Mechanical Properties Of Structural Steels Research Articles

Effect of Severe Plastic Deformation on Microstructural and Mechanical Properties of Structural Steel IS2062

The microstructural and mechanical properties of structural steel (Hypoeutectoid steel) processed by equal channel angular pressing (ECAP), up to four passes, at room temperature with rounded 1200 channel angle ECAP pressing die was studied. The grain refinement and grain size distribution were analyzed using electron backscatter diffraction. Mechanical properties such as microhardness, yield strength, ultimate tensile strength, and strain hardening exponent were experimentally determined and correlated with the microstructure. With the increased number of ECAP passes, an improvement in strength was observed and ductility decreased due to work hardening. The change in morphology, such as grain refinement and increased high angle disorientation boundaries with dislocation density contribute to strengthening. TEM analysis confirmed the dislocation structure in deformed samples.

Optimal Mechanical Properties of Structural Steel for the Prevention of Embrittlement

With a view to ensuring structural stability of steels and alloys, a system for harmonizing the plasticity, strength, and deformation resistance of structural steels is developed. Principles for the formation of such properties are outlined. Means of controlling the change in these properties are considered. The sensitivity of some characteristics of the metal to changes in others is discussed. The reserves of strength in various structural steels are compared in terms of their ability to resist brittle failure, on the basis of the mechanical stability Kms and the embrittlement expressed as the deformational strength (fracture resistance) Br. The quality of structural steels is assessed in terms of their ability to resist embrittlement. The proposed approach here is to assess the quality of structural steels in terms of their deformational strength at specified yield point σ0.2, which reflects the resistance to embrittlement.

ФИЗИКО-ХИМИЧЕСКИЕ МОДЕЛИ ДЛЯ ЭКСПЕРТНОЙ ОЦЕНКИ МЕХАНИЧЕСКИХ СВОЙСТВ КОНСТРУКЦИОННЫХ СТАЛЕЙ

The aim of the study is to develop an adapted methodology for assessing the influence of the chemical composition on the properties of multicomponent steels and finished rolled products. An approach to predicting the mechanical properties of structural steels with regard to heat treatment parameters, based on the concept of a directed chemical bond in the description of interatomic interaction in the melt, is presented. The physico-chemical models of the structure of the melts, which interconnect their composition, structure, and properties, were developed in the Iron and Steel Institute of NAS Ukraine. The representation of the element-by-element composition of multicomponent steels in the integral parameters of the interatomic interaction makes it possible to reduce the parametricity of the models. The role of various pairing interactions of alloying, microalloying and impurity elements in the formation of properties of steels and alloys was evaluated. A factor analysis has been carried out, the chemical composition of the steel has been structured into various subsystems. It is shown that the most significant subsystems are the matrix m (C, Si, Mn) and microalloying ml (Cr, Mo, V, Ni, Ti, Nb). For two samples of structural steels with significant technological differences and features (1-st group - low alloyed steels: St3sp, VSt3sp, VMSt3sp; 2-nd group: 09Г2ФБ, 10ХСНД, 15ХСНД, 14Г2САФ, 14Г2АФ, 16Г2АФ) dependencies of the type are obtained: σВ (σ0,2, δ5) = f (interatomic interaction parameters, Vcool). It is shown that the most important parameters for calculating the σB, σ0.2 and δ5 matrix subsystem m are the integral parameters of the interatomic interaction d and ZY, dm and tgαm, and for the microalloying subsystem ml - ZYml and dml, as well as the cooling rate Vcool for both subsystems. The developed semi-empirical models are recommended for expert assessment of the mechanical properties of structural steels and for use in automated control systems and automated process control systems.

Влияние термической и термоциклической обработки на механические свойства конструкционных сталей

Влияние термической и термоциклической обработки на механические свойства конструкционных сталей

Characterization of strain rate effects on the plastic properties of structural steel using nanoindentation

