Mechanical Properties Of Steel Research Articles

Structural changes of multiphase low-carbon steel in deformation and heat treatment

The influence of the rolling parameters on the structural and phase transformations and mechanical properties of steel is analyzed. At a particular combination of temperature, strain, and strain rate, fine-grain austenite structure may be obtained, with highly developed polygonal substructure. For low-carbon steel, the best combination of cooling and winding parameters after rolling is as follows: tfr = 800–850°C; tin.co = 750°C; vco = 80°C/s; twi = 500°C.

Cleanness and Mechanical Properties of Steel after Remelting under Different Slags by ESR

Quality of machine production is very close-knit with quality of metallurgical semi-products and with improvement their working properties. It can be achieved first of all by decrease of sulphur and non-metallic inclusions content in metal. Improvement of working properties provide remelted processes above an electro slag remelting (ESR). The slags play very important role by ESR process. By experiments steel with next chemical composition was used: C (0,9 – 1,1%), Mn (0,30 – 0,50%), Si (0,15 – 0,35%), Cr (1,30 – 1,65%), Ni (max.0,30%), Cu (max.0,25%), P (max.0,027%), S (max.0,030%). The steel was remelted under 8 types of slags on the base of CaO, Al2O3, CaF2 and SiO2 in different ratios. The contribution deals with influence of chemical composition of slag on mechanical properties and cleannes of metal after electro slag remelting. Variation of slag chemical composition enables to change chemical composition of remelted steel, to reduce the non-metallic inclusions and sulphur content and to improve the mechanical properties of steel.

Analysis of Mechanical Properties of Individual Phases in Steels by Depth Sensing Indentation

The macroscopic mechanical properties of steel are highly dependent upon microstructure, morphology, and distribution of each phase present. Nanomechanical testing (Depth sensing indentation) provides a straightforward solution for quantitatively characterizing each of these phases because it is very powerful technique for characterization of materials in small volumes. Measuring the intrinsic properties of each phase separately in multiphase materials gives information that is valuable for the development of new materials and for modelling [1]. In this work, depth sensing indentation has been used to reveal mechanical properties of different phases in steel sheets.

MICROSTRUCTURE MODELING AND PREDICTION OF THE MECHANICAL PROPERTIES OF ADVANCED HIGH STRENGTH STEELS

Dual phase (DP) steels were modeled using 2D and 3D representative volume elements (RVE). Both the 2D and 3D models were generated using the Monte-Carlo-Potts method to represent the realistic microstructural details. In the 2D model, a balance between computational efficiency and required accuracy in truly representing heterogeneous microstructure was achieved. In the 3D model, a stochastic template was used to generate a model with high spatial fidelity. The 2D model proved to be efficient for characterization of the mechanical properties of a DP steel where the effect of phase distribution, morphology and strain partitioning was studied. In contrast, the current 3D modeling technique was inefficient and impractical due to significant time cost. It is shown that the newly proposed 2D model generation technique is versatile and sufficiently accurate to capture mechanical properties of steels with heterogeneous microstructure.

Effect of Heat Treatment on Mechanical Properties of Steels of Strength Class K65 (X80)

The evolution of mechanical properties of two steels of strength class K65 (X80) is studied under heating in the intercritical temperature range and from 150°C to the lower boundary of the intercritical range.

Hot Rolled Coil Property Heterogeneities due to Coil Cooling: Impact and Prediction

The importance of coil cooling conditions on mechanical properties uniformity of HSLA and AHSS steel grades is discussed. It is namely shown that hot rolled coil under conventional industrial production can be cooled non-uniformly. That is why to predict correctly the final steel microstructure and mechanical properties of hot-rolled products an accurate description of not only run-out table condition but also of coil cooling should be done. Two solutions to provide accurate description of coil cooling were tested. First one is to use 2D finite element (FE) thermal model. When coupled with the ArcelorMittal metallurgical model to predict hot-rolled microstructure and properties (TACSI) it matches well the industrial data within +/-15-20MPa both for the tensile and yield strength. However, this approach is recognized to be heavy and time consuming. A second solution, a new 2D coil cooling simplified model incorporated in TACSI model, proved to be quite efficient, as it leads to performances similar to the more detailed first solution. Moreover, it is able to compute the coupling between the thermal evolution of the hot band and the kinetics of phase transformation during coil coiling and cooling, and will enable a better evaluation of the final mechanical properties especially for the grades for which the phase transformation is not completed before hot band coiling.

