根據相圖，多數(shu)合金(jin)(jin)元(yuan)(yuan)素在(zai)固(gu)(gu)(gu)相中(zhong)的溶(rong)(rong)(rong)解度(du)要低(di)于液相，因此(ci)在(zai)凝固(gu)(gu)(gu)過(guo)(guo)程中(zhong)溶(rong)(rong)(rong)質(zhi)(zhi)原子不(bu)斷被排出到液相，這種固(gu)(gu)(gu)液界面兩側溶(rong)(rong)(rong)質(zhi)(zhi)濃(nong)(nong)度(du)的差異導致合金(jin)(jin)凝固(gu)(gu)(gu)后溶(rong)(rong)(rong)質(zhi)(zhi)元(yuan)(yuan)素成(cheng)分(fen)不(bu)均(jun)勻性(xing)，稱作偏(pian)(pian)(pian)析(xi)(xi)(xi)。溶(rong)(rong)(rong)質(zhi)(zhi)元(yuan)(yuan)素分(fen)布不(bu)均(jun)勻性(xing)發生在(zai)微(wei)觀(guan)(guan)結構形(xing)(xing)(xing)成(cheng)范(fan)圍(wei)(wei)(wei)內（有10~100μm的樹狀(zhuang)枝晶），此(ci)時(shi)為微(wei)觀(guan)(guan)偏(pian)(pian)(pian)析(xi)(xi)(xi)。溶(rong)(rong)(rong)質(zhi)(zhi)元(yuan)(yuan)素通過(guo)(guo)對流傳(chuan)質(zhi)(zhi)等質(zhi)(zhi)量傳(chuan)輸，將導致大范(fan)圍(wei)(wei)(wei)內成(cheng)分(fen)不(bu)均(jun)勻性(xing)，即(ji)形(xing)(xing)(xing)成(cheng)了宏觀(guan)(guan)偏(pian)(pian)(pian)析(xi)(xi)(xi)。宏觀(guan)(guan)偏(pian)(pian)(pian)析(xi)(xi)(xi)可以認(ren)為是(shi)由凝固(gu)(gu)(gu)過(guo)(guo)程中(zhong)液體和(he)固(gu)(gu)(gu)體相對運動和(he)溶(rong)(rong)(rong)質(zhi)(zhi)再分(fen)配過(guo)(guo)程共同導致的。此(ci)外，在(zai)凝固(gu)(gu)(gu)早期所(suo)形(xing)(xing)(xing)成(cheng)的固(gu)(gu)(gu)體相或非金(jin)(jin)屬夾雜的漂浮和(he)下沉也會造成(cheng)宏觀(guan)(guan)偏(pian)(pian)(pian)析(xi)(xi)(xi)。一般認(ren)為在(zai)合金(jin)(jin)鑄件或鑄錠(ding)內，從幾毫米(mi)到幾厘米(mi)甚至(zhi)幾米(mi)范(fan)圍(wei)(wei)(wei)內濃(nong)(nong)度(du)變化為宏觀(guan)(guan)偏(pian)(pian)(pian)析(xi)(xi)(xi)。因為溶(rong)(rong)(rong)質(zhi)(zhi)在(zai)固(gu)(gu)(gu)態中(zhong)的擴散系數(shu)很低(di)，而成(cheng)分(fen)不(bu)均(jun)勻性(xing)范(fan)圍(wei)(wei)(wei)又很大，所(suo)以在(zai)凝固(gu)(gu)(gu)完(wan)成(cheng)后，宏觀(guan)(guan)偏(pian)(pian)(pian)析(xi)(xi)(xi)很難通過(guo)(guo)加工處理來消除，因此(ci)抑制(zhi)宏觀(guan)(guan)偏(pian)(pian)(pian)析(xi)(xi)(xi)的產生主要是(shi)對工藝參數(shu)進(jin)行(xing)優(you)化，如控制(zhi)合金(jin)(jin)成(cheng)分(fen)、施加外力場（磁場等）、優(you)化鑄錠(ding)幾何形(xing)(xing)(xing)狀(zhuang)、適當加大冷卻(que)速率等。

