Low Carbon Structural Steel Research Articles

Post Underwater Wet Welding Heat Treatment by Underwater Wet Induction Heating

Wet welding procedures of Class A structural ship steels frequently fail to comply with the American Welding Society (AWS) D3.6M, Underwater Welding Code, in the maximum hardness criterion for the heat-affected zone (HAZ). The maximum hardness accepted in a welded joint is 325 HV for higher-strength steel (yield strength > 350 MPa). In multi-pass welds, this problem occurs frequently and is restricted to the HAZ of the capping passes. The HAZ of the root and filling passes are softened by the reheating promoted by their respective subsequent passes. This paper presents the results of exploratory research into postweld underwater electromagnetic induction heating. The objective of the research was to evaluate the ability of induction heating to soften the specific high-hardness HAZs in underwater conditions. The results showed that this technique could reduce the maximum HAZ hardness of low-carbon structural ship steel welds to values below 325 HV, which is the maximum accepted by AWS for Class A welds. The induction-heated zone reached a maximum depth of about 10 mm, which is considered adequate to treat the HAZ of cap-ping passes in underwater wet welds.

Effect of Deformation-Thermal Processing on the Microstructure and Mechanical Properties of Low-Carbon Structural Steel

Effect of Deformation-Thermal Processing on the Microstructure and Mechanical Properties of Low-Carbon Structural Steel

Production of structural steel heavy plates up to 100 mm by TMCP with final accelerated cooling for wind generators and bridgebuilding. Part 1

Growing interest in the production of heavy plates in thickness range 60-100 mm and steel grades S420M / S420ML in compliance with EN 10025-4:2019 is noted. The first part of publication provides an overview of present-day requirements to the chemical composition and mechanical properties of S420M and S420ML heavy plates. Authors describes the specifics of designing the chemical composition and selecting the technological parameters for the thermomechanical processing with accelerated cooling (TMCP+ACC) of heavy plates in high thickness groups. Publication provides description of the main equipment of NLMK DanSteel Mill Quarto 4200 that is used for production of heavy plates from low-carbon structural steels by using TMCP+ACC process. The second part of publication provides Brief description of the specific temperature and cooling parameters of rolling and cooling stages during production of 60-100 mm heavy plates in TMCP+ACC is given, and the effect of these parameters on the formation of the final microstructural condition and mechanical properties in different thickness layers of heavy plates is investigated.

Stability of Untransformed Austenite in M/A Phase of Bainitic Structure of Low-Carbon Steel

Stability of Untransformed Austenite in M/A Phase of Bainitic Structure of Low-Carbon Steel

Fatigue Strength of Structural Steel DAN400 Plate Produced by Thermomechanical Treatment Technology with Accelerated Cooling

Fatigue properties of contemporary low-carbon micro-alloyed structural steel grades have not been studied sufficiently in spite of a large amount of available reference information. This slows down and hinders introduction of the latest generation of structural steel grades into production chains for manufacturers of heavy machinery and structures. According to multicycle fatigue test results for plate steel grade DAN400 36 mm thick with σy = 450 MPa, Cequ = 0.27%, and Pwi = 0.12% produced by thermomechanical treatment technology with accelerated cooling (TMTT + AC) the fatigue strength (σ–1, MPa) on a base of two million cycles, the index of the left-hand branch of the fatigue curve m = 1/α, and coefficients C and α in the equation for the left-hand branch of the fatigue curve σ–1 = С·N–α are determined. An experimental fatigue curve is constructed on double logarithmic coordinates for the test steel.

Performance Enhancement in Borocarburized Low-Carbon Steel by Double Glow Plasma Surface Alloying

In this paper, the performance of low-carbon steel is enhanced after introducing a borocarburized diffusion layer via double glow plasma surface alloying technology. Due to the boron-carbon gradient structure of low-carbon steel, the protective coating exhibits an excellent wear and corrosion resistance. Interestingly, the borocarburized layer consists of a 64 μm carburized layer and a 27 μm boride layer, which plays an effective role in enhancing the microhardness of borocarburized low-carbon steel, exhibiting a 1440 Vickers hardness increase in the surface microhardness of low-carbon steel. The potentiodynamic polarization measurement and impedance measurement results indicate that the boride protective film can effectively prevent aggressive chloride ions from invading the substrate, which indicates an excellent property of corrosion resistance. This systematic study paves a promising way for the future application of hard coatings in severe environments.