Influence of deep cryogenic treatment on the thermal decomposition of Fe–C martensite

The beneficial effects of deep cryogenic treatment (DCT) at temperatures close to −180 °C on certain mechanical properties of steels are well known, although the metallurgical base mechanism of DCT still needs further clarification. In this study, the thermal decomposition of steel martensite (100Cr6) subjected to low-temperature soaking over different periods (SDCT = 5 min at −180 °C, LDCT = 24 h at −180 °C) is investigated by means of differential scanning calorimetry and dilatometry. The results were compared with those for the same conventionally quenched and tempered steel. Isochronal annealing experiments at different heating rates were performed, in order to highlight the main tempering stages and to obtain their relevant activation energies. DCT was clearly shown to lower the Ea of the pre-precipitation process more intensely than in the quenched steel. This result may probably be ascribed to an increased dislocation density and to the activation of the carbon segregation process in larger amounts of martensite. The precipitation of transition carbides was also enhanced by the low-temperature conditioning of martensite. As expected, DCT transformed the retained austenite, so that the corresponding peaks almost disappeared from both the dilatometric and the DSC patterns.

Influence of Aging Time on the Tensile Strenght of a Duplex Stainless Steel

This article was aimed at studying the influence of different aging times during the precipitation phase of the UNS S31803 (SAF 2205) duplex steel. To do so, all the test specimens were solution heat treated at 1050oC for 1 hour and quenched in water. After this step, the samples were aged at 850°C for periods of 10, 60 and 600 minutes and cooled in water. The aging heat treatments (TT) were performed in order to precipitate the sigma phase. Samples were subjected to microhardness and tensile tests so that the influence of the microstructural changes over the mechanical properties of the steel was assessed. Based on the microhardness and tensile test data, it was possible to verify a significant change over the mechanical properties of the UNS S31803 steel.

Microstructural Characterization and Evaluation of Mechanical Properties of Steel with Different Biphasic Microstructures Obtained from LNE 500 Steel

In this work was carried out the microstructural characterization and evaluation of mechanical properties of steel with different microstructures. The intercritical region and the existing phases in function of temperature were determined using the THERMOCALC software. The samples of steel were quenched at different temperatures to obtain differents microstructures consisting of ferrite, pearlite and martensite. The microstructural characterization of the samples was performed by qualitative and quantitative metallography. The determination of volume was performed with the "Image J" software. The mechanical properties were determined by uniaxial stress test, which determined the parameters: yield strength, tensile strength, breaking point and total elongation.

Multiscale Modelling of Mechanical Properties of Steel Deformed in Semi-Solid State – Experimental Background

The paper reports the results of experimental and theoretical work leading to the construction of a multiscale mathematical model describing the phenomena accompanying the steel deformation in semi-solid state as well as at extra-high temperatures. Conducted experiments and simulations confirms the need to seek new methods to obtain precise characteristics in the context of detailed computer simulations. The investigations presented in the current paper has shown, that temperature distribution inside the controlled semi-solid volume is strongly heterogeneous and non-uniform. Axial-symmetrical model (core of the old methodology) does not take into account all the physical phenomena accompanying the deformation. Finally, the error of the predicted strain-stress curves can still be improved. The proposed solution of the presented problem is application of both fully three-dimensional solution and more adequate solidification model taking into consideration evolution of forming steel microstructure. Contrary to the current model the new approach should allow to better capture the physical principles of semi-solid steel deformation in micro-scale. Additionally, the new complex methodology should allow to transfer the characteristics of the material behaviour between the micro-and macro-scale. As a consequence the final results should be more precise and accurate.

Online Detection and Control of Strip Steel Mechanical Properties in Skin-Pass Process

Firstly, the online detecting and controlling models of the strip steel mechanical properties in skin-pass process are proposed in this paper. The models are used to overcome the shortage of the conventional monitoring methods, and to reduce the fluctuations of the mechanical properties of the strip. The new online detecting and controlling models can real-time forecast the mechanical properties of the running strip from the online monitoring devices. The bias control between the forecasting and the target values of the mechanical properties can be corrected by adjusting the strip elongation . As a result , the fluctuations of the mechanical properties of the strip are reduced ,and move over,it is helpful to prevent the higher yield strength and lower tensile strength, and to maintain good formability strip.The experiments are done and verify the validity of the approach.

