Deformation Of Steel Research Articles

Effects of Material Deformation Due to Aging of Electrical Steel on the Brushless Wound-Field Synchronous Generator

This study analyzes the material deformation of electrical steel with aging and its effects on the electromagnetic and thermal characteristics of a Brushless Wound-Field Synchronous Generator (BL-WFSG). First, in order to confirm the material deformation of electrical steel applied to the BL-WFSG, magnetic property tests are performed on the core sheets of the old and new generators. Those two generators are made of the same material, so there was no difference except for their usage time. Based on the results of the magnetic property tests, an electromagnetic field analysis is performed on the old and new generators, and analysis results are compared in order to confirm the effects of material deformation on the electromagnetic characteristics of BL-WFSG. Then, a thermal analysis is performed on the old and new generators using losses calculated by electromagnetic field analysis as heat sources, and analysis results are compared in order to confirm the effects of material deformation on the thermal characteristics of BL-WFSG. Finally, an additional electromagnetic analysis is performed on both the old and new generators, using the exact winding resistances that were calculated in the thermal analysis for each respective generator in order to calculate and compare the efficiency of the old and new generators. Through this process, the authors confirmed the effects of material deformation of the rotor and stator cores due to aging on the electromagnetic and thermal characteristics of the BL-WFSG.

In-situ TEM investigation on deformation mechanisms of a fine-grained 316L stainless steel

The present study explores the deformation behavior of fine-grained 316L stainless steel through in-situ tensile transmission electron microscopy (TEM), with a focus on both intergranular and intragranular deformation. The results demonstrate that grain boundaries are a critical factor in accommodating plastic deformation and serve as the primary dislocation sources (DS) for dislocation emission into the grain interior. The propagation of plastic deformation within grains occurs through the successive activation of grain boundary DSs. In addition, the fine-grained sample exhibits active deformation twin and cross-slip of extended dislocations due to its proper apparent stacking fault energy (SFE) of 27 mJ/m2 and high internal stress, which significantly enhances its strain hardening ability. These findings shed light on the underlying mechanisms of plastic deformation in fine-grained 316L stainless steel and have important implications for the design of metallic materials with superior mechanical properties.

Discontinuous yielding with remarkable Lüders deformation in a duplex stainless steel during tensile deformation at 77 K

Duplex stainless steels with ultrafine- or fine-grained microstructures showed pronounced discontinuous yielding and Lüders banding behavior during tensile deformation at 77 K. In particular, sample with high-stability "eye"-shaped structures and ultrafine grains exhibited a yield strength of 1750 MPa, a yield drop of 87 MPa and a Lüders strain of 0.23.

In situ observation of solidification in peritectic steels and evaluation of the strains induced in the solidifying shell

In the continuous casting of peritectic steels, unevenness and cracks of the solidifying shell are typical casting defects. This study focuses on the ferrite–austenite transformation and the influence of the transformation on the solidifying shell deformation. In situ observations revealed that the austenite hardly nucleated and, consequently, the undercooled ferrite massively transformed to the austenite in the solid state. Simultaneously, the austenite rapidly solidified in the remaining liquid. The volume changes due to the ferrite–austenite transformation and the solidification shrinkage were measured using time-resolved tomography. On the basis of the observations and measurements, a model that includes the ferrite–austenite transformation and the austenite solidification was proposed to evaluate the volumetric strains in the solidifying shell. There was a sharp peak in the volumetric strains derived from the model at hypo-peritectic compositions. This work demonstrates the need to include the ferrite–austenite transformation in the solid state and the rapid austenite solidification for understanding the solidifying shell deformation in peritectic steels.

Arrhenius constitutive model and dynamic recrystallization behavior of 18CrNiMo7-6 steel

