馬氏體(ti)低溫(wen)(wen)用(yong)鋼主要是(shi)指制(zhi)造、運(yun)輸及(ji)儲存液化氣(qi)體(ti)的(de)機械(xie)設備、超導設備、核聚變反(fan)應設備等(deng)所(suo)用(yong)的(de)超高強度(du)、超低溫(wen)(wen)材料。這里只(zhi)涉及(ji)常(chang)壓下液化溫(wen)(wen)度(du)在-103℃以下的(de)常(chang)用(yong)氣(qi)體(ti)（乙烯：-103℃;天然氣(qi)：-165℃;氧(yang)：-183℃;空氣(qi)：-190℃;氮：-196℃;氫：-253℃;氯：-269℃)及(ji)一些液化溫(wen)(wen)度(du)在-180--80℃之間(jian)的(de)碳(tan)氫化合(he)物(wu)（如甲烷(wan)、乙烷(wan)）等(deng)所(suo)用(yong)的(de)高合(he)金(jin)細(xi)晶粒鐵素體(ti)鋼。


  作為(wei)低溫(wen)用鋼，應(ying)具有(you)如(ru)下性(xing)(xing)能：低溫(wen)下組織穩(wen)定(ding)，不產(chan)生相變，以保持力學性(xing)(xing)能及物理性(xing)(xing)較為(wei)穩(wen)定(ding)；有(you)良(liang)好的低溫(wen)韌性(xing)(xing)：良(liang)好的焊接(jie)性(xing)(xing)和加工性(xing)(xing)能；有(you)時(shi)還有(you)其他(ta)特殊要求，如(ru)無磁性(xing)(xing)等(deng)。


  9%Ni鋼是低碳馬氏體型低溫用(yong)(yong)(yong)鋼，作為液化天然(ran)氣（LNG)及(ji)液氨用(yong)(yong)(yong)鋼，已被世界各國普遍采用(yong)(yong)(yong)，其使(shi)用(yong)(yong)(yong)溫度(du)可達-196℃。


  9%Ni鋼的化(hua)學成分如(ru)表1-14所示


14.jpg


  鋼(gang)中(zhong)鎳(nie)(nie)含(han)量對韌(ren)(ren)(ren)性(xing)(xing)(xing)(xing)(xing)有(you)很大(da)影響，隨著鎳(nie)(nie)含(han)量的提(ti)(ti)高(gao)(gao)，脆(cui)性(xing)(xing)(xing)(xing)(xing)轉(zhuan)變(bian)，溫(wen)(wen)度(du)不(bu)斷下降(jiang)(jiang)，而(er)韌(ren)(ren)(ren)性(xing)(xing)(xing)(xing)(xing)提(ti)(ti)高(gao)(gao)。鋼(gang)中(zhong)碳含(han)量增(zeng)大(da)，其韌(ren)(ren)(ren)性(xing)(xing)(xing)(xing)(xing)下降(jiang)(jiang)，低(di)(di)溫(wen)(wen)轉(zhuan)變(bian)溫(wen)(wen)度(du)升高(gao)(gao)，焊接性(xing)(xing)(xing)(xing)(xing)惡化。鋼(gang)中(zhong)硅是重要(yao)的脫氧劑，但又(you)容易形成夾雜物(wu)而(er)危害韌(ren)(ren)(ren)性(xing)(xing)(xing)(xing)(xing)。錳可以細化晶粒，又(you)可提(ti)(ti)高(gao)(gao)Mn/C比(bi)，提(ti)(ti)高(gao)(gao)韌(ren)(ren)(ren)性(xing)(xing)(xing)(xing)(xing)，降(jiang)(jiang)低(di)(di)低(di)(di)溫(wen)(wen)轉(zhuan)變(bian)溫(wen)(wen)度(du)。氧是降(jiang)(jiang)低(di)(di)韌(ren)(ren)(ren)性(xing)(xing)(xing)(xing)(xing)、提(ti)(ti)高(gao)(gao)低(di)(di)溫(wen)(wen)轉(zhuan)變(bian)溫(wen)(wen)度(du)的元素，因此必須控制。磷不(bu)僅與氧有(you)類似(si)的作用(yong)，即降(jiang)(jiang)低(di)(di)韌(ren)(ren)(ren)性(xing)(xing)(xing)(xing)(xing)，提(ti)(ti)高(gao)(gao)脆(cui)性(xing)(xing)(xing)(xing)(xing)轉(zhuan)變(bian)溫(wen)(wen)度(du)，而(er)且(qie)還(huan)惡化焊接性(xing)(xing)(xing)(xing)(xing)，所以必須嚴格控制。