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充氫超高強(qiáng)度鋼拉伸變形的原位中子衍射研究
發(fā)布人：上海艾荔艾金屬材料有限公司www.jshcn.cn
更新時(shí)間：2015-09-22
利用飛行時(shí)間法中子衍射對(duì)比研究了充氫與未充氫 1250 MPa 超高強(qiáng)度鋼的拉伸變形行為與軸向晶格變形特征,
并觀察了斷口區(qū)組織形貌與晶粒取向特征. 在無(wú)加載條件下, 充氫試樣的軸向(110)與(200)面間距分別大于與小于未充氫
試樣的對(duì)應(yīng)面間距, 顯示出四面體間隙中氫原子的進(jìn)入使軸向(110)面間距有所增加, 同時(shí)內(nèi)部應(yīng)力的平衡作用使軸向(200)
面間距有所減少. 未充氫試樣在達(dá)到 1250 MPa 抗拉強(qiáng)度發(fā)生頸縮塑性斷裂, 而含有 8.0?10-6可擴(kuò)散氫的試樣在分步加載至 500 MP
充氫超高強(qiáng)度鋼拉伸變形的原位中子衍射研究TENSILE DEFORMATION BEHAVIOR OF HYDROGEN CHARGED ULTRAHIGH?STRENGTH STEEL STUDIED BY IN SITU NEUTRON DIFFRACTION?
利用飛行時(shí)間法中子衍射對(duì)比研究了充氫與未充氫 1250 MPa 超高強(qiáng)度鋼的拉伸變形行為與軸向晶格變形特征,?并觀察了斷口區(qū)組織形貌與晶粒取向特征. 在無(wú)加載條件下, 充氫試樣的軸向(110)與(200)面間距分別大于與小于未充氫試樣的對(duì)應(yīng)面間距, 顯示出四面體間隙中氫原子的進(jìn)入使軸向(110)面間距有所增加, 同時(shí)內(nèi)部應(yīng)力的平衡作用使軸向(200)面間距有所減少. 未充氫試樣在達(dá)到 1250 MPa 抗拉強(qiáng)度發(fā)生頸縮塑性斷裂, 而含有 8.0?10-6可擴(kuò)散氫的試樣在分步加載至?500MPa時(shí)發(fā)生脆性斷. 中子衍射分析表明, 未充氫試樣在拉應(yīng)力加載至500 MPa時(shí)均基本符合線彈性變形, 但至700 MPa時(shí), 軸向{200}晶粒較其余取向晶粒優(yōu)先顯示非線彈性變形, 至 800 MPa 時(shí)軸向{110}晶粒也出現(xiàn)非線彈性變形, 軸向{200}晶粒優(yōu)先產(chǎn)生微屈服現(xiàn)象, 而軸向{211}晶粒仍然處于線彈性階段; 充氫試樣在拉伸至 300 MPa 時(shí), 軸向{110}晶粒出現(xiàn)非線彈性變形, 至 400 MPa 時(shí)軸向{200}晶粒也出現(xiàn)非線彈性變形, 軸向{110}晶粒優(yōu)先產(chǎn)生微屈服現(xiàn)象, 軸向{211}晶粒仍處于線彈性階段. 斷口剖面觀察顯未充氫試樣內(nèi)形成明顯的軸向{110}拉伸纖維織構(gòu), 而氫脆試樣內(nèi)除了明顯的晶界裂紋萌生, 還有晶內(nèi)裂紋擴(kuò)展與局部晶體轉(zhuǎn)動(dòng)特征. 基于不同取向晶粒的微屈服概念, 解釋了充氫導(dǎo)致軸向{110}晶粒優(yōu)先微屈服而不是軸向{200}晶粒優(yōu)先微屈服, 同時(shí)以氫伴隨微區(qū)塑性變形的方式發(fā)生脆性斷裂.?
The tensile deformation behavior and the axial lattice strain response of 1250 MPa ultra-high?strength steels with and without hydrogen charging were comparably investigated using neutron diffraction?together with the fracture morphology and microstructure observation. Before tensile loading, the axial (110)?lattice plane spacing of hydrogen charged steel was found larger than that of non-charged specimen while the?axial (200) lattice plane spacing of the former was smaller than that of the latter, suggesting that the hydrogen?atoms occupied the tetrahedral site promoted the increment of axial (110) lattice plane spacing while the?balanced internal stress resulted in the proper decrement of axial (200) lattice plane spacing. The necking and?ductile fracture after approaching the 1250?MPa tensile strength occurred in the?non-charged specimen, while the brittle?fracture occurred in the 8.0?10-6?hydrogen charged specimen at 500 MPa holding during step-by-step loading.?The neutron diffraction analysis showed that in the non-charged specimen, the linear elastic deformation was?kept up to 500 MPa loading, the nonlinear elastic deformation was observed preferably on the axial (200)?reflection at 700 MPa, and then on the axial (110) reflection at 800 MPa; the axial {200} grain?orientation-dependent microyielding was observed preferably at 800MPa while the (211) reflection was still?under linear elastic deformation. Comparably, in the hydrogen charged specimen, the nonlinear elastic?deformation was observed preferably on the axial (110) reflection at 300 MPa, and then on the axial (200)?reflection at 400 MPa; the axial {110} grain orientation-dependent microyielding was observed preferably at?400MPa while the axial (211) reflection was still under linear elastic deformation. The microstructure?observation under fracture surface confirmed the typical <110>-oriented tensile fiber texture in the non-charged?specimen while the intergranular cracks along grain boundaries, quasi-cleavage/cleavage cracks and local?crystal rotation in various grains of the hydrogen charged specimen. A concept about crystallographic orientation?dependent microyielding was employed here to explain the above results, i.e. the hydrogen charging promoted?the axial {110} grain orientation-dependent microyielding rather than axial {200} grain orientation-dependent?microyielding, and the diffusible hydrogen embrittled the matrix microstructure, accompanying with local?plastic deformation.?
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