Texture Evolution and Residual Stress Relaxation in a Cold-Rolled Al-Mg-Si-Cu Alloy Using Vibratory Stress Relief Technique

Over the last half century, vibratory stress relief (VSR) has come to be recognized as a technique with several unique benefits, and it has found applications in various industries. However, the mechanisms involved remain unclear, and the textures corresponding to residual stress relaxation were rarely reported in the existing literature. The purpose of this study is to discuss the texture evolution and residual stress relaxation in a cold-rolled Al-Mg-Si-Cu alloy using VSR technique. All the residual stress measurements were performed using a standard X-ray diffraction (XRD) technique. Measurement of texture was performed on the specimen surface using conventional pole figure (PF) as well as orientation distribution functions (ODFs) methods. Results indicate that the VSR technique can be applied to weaken the α-fiber and cause the residual stress of the rolled samples to gradually approach uniformity in XRD analysis. The best relaxation of the compressive residual stress reaches about 52.6 pct, but relaxation of the tensile residual stress is less than 10 pct. After the VSR process for 20 minutes, the texture intensities of PFs (200) and (220) as compared to those in nonvibration are nearly homogeneously distributed. Furthermore, the texture of (111) PF perpendicular to normal direction (ND), which is affected by vibratory force parallel to ND, almost disappears.     

The Residual Stress Relaxation Behavior of Weldments During Cyclic Loading

Accurate measurement of residual stress is necessary to obtain reliable predictions of fatigue lifetime and enable estimation of time-to-facture for any given stress level. In this article, relaxation of welding residual stresses as a function of cyclic loading was documented on three common steels: AISI 1008, ASTM A572, and AISI 4142. Welded specimens were subjected to cyclic bending (R = 0.1) at different applied stresses, and the residual stress relaxation existing near the welds was measured as a function of cycles. The steels exhibited very different stress relaxation behaviors during cyclic loadings, which can be related to the differences in the microstructures of the specimens. A phenomenological model, which treats dislocation motion during cyclic loading as being analogous to creep of dislocations, is proposed for estimation of the residual stress relaxation.     

The Effect of Aging on the Relaxation of Residual Stress in Cast Aluminum

Most cast aluminum-engineered components are water quenched after the solution-treatment cycle of the casting process. This rapid water quenching has the potential to induce high residual stresses in regions of the castings. Reducing the amount of residual stress can have a promising effect on the life of the component. This study was conducted to quantify how aging affects the amount of residual stress in an aluminum casting. An engineered high residual stress test sample and quenching technique has been developed, and a relaxation study has been completed. The study focused on four different temperatures: 463 K, 493 K, 513 K, and 533 K (190 °C, 220 °C, 240 °C, and 260 °C) and a range of aging times (0.3 to 336 hours). The aging data were used to verify a stress relaxation model. The results indicated that as the aging temperature increased, the amount of relaxation of the residual stress increased.     

Numerical Analysis of Distortion due to Inhomogeneous Distribution of Martensite Start Temperature within SAE 52100 Bearing Rings

This paper reports about numerical investigations regarding the spatial distribution of martensite start temperature (M_s) within bearing rings made out of SAE 52100 (100Cr6). Out‐of‐roundness values due to inhomogeneous M_s distribution are calculated by means of FE simulations. In a first step the distribution of M_s is modelled with simple trigonometric functions with different wavelengths and amplitudes of M_s. In addition, more complex distributions of M_s are investigated by means of superposition of different trigonometric functions. Simulations with the commercial FE simulation program SYSWELD^® yield dependencies of out‐of‐roundness values of bearing rings on wavelength and amplitude of M_s. The numerical study is supplemented by experimental investigations concerning the distribution of M_s. Typical scatter‐bands of M_s within a work piece were found to be ± 10 K. Concerning this scatter‐band, different possible distributions of M_s are analysed by Fourier transformation. With the resulting trigonometric functions the out‐of‐roundness values are calculated and compared with experimental data.     

