一、氮氣孔的形成機理

  在(zai)21.5Cr5Mn1.5Ni0.25N含氮(dan)雙相(xiang)(xiang)(xiang)鋼(gang)凝固(gu)(gu)過程(cheng)中，氮(dan)氣(qi)(qi)(qi)孔形(xing)成(cheng)(cheng)和(he)凝固(gu)(gu)前(qian)沿處［％N]1iq隨距離變化的(de)(de)(de)(de)(de)(de)規律如圖(tu)(tu)(tu)2-55所(suo)示。由于糊狀(zhuang)區內(nei)大(da)(da)量(liang)枝(zhi)(zhi)晶(jing)網狀(zhuang)結構的(de)(de)(de)(de)(de)(de)形(xing)成(cheng)(cheng)，液(ye)(ye)(ye)相(xiang)(xiang)(xiang)的(de)(de)(de)(de)(de)(de)對(dui)流(liu)(liu)只存(cun)在(zai)于一(yi)次(ci)枝(zhi)(zhi)晶(jing)尖端位(wei)置附(fu)近。且(qie)枝(zhi)(zhi)晶(jing)間(jian)幾乎(hu)無液(ye)(ye)(ye)相(xiang)(xiang)(xiang)的(de)(de)(de)(de)(de)(de)流(liu)(liu)動。因此(ci)，枝(zhi)(zhi)晶(jing)間(jian)殘余(yu)液(ye)(ye)(ye)相(xiang)(xiang)(xiang)中的(de)(de)(de)(de)(de)(de)氮(dan)傳(chuan)質主要(yao)依靠氮(dan)的(de)(de)(de)(de)(de)(de)擴散行為，且(qie)糊狀(zhuang)區內(nei)氮(dan)傳(chuan)質速(su)率(lv)非(fei)常小(xiao)(xiao)。初始相(xiang)(xiang)(xiang)貧(pin)氮(dan)鐵素(su)(su)體(ti)相(xiang)(xiang)(xiang)8的(de)(de)(de)(de)(de)(de)氮(dan)溶解度和(he)糊狀(zhuang)區的(de)(de)(de)(de)(de)(de)氮(dan)傳(chuan)質速(su)率(lv)較低，導(dao)致(zhi)在(zai)貧(pin)氮(dan)鐵素(su)(su)體(ti)相(xiang)(xiang)(xiang)枝(zhi)(zhi)晶(jing)附(fu)近的(de)(de)(de)(de)(de)(de)液(ye)(ye)(ye)相(xiang)(xiang)(xiang)中出現氮(dan)富集，且(qie)［％N]iq迅速(su)增(zeng)大(da)(da)，如圖(tu)(tu)(tu)2-55(a)所(suo)示。根據Yang和(he) Leel70]、Svyazhin 等、Ridolfi 和(he) Tassal的(de)(de)(de)(de)(de)(de)報道可知，當［％N]iq的(de)(de)(de)(de)(de)(de)最大(da)(da)值超(chao)過氮(dan)氣(qi)(qi)(qi)泡(pao)(pao)(pao)(pao)形(xing)成(cheng)(cheng)的(de)(de)(de)(de)(de)(de)臨界氮(dan)質量(liang)分數（［％N]pore)時(shi)，該區域有(you)氣(qi)(qi)(qi)泡(pao)(pao)(pao)(pao)形(xing)成(cheng)(cheng)的(de)(de)(de)(de)(de)(de)可能(neng)性，如圖(tu)(tu)(tu)2-55(b)所(suo)示。在(zai)后續的(de)(de)(de)(de)(de)(de)凝固(gu)(gu)過程(cheng)中，隨著包晶(jing)反應的(de)(de)(de)(de)(de)(de)進行，富氮(dan)奧氏體(ti)相(xiang)(xiang)(xiang)γ以(yi)(yi)異(yi)質形(xing)核(he)的(de)(de)(de)(de)(de)(de)方(fang)式在(zai)鐵素(su)(su)體(ti)相(xiang)(xiang)(xiang)8枝(zhi)(zhi)晶(jing)的(de)(de)(de)(de)(de)(de)表面(mian)開(kai)始形(xing)核(he)長(chang)(chang)(chang)大(da)(da)，逐(zhu)漸包裹鐵素(su)(su)體(ti)相(xiang)(xiang)(xiang)枝(zhi)(zhi)晶(jing)表面(mian)，并開(kai)始捕獲殘余(yu)液(ye)(ye)(ye)相(xiang)(xiang)(xiang)中的(de)(de)(de)(de)(de)(de)氮(dan)氣(qi)(qi)(qi)泡(pao)(pao)(pao)(pao)，對(dui)比圖(tu)(tu)(tu)2-51和(he)圖(tu)(tu)(tu)2-56可知，此(ci)時(shi)枝(zhi)(zhi)晶(jing)間(jian)殘余(yu)［％N]1ig的(de)(de)(de)(de)(de)(de)增(zeng)長(chang)(chang)(chang)速(su)率(lv)減(jian)(jian)(jian)小(xiao)(xiao)。對(dui)平衡凝固(gu)(gu)而(er)言，殘余(yu)液(ye)(ye)(ye)相(xiang)(xiang)(xiang)中氮(dan)氣(qi)(qi)(qi)泡(pao)(pao)(pao)(pao)形(xing)成(cheng)(cheng)以(yi)(yi)后，氮(dan)的(de)(de)(de)(de)(de)(de)富集程(cheng)度減(jian)(jian)(jian)弱，［％N]1iq增(zeng)長(chang)(chang)(chang)速(su)率(lv)的(de)(de)(de)(de)(de)(de)減(jian)(jian)(jian)小(xiao)(xiao)程(cheng)度明顯(xian)；相(xiang)(xiang)(xiang)比之下，Scheil凝固(gu)(gu)過程(cheng)中，氮(dan)氣(qi)(qi)(qi)泡(pao)(pao)(pao)(pao)形(xing)成(cheng)(cheng)以(yi)(yi)后，殘余(yu)液(ye)(ye)(ye)相(xiang)(xiang)(xiang)中氮(dan)富集狀(zhuang)態有(you)所(suo)緩(huan)解，但幅(fu)度很小(xiao)(xiao)。隨著凝固(gu)(gu)界面(mian)的(de)(de)(de)(de)(de)(de)進一(yi)步(bu)推移，被捕獲的(de)(de)(de)(de)(de)(de)氮(dan)氣(qi)(qi)(qi)泡(pao)(pao)(pao)(pao)在(zai)奧氏體(ti)相(xiang)(xiang)(xiang)表面(mian)開(kai)始長(chang)(chang)(chang)大(da)(da)，并沿凝固(gu)(gu)方(fang)向拉(la)長(chang)(chang)(chang)，如圖(tu)(tu)(tu)2-55(c)所(suo)示。

