根據相(xiang)(xiang)(xiang)(xiang)圖，多數(shu)合金元(yuan)(yuan)素(su)在(zai)固(gu)(gu)相(xiang)(xiang)(xiang)(xiang)中(zhong)(zhong)的(de)(de)溶(rong)(rong)解(jie)度(du)(du)要低于液相(xiang)(xiang)(xiang)(xiang)，因此(ci)在(zai)凝(ning)固(gu)(gu)過程中(zhong)(zhong)溶(rong)(rong)質(zhi)原子不(bu)(bu)斷被排(pai)出到液相(xiang)(xiang)(xiang)(xiang)，這種固(gu)(gu)液界(jie)面(mian)兩(liang)側溶(rong)(rong)質(zhi)濃度(du)(du)的(de)(de)差異導(dao)致(zhi)合金凝(ning)固(gu)(gu)后(hou)溶(rong)(rong)質(zhi)元(yuan)(yuan)素(su)成分(fen)不(bu)(bu)均(jun)(jun)(jun)勻(yun)性，稱作偏(pian)析(xi)(xi)。溶(rong)(rong)質(zhi)元(yuan)(yuan)素(su)分(fen)布不(bu)(bu)均(jun)(jun)(jun)勻(yun)性發生在(zai)微(wei)觀(guan)(guan)結構形(xing)成范(fan)圍(wei)(wei)(wei)內(nei)（有10~100μm的(de)(de)樹狀枝晶），此(ci)時(shi)為(wei)(wei)微(wei)觀(guan)(guan)偏(pian)析(xi)(xi)。溶(rong)(rong)質(zhi)元(yuan)(yuan)素(su)通過對(dui)(dui)流(liu)傳質(zhi)等質(zhi)量傳輸，將(jiang)導(dao)致(zhi)大(da)范(fan)圍(wei)(wei)(wei)內(nei)成分(fen)不(bu)(bu)均(jun)(jun)(jun)勻(yun)性，即形(xing)成了宏(hong)(hong)觀(guan)(guan)偏(pian)析(xi)(xi)。宏(hong)(hong)觀(guan)(guan)偏(pian)析(xi)(xi)可以認(ren)為(wei)(wei)是由凝(ning)固(gu)(gu)過程中(zhong)(zhong)液體(ti)和固(gu)(gu)體(ti)相(xiang)(xiang)(xiang)(xiang)對(dui)(dui)運動和溶(rong)(rong)質(zhi)再分(fen)配(pei)過程共(gong)同導(dao)致(zhi)的(de)(de)。此(ci)外(wai)，在(zai)凝(ning)固(gu)(gu)早期(qi)所形(xing)成的(de)(de)固(gu)(gu)體(ti)相(xiang)(xiang)(xiang)(xiang)或非金屬夾(jia)雜的(de)(de)漂(piao)浮和下沉也會造成宏(hong)(hong)觀(guan)(guan)偏(pian)析(xi)(xi)。一般認(ren)為(wei)(wei)在(zai)合金鑄(zhu)(zhu)件(jian)或鑄(zhu)(zhu)錠(ding)內(nei)，從(cong)幾毫米到幾厘(li)米甚(shen)至幾米范(fan)圍(wei)(wei)(wei)內(nei)濃度(du)(du)變化(hua)為(wei)(wei)宏(hong)(hong)觀(guan)(guan)偏(pian)析(xi)(xi)。因為(wei)(wei)溶(rong)(rong)質(zhi)在(zai)固(gu)(gu)態(tai)中(zhong)(zhong)的(de)(de)擴散系數(shu)很(hen)(hen)低，而成分(fen)不(bu)(bu)均(jun)(jun)(jun)勻(yun)性范(fan)圍(wei)(wei)(wei)又很(hen)(hen)大(da)，所以在(zai)凝(ning)固(gu)(gu)完成后(hou)，宏(hong)(hong)觀(guan)(guan)偏(pian)析(xi)(xi)很(hen)(hen)難(nan)通過加(jia)工處理(li)來消除，因此(ci)抑制(zhi)宏(hong)(hong)觀(guan)(guan)偏(pian)析(xi)(xi)的(de)(de)產生主要是對(dui)(dui)工藝(yi)參(can)數(shu)進行優(you)化(hua)，如(ru)控(kong)制(zhi)合金成分(fen)、施(shi)加(jia)外(wai)力場（磁場等）、優(you)化(hua)鑄(zhu)(zhu)錠(ding)幾何形(xing)狀、適(shi)當加(jia)大(da)冷卻速(su)率(lv)等。