In order to analyze the thermal deformation and dynamic recrystallization behavior of 18CrNiMo7-6 steel, the isothermal compression tests are carried out on Gleeble-3500 thermal simulator machine at deformation temperatures 973.15 K–1273.15 K with strain rates 0.001 s−1–1 s−1. Based on the true stress σ0.3, the Arrhenius constitutive models are constructed by using characterization parameters and physical base parameters, and the determination coefficients between the predicted values of the two models and the measured values are 0.98378 and 0.97613, respectively. The constitutive models of characterization parameters and physical base parameters considering strain effect are also constructed, and a comparative analysis is made. The results show that the predicted values of the characterization parameters constitutive model is closer to the measured values in the low strain region. After reaching the peak strain, the predicted values of the two constitutive models are close to the measured values, and both have high prediction accuracy. The dynamic recrystallization models are established to characterize the recrystallization behavior. The recrystallization activation energy of 18CrNiMo7-6 steel is 169.6793 kJ mol−1, the ratio of critical strain to peak strain is about 0.47074, and the ratio of critical stress to peak stress is about 0.94059. The activation energy of 50% dynamic recrystallization is 29.9844 kJ mol−1. The dynamic recrystallized grain size increases with increasing deformation temperature or decreasing strain rate, and the activation energy of grain growth is −49.9237 kJ mol−1.

A Comparative Study of Deterministic and Stochastic Models of Microstructure Evolution during Multi-Step Hot Deformation of Steels.

Modern construction materials, including steels, have to combine strength with good formability. In metallic materials, these features are obtained for heterogeneous multiphase microstructures. Design of such microstructures requires advanced numerical models. It has been shown in our earlier works that models based on stochastic internal variables meet this requirement. The focus of the present paper is on deterministic and stochastic approaches to modelling hot deformation of multiphase steels. The main aim was to survey recent advances in describing the evolution of dislocations and grain size accounting for the stochastic character of the recrystallization. To present a path leading to this objective, we reviewed several papers dedicated to the application of internal variables and statistical approaches to modelling recrystallization. Following this, the idea of the model with dislocation density and grain size being the stochastic internal variables is described. Experiments composed of hot compression of cylindrical samples are also included for better presentation of the utility of this approach. Firstly, an empirical data describing the loads as a function of time during compression and data needed to create histograms of the austenite grain size after the tests were collected. Using the measured data, identification and validation of the models were performed. To present possible applications of the model, it was used to produce a simulation imitating industrial hot-forming processes. Finally, calculations of the dislocation density and the grain size distribution were utilized as inputs in simulations of phase transformations during cooling. Distributions of the ferrite volume fraction and the ferrite grain size after cooling recapitulate the paper. This should give readers good overview on the application of collected equations in practice.

Reductions in the Laser Welding Deformation of STS304 Cylindrical Structure Using the Pre-Stress Method

Welding deformation occurs due to non-uniform thermal expansion, thermal contraction, restraint, and phase transformation in a metal by a local welding heat source. This causes problems such as low buckling strength and the reduced workability of the production process. Correcting welding deformations in stainless steel using heat—such as by linear heating—causes metal sensitization, which should be avoided. Herein, welding deformation was reduced by applying tension stress instead of correcting the deformation by heating. A deformation-prevention jig was used to reduce welding deformation during the manufacturing of a cylinder made of STS304 by laser welding. The tensile stress was induced by pushing the cylinder shell outward using the deformation-prevention jig. A thermo-elastoplastic analysis was performed to investigate the effects of the magnitude of the tensile stress on welding deformation. Furthermore, the parametric results—which indicated a reduction in welding deformation—were verified through experiments. The thermo-elastoplastic analysis suggested that deformation did not occur when the magnitude of tensile stress was approximately 50% of the yield stress of the base metal. Moreover, the deformation was experimentally reduced by 11–20% when a tensile stress of 30 MPa was applied to the cylinder, compared with that in the absence of tensile stress.

Evaluation of Sample Preparation Importance for Digital Image Correlation during Cold Deformation

In this paper, tests were performed by monitoring changes of strain amounts and their distribution by digital image correlation during static tensile testing of steel. The influence of different combination of speckles application on the sample surface (white speckles on the black sample surface and black speckles on the white sample surface) during cold deformation of steel was tested with the non-contacting digital image correlation. Strain amounts obtained by digital image correlation analysis of tested samples, with white on black and black on white painted speckle patterns, were compared. Different analysis for determining and monitoring strain amounts, provided by digital image correlation software, were used in this paper. The strain amounts were compared during cold deformation until the occurrence of sample fracture in both combinations of speckles application on the sample surface. Research has shown the importance of proper sample preparation for determination strain amounts and insignificant minor differences of strain amounts, between different sample preparations for digital image correlation, during cold deformation of tested steel.

