根(gen)據(ju)相(xiang)圖，多(duo)數合金(jin)元(yuan)(yuan)素在(zai)(zai)固(gu)(gu)(gu)(gu)(gu)(gu)相(xiang)中的(de)(de)溶(rong)解度要低(di)(di)于(yu)液(ye)相(xiang)，因(yin)(yin)此在(zai)(zai)凝(ning)(ning)固(gu)(gu)(gu)(gu)(gu)(gu)過(guo)程(cheng)中溶(rong)質(zhi)(zhi)(zhi)原子不(bu)(bu)斷被排(pai)出到液(ye)相(xiang)，這種固(gu)(gu)(gu)(gu)(gu)(gu)液(ye)界面兩側(ce)溶(rong)質(zhi)(zhi)(zhi)濃(nong)度的(de)(de)差(cha)異導致(zhi)(zhi)合金(jin)凝(ning)(ning)固(gu)(gu)(gu)(gu)(gu)(gu)后溶(rong)質(zhi)(zhi)(zhi)元(yuan)(yuan)素成(cheng)分(fen)(fen)不(bu)(bu)均(jun)(jun)勻性(xing)，稱作偏(pian)(pian)析(xi)(xi)。溶(rong)質(zhi)(zhi)(zhi)元(yuan)(yuan)素分(fen)(fen)布不(bu)(bu)均(jun)(jun)勻性(xing)發(fa)生(sheng)(sheng)在(zai)(zai)微觀(guan)(guan)結(jie)構形成(cheng)范圍(wei)(wei)內(nei)（有10~100μm的(de)(de)樹(shu)狀(zhuang)枝晶(jing)），此時(shi)為(wei)微觀(guan)(guan)偏(pian)(pian)析(xi)(xi)。溶(rong)質(zhi)(zhi)(zhi)元(yuan)(yuan)素通(tong)過(guo)對(dui)流傳(chuan)質(zhi)(zhi)(zhi)等質(zhi)(zhi)(zhi)量傳(chuan)輸，將導致(zhi)(zhi)大(da)范圍(wei)(wei)內(nei)成(cheng)分(fen)(fen)不(bu)(bu)均(jun)(jun)勻性(xing)，即形成(cheng)了宏觀(guan)(guan)偏(pian)(pian)析(xi)(xi)。宏觀(guan)(guan)偏(pian)(pian)析(xi)(xi)可以認為(wei)是由凝(ning)(ning)固(gu)(gu)(gu)(gu)(gu)(gu)過(guo)程(cheng)中液(ye)體和固(gu)(gu)(gu)(gu)(gu)(gu)體相(xiang)對(dui)運動(dong)和溶(rong)質(zhi)(zhi)(zhi)再分(fen)(fen)配過(guo)程(cheng)共同導致(zhi)(zhi)的(de)(de)。此外(wai)(wai)，在(zai)(zai)凝(ning)(ning)固(gu)(gu)(gu)(gu)(gu)(gu)早期所(suo)形成(cheng)的(de)(de)固(gu)(gu)(gu)(gu)(gu)(gu)體相(xiang)或非金(jin)屬夾雜的(de)(de)漂浮(fu)和下沉(chen)也會造(zao)成(cheng)宏觀(guan)(guan)偏(pian)(pian)析(xi)(xi)。一般認為(wei)在(zai)(zai)合金(jin)鑄(zhu)件(jian)或鑄(zhu)錠內(nei)，從幾毫米到幾厘米甚至(zhi)幾米范圍(wei)(wei)內(nei)濃(nong)度變化(hua)為(wei)宏觀(guan)(guan)偏(pian)(pian)析(xi)(xi)。因(yin)(yin)為(wei)溶(rong)質(zhi)(zhi)(zhi)在(zai)(zai)固(gu)(gu)(gu)(gu)(gu)(gu)態中的(de)(de)擴(kuo)散(san)系數很(hen)(hen)低(di)(di)，而成(cheng)分(fen)(fen)不(bu)(bu)均(jun)(jun)勻性(xing)范圍(wei)(wei)又(you)很(hen)(hen)大(da)，所(suo)以在(zai)(zai)凝(ning)(ning)固(gu)(gu)(gu)(gu)(gu)(gu)完成(cheng)后，宏觀(guan)(guan)偏(pian)(pian)析(xi)(xi)很(hen)(hen)難通(tong)過(guo)加工處理來消除，因(yin)(yin)此抑(yi)制宏觀(guan)(guan)偏(pian)(pian)析(xi)(xi)的(de)(de)產生(sheng)(sheng)主要是對(dui)工藝參數進行優化(hua)，如控制合金(jin)成(cheng)分(fen)(fen)、施加外(wai)(wai)力場（磁場等）、優化(hua)鑄(zhu)錠幾何形狀(zhuang)、適當加大(da)冷卻(que)速率(lv)等。

