The cut-groove technique to infer interfacial effects during hot rolling

This article presents a novel experimental technique to infer the coupled effects of friction and heat transfer during the hot rolling of steels. The technique, termed the “cut-groove” method, relates the behavior of the deforming grooves cut on the strip surface to the local effects of friction and heat transfer. Validation of the experimentally observed groove shapes involved developing two-dimensional (2-D) and three-dimensional (3-D) finite-element (FE) models that employed a probabilistic distribution diagram (PDD). The PDD framework modeled the roll-strip interface and accounted for the variations in the oxide scale as distinct states that affect both friction and heat transfer. The numerically predicted groove openings are in good agreement with the experimentally observed groove shapes, particularly for the 2-D case. For the 3-D model, deviations are observed at regions close to the strip edges that are affected by nonplanar strain arising from spread during laboratory rolling. S. DAS, formerly Student, Department of Engineering Materials, and later Research Associate, Institute of Microstructural and Mechanical Process Engineering, The University of Sheffield (IMMPETUS), Sheffield, SI 3JD, United Kingdom     

加工条件对管线钢组织影响的实验研究

管线钢的最终组织和性能与控轧工艺以及加速冷却直接相关。采用一种新型的模拟轧制过程设备来研究X70级别管线钢在热变形冷却后的组织；设计了一系列的平面应变压缩实验来模拟板带轧制过程参数特别是精轧温度和冷却速率对最终组织的影响。采用恒定的变形速度70 s-1以及恒定的道次间隙时间，在850、900、950 ℃温度下的单道次和多道次压缩变形，随后研究2种不同冷却速率（3 ℃/s，6 ℃/s）获得的最终微观组织。观察发现，对于950、900、850 ℃的变温变形，出现了严重的混晶现象，而850 ℃下进行的3次压缩试样在6 ℃/s冷却到660 ℃后铁素体晶粒尺寸达到4.3 μm。     

Microstructure Evolution as an Effect of Strain Reversal During the Hot Deformation of Microalloyed Steels

Susceptibility of the steel for further cold processing strongly depends on the whole prior history of deformation in the hot working regime.In the industrial hot working processes,e.g.at the roughing stage of hot rolling,or forging,material undergoes complex deformation modes that leads to gradients of both microstructure and properties across the deformed cross-section.Torsion and multiaxial compression tests with different amounts of strain reversals were conducted at elevated temperatures to study the effect of applied strain path on the phenomena occurring during microstructure evolution of Nb-microalloyed steels.Gathered results will provide data for the modification of existing constitutive equations that mostly do not account for the strain path changes.Better through-process modelling will then enable to achieve better properties and quality of the products for further cold processing.     

CELLULAR AUTOMATA MODELLING OF GRAIN COARSENING DURING REHEATING AND VALIDATION WITH THE EXPERIMENTAL RESULTS

1. IntroductionG rain coarsening isthe processby w hich the m ean grain size ofan aggregate ofcrystalsincreases.A n understanding ofgrain coarsening isoffundam entalim portance forpredicting the average grain sizeand grain size distribution,w hich are dir…     

Influence of thermomechanical processing parameters on critical temperatures to develop an Advanced High-Strength Steel microstructure

Journal of Materials Science - A good selection of the thermomechanical processing parameters will optimize the function of alloying elements to get the most of mechanical properties in Advanced...     

Solid–liquid structural break-up in M2 tool steel for semi-solid metal processing

The success of semi-solid metal processing mostly depends on the formation of suitable starting microstructure, which must consist of solid metal spheroids in a liquid matrix. Various methods of obtaining this structure have been established; they include recrystallisation and partial melting (RAP), strain-induced melt-activated (SIMA), or simple mechanical stirring, to name a few. These methods, as widely discussed, have mostly been applied with light alloys, mainly aluminium based. This article discusses solid–liquid structural break-up in M2 tool steel subjected to a direct re-melting procedure from the as-annealed condition. The role of carbide dissolution in the grain boundary liquation of the steel is described. This leads to the production of near spheroidal solid grains in a liquid matrix, a microstructure suitable for the thixoforming process. Microstructural examination revealed that carbide particles contained in bands at 1220 °C slowly disappeared with temperature. At 1300 °C, the solid grains seemed to be free from carbides. Most of the carbides had now re-precipitated at the grain boundaries. Thixoforming carried out at 1340 and 1360 °C revealed the thixotropic properties of the semi-solid metal slurries. The results indicate a widening of the range of potential routes to thixoformable microstructures.     

On the Solidification of a H23 Tool Steel

The H23 tool steel contains high concentration of carbide forming elements, which affect the microstructure and mechanical properties. This present study described the microstructure and mechanical properties of the as cast H23 tool steel. The steel was prepared by vacuum induction melting. The microstructural investigation used XRD and electron microscope. The nano hardness and elastic moduli of matrix and carbide were also measured. The results show that the as cast microstructure consisted of ferrite matrix and M₆C, MC and M₂₃C₆ carbides. The eutectic M₆C carbides had two different morphologies owing to different growth mechanisms. There was agreement between the experimental results and the calculated solidification path for the H23 tool steel regarding the presence of carbides in the microstructure. The nanohardness and elastic moduli of ferrite matrix and M₆C carbides were respectively 4.2 ± 0.2 and 10.6 ± 1.2 and 198.3 ± 10.2 and 253.5 ± 11.7 GPa.     

Influence of Strain History and Cooling Rate on the Austenite Decomposition Behavior and Phase Transformation Products in a Microalloyed Steel

The effect of simple strain path changes as well as post-deformation continuous cooling rate during thermomechanical-controlled processing of microalloyed steel was studied using laboratory physical simulation. The phase transformation characteristics were directly analyzed by dilatometry under various cooling rates. The microstructures of the transformation products were characterized quantitatively using EBSD. The results have shown that while strain path changes impose a considerable influence on the hot flow behavior of the austenite, the cooling rate following hot deformation is the determining factor of the phase transformation mechanism and behavior which establishes the final transformation products and subsequent mechanical properties.