根據相(xiang)圖，多數合金元(yuan)素(su)在(zai)固(gu)(gu)相(xiang)中(zhong)的溶(rong)解度要低于液(ye)相(xiang)，因(yin)此(ci)(ci)在(zai)凝(ning)固(gu)(gu)過(guo)(guo)程(cheng)中(zhong)溶(rong)質(zhi)(zhi)原(yuan)子(zi)不斷被排(pai)出到液(ye)相(xiang)，這(zhe)種固(gu)(gu)液(ye)界面兩側溶(rong)質(zhi)(zhi)濃(nong)度的差異導致合金凝(ning)固(gu)(gu)后(hou)溶(rong)質(zhi)(zhi)元(yuan)素(su)成(cheng)分不均(jun)勻(yun)性(xing)(xing)，稱作(zuo)偏(pian)析(xi)(xi)(xi)(xi)。溶(rong)質(zhi)(zhi)元(yuan)素(su)分布不均(jun)勻(yun)性(xing)(xing)發生(sheng)在(zai)微(wei)(wei)觀結構(gou)形(xing)成(cheng)范(fan)圍內（有10~100μm的樹狀(zhuang)枝晶），此(ci)(ci)時為(wei)微(wei)(wei)觀偏(pian)析(xi)(xi)(xi)(xi)。溶(rong)質(zhi)(zhi)元(yuan)素(su)通(tong)過(guo)(guo)對流傳質(zhi)(zhi)等(deng)質(zhi)(zhi)量傳輸(shu)，將導致大范(fan)圍內成(cheng)分不均(jun)勻(yun)性(xing)(xing)，即形(xing)成(cheng)了宏(hong)(hong)觀偏(pian)析(xi)(xi)(xi)(xi)。宏(hong)(hong)觀偏(pian)析(xi)(xi)(xi)(xi)可以認(ren)為(wei)是(shi)由(you)凝(ning)固(gu)(gu)過(guo)(guo)程(cheng)中(zhong)液(ye)體(ti)(ti)和(he)(he)固(gu)(gu)體(ti)(ti)相(xiang)對運動和(he)(he)溶(rong)質(zhi)(zhi)再(zai)分配過(guo)(guo)程(cheng)共(gong)同導致的。此(ci)(ci)外，在(zai)凝(ning)固(gu)(gu)早(zao)期(qi)所形(xing)成(cheng)的固(gu)(gu)體(ti)(ti)相(xiang)或(huo)非(fei)金屬夾雜的漂浮和(he)(he)下沉也會造成(cheng)宏(hong)(hong)觀偏(pian)析(xi)(xi)(xi)(xi)。一(yi)般認(ren)為(wei)在(zai)合金鑄(zhu)件或(huo)鑄(zhu)錠(ding)內，從幾毫(hao)米(mi)到幾厘米(mi)甚至幾米(mi)范(fan)圍內濃(nong)度變化(hua)為(wei)宏(hong)(hong)觀偏(pian)析(xi)(xi)(xi)(xi)。因(yin)為(wei)溶(rong)質(zhi)(zhi)在(zai)固(gu)(gu)態中(zhong)的擴散系數很低，而(er)成(cheng)分不均(jun)勻(yun)性(xing)(xing)范(fan)圍又很大，所以在(zai)凝(ning)固(gu)(gu)完成(cheng)后(hou)，宏(hong)(hong)觀偏(pian)析(xi)(xi)(xi)(xi)很難通(tong)過(guo)(guo)加(jia)工(gong)處(chu)理來(lai)消除，因(yin)此(ci)(ci)抑制宏(hong)(hong)觀偏(pian)析(xi)(xi)(xi)(xi)的產生(sheng)主要是(shi)對工(gong)藝參數進行優化(hua)，如控制合金成(cheng)分、施加(jia)外力(li)場(chang)（磁場(chang)等(deng)）、優化(hua)鑄(zhu)錠(ding)幾何形(xing)狀(zhuang)、適當加(jia)大冷卻(que)速率等(deng)。

  宏觀偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)是(shi)大范圍內(nei)(nei)的(de)(de)(de)(de)(de)(de)成(cheng)分(fen)(fen)不均勻(yun)現象，按其(qi)(qi)表(biao)現形式可分(fen)(fen)為正(zheng)(zheng)偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)、反(fan)偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)和(he)(he)比(bi)重偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)等。