冷軋及退火制備的超細(xì)晶粒雙相Mn12Ni2MoTi(Al)鋼

冷軋及退火制備的超細(xì)晶粒雙相Mn12Ni2MoTi(Al)鋼AN ULTRAFINE GRAINED DUPLEX Mn12Ni2MoTi(Al) STEEL FABRICATED BY COLD ROLLING AND ANNEALING

采用 XRD, SEM, TEM, 硬度測試和拉伸實驗研究了冷軋 Mn12Ni2MoTi(Al)鋼經(jīng)不同工藝退火后的顯微組織及力學(xué)性能. 結(jié)果表明, 馬氏體 Mn12Ni2MoTi(Al)鋼經(jīng) 65%冷軋及 710~745 ℃退火處理后轉(zhuǎn)變成主要由奧氏體晶粒和鐵素體晶粒組成的亞微米級超細(xì)晶粒雙相組織, 并且彌散分布著第二相析出物顆粒; 在退火中形成的富Ti, Mo及Si的第二相顆粒阻礙了超細(xì)再結(jié)晶晶粒的粗化, 從而提高了鋼的屈服強(qiáng)度和熱穩(wěn)定性; 經(jīng)710 ℃, 24 h長時間退火后, 超細(xì)晶粒雙相鋼的平均晶粒尺寸仍然小于500 nm; 超細(xì)晶粒雙相鋼延伸率隨室溫奧氏體體積分?jǐn)?shù)增加而增加, 室溫奧氏體體積分?jǐn)?shù)隨退火溫度升高或退火時間延長先增加后降低, 且在745 ℃, 0.5 h 退火時達(dá)到最大值. 超細(xì)晶粒鋼的屈服強(qiáng)度和總延伸率可達(dá)到 900 MPa和 23%以上, 比同種材料淬火馬氏體鋼提高了約一倍。

For decades, transformation induced plasticity (TRIP) assisted steels with high tensile strength and exceptional ductility at room temperature have attracted a great deal of attentions. Their applications are often limited due to the low yield strength．In this work, an ultrafine grained (UFG) duplex Mn12Ni2MoTi(Al) TRIP steel with high yield strength and good ductility is fabricated by cold rolling and subsequent annealing at 710~745 ℃. The microstructure and mechanical properties of the steels with different heat treatment conditions are investigated by means of XRD, SEM, TEM, hardness and tensile test．It is found that after annealing at 710~745 ℃, the deformation microstructure of the cold-rolled samples has transformed into a sub-micron ultrafine grained (UFG) duplex microstructure consisting of austenite, ferrite and dispersed second-phase precipitations. The second-phase precipitations formed during annealing are rich in Ti, Mo and Si, and play an important role in preventing the ultrafine grains from coarsening, which results in high yield strength and good thermal stability. After annealing at 710 ℃ for 24 h, the average grain size of the UFG steel is still less than 500 nm. The elongation of the UFG duplex steel is increasing with the increment of the volume fraction of austenite in the UFG duplex steel at room temperature. The volume fraction of austenite in the UFG duplex steel at room temperature first increases and then decreases with the annealing temperature and time increasing, and reaches the maximum value when annealing at 745 ℃ for 0.5 h. The yield strength and total elongation of the UFG steel can be as large as 900 MPa and 23%, respectively, which are about double those of the quenched martensitic sample.

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