共查询到20条相似文献,搜索用时 15 毫秒
1.
《Materials Science & Technology》2013,29(3):266-272
AbstractAustenite formation during a continuous heating in a low carbon niobium microalloyed steel with a pearlite and ferrite initial microstructure has been studied. Characteristic transformation temperatures, Ac 1, Ac θ and Ac 3 and the evolution of austenite formation have been determined by combining dilatometry and metallography in a range of heating rates from 0˙05 to 10 K s–1. It has been observed that nucleation and growth of austenite depends highly on the applied heating rate. At low heating rates (0˙05 K s–1) nucleation of austenite takes place both at pearlite nodules and at ferrite grain boundaries, while for higher heating rates (≥0˙5 K s–1), nucleation at grain boundaries is barely present compared to the nucleation at pearlite nodules. The heating rate also affects the austenite growth path and morphology and, thus, the distribution of martensite in the dual phase microstructure obtained at room temperature. 相似文献
2.
《Materials Science & Technology》2013,29(11):1557-1563
AbstractA laboratory study was carried out to determine the characteristics of austenite grain growth and recrystallisation, strain induced precipitation, and continuous cooling transformation kinetics for two microalloyed medium carbon steels (1541 + Ti,V and 1541 + Nb). Austenite grain refinement is achieved by a combination of undissolved carbonitride precipitates at the reheat temperature, deformation recrystallisation at temperatures above T NR and strain induced carbonitride precipitation. Deformation below T NR promotes transformation to grain boundary ferrite (GBF), intragranular ferrite (IGF), and pearlite (P) at the expense of bainite (B) in both steels. This is attributed to increased density of nucleation sites for ferrite and pearlite at austenite grain boundaries, twin boundaries, and deformation bands. The results suggest that thermomechanical forging schedules could be designed to produce refined F + P microstructure, and hence, to realise improved strength, toughness, and machinability in the forging. 相似文献
3.
《Materials Science & Technology》2013,29(3):357-362
AbstractThe phase transformation points of a medium carbon V - Ti - N microalloyed steel were determined, as were the continuous cooling transformation curves of austenite heated at 1100 ° C without deformation and heated at 1200 ° C with two pass deformation. The data have been further used to analyse the real production scheme of N80 grade hot rolled non-quenched/tempered seamless tubes. The results have showed clearly that the commonly used 'in line normalisation' is not always necessary in the non-quenched/tempered production process of N80 grade hot rolled seamless oil well tubes. The above viewpoint has been further demonstrated by the microstructural examination of specimens sampled from industrial production. 相似文献
4.
《Materials Science & Technology》2013,29(11):1354-1361
AbstractTo develop any multiphase transformation induced plasticity (TRIP) assisted steel through thermomechanical processing routes, the effects of materials and process variables are to be thoroughly identified. Accordingly, the present work was programmed to study the influence of the state of prior austenite on the subsequent transformations and the related final phase combinations. In this framework, using a low carbon TRIP assisted multiphase steel, the compression specimens were subjected to different thermomechanical processing schedules to generate different prior austenite characteristics. The results indicated that the characteristics of martensite/austenite (M/A) microcomponent in the final microstructure were dictated by the state of prior austenite. In fact, increasing prior austenite grain size led to large decrease in the amount of M/A phase and this, in turn, resulted to higher strength without sacrificing the ductility. It was also found that static recrystallisation of austenite brings about more percentage of M/A phase compared with dynamic recrystallisation. 相似文献
5.
6.
《Materials Science & Technology》2013,29(6):615-626
AbstractGrain boundary engineering (GBE) involves the use of microstructural design to improve bulk material properties and enhance resistance to intergranular degradation. More specifically, the patented GBE procedure involves the design and control of fcc metallic microstructures using thermomechanical treatments and grain boundary characterisation based on the coincidence site lattice model. The phenomenon of multiple twinning is used to create a ‘twin limited’ microstructure, i.e. a microstructure composed entirely of special grain boundaries and triple junctions that is highly resistant to intergranular degradation. However, the theory behind GBE is not fully developed and therefore further study of the interfacial geometry, including the grain boundary plane and its role in GBE, is required to improve understanding of multiple twinning with the ultimate aim of improving the bulk and intergranular properties of metallic materials. An introduction to GBE is presented, including a number of cases where grain boundary design has improved the properties of fcc alloys for industrial applications. The theoretical characterisation of grain boundaries, including interfacial structure and geometry, is reviewed, highlighting the problems associated with microstructural characterisation based on limited knowledge of the grain boundary geometry. The importance of the grain boundary network is discussed: the grain boundary and triple junction character distributions are known to have a significant influence on bulk properties. Finally, the role of the interfacial plane is considered. It is concluded that although GBE has produced significant results, its theoretical basis and the ultimate creation of twin limited microstructures require further development. 相似文献
7.