  氮(dan)氣(qi)(qi)(qi)孔(kong)(kong)沿徑向(xiang)(xiang)生(sheng)長(chang)，生(sheng)長(chang)方向(xiang)(xiang)與(yu)凝固方向(xiang)(xiang)一(yi)致，那么氮(dan)氣(qi)(qi)(qi)孔(kong)(kong)初始形成(cheng)(cheng)位置靠近鑄(zhu)錠邊(bian)部(bu)，且氮(dan)氣(qi)(qi)(qi)泡初始位置邊(bian)緣全由奧氏體相(xiang)γ構成(cheng)(cheng)（圖(tu)2-57中I區），與(yu)圖(tu)2-55描(miao)述相(xiang)符。隨著氮(dan)氣(qi)(qi)(qi)孔(kong)(kong)被拉長(chang)，鐵素體相(xiang)和奧氏體相(xiang)以體積分數比約為0.92的(de)關系交(jiao)替在氮(dan)氣(qi)(qi)(qi)泡周圍形成(cheng)(cheng)，直到氮(dan)氣(qi)(qi)(qi)孔(kong)(kong)閉合。凝固結束后，氮(dan)氣(qi)(qi)(qi)孔(kong)(kong)的(de)宏觀形貌類似(si)于(yu)橢圓形，與(yu)Wei等的(de)研究結果一(yi)致

