变形晶界对低碳钢显微组织的影响

对不同温度下变形和变形后再加热到奥氏体区的低碳钢SS400的显微组织进行了研究,结果表明：变形使奥氏体和铁素体晶界呈锯齿状,锯齿状的奥氏体晶界优先成为铁素体的形核位置,锯齿状的铁素体晶界有利于铁素体再结晶核心的形成。     

磷元素在钢中的晶界偏聚

磷元素在钢中的晶界偏聚可以分为两类,即平衡偏聚和非平衡偏聚.介绍了这两类偏聚现象以及偏聚理论.以磷对晶界结合力、晶界扩散和晶界能的影响机理为基础,分析了磷元素对钢力学性能的影响和磷在钢中发生晶界偏聚的原因.     

Grain Boundary Segregation Behavior of Boron in Low-Alloy Steel

The boron concentration profiles around prior austenite grain boundaries in Fe-0.05C-0.5Mo-0.001B (mass pct) are examined using aberration-corrected STEM-EELS. In order to obtain the precise distribution of boron around the boundaries, tilt series measurements with thin specimens (<30 nm) are performed and the EEL spectra are analyzed by principal component analysis (PCA) and multivariate curve resolution (MCR). The boron concentration profile changes with the cooling rate from the solid solution temperature. The concentration at grain boundaries is maximized at a medium rate (30 °C/s), where the concentration reaches 8 at. pct, and it decreases at a larger (250 °C/s) or smaller (5 °C/s) rate. On the other hand, the boron distribution becomes wider as the cooling rate becomes smaller. The current results suggest that the boron segregation in the alloy is formed by the “non-equilibrium segregation mechanism.”     

Effect of Post-annealing on Grain Boundary of Nano-crystalline Cu Processed by Powder High-Pressure Torsion

High tensile strength of 616 MPa and improved ductility of 7.6 pct were obtained in powder-consolidated pure Cu processed by high-pressure torsion (HPT) at room temperature followed by post-annealing at 673 K (400 °C). The powder-HPT consolidation process maintained nano-crystalline microstructures even after post-annealing due to the presence of well-dispersed oxide particles in the matrix. Higher ductility in the post-annealed specimen is attributed to higher fraction of stable Σ3 coincidence site lattice boundaries than that in the HPT-processed Cu.     

The Role of Grain Orientation and Grain Boundary Characteristics in the Mechanical Twinning Formation in a High Manganese Twinning-Induced Plasticity Steel

In the current study, the dependence of mechanical twinning on grain orientation and grain boundary characteristics was investigated using quasi in-situ tensile testing. The grains of three main orientations (i.e., 〈111〉, 〈110〉, and 〈100〉 parallel to the tensile axis (TA)) and certain characteristics of grain boundaries (i.e., the misorientation angle and the inclination angle between the grain boundary plane normal and the TA) were examined. Among the different orientations, 〈111〉 and 〈100〉 were the most and the least favored orientations for the formation of mechanical twins, respectively. The 〈110〉 orientation was intermediate for twinning. The annealing twin boundaries appeared to be the most favorable grain boundaries for the nucleation of mechanical twinning. No dependence was found for the inclination angle of annealing twin boundaries, but the orientation of grains on either side of the annealing twin boundary exhibited a pronounced effect on the propensity for mechanical twinning. Annealing twin boundaries adjacent to high Taylor factor grains exhibited a pronounced tendency for twinning regardless of their inclination angle. In general, grain orientation has a significant influence on twinning on a specific grain boundary.     

The Distribution of Grain Boundary Planes in Interstitial Free Steel

The grain boundary character distribution in a commercial IF steel has been measured as a function of lattice misorientation and boundary plane orientation. The grain boundary plane distribution revealed a relatively low anisotropy with a tendency for grain boundaries to terminate on low index planes having relatively low surface energy and large interplanar spacings. Although the most common grain boundary plane orientation was (111), grain boundaries terminated on higher index planes were sometimes found. For instance, at a misorientation angle of 60?deg about [111], symmetric {112} tilt boundaries were far more populous than [111] twist boundaries. The current observation revealed an inverse relationship between the measured populations and the previously reported grain boundary energies.     

Texture and Grain Boundary Network Evolution of Laser Powder Bed Fusion Processed Pure Ni During Post-printing Annealing

Metallurgical and Materials Transactions A - Commercially pure Ni was additively manufactured using laser powder bed fusion. The printed specimens were then subjected to annealing treatments in a...     

A Study of Submicron Grain Boundary Precipitates in Ultralow Carbon 316LN Steels

This article reports our efforts in characterization of an ultralow carbon 316LN-type stainless steel. The carbon content in the material is one-third that in a conventional 316LN, which further inhibits the formation of grain boundary carbides and therefore sensitizations. Our primary effort is focused on characterization of submicron size precipitates in the materials with the electron backscatter diffraction (EBSD) technique complemented by Auger electron spectroscopy (AES). Thermodynamic calculations suggested that several precipitates, such as M₂₃C₆, Chi, Sigma, and Cr₂N, can form in a low carbon 316LN. In the steels heat treated at 973 K (700 °C) for 100 hours, a combination of EBSD and AES conclusively identified the grain boundary precipitates (≥100 nm) as Cr₂N, which has a hexagonal closed-packed crystallographic structure. Increases of the nitrogen content promote formation of large size Cr₂N precipitates. Therefore, prolonged heat treatment at relatively high temperatures of ultralow carbon 316LN steels may result in a sensitization.     