  宏(hong)觀(guan)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)是大范圍內(nei)的(de)(de)(de)(de)(de)(de)(de)成(cheng)分(fen)不(bu)均勻現象，按其(qi)(qi)表現形(xing)式可分(fen)為(wei)正(zheng)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)、反(fan)(fan)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)和(he)(he)比重(zhong)(zhong)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)等(deng)。①. 正(zheng)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)：對(dui)平衡(heng)分(fen)配系(xi)數(shu)o<1的(de)(de)(de)(de)(de)(de)(de)合(he)金(jin)系(xi)鑄(zhu)(zhu)錠(ding)先凝(ning)(ning)固(gu)(gu)的(de)(de)(de)(de)(de)(de)(de)部(bu)(bu)分(fen)，其(qi)(qi)溶(rong)(rong)質含量低(di)于(yu)后凝(ning)(ning)固(gu)(gu)的(de)(de)(de)(de)(de)(de)(de)部(bu)(bu)分(fen)。對(dui)ko>1的(de)(de)(de)(de)(de)(de)(de)合(he)金(jin)系(xi)則(ze)正(zheng)好相(xiang)反(fan)(fan)，其(qi)(qi)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)程度(du)與凝(ning)(ning)固(gu)(gu)速率、液(ye)體對(dui)流以(yi)及溶(rong)(rong)質擴散等(deng)條件有(you)關(guan)。②. 反(fan)(fan)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)：在ko<1的(de)(de)(de)(de)(de)(de)(de)合(he)金(jin)鑄(zhu)(zhu)錠(ding)中(zhong)，其(qi)(qi)外層溶(rong)(rong)質元(yuan)素高于(yu)內(nei)部(bu)(bu)，和(he)(he)正(zheng)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)相(xiang)反(fan)(fan)，故稱(cheng)為(wei)反(fan)(fan)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)。③. 比重(zhong)(zhong)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)：是由(you)合(he)金(jin)凝(ning)(ning)固(gu)(gu)時形(xing)成(cheng)的(de)(de)(de)(de)(de)(de)(de)初(chu)晶(jing)相(xiang)和(he)(he)溶(rong)(rong)液(ye)之間的(de)(de)(de)(de)(de)(de)(de)比重(zhong)(zhong)顯著差(cha)別引(yin)(yin)起(qi)的(de)(de)(de)(de)(de)(de)(de)一種(zhong)宏(hong)觀(guan)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)，主要存在于(yu)共晶(jing)系(xi)和(he)(he)偏(pian)(pian)(pian)(pian)(pian)晶(jing)系(xi)合(he)金(jin)中(zhong)。如圖2-49所(suo)示，由(you)于(yu)溶(rong)(rong)質元(yuan)素濃度(du)相(xiang)對(dui)低(di)的(de)(de)(de)(de)(de)(de)(de)等(deng)軸晶(jing)沉積導致在鑄(zhu)(zhu)錠(ding)的(de)(de)(de)(de)(de)(de)(de)底部(bu)(bu)出(chu)現負(fu)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)；由(you)于(yu)浮(fu)力和(he)(he)在凝(ning)(ning)固(gu)(gu)的(de)(de)(de)(de)(de)(de)(de)最后階段收縮所(suo)引(yin)(yin)起(qi)的(de)(de)(de)(de)(de)(de)(de)晶(jing)間流動，在頂部(bu)(bu)會出(chu)現很嚴重(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)正(zheng)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)（頂部(bu)(bu)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)）。A型(xing)(xing)(xing)(xing)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)是溶(rong)(rong)質富集的(de)(de)(de)(de)(de)(de)(de)等(deng)軸晶(jing)帶，由(you)溶(rong)(rong)質受浮(fu)力作用流動穿過(guo)柱狀(zhuang)(zhuang)晶(jing)區，其(qi)(qi)方向(xiang)(xiang)與等(deng)溫線移(yi)動速度(du)方向(xiang)(xiang)一致但(dan)速率更(geng)快所(suo)導致。A型(xing)(xing)(xing)(xing)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)形(xing)狀(zhuang)(zhuang)與流動類型(xing)(xing)(xing)(xing)有(you)關(guan)。V型(xing)(xing)(xing)(xing)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)位于(yu)鑄(zhu)(zhu)錠(ding)中(zhong)心，源于(yu)中(zhong)心形(xing)成(cheng)等(deng)軸晶(jing)區和(he)(he)容易斷(duan)裂的(de)(de)(de)(de)(de)(de)(de)連接疏松的(de)(de)(de)(de)(de)(de)(de)網狀(zhuang)(zhuang)物(wu)的(de)(de)(de)(de)(de)(de)(de)形(xing)成(cheng)，之后裂紋(wen)沿切(qie)應力面展開為(wei)V型(xing)(xing)(xing)(xing)，并且充滿了富集元(yuan)素的(de)(de)(de)(de)(de)(de)(de)液(ye)相(xiang)。而沿鑄(zhu)(zhu)錠(ding)側壁分(fen)布的(de)(de)(de)(de)(de)(de)(de)帶狀(zhuang)(zhuang)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)則(ze)是由(you)凝(ning)(ning)固(gu)(gu)過(guo)程初(chu)期的(de)(de)(de)(de)(de)(de)(de)不(bu)穩(wen)定傳熱和(he)(he)流動導致的(de)(de)(de)(de)(de)(de)(de)。

  對(dui)于(yu)宏(hong)觀(guan)(guan)偏(pian)析(xi)(xi)(xi)的(de)研究主(zhu)要有(you)實驗(yan)檢(jian)(jian)測和(he)模擬計(ji)算(suan)兩種(zhong)手(shou)段。實驗(yan)檢(jian)(jian)測包括(kuo)硫(liu)印檢(jian)(jian)驗(yan)法、原(yuan)位分(fen)析(xi)(xi)(xi)法、火花放電原(yuan)子發射光(guang)譜法、鉆孔(kong)取樣法以及(ji)化學分(fen)析(xi)(xi)(xi)法等。模擬計(ji)算(suan)是通過(guo)數(shu)(shu)值求解能(neng)量、動量以及(ji)溶質傳輸等數(shu)(shu)學模型(xing)，進而(er)探討元素成分(fen)不均(jun)勻性的(de)方法；進入(ru)20世紀后，人們對(dui)凝(ning)固(gu)(gu)過(guo)程中的(de)宏(hong)觀(guan)(guan)偏(pian)析(xi)(xi)(xi)現象進行了大(da)量系統的(de)研究。Flemings研究表明鑄錠中多種(zhong)不同的(de)宏(hong)觀(guan)(guan)偏(pian)析(xi)(xi)(xi)都(dou)可(ke)由凝(ning)固(gu)(gu)時的(de)傳熱、流動和(he)傳質過(guo)程來(lai)定(ding)量描述(shu)，從(cong)而(er)為宏(hong)觀(guan)(guan)偏(pian)析(xi)(xi)(xi)的(de)定(ding)量計(ji)算(suan)提(ti)供可(ke)能(neng)性，隨著計(ji)算(suan)機計(ji)算(suan)能(neng)力迅猛提(ti)升(sheng)，宏(hong)觀(guan)(guan)偏(pian)析(xi)(xi)(xi)的(de)模擬計(ji)算(suan)得到了迅速(su)發展(zhan)，主(zhu)要分(fen)為多區域法和(he)連續介質法等。

  對于高氮(dan)不銹鋼，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。