Performance characteristics of GMAW process parameters of multi-bead overlap weld claddings

The effect of Gas Metal Arc Welding process parameters on the bead geometry of stainless steel (SS) claddings can be studied using statistical Taguchi L9 design of experimental model. In this study deposits were made with continuously varying weld bead overlaps of 0 – 100%. Cladding is proposed to impart corrosion inhibition properties to the low carbon structural steel plate. Selection of welding process parameters affects the arc stability, heat input deposition rate and quality of the surfaced layer represented by the percentage dilution. Minimization of heat input leads the reduced deposition rate and increased occurrences of weld bead defects like porosity, lack of fusion and cracking. In this context, it is important to identify the extent of influence exerted by the controlled welding parameters on the bead geometry. The reinforcement dimensions play an important role in the cladding process. Stainless steel claddings are deposited by automated Gas Metal Arc Welding (GMAW) process by using Taguchi L9 design of experiment. The selected input variables are Welding voltage (WV), Wire feed rate (WFR), Welding speed (WS) and NTPD. The responses identified governing the bead geometry like bead width (w) and height of the reinforcement (h) in different bead overlaps like 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%. The paper also explores the variation in the bead geometry at different levels of overlap percentages including hardness evaluation.

Dilatometric Analysis of the Austenite Decomposition in Undeformed and Deformed Low-Carbon Structural Steel.

This paper aims to analyze the effect of deformation on the phase transformation kinetics of low-carbon structural steel. The steel used for the investigation was subjected to two different dilatometric analyses using a DIL 805A/D device. The first analysis was to determine the phase transformation kinetics without deformation of austenite before cooling. Then, the analysis under deformation conditions was conducted to investigate the deformation effect on the transformation kinetics. Microscopic studies by light microscopy were performed. The essential part of the research was hardness analysis for different cooling rates and the creation of continuous-cooling-transformation (CCT) and deformation continuous-cooling-transformation (DCCT) diagrams. It was found that the deformation of the samples before cooling increases a diffusion rate in the austenite resulting in the corresponding increase of ferritic, pearlitic, and bainitic start temperatures, as well as shifting the austenite transformation product regions to a longer time. The increase of the transformation area and a decrease in grain size are observed for the deformed samples.

The effect of elastic deformation on the minor hysteresis loops of low carbon steel

The effect of elastic tensile deformations on the magnetic permeability of a structural low-carbon steel 20K (0.23 % C, 0.20 % Si, 0.46 % Mn) at various magnetic states was experimentally studied. To obtain these parameters, the measurements of minor hysteresis loops, which begin in the demagnetized state and in the remanent magnetization state, were carried out. The maximum tensile stress equal to 250 MPa that corresponds to 90 % of the conditional yield strength of studied steel. Stress dependences of the initial and reversible magnetic permeabilities as well as differential magnetic permeability along the descending branch of the minor hysteresis loop, which starts in the remanent magnetization state, are non-monotonic. They have extremums at σ = 50–70 MPa. However, stress dependences of the sums of those parameters are monotonic. The relative changes reach 25 % at tensile stresses of 250 MPa which make the promise of using the sums of magnetic permeabilities as parameters for assessing the magnitude of tensile stresses.

Failure characterization of a structural welded component of an ancient bridge

Abstract The development of railroads promoted the innumerable railway bridges building in Brazil mainly at the end of 19th and the beginning of the 20th century. In those period, girders and other bridges components were built with a growth production demand promoting challenges in the control and volume of manufacturing production process taking into account that the metallurgical knowledge was in early stages. Nowadays, innumerable railway bridges are still in service and their proper maintenance is sometimes ignored. Thus, this work determine the type of metallic material and failure mechanism of structural arch and “L” shapes girders components from Desengano Bridge taking into account that some repairs were performed during their life span. The investigation conducted in this work showed that the structural components analyzed were constructed by puddle or wrought iron process, which is characterized by high levels of P and S in their composition. Meanwhile a reinforcement plate welded to the arch girder was added in a corrective maintenance of the bridge, especially because the plate material matches the current structural low carbon steel. The fracture surface revealed that the crack has dendritic inclusions with typical hot solidification crack aspect. Finally, it should be considered that metallic parts of any ancient bridge, especially those ones containing rivets as an essential rule, in first instance cannot be repaired in situ by welding.

Feasibility Evaluation of Local Laser Treatment for Strengthening of Thin-Walled Structures from Low-Carbon Steel Subjected to Bending.

This paper is devoted to investigating numerically, by finite element analysis (FEA), and analytically the influences and effects of laser processing of the surface of thin-plate, low-carbon structural steel. The plate mechanical properties—axial and flexural stiffnesses, force-deflection behavior and cross-section force-strain behavior—are investigated after different laser treatments. An analytical methodology of the estimation of the cross-section area of the laser-processed metal is also proposed in the present article, that can be applied to choosing the reasonable distance between the centers of the laser-processed tracks. The methodology takes into account the width of the laser-processed tracks and the distances between these tracks. The experimental, finite element numerical and analytical analyses showed that the laser treatments of the surface of the steel plate increase the yield point of the laser-processed metal and the axial and flexural stiffnesses of the plate.