Monitoring the evolution of resistance-welded WC-10Co/B318 steel joint based on welding time

In this study, the authors investigate the resistance welding of WC-10Co pellets and B318 steel for use in the blade of a bimetallic band saw. We used the welding time as the basis to identify the mechanism of evolution of the welded joint by analyzing the welding process as well as the dynamic resistance, depth of penetration, distributions of the temperature and stress fields, macromorphology, microstructural transformation, and mechanical properties of the joint. The results showed that the deformation of the joint and the distribution of the temperature field obtained by numerical simulations were consistent with those captured by a high-speed camera, where this verifies the reliability of the model used for the simulation. The deformation in B318 steel was much greater than that in WC-10Co. The process of evolution of the joint was as follows: The resistance-induced heat that was generated melted a small amount of the Ni layer and the B318 steel at the center of their interface. A transition layer was then formed among WC-10Co, the Ni layer, and the B318 steel. Following this, the transition layer at the center was melted and extruded, where the WC-10Co and B318 steel came into direct contact and a metallurgical reaction occurred between them, while the edges of B318 steel and WC-10Co began to contact. The reactants at the center of the interface were then extruded and metallurgical bonding slowly began along the edges. Finally, the Ni layer disappeared, the steel groove was fully combined with WC-10Co, and some of the reactants that had not been discharged in time solidified at the interface to form a reaction layer.

Evolution of the Lamellar Pearlite Structure of Rail Steel under Tension

In this paper, the properties of rail steel subjected to fracture under uniaxial tension deformation are studied. Mechanical properties of rail steel, defective substructure of lamellar pearlite, and fracture surface of rail steel are investigated using methods of modern physical materials science.
 Tensile strength is found to vary from 1247 to 1335 MPa, and the fracture strain of the samples changes from 0.22 to 0.26. The deformation of the rail steel is accompanied by the process of breaking the ferrite plates into fragments by low angle boundaries along with the significant increase in the scalar dislocation density to 7.9-1010 cm-2 (the scalar dislocation density of the original rail steel is 3.2 -1010 cm-2). Also, there is a formation of internal stress fields appearing in the form of bend extinction contours. The sources of stress fields are identified. It is revealed that cementite plates are fractured by cutting and dissolution with subsequent transfer of carbon to ferrite plates by moving dislocations and formation of round-shaped nanodimensional (8.3 nm) round shaped particles of tertiary cementite. It is shown that the dissolution of cementite plates is accompanied by fragmentation (into coherent scattering regions with an average size of 9.3 nm).

In situ observation of deformation and failure behavior in the burn-through instability zone of in-service welding

Based on the in-situ high-temperature SEM and laser scanning confocal microscope (LSCM), the high-temperature plastic deformation and failure behavior of X65 pipeline steel at 1000℃ and 1200℃ were studied in this paper, and the strain evolution behavior in this process was analyzed by DIC technology. In this study, the precipitation and dissolution of carbide at the austenite grain boundary were observed during the in situ heating process. The external load showed a great effect on the growth of the grains, and the grains grew rapidly by swallowing each other. The grain size, material performance, and misorientation played an important role during the deformation and crack evolution. At high temperatures, cracks were mainly initiated and propagated in the position with a large plastic strain. The strain concentration showed a significant effect on crack initiation.

Thermal softening behavior up to fracture initiation during high-rate deformation

This work proposes an innovative method to analyze the softening behavior due to adiabatic heat up to the fracture onset during high-rate deformation of AISI4340 steel at room temperature. To derive the rate- and temperature-dependent constitutive equation considering the post-necking behavior, uniaxial (UT) and notched tension (NT) specimens were tested at three strain rates of 10-3/s, 100/s and 103/s. The full fields of strain and temperature were measured until fracture initiation with high-speed digital and thermal imaging cameras, respectively. In particular, this research focused on observing the abrupt localized temperature increase in the post-necking phase, which was achieved through the use of a newly configured split Hopkinson tension bar (SHTB) system. It enabled an experimental investigation of the effect of adiabatic heat on localized behavior up to fracture at high strain rates (103/s). As the strain rate increased, the strain-localization occurred more quickly, and a higher temperature was experimentally observed at the location where fracture initiated. The experimentally measured thermal field was newly utilized for inverse optimization, to determine the thermal softening effect of the constitutive model considering adiabatic heat up to the onset of fracture including post-necking. Finally, a hybrid experimental-numerical approach was used to investigate the physical quantities of local strain, strain rate, temperature inside the specimen where fracture actually began.

