根據相(xiang)(xiang)圖，多數(shu)合(he)(he)金(jin)(jin)元素在(zai)固(gu)(gu)(gu)(gu)相(xiang)(xiang)中(zhong)(zhong)的(de)(de)(de)(de)溶(rong)解度(du)(du)要低(di)于液相(xiang)(xiang)，因此在(zai)凝(ning)固(gu)(gu)(gu)(gu)過程中(zhong)(zhong)溶(rong)質(zhi)(zhi)原(yuan)子不(bu)斷被排出到(dao)液相(xiang)(xiang)，這(zhe)種固(gu)(gu)(gu)(gu)液界(jie)面兩側溶(rong)質(zhi)(zhi)濃度(du)(du)的(de)(de)(de)(de)差異(yi)導(dao)(dao)致(zhi)合(he)(he)金(jin)(jin)凝(ning)固(gu)(gu)(gu)(gu)后溶(rong)質(zhi)(zhi)元素成(cheng)分不(bu)均勻(yun)性，稱(cheng)作偏(pian)(pian)析(xi)。溶(rong)質(zhi)(zhi)元素分布不(bu)均勻(yun)性發生(sheng)在(zai)微觀(guan)結構(gou)形(xing)(xing)成(cheng)范(fan)(fan)圍內（有10~100μm的(de)(de)(de)(de)樹狀(zhuang)枝晶），此時為(wei)微觀(guan)偏(pian)(pian)析(xi)。溶(rong)質(zhi)(zhi)元素通(tong)過對流傳(chuan)質(zhi)(zhi)等質(zhi)(zhi)量傳(chuan)輸，將(jiang)導(dao)(dao)致(zhi)大(da)(da)范(fan)(fan)圍內成(cheng)分不(bu)均勻(yun)性，即形(xing)(xing)成(cheng)了宏觀(guan)偏(pian)(pian)析(xi)。宏觀(guan)偏(pian)(pian)析(xi)可以認(ren)為(wei)是由凝(ning)固(gu)(gu)(gu)(gu)過程中(zhong)(zhong)液體(ti)和(he)(he)固(gu)(gu)(gu)(gu)體(ti)相(xiang)(xiang)對運動和(he)(he)溶(rong)質(zhi)(zhi)再分配過程共(gong)同(tong)導(dao)(dao)致(zhi)的(de)(de)(de)(de)。此外(wai)，在(zai)凝(ning)固(gu)(gu)(gu)(gu)早(zao)期所(suo)形(xing)(xing)成(cheng)的(de)(de)(de)(de)固(gu)(gu)(gu)(gu)體(ti)相(xiang)(xiang)或(huo)非金(jin)(jin)屬夾雜(za)的(de)(de)(de)(de)漂浮和(he)(he)下(xia)沉也會(hui)造(zao)成(cheng)宏觀(guan)偏(pian)(pian)析(xi)。一般認(ren)為(wei)在(zai)合(he)(he)金(jin)(jin)鑄件或(huo)鑄錠(ding)內，從幾(ji)毫(hao)米到(dao)幾(ji)厘(li)米甚至幾(ji)米范(fan)(fan)圍內濃度(du)(du)變化為(wei)宏觀(guan)偏(pian)(pian)析(xi)。因為(wei)溶(rong)質(zhi)(zhi)在(zai)固(gu)(gu)(gu)(gu)態中(zhong)(zhong)的(de)(de)(de)(de)擴散系數(shu)很(hen)低(di)，而(er)成(cheng)分不(bu)均勻(yun)性范(fan)(fan)圍又很(hen)大(da)(da)，所(suo)以在(zai)凝(ning)固(gu)(gu)(gu)(gu)完成(cheng)后，宏觀(guan)偏(pian)(pian)析(xi)很(hen)難通(tong)過加(jia)(jia)工處(chu)理來(lai)消(xiao)除，因此抑制宏觀(guan)偏(pian)(pian)析(xi)的(de)(de)(de)(de)產生(sheng)主要是對工藝參(can)數(shu)進行優化，如控制合(he)(he)金(jin)(jin)成(cheng)分、施(shi)加(jia)(jia)外(wai)力(li)場(chang)（磁場(chang)等）、優化鑄錠(ding)幾(ji)何形(xing)(xing)狀(zhuang)、適當加(jia)(jia)大(da)(da)冷卻速(su)率等。

