一、氮氣孔(kong)的形成機理

  在(zai)(zai)21.5Cr5Mn1.5Ni0.25N含氮(dan)(dan)(dan)(dan)(dan)雙相(xiang)(xiang)(xiang)(xiang)(xiang)鋼(gang)凝(ning)固過(guo)程中(zhong)，氮(dan)(dan)(dan)(dan)(dan)氣孔形(xing)(xing)成(cheng)和(he)凝(ning)固前(qian)沿處［％N]1iq隨(sui)距離變化的(de)(de)(de)規律如(ru)圖(tu)(tu)2-55所(suo)示。由于糊狀(zhuang)(zhuang)區(qu)內(nei)大量(liang)枝(zhi)晶(jing)網狀(zhuang)(zhuang)結構的(de)(de)(de)形(xing)(xing)成(cheng)，液(ye)(ye)相(xiang)(xiang)(xiang)(xiang)(xiang)的(de)(de)(de)對流(liu)只(zhi)存在(zai)(zai)于一次枝(zhi)晶(jing)尖端(duan)位置附近。且(qie)枝(zhi)晶(jing)間(jian)幾乎無(wu)液(ye)(ye)相(xiang)(xiang)(xiang)(xiang)(xiang)的(de)(de)(de)流(liu)動。因(yin)此，枝(zhi)晶(jing)間(jian)殘(can)余液(ye)(ye)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)的(de)(de)(de)氮(dan)(dan)(dan)(dan)(dan)傳質主要(yao)依靠氮(dan)(dan)(dan)(dan)(dan)的(de)(de)(de)擴散行為(wei)，且(qie)糊狀(zhuang)(zhuang)區(qu)內(nei)氮(dan)(dan)(dan)(dan)(dan)傳質速率非常小(xiao)(xiao)。初(chu)始(shi)(shi)(shi)相(xiang)(xiang)(xiang)(xiang)(xiang)貧(pin)氮(dan)(dan)(dan)(dan)(dan)鐵(tie)素(su)(su)體(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)8的(de)(de)(de)氮(dan)(dan)(dan)(dan)(dan)溶解(jie)度和(he)糊狀(zhuang)(zhuang)區(qu)的(de)(de)(de)氮(dan)(dan)(dan)(dan)(dan)傳質速率較低，導致在(zai)(zai)貧(pin)氮(dan)(dan)(dan)(dan)(dan)鐵(tie)素(su)(su)體(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)枝(zhi)晶(jing)附近的(de)(de)(de)液(ye)(ye)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)出現氮(dan)(dan)(dan)(dan)(dan)富(fu)(fu)集(ji)，且(qie)［％N]iq迅(xun)速增(zeng)大，如(ru)圖(tu)(tu)2-55(a)所(suo)示。根據(ju)Yang和(he) Leel70]、Svyazhin 等、Ridolfi 和(he) Tassal的(de)(de)(de)報道可(ke)知(zhi)，當［％N]iq的(de)(de)(de)最大值超過(guo)氮(dan)(dan)(dan)(dan)(dan)氣泡(pao)(pao)形(xing)(xing)成(cheng)的(de)(de)(de)臨界氮(dan)(dan)(dan)(dan)(dan)質量(liang)分數（［％N]pore)時，該區(qu)域有氣泡(pao)(pao)形(xing)(xing)成(cheng)的(de)(de)(de)可(ke)能(neng)性，如(ru)圖(tu)(tu)2-55(b)所(suo)示。在(zai)(zai)后(hou)續(xu)的(de)(de)(de)凝(ning)固過(guo)程中(zhong)，隨(sui)著包晶(jing)反(fan)應的(de)(de)(de)進(jin)行，富(fu)(fu)氮(dan)(dan)(dan)(dan)(dan)奧氏(shi)體(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)γ以異質形(xing)(xing)核的(de)(de)(de)方式在(zai)(zai)鐵(tie)素(su)(su)體(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)8枝(zhi)晶(jing)的(de)(de)(de)表面(mian)(mian)開始(shi)(shi)(shi)形(xing)(xing)核長(chang)(chang)大，逐漸包裹(guo)鐵(tie)素(su)(su)體(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)枝(zhi)晶(jing)表面(mian)(mian)，并開始(shi)(shi)(shi)捕(bu)獲殘(can)余液(ye)(ye)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)的(de)(de)(de)氮(dan)(dan)(dan)(dan)(dan)氣泡(pao)(pao)，對比圖(tu)(tu)2-51和(he)圖(tu)(tu)2-56可(ke)知(zhi)，此時枝(zhi)晶(jing)間(jian)殘(can)余［％N]1ig的(de)(de)(de)增(zeng)長(chang)(chang)速率減小(xiao)(xiao)。對平衡(heng)凝(ning)固而言，殘(can)余液(ye)(ye)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)氮(dan)(dan)(dan)(dan)(dan)氣泡(pao)(pao)形(xing)(xing)成(cheng)以后(hou)，氮(dan)(dan)(dan)(dan)(dan)的(de)(de)(de)富(fu)(fu)集(ji)程度減弱，［％N]1iq增(zeng)長(chang)(chang)速率的(de)(de)(de)減小(xiao)(xiao)程度明顯(xian)；相(xiang)(xiang)(xiang)(xiang)(xiang)比之下，Scheil凝(ning)固過(guo)程中(zhong)，氮(dan)(dan)(dan)(dan)(dan)氣泡(pao)(pao)形(xing)(xing)成(cheng)以后(hou)，殘(can)余液(ye)(ye)相(xiang)(xiang)(xiang)(xiang)(xiang)中(zhong)氮(dan)(dan)(dan)(dan)(dan)富(fu)(fu)集(ji)狀(zhuang)(zhuang)態有所(suo)緩解(jie)，但幅度很小(xiao)(xiao)。隨(sui)著凝(ning)固界面(mian)(mian)的(de)(de)(de)進(jin)一步推(tui)移，被捕(bu)獲的(de)(de)(de)氮(dan)(dan)(dan)(dan)(dan)氣泡(pao)(pao)在(zai)(zai)奧氏(shi)體(ti)(ti)相(xiang)(xiang)(xiang)(xiang)(xiang)表面(mian)(mian)開始(shi)(shi)(shi)長(chang)(chang)大，并沿凝(ning)固方向拉(la)長(chang)(chang)，如(ru)圖(tu)(tu)2-55(c)所(suo)示。