Microscopically-Determined Static Recrystallization of Copper During Holding Without Stress or with Stress Relaxation After Hot Working

Abstract

After deformation to 0.15 in the range 450–540°C and 1.8 × 10^?3 to 1.8 s^?l in compression or torsion, the recrystallization of ETP Cu determined microscopically is compared to the restoration measured mechanically during intervals of holding at the deformation temperature under both stress-free and stress-relaxation conditions. Recrystallization is initially much slower than softening, the difference being due to recovery, but finally they become equal at about 85%. TEM substructures sharpen considerably during intervals up to 100 s. Recovery and recrystallization occur more rapidly as strain rate and temperature rise in both modes of holding, but in stress relaxation the former is slowed down and as a result the latter is speeded up.     

Evaluation of Strain Hardening During Uniaxial Tensile Loading Followed by Stress Relaxation and Reloading

Metallurgical and Materials Transactions A - The estimation of strain hardening during uniaxial tensile loading followed by stress relaxation and reloading is required to quantify the strain aging...     

Relating Residual Stress and Substructural Evolution During Tensile Deformation of an Aluminum-Manganese Alloy

Interrupted tensile tests were coupled with ex situ measurements of residual stress and microtexture. The residual stress quantification involved measurements of six independent Laue spots and conversion of the interplanar spacings to the residual stress tensor. A clear orientation-dependent residual stress evolution emerged from the experiments and the numerical simulations. For the orientations undergoing negligible changes in ρ _GND (density of geometrically necessary dislocation), the residual stress developments appeared to be governed by the elastic stiffness of the grain clusters. For the others, the evolution of the residual stress and ρ _GND exhibited a clear orientation-dependent scaling.     

Kinetics of Structure Formation in the Heating of Cold-Rolled Automotive Steel Sheet

The softening kinetics associated with recovery and recrystallization is investigated, along with the kinetics of phase transformation (austenitization) on heating cold-rolled autompotive steel sheet. The kinetics of softening in isothermal holding is studied using the Gleeble 3800 system for 12 steels, and the phase transformation in continuous heating at constantrate is studied for 6 steels of different strength class, with different chemical composition. Considerable slowing of the steel’s recovery and recrystallization is observed with increase in the Mn and Ti content in the ferrite solid solution. The grain size of the recrystallized ferrite hardly depends on the annealing temperature. The results may be used in developing a quantitative integral model to describe the complex microstructural evolution of cold-rolled steel sheet on annealing in industrial production.     

残余应力的危害及对策

文中阐述了残余应力在材料或设备使用过程中的不良影响,并详细介绍了目前消除残余应力的若干方法.希望能够对今后提高产品内部质量、提高构件的疲劳寿命及减少安全隐患方面提供一些有效对策.     

Influence of Heating Rate on Ferrite Recrystallization and Austenite Formation in Cold-Rolled Microalloyed Dual-Phase Steels

Compared with other dual-phase (DP) steels, initial microstructures of cold-rolled martensite-ferrite have scarcely been investigated, even though they represent a promising industrial alternative to conventional ferrite-pearlite cold-rolled microstructures. In this study, the influence of the heating rate (over the range of 1 to 10 K/s) on the development of microstructures in a microalloyed DP steel is investigated; this includes the tempering of martensite, precipitation of microalloying elements, recrystallization, and austenite formation. This study points out the influence of the degree of ferrite recrystallization prior to the austenite formation, as well as the importance of the cementite distribution. A low heating rate giving a high degree of recrystallization, leads to the formation of coarse austenite grains that are homogenously distributed in the ferrite matrix. However, a high heating rate leading to a low recrystallization degree, results in a banded-like structure with small austenite grains surrounded by large ferrite grains. A combined approach, involving relevant multiscale microstructural characterization and modeling to rationalize the effect of the coupled processes, highlights the role of the cold-worked initial microstructure, here a martensite-ferrite mixture: recrystallization and austenite formation commence in the former martensite islands before extending in the rest of the material.     

Phase Transformation Kinetics During Annealing of Cold-Rolled AISI 309Si Stainless Steel

Metallurgical and Materials Transactions A - The effects of cold rolling and the subsequent annealing were studied for the AISI 309Si stainless steel. During annealing of cold-rolled sheets, the...     

Microstructural Evolutions During Reversion Annealing of Cold-Rolled AISI 316 Austenitic Stainless Steel

Metallurgical and Materials Transactions A - Microstructural evolutions during reversion annealing of a plastically deformed AISI 316 stainless steel were investigated and three distinct stages...     

