亚共析钢中魏氏组织形态的研究

本文用各种不同的加热温度和不同的冷却方式,对20A深冲弹钢中出现的各种铁素体形态进行了光学金相和电子金相的观察,经过分析表明,在含碳量一定的低碳钢中,铁素体的形态和冷却方式,冷却速度有关,并且这些形态大都符合Dubè所作的分类。本文根据铁素体片的形态讨论了它的形核和长大的机构学。     

The formation of austenite from mixtures of ferrite and cementite as observed by HVEM

The detailed mechanism of the transformation of various mixtures of ferrite and austenite was studied byin situ experiments in a high voltage electron microscope. Various phenomena were observed which seemed to be controlled by the rate of carbon diffusion when the γ/α interface was curved. The effect of manganese was studied by using commercial steels. In agreement with theoretical predictions based upon the local equilibrium model, the dissolution of cementite in ferrite can be more or less prevented by manganese. The effect on the dissolution in austenite is smaller. The reaction from lamellar pearlite to austenite is more complex, the cementite lamellae providing carbon to the austenite but also acting as barriers. M. NEMOTO, formerly with Division of Physical Metallurgy, The Royal Institute of Technology, S-100 44 Stockholm 70, Sweden     

Dependence of tensile properties on microstructural features of bimodal-sized ferrite/cementite steels

A medium-carbon steel was processed through different warm rolling techniques, and the microstruc-tural features with bimodal grain size distribution were found to be different.The combination of strength and ductility was ameliorated in the steel processed through warm rolling characterized by biaxial reduction.The enhanced strength is attributed to the densely distributed fine intragranular ce-mentite particles and the small grain size in the coarse grain regions.The enhanced uniform elonga-tion is due to the improved work hardening behavior at the large-strain stage.This work hardening behavior is predominantly ascribed to the finely dispersed intragranular particles.The relatively small grain size with nearly equiaxed shape in the coarse grain regions helps stabilize the uniform deforma-tion to a large strain.     

The role of ledges in the proeutectoid ferrite and proeutectoid cementite reactions in steel

The influence of interphase boundary ledges on the growth and morphology of proeutectoid ferrite and proeutectoid cementite precipitates in steel is examined. After reviewing current theoretical treatments of growth by the ledge mechanism, investigations that clearly document the presence and motion of ledges with thermionic emission electron microscopy (THEEM) and transmission electron microscopy (TEM) are reviewed. A fundamental distinction is made between two types of ledges: (1) mobile growth ledges whose lateral migration displaces the inter-phase boundary and (2) misfit-compensating structural ledges. Both types of ledges strongly affect the apparent habit plane and aspect ratio of precipitate plates. Agreement between measured growth rates of proeutectoid ferrite and cementite (plates and allotriomorphs) and predicted growth kinetics assuming volume diffusion-controlled migration of ledge-free disordered boundaries is shown to be consistently poor. Physically realistic growth models should incorporate the ledge mechanism. More accurate comparisons of the growth models with experimental data will need to account for observed ledge heights, interledge spacings, and ledge velocities. In this vein, the sluggish growth kinetics of cementite allotriomorphs observed in an Fe-C alloy are shown to be quantitatively consistent with a strong increase in interledge spacing with time. This paper is based on a presentation made in the symposium “The Role of Ledges in Phase Transformations” presented as part of the 1989 Fall Meeting of TMS-MSD, October 1–5, 1989, in Indianapolis, IN, under the auspices of the Phase Transformations Committee of the Materials Science Division, ASM INTERNATIONAL.     

Microstructural evolution of submicron sized ferrite in bimodal structural ultrafine grained ferrite/cementite steels by annealing below austenized temperature

The microstructural evolution of submicron sized ferrite in bimodal structural ultrafine grained ferrite/cementite steels with 0.15 pct carbon content and 0.45 pct carbon content upon annealing below the austenized temperature was investigated. The average grain sizes of the ferrites with a normal density and with a high density of cementite particles were plotted, respectively, as a function of the annealed temperature and time, and exhibited different coarsening behaviors. The average grain sizes of the ferrites with a normal density of cementite particles gradually coarsened by increasing the annealing temperature or time, while those with a high density of cementite particles hardly changed at first, and then coarsened after reaching a certain annealing condition. The coarsening of the ferrite grain size in the steel with 0.15 pct carbon content occurred much more readily than that in the steel with 0.45 pct carbon content upon annealing. The spacing and the critical spacing of cementite particle were measured and hypothetically calculated, respectively. The size and the distribution of cementite particles was one of the critical factors affecting the microstructural evolution in this type of cementite particle spherodized steels. Most of the coarsening of the ferrite grain size occurred after the cementite particle spacing reached the required critical value.     

