根(gen)據相(xiang)圖，多(duo)數(shu)合(he)金(jin)元素在(zai)(zai)(zai)固(gu)相(xiang)中(zhong)的(de)溶(rong)(rong)解度要低(di)于(yu)液(ye)相(xiang)，因此在(zai)(zai)(zai)凝(ning)固(gu)過(guo)(guo)(guo)(guo)程(cheng)(cheng)中(zhong)溶(rong)(rong)質(zhi)(zhi)原子(zi)不(bu)斷被排出到液(ye)相(xiang)，這種固(gu)液(ye)界(jie)面兩側溶(rong)(rong)質(zhi)(zhi)濃度的(de)差異(yi)導(dao)致(zhi)合(he)金(jin)凝(ning)固(gu)后(hou)(hou)溶(rong)(rong)質(zhi)(zhi)元素成(cheng)分(fen)不(bu)均(jun)(jun)勻(yun)性(xing)，稱作(zuo)偏(pian)析(xi)(xi)。溶(rong)(rong)質(zhi)(zhi)元素分(fen)布不(bu)均(jun)(jun)勻(yun)性(xing)發生(sheng)在(zai)(zai)(zai)微觀(guan)結構形(xing)(xing)成(cheng)范圍內（有(you)10~100μm的(de)樹狀(zhuang)枝晶），此時(shi)為(wei)微觀(guan)偏(pian)析(xi)(xi)。溶(rong)(rong)質(zhi)(zhi)元素通過(guo)(guo)(guo)(guo)對(dui)流傳質(zhi)(zhi)等(deng)質(zhi)(zhi)量傳輸，將導(dao)致(zhi)大范圍內成(cheng)分(fen)不(bu)均(jun)(jun)勻(yun)性(xing)，即形(xing)(xing)成(cheng)了宏(hong)觀(guan)偏(pian)析(xi)(xi)。宏(hong)觀(guan)偏(pian)析(xi)(xi)可以認為(wei)是由凝(ning)固(gu)過(guo)(guo)(guo)(guo)程(cheng)(cheng)中(zhong)液(ye)體和(he)固(gu)體相(xiang)對(dui)運動和(he)溶(rong)(rong)質(zhi)(zhi)再分(fen)配過(guo)(guo)(guo)(guo)程(cheng)(cheng)共同導(dao)致(zhi)的(de)。此外，在(zai)(zai)(zai)凝(ning)固(gu)早(zao)期(qi)所(suo)形(xing)(xing)成(cheng)的(de)固(gu)體相(xiang)或(huo)非(fei)金(jin)屬夾(jia)雜的(de)漂浮和(he)下沉也會造(zao)成(cheng)宏(hong)觀(guan)偏(pian)析(xi)(xi)。一般認為(wei)在(zai)(zai)(zai)合(he)金(jin)鑄件或(huo)鑄錠內，從幾(ji)毫米到幾(ji)厘米甚至幾(ji)米范圍內濃度變(bian)化(hua)為(wei)宏(hong)觀(guan)偏(pian)析(xi)(xi)。因為(wei)溶(rong)(rong)質(zhi)(zhi)在(zai)(zai)(zai)固(gu)態中(zhong)的(de)擴散系數(shu)很低(di)，而成(cheng)分(fen)不(bu)均(jun)(jun)勻(yun)性(xing)范圍又很大，所(suo)以在(zai)(zai)(zai)凝(ning)固(gu)完成(cheng)后(hou)(hou)，宏(hong)觀(guan)偏(pian)析(xi)(xi)很難(nan)通過(guo)(guo)(guo)(guo)加(jia)(jia)工處理來消(xiao)除，因此抑制宏(hong)觀(guan)偏(pian)析(xi)(xi)的(de)產生(sheng)主(zhu)要是對(dui)工藝(yi)參數(shu)進(jin)行優(you)化(hua)，如控(kong)制合(he)金(jin)成(cheng)分(fen)、施加(jia)(jia)外力場(chang)（磁場(chang)等(deng)）、優(you)化(hua)鑄錠幾(ji)何形(xing)(xing)狀(zhuang)、適(shi)當加(jia)(jia)大冷卻速率等(deng)。

