TRIP鋼高速拉伸時的馬氏體轉變行為分析

TRIP鋼高速拉伸時的馬氏體轉變行為分析ANALYSIS OF THE MARTENSITIC TRANSFORMATION DURING TENSION OF HIGH MANGANESE TRIP STEEL AT HIGH STRAIN RATES

利用 EBSD 技術對不同應變速率下單向拉伸高錳 TRIP 鋼中的馬氏體相變進行了觀察, 使用 XRD 數據計算了奧氏體(γ)、hcp 馬氏體(ε-M)和 bcc 馬氏體(ε-M)的體積分數, 并對 γ→ε-M 和 ε-M→α′-M2 階段相變的變體選擇進行了理論計算. 結果表明, 高速拉伸時 TRIP 行為仍然具有取向依賴性, 這是由不同取向 γ 晶粒內 α′-M 變體的機械功差異引起的. 應變速率的提高促進 ε-M→α′-M 轉變, 但總的馬氏體轉變量降低, 即高速拉伸抑制了TRIP 效應. TRIP 鋼靜態(tài)拉伸時 α′-M 變體選擇較強, 動態(tài)拉伸時變體選擇減弱. 靜態(tài)拉伸時, <111>γ和<100>γ晶粒內 α′-M 變體選擇可用局部應力對變體做功來計算. 高速拉伸時, 需結合應力對 α′-M 變體做功大小及應變能、界面能來分析這些 γ 晶粒內的變體選擇規(guī)律. 與 1 個 α′-M 變體單獨出現(xiàn)相比, 一對具有特殊取向關系的變體同時出現(xiàn), 可以降低變體的應變能, 使得不利變體能夠出現(xiàn).

Among the wide variety of recently developed steels, high manganese transformation-induced plasticity (TRIP) steels with low stacking fault energy (SFE) are particularly promising. Outstanding mechanical properties combining a high ductility and a high strength are then obtained. Compared to the static deformation of high Mn TRIP steels, the behaviors of martensitic transformation and mechanical properties of such steels during dynamic deformation may be different. In this work, martensitic transformation of high manganese TRIP steel at different strain rates was characterized by the EBSD technique. The volume fractions of austenite (γ), hcp martensite (ε-M) and bcc martensite (α′-M) were calculated based on the XRD data. Meanwhile, Variant selections of martensitic transformation in γ→ε-M and ε-M→α′-M transformation were investigated by theoretical calculation. It is shown that orientation dependence of TRIP effect during tension exists even at high strain rates and can be ascribed to the influence of mechanical work in differently oriented γ grains. The transformation of ε-M→α′-M was promoted, but the total amount of transformed martensite decreased, which means that TRIP effect was restricted at high strain rates. The α′-M variant selection is more obvious during static tension and became weaker during dynamic tensile deformation. α′-M variant selection can be predicted by the calculated mechanical works induced by the local stress in <111>γ and <100>γ grains during static tension. However, during dynamic tension, the mechanism of variant selection needs to be explained by analyzing the mechanical works induced by the local stress, the strain energy and the interfacial energy in these grains comprehensively. Compared to the occurrence of a single α′-M variant, a pair of α′-M variants having specific orientation relationship reduces the strain energy, then unfavored α′-M variants appear.

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