Effect of temperature and strain on the formation of elongated fine grained structure in middle carbon steel during large plastic deformation

The influence of deformation temperature and strain rate on the mechanisms of elongated fine grain (EFG) formation in the medium-carbon steel was studied. Compression tests were carried out at the temperatures in range of 673-973K at three different strain rates: 10−2, 1.3*10−3 and 10−4 s−1. Presence of two temperature intervals with different dominant mechanisms of deformation was identified: low temperature (673-823K) interval and high temperature (873-973K) interval. Microstructure evolution during deformation at strain rate of 1.3*10−3 s−1 and different temperatures was studied. Also was investigated the microstructure and mechanical properties of steel after warm plastic deformation. EFG structure formation in steel by caliber rolling at temperatures 673 and 773K on strain ε ~ 1.1 results in a significant increase of toughness, including at low temperatures, while improving strength.

Experimental Study on Mechanical Properties of Steel and Polypropylene Fiber-Reinforced Concrete

The mechanical tests of normal concrete (NC) specimens, steel fiber reinforced concrete (SFRC) specimens and polypropylene fiber reinforced concrete (PPFRC) specimens have been carried out. Fiber-reinforced concretes containing different volume fraction and aspect ratio of steel and polypropylene fibers were compared in terms of compressive, splitting tensile, ultimate tensile properties. Test results indicate that the mechanical properties of NC can be improved by addition of steel fibers and can be enhanced with the increase of fiber content. However, polypropylene fiber may cause opposite effect, if volume fraction too high.

Effect of Cold Rolling and Isothermal Holding before Austenitization on Mechanical Properties in Steels

Effect of pre-treatments before austenitization on mechanical properties in steels has been investigated. Pre-treatments are cold rolling and isothermal holding below A1 before austenitization. Pre-treatments were performed in order to introduce dislocation network in austenite (γ), which acts as nucleation site for “bainite laths within γ grain (BWING)”. During the pre-treatment of isothermal holding below A1, carbon segregation and/or carbide formation might occur at grain boundary of ferrite (α). Thin γ layer might be formed around the region where carbon segregation and/or carbide formation occurred in the beginning of austenitization. Transformation strain due to α → γ would be effectively relaxed by the deformation of thin γ film, because α had been already hardened by the cold rolling. Dislocations might be introduced dominantly into the thin γ film, and stable dislocation network even in the high temperature region of γ might be formed. BWING nucleates around the dislocation network to relax the strain field around dislocation network. BWING would nucleate also at ( BWING / γ ) interface cooperatively to relax the strain around the interface, resulting in the formation of “aggregate of bainite laths with nearly parallel slip systems between neighboring bainite laths (ALPS)”. Larger ALPS containing a lot of BWINGs might be formed in the pre-treated steel, and improves tensile strength and toughness.

Effects of ALPS on Mechanical Property in Bainitic Steels

Aggregate of bainite laths with almost parallel slip systems between neighboring bainite laths, hereafter referred to as ALPS, has great effect on the improvement of mechanical properties in steels. Elongation increases remarkably with increasing the number of bainite laths within an ALPS. When a bainite lath begins to deform, the neighboring bainite lath also easily deforms to relax the deformation strain, because of good parallelism between their slip systems. Under the cooperative deformation of bainite laths, the area of interface between neighboring bainite laths increases during deformation. The increase in the area of interface between neighboring bainite laths suppresses localization of dislocations at the interface, that is, dislocation density per unit area of the interface between neighboring bainite laths hardly increases, resulting in the suppression of nucleation of cracks at the interface between neighboring bainite laths. Ductile fracture would occur along the boundary between ALPSs. It could be suggested that larger ALPS and/or ALPS consisting of large number of bainite laths induce larger elongation in steels.On the other hand, it has been reported that tensile strength increases in proportion to inverse of square root of d, the d being the average size of bainite laths [1]. In order to form fine bainite lath, dislocation network instead of inclusion in austenite was utilized as nucleation site for bainite lath. Great barriers to be overcome exist for the improvement of both strength and toughness. An idea for the improvement of both strength and toughness is shown in this study.