魏氏组织形成机理及对钢管性能影响的分析研究

利用万能光学显微镜、扫描电子显微镜、透射电子显微镜等大型精密仪器对低碳低合金钢管中出现的魏氏组织进行了级别判定、高倍形貌观察和精细结构研究;对不同温度和冷速条件下进行热处理工艺试验的管材进行了力学性能对比.通过试验确定了魏氏组织的形成温度范围和形成魏氏组织的冷速区间,搞清了魏氏组织对钢性能(尤其是冲击性能)的影响规律.分析研究了魏氏组织的形成机理.     

High temperature plastic-flow behavior of mixtures of austenite,cementite, ferrite,and pearlite in plain-carbon steels

The plastic-flow behavior of ferrite + pearlite, pearlite + cementite, and austenite + cementite mixtures in plain carbon steels has been examined over the temperature range 500 to 1050 °C, strain-rate range 6 x l0⁻⁶ to 2 x l0⁻² s⁻¹, and carbon range 0.005C to 1.89C. Up to the eutectoid temperature the strength of the ferrite + pearlite mixture more than doubles as the carbon content increases from 0.005C to 0.7C, so that whereas in low-carbon steels the ferrite is weaker than the higher temperature austenite phase, in eutectoid steels the fully pearlitic structure is stronger than the fully austenitic structure. Manganese and silicon strengthen ferrite more effectively than they do austenite. A 0.17 pct phosphorus addition strengthens the ferrite + pearlite mixture across the range of microstructures from fully ferritic to fully pearlitic. Beyond the eutectoid composition, the amount of proeutectoid cementite does not significantly affect the strength of the pearlite, but above the eutectoid temperature it appreciably strengthens the austenite and cementite mixture at the strain rate of 2 X 10^-2 s^-1.     

Q345B高压化肥管中魏氏组织消除的实践应用

文章针对Q345 B高压化肥管纵向冲击性能不合格的问题,采用金相显微镜对其组织进行微观分析,发现造成冲击性能不合的原因是组织中存在大量的魏氏组织.采用正火热处理工艺对样管进行处理,结果表明:采用正火处理可以将钢中的魏氏组织消除,且纵向冲击功大于120 J,达到GB 6479—2013标准中冲击下限值的3倍.     

魏氏组织对20钢主蒸汽管道焊缝材质状态的影响

对焊缝中存在的魏氏组织进行了级别判定,并对存在魏氏组织的焊缝进行了性能试验(冲击性能试验、拉伸性能试验、硬度测试)。分析了魏氏组织的形成机理,研究了魏氏组织对焊缝材质状态(尤其是冲击性能)的影响,对存在魏氏组织的焊缝进行了材质状态评价。     

汽车活塞杆用45钢魏氏组织预防措施以及工艺优化

魏氏组织为亚共析钢钢中容易产生的有害组织,汽车活塞杆用45钢要求不得有魏氏组织,正常工艺(坯1120～1200℃均热,终轧950℃)生产的45钢存在0.5 ～1.0级的魏氏组织;通过将钢中Al含量由原0.013％提高至0.038％、坯均热温度降至1070～1100℃、终轧温度降至800℃,魏氏组织级别由0.5 ～1.0...     

超快冷技术下Q345升级钢魏氏组织的形成及控制

针对超快冷技术应用带来的Q345中厚板升级钢魏氏组织问题,结合现场实际工艺条件,通过实验室试验研究与仿真模拟计算,分析了魏氏组织出现的原因,并提出解决措施,工艺参数经过现场精确调整,取得了较好的效果。     

Low absorbed energy ductile dimple fracture in lower shelf region in an ultrafine grained ferrite/cementite steel

The curve of absorbed energyvs test temperature for an ultrafine grained ferrite/cementite steel showed a transition from an upper shelf energy to a lower shelf energy,i.e., a transition from an energy-absorbent ductile mode to an energy-absorbent brittle mode. Some dense and small-sized dimples were observed in the lower shelf region. A significant and consistent difference existed between ductile-to-brittle transition temperature and impact energy transition temperature, that is, low absorbed energy but undergoing a ductile dimple fracture at a certain low temperature.     

Structure and some properties of niobium carbide single crystals

Conclusions High-purity niobium carbide single crystals of different compositions within the range of homogeneity of the carbide were grown by crystallization from a melt. X-ray diffraction studies and metallographic examinations revealed that the single crystals obtained contained both perfect regions and regions distorted by thermal stresses and composition heterogeneities. As a result of x-ray diffraction studies, the presence of substructures of the first and second orders in the single crystals was established. Maximum disorientation was found to attain 0.2–0.5° for blocks of the first order and to be about 0.05° for blocks of the second order. The density of dislocations in the niobium single carbides was on the order of 10⁵ cm^–2. Within the limits of niobium carbide compositions investigated no differences in mechanical properties (microhardness and resistance to cracking) were detected. It was established that in single crystals of compositions NbC_0.78-NbC_0.82 room-temperature deformation took place over the {111} 110 system. The room-temperature fracture of the single crystals was mainly brittle in character.Translated from Poroshkovaya Metallurgiya, No. 12(228), pp. 81–86, December, 1981.     

