根據(ju)相圖，多數合(he)金(jin)(jin)元素在(zai)(zai)固(gu)(gu)(gu)相中的(de)溶(rong)解度要(yao)低于液(ye)(ye)相，因此(ci)在(zai)(zai)凝(ning)(ning)(ning)固(gu)(gu)(gu)過(guo)(guo)(guo)程(cheng)(cheng)中溶(rong)質(zhi)原子不斷被排出到液(ye)(ye)相，這(zhe)種固(gu)(gu)(gu)液(ye)(ye)界(jie)面(mian)兩側溶(rong)質(zhi)濃(nong)度的(de)差(cha)異(yi)導致合(he)金(jin)(jin)凝(ning)(ning)(ning)固(gu)(gu)(gu)后(hou)溶(rong)質(zhi)元素成(cheng)(cheng)(cheng)(cheng)(cheng)分不均(jun)勻(yun)性(xing)，稱作(zuo)偏(pian)(pian)析(xi)。溶(rong)質(zhi)元素分布不均(jun)勻(yun)性(xing)發生(sheng)在(zai)(zai)微(wei)觀(guan)結構形成(cheng)(cheng)(cheng)(cheng)(cheng)范圍內（有10~100μm的(de)樹(shu)狀枝晶），此(ci)時為(wei)微(wei)觀(guan)偏(pian)(pian)析(xi)。溶(rong)質(zhi)元素通(tong)過(guo)(guo)(guo)對(dui)(dui)流(liu)傳質(zhi)等(deng)(deng)質(zhi)量傳輸，將導致大范圍內成(cheng)(cheng)(cheng)(cheng)(cheng)分不均(jun)勻(yun)性(xing)，即形成(cheng)(cheng)(cheng)(cheng)(cheng)了宏觀(guan)偏(pian)(pian)析(xi)。宏觀(guan)偏(pian)(pian)析(xi)可以認為(wei)是(shi)由凝(ning)(ning)(ning)固(gu)(gu)(gu)過(guo)(guo)(guo)程(cheng)(cheng)中液(ye)(ye)體(ti)和固(gu)(gu)(gu)體(ti)相對(dui)(dui)運動和溶(rong)質(zhi)再分配過(guo)(guo)(guo)程(cheng)(cheng)共同(tong)導致的(de)。此(ci)外(wai)，在(zai)(zai)凝(ning)(ning)(ning)固(gu)(gu)(gu)早期所形成(cheng)(cheng)(cheng)(cheng)(cheng)的(de)固(gu)(gu)(gu)體(ti)相或非金(jin)(jin)屬夾雜的(de)漂(piao)浮和下沉也會造(zao)成(cheng)(cheng)(cheng)(cheng)(cheng)宏觀(guan)偏(pian)(pian)析(xi)。一(yi)般認為(wei)在(zai)(zai)合(he)金(jin)(jin)鑄(zhu)件或鑄(zhu)錠內，從幾毫米到幾厘米甚(shen)至幾米范圍內濃(nong)度變化為(wei)宏觀(guan)偏(pian)(pian)析(xi)。因為(wei)溶(rong)質(zhi)在(zai)(zai)固(gu)(gu)(gu)態中的(de)擴散系數很低，而成(cheng)(cheng)(cheng)(cheng)(cheng)分不均(jun)勻(yun)性(xing)范圍又很大，所以在(zai)(zai)凝(ning)(ning)(ning)固(gu)(gu)(gu)完成(cheng)(cheng)(cheng)(cheng)(cheng)后(hou)，宏觀(guan)偏(pian)(pian)析(xi)很難通(tong)過(guo)(guo)(guo)加工處理來(lai)消除(chu)，因此(ci)抑制(zhi)宏觀(guan)偏(pian)(pian)析(xi)的(de)產生(sheng)主(zhu)要(yao)是(shi)對(dui)(dui)工藝參數進行優(you)(you)化，如控制(zhi)合(he)金(jin)(jin)成(cheng)(cheng)(cheng)(cheng)(cheng)分、施(shi)加外(wai)力(li)場（磁場等(deng)(deng)）、優(you)(you)化鑄(zhu)錠幾何形狀、適當加大冷卻速率等(deng)(deng)。