  宏觀偏(pian)(pian)析(xi)(xi)是(shi)(shi)大范圍內的(de)(de)(de)(de)(de)(de)(de)成(cheng)(cheng)分不均(jun)勻現象，按(an)其表現形(xing)(xing)式可分為(wei)正偏(pian)(pian)析(xi)(xi)、反偏(pian)(pian)析(xi)(xi)和(he)(he)比(bi)重(zhong)(zhong)偏(pian)(pian)析(xi)(xi)等(deng)(deng)。①. 正偏(pian)(pian)析(xi)(xi)：對(dui)平衡(heng)分配系(xi)(xi)數o<1的(de)(de)(de)(de)(de)(de)(de)合金(jin)系(xi)(xi)鑄(zhu)(zhu)(zhu)錠(ding)先(xian)凝(ning)(ning)固的(de)(de)(de)(de)(de)(de)(de)部分，其溶(rong)質(zhi)(zhi)含(han)量低于(yu)后凝(ning)(ning)固的(de)(de)(de)(de)(de)(de)(de)部分。對(dui)ko>1的(de)(de)(de)(de)(de)(de)(de)合金(jin)系(xi)(xi)則正好相(xiang)反，其偏(pian)(pian)析(xi)(xi)程度與(yu)凝(ning)(ning)固速率(lv)、液體對(dui)流(liu)以及溶(rong)質(zhi)(zhi)擴(kuo)散等(deng)(deng)條件有(you)關(guan)。②. 反偏(pian)(pian)析(xi)(xi)：在(zai)ko<1的(de)(de)(de)(de)(de)(de)(de)合金(jin)鑄(zhu)(zhu)(zhu)錠(ding)中，其外(wai)層溶(rong)質(zhi)(zhi)元素高于(yu)內部，和(he)(he)正偏(pian)(pian)析(xi)(xi)相(xiang)反，故稱為(wei)反偏(pian)(pian)析(xi)(xi)。③. 比(bi)重(zhong)(zhong)偏(pian)(pian)析(xi)(xi)：是(shi)(shi)由(you)合金(jin)凝(ning)(ning)固時形(xing)(xing)成(cheng)(cheng)的(de)(de)(de)(de)(de)(de)(de)初晶相(xiang)和(he)(he)溶(rong)液之(zhi)間的(de)(de)(de)(de)(de)(de)(de)比(bi)重(zhong)(zhong)顯著差(cha)別引(yin)(yin)起的(de)(de)(de)(de)(de)(de)(de)一種宏觀偏(pian)(pian)析(xi)(xi)，主要存在(zai)于(yu)共晶系(xi)(xi)和(he)(he)偏(pian)(pian)晶系(xi)(xi)合金(jin)中。如圖2-49所(suo)示，由(you)于(yu)溶(rong)質(zhi)(zhi)元素濃度相(xiang)對(dui)低的(de)(de)(de)(de)(de)(de)(de)等(deng)(deng)軸(zhou)晶沉積(ji)導致(zhi)(zhi)在(zai)鑄(zhu)(zhu)(zhu)錠(ding)的(de)(de)(de)(de)(de)(de)(de)底部出(chu)(chu)現負偏(pian)(pian)析(xi)(xi)；由(you)于(yu)浮力(li)和(he)(he)在(zai)凝(ning)(ning)固的(de)(de)(de)(de)(de)(de)(de)最(zui)后階(jie)段收縮所(suo)引(yin)(yin)起的(de)(de)(de)(de)(de)(de)(de)晶間流(liu)動(dong)(dong)(dong)，在(zai)頂(ding)部會出(chu)(chu)現很嚴重(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)正偏(pian)(pian)析(xi)(xi)（頂(ding)部偏(pian)(pian)析(xi)(xi)）。