二、氮(dan)(dan)微觀偏(pian)析對氮(dan)(dan)氣(qi)孔的影(ying)響

  氮(dan)(dan)(dan)的(de)(de)(de)(de)(de)(de)分(fen)配系數較(jiao)小(xiao)，導致(zhi)液(ye)相(xiang)(xiang)(xiang)向(xiang)固相(xiang)(xiang)(xiang)轉變的(de)(de)(de)(de)(de)(de)過(guo)程(cheng)中(zhong)(zhong)，固相(xiang)(xiang)(xiang)會(hui)將多余(yu)(yu)的(de)(de)(de)(de)(de)(de)氮(dan)(dan)(dan)轉移到殘(can)余(yu)(yu)液(ye)相(xiang)(xiang)(xiang)中(zhong)(zhong)，形(xing)(xing)(xing)成(cheng)(cheng)(cheng)氮(dan)(dan)(dan)偏(pian)析(xi)。在(zai)氮(dan)(dan)(dan)偏(pian)析(xi)程(cheng)度(du)逐漸加重的(de)(de)(de)(de)(de)(de)過(guo)程(cheng)中(zhong)(zhong)，當殘(can)余(yu)(yu)液(ye)相(xiang)(xiang)(xiang)中(zhong)(zhong)氮(dan)(dan)(dan)質量分(fen)數超(chao)過(guo)其(qi)飽和(he)度(du)時，極易形(xing)(xing)(xing)成(cheng)(cheng)(cheng)氮(dan)(dan)(dan)氣(qi)(qi)泡(pao)。隨著凝固的(de)(de)(de)(de)(de)(de)進行，若氣(qi)(qi)泡(pao)無法上浮而(er)被捕獲(huo)，凝固結(jie)束后就會(hui)在(zai)鑄(zhu)(zhu)(zhu)錠(ding)內部(bu)形(xing)(xing)(xing)成(cheng)(cheng)(cheng)氣(qi)(qi)孔(kong)。因此(ci)，凝固過(guo)程(cheng)中(zhong)(zhong)氮(dan)(dan)(dan)偏(pian)析(xi)和(he)溶(rong)解度(du)對(dui)鑄(zhu)(zhu)(zhu)錠(ding)中(zhong)(zhong)最終氮(dan)(dan)(dan)氣(qi)(qi)孔(kong)的(de)(de)(de)(de)(de)(de)形(xing)(xing)(xing)成(cheng)(cheng)(cheng)有至關(guan)重要(yao)的(de)(de)(de)(de)(de)(de)作用(yong)。氮(dan)(dan)(dan)氣(qi)(qi)孔(kong)多數情況下與疏(shu)松縮(suo)(suo)孔(kong)共(gong)存，內壁凹凸不平呈現裂紋狀，且(qie)整個(ge)氣(qi)(qi)孔(kong)形(xing)(xing)(xing)狀不規則，如圖(tu)2-58所示。此(ci)類氣(qi)(qi)孔(kong)不僅與鋼液(ye)中(zhong)(zhong)氣(qi)(qi)泡(pao)的(de)(de)(de)(de)(de)(de)形(xing)(xing)(xing)成(cheng)(cheng)(cheng)有關(guan)，還受凝固收縮(suo)(suo)等(deng)因素的(de)(de)(de)(de)(de)(de)影響，且(qie)多數分(fen)布于鑄(zhu)(zhu)(zhu)錠(ding)心(xin)部(bu)，尤其(qi)在(zai)中(zhong)(zhong)心(xin)等(deng)軸(zhou)(zhou)晶區。這主要(yao)由于中(zhong)(zhong)心(xin)等(deng)軸(zhou)(zhou)晶區內枝(zhi)晶生(sheng)長較(jiao)發(fa)達，容易形(xing)(xing)(xing)成(cheng)(cheng)(cheng)復雜的(de)(de)(de)(de)(de)(de)網狀結(jie)構(gou)，從而(er)將液(ye)相(xiang)(xiang)(xiang)分(fen)割成(cheng)(cheng)(cheng)無數個(ge)獨立(li)的(de)(de)(de)(de)(de)(de)液(ye)相(xiang)(xiang)(xiang)區域，當發(fa)生(sheng)凝固收縮(suo)(suo)時，難以進行補縮(suo)(suo)，在(zai)形(xing)(xing)(xing)成(cheng)(cheng)(cheng)疏(shu)松縮(suo)(suo)孔(kong)的(de)(de)(de)(de)(de)(de)同時，局部(bu)鋼液(ye)靜(jing)壓力降低，促(cu)使氮(dan)(dan)(dan)從殘(can)余(yu)(yu)液(ye)相(xiang)(xiang)(xiang)中(zhong)(zhong)析(xi)出，從而(er)形(xing)(xing)(xing)成(cheng)(cheng)(cheng)了(le)氮(dan)(dan)(dan)氣(qi)(qi)孔(kong)和(he)疏(shu)松縮(suo)(suo)孔(kong)共(gong)存的(de)(de)(de)(de)(de)(de)宏觀缺陷。