Improvement of low temperature impact toughness through flux modification for submerged arc welded low carbon steel E350 plates

Objectives: To analyse the effects of rutile (TiO2) and Alumina (Al2O3) on impact toughness properties of Submerged arc welded joints for low temperature applications. Methods: Al2O3 and TiO2 have been added to F7AZ/PZ-EL8 Submerged arc welding (SAW) flux in varying quantities and the base material used for joining is low carbon structural steel having E350 grade. To verify the effect of these elements by flux modification, the Charpy V-Notch impact tests, scanning electron microscope (SEM) fractography and visible light microscopy (VLM) have been conducted. Findings: Charpy V-Notch impact testing and analysis have shown that there is considerable improvement in the impact properties of welds with the addition of 20% TiO2 and 20% Al2O3 in the 80% of flux as separate constituents i.e., when these elements have been added in the flux in separate form or two new modified fluxes were prepared, where one is doped with alumina and other is with rutile. Fractography of welds with addition of 20% alumina in 80% F7AZ/PZ-EL8 SAW fluxes are having best impact properties at lower temperature and addition of 20% rutile also as almost effective as alumina in flux. consequently, mode of failure is ductile fracture with dimples as a result of good amount of acicular ferrite microstructure. Novelty: Analysis of previous studies implicated that there is lack of significant studies in the low temperature impact properties of low carbon steel submerged arc welds. Present study shows that the significant improvement in the toughness properties of welds at lower temperature of -40◦C can be achieved through flux modification, it would ensure the application of Low carbon steel structures at lower working temperature. The applications may be pressure vessels, ships or containers. Keywords: Submerged arc welding (SAW); low temperature impact toughness; flux modification; low carbon steels

Weld structure of low-carbon structural steel formed by ultrasonic-assisted laser welding

Abstract The present study is aimed to examine the structure of a welded joint of low-carbon structural steel A 516–55 formed by melting under laser irradiation and by subsequent melt solidification. The main disadvantage of the weld structure in this steel is the formation of plate- and needle-like Widmanstatten ferrite in the conditions of ultra-fast heating and cooling which adversely affects the strength properties of the welded joints. It is shown that the application of ultrasonic vibrations during welding changes the melt solidification conditions and positively affects the dispersion of dendrites and growing Widmanstatten ferrite crystals.

Small Angle Neutron Scattering Study of Nanoscale Structure of Low-Carbon Steel After Rolling with Shear Followed by Cold Drawing

Small angle neutron scattering was applied to steel produced by rolling with shear (RS) technology and compared to samples produced by standard technology (ST). Based on small angle neutron scattering measurements the morphology of the grains and pores of RS steels were compared to those of the ST steels. The scattering in small scattering vector region showed anisotropy, attributed to the elongation of the pores; the pearlite lamellae distances along and perpendicular to the rolling directions differed by a factor of 1.5. The results of the Small angle neutron scattering measurements were in accordance with the electrical characteristics of the specimens. They showed smaller and less anisotropic average sizes of the cracks and nanopores for the RS samples than for the ST rods. This confirms the dynamic healing of the nanosized defects during the cold drawing of the RS rods. This fundamental result shows that during severe plastic deformation a cyclic process of nucleation and healing of the nanovoids took place. However, during the standard deformation process only nucleation of the nanovoids is present.

Structural integrity study of steel railway gearbox housing

Abstract The present work presents a new approach to study the structural integrity of railway component. This railway component is a gearbox housing manufactured by welding, bending, and bolting in structural low carbon steel. During maintenance procedures two non-expected cracks were detected through the non-destructive liquid penetrant testing; one in the middle of gearbox housing cover and the other in the central body of the component, near of one weld zone. The new approach developed in this work is divided in two parts: finite elements simulation and numerical simulation. The first part started by simulate the load service applying vibration analyse. Software Abaqus/CAE 6.14 © was used. Four different refined meshes were considered and analysed. And the membrane and bending stresses were determined through stress linearization of the critical vibration modes for each zone (cover and body). To the numerical simulation two programs in Octave language were developed. The Stress Intensity Factor Range (SIFR) and the formulation of standard BS 7910:2013+A1:2015 was used for embedded and superficial flaw types. The programs developed returned the values of SIFR for different scenarios of initial flaws position and geometrical parameters. The expected lifetime of the component was determined for the maximum crack depth corresponding to 75% of the zones’ thickness.

