根(gen)據相(xiang)圖，多數(shu)合金(jin)元(yuan)(yuan)素在(zai)(zai)固相(xiang)中(zhong)的(de)(de)(de)(de)溶(rong)(rong)(rong)(rong)(rong)解度要低于液相(xiang)，因此在(zai)(zai)凝(ning)(ning)(ning)固過程(cheng)中(zhong)溶(rong)(rong)(rong)(rong)(rong)質(zhi)原(yuan)子(zi)不(bu)(bu)(bu)斷被(bei)排出到液相(xiang)，這種固液界面兩(liang)側溶(rong)(rong)(rong)(rong)(rong)質(zhi)濃(nong)度的(de)(de)(de)(de)差(cha)異導(dao)致(zhi)合金(jin)凝(ning)(ning)(ning)固后溶(rong)(rong)(rong)(rong)(rong)質(zhi)元(yuan)(yuan)素成(cheng)(cheng)(cheng)分(fen)不(bu)(bu)(bu)均勻(yun)(yun)性(xing)，稱作(zuo)偏(pian)析(xi)(xi)。溶(rong)(rong)(rong)(rong)(rong)質(zhi)元(yuan)(yuan)素分(fen)布不(bu)(bu)(bu)均勻(yun)(yun)性(xing)發生在(zai)(zai)微觀(guan)結構形成(cheng)(cheng)(cheng)范圍(wei)內（有10~100μm的(de)(de)(de)(de)樹狀(zhuang)枝(zhi)晶），此時為(wei)微觀(guan)偏(pian)析(xi)(xi)。溶(rong)(rong)(rong)(rong)(rong)質(zhi)元(yuan)(yuan)素通過對(dui)流傳質(zhi)等(deng)質(zhi)量傳輸，將導(dao)致(zhi)大(da)(da)(da)范圍(wei)內成(cheng)(cheng)(cheng)分(fen)不(bu)(bu)(bu)均勻(yun)(yun)性(xing)，即(ji)形成(cheng)(cheng)(cheng)了宏(hong)(hong)(hong)觀(guan)偏(pian)析(xi)(xi)。宏(hong)(hong)(hong)觀(guan)偏(pian)析(xi)(xi)可(ke)以認為(wei)是由凝(ning)(ning)(ning)固過程(cheng)中(zhong)液體和固體相(xiang)對(dui)運動和溶(rong)(rong)(rong)(rong)(rong)質(zhi)再(zai)分(fen)配過程(cheng)共同導(dao)致(zhi)的(de)(de)(de)(de)。此外(wai)，在(zai)(zai)凝(ning)(ning)(ning)固早期所形成(cheng)(cheng)(cheng)的(de)(de)(de)(de)固體相(xiang)或(huo)非金(jin)屬夾雜(za)的(de)(de)(de)(de)漂浮和下沉也(ye)會造成(cheng)(cheng)(cheng)宏(hong)(hong)(hong)觀(guan)偏(pian)析(xi)(xi)。一般認為(wei)在(zai)(zai)合金(jin)鑄(zhu)件或(huo)鑄(zhu)錠內，從幾毫米到幾厘米甚至幾米范圍(wei)內濃(nong)度變化為(wei)宏(hong)(hong)(hong)觀(guan)偏(pian)析(xi)(xi)。因為(wei)溶(rong)(rong)(rong)(rong)(rong)質(zhi)在(zai)(zai)固態中(zhong)的(de)(de)(de)(de)擴散系數(shu)很(hen)低，而成(cheng)(cheng)(cheng)分(fen)不(bu)(bu)(bu)均勻(yun)(yun)性(xing)范圍(wei)又很(hen)大(da)(da)(da)，所以在(zai)(zai)凝(ning)(ning)(ning)固完成(cheng)(cheng)(cheng)后，宏(hong)(hong)(hong)觀(guan)偏(pian)析(xi)(xi)很(hen)難通過加(jia)工處(chu)理(li)來消除，因此抑制(zhi)宏(hong)(hong)(hong)觀(guan)偏(pian)析(xi)(xi)的(de)(de)(de)(de)產生主(zhu)要是對(dui)工藝參數(shu)進(jin)行優(you)化，如控制(zhi)合金(jin)成(cheng)(cheng)(cheng)分(fen)、施加(jia)外(wai)力場（磁場等(deng)）、優(you)化鑄(zhu)錠幾何形狀(zhuang)、適當加(jia)大(da)(da)(da)冷卻速率等(deng)。