  氮(dan)氣(qi)孔(kong)沿徑向生(sheng)長，生(sheng)長方(fang)向與(yu)凝(ning)固方(fang)向一致(zhi)(zhi)，那么氮(dan)氣(qi)孔(kong)初(chu)始形成(cheng)位置靠近鑄錠邊部(bu)，且氮(dan)氣(qi)泡初(chu)始位置邊緣全由奧氏(shi)(shi)體相(xiang)γ構成(cheng)（圖(tu)2-57中I區(qu)），與(yu)圖(tu)2-55描述相(xiang)符。隨著氮(dan)氣(qi)孔(kong)被拉長，鐵素體相(xiang)和奧氏(shi)(shi)體相(xiang)以(yi)體積分數比(bi)約為0.92的關系交替在(zai)氮(dan)氣(qi)泡周(zhou)圍形成(cheng)，直到(dao)氮(dan)氣(qi)孔(kong)閉合。凝(ning)固結(jie)束(shu)后，氮(dan)氣(qi)孔(kong)的宏(hong)觀形貌類似于(yu)橢圓形，與(yu)Wei等的研究結(jie)果一致(zhi)(zhi)

二、氮微觀偏析對氮氣孔的影響

  氮(dan)(dan)的(de)分配系數較小(xiao)，導(dao)致(zhi)液(ye)(ye)相(xiang)(xiang)向固(gu)(gu)(gu)(gu)(gu)(gu)相(xiang)(xiang)轉變的(de)過程(cheng)中(zhong)(zhong)(zhong)，固(gu)(gu)(gu)(gu)(gu)(gu)相(xiang)(xiang)會將多余的(de)氮(dan)(dan)轉移到殘余液(ye)(ye)相(xiang)(xiang)中(zhong)(zhong)(zhong)，形(xing)(xing)成(cheng)(cheng)氮(dan)(dan)偏析。在氮(dan)(dan)偏析程(cheng)度(du)逐漸加重的(de)過程(cheng)中(zhong)(zhong)(zhong)，當殘余液(ye)(ye)相(xiang)(xiang)中(zhong)(zhong)(zhong)氮(dan)(dan)質量分數超過其飽和度(du)時，極易形(xing)(xing)成(cheng)(cheng)氮(dan)(dan)氣(qi)(qi)(qi)泡。隨著凝(ning)固(gu)(gu)(gu)(gu)(gu)(gu)的(de)進行，若氣(qi)(qi)(qi)泡無法(fa)上浮而被捕獲，凝(ning)固(gu)(gu)(gu)(gu)(gu)(gu)結束后就會在鑄錠(ding)內部(bu)形(xing)(xing)成(cheng)(cheng)氣(qi)(qi)(qi)孔。因此，凝(ning)固(gu)(gu)(gu)(gu)(gu)(gu)過程(cheng)中(zhong)(zhong)(zhong)氮(dan)(dan)偏析和溶解度(du)對鑄錠(ding)中(zhong)(zhong)(zhong)最終(zhong)氮(dan)(dan)氣(qi)(qi)(qi)孔的(de)形(xing)(xing)成(cheng)(cheng)有(you)至關重要的(de)作用。氮(dan)(dan)氣(qi)(qi)(qi)孔多數情況下與疏松縮(suo)孔共(gong)存，內壁(bi)凹凸不平(ping)呈(cheng)現裂紋狀，且(qie)整個氣(qi)(qi)(qi)孔形(xing)(xing)狀不規則，如圖2-58所(suo)示(shi)。