  宏觀(guan)偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)是大范圍內(nei)的(de)(de)(de)(de)(de)(de)(de)(de)(de)成(cheng)分(fen)不均勻(yun)現(xian)象，按其(qi)表現(xian)形(xing)(xing)式(shi)可分(fen)為(wei)正(zheng)偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)、反偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)和比重偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)等。①. 正(zheng)偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)：對(dui)平(ping)衡(heng)分(fen)配系數o<1的(de)(de)(de)(de)(de)(de)(de)(de)(de)合(he)金(jin)(jin)系鑄(zhu)錠(ding)先凝(ning)固(gu)(gu)的(de)(de)(de)(de)(de)(de)(de)(de)(de)部(bu)分(fen)，其(qi)溶(rong)質含(han)量低(di)于(yu)(yu)后(hou)凝(ning)固(gu)(gu)的(de)(de)(de)(de)(de)(de)(de)(de)(de)部(bu)分(fen)。對(dui)ko>1的(de)(de)(de)(de)(de)(de)(de)(de)(de)合(he)金(jin)(jin)系則正(zheng)好相(xiang)反，其(qi)偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)程(cheng)度(du)與凝(ning)固(gu)(gu)速率、液(ye)體對(dui)流(liu)(liu)(liu)以(yi)及溶(rong)質擴散等條件有關。②. 反偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)：在(zai)ko<1的(de)(de)(de)(de)(de)(de)(de)(de)(de)合(he)金(jin)(jin)鑄(zhu)錠(ding)中(zhong)，其(qi)外(wai)層溶(rong)質元素高(gao)于(yu)(yu)內(nei)部(bu)，和正(zheng)偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)相(xiang)反，故稱為(wei)反偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)。③. 比重偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)：是由(you)(you)合(he)金(jin)(jin)凝(ning)固(gu)(gu)時(shi)形(xing)(xing)成(cheng)的(de)(de)(de)(de)(de)(de)(de)(de)(de)初(chu)晶(jing)相(xiang)和溶(rong)液(ye)之間的(de)(de)(de)(de)(de)(de)(de)(de)(de)比重顯著差別引(yin)起的(de)(de)(de)(de)(de)(de)(de)(de)(de)一(yi)種宏觀(guan)偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)，主要(yao)存在(zai)于(yu)(yu)共晶(jing)系和偏(pian)(pian)(pian)(pian)晶(jing)系合(he)金(jin)(jin)中(zhong)。如圖2-49所(suo)示，由(you)(you)于(yu)(yu)溶(rong)質元素濃度(du)相(xiang)對(dui)低(di)的(de)(de)(de)(de)(de)(de)(de)(de)(de)等軸(zhou)晶(jing)沉積導致(zhi)在(zai)鑄(zhu)錠(ding)的(de)(de)(de)(de)(de)(de)(de)(de)(de)底部(bu)出現(xian)負偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)；由(you)(you)于(yu)(yu)浮(fu)力(li)和在(zai)凝(ning)固(gu)(gu)的(de)(de)(de)(de)(de)(de)(de)(de)(de)最后(hou)階段(duan)收縮所(suo)引(yin)起的(de)(de)(de)(de)(de)(de)(de)(de)(de)晶(jing)間流(liu)(liu)(liu)動，在(zai)頂部(bu)會出現(xian)很嚴重的(de)(de)(de)(de)(de)(de)(de)(de)(de)正(zheng)偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)（頂部(bu)偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)）。