Internal Stresses and Dislocation Structure of Low-Carbon Steel after Electrolyte-Plasma Nitrocementation

Internal Stresses and Dislocation Structure of Low-Carbon Steel after Electrolyte-Plasma Nitrocementation

The impact toughness and mechanism of low-carbon steel fracture at low temperatures

The goal of the work is to study the effect of severe plastic deformation (SPD) on the impact toughness and fracture mechanism of St3sp low-carbon structural steel within a test temperature range of 293 – 213 K. The issues of deformation processing of steel St3sp billets using SPD method in conditions of the equal-channel angular pressing scheme (ECAP) are considered. The results of low-temperature tests by impact bending of Charpy steel samples in various states are presented. The impact toughness decreased by ~1.3 times as a result of ECAP in 16 passes. It is shown that the temperature dependence of the impact toughness of steel subjected to ECAP differs from that for steel in the delivery condition. A fractographic study of the fracture mechanisms of the steel in the initial state and after processing by ECAP at a test temperature of 293 – 213 K is carried out. It is shown that for the steel in the initial the transition from fracture with the formation of viscous and brittle fracture zones at 293 K to brittle at 213 K occurs through successive expansion of the brittle fracture area with decreasing temperature, whereas for hardened steel, the mixed fracture area appears in the local region at 233 K and expands to the entire cross section of the sample at 213 K. The microstructure formed as a result of ECAP in 16 passes in the temperature range up to 213 K prevents pure brittle fracture and leads to a mixed fracture pattern.

Plastic damage evolution in structural steel and its non-destructive evaluation

This paper reports the plastic damage evolution in low carbon structural steel and its NDT evaluation. The SEM observations reveal that the voids initiation, growth, coalescence, micro-crack propagation, and macro-crack formation are the main failure forms. The EBSD results show that with the increasing plastic strain, the KAM and ρ GND within grains in LC steel increased continuously. Meanwhile, the BS value and the IPF maps quality decreased significantly. Besides, the TEM observations show that the plastic strain induced dislocation density increase and inhomogeneous dislocation distribution in LC steel, the dislocation nets structures were developed at the later plastic stages, which consist of high-density dislocation tangles. Also, the magnetic hysteresis-loop changed distinctly after the plastic strain, and the Coercivity is sensitive to the change of dislocation structure/density. Therefore, the electromagnetic technique can be utilized to assess the plastic damage in LC steel.

Experimental Study of Residual Stresses in Hybrid Laser Arc and Submerged Arc-Welded 10-mm-Thick Low-Carbon Steel Plates

Abstract Offshore structures are constantly exposed to a multihazard marine environment that threatens their structural integrity. This imposes a high risk for extensive structural failures while various deterioration mechanisms may degrade the available capacity of the structures. Thus, no reliable decisions can be reached regarding design, operation, and survivability of the structures unless a deep comprehension of their fatigue performance is available, including welding-induced residual stresses. In particular, the continuous increase in size of the weldments for the offshore wind industry needs special attention with regard to welding-induced residual stresses, as they can reduce fatigue life, promote distortion, and contribute to stress corrosion cracking. Thus, the current design methods and increased structural dimensions as well as new design and manufacturing methods need to be inspected, understood, and optimized. Related to this, there is a growing need for evaluation of the effect of welding methods with various heat input density distributions. This article deals with the influence of welding method on the welding-induced residual stresses in 10-mm-thick low-carbon structural steel plates. The residual stresses are investigated in hybrid laser-arc welded and submerged arc butt-welded steel plates by means of experimental temperature profile measurements and neutron diffraction measurements and in accordance with existing production procedures. The residual stresses were measured at three different depths in the plates. The goal of the analysis is to gain a comprehensive understanding of the distribution and development of residual stresses in relation to the welding method for better control of the residual stresses and distortion. The repeatability of the neutron diffraction measurements is also investigated and reported in this article.

New formulation of nonlinear kinematic hardening model, Part I: A Dirac delta function approach

Abstract A new mathematical modelling framework for simulation of metal cyclic plasticity is proposed and experimental validation based on tension-compression cyclic testing of S355J2 low carbon structural steel presented over the two parts of this paper. The advantages and limitations of the stress-strain curve shape modelling given by “Armstrong and Frederick” type hardening rules are discussed and a new formulation for kinematic hardening is proposed for more accurate representation of the stress-strain dependence under cyclic loading conditions. The proposed model is shown to describe the shape of the stress-strain curve accurately under various different loading conditions. Transition effects occurring at loading reversals are incorporated through a new framework of Dirac delta functions. In addition to the yield surface, stress supersurfaces able to expand and instantly move to simulate a shift of stress-strain curves during loading reversals are determined. This also enables inclusion of the behaviour of monotonic stress-strain curves with yield plateau deformation in one mathematical model. The influence of the first stress invariant on the shape of a stress-strain curve in tension and compression directions observed in many metals is incorporated into the kinematic hardening rule. The ability of the model to accurately describe transition from elastic to elastic-plastic deformation at small offset strain yield points naturally accounts for nonlinearity of an unloading stress-strain curve after plastic pre-strain. Development of the model to include mixed cyclic hardening/softening, ratcheting and mean stress relaxation is presented in a companion paper (Part II), which includes experimental validation of the modelling framework.