此類氣(qi)(qi)(qi)孔不僅與鋼液(ye)(ye)中(zhong)(zhong)(zhong)氣(qi)(qi)(qi)泡的(de)形(xing)(xing)成(cheng)(cheng)有(you)關，還受(shou)凝(ning)固(gu)(gu)(gu)(gu)(gu)(gu)收縮(suo)等(deng)因素(su)的(de)影響，且(qie)多數分布于(yu)鑄錠(ding)心(xin)(xin)部(bu)，尤其在中(zhong)(zhong)(zhong)心(xin)(xin)等(deng)軸晶(jing)區(qu)。這主要由于(yu)中(zhong)(zhong)(zhong)心(xin)(xin)等(deng)軸晶(jing)區(qu)內枝晶(jing)生長較發達，容(rong)易形(xing)(xing)成(cheng)(cheng)復(fu)雜(za)的(de)網狀結構，從(cong)而將液(ye)(ye)相(xiang)(xiang)分割成(cheng)(cheng)無數個獨立的(de)液(ye)(ye)相(xiang)(xiang)區(qu)域，當發生凝(ning)固(gu)(gu)(gu)(gu)(gu)(gu)收縮(suo)時，難以進行補縮(suo)，在形(xing)(xing)成(cheng)(cheng)疏松縮(suo)孔的(de)同時，局部(bu)鋼液(ye)(ye)靜壓力降低，促使氮(dan)(dan)從(cong)殘余液(ye)(ye)相(xiang)(xiang)中(zhong)(zhong)(zhong)析出(chu)，從(cong)而形(xing)(xing)成(cheng)(cheng)了氮(dan)(dan)氣(qi)(qi)(qi)孔和疏松縮(suo)孔共(gong)存的(de)宏觀缺陷。

  平衡凝(ning)固(gu)(gu)(gu)時，19Cr14Mn0.9N含氮(dan)(dan)(dan)奧氏(shi)體(ti)(ti)不(bu)(bu)銹(xiu)鋼殘余液相(xiang)中(zhong)(zhong)(zhong)氮(dan)(dan)(dan)偏析(xi)與(yu)體(ti)(ti)系氮(dan)(dan)(dan)溶(rong)解度的(de)差值(zhi)(zhi)如圖2-59所示。凝(ning)固(gu)(gu)(gu)初期鐵素體(ti)(ti)阱（ferrite trap)的(de)形(xing)成(cheng)，導致氮(dan)(dan)(dan)溶(rong)解度的(de)降低，進而使氮(dan)(dan)(dan)偏析(xi)與(yu)體(ti)(ti)系氮(dan)(dan)(dan)溶(rong)解度差值(zhi)(zhi)呈(cheng)現出略微增大的(de)趨(qu)勢。但(dan)在后續凝(ning)固(gu)(gu)(gu)過(guo)程(cheng)中(zhong)(zhong)(zhong)，隨著鐵素體(ti)(ti)阱的(de)消(xiao)失以(yi)(yi)及富(fu)氮(dan)(dan)(dan)奧氏(shi)體(ti)(ti)相(xiang)的(de)不(bu)(bu)斷形(xing)成(cheng)，差值(zhi)(zhi)減小(xiao)；在整個凝(ning)固(gu)(gu)(gu)過(guo)程(cheng)中(zhong)(zhong)(zhong)差值(zhi)(zhi)始終較(jiao)小(xiao)，且變化幅度較(jiao)窄(zhai)。對于19Cr14Mn0.9N 含氮(dan)(dan)(dan)奧氏(shi)體(ti)(ti)不(bu)(bu)銹(xiu)鋼，液相(xiang)中(zhong)(zhong)(zhong)氮(dan)(dan)(dan)氣泡(pao)的(de)形(xing)成(cheng)趨(qu)勢較(jiao)小(xiao)，難以(yi)(yi)在鑄錠(ding)內(nei)形(xing)成(cheng)獨立內(nei)壁光滑(hua)的(de)規則氮(dan)(dan)(dan)氣孔(kong)。