  平(ping)衡凝固(gu)時，19Cr14Mn0.9N含氮(dan)(dan)(dan)(dan)(dan)(dan)奧(ao)氏體不銹鋼(gang)殘余液相(xiang)中氮(dan)(dan)(dan)(dan)(dan)(dan)偏析(xi)與體系(xi)(xi)氮(dan)(dan)(dan)(dan)(dan)(dan)溶解(jie)度(du)的(de)差(cha)值如圖2-59所(suo)示(shi)。凝固(gu)初期鐵(tie)素體阱(jing)（ferrite trap)的(de)形(xing)成，導(dao)致氮(dan)(dan)(dan)(dan)(dan)(dan)溶解(jie)度(du)的(de)降低，進而使氮(dan)(dan)(dan)(dan)(dan)(dan)偏析(xi)與體系(xi)(xi)氮(dan)(dan)(dan)(dan)(dan)(dan)溶解(jie)度(du)差(cha)值呈現出(chu)略(lve)微增大的(de)趨(qu)勢。但(dan)在(zai)后(hou)續凝固(gu)過程中，隨著鐵(tie)素體阱(jing)的(de)消失(shi)以及富氮(dan)(dan)(dan)(dan)(dan)(dan)奧(ao)氏體相(xiang)的(de)不斷形(xing)成，差(cha)值減(jian)小；在(zai)整個凝固(gu)過程中差(cha)值始終較(jiao)小，且變(bian)化幅度(du)較(jiao)窄。對于19Cr14Mn0.9N 含氮(dan)(dan)(dan)(dan)(dan)(dan)奧(ao)氏體不銹鋼(gang)，液相(xiang)中氮(dan)(dan)(dan)(dan)(dan)(dan)氣泡(pao)的(de)形(xing)成趨(qu)勢較(jiao)小，難以在(zai)鑄錠內形(xing)成獨立(li)內壁光滑的(de)規則氮(dan)(dan)(dan)(dan)(dan)(dan)氣孔(kong)。

  此外(wai)，目前(qian)有(you)人對奧(ao)氏體鋼(gang)(gang)凝(ning)固(gu)過(guo)程(cheng)中(zhong)(zhong)(zhong)(zhong)氮(dan)(dan)(dan)(dan)(dan)氣(qi)孔(kong)的(de)(de)形成(cheng)(cheng)(cheng)進行了(le)大量(liang)(liang)研究，如(ru)Yang和Leel901研究了(le)奧(ao)氏體鋼(gang)(gang)16Cr3NixMn(x=9和11)凝(ning)固(gu)過(guo)程(cheng)中(zhong)(zhong)(zhong)(zhong)壓力(li)和初始氮(dan)(dan)(dan)(dan)(dan)質量(liang)(liang)分(fen)數(shu)等(deng)因(yin)素對氮(dan)(dan)(dan)(dan)(dan)氣(qi)孔(kong)形成(cheng)(cheng)(cheng)的(de)(de)影響規(gui)律(lv)，并建(jian)立了(le)相(xiang)(xiang)應的(de)(de)預測模(mo)型(xing)。Ridolfi和Tassal[84]分(fen)析(xi)了(le)氮(dan)(dan)(dan)(dan)(dan)偏(pian)析(xi)、合金元素、冷(leng)卻速(su)率以及枝晶間距(ju)對奧(ao)氏體鋼(gang)(gang)中(zhong)(zhong)(zhong)(zhong)氮(dan)(dan)(dan)(dan)(dan)氣(qi)孔(kong)的(de)(de)影響規(gui)律(lv)，并揭示(shi)了(le)奧(ao)氏體鋼(gang)(gang)中(zhong)(zhong)(zhong)(zhong)氮(dan)(dan)(dan)(dan)(dan)氣(qi)孔(kong)形成(cheng)(cheng)(cheng)機(ji)理。然而，目前(qian)對于雙(shuang)相(xiang)(xiang)鋼(gang)(gang)中(zhong)(zhong)(zhong)(zhong)氮(dan)(dan)(dan)(dan)(dan)氣(qi)孔(kong)形成(cheng)(cheng)(cheng)的(de)(de)研究較(jiao)少，且主要(yao)集中(zhong)(zhong)(zhong)(zhong)在合金元素、鑄造(zao)方式、冷(leng)卻速(su)率等(deng)因(yin)素對氮(dan)(dan)(dan)(dan)(dan)氣(qi)孔(kong)影響規(gui)律(lv)的(de)(de)研究，鮮(xian)有(you)對雙(shuang)相(xiang)(xiang)鋼(gang)(gang)中(zhong)(zhong)(zhong)(zhong)氮(dan)(dan)(dan)(dan)(dan)氣(qi)孔(kong)形成(cheng)(cheng)(cheng)機(ji)理的(de)(de)報道。以21.5Cr5Mn1.5Ni0.25N含氮(dan)(dan)(dan)(dan)(dan)雙(shuang)相(xiang)(xiang)鋼(gang)(gang)為例，氮(dan)(dan)(dan)(dan)(dan)偏(pian)析(xi)與溶解度(du)的(de)(de)差(cha)值(zhi)在整個凝(ning)固(gu)過(guo)程(cheng)中(zhong)(zhong)(zhong)(zhong)的(de)(de)變化趨勢，如(ru)圖2-59所示(shi)。隨著凝(ning)固(gu)的(de)(de)進行，氮(dan)(dan)(dan)(dan)(dan)偏(pian)析(xi)始終大于氮(dan)(dan)(dan)(dan)(dan)溶解度(du)，且差(cha)值(zhi)呈現出快速(su)增(zeng)大的(de)(de)趨勢。因(yin)此，在21.5Cr5Mn1.5Ni0.25N 含氮(dan)(dan)(dan)(dan)(dan)雙(shuang)相(xiang)(xiang)鋼(gang)(gang)凝(ning)固(gu)過(guo)程(cheng)中(zhong)(zhong)(zhong)(zhong)，氮(dan)(dan)(dan)(dan)(dan)偏(pian)析(xi)嚴重，殘余(yu)液相(xiang)(xiang)內(nei)氮(dan)(dan)(dan)(dan)(dan)氣(qi)泡(pao)形成(cheng)(cheng)(cheng)趨勢較(jiao)大，明顯高于19Cr14Mn0.9N含氮(dan)(dan)(dan)(dan)(dan)奧(ao)氏體不銹(xiu)鋼(gang)(gang)。