SM490, a structural steel, has been widely used in the construction of buildings, bridges, and tunnels due to excellent machinability and weldability. Since the mechanical properties of structural steel are important material input data in engineering design as well as in both static and dynamic analyses of structure, the important task is to deeply understand the mechanical properties of structural steel and the effecting factors on these properties, in which the strain rate effect is most important. In this study, the indentation strain rate effects on the mechanical properties of SM490 steel, including hardness, yield strength, the strain hardening exponent and shear stress were investigated using the nondestructive indenting technique. The dynamic tensile tests were performed at different strain rates to demonstrate that the strain rate effects on the hardness and yield strength investigated by using indentation are reliable. The strain rate sensitivity value of SM490 steel obtained using the nondestructive indentation experiment was reported. The linear relation between the indentation strain rate (ε̇I) and uniaxial strain rate (∈̇) was discovered, and the coefficient C2 of 0.15 relating to both strain rates was well estimated. A modified method was also proposed to determine the values of plastic properties considering uncertain contact stiffness at high indentation strain rates. The results were used to assess and understand the variation of mechanical properties of SM490 as the indentation strain rate changes.

Investigating of the tensile mechanical properties of structural steels at high strain rates

St37 and St52 structural steel plates were tested in uniaxial tension at room temperature over various strain rates ranging from 0.001/s to 0.1/s. The yield stress, flow stress and fracture behavior of steels were analyzed. It was found that the strain rate has a strong effect on the tensile mechanical properties of St37 steel, while St52 has a less sensitive strain rate and that the yield strength of both steels exhibits a higher strain sensitivity rate than the other mechanical properties. An increase in the loading rate from 0.001/s to 0.1/s led to a %30 increase in the lower yield strength of St37 steel and an increase of %6 for St52. The equations were derived to express the yield stress behavior with the strain rate. The ductile dimple fracture was observed in static and dynamic conditions; however, increasing the strain rate resulted in a pronounced cleavage-type fracture in both steels. The St37 fracture strain decreased considerably by increasing the strain rate.

Effect of structural steel ion plasma nitriding on material durability in pulsed high magnetic fields

The work was aimed to study the influence of plasma nitriding on electrical and mechanical properties of structural steels and their durability in pulsed high magnetic field. The plates and cylindrical magnetic flux concentrators were made of several steel grades (30KhGS, 40Kh, 50KhGA, 38Kh2MYuA, and U8A), heat-treated, and subjected to the low-temperature (400, 500°C) plasma nitriding. Electrical and mechanical properties of materials, phase composition of steel surface layer, microstructure and microhardness profiles were investigated on the plates before and after plasma treatment. Microstructure and microhardness profiles across the subsurface layer of plasma treated and untreated concentrators applied for high magnetic field generation were also studied. Magnetic field of 50 T under tens of microseconds in duration inside the flux concentrators was generated by long-life outer coil.

WES 2808 for Brittle Fracture Assessment of Steel Components Under Seismic Conditions Part II: Change in Mechanical Properties of Structural Steels by Pre-strain and Dynamic Loading

The yield strength and tensile strength of the steels are varied by pre-straining, dynamic loading and temperature. In addition, the fracture toughness is strongly affected by the strength variation. Therefore, the fracture assessment of steel weldments under seismic loading condition needs to be considered the effects of strength variation caused by cyclic and dynamic large strain. In WES 2808:2003, the estimation method of strength increase with superposition effect of pre-straining, dynamic loading and temperature was proposed in the strength range of 400 - 590 MPa class steel plate, 400 - 490 MPa class H-section steel and 590 MPa class weld metal. However, 780 MPa class steel plate has recently begun to be applied in building structures. Therefore, the strength range of the estimation method needs to be expanded.In this study, the dependence of strength variation on pre-straining for 780 MPa class steel plate was investigated by experiment. And the applicability of the WES 2808 strength estimation methods for 400 - 780 MPa class steel was investigated.As a result, the effects of pre-straining on both the yield strength and tensile strength of the 780 MPa class steel were revealed. In addition, new equations that are based on old equations of WES 2808:2003 for estimating the strength with varied pre-straining are proposed. The strength range of the estimation method could be expanded.

Modeling and Analysis of Mechanical Properties in Structural Steel-DOE Approach

Abstract The present work focuses on the modeling and analysis of mechanical properties of structural steel. The effect of major alloying elements namely carbon, manganese and silicon has been investigated on mechanical properties of structural steel. Design of experiments is used to develop linear models for the responses namely Yield strength, Ultimate tensile strength and Elongation. The experiments have been conducted as per the full factorial design where all process variables are set at two levels. The main effect plots showed that the alloying elements Manganese and Silicon have positive contribution on Ultimate tensile strength and Yield strength. However, Carbon and Manganese showed more contribution as compared to Silicon. All three alloying elements are found to have negative contribution towards the response- Elongation. The present work is found to be useful to control the mechanical properties of structural steel by varying the major alloying elements. Minitab software has been used for statistical analysis. The linear regression models have been tested for the statistical adequacy by utilizing ANOVA and statistical significance test. Further, the prediction capability of the developed models is tested with the help of test cases. It is found that all linear regression models are found to be statistically adequate with good prediction capability. The work is useful to foundrymen to choose alloying elements composition to get desirable mechanical properties.