Modeling of the Recrystallization and Austenite Formation Overlapping in Cold-Rolled Dual-Phase Steels During Intercritical Treatments

Austenite formation kinetics of a DP1000 steel was investigated from a ferrite–pearlite microstructure (either fully recrystallized or cold-rolled) during typical industrial annealing cycles by means of dilatometry and optical microscopy after interrupted heat treatments. A marked acceleration of the kinetics was found when deformed ferrite grains were present in the microstructure just before austenite formation. After having described the austenite formation kinetics without recrystallization and the recrystallization kinetics of the steel without austenite formation by simple JMAK laws, a mixture law was used to analyze the kinetics of the cold-rolled steel for which austenite formation and recrystallization may occur simultaneously. In the case where the interaction between these two phenomena is strong, three main points were highlighted: (i) the heating rate greatly influences the austenite formation kinetics, as it affects the degree of recrystallization at the austenite start temperature; (ii) recrystallization inhibition above a critical austenite fraction accelerates the austenite formation kinetics; (iii) the austenite fractions obtained after a 1 hour holding deviate from the local equilibrium fractions given by Thermo-Calc, contrary to the case of the recrystallized steel. This latter result could be due to the fact that the dislocations of the deformed ferrite matrix could promote the diffusion of the alloying elements of the steel and accelerate austenite formation.     

绕线式电动机集电环发热的原因和对策

详细分析了冶金工厂中常用的绕线式交流电动机集电环发热的各种原因，提出了相应的处理方法及预防措施。     

结晶器水泵轴承发热故障分析与处理

分析了涟钢棒材厂炼钢线结晶器水泵轴承发热故障原因,并进行了相关处理,确保了水泵的正常运行.     

Effect of Annealing Time on Microstructure and Mechanical Properties of Cold-Rolled Niobium and Titanium Bearing Micro-alloyed Steel Strips

Effects of annealing time on microstructure of cold-rolled niobium-titanium bearing micro-alloyed steel strips were investigated by optical microscopy, scanning electron microscopy, electron back-scatter diffraction (EBSD) and transmission electron microscopy. The complete recrystallization annealing temperature of 670 °C and complete annealing time of 9 min were determined using Vickers-hardness testing and EBSD analysis. The ferrite microstructure with spheric cementite particles and nano-scale precipitates of Nb(C, N) in matrix was obtained. The kinetics of the ferrite grain growth is lowered due to ferrite grain boundaries pinned by the cementite particles, so the ferrite grain size of 5. 5 μm remains unchanged among the annealing time ranging from 9 to 30 min. In addition, the strength of tested steel also keeps unchanged with the increase of annealing time. The higher yield strength of approximately 420 MPa can be obtained by grain refinement and precipitation hardening and the higher elongation of approximately 40% and work-hardening exponent of approximately 0. 2 can be gained due to grain refinement and presence of cementite particles, indicating that the balance of strength, ductility and forming property is realized.     

Thermal Relaxation of Residual Stresses in Nickel-Based Superalloy Inertia Friction Welds

This article describes an experimental study aimed at characterizing the extent of residual stress relaxation during thermal treatment of inertia friction-welded alloy 720Li nickel-based superalloy welded tubular rings. In the as-welded condition, yield level tensile hoop stresses were found by neutron diffraction in the weld region along with axial bending stresses (tensile toward the inner diameter (ID)/compressive toward the outer). The evolution of these residual stress levels during postweld heat treatment (PWHT) was mapped experimentally over the weld cross section. After 8 hours of PWHT, the axial stresses relaxed by 70 pct, whereas the hoop stresses reduced by only 50 pct. Some scatter of residual stress evolution was found between samples, particularly for the axial stress direction. This was attributed to substandard tooling to grip the rings. The results on subscale samples were transferred to a full-scale aeroengine (650-mm diameter) compressor drum assembly that was postweld heat treated for 8 hours. It was found that the residual stresses, particularly in the axial direction, were noticeably lower in this full-scale weld component compared to the subscale weld heat treated for the same time. The differences seem to be best rationalized by the different standards of jigging used during joining these two types of welds.