  此外，目前有(you)人對(dui)(dui)奧氏體(ti)(ti)鋼(gang)(gang)凝固(gu)過(guo)程中(zhong)(zhong)(zhong)氮(dan)(dan)(dan)(dan)(dan)氣(qi)孔(kong)(kong)的(de)(de)形(xing)(xing)(xing)成(cheng)(cheng)進(jin)行了大(da)量研(yan)(yan)究(jiu)，如Yang和Leel901研(yan)(yan)究(jiu)了奧氏體(ti)(ti)鋼(gang)(gang)16Cr3NixMn(x=9和11)凝固(gu)過(guo)程中(zhong)(zhong)(zhong)壓力和初始氮(dan)(dan)(dan)(dan)(dan)質(zhi)量分數等因(yin)素對(dui)(dui)氮(dan)(dan)(dan)(dan)(dan)氣(qi)孔(kong)(kong)形(xing)(xing)(xing)成(cheng)(cheng)的(de)(de)影響(xiang)規律，并(bing)建立(li)了相(xiang)(xiang)(xiang)(xiang)應的(de)(de)預測模型。Ridolfi和Tassal[84]分析(xi)了氮(dan)(dan)(dan)(dan)(dan)偏析(xi)、合(he)金(jin)元素、冷(leng)卻速率以(yi)及枝晶(jing)間距(ju)對(dui)(dui)奧氏體(ti)(ti)鋼(gang)(gang)中(zhong)(zhong)(zhong)氮(dan)(dan)(dan)(dan)(dan)氣(qi)孔(kong)(kong)的(de)(de)影響(xiang)規律，并(bing)揭示了奧氏體(ti)(ti)鋼(gang)(gang)中(zhong)(zhong)(zhong)氮(dan)(dan)(dan)(dan)(dan)氣(qi)孔(kong)(kong)形(xing)(xing)(xing)成(cheng)(cheng)機理。然而，目前對(dui)(dui)于(yu)雙相(xiang)(xiang)(xiang)(xiang)鋼(gang)(gang)中(zhong)(zhong)(zhong)氮(dan)(dan)(dan)(dan)(dan)氣(qi)孔(kong)(kong)形(xing)(xing)(xing)成(cheng)(cheng)的(de)(de)研(yan)(yan)究(jiu)較少，且(qie)主要集中(zhong)(zhong)(zhong)在(zai)合(he)金(jin)元素、鑄(zhu)造方式、冷(leng)卻速率等因(yin)素對(dui)(dui)氮(dan)(dan)(dan)(dan)(dan)氣(qi)孔(kong)(kong)影響(xiang)規律的(de)(de)研(yan)(yan)究(jiu)，鮮(xian)有(you)對(dui)(dui)雙相(xiang)(xiang)(xiang)(xiang)鋼(gang)(gang)中(zhong)(zhong)(zhong)氮(dan)(dan)(dan)(dan)(dan)氣(qi)孔(kong)(kong)形(xing)(xing)(xing)成(cheng)(cheng)機理的(de)(de)報道。以(yi)21.5Cr5Mn1.5Ni0.25N含(han)氮(dan)(dan)(dan)(dan)(dan)雙相(xiang)(xiang)(xiang)(xiang)鋼(gang)(gang)為例，氮(dan)(dan)(dan)(dan)(dan)偏析(xi)與(yu)溶(rong)(rong)解度(du)的(de)(de)差(cha)值在(zai)整個凝固(gu)過(guo)程中(zhong)(zhong)(zhong)的(de)(de)變化趨勢(shi)，如圖2-59所示。隨著凝固(gu)的(de)(de)進(jin)行，氮(dan)(dan)(dan)(dan)(dan)偏析(xi)始終(zhong)大(da)于(yu)氮(dan)(dan)(dan)(dan)(dan)溶(rong)(rong)解度(du)，且(qie)差(cha)值呈現出快速增(zeng)大(da)的(de)(de)趨勢(shi)。因(yin)此，在(zai)21.5Cr5Mn1.5Ni0.25N 含(han)氮(dan)(dan)(dan)(dan)(dan)雙相(xiang)(xiang)(xiang)(xiang)鋼(gang)(gang)凝固(gu)過(guo)程中(zhong)(zhong)(zhong)，氮(dan)(dan)(dan)(dan)(dan)偏析(xi)嚴重，殘余液相(xiang)(xiang)(xiang)(xiang)內氮(dan)(dan)(dan)(dan)(dan)氣(qi)泡形(xing)(xing)(xing)成(cheng)(cheng)趨勢(shi)較大(da)，明顯高于(yu)19Cr14Mn0.9N含(han)氮(dan)(dan)(dan)(dan)(dan)奧氏體(ti)(ti)不銹鋼(gang)(gang)。