《Materials Science & Technology》2013,29(8):883-892
AbstractThe paper describes the precipitation behaviour in a thermomechanically processed V bearing microalloyed steel containing small additions of Ti and Nb (0·007–0·008 wt-%) using analytical transmission electron microscopy. An intriguing aspect is the significant precipitation of titanium and niobium at these low concentrations, contributing to strength. A high density of multimicroalloyed precipitates of (V, Nb, Ti)(C, N) are observed instead of simple TiN, TiC, and NbC precipitates. They are characterised as cuboidal (45–70 nm), spherical (20–45 nm), irregular (20–45 nm), and fine (10–20 nm). Estimation of solubility products of carbides and nitrides of V, Nb, and Ti implies that the precipitation of titanium occurs primarily in austenite. Interphase precipitation of niobium occurs during austenite to ferrite transformation, while complete precipitation of vanadium takes place in the austenite–ferrite region close to completion of transformation. Substoichiometric concentrations of Ti and Nb, the presence of nitrogen, and the mutual extensive solubility of microalloying carbonitrides explains the formation of core shell (triplex/duplex) precipitates with highly stable nitrides ((Ti, Nb, V)N) in the core and carbides ((Ti, Nb, V)C) in the shell. The qualitative stochiometric ratios of triplex and duplex carbonitrides were Ti0·53Nb0·35V0·12 and Ti0·6V0·4, Nb0·51V0·49 and Ti0·64Nb0·36. Extensive precipitation of fine carbides on dislocation substructures, and sub-boundaries occurred. They were generally characterised as vanadium carbide precipitates with ordered cubic L12 structure and exhibited a Baker–Nutting orientation relationship with the ferrite matrix. M4C3 types of carbides were also observed similar to the steel, having high concentrations of Ti and Nb. 相似文献
8.
《Materials Science & Technology》2013,29(10):1317-1325
AbstractA mathematical model has been developed to optimise process parameters for production of API grade steel plates by thermomechanical controlled processing at a plate mill in Bhilai Steel Plant, India. The model comprises the prediction of the microstructural evolution during hot rolling, the subsequent phase transformation, and, finally, the mechanical properties of microalloyed steels. Effects of chemistry and mill parameters on recrystallisation, grain growth, and precipitation kinetics were taken into consideration to describe the metallurgical processes. . The model has been validated through laboratory experiments as well as full-scale rolling at the plate mill. 相似文献
9.
Microstructural evolution during simulated OLAC processing of a low-carbon microalloyed steel 总被引:5,自引:0,他引:5
The microstructural evolution during simulated on-line accelerated cooling (OLAC) of a commercial Grade 80 pipe steel was studied using a quench deformation dilatometer. The transformed matrix microstructure contains various amounts of polygonal ferrite, granular bainite and acicular ferrite, depending mainly on the accelerated-cooling interrupt temperature. The final microstructure is predicted well by drawing the OLAC schedule on the appropriate CCT diagram. Three distinct groups of precipitates are found in the final microstructure, which form during reheat, austenite deformation, and cooling, respectively. The distribution and composition of the precipitates varies widely with steel composition and processing schedule. The microstructure of industrially processed plate agrees well with that of corresponding laboratory simulations. 相似文献
10.
《Materials Science & Technology》2013,29(3):260-264
AbstractIn this paper the cyclic stress–strain response, low cycle fatigue (LCF) behaviour, and evolution of dislocation structures under LCF loading in the case of a low carbon microalloyed steel are discussed. The cyclic stress response revealed cyclic softening resulting from the propagation of Lüders bands. The experimental LCF life was compared with the life predicted using Tomkins' model and the modified universal slopes (MUS) equation. While the life predicted by Tomkins' model showed good correlation with the experimental results, the life predicted using the MUS equation grossly overestimated the life. Inclusion induced delaminations under cyclic loading were thought to be responsible for the overestimation by the MUS equation. Low energy dislocation structures, i.e. cells, were observed near the fracture surfaces. Interrupted tests revealed cell formation after 10 cycles at a total strain amplitude of 0·3%. 相似文献
11.