  宏觀偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)是(shi)(shi)(shi)大范圍內(nei)的(de)(de)(de)(de)(de)(de)(de)成(cheng)分(fen)(fen)不均(jun)勻現(xian)象，按其(qi)表(biao)現(xian)形式可分(fen)(fen)為(wei)(wei)正(zheng)(zheng)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)、反(fan)(fan)(fan)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)和(he)比(bi)(bi)重(zhong)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)等(deng)。①. 正(zheng)(zheng)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)：對(dui)平衡分(fen)(fen)配(pei)系(xi)(xi)數o<1的(de)(de)(de)(de)(de)(de)(de)合(he)(he)金(jin)系(xi)(xi)鑄(zhu)(zhu)錠(ding)先凝(ning)固(gu)的(de)(de)(de)(de)(de)(de)(de)部(bu)(bu)分(fen)(fen)，其(qi)溶質(zhi)(zhi)含(han)量(liang)低于(yu)(yu)(yu)后(hou)(hou)凝(ning)固(gu)的(de)(de)(de)(de)(de)(de)(de)部(bu)(bu)分(fen)(fen)。對(dui)ko>1的(de)(de)(de)(de)(de)(de)(de)合(he)(he)金(jin)系(xi)(xi)則正(zheng)(zheng)好相(xiang)(xiang)反(fan)(fan)(fan)，其(qi)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)程度與凝(ning)固(gu)速(su)率、液體(ti)對(dui)流以及溶質(zhi)(zhi)擴散等(deng)條件有關。②. 反(fan)(fan)(fan)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)：在ko<1的(de)(de)(de)(de)(de)(de)(de)合(he)(he)金(jin)鑄(zhu)(zhu)錠(ding)中，其(qi)外層溶質(zhi)(zhi)元素(su)高于(yu)(yu)(yu)內(nei)部(bu)(bu)，和(he)正(zheng)(zheng)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)相(xiang)(xiang)反(fan)(fan)(fan)，故(gu)稱為(wei)(wei)反(fan)(fan)(fan)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)。③. 比(bi)(bi)重(zhong)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)：是(shi)(shi)(shi)由合(he)(he)金(jin)凝(ning)固(gu)時形成(cheng)的(de)(de)(de)(de)(de)(de)(de)初晶(jing)相(xiang)(xiang)和(he)溶液之(zhi)(zhi)間的(de)(de)(de)(de)(de)(de)(de)比(bi)(bi)重(zhong)顯著差(cha)別引起的(de)(de)(de)(de)(de)(de)(de)一種宏觀偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)，主要(yao)存在于(yu)(yu)(yu)共晶(jing)系(xi)(xi)和(he)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)晶(jing)系(xi)(xi)合(he)(he)金(jin)中。如圖2-49所(suo)示，由于(yu)(yu)(yu)溶質(zhi)(zhi)元素(su)濃度相(xiang)(xiang)對(dui)低的(de)(de)(de)(de)(de)(de)(de)等(deng)軸(zhou)晶(jing)沉積導(dao)致在鑄(zhu)(zhu)錠(ding)的(de)(de)(de)(de)(de)(de)(de)底部(bu)(bu)出現(xian)負(fu)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)；由于(yu)(yu)(yu)浮(fu)力(li)和(he)在凝(ning)固(gu)的(de)(de)(de)(de)(de)(de)(de)最后(hou)(hou)階段收縮所(suo)引起的(de)(de)(de)(de)(de)(de)(de)晶(jing)間流動(dong)(dong)，在頂(ding)部(bu)(bu)會出現(xian)很嚴重(zhong)的(de)(de)(de)(de)(de)(de)(de)正(zheng)(zheng)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)（頂(ding)部(bu)(bu)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)）。