Transformation of fine structure of lamellar pearlite under deformation of rail steel

The defective substructure of polycrystalline bodies causes substructural hardening and mechanical properties. Perlite, which is the main structural component of rails, undergoes a significant transformation during deformation, which is accompanied by a number of processes. In this paper, the methods of modern physical materials science were used to study and analyze the defective substructure of perlite of lamellar morphology and the properties of rail steel subjected to destruction under deformation conditions by single-axis stretching of flat samples. It was established that the ultimate strength varies from 1247 to 1335 MPa, and the relative deformation to failure – from 0.69 to 0.75. The formation of three zones of the fracture surface was observed: fibrous, radial and shear zones. Their shape and sizes were analyzed. Deformation of rail steel is accompanied by destruction of cementite plates of perlite colonies and repeated release of nanoscale particles of tertiary cementite approximately 8.3 nm in size in the volume of ferrite plates. The main mechanisms of destruction of cementite plates are cutting and dissolution. The dislocation substructure is represented by a chaotic distribution of dislocations and their clusters. The scalar density of dislocations in ferrite increases from 3.2·1010 cm–2 in the initial state to 7.9·1010 cm–2 when it is destroyed. Deformation is accompanied by formation of internal stress fields, manifested in the form of bending extinction contours. The sources of stress fields are the interface of cementite and ferrite plates, as well as grain boundaries. Fragmentation of ferrite and cementite plates was revealed. The average size of cementite fragments is 9.3 nm. In fracture zone of the rail steel sample, rotation of perlite grains was noted, indicating the presence of a rotational mode of deformation. Electron microscopic images of cementite plates show a change in the contrast, which may be associated with the formation of Cottrell’s atmospheres.

Partitioning of C and Mn During Intercritical Annealing and Transformation of Retained Austenite During Deformation in Medium Mn Steel

Herein, high‐strength medium Mn steel is obtained by intercritical annealing and quenching processes. Experimental steel with a chemical composition of Fe–0.2C–8.0Mn–1.6Si–1.3Al (wt%) is treated. The microstructures of the obtained samples comprise ferrite/martensite and retained austenite (RA) phases. The partitioning behavior of carbon and manganese during the intercritical annealing process is simulated using DICTRA. The sample annealed at 700 °C for 10 min has the best mechanical properties, with a product of strength and elongation as high as 47.25 GPa%. The deformation response of the RA is studied. The γ→α′ transformation mainly occurs in the early stage of deformation, whereas the γ→ε→α′ transformation mainly occurs in the later stage of deformation. The stress is mainly distributed at the deformed martensite and RA, and most of the stress is concentrated at the low‐angle grain boundary. During the deformation process, both the Kurdjumov–Sachs interface and the Nishiyama–Wasserman interface between the RA and deformed martensite decrease, but the Kurdjumov–Sachs interface decreases more obviously.

The microstructure and mechanical properties of 316L austenitic stainless steel prepared by forge and laser melting deposition

In this study, the 316L austenitic stainless steel blocks were prepared by forge and laser melting deposition (LMD). To clarify the effect of deposition strategy on microstructure and mechanical properties of 316L samples, three different deposition strategies (30°, 67° and 90°) are selected. The results showed that the molten pool of LMDed sample consists of a large number of coarse columnar grains and a few irregular equiaxed grains, which contains plentiful cellular and fiber sub-structures with an average size of ∼4 μm. The LMD process can significantly improve the comprehensive mechanical properties perpendicular to the build direction of 316L austenitic stainless steel, which was mainly attributed to sub-structural strengthening, but also slightly due to the local misorientation and texture distribution. The yield strength and ultimate tensile strength of R90 sample increased to 484.0 MPa and 627.6 MPa from 305.3 MPa to 601.4 MPa of as-forged 316L, and its elongation has a negligible reduction. The sub-structures produced during solidification have the same fine grain strengthening effect as the high-angle grain boundary, and the yield strength and average size of sub-structures conform to the Hall-Petch relationship. The deterioration of the plastic deformation capacity of the R67 sample is attributed to the larger thermal stress and texture distribution with a certain hard orientation. The plastic deformation of as-forged sample is mainly coordinated by multi-system slip, while twinning and slip are activated together during deformation of LMDed 316L austenitic stainless steel. The grain boundary map indicated that the strain location preferentially appears along cell wall of sub-structures, which promotes the formation of sub-grain boundaries during deformation of LMDed samples.