①. 正(zheng)(zheng)偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)：對(dui)平衡分(fen)(fen)配(pei)系(xi)(xi)數(shu)o<1的(de)(de)(de)(de)(de)(de)合(he)金(jin)系(xi)(xi)鑄(zhu)(zhu)錠(ding)(ding)先凝(ning)固(gu)(gu)的(de)(de)(de)(de)(de)(de)部(bu)(bu)分(fen)(fen)，其(qi)(qi)溶(rong)質含量低(di)于(yu)后凝(ning)固(gu)(gu)的(de)(de)(de)(de)(de)(de)部(bu)(bu)分(fen)(fen)。對(dui)ko>1的(de)(de)(de)(de)(de)(de)合(he)金(jin)系(xi)(xi)則正(zheng)(zheng)好相(xiang)反(fan)，其(qi)(qi)偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)程度與(yu)凝(ning)固(gu)(gu)速(su)率、液(ye)體對(dui)流以及溶(rong)質擴散等條(tiao)件有關。②. 反(fan)偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)：在(zai)ko<1的(de)(de)(de)(de)(de)(de)合(he)金(jin)鑄(zhu)(zhu)錠(ding)(ding)中(zhong)(zhong)，其(qi)(qi)外層溶(rong)質元素(su)(su)高于(yu)內(nei)(nei)部(bu)(bu)，和(he)(he)正(zheng)(zheng)偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)相(xiang)反(fan)，故稱為反(fan)偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)。③. 比(bi)重偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)：是(shi)由(you)合(he)金(jin)凝(ning)固(gu)(gu)時形成(cheng)的(de)(de)(de)(de)(de)(de)初晶(jing)相(xiang)和(he)(he)溶(rong)液(ye)之間(jian)(jian)的(de)(de)(de)(de)(de)(de)比(bi)重顯(xian)著差別引(yin)起的(de)(de)(de)(de)(de)(de)一(yi)種宏觀偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)，主要(yao)存(cun)在(zai)于(yu)共晶(jing)系(xi)(xi)和(he)(he)偏(pian)(pian)(pian)(pian)晶(jing)系(xi)(xi)合(he)金(jin)中(zhong)(zhong)。如圖2-49所示，由(you)于(yu)溶(rong)質元素(su)(su)濃度相(xiang)對(dui)低(di)的(de)(de)(de)(de)(de)(de)等軸(zhou)晶(jing)沉(chen)積導致(zhi)在(zai)鑄(zhu)(zhu)錠(ding)(ding)的(de)(de)(de)(de)(de)(de)底部(bu)(bu)出現負(fu)偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)；由(you)于(yu)浮(fu)力和(he)(he)在(zai)凝(ning)固(gu)(gu)的(de)(de)(de)(de)(de)(de)最后階段收縮所引(yin)起的(de)(de)(de)(de)(de)(de)晶(jing)間(jian)(jian)流動(dong)，在(zai)頂(ding)部(bu)(bu)會(hui)出現很嚴重的(de)(de)(de)(de)(de)(de)正(zheng)(zheng)偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)（頂(ding)部(bu)(bu)偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)）。