  宏觀偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)是(shi)大(da)范圍(wei)內(nei)的(de)(de)(de)(de)(de)(de)(de)成分不均(jun)勻現(xian)象，按(an)其(qi)表(biao)現(xian)形(xing)式可分為(wei)正(zheng)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)、反(fan)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)和(he)比(bi)重偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)等(deng)(deng)。①. 正(zheng)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)：對平衡分配(pei)系數o<1的(de)(de)(de)(de)(de)(de)(de)合金(jin)(jin)系鑄(zhu)錠(ding)先凝(ning)(ning)(ning)固(gu)(gu)的(de)(de)(de)(de)(de)(de)(de)部(bu)分，其(qi)溶(rong)質(zhi)(zhi)含量低于(yu)(yu)后(hou)凝(ning)(ning)(ning)固(gu)(gu)的(de)(de)(de)(de)(de)(de)(de)部(bu)分。對ko>1的(de)(de)(de)(de)(de)(de)(de)合金(jin)(jin)系則(ze)正(zheng)好(hao)相(xiang)(xiang)反(fan)，其(qi)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)程度與(yu)凝(ning)(ning)(ning)固(gu)(gu)速率、液體對流(liu)以及溶(rong)質(zhi)(zhi)擴散等(deng)(deng)條件有(you)關(guan)。②. 反(fan)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)：在ko<1的(de)(de)(de)(de)(de)(de)(de)合金(jin)(jin)鑄(zhu)錠(ding)中(zhong)，其(qi)外層溶(rong)質(zhi)(zhi)元素(su)高于(yu)(yu)內(nei)部(bu)，和(he)正(zheng)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)相(xiang)(xiang)反(fan)，故稱為(wei)反(fan)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)。③. 比(bi)重偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)：是(shi)由(you)(you)合金(jin)(jin)凝(ning)(ning)(ning)固(gu)(gu)時(shi)形(xing)成的(de)(de)(de)(de)(de)(de)(de)初(chu)晶相(xiang)(xiang)和(he)溶(rong)液之間的(de)(de)(de)(de)(de)(de)(de)比(bi)重顯著差別引(yin)起的(de)(de)(de)(de)(de)(de)(de)一種宏觀偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)，主要(yao)存在于(yu)(yu)共晶系和(he)偏(pian)(pian)(pian)(pian)(pian)晶系合金(jin)(jin)中(zhong)。如圖2-49所(suo)示，由(you)(you)于(yu)(yu)溶(rong)質(zhi)(zhi)元素(su)濃度相(xiang)(xiang)對低的(de)(de)(de)(de)(de)(de)(de)等(deng)(deng)軸(zhou)晶沉積導(dao)致(zhi)在鑄(zhu)錠(ding)的(de)(de)(de)(de)(de)(de)(de)底部(bu)出(chu)(chu)現(xian)負(fu)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)；由(you)(you)于(yu)(yu)浮力(li)和(he)在凝(ning)(ning)(ning)固(gu)(gu)的(de)(de)(de)(de)(de)(de)(de)最后(hou)階段收縮所(suo)引(yin)起的(de)(de)(de)(de)(de)(de)(de)晶間流(liu)動(dong)，在頂部(bu)會出(chu)(chu)現(xian)很嚴重的(de)(de)(de)(de)(de)(de)(de)正(zheng)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)（頂部(bu)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)）。