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The morphologies and the formation mechanisms of isothermally transformed Widmanstatten ferrite and bainite in various steels
were investigated. Widmanstatten ferrite often grew from the grain boundary ferrite allotriomorph formed by a diffusional
mechanism in the temperature range of the upper C-curve, whereas, bainite grew directly from an austenite grain boundary showing
its own C-curve in a TIT diagram at temperatures between Bs (bainite starting temperature) and Ms (martensite starting temperature).
Both structures accompanied well-defined surface reliefs of the invariant plane strain-type, and were in the shape of a lath
or a plate consisting of several parallel needle-like ferrite subunits with parallelogram cross sc:ctions. The crystallographic
properties of Widmanstatten ferrite and upper bainite were similar to those of lath martensite. Therefore, it was concluded
that the difference between bainitic ferrite and Widmanstatten ferrite existed only in the nucleation events, where both structures
grew by the same mechanism. 相似文献
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Investigations were carried out into the formation of Widmanstatten ferrite in the structure of the section of incomplete recrystallization of the heat-affected zone of welded joints in heat-resisting pearlitic steels in the conditions of heating during welding. 相似文献
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<正> 一般认为亚共析钢中魏氏组织降低机械性能,尤其是不利于冲击韧性。近年来研究结果则认为魏氏组织可以提高机械性能,也有人认为具有魏氏组织的亚共析钢,由于冷却速度快,增加了珠光体量,细化了铁素体晶粒,从而抵销了针状铁素体的不良影响。另一些人指出切变机制使针状铁素体中有较高密度的位错和较细的亚结构,提高了钢的机械性能。本文根据对裂纹扩展行为的观察,探讨铁素体影响钢的机械性能的原因。 本实验采用25铸钢作试样,其化学成分(wt-%)为:C 0.28,Si 0.37,Mn 0.61,S 相似文献
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对低Al,高Ti,Nb(合金A)和高Al、低Ti,Nb(合金B)两种成分特征的Fe-Ni-Cr-Co-Nb-Ti-Al合金宏观和微观铸态组织的观察分析表明,合金A凝固速度较快,柱状晶区较大;两者枝晶间及铸态晶界上都分布着较多块(厚片)状富含Nb和Ti的MC和Laves相多晶体;合金B柱状晶区晶界Laves相较多;合金A晶界MC和Laves相附近析 体状γ′和η相及胞状η相;合金BKγ′的尺寸仅约为 相似文献
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45钢制手柄轴,由于其直径是对淬火开裂敏感的尺寸,加之有网状铁素体和魏氏组织等原材料缺陷.淬火时常常开裂。采取正火处理和适当降低奥氏体化温度及预冷淬火等措施,取得了防止手柄轴淬裂的令人满意的效果。 相似文献
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关于铁合金中相变的详尽显微组织方面的早期研究之一是由艾伯特·苏佛教授的学生周志宏(哈佛大学博士,1928年)完成的。该项研究描述了铁碳合金中魏氏组织和马氏体的形成,所用合金具有宽的碳含量范围,热处理时采用的冷却速率范围也是宽的。还描述了一种独特的汞浴淬火方法。此研究工作从未完全发表过。本文援引该博士论文中的一些原始显微组织照片和部分原文,并试图用我们现今对于铁合金相变的理解来阐明和重新诠释。文中还包括中国引进现代工业和科学的历史背景,以及周志宏对苏佛教授的个人回忆。 相似文献
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本文研究了低碳合金钢奥氏体在连续冷却或等温转变过程中形成的组织形态和转变机理。结果表明在中温贝氏体区得到“粒状贝氏体”组织,在先共析转变区得到“粒状组织”。两者都有“铁素体基体+小岛”形貌。但前者有表面浮凸现象,铁素体呈长条状,与母相维持K-S关系,惯习面为{111}_γ,小岛也多星长条状平行排列。后者无表面浮凸,铁素体呈无规则形状,与母相无严格位向关系,小岛亦呈无规则排列。然而这两种组织都是由扩散型相变机制形成的。最后,提出了形成这两种组织的相变模型。 相似文献
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Relationship among Microstructure, Defects and Performance of Ti60 Titanium Alloy Fabricated by Laser Solid Forming 总被引:1,自引:0,他引:1
研究了激光立体成形Ti60合金的缺陷及微观组织对于性能的影响。结果表明,激光功率对于激光成形试样的微观组织有明显的影响,大激光功率会形成魏氏组织,小功率则会形成网篮组织。魏氏组织的持久性能显著的低于网篮组织,其表现为脆性沿晶断裂,而网篮组织则为韧性断裂。同时冶金缺陷也会影响其持久性能。采用气雾化法制备的粉末(粉末B)作为成形粉末在成形过程中会形成气孔,而采用旋转电极法制备的粉末(粉末A)则无气孔产生。相较于无气孔的试样(采用粉末A制备的试样),当存在气孔(采用粉末B制备的试样)时其高温持久性能会由100 h降至25 h。 相似文献
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Alberto Lara-Guevara Ignacio Rojas-Rodríguez Ruben Velazquez-Hernandez David Jaramillo-Vigueras Karina del Ángel-Sánchez Mario E. Rodríguez-García 《Journal of Materials Engineering and Performance》2017,26(5):2040-2046
SAE4320H steel was characterized by photothermal radiometry spectroscopy, scanning electron microscopy, x-ray diffraction, and Vickers microhardness, to study metallurgical property changes as a result of the annealing heat treatment. Photothermal radiometry (PTR) images of hot forged and annealed SAE4320H steel were obtained to study the thermal changes, as a consequence of metallurgical microstructure changes that were produced by the heat treatment conditions. X-ray diffraction showed that the annealing process improves the crystalline quality of the SAE4320H steel and releases of any thermal stress. Widmanstatten microstructure was identified as a typical structure after the forging process. The Widmanstatten is a metallographic microstructure transformation to ferrite and pearlite which affected SAE4320H steel hardness and thermal properties. Vickers test showed that the hardness decreases as a result of the annealing process. A positive correlation between Vickers microhardness and PTR amplitude images was found, indicating that the annealing process increases the PTR signal. This methodology allows the determination of the changes in the Vickers microhardness from a non-contact and remote method as in PTR. 相似文献
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通过采用化学分析、组织观察和力学检验等手段对Q345T钢板桩初检与复检力学性能检验结果差别较大的原因进行了分析。结果表明,组织中带状组织、魏氏体组织,以及带状的夹杂物是导致钢材强度低的主要原因。追溯钢材的整个生产过程可知,钢水冶炼时除杂除气不充分、板坯浇铸后期杂质聚集偏析、加热温度控制不均匀是造成钢材组织与性能不合格的根本原因。 相似文献
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Results of investigation of metallographic special features of corrosion damage in longitudinal welded joints of a main heating system with diameters of 1400 mm and wall thicknesses of 40 mm are presented. It is shown that the nucleation of corrosion pits takes place along the fusion line on the internal wall of the heating system in the areas with high hardness (188–223 HV10) and the presence of a large amount of bainite and Widmanstatten ferrite in the structure. 相似文献