In this work, the microstructures and tensile properties of a commercial magnesium alloy “AZ61” processed by a combination of hot extrusion and thermomechanical processing (TMP) were investigated. The TMP was consisting of two or three hot rolling steps with large reductions per pass, thus allowing significant grain refinement. The microstructural evolution has been studied by means of optical and scanning electron microscopes, as well as X-ray diffraction analysis. The as-cast material is extruded in the form of a cylinder with initial diameter of 250 mm to a final diameter of 110 mm (80% reduction in cross-sectional area). Then hot rolling regimes were performed at 300 °C with different percentage of strain per pass. Tensile and hardness tests were performed in the samples (as-cast, extruded, and rolled) at room temperature in order to evaluate the mechanical properties of the material. The results of experiments demonstrated that fine grain size might be achieved in magnesium alloy AZ61 by using a two-step processing route involving an initial extrusion step followed by thermomechanical processing with large reduction in thickness per pass. This two-step process, designed to achieve average grain sizes of 10–20 μm. 相似文献
12.
《Materials Science & Technology》2013,29(10):1266-1272
AbstractIsothermal and thermomechanical fatigue (TMF) behaviour (including cyclic stress response and number of cycles to failure) of a Ti – 5.6Al – 4.8Sn – 2.0Zr – 1.0Mo – 0.32Si – 0.8Nd (wt-%) hightemperature titanium alloy was examined. The purpose of the present investigation was to understand the effect of temperature fluctuation on the cyclic behaviour and fatigue life of this alloy and to test the suitability of lifetime prediction based on isothermal laboratory data. The results indicated that both the level of peak stress and fatigue life were decreasing with increasing test temperature from 400°C to 650°C in isothermal fatigue (IF) tests. In TMF tests run between 400°C and 600°C, the peak stresses corresponding to 600°C coincide well with that found in IF tests run at 600°C, while a slight increase in cyclic hardening was found for peak stress corresponding to 400°C compared to that found in a 400°C/IF test. This increase in cyclic hardening became more pronounced when the maximum temperature increased to 650°C. Fatigue life in 'out of phase' (OP) condition was found to be shorter than under an equivalent 'in phase' (IP) condition, and this gap increased with decreasing mechanical strain amplitude. The results indicate that lifetime prediction based on isothermal laboratory data may lead to non-conservative results if thermal fluctuations are present in components made of the present alloy. 相似文献
13.
Semi-solid processing of magnesium alloys is generally based on conventional magnesium-based casting alloys such as Mg–Al series. However, these casting alloys do not give such high mechanical properties as the alloys that are conventionally wrought such as Mg–Zn series. In this paper, a ZK60 magnesium alloy with the addition of Y was thixoforged. The semi-solid thermal transformation (SSTT) route and the recrystallisation and partial melting (RAP) route were used to obtain the semi-solid feedstocks for thixoforging. Microstructural evolution during partial remelting was studied at temperatures for times. Tensile mechanical properties of thixoforged components at room temperature were examined. Results show that a fine spheroidal microstructure can be obtained by the RAP route. Compared to the RAP route, the SSTT alloy shows coarsened solid grains with a relatively high proportion of intragranular liquid droplets. With prolonged holding time, the solid grain sizes of the SSTT alloy and the RAP alloy increased. Coalescence was dominant in the SSTT alloy and Ostwald ripening was dominant in the RAP alloy. Thixoforging for the SSTT alloy and the RAP alloy resulted in successful filling of the die. The tensile properties of the thixoforged RAP alloy were satisfactory and exceeded those of the thixoforged SSTT alloy. However, the mechanical properties of both the thixoforged SSTT alloy and the thixoforged RAP alloy decreased with prolonged holding time. 相似文献
14.
Stress–strain behaviour in tension and in torsion was studied in ferrite–pearlite and ferrite–bainite microstructures of C–Mn steel. The fatigue tests were performed under reverse torsional loading on hour-glass shape specimens. The cyclic plasticity in torsion was found at about 37% of the monotonic yield stress in both ferrite–pearlite and ferrite–bainite microstructures. The ferrite phase in the direction of maximum shear stress was the preferable site for crack nucleation. The ferrite–bainite microstructure showed better fatigue properties than the ferrite–pearlite microstructure. 相似文献
15.