A型偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)是(shi)溶(rong)質(zhi)(zhi)富(fu)集的(de)(de)(de)(de)(de)(de)(de)等(deng)(deng)軸(zhou)晶帶(dai)(dai)，由(you)(you)溶(rong)質(zhi)(zhi)受浮力(li)作用流(liu)動(dong)穿過柱(zhu)狀晶區，其(qi)方向與(yu)等(deng)(deng)溫線移動(dong)速度方向一致(zhi)但速率更快所(suo)導(dao)致(zhi)。A型偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)形(xing)狀與(yu)流(liu)動(dong)類型有(you)關(guan)。V型偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)位于(yu)(yu)鑄(zhu)錠(ding)中(zhong)心，源于(yu)(yu)中(zhong)心形(xing)成等(deng)(deng)軸(zhou)晶區和(he)容易斷裂(lie)的(de)(de)(de)(de)(de)(de)(de)連接疏松的(de)(de)(de)(de)(de)(de)(de)網狀物(wu)的(de)(de)(de)(de)(de)(de)(de)形(xing)成，之后(hou)裂(lie)紋沿切(qie)應力(li)面展(zhan)開為(wei)V型，并且充滿了富(fu)集元素(su)的(de)(de)(de)(de)(de)(de)(de)液相(xiang)(xiang)。而沿鑄(zhu)錠(ding)側壁分布(bu)的(de)(de)(de)(de)(de)(de)(de)帶(dai)(dai)狀偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)則(ze)是(shi)由(you)(you)凝(ning)(ning)(ning)固(gu)(gu)過程初(chu)期的(de)(de)(de)(de)(de)(de)(de)不穩(wen)定傳熱(re)和(he)流(liu)動(dong)導(dao)致(zhi)的(de)(de)(de)(de)(de)(de)(de)。

  對于宏(hong)觀偏(pian)析(xi)的(de)研(yan)究主(zhu)要(yao)有實驗(yan)檢測和(he)(he)模(mo)擬計(ji)(ji)算(suan)兩(liang)種(zhong)手段。實驗(yan)檢測包括硫印檢驗(yan)法(fa)、原位(wei)分析(xi)法(fa)、火花放電原子(zi)發射光譜法(fa)、鉆孔(kong)取樣法(fa)以及化學分析(xi)法(fa)等。模(mo)擬計(ji)(ji)算(suan)是通(tong)過(guo)數值(zhi)求解(jie)能量(liang)、動量(liang)以及溶質(zhi)(zhi)傳輸等數學模(mo)型，進而探討元素成分不均(jun)勻性(xing)的(de)方法(fa)；進入20世(shi)紀后，人們對凝固過(guo)程中的(de)宏(hong)觀偏(pian)析(xi)現(xian)象進行了大(da)量(liang)系(xi)統的(de)研(yan)究。Flemings研(yan)究表(biao)明(ming)鑄錠中多種(zhong)不同的(de)宏(hong)觀偏(pian)析(xi)都可(ke)由凝固時的(de)傳熱、流動和(he)(he)傳質(zhi)(zhi)過(guo)程來定量(liang)描述(shu)，從而為宏(hong)觀偏(pian)析(xi)的(de)定量(liang)計(ji)(ji)算(suan)提供可(ke)能性(xing)，隨(sui)著計(ji)(ji)算(suan)機(ji)計(ji)(ji)算(suan)能力(li)迅(xun)猛提升，宏(hong)觀偏(pian)析(xi)的(de)模(mo)擬計(ji)(ji)算(suan)得到了迅(xun)速發展，主(zhu)要(yao)分為多區域法(fa)和(he)(he)連(lian)續(xu)介質(zhi)(zhi)法(fa)等。

  對于高氮不銹(xiu)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。