Effects of copper on proeutectoid cementite precipitation

The effect of copper on proeutectoid cementite precipitation was investigated by examining the isothermal transformation characteristics of Fe-C and Fe-C-Cu alloys that had comparable carbon contents. The TTT diagrams generated for the Fe-1.43 wt pct C and the Fe-1.49 wt pct C-4.90 wt pct Cu alloys showed that the kinetics of proeutectoid cementite precipitation were not significantly affected by copper. The morphology of the proeutectoid cementite, as seen in the optical microscope, was also substantially the same in both alloys. However, transmission electron microscopy revealed the presence of small epsilon-copper precipitates within the proeutectoid cementite of the copper containing steel. It was concluded that this precipitation of ε-Cu took place at the cementite : austenite interphase boundaries, and that the transport of copper to the precipitates was accomplished by interphase boundary diffusion. The small influence of copper on the kinetics of proeutectoid cementite precipitation is discussed in terms of diffusional growth theories and the structure of the cementite : austenite interphase boundary.     

亚共析钢中魏氏组织对材料脆化倾向的影响

用两种不同的试验方法,即带有尖锐缺口的室温冲击试验和带有缺口于-80℃下进行快速拉伸试验,对15A深冲弹钢中两种不同的铁素体形态（魏氏铁素体及状块铁素体）进行了材料脆化倾向的研究。结果表明,在原奥氏体晶粒大小相同的条件下,具有魏氏铁素体的试样其脆化倾向较小,而块状铁素体试样的脆化倾向较大。本文对这些结果作了进一步的讨论。
关于15A和20A深冲弹钢中出现魏氏组织对冲击韧性和脆性转变温度的影响,近两年来国内曾有过多次研究。〔1〕〔2〕他们的结果均表明,在具有魏氏铁素体组织的试样中,其中冲击值均比不具有魏氏组织的块状铁素体为高,且脆性转变温度比块状铁素体的为低。近年来为了提高热轧钢板的韧性,采用轧后快冷,获得针状铁素体组织〔3〕。
为了进一步弄清深冲弹钢中魏氏组织对机械性能的影响,使含有魏氏组织和不含魏氏组织（块状铁素体）的脆化趋势更加明显,本文从两个方面进行了研究:一为带有尖锐缺口的冲击试验,一为在-80℃对带有缺口的试样塑性和韧性降低的缺口敏感性。由于单纯室温缺口冲击试验使材料脆化的趋势,没有用降低温度的方法使材料脆化来得显著,故又采取了降低温度和快速形变结合的方式,使具有魏氏组织和不含魏氏组织的脆化倾向更趋明显,以便更好地进行比较。
本文从力性实验数据和断口分析中均表明,具有魏氏组织的试样,其脆化倾向反比块状铁素体的小,因此,长期以来,笼统的认为反有魏氏组织都必定降低冲击值使脆化倾向中大的看法,是值得商确的。     

Growth of chromium carbide layer on austenite and cementite

Determination of the growth of the carbide layer M₇C₃ on cementite and austenite with cementite and comparison with the growth on austenite. Micrographs of Fe-C alloys containing 5.5% C and of different chromium contents obtained by chromizing after various annealing treatments for determination of the morphology of the layer. Presentation of a model of the growth of M₇C₃-M₃C layers on cementite based on the performed investigations.     

The interfacial structure and habit plane of proeutectoid cementite plates

Three groups of previous investigators independently reported the anomalous result that the austenite habit plane of proeutectoid cementite plates, as determined with optical microscopy, is not unique. The present investigation utilized transmission electron microscopy (TEM) to study the interfacial structure and habit plane of proeutectoid cementite plates in a matrix of retained austenite in an Fe-0.81% C-12.3% Mn alloy in order to explain this unusual result. The broad faces of cementite plates were found to contain two types of structural feature: (1) large, kinked ledges with heights (h) of about 7 nm and spacings (λ) between 30 and 100 nm, and (2) a finely spaced set of straight ledges, with h ≈ nm or less and λ ≈ 4–6 nm, whose direction is nearly [110]_A ||[010]_C. Matching of atom spacings showed this to be a direction of good fit between the austenite and cementite lattices. The apparent habit plane, measured with conventional TEM techniques, was always less than 10° (and in most cases less than 5°) from (113)_A ||(101)_C. Atom matching studies also demonstrated that this pair of planes exhibits superior matching, and is thus likely to provide the conjugate atomic habit planes of the teraces of ledges. Thus, the non-uniqueness of the “optical microscopy apparent habit plane” of proeutectoid cementite plates appears to arise from the presence of arrays of ledges, combined with the sympathetic nucleation of new plates, on their broad faces.