  氮氣(qi)泡形(xing)成和長(chang)大(da)具有重要的(de)(de)作用（圖2-60).其(qi)中(zhong)(zhong)，σ為(wei)氣(qi)液界面(mian)的(de)(de)表面(mian)張力，r為(wei)氣(qi)泡半徑。結合經(jing)典形(xing)核理論，氮氣(qi)泡在(zai)鋼液中(zhong)(zhong)穩定存在(zai)的(de)(de)必(bi)要條(tiao)件為(wei)氣(qi)泡內壓力大(da)于作用于氣(qi)泡的(de)(de)所有壓力之和，即(ji)

  式中(zhong)，Aso由凝(ning)固過程(cheng)中(zhong)除(chu)氮以(yi)外其他合(he)金元(yuan)素的(de)微觀(guan)偏(pian)析(xi)進行計算(suan)(suan)，其值隨(sui)著枝(zhi)晶(jing)(jing)間(jian)殘余液相中(zhong)氮溶(rong)解(jie)度的(de)增加而(er)減小，表(biao)(biao)征了(le)枝(zhi)晶(jing)(jing)間(jian)殘余液相中(zhong)氮溶(rong)解(jie)度對氮氣泡(pao)形成的(de)影響程(cheng)度；Ase表(biao)(biao)征了(le)枝(zhi)晶(jing)(jing)間(jian)氮偏(pian)析(xi)對氮氣泡(pao)形成的(de)影響程(cheng)度，可(ke)由凝(ning)固過程(cheng)中(zhong)枝(zhi)晶(jing)(jing)間(jian)殘余液相中(zhong)氮偏(pian)析(xi)計算(suan)(suan)獲(huo)得，其值隨(sui)著氮偏(pian)析(xi)的(de)增大而(er)增大。此外，用(yong)于(yu)計算(suan)(suan)Aso和Ase時所(suo)需的(de)合(he)金元(yuan)素偏(pian)析(xi)均由鋼凝(ning)固相變所(suo)致(zhi)。