A型(xing)(xing)偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)是(shi)溶(rong)質富(fu)集的(de)(de)(de)(de)(de)(de)等軸(zhou)晶(jing)帶，由(you)溶(rong)質受浮(fu)力作用流動(dong)穿過柱狀(zhuang)(zhuang)晶(jing)區，其(qi)(qi)方向與(yu)等溫線移動(dong)速(su)度方向一(yi)致(zhi)但速(su)率更快所導致(zhi)。A型(xing)(xing)偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)形狀(zhuang)(zhuang)與(yu)流動(dong)類(lei)型(xing)(xing)有關。V型(xing)(xing)偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)位(wei)于(yu)鑄(zhu)(zhu)錠(ding)(ding)中(zhong)(zhong)心(xin)(xin)，源于(yu)中(zhong)(zhong)心(xin)(xin)形成(cheng)等軸(zhou)晶(jing)區和(he)(he)容易斷裂(lie)(lie)的(de)(de)(de)(de)(de)(de)連接疏松的(de)(de)(de)(de)(de)(de)網狀(zhuang)(zhuang)物的(de)(de)(de)(de)(de)(de)形成(cheng)，之后裂(lie)(lie)紋沿(yan)切應力面展(zhan)開為V型(xing)(xing)，并且(qie)充滿了富(fu)集元素(su)(su)的(de)(de)(de)(de)(de)(de)液(ye)相(xiang)。而沿(yan)鑄(zhu)(zhu)錠(ding)(ding)側壁分(fen)(fen)布(bu)的(de)(de)(de)(de)(de)(de)帶狀(zhuang)(zhuang)偏(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)則是(shi)由(you)凝(ning)固(gu)(gu)過程初期的(de)(de)(de)(de)(de)(de)不穩(wen)定傳熱(re)和(he)(he)流動(dong)導致(zhi)的(de)(de)(de)(de)(de)(de)。

  對于宏(hong)(hong)觀(guan)(guan)偏析(xi)(xi)的(de)研(yan)究(jiu)(jiu)主要有實驗檢測(ce)和(he)模(mo)擬(ni)計(ji)(ji)算(suan)(suan)兩種(zhong)手段。實驗檢測(ce)包括硫(liu)印檢驗法、原位分(fen)(fen)析(xi)(xi)法、火(huo)花放電(dian)原子發射(she)光譜法、鉆孔取樣法以(yi)及化學(xue)分(fen)(fen)析(xi)(xi)法等(deng)。模(mo)擬(ni)計(ji)(ji)算(suan)(suan)是通(tong)過數值求解能(neng)量、動量以(yi)及溶質(zhi)(zhi)傳輸(shu)等(deng)數學(xue)模(mo)型，進(jin)而(er)探討元(yuan)素(su)成(cheng)分(fen)(fen)不(bu)均勻性的(de)方法；進(jin)入20世紀(ji)后，人們對凝(ning)固過程(cheng)中(zhong)的(de)宏(hong)(hong)觀(guan)(guan)偏析(xi)(xi)現象進(jin)行了大量系統(tong)的(de)研(yan)究(jiu)(jiu)。Flemings研(yan)究(jiu)(jiu)表明(ming)鑄錠中(zhong)多(duo)(duo)種(zhong)不(bu)同的(de)宏(hong)(hong)觀(guan)(guan)偏析(xi)(xi)都可由凝(ning)固時的(de)傳熱、流動和(he)傳質(zhi)(zhi)過程(cheng)來定(ding)量描述，從而(er)為(wei)宏(hong)(hong)觀(guan)(guan)偏析(xi)(xi)的(de)定(ding)量計(ji)(ji)算(suan)(suan)提供可能(neng)性，隨著計(ji)(ji)算(suan)(suan)機計(ji)(ji)算(suan)(suan)能(neng)力迅猛提升，宏(hong)(hong)觀(guan)(guan)偏析(xi)(xi)的(de)模(mo)擬(ni)計(ji)(ji)算(suan)(suan)得(de)到了迅速發展，主要分(fen)(fen)為(wei)多(duo)(duo)區域法和(he)連續介質(zhi)(zhi)法等(deng)。

  對于高(gao)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。