  宏(hong)觀偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)是(shi)(shi)大范圍內的(de)(de)(de)(de)成分(fen)不均勻現(xian)象，按其(qi)表現(xian)形(xing)式可分(fen)為(wei)正偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)、反(fan)(fan)(fan)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)和(he)(he)比重(zhong)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)等。①. 正偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)：對平衡分(fen)配系(xi)數o<1的(de)(de)(de)(de)合(he)金(jin)系(xi)鑄(zhu)錠(ding)先(xian)凝(ning)固(gu)的(de)(de)(de)(de)部(bu)(bu)(bu)分(fen)，其(qi)溶(rong)質(zhi)含量低于(yu)(yu)(yu)后凝(ning)固(gu)的(de)(de)(de)(de)部(bu)(bu)(bu)分(fen)。對ko>1的(de)(de)(de)(de)合(he)金(jin)系(xi)則正好(hao)相(xiang)反(fan)(fan)(fan)，其(qi)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)程度與(yu)凝(ning)固(gu)速率、液(ye)(ye)體對流(liu)以及溶(rong)質(zhi)擴散等條件有關(guan)。②. 反(fan)(fan)(fan)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)：在(zai)(zai)ko<1的(de)(de)(de)(de)合(he)金(jin)鑄(zhu)錠(ding)中(zhong)(zhong)，其(qi)外(wai)層溶(rong)質(zhi)元素(su)高(gao)于(yu)(yu)(yu)內部(bu)(bu)(bu)，和(he)(he)正偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)相(xiang)反(fan)(fan)(fan)，故稱(cheng)為(wei)反(fan)(fan)(fan)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)。③. 比重(zhong)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)：是(shi)(shi)由(you)(you)合(he)金(jin)凝(ning)固(gu)時形(xing)成的(de)(de)(de)(de)初晶(jing)(jing)(jing)相(xiang)和(he)(he)溶(rong)液(ye)(ye)之間的(de)(de)(de)(de)比重(zhong)顯著差(cha)別引起的(de)(de)(de)(de)一種宏(hong)觀偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)，主要存(cun)在(zai)(zai)于(yu)(yu)(yu)共晶(jing)(jing)(jing)系(xi)和(he)(he)偏(pian)(pian)(pian)(pian)(pian)晶(jing)(jing)(jing)系(xi)合(he)金(jin)中(zhong)(zhong)。如圖2-49所(suo)示，由(you)(you)于(yu)(yu)(yu)溶(rong)質(zhi)元素(su)濃度相(xiang)對低的(de)(de)(de)(de)等軸(zhou)晶(jing)(jing)(jing)沉積導(dao)致在(zai)(zai)鑄(zhu)錠(ding)的(de)(de)(de)(de)底部(bu)(bu)(bu)出現(xian)負偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)；由(you)(you)于(yu)(yu)(yu)浮力和(he)(he)在(zai)(zai)凝(ning)固(gu)的(de)(de)(de)(de)最(zui)后階段(duan)收縮所(suo)引起的(de)(de)(de)(de)晶(jing)(jing)(jing)間流(liu)動(dong)，在(zai)(zai)頂部(bu)(bu)(bu)會(hui)出現(xian)很嚴重(zhong)的(de)(de)(de)(de)正偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)（頂部(bu)(bu)(bu)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)）。