  宏觀偏(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)是大范圍內(nei)的(de)(de)(de)成(cheng)分(fen)不均勻現象(xiang)，按其(qi)表現形式可(ke)分(fen)為正(zheng)偏(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)、反(fan)偏(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)和(he)(he)比重(zhong)偏(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)等(deng)(deng)。①. 正(zheng)偏(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)：對平衡分(fen)配系數o<1的(de)(de)(de)合(he)(he)金系鑄(zhu)錠(ding)(ding)先凝(ning)固(gu)的(de)(de)(de)部(bu)(bu)分(fen)，其(qi)溶(rong)(rong)質含量(liang)低(di)于(yu)(yu)后凝(ning)固(gu)的(de)(de)(de)部(bu)(bu)分(fen)。對ko>1的(de)(de)(de)合(he)(he)金系則正(zheng)好相(xiang)反(fan)，其(qi)偏(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)程度(du)與(yu)凝(ning)固(gu)速率、液(ye)體(ti)對流(liu)(liu)以及溶(rong)(rong)質擴散等(deng)(deng)條件有關(guan)。②. 反(fan)偏(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)：在(zai)ko<1的(de)(de)(de)合(he)(he)金鑄(zhu)錠(ding)(ding)中，其(qi)外層溶(rong)(rong)質元(yuan)素(su)高(gao)于(yu)(yu)內(nei)部(bu)(bu)，和(he)(he)正(zheng)偏(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)相(xiang)反(fan)，故稱為反(fan)偏(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)。③. 比重(zhong)偏(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)：是由合(he)(he)金凝(ning)固(gu)時形成(cheng)的(de)(de)(de)初晶(jing)相(xiang)和(he)(he)溶(rong)(rong)液(ye)之間的(de)(de)(de)比重(zhong)顯著差(cha)別引起的(de)(de)(de)一種宏觀偏(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)，主要存在(zai)于(yu)(yu)共晶(jing)系和(he)(he)偏(pian)(pian)(pian)晶(jing)系合(he)(he)金中。如圖2-49所示，由于(yu)(yu)溶(rong)(rong)質元(yuan)素(su)濃度(du)相(xiang)對低(di)的(de)(de)(de)等(deng)(deng)軸晶(jing)沉(chen)積導致(zhi)在(zai)鑄(zhu)錠(ding)(ding)的(de)(de)(de)底(di)部(bu)(bu)出(chu)(chu)現負偏(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)；由于(yu)(yu)浮(fu)力和(he)(he)在(zai)凝(ning)固(gu)的(de)(de)(de)最后階段(duan)收縮所引起的(de)(de)(de)晶(jing)間流(liu)(liu)動，在(zai)頂部(bu)(bu)會出(chu)(chu)現很嚴重(zhong)的(de)(de)(de)正(zheng)偏(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)（頂部(bu)(bu)偏(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)）。A型偏(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)是溶(rong)(rong)質富(fu)集(ji)的(de)(de)(de)等(deng)(deng)軸晶(jing)帶，由溶(rong)(rong)質受浮(fu)力作用流(liu)(liu)動穿過(guo)柱狀(zhuang)晶(jing)區(qu)，其(qi)方向與(yu)等(deng)(deng)溫線(xian)移(yi)動速度(du)方向一致(zhi)但(dan)速率更快所導致(zhi)。A型偏(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)形狀(zhuang)與(yu)流(liu)(liu)動類型有關(guan)。V型偏(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)位于(yu)(yu)鑄(zhu)錠(ding)(ding)中心，源于(yu)(yu)中心形成(cheng)等(deng)(deng)軸晶(jing)區(qu)和(he)(he)容(rong)易斷裂的(de)(de)(de)連接疏松的(de)(de)(de)網(wang)狀(zhuang)物(wu)的(de)(de)(de)形成(cheng)，之后裂紋沿(yan)切(qie)應力面(mian)展開(kai)為V型，并(bing)且充(chong)滿了富(fu)集(ji)元(yuan)素(su)的(de)(de)(de)液(ye)相(xiang)。而沿(yan)鑄(zhu)錠(ding)(ding)側壁分(fen)布的(de)(de)(de)帶狀(zhuang)偏(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)則是由凝(ning)固(gu)過(guo)程初期的(de)(de)(de)不穩定(ding)傳熱和(he)(he)流(liu)(liu)動導致(zhi)的(de)(de)(de)。

  對(dui)于(yu)宏觀(guan)(guan)偏(pian)(pian)析(xi)的(de)研究主(zhu)要(yao)有實驗(yan)檢(jian)測(ce)和模擬計(ji)算(suan)(suan)兩種手(shou)段。實驗(yan)檢(jian)測(ce)包括硫印檢(jian)驗(yan)法(fa)(fa)、原位分析(xi)法(fa)(fa)、火花放(fang)電原子(zi)發(fa)射光譜(pu)法(fa)(fa)、鉆孔取樣法(fa)(fa)以及(ji)化學(xue)分析(xi)法(fa)(fa)等。模擬計(ji)算(suan)(suan)是通過(guo)數值求解能量、動量以及(ji)溶質(zhi)傳(chuan)輸等數學(xue)模型，進而探討元素(su)成分不均(jun)勻性的(de)方法(fa)(fa)；進入(ru)20世紀后，人們對(dui)凝(ning)固(gu)過(guo)程中(zhong)的(de)宏觀(guan)(guan)偏(pian)(pian)析(xi)現(xian)象進行了大量系(xi)統的(de)研究。Flemings研究表明(ming)鑄錠中(zhong)多種不同的(de)宏觀(guan)(guan)偏(pian)(pian)析(xi)都可(ke)由凝(ning)固(gu)時的(de)傳(chuan)熱、流動和傳(chuan)質(zhi)過(guo)程來定量描述(shu)，從而為(wei)宏觀(guan)(guan)偏(pian)(pian)析(xi)的(de)定量計(ji)算(suan)(suan)提供(gong)可(ke)能性，隨(sui)著計(ji)算(suan)(suan)機(ji)計(ji)算(suan)(suan)能力迅(xun)猛提升，宏觀(guan)(guan)偏(pian)(pian)析(xi)的(de)模擬計(ji)算(suan)(suan)得到了迅(xun)速發(fa)展，主(zhu)要(yao)分為(wei)多區域法(fa)(fa)和連續介(jie)質(zhi)法(fa)(fa)等。

  對于高氮不銹鋼，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。