Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： The volume fraction, morphology and size of reversed austenite in 5.5Ni steel tempered at different temperatures were characterized by X-ray diffraction, scanning electron microscope and transmission electron microscope, and the influence of tempering temperature on mechanical properties of 5.5Ni steel was investigated. The results show that there was no significant change in either the tensile strength or yield strength for the steel tempered in the range from 580℃ to 600℃. There was a slight increment in tensile strength but a great decrement in yield strength, besides, a maximum elongation was obtained for the steel tempered at 620℃. As the tempering temperature increased from 580℃ to 620℃, the volume fraction of reversed austenite in 5.5Ni steel increased gradually but impact energy decreased. Stable, homogeneous, dispersive and fine lamella-like reversed austenite is the main reason of the high impact energy of 148 J when the steel tempered at 580℃. Two types of reversed austenite including lamella ones and block ones were detected in this steel. The former had different length with a width of about 20 nm which could improve the low temperature toughness of the steel. The latter had a size of about 200 nm and tended to gathering together as clusters which were detrimental to the low temperature toughness of the steel.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： Fe-C-Mo-M steels (where M is Nb, V or Ti, ~0.1%, and Mo ≤0.2% ) were produced by thermal mechanical control processing (TMCP), and then their performance was characterized in terms of failure temperature by means of constant load tensile test while heating from ambient temperature up to 800oC with a heating rate 28 oC/min. The boundary misorientation of the steels after TMCP was examined by electron back scattered diffraction (EBSD), and the precipitates of MC type carbides were characterized by transmission electron microscopy (TEM). The results show that the addition of 0.2% Mo in Fe-C-Nab/V steels increases the failure temperature of steels by 40℃. It is believed that the low-angle grain boundary provided the favorable nucleation site for MC type carbides, which in turn will accelerate the kinetics of precipitation process. The fine and dispersed precipitates of MC type carbides induce significant precipitation strengthening for the steels during the constant load tensile process, thus resulting in higher failure temperature. Among the tested steels, the failure temperature of Ti-Mo steel is the highest due to its highest low-angle grain boundary density which results in the fast precipitation of MC type carbides. The failure temperature of Nb-Mo steel comes the second and that of the V-Mo steels is the lowest because of its lowest low angle grain boundary density leading to the lowest density of precipitated MC type carbides.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： Effect of nitrogen addition on continuous cooling transformation behavior of vanadium microalloyed steels was investigated. Therefor, CCT curves of three experimental steels with different vanadium and nitrogen content were measured by thermal dilatometer; the microstructural evolution of the steels with the varying cooling rates was characterized; their precipitation behavior was tracked, and planer lattice misfit degree of the precipitates with the ferrite matrix was calculated. The results show that ferrite transformation is promoted by nitrogen addition, and the starting temperature of transformation and the critical cooling rate for full bainite transformation are increased as well. For cooling rates in a range 0.8-1.6℃/s, the microstructure of steels with low nitrogen consists of granular bainite + lath like bainite, while acicular ferrite also exists; during or after the γ-α transformation vanadium compounds in low nitrogen steels precipitate mainly as VC, the quantity of which increases with the increasing vanadium content. However, for the steel rich in nitrogen, vanadium compounds precipitate as VN in austenite at high temperature. The lattice misfit degree of ferrite with the precipitates of austenite, VC and VN, which occurred at 900℃are 6.72%, 3.89% and 1.55% respectively. It indicates that VN precipitates act as preferential nucleation sites for ferrites and promote the ferrite transformation.
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-15 Cooperative journals: 《金属学报》
Abstract：利用OM, EBSD, XRD及物理化学相分析法，对不同卷取温度下Ti-V-Mo复合微合金化热轧高强钢的强化增量进行了估算和分析，分别讨论了卷取温度对屈服强度和MC相粒子对均匀塑性的影响规律。结果表明，在600 ℃卷取时，实验钢具有最佳的综合力学性能：抗拉强度UTS为1134 MPa，屈服强度YS为1080 MPa, 延伸率A为13.2％, 均匀延伸率Au为6.8％，其析出强化增量σp高达444～480 MPa左右，主要是由质量分数高达72.6 wt％的10 nm以下的(Ti, V, Mo)C粒子提供的。析出强化和细晶强化是实验钢主要的强化方式，σp的改变是导致实验钢不同卷取温度下YS变化的主要因素。随着卷取温度由500 ℃升高至600 ℃，实验钢的UTS和YS不断增加，Au不但没有降低，反而呈线性缓慢增加。其主要原因是σp对屈服强度的贡献量不断提高，在提高强度的同时改善了均匀塑性。
Hits
Hits
Downloads
Comment