  氮氣(qi)(qi)泡(pao)(pao)(pao)(pao)形成(cheng)和長(chang)大(da)具有重要(yao)的作用（圖(tu)2-60).其中，σ為氣(qi)(qi)液(ye)界面的表面張力，r為氣(qi)(qi)泡(pao)(pao)(pao)(pao)半徑。結合經典形核理論，氮氣(qi)(qi)泡(pao)(pao)(pao)(pao)在(zai)鋼(gang)液(ye)中穩定存在(zai)的必要(yao)條件為氣(qi)(qi)泡(pao)(pao)(pao)(pao)內(nei)壓力大(da)于作用于氣(qi)(qi)泡(pao)(pao)(pao)(pao)的所有壓力之(zhi)和，即

  式中，Aso由凝(ning)固(gu)過程(cheng)中除氮(dan)以外(wai)(wai)其他合(he)金(jin)元素(su)的(de)(de)(de)微觀(guan)偏(pian)析進行計(ji)(ji)算(suan)，其值(zhi)隨(sui)著枝(zhi)(zhi)晶間(jian)殘余(yu)液相(xiang)(xiang)中氮(dan)溶(rong)解(jie)度(du)的(de)(de)(de)增加而減(jian)小，表(biao)征(zheng)了枝(zhi)(zhi)晶間(jian)殘余(yu)液相(xiang)(xiang)中氮(dan)溶(rong)解(jie)度(du)對氮(dan)氣泡(pao)(pao)形成(cheng)的(de)(de)(de)影響程(cheng)度(du)；Ase表(biao)征(zheng)了枝(zhi)(zhi)晶間(jian)氮(dan)偏(pian)析對氮(dan)氣泡(pao)(pao)形成(cheng)的(de)(de)(de)影響程(cheng)度(du)，可由凝(ning)固(gu)過程(cheng)中枝(zhi)(zhi)晶間(jian)殘余(yu)液相(xiang)(xiang)中氮(dan)偏(pian)析計(ji)(ji)算(suan)獲得(de)，其值(zhi)隨(sui)著氮(dan)偏(pian)析的(de)(de)(de)增大而增大。此外(wai)(wai)，用于計(ji)(ji)算(suan)Aso和Ase時所需的(de)(de)(de)合(he)金(jin)元素(su)偏(pian)析均由鋼凝(ning)固(gu)相(xiang)(xiang)變(bian)所致。