Investigations of Nucleate Boiling Processes During Quenching Based on Possibilities of Noise Control System

A new method for evaluating and control of the optimal concentration of water salt solutions is proposed which is based on the possibilities of sound control system. Water salt solutions as quenchants are used in the practice to intensify hardening processes. In this paper, it is shown that water salt solutions are used for low and medium carbon alloy steels to create high compressive residual stresses at the surface of steel parts and improve mechanical properties of steels. It is underlined that quenching in water salt solutions must be interrupted at the appropriate time to prevent crack formation during fast cooling. When interruption occurs at the surface of steel parts, compressive residual stresses are formed and self-tempering takes place. During this time, at the core, a bainitic structure is formed which has enough strength and high plastic properties to prevent crack formation at the core where tensile stresses could be. It is shown that salt solutions can be also used for quenching of big steel parts like rollers and rotors. The benefits from the technology proposed are discussed in this paper. In the future, organic salt solutions can be replaced by organic salt solutions which prevent corrosion completely.

The Effect of Si on the Intermetallics Formation during Hot Dip Aluminizing

When applying an aluminium coating on a steel substrate, the corrosion resistance of aluminium is combined with the mechanical properties of steel. There are different ways to coat steel among which hot dipping is the most applied because it is technically feasible in large volumes and economically the most beneficial one. Although aluminized steel accounts for about 5% of the total world production of all hot dip coated steels, the interactions between the molten aluminium and steel substrate are not yet completely understood. During hot dipping, several intermetallic layers are formed between the outer nearly pure aluminium layer and the steel substrate. These layers mostly comprise of a thin FeAl3 and a thicker Fe2Al5 layer. The thickness of these intermetallic layers must be kept minimal since they embrittle the coating. Thickness reduction of the intermetallics is mainly realized by silicon addition to the aluminium bath. In this work, the formation of intermetallic layers was investigated for a deep drawing steel grade which was hot dipped in aluminium baths with six different Si contents ranging from 1 to 10 wt%Si. The Si-addition was demonstrated to lead to a decrease in the thickness of the intermetallic layers and a flattening of the intermetallic-steel interface. An increase in Si also led to the formation of other intermetallic compounds, which are investigated by a systematic analysis by scanning electron microscopy (SEM), Energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD) on multiple samples and discussed in terms of the Si-effect on a possible formation mechanism for the intermetallics.

Characterisation of the Shear Stud-Concrete Connection Using Finite Element Analysis

The degradation of the connection between shear studs and concrete is a complicated phenomenon that depends on many factors, including; interfacial properties, concrete crushing and steel yielding. The purpose of this paper is to outline the scope and methodology of the research project being undertaken to characterise the shear stud-concrete interface of a composite beam using finite element analysis. A mesoscopic model will be created for a section of the interface. With the use of a multi-scale approach, the mesoscopic model will be incorporated into a global model. The influence of steel roughness and mechanical properties will be included. Concrete is to be modelled as heterogeneous, comprising discrete regions of aggregate, cement matrix, and an interfacial transition zone (ITZ). The effect of the ITZ will be taken into account using a zero thickness cohesive element. Experimental testing using a push-up rig is to be conducted to verify the numerical models. The ultimate aim is to develop a simplified representation of the shear stud-concrete interface that can be used in a large scale finite element model of a composite member to correctly capture the behaviour of the shear stud-concrete interface in the elastic and inelastic state.

Martensite formation in stainless steels under transient loading

We present a 3D elastoplastic phase-field model to study the martensite formation in stainless steels under transient loading. Linear isotropic strain hardening is considered. Our results show that various combinations of martensite variants, which minimize the mechanical energy and maximize the net available driving force, are favored under different transient loading directions. The mechanical properties of steels under transient loading depend on the direction of loading. The areas where the load is applied, i.e. the grain boundaries, become favorable martensite nucleation sites.

Effects of Quenching and Partitioning Process on Mechanical Properties of a Hot-Stamping Steel

As a novel heat treatment process, Q&P (quenching and partitioning) process can be applied to enhance the ductility of steels. In this paper, the effects of different parameters of Q&P process (such as quenching temperature, partitioning temperature and partitioning time) on mechanical properties and microstructure of 22MnB5 steel was investigated. Analysis demonstrated that austenite can be stabilized via Q&P process and the volume fraction of retained austenite increases with the partitioning temperature and the partitioning time. The mechanical properties of the steel can be controlled to acquire the steel with excellent strength-ductility balance by Q&P process.