A型偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)是(shi)(shi)溶(rong)質(zhi)富集(ji)的(de)(de)(de)(de)等軸(zhou)晶(jing)(jing)(jing)帶(dai)，由(you)(you)溶(rong)質(zhi)受浮力作用流(liu)動(dong)穿(chuan)過柱狀(zhuang)(zhuang)晶(jing)(jing)(jing)區，其(qi)方向(xiang)與(yu)等溫(wen)線移動(dong)速度方向(xiang)一致但速率更快所(suo)導(dao)致。A型偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)形(xing)狀(zhuang)(zhuang)與(yu)流(liu)動(dong)類型有關(guan)。V型偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)位于(yu)(yu)(yu)鑄(zhu)錠(ding)中(zhong)(zhong)心，源(yuan)于(yu)(yu)(yu)中(zhong)(zhong)心形(xing)成等軸(zhou)晶(jing)(jing)(jing)區和(he)(he)容易斷裂的(de)(de)(de)(de)連接疏(shu)松(song)的(de)(de)(de)(de)網狀(zhuang)(zhuang)物(wu)的(de)(de)(de)(de)形(xing)成，之后裂紋沿切應力面展開為(wei)V型，并且充滿了富集(ji)元素(su)的(de)(de)(de)(de)液(ye)(ye)相(xiang)。而沿鑄(zhu)錠(ding)側壁分(fen)布的(de)(de)(de)(de)帶(dai)狀(zhuang)(zhuang)偏(pian)(pian)(pian)(pian)(pian)析(xi)(xi)(xi)(xi)(xi)(xi)則是(shi)(shi)由(you)(you)凝(ning)固(gu)過程初期的(de)(de)(de)(de)不穩定(ding)傳熱和(he)(he)流(liu)動(dong)導(dao)致的(de)(de)(de)(de)。

  對(dui)于宏(hong)觀(guan)(guan)偏(pian)析的(de)(de)研(yan)究(jiu)主(zhu)要有實驗檢(jian)測(ce)和(he)(he)模(mo)擬(ni)(ni)計(ji)算(suan)(suan)兩(liang)種(zhong)手段(duan)。實驗檢(jian)測(ce)包括硫(liu)印檢(jian)驗法(fa)(fa)(fa)、原位分析法(fa)(fa)(fa)、火花放電(dian)原子發(fa)射光譜法(fa)(fa)(fa)、鉆孔取樣法(fa)(fa)(fa)以及化學分析法(fa)(fa)(fa)等。模(mo)擬(ni)(ni)計(ji)算(suan)(suan)是通(tong)過數值求解能量(liang)(liang)、動量(liang)(liang)以及溶質(zhi)(zhi)傳(chuan)輸等數學模(mo)型，進而探討元素(su)成分不(bu)(bu)均勻性的(de)(de)方法(fa)(fa)(fa)；進入(ru)20世紀后，人們對(dui)凝固過程中的(de)(de)宏(hong)觀(guan)(guan)偏(pian)析現象進行了大量(liang)(liang)系統(tong)的(de)(de)研(yan)究(jiu)。Flemings研(yan)究(jiu)表明鑄錠(ding)中多(duo)種(zhong)不(bu)(bu)同(tong)的(de)(de)宏(hong)觀(guan)(guan)偏(pian)析都可由凝固時的(de)(de)傳(chuan)熱、流動和(he)(he)傳(chuan)質(zhi)(zhi)過程來定量(liang)(liang)描述，從而為宏(hong)觀(guan)(guan)偏(pian)析的(de)(de)定量(liang)(liang)計(ji)算(suan)(suan)提(ti)(ti)供可能性，隨(sui)著計(ji)算(suan)(suan)機(ji)計(ji)算(suan)(suan)能力迅猛提(ti)(ti)升，宏(hong)觀(guan)(guan)偏(pian)析的(de)(de)模(mo)擬(ni)(ni)計(ji)算(suan)(suan)得到了迅速(su)發(fa)展，主(zhu)要分為多(duo)區(qu)域法(fa)(fa)(fa)和(he)(he)連續介(jie)質(zhi)(zhi)法(fa)(fa)(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。