The effect of strain aging on the microstructure, including copper precipitation, and mechanical properties of an industrially produced Cu-containing microalloyed low carbon pipeline steel has been investigated. The precipitation of round bcc-Cu particles with diameters of ~7?nm has been clearly observed in the microstructure after strain aging. The strength of pipeline steel significantly increased while the elongation and impact toughness did not apparently decrease. Unlike welded pipe, few carbon atoms in supersaturated solid solution diffuse to the mobile dislocations, forming Cottrell atmospheres and producing strain aging phenomenon in seamless pipe. This difference is attributed to the different pipe making technique: thermo mechanically controlled processed for welded pipe and traditional heat-treatment for seamless pipe. 相似文献
16.
《Materials Science & Technology》2013,29(7):832-837
AbstractDuring continuous heating of a cold rolled low carbon steel, a dilatometric anomaly has been detected before the well known ferrite to austenite transformation. The detailed study of the processes occurring during the heating and comparison with the case of an ultralow carbon steel showed that this anomaly is related to the change in dislocation density during recrystallisation. 相似文献
17.
采用Gleeble-1500热模拟试验机对一种中碳钒微合金钢在变形温度900~1 100℃、应变速率0.01~10 s-1条件下的热变形行为进行研究.分别建立了实验钢的幂律、指数和双曲正弦本构方程,观察了实验钢在不同变形条件下的显微组织,得出了实验钢的动态再结晶稳态晶粒尺寸和峰值应变与Zener-Hollomon参数的关系.结果表明:双曲正弦本构方程具有最高的拟合精度;实验钢热变形激活能Q为273.225 kJ/mol,与奥氏体的自扩散激活能(270 kJ/mol)十分接近,说明实验钢在此变形条件下的速率控制机制是扩散控制的位错攀移;显微组织观察表明,实验钢的动态再结晶行为受变形温度和应变速率的影响;拟合得出实验钢的动态再结晶稳态晶粒尺寸(Ds)和峰值应变与Z参数的关系为ln Ds=-0.200 31ln Z+7.941 65和lnεp=0.184 56ln Z-5.373 83. 相似文献
18.
This paper reports the fatigue behaviour of friction welded medium carbon steel–austenitic stainless steel (MCS–ASS) dissimilar joints. Commercial grade medium carbon steel rods of 12 mm diameter and AISI 304 grade austenitic stainless steel rods of 12 mm diameter were used to fabricate the joints. A constant speed, continuous drive friction welding machine was used to fabricate the joints. Fatigue life of the joints was evaluated conducting the experiments using rotary bending fatigue testing machine (R = −1). Applied stress vs. number of cycles to failure (S–N) curve was plotted for unnotched and notched specimens. Basquin constants, fatigue strength, fatigue notch factor and notch sensitivity factor were evaluated for the dissimilar joints. Fatigue strength of the joints is correlated with microstructure, microhardness and tensile properties of the joints. 相似文献
19.
In the present work, high temperature tensile properties and abrasive wear performance of a microalloyed medium carbon steel has been examined. Tensile and abrasive wear testing were carried out on as-received and heat treated specimens. The research has shown that microalloyed medium carbon steel was susceptible to dynamic strain ageing due to interaction of mobile dislocations and solid atoms, such as carbon and/or nitrogen. The interaction between dislocations and solid atoms at 200–300 °C changes the work hardening rate and contributes to dynamic strain ageing. These interactions also increased abrasive wear resistance of the microalloyed medium carbon steel at 300 °C. Therefore, the inference can be drawn that dynamic strain ageing caused an improvement on abrasion resistance. 相似文献
20.
M. Ghasri-Khouzani 《Materials Science & Technology》2017,33(10):1159-1170
A Fe-30Mn-0.6C sheet steel was decarburised and/or annealed to obtain four Fe-30Mn-C alloys with carbon contents of 0.06, 0.2, 0.4 and 0.6 wt-%. The primary deformation products were found to be mechanical twins for the 0.2C, 0.4C and 0.6C alloys and a combination of mechanical twins and ε-martensite for the 0.06C alloy. Both the ε-martensite and mechanical twin formation kinetics increased sigmoidally with true strain such that the final twin volume fraction increased with increasing alloy SFE and C content, where the latter finding disagrees with some of the accepted models for high-Mn twinning induced plasticity steels. Moreover, the activation stress for twin formation was found to increase linearly with alloy SFE, per a model previously proposed by the present authors. 相似文献