Characteristics of Strain-Induced Ferrite in Low Carbon Steel

Itiswellknownthatthestrain inducedtrans formationfromaustenitetoferritecanleadtograinrefinement .Thushighermechanicalpropertiessuchasstrengthandductilitycanbeobtained[1,2 ] .Someresearcheshavebeencarriedoutonthenucleationofstrain inducedferriteinthepastyears .PDHodgsonetalsuggestedthattheaustenitegrainsshouldbeascoarseaspossibletodecreasenucleationatgrainbo undaries[3 ] .PJHurleyetalconsideredthatthecel lularboundaryofdislocationsuppliesthesitesfornu cleationofstrain inducedferrite[4] .Yang…     

半固态高碳工具钢的变形特性

采用Gleeble-1500热/力模拟机，对电磁搅拌法制备的高碳(碳含量大于1％)工具钢半固态坯料进行压缩实验，研究半固态高碳钢在不同变形温度、不同变形速率下的应力一应变关系，同时与相同冷却条件下的常规铸态坯料进行了对比分析。结果表明：在固一液两相区变形时，半固态坯料的流变应力明显低于常规铸态坯料，且随温度的升高而降低；当变形速率降低时，应力峰值升高，同时热软化现象明显。     

An Ultra-low Carbon, Thermomechanically Controlled Processed Microalloyed Steel: Microstructure and Mechanical Properties

In the current study, a novel ultra-low carbon, high-molybdenum-bearing microalloyed steel has been thermomechanically processed. Transformation of this steel during continuous cooling has been assessed. Variation in the microstructure and mechanical properties at different finish rolling temperatures has been studied. The average grain size, misorientation of grain boundary, and distribution of ferrite grains have been analyzed by using electron backscatter diffraction. The lower yield strength (251 to 377?MPa) with moderate tensile strength (406 to 506?MPa) along with high ductility (30 to 47?pct) has been achieved in the selected range of finish rolling temperatures. Superior impact toughness value in the range of 153 to 162?J is obtained in the subsize specimen even at subzero temperatures (233?K [?40?°C]), which is attributed to fine average ferrite grain size. The acicular ferrite dominated microstructure obtained at the 1023?K (750?°C) finish rolling temperature is the most attractive microstructure for pipeline applications due to its excellent combination of strength and toughness.     

Surface Ferrite Grain Refinement and Mechanical Properties of Low Carbon Steel Plates

Considering the specialities of the steel plate production, the TMCP study has been carried out with Gleeble 2000 tester to explore the possibility of fine grained ferrite in the low carbon steel plates with the chemical composition of C 0.13--0.18, Si 0.12-0.18, Mn 0.50-0. 65, P 0. 010-0. 025, and S 0. 005-0. 028. The plates with thickness of 8. 7 mm in which the ferrite grain size is smaller than 8μm have been produced by special de- formation process in the laboratory. Furthermore, the trial production of special plain carbon steel plates of 16-25 mm in thickness and 2 000- 2 800 mm in width with fine grained ferrite has been successfully carried out in the Shougang Steel Plate Rolling Plant. The ferrite grain size is 5.5-7μm in the surface layers and 9.5-15μm in the central layer respectively. The yield strength is 320- 360 MPa, tensile strength is 440-520 MPa and the elongation is 25%- 34 %. It is very important for the rolling plants to improve the low carbon steel plates＇ mechanical properties. The results show that the ferrite grains in the surface layer can be refined effectively by the appropriate rolling process, and the strength can be also increased.     

晶界工程抑制SUS304不锈钢晶界贫铬机制

利用电子显微镜研究了形变热加工处理对晶界结构的影响。研究表明,敏化处理后,因预应变处理而引入孪晶的晶界工程(GBE)可以在大角度晶界得到高比例的非连续分布的低能晶界。在大角度晶界上形成的局部的低能晶界的贫铬程度明显低于原来的大角度晶界的贫铬程度。非连续分布的低能晶界阻断了大角度晶界贫铬的连续性,有效抑制来自于材料表面的沿晶腐蚀。     

Coupling Effect of Prior Austenite Grain Size and Inclusion Characteristics on Acicular Ferrite Formation in Ti-Zr Deoxidized Low Carbon Steel

Metallurgical and Materials Transactions B - The coupling effect of prior austenite grain size and inclusion characteristics on acicular ferrite (AF) formation was investigated in Ti-Zr deoxidized...     

Relationship Between Grain Boundary Segregation of Antimony and Temper Embrittlement in Titanium-Doped Nickel-Chromium Steel

The antimony segregation at grain boundary was observed and the temper embrittlement in titanium-doped nickel-chromium steel was analyzed. It is concluded that the antimony segregation at grain boundary is nonequilibium and the kinetics of temper embrittlement agrees well with those of nonequilibrium antimony segregation at grain boundary. Besides, the mechanism of nonequilibrium antimony segregation at grain boundary proved to be the most satisfactory one among the existing mechanisms to interpret the antimony-induced embrittlement kinetics in the nickel-chrominm steel. Based on these, the activation energy and frequency factor of diffusion of antimony-vacancy complexes were obtained according to the concept of critical time in nonequilibrium grain boundary segregation theory.     

碳含量及晶粒尺寸对微合金钢激活能的影响

通过对3种常用应力函数的回归计算，认为双曲正弦函数的回归精度最高。以此为基础，确定了11种分别含Mo、Ti、V、Nb钢的激活能，进而建立了激活能与材料化学成分、原始晶粒尺寸关系的BP网络模型。并得出表观激活能随钢中碳含量增大而增大，随原始晶粒尺寸的增大而减小的结论。