、液體(ti)對(dui)(dui)流以及溶(rong)(rong)質(zhi)(zhi)擴(kuo)散(san)等(deng)條件有關(guan)。②. 反偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)(xi)：在(zai)ko<1的(de)(de)(de)(de)(de)合金鑄(zhu)(zhu)錠(ding)(ding)(ding)中(zhong)，其(qi)(qi)(qi)外層溶(rong)(rong)質(zhi)(zhi)元(yuan)(yuan)素高于(yu)(yu)(yu)內部，和(he)(he)正(zheng)(zheng)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)(xi)相反，故稱為(wei)反偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)(xi)。③. 比(bi)重偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)(xi)：是(shi)由(you)合金凝固時形成的(de)(de)(de)(de)(de)初晶(jing)(jing)(jing)相和(he)(he)溶(rong)(rong)液之(zhi)(zhi)間的(de)(de)(de)(de)(de)比(bi)重顯著差別引起的(de)(de)(de)(de)(de)一種(zhong)宏觀(guan)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)(xi)，主要存在(zai)于(yu)(yu)(yu)共晶(jing)(jing)(jing)系(xi)和(he)(he)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)(pian)晶(jing)(jing)(jing)系(xi)合金中(zhong)。如圖2-49所示，由(you)于(yu)(yu)(yu)溶(rong)(rong)質(zhi)(zhi)元(yuan)(yuan)素濃(nong)度相對(dui)(dui)低的(de)(de)(de)(de)(de)等(deng)軸晶(jing)(jing)(jing)沉積導(dao)致在(zai)鑄(zhu)(zhu)錠(ding)(ding)(ding)的(de)(de)(de)(de)(de)底(di)部出現負(fu)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)(xi)；由(you)于(yu)(yu)(yu)浮(fu)力和(he)(he)在(zai)凝固的(de)(de)(de)(de)(de)最后(hou)階段(duan)收(shou)縮所引起的(de)(de)(de)(de)(de)晶(jing)(jing)(jing)間流動(dong)，在(zai)頂(ding)部會出現很(hen)嚴重的(de)(de)(de)(de)(de)正(zheng)(zheng)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)(xi)（頂(ding)部偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)(xi)）。A型(xing)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)(xi)是(shi)溶(rong)(rong)質(zhi)(zhi)富集的(de)(de)(de)(de)(de)等(deng)軸晶(jing)(jing)(jing)帶，由(you)溶(rong)(rong)質(zhi)(zhi)受浮(fu)力作(zuo)用(yong)流動(dong)穿過(guo)柱狀(zhuang)晶(jing)(jing)(jing)區(qu)(qu)，其(qi)(qi)(qi)方向(xiang)與等(deng)溫線移動(dong)速度方向(xiang)一致但(dan)速率更(geng)快所導(dao)致。A型(xing)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)(xi)形狀(zhuang)與流動(dong)類型(xing)有關(guan)。V型(xing)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)(xi)位于(yu)(yu)(yu)鑄(zhu)(zhu)錠(ding)(ding)(ding)中(zhong)心(xin)，源(yuan)于(yu)(yu)(yu)中(zhong)心(xin)形成等(deng)軸晶(jing)(jing)(jing)區(qu)(qu)和(he)(he)容(rong)易斷(duan)裂的(de)(de)(de)(de)(de)連接疏松的(de)(de)(de)(de)(de)網狀(zhuang)物(wu)的(de)(de)(de)(de)(de)形成，之(zhi)(zhi)后(hou)裂紋沿切應力面展開為(wei)V型(xing)，并且充滿了富集元(yuan)(yuan)素的(de)(de)(de)(de)(de)液相。而沿鑄(zhu)(zhu)錠(ding)(ding)(ding)側(ce)壁分(fen)布的(de)(de)(de)(de)(de)帶狀(zhuang)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)(xi)則(ze)(ze)是(shi)由(you)凝固過(guo)程初期的(de)(de)(de)(de)(de)不穩定(ding)傳熱(re)和(he)(he)流動(dong)導(dao)致的(de)(de)(de)(de)(de)。

  對(dui)于宏觀偏(pian)(pian)析的(de)(de)(de)研究主(zhu)(zhu)要有實驗(yan)檢測和模(mo)(mo)擬(ni)計(ji)(ji)算(suan)兩種手段。實驗(yan)檢測包括硫印檢驗(yan)法(fa)(fa)(fa)(fa)、原(yuan)(yuan)位分析法(fa)(fa)(fa)(fa)、火花放電原(yuan)(yuan)子發射光譜法(fa)(fa)(fa)(fa)、鉆孔(kong)取樣法(fa)(fa)(fa)(fa)以及化學分析法(fa)(fa)(fa)(fa)等(deng)。模(mo)(mo)擬(ni)計(ji)(ji)算(suan)是通過(guo)數值求解能(neng)量(liang)(liang)、動(dong)量(liang)(liang)以及溶質傳輸等(deng)數學模(mo)(mo)型(xing)，進而(er)探討元(yuan)素成分不均勻性的(de)(de)(de)方法(fa)(fa)(fa)(fa)；進入(ru)20世紀(ji)后(hou)，人們對(dui)凝(ning)固過(guo)程(cheng)中的(de)(de)(de)宏觀偏(pian)(pian)析現(xian)象進行(xing)了大(da)量(liang)(liang)系統的(de)(de)(de)研究。Flemings研究表(biao)明鑄(zhu)錠中多種不同的(de)(de)(de)宏觀偏(pian)(pian)析都(dou)可(ke)由凝(ning)固時的(de)(de)(de)傳熱、流(liu)動(dong)和傳質過(guo)程(cheng)來定量(liang)(liang)描述，從而(er)為宏觀偏(pian)(pian)析的(de)(de)(de)定量(liang)(liang)計(ji)(ji)算(suan)提供可(ke)能(neng)性，隨著計(ji)(ji)算(suan)機計(ji)(ji)算(suan)能(neng)力迅(xun)猛提升(sheng)，宏觀偏(pian)(pian)析的(de)(de)(de)模(mo)(mo)擬(ni)計(ji)(ji)算(suan)得到了迅(xun)速發展，主(zhu)(zhu)要分為多區域法(fa)(fa)(fa)(fa)和連續(xu)介質法(fa)(fa)(fa)(fa)等(deng)。

  對于高氮不銹(xiu)鋼(gang)，改善氮偏析以及消除氣孔等凝固缺陷，優化制備工藝制度，是高氮奧氏體不銹鋼制備技術中亟待解決的難題之一。氮作為重要合金元素之一，其偏析程度對材料強度、韌性、抗蠕變性、耐磨性和耐腐蝕等性能的均勻性至關重要，直接影響材料的服役壽命。與高氮不銹鋼中鉻、錳等其他元素相比，氮的分配系數較小，氮偏析嚴重，易形成氮氣泡，凝固末了殘留在鑄錠中形成氮氣孔等凝固缺陷，甚至導致材料直接報廢，因此氮偏析的控制對高氮不銹鋼制備而言至關重要。不同壓力和不同初始氮含量下21.5Cr5Mn1.5Ni0.25N含氮雙相鋼中氮偏析導致氮氣孔的形貌如圖2-50所示，其中D1、D3和D5分別在0.04MPa、0.1MPa和0.13MPa下完成凝固，不同氮質量分數的D2(0.25%N)、D3(0.26%N)和D4(0.29%N)均在0.1MPa下凝固。