A型(xing)偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)是溶(rong)質富(fu)集(ji)(ji)的(de)(de)(de)(de)(de)(de)(de)(de)(de)等軸(zhou)晶(jing)帶，由(you)(you)溶(rong)質受(shou)浮(fu)力(li)作(zuo)用流(liu)(liu)(liu)動穿(chuan)過(guo)柱狀(zhuang)(zhuang)晶(jing)區，其(qi)方向與等溫線(xian)移動速度(du)方向一(yi)致(zhi)但速率更快所(suo)導致(zhi)。A型(xing)偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)形(xing)(xing)狀(zhuang)(zhuang)與流(liu)(liu)(liu)動類(lei)型(xing)有關。V型(xing)偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)位于(yu)(yu)鑄(zhu)錠(ding)中(zhong)心，源于(yu)(yu)中(zhong)心形(xing)(xing)成(cheng)等軸(zhou)晶(jing)區和容易斷(duan)裂的(de)(de)(de)(de)(de)(de)(de)(de)(de)連接疏松的(de)(de)(de)(de)(de)(de)(de)(de)(de)網狀(zhuang)(zhuang)物的(de)(de)(de)(de)(de)(de)(de)(de)(de)形(xing)(xing)成(cheng)，之后(hou)裂紋沿切應力(li)面展開為(wei)V型(xing)，并且(qie)充滿(man)了富(fu)集(ji)(ji)元素的(de)(de)(de)(de)(de)(de)(de)(de)(de)液(ye)相(xiang)。而沿鑄(zhu)錠(ding)側壁分(fen)布的(de)(de)(de)(de)(de)(de)(de)(de)(de)帶狀(zhuang)(zhuang)偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)則是由(you)(you)凝(ning)固(gu)(gu)過(guo)程(cheng)初(chu)期的(de)(de)(de)(de)(de)(de)(de)(de)(de)不穩定傳熱和流(liu)(liu)(liu)動導致(zhi)的(de)(de)(de)(de)(de)(de)(de)(de)(de)。

  對于宏觀偏(pian)(pian)析(xi)(xi)的(de)(de)研究(jiu)(jiu)(jiu)主(zhu)要有(you)實驗(yan)(yan)檢(jian)(jian)測(ce)和(he)模擬計算(suan)(suan)兩種(zhong)手段。實驗(yan)(yan)檢(jian)(jian)測(ce)包括(kuo)硫印檢(jian)(jian)驗(yan)(yan)法、原位分(fen)析(xi)(xi)法、火花放電(dian)原子(zi)發(fa)射光譜法、鉆(zhan)孔取樣法以(yi)及化學分(fen)析(xi)(xi)法等(deng)。模擬計算(suan)(suan)是通過數值求解能量(liang)(liang)、動量(liang)(liang)以(yi)及溶質(zhi)(zhi)傳(chuan)輸(shu)等(deng)數學模型(xing)，進(jin)而(er)(er)探(tan)討元素成分(fen)不均(jun)勻性(xing)的(de)(de)方(fang)法；進(jin)入20世紀后，人們對凝(ning)固(gu)過程中的(de)(de)宏觀偏(pian)(pian)析(xi)(xi)現象進(jin)行了大量(liang)(liang)系(xi)統的(de)(de)研究(jiu)(jiu)(jiu)。Flemings研究(jiu)(jiu)(jiu)表明鑄錠中多(duo)種(zhong)不同的(de)(de)宏觀偏(pian)(pian)析(xi)(xi)都可由凝(ning)固(gu)時的(de)(de)傳(chuan)熱(re)、流動和(he)傳(chuan)質(zhi)(zhi)過程來定(ding)量(liang)(liang)描述，從(cong)而(er)(er)為宏觀偏(pian)(pian)析(xi)(xi)的(de)(de)定(ding)量(liang)(liang)計算(suan)(suan)提(ti)供可能性(xing)，隨著計算(suan)(suan)機計算(suan)(suan)能力迅(xun)猛提(ti)升，宏觀偏(pian)(pian)析(xi)(xi)的(de)(de)模擬計算(suan)(suan)得到了迅(xun)速發(fa)展，主(zhu)要分(fen)為多(duo)區域(yu)法和(he)連續介(jie)質(zhi)(zhi)法等(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。