Constitutive model for ASTM A992 steel at elevated temperature

It is essential to know the mechanical properties of structural steel at elevated temperatures, for analysis of structural response to fire or other high temperature extremes. One of the key elements for such analyses is the availability of a constitutive model for material stress-strain response. This paper provides recommended engineering stress-strain equations for ASTM A992 steel for temperatures up to 1000°C, based on an extensive series of tests. These recommended stress-strain equations are compared with experimental data and with stress-strain equations recommended by Eurocode 3 (EC3) and by the US National Institute of Standards and Technology (NIST).

The effect of laser beam wobbling mode in welding process for structural steels

A laser welding process using a 30-kW fiber laser with scanning mode optics is investigated in the paper. Welding is conducted in two ways: constant laser beam trajectory and wobbling trajectory with the use of lower speed and power. The main goal was to investigate the influence of the second wobbling laser welding pass on microstructure and mechanical properties of structural steel. The following parameters were monitored: visual control and mechanical properties (microhardness, three-point bend, and Charpy impact V-notch test); metallographic analysis and 2D and 3D computer tomography (CT) were also done. The results show that after the second welding pass, with wobbling trajectory of laser beam, middle and cap parts of the seam have a lower microhardness, in relation to the root part. It can be explained by annealing influence of the second wobbling pass at weld metal.

Mechanical properties of partially damaged structural steel induced by high strain rate loading at elevated temperatures – An experimental investigation

In structural engineering practice, understanding the behaviour of steel under extreme loading conditions is essential for accurate prediction of material response when subjected to a combination of severe load scenarios such as collision by heavy objects and a following fire. Hitherto, the combined effects of high strain loading and subsequent elevated temperature have not been widely investigated on the mechanical properties of structural steel. A comprehensive test program is carried out to investigate the post-impact fire properties of Grade 350 steel under well-defined conditions, the results of which are reported in this paper. Coupon specimens have undergone interrupting high strain rate (HSR) tensile loading at impact level, controlled locally at different levels of elongation, to account for different deformation states. Three different damage levels are introduced with respect to the displacement corresponding to the ultimate stress (fu). Subsequently, the partly damaged specimens are subjected to steady-state quasi-static tensile loading to failure at temperatures ranging from ambient to 600 °C. The overall stress–strain relationship, as well as the mechanical properties of pre-damaged steel, are presented at elevated temperatures and compared to those of each individual loading scenario. The test results demonstrate that the effects of these combined actions are profoundly different from those in which the structure is subjected to either high strain rate or thermal loading individually. It is shown that the strength and ductility of mild steel is significantly dependent on the rate of loading, the pre-deformation history and the temperature to which it is subsequently exposed. This necessitates the development of models which take into account the coupled effect of high strain rate and temperature in rational fire analysis and design of steel structures.

Assessment of strain measurement techniques to characterise mechanical properties of structural steel

Strain measurement is important in mechanical testing. A wide variety of techniques exists for measuring strain in the tensile test; namely the strain gauge, extensometer, stress and strain determined by machine crosshead motion, Geometric Moire technique, optical strain measurement techniques and others. Each technique has its own advantages and disadvantages. The purpose of this study is to quantitatively compare the strain measurement techniques. To carry out the tensile test experiments for S 235, sixty samples were cut from the web of the I-profile in longitudinal and transverse directions in four different dimensions. The geometry of samples are analysed by 3D scanner and vernier caliper. In addition, the strain values were determined by using strain gauge, extensometer and machine crosshead motion. Three techniques of strain measurement are compared in quantitative manner based on the calculation of mechanical properties (modulus of elasticity, yield strength, tensile strength, percentage elongation at maximum force) of structural steel. A statistical information was used for evaluating the results. It is seen that the extensometer and strain gauge provided reliable data, however the extensometer offers several advantages over the strain gauge and crosshead motion for testing structural steel in tension. Furthermore, estimation of measurement uncertainty is presented for the basic material parameters extracted through strain measurement.