  氮(dan)氣泡的(de)形核和(he)長大(da)過程(cheng)復雜，且(qie)影響因素眾多，包括凝(ning)(ning)(ning)固(gu)(gu)(gu)(gu)(gu)收縮、冶煉環境以及(ji)坩堝材質等。因此，很(hen)難(nan)采用Pg值精確預測凝(ning)(ning)(ning)固(gu)(gu)(gu)(gu)(gu)過程(cheng)中氮(dan)氣泡的(de)形成(cheng)和(he)長大(da)。然(ran)而基于(yu)Yang等的(de)實驗(yan)研究［70,77],在評估凝(ning)(ning)(ning)固(gu)(gu)(gu)(gu)(gu)壓力(li)(li)、合金成(cheng)分等因素對氮(dan)氣泡形成(cheng)的(de)影響程(cheng)度時，Pg起關鍵作用。實際(ji)凝(ning)(ning)(ning)固(gu)(gu)(gu)(gu)(gu)過程(cheng)介于(yu)平(ping)衡(heng)凝(ning)(ning)(ning)固(gu)(gu)(gu)(gu)(gu)（固(gu)(gu)(gu)(gu)(gu)／液相中溶質完全擴(kuo)散(san)）和(he)Scheil凝(ning)(ning)(ning)固(gu)(gu)(gu)(gu)(gu)（固(gu)(gu)(gu)(gu)(gu)相無(wu)溶質擴(kuo)散(san)，液相中完全擴(kuo)散(san)）之間70].因此，可(ke)分別計算平(ping)衡(heng)凝(ning)(ning)(ning)固(gu)(gu)(gu)(gu)(gu)和(he)Scheil凝(ning)(ning)(ning)固(gu)(gu)(gu)(gu)(gu)過程(cheng)中的(de)Aso、Ase和(he)Pg,闡明實際(ji)凝(ning)(ning)(ning)固(gu)(gu)(gu)(gu)(gu)過程(cheng)中壓力(li)(li)等因素對氮(dan)氣泡形成(cheng)的(de)影響規律。

  現(xian)以21.5Cr5Mn1.5Ni0.25N含(han)氮(dan)雙(shuang)相鋼D1鑄(zhu)(zhu)錠(ding)為(wei)例，對凝固(gu)過程中Aso、Ase和P8的(de)變化趨勢進(jin)行計算(suan)。圖2-61描(miao)述了ΔAso(=Asa-Aso,0)和AAse(=Ase-Ase,o)隨固(gu)相質量分數的(de)變化趨勢（Aso,0和Asc,0分別為(wei)D1鑄(zhu)(zhu)錠(ding)凝固(gu)時Aso和Ase的(de)初始值(zhi)）。

  在(zai)平衡凝固(gu)和(he)(he)Scheil凝固(gu)過(guo)(guo)程(cheng)(cheng)(cheng)中(zhong)(zhong)，ΔAso的(de)(de)最(zui)小值(zhi)分(fen)別(bie)為－0.145和(he)(he)－0.397,與(yu)此(ci)相對(dui)應的(de)(de)ΔAse值(zhi)最(zui)大，分(fen)別(bie)為0.68和(he)(he)0.92.在(zai)整個凝固(gu)過(guo)(guo)程(cheng)(cheng)(cheng)中(zhong)(zhong)，由于(yu)ΔAse與(yu)ΔAso之和(he)(he)始(shi)終大于(yu)零，因而枝(zhi)晶(jing)間殘(can)余液相中(zhong)(zhong)氮(dan)(dan)偏析對(dui)D1 鑄(zhu)錠(ding)凝固(gu)過(guo)(guo)程(cheng)(cheng)(cheng)中(zhong)(zhong)氮(dan)(dan)氣(qi)泡形成的(de)(de)影響大于(yu)氮(dan)(dan)溶解度，起主(zhu)導作用。此(ci)外，在(zai)整個凝固(gu)過(guo)(guo)程(cheng)(cheng)(cheng)中(zhong)(zhong)，P8變化趨勢如圖(tu)2-62所示，其變化規律與(yu)Young等(deng)(deng)。的(de)(de)研究(jiu)結果一致，Pg的(de)(de)最(zui)大值(zhi)Pg與(yu)Ase+Aso的(de)(de)最(zui)大值(zhi)相對(dui)應，且在(zai)平衡凝固(gu)和(he)(he) Scheil 凝固(gu)過(guo)(guo)程(cheng)(cheng)(cheng)中(zhong)(zhong)分(fen)別(bie)為0.63MPa和(he)(he)0.62MPa.此(ci)外，可通過(guo)(guo)對(dui)比(bi)不同(tong)鑄(zhu)錠(ding)中(zhong)(zhong)的(de)(de)探討凝固(gu)壓力、初始(shi)氮(dan)(dan)質量分(fen)數以(yi)及(ji)合金元素（鉻和(he)(he)錳(meng)）等(deng)(deng)對(dui)液相中(zhong)(zhong)氮(dan)(dan)氣(qi)泡形成的(de)(de)影響，進而明晰各因素對(dui)氮(dan)(dan)氣(qi)孔形成的(de)(de)影響規律。