Deformation and phase transformation mechanisms of 40Cr10Si2Mo steel during hot compression

Deformation and phase transformation mechanisms of 40Cr10Si2Mo steel during hot compression

Anisotropic Hardening of TRIP780 Steel Sheet: Experiments and Analytical Modeling

By combining experimental and theoretical models, this research investigates the anisotropic hardening behaviors of TRIP780 steel. The specimens of TRIP780 steel were subjected to uniaxial tensile and bulging tests under different loading conditions to obtain hardening data. The experimental results show that the strength and plastic deformation of TRIP780 steel vary with the loading directions, which indicates that TRIP780 steel has anisotropy characteristics. In this paper, the dichotomous method is used to ensure the convexity of the Chen-coupled quadratic and non-quadratic (CQN) function. Comparing the predictions of the hardening behavior of the TRIP780 steel sheet by the Yld2000-2d, Stoughton-Yoon'2009 and Chen-CQN functions, the results show that the Chen-CQN function exhibits the advantages of simple numerical implementation and a more realistic prediction of yield stress compared to the former two, respectively. Comparing the prediction of Chen-CQN function with the experimental hardening data, the results show that the deviation between the experimental data and the experimental response given by the function is always within 3%, and this function maintains an accurate prediction under different stress states, indicating that the Chen-CQN yield function has accuracy and flexibility for the characterization of the yield surface of TRIP780 steel.

Evaluation of Deformation and Fracture Behavior in 304L Austenitic Steel Harmonic Structures through Nanoindentation

In article number 2200354, Ohmura and co-workers studied mechanical properties, including the deformation and fracture behaviors of SUS304L steel with harmonic structures using nanoindentation techniques. They perform nanoindentation on small specimens up to a few micrometers thick, making nanoindentation the most versatile technique for the small-scale characterization of various materials. An excellent 3D mapping of the profile can be derived for mechanical properties.

Experimental study on the shear performance of quasi-NPR steel bolted rock joints

Quasi-NPR (negative Poisson’s ratio) steel is a new type of super bolt material with high strength, high ductility, and a micro-negative Poisson’s effect. This material overcomes the contrasting characteristics of the high strength and high ductility of steel and it has significant energy-absorbing characteristics, which is of high value in deep rock and soil support engineering. However, research on the shear resistance of quasi-NPR steel has not been carried out. To study the shear performance of quasi-NPR steel bolted rock joints, indoor shear tests of bolted rock joints under different normal stress conditions were carried out. Q235 steel and #45 steel, two representative ordinary bolt steels, were set up as a control group for comparative tests to compare and analyze the shear strength, deformation and instability mode, shear energy absorption characteristics, and bolting contribution of different types of bolts. The results show that the jointed rock masses without bolt reinforcement undergo brittle failure under shear load, while the bolted jointed rock masses show obvious ductile failure characteristics. The shear deformation capacity of quasi-NPR steel is more than 3.5 times that of Q235 steel and #45 steel. No fracture occurs in the quasi-NPR steel during large shear deformation and it can provide stable shear resistance. However, the other two types of control bolts become fractured under the same conditions. Quasi-NPR steel has significant energy-absorbing characteristics under shear load and has obvious advantages in terms of absorbing the energy released by shear deformation of jointed rock masses as compared with ordinary steel. In particular, the shear force plays a major role in resisting the shear deformation of Q235 steel and #45 steel, therefore, fracture failure occurs under small bolt deformation. However, the axial force of quasi-NPR steel can be fully exerted when resisting joint shear deformation; the steel itself does not break when large shear deformation occurs, and the supporting effect of the jointed rock mass is effectively guaranteed.

Complex Network Methods for Plastic Deformation Dynamics in Metals

Plastic deformation of DC04 steel is regarded as a nonlinear, complex, irreversible, and self-organized process. The stress–strain time series analysis provided the possibility to identify areas of (quasi-)elastic deformation, plastic deformation, and necking. The latter two regions are the most informative. The area of inelastic deformation is reflected by collective, self-organized processes that lead to the formation of pores, and finally, the development of microcracks and a general crack as the cause of sample failure. Network measures for the quantitative assessment of the structural deformations in metals are proposed. Both spectral and topological measures of network complexity were found to be especially informative. According to our results, they can be used not only to classify the stages of plastic deformation, but also, they can be applied as a precursor of the material destruction process.