A型偏(pian)(pian)析(xi)(xi)是(shi)(shi)溶(rong)質(zhi)(zhi)富(fu)集(ji)的(de)(de)(de)(de)(de)(de)(de)等(deng)(deng)軸(zhou)晶帶，由(you)溶(rong)質(zhi)(zhi)受浮力(li)作(zuo)用流(liu)動(dong)(dong)(dong)穿過柱狀晶區，其方向與(yu)等(deng)(deng)溫線(xian)移動(dong)(dong)(dong)速度方向一致(zhi)(zhi)但速率(lv)更快所(suo)導致(zhi)(zhi)。A型偏(pian)(pian)析(xi)(xi)形(xing)(xing)狀與(yu)流(liu)動(dong)(dong)(dong)類型有(you)關(guan)。V型偏(pian)(pian)析(xi)(xi)位于(yu)鑄(zhu)(zhu)(zhu)錠(ding)中心，源于(yu)中心形(xing)(xing)成(cheng)(cheng)等(deng)(deng)軸(zhou)晶區和(he)(he)容易斷裂的(de)(de)(de)(de)(de)(de)(de)連接疏松(song)的(de)(de)(de)(de)(de)(de)(de)網狀物的(de)(de)(de)(de)(de)(de)(de)形(xing)(xing)成(cheng)(cheng)，之(zhi)后裂紋沿(yan)切應力(li)面展開為(wei)V型，并且充(chong)滿了富(fu)集(ji)元素的(de)(de)(de)(de)(de)(de)(de)液相(xiang)。而沿(yan)鑄(zhu)(zhu)(zhu)錠(ding)側(ce)壁分布的(de)(de)(de)(de)(de)(de)(de)帶狀偏(pian)(pian)析(xi)(xi)則是(shi)(shi)由(you)凝(ning)(ning)固過程初期的(de)(de)(de)(de)(de)(de)(de)不穩定傳(chuan)熱(re)和(he)(he)流(liu)動(dong)(dong)(dong)導致(zhi)(zhi)的(de)(de)(de)(de)(de)(de)(de)。

  對于宏觀偏析(xi)(xi)的(de)(de)研究主要(yao)(yao)有實驗(yan)(yan)檢測和模(mo)(mo)擬(ni)計算(suan)兩種手段。實驗(yan)(yan)檢測包括硫印檢驗(yan)(yan)法(fa)、原位分(fen)(fen)析(xi)(xi)法(fa)、火(huo)花放電(dian)原子(zi)發射光譜法(fa)、鉆孔取樣(yang)法(fa)以及化學(xue)(xue)分(fen)(fen)析(xi)(xi)法(fa)等(deng)。模(mo)(mo)擬(ni)計算(suan)是通過數(shu)(shu)值求解能量(liang)、動量(liang)以及溶質(zhi)傳(chuan)(chuan)輸等(deng)數(shu)(shu)學(xue)(xue)模(mo)(mo)型，進(jin)而探討元(yuan)素成(cheng)分(fen)(fen)不均勻(yun)性(xing)(xing)的(de)(de)方法(fa)；進(jin)入20世紀(ji)后，人們(men)對凝固(gu)過程(cheng)(cheng)中的(de)(de)宏觀偏析(xi)(xi)現象進(jin)行了大量(liang)系統的(de)(de)研究。Flemings研究表明(ming)鑄錠(ding)中多(duo)種不同(tong)的(de)(de)宏觀偏析(xi)(xi)都可由凝固(gu)時的(de)(de)傳(chuan)(chuan)熱、流動和傳(chuan)(chuan)質(zhi)過程(cheng)(cheng)來定(ding)(ding)量(liang)描述，從而為宏觀偏析(xi)(xi)的(de)(de)定(ding)(ding)量(liang)計算(suan)提(ti)供(gong)可能性(xing)(xing)，隨(sui)著計算(suan)機計算(suan)能力迅猛提(ti)升，宏觀偏析(xi)(xi)的(de)(de)模(mo)(mo)擬(ni)計算(suan)得(de)到了迅速發展，主要(yao)(yao)分(fen)(fen)為多(duo)區域法(fa)和連續(xu)介質(zhi)法(fa)等(deng)。

  對于高氮不(bu)銹鋼，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。