  氮氣(qi)泡的形核和(he)長大過程(cheng)(cheng)復雜，且影(ying)響(xiang)(xiang)因(yin)素(su)眾多，包括凝(ning)(ning)(ning)(ning)固(gu)(gu)(gu)(gu)收縮、冶煉環境以及坩堝材質(zhi)(zhi)等(deng)。因(yin)此(ci)，很(hen)難采(cai)用(yong)Pg值精(jing)確預測(ce)凝(ning)(ning)(ning)(ning)固(gu)(gu)(gu)(gu)過程(cheng)(cheng)中(zhong)氮氣(qi)泡的形成(cheng)(cheng)和(he)長大。然而基(ji)于Yang等(deng)的實驗研究［70,77],在評估(gu)凝(ning)(ning)(ning)(ning)固(gu)(gu)(gu)(gu)壓力、合(he)金(jin)成(cheng)(cheng)分等(deng)因(yin)素(su)對氮氣(qi)泡形成(cheng)(cheng)的影(ying)響(xiang)(xiang)程(cheng)(cheng)度時，Pg起關鍵作用(yong)。實際凝(ning)(ning)(ning)(ning)固(gu)(gu)(gu)(gu)過程(cheng)(cheng)介于平衡(heng)(heng)凝(ning)(ning)(ning)(ning)固(gu)(gu)(gu)(gu)（固(gu)(gu)(gu)(gu)／液相中(zhong)溶質(zhi)(zhi)完全擴(kuo)散）和(he)Scheil凝(ning)(ning)(ning)(ning)固(gu)(gu)(gu)(gu)（固(gu)(gu)(gu)(gu)相無溶質(zhi)(zhi)擴(kuo)散，液相中(zhong)完全擴(kuo)散）之間70].因(yin)此(ci)，可分別計(ji)算平衡(heng)(heng)凝(ning)(ning)(ning)(ning)固(gu)(gu)(gu)(gu)和(he)Scheil凝(ning)(ning)(ning)(ning)固(gu)(gu)(gu)(gu)過程(cheng)(cheng)中(zhong)的Aso、Ase和(he)Pg,闡明實際凝(ning)(ning)(ning)(ning)固(gu)(gu)(gu)(gu)過程(cheng)(cheng)中(zhong)壓力等(deng)因(yin)素(su)對氮氣(qi)泡形成(cheng)(cheng)的影(ying)響(xiang)(xiang)規(gui)律(lv)。

  現(xian)以(yi)21.5Cr5Mn1.5Ni0.25N含氮雙相鋼D1鑄錠(ding)為(wei)例，對凝(ning)固過程(cheng)中Aso、Ase和(he)(he)P8的變(bian)化趨勢(shi)進行計算。圖2-61描(miao)述了(le)ΔAso(=Asa-Aso,0)和(he)(he)AAse(=Ase-Ase,o)隨固相質(zhi)量分數的變(bian)化趨勢(shi)（Aso,0和(he)(he)Asc,0分別為(wei)D1鑄錠(ding)凝(ning)固時(shi)Aso和(he)(he)Ase的初(chu)始值）。

  在平衡(heng)凝(ning)固(gu)和Scheil凝(ning)固(gu)過(guo)程中，ΔAso的(de)(de)(de)最(zui)小值(zhi)(zhi)(zhi)分別(bie)為(wei)－0.145和－0.397,與(yu)此(ci)相對應的(de)(de)(de)ΔAse值(zhi)(zhi)(zhi)最(zui)大(da)，分別(bie)為(wei)0.68和0.92.在整(zheng)個(ge)凝(ning)固(gu)過(guo)程中，由(you)于(yu)ΔAse與(yu)ΔAso之和始(shi)終大(da)于(yu)零，因(yin)而(er)(er)枝晶(jing)間殘余液(ye)相中氮(dan)偏(pian)析對D1 鑄錠凝(ning)固(gu)過(guo)程中氮(dan)氣泡形成的(de)(de)(de)影響大(da)于(yu)氮(dan)溶解度，起主導作(zuo)用。此(ci)外，在整(zheng)個(ge)凝(ning)固(gu)過(guo)程中，P8變化(hua)趨勢(shi)如圖2-62所示，其變化(hua)規律(lv)與(yu)Young等。的(de)(de)(de)研究結果一(yi)致，Pg的(de)(de)(de)最(zui)大(da)值(zhi)(zhi)(zhi)Pg與(yu)Ase+Aso的(de)(de)(de)最(zui)大(da)值(zhi)(zhi)(zhi)相對應，且在平衡(heng)凝(ning)固(gu)和 Scheil 凝(ning)固(gu)過(guo)程中分別(bie)為(wei)0.63MPa和0.62MPa.此(ci)外，可通(tong)過(guo)對比不同(tong)鑄錠中的(de)(de)(de)探討凝(ning)固(gu)壓力、初始(shi)氮(dan)質量分數以(yi)及(ji)合金元素（鉻(ge)和錳）等對液(ye)相中氮(dan)氣泡形成的(de)(de)(de)影響，進而(er)(er)明晰各(ge)因(yin)素對氮(dan)氣孔形成的(de)(de)(de)影響規律(lv)。