일반 구조용 강재 적용 H형강 보부재의 해석에 의한 고온내력 평가 연구

화재와 같은 고온 시 구조부재의 붕괴를 방지함으로써 재실자와 소방관계자 그리고 재산을 보호할 수 있는 방법은 구조부재의 내화성능을 확보하는 것이며, 이는 시방적 내화설계방법인 내화시험을 통하여 확보되어 왔다. 그러나 내화시험에 수반되는 시험체 제작과 운반 그리고 막대한 시험 비용의 반복적 사용 등은 새로운 공법과 재료 개발의 문제점으로 대두되었다. 따라서 본 연구에서는 일반 등급(SS 400) 강재의 고온 시 항복강도, 탄성계수와 열전달 및 열응력 해석을 적용하여 H형강 보부재의 표면온도 상승 및 고온 시 내력 변화를 평가하였다. 또한 H형강 보부재의 길이 변화에 따른 고온 시의 보부재의 내력평가를 수행하여 각각의 길이변화에 따른 내력 변화의 차이를 평가하였다. Structural stability of structural beams at high temperature had been evaluated though a horizontal furnace and a standard fire curve. If a structural method and a material are satisfied with the fire test, those are seemed to be guaranteed the safety of residences, fire services men, and properties of the buildings. However, that requires not only longer period but higher cost for making and testing of each structural element. That restrained from developing new methods and new fire protective materials. In this study, an analytic method was executed to demonstrate whether the analytic method using mechanical properties of structural steel at high temperature with heat transfer theory works is working. In this paper, the surface temperature rising and variance of structural stability of a simple H-section beam with a standard fire curve were evaluated and structural stabilities of H-section beam according to differences from length of beam were suggested.

On Problems of Characteristic and Nominal Values of Steel Yield Strength and Their Influence on Design Resistance of Steel Structural Members

ABSTRACTThe paper deals with the problems of mechanical properties of structural steels used for load-carrying structures of civil engineering constructions. The attention is mainly paid to the values of yield strength from the viewpoint of the design concept of European Standards, i.e. Eurocode 3 for the design of steel structures, with respect to the structural reliability given by the failure probability. In the case of other materials, concrete or timber for example, characteristic and design values of strength given by the corresponding failure probability are used in the design procedures, where the partial safety factor of material is γM > 1.0. However, in the case of steel, the nominal values instead of characteristic values of steel yield strength are utilized in the structural design procedure, with the partial safety factor for material of γM = 1.0. These values have been derived based on the statistical and probabilistic evaluation of the data sets of actual material properties obtained from various recent steel producers. The paper presents the brief information on the results of the study oriented to the influence of the nominal or characteristic value of yield strength on the design resistance, which is shown on the examples of the member subjected to tension and bending moment, respectively. The influence mentioned is shown using the examples of structural steels used in constructions of the age of about 40 and 100 years.

On Problems of Mechanical Properties of Structural Steel in Load-Carrying Structure of Historical Building Construction

The paper is focused on the problems of the mechanical properties of steel used for load-carrying structures of civil engineering constructions, especially from the viewpoint of properties of old steels used in historical constructions in comparison with current steels. Chemical composition and physical-mechanical properties of historical steels can be important, for example, in the case of reconstructions, when for the static assessment and evaluation of existing constructions subjected to new (higher) loading actions, material properties of load-carrying structure must be known. In the case of constructions aged about 100 years, usually no project documentation and no information about used material and its properties exist. Then, the properties must be determined using material tests carried-out on the test specimens taken from the real existing structure. But here the sampling of test specimens is limited by the possibilities of existing structural system and by the dimension of particular members from which the specimens are taken, so that the test specimen dimensions and number are limited. Thus, the evaluation of material properties for obtaining representative design values can be more difficult and less reliable than in the case of the large test number. But the main problem is to determine the usable design values of material properties (design yield and ultimate strength) to utilize them for the reliable static re-design of existing structure under actual loading actions. Some problems indicated above have been shown on the example of the material analysis of steel load-carrying structure of slaughterhouse aged more than 100 years. This analysis has been performed recently within the framework of the construction exploration in connection with the intended revitalization of historical “industrial zone” in the city of Brno, Czech Republic.