A型(xing)(xing)(xing)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)是(shi)(shi)(shi)溶質(zhi)(zhi)富(fu)(fu)集的(de)(de)(de)(de)(de)(de)(de)等(deng)軸(zhou)晶(jing)帶，由溶質(zhi)(zhi)受浮(fu)力(li)作(zuo)用流動(dong)(dong)穿過柱狀晶(jing)區，其(qi)方向(xiang)與等(deng)溫線移動(dong)(dong)速(su)度方向(xiang)一致但速(su)率更(geng)快所(suo)導(dao)致。A型(xing)(xing)(xing)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)形狀與流動(dong)(dong)類型(xing)(xing)(xing)有關。V型(xing)(xing)(xing)偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)位于(yu)(yu)(yu)鑄(zhu)(zhu)錠(ding)中心(xin)，源于(yu)(yu)(yu)中心(xin)形成(cheng)等(deng)軸(zhou)晶(jing)區和(he)容易斷裂的(de)(de)(de)(de)(de)(de)(de)連接疏松(song)的(de)(de)(de)(de)(de)(de)(de)網狀物的(de)(de)(de)(de)(de)(de)(de)形成(cheng)，之(zhi)(zhi)后(hou)(hou)裂紋沿切應力(li)面展開(kai)為(wei)(wei)V型(xing)(xing)(xing)，并(bing)且充(chong)滿(man)了富(fu)(fu)集元素(su)的(de)(de)(de)(de)(de)(de)(de)液相(xiang)(xiang)。而沿鑄(zhu)(zhu)錠(ding)側(ce)壁分(fen)(fen)布的(de)(de)(de)(de)(de)(de)(de)帶狀偏(pian)(pian)(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)則是(shi)(shi)(shi)由凝(ning)固(gu)過程初期的(de)(de)(de)(de)(de)(de)(de)不穩定(ding)傳(chuan)熱和(he)流動(dong)(dong)導(dao)致的(de)(de)(de)(de)(de)(de)(de)。

  對(dui)于宏觀偏(pian)析的研(yan)究(jiu)主要有實驗檢測和模(mo)擬計(ji)(ji)算(suan)(suan)(suan)(suan)兩種手(shou)段。實驗檢測包括硫印檢驗法(fa)、原位分(fen)析法(fa)、火花放電(dian)原子發(fa)射光譜(pu)法(fa)、鉆孔取(qu)樣法(fa)以(yi)及(ji)化學(xue)分(fen)析法(fa)等。模(mo)擬計(ji)(ji)算(suan)(suan)(suan)(suan)是通過(guo)數(shu)(shu)值(zhi)求解能(neng)量、動量以(yi)及(ji)溶質(zhi)傳(chuan)輸等數(shu)(shu)學(xue)模(mo)型(xing)，進而探討元素(su)成分(fen)不均勻(yun)性(xing)的方法(fa)；進入20世紀后，人們對(dui)凝(ning)固(gu)過(guo)程中的宏觀偏(pian)析現象進行了大量系統的研(yan)究(jiu)。Flemings研(yan)究(jiu)表(biao)明鑄錠(ding)中多(duo)種不同的宏觀偏(pian)析都可由(you)凝(ning)固(gu)時的傳(chuan)熱、流動和傳(chuan)質(zhi)過(guo)程來定(ding)量描(miao)述，從而為(wei)宏觀偏(pian)析的定(ding)量計(ji)(ji)算(suan)(suan)(suan)(suan)提(ti)供可能(neng)性(xing)，隨著計(ji)(ji)算(suan)(suan)(suan)(suan)機計(ji)(ji)算(suan)(suan)(suan)(suan)能(neng)力(li)迅猛提(ti)升，宏觀偏(pian)析的模(mo)擬計(ji)(ji)算(suan)(suan)(suan)(suan)得到(dao)了迅速發(fa)展，主要分(fen)為(wei)多(duo)區域法(fa)和連續介質(zhi)法(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。