Elevated-temperature mechanical properties of high strength structural steel S460N: Experimental study and recommendations for fire-resistance design

Fire-resistance design is one of the most important considerations when structural engineers conduct design of steel structures. As a basis of analyzing fire performance of steel structures, elevated-temperature mechanical properties of structural steels are significant for practical design. The recommendations of current European, American, Australian and British standards were mainly obtained from mild steels, which are in question when used to conduct fire-resistance design of high strength steel structures. In order to reveal the elevated-temperature mechanical properties of high strength steel S460N, tensile tests were conducted at various temperatures ranged 20–700°C. The elevated-temperature reduction factors of elastic modulus, yield and ultimate strengths of S460N were obtained and compared with current design standards and available literature. According to the comparison between this research result on S460N and the available research results in literature on S460N, S460M and various mild steels, it is found that the deterioration of mechanical properties of structural steels at elevated temperature is dependent on steel grades. Thus the recommendations in current design standards are not applicable to high strength structural steels. Further unique predictive equations for the deterioration of high strength structural steel S460 at elevated temperatures were proposed and validated with available literature.

Deterioration of mechanical properties of high strength structural steel S460N under transient state fire condition

911 World Trade Centre Tragedy put fire safety of constructional steel structures into question. Since then, more and more research attention has been paid to the elevated-temperature mechanical properties of structural steels, which is a critical basis of evaluating the fire performance of steel structures. In the literature the available mechanical properties of structural steels under fire conditions were mainly obtained from steady state test method, as steady state test method is easier to perform than transient state test method and offers stress–strain curves directly. However, the transient state fire condition is considered to be more realistic to represent the real condition when constructions are exposed to fire. In order to reveal the deterioration of mechanical properties of the commonly used high strength structural steel S460N under transient state fire condition, tensile tests were conducted under various constant stress levels up to 800MPa. The reduction factors of elastic modulus, yield and ultimate strengths of S460N under transient state fire condition were obtained and compared with current leading design standards and available literature. The application of such accurate elevated-temperature mechanical properties reduction factors of S460N can ensure a safe fire-resistance design and evaluation of steel structures with high strength steel S460N under transient state fire condition. This experimental study also supports other relative research on fire performance of steel structures with S460N under transient state fire condition.

Creep Properties of ASTM A992 Steel at Elevated Temperatures

In moving towards an engineered performance-based approach to structural fire safety, a sound knowledge of the elevated-temperature properties of structural steel is crucial. Of all mechanical properties of structural steel at elevated temperatures, material creep is particularly important. Under fire conditions, behavior of steel members and structures can be highly time-dependent. As a result, understanding the time-dependent mechanical properties of structural steel at high temperatures becomes essential. This paper presents preliminary results of a comprehensive on-going research project aimed at characterizing the material creep behavior of ASTM A992 steel at elevated temperatures. Such creep properties are presented in the form of strain-time curves for materials from the web and the flanges of a W4×13 wide flange section and from the web of a W30×99 section. The test results are then compared against material creep models for structural steel developed by Harmathy, and by Fields and Fields to evaluate the predictions of these models. The preliminary results clearly indicate that material creep is significant within the time, temperature, and stress regimes expected in a builing fire. The results also demonstrate the need for a more reliable creep model for steel for strcutural-fire engineering analysis.

Creep Properties of ASTM A992 Steel at Elevated Temperatures

In moving towards an engineered performance-based approach to structural fire safety, a sound knowledge of the elevated-temperature properties of structural steel is crucial. Of all mechanical properties of structural steel at elevated temperatures, material creep is particularly important. Under fire conditions, behavior of steel members and structures can be highly time-dependent. As a result, understanding the time-dependent mechanical properties of structural steel at high temperatures becomes essential. This paper presents preliminary results of a comprehensive on-going research project aimed at characterizing the material creep behavior of ASTM A992 steel at elevated temperatures. Such creep properties are presented in the form of strain-time curves for materials from the web and the flanges of a W4×13 wide flange section and from the web of a W30×99 section. The test results are then compared against material creep models for structural steel developed by Harmathy, and by Fields and Fields to evaluate the predictions of these models. The preliminary results clearly indicate that material creep is significant within the time, temperature, and stress regimes expected in a builing fire. The results also demonstrate the need for a more reliable creep model for steel for strcutural-fire engineering analysis.