High-strength Low-carbon Steel Research Articles

Refinement mechanism of nanoscale Cu-rich precipitates by Mo addition and its effect on strength-toughness of Cu-bearing low carbon high strength steel

Effect of Mo element on the precipitation behavior of nanoscale Cu-rich particles in Cu-bearing low carbon high strength steels was investigated in this work. The addition of 0.82 wt% Mo refined the size of grain interior Cu-rich particles (ICRPs) from 12 nm to 8 nm, accompanied by the structure changed from 3R-Cu to 9R-Cu. Mo also inhibited the formation of grain boundary Cu-rich particles (BCRPs) with the size of ∼30 nm. The calculation of phase field method indicated that Mo was repelled from Cu-rich particles and enriched in α-Fe matrix, which suppressed the diffusion of Cu atoms and merger of Cu-rich particles. The measured yield strength of CuMo-bearing steel increased by 87 MPa, mainly due to the refinement of ICRPs. The reduction of BCRPs suppressed the crack initiation and propagation at grain boundaries, which contributed to the increment of absorbed energy at −40 °C by 41J.

The mechanism of fire resistance of a low carbon high-strength multi-functional steel for building construction

The mechanism of fire resistance of a low carbon high-strength multi-functional steel for building construction

Effect of Nb on microstructure and mechanical properties between base metal and high heat input coarse-grain HAZ in a Ti-deoxidized low carbon high strength steel

In this paper, a Ti-deoxidized low carbon high strength steel plate with different Nb content was obtained by thermal mechanical control processing (TMCP) methods. The coarse-grain heat-affected zone (CGHAZ) under high heat input of 300 kJ/cm conditions was simulated. The effects of Nb on microstructure and mechanical properties in base metal (BM) and CGHAZ were analyzed. The results showed that high content of Nb addition is not conducive to the improvement of toughness, especially in high heat input CGHAZ. A certain amount of Nb inhibites the formation of ferrite, while promotes the bainite transformation with coarse carbides during high heat input welding process. Although high-angle grain boundary has a certain hindrance to the crack propagation, the coarse carbides caused by the enhanced hardenability in Nb-bearing steels stimulates the crack initiation sensitively. Besides, the uneven prior austenite grains may also take responsibility to the deterioration of toughness in Nb-bearing CGHAZ. In general, the content of Nb should be carefully added when impact toughness of CGHAZ is considered during high heat input welding in Ti-deoxidized low carbon high strength steel.

Effect of Austenite Grain Size on the Bainitic Transformation in a 690 MPa Grade High-Strength Multi-Functional Construction Steel

A high-strength low-carbon construction structural steel was investigated in the laboratory. The various austenite grain sizes were obtained by austenitizing the steel at different temperatures. The effect of austenite grain size on bainite transformation was studied by the dilatometer. The results show that the microstructure of high-strength low-carbon structural steels mainly includes granular bainite, lath-like bainite and martensite-austenite (M-A). The microstructure changes from granular bainite to lath-like bainite with the increase in austenitizing temperature or austenite grain size. When the samples were heated at the lower temperature of 860 °C, the bainite starting temperature was relatively high, which was mainly attributed to the promotion of the granular bainitic nucleation and the formation of the solute-depleted regions in the austenite. Compared to 860 and 1260 °C, the bainite transformation rate in the specimen austenitized at 1000 °C is the highest because of the small prior austenite grain size and larger transformation driving force.

Improvement of Cu-rich precipitation strengthening for high-strength low carbon steel strengthened via Ti-microalloying

This present work aims to improve the precipitation strengthening of nanoscale Cu-rich particles in high-strength low carbon steel by Ti microalloying. Ti microalloying increased the density of small-angle boundaries and dislocations, which increased the nucleation sites and refined the dimension of Cu-rich particles. By adding 0.05 wt% Ti, the size of Cu-rich particles were refined from 22 nm to 7 nm. The structure of Cu-rich particles in Ti-free steel was incoherent FCC-Cu, whose mismatch degree with α-Fe matrix was 0.28. By adding 0.02 wt% and 0.05 wt% Ti, the structure of Cu-rich particles transformed into semi-coherent 3R-Cu and 9R-Cu, respectively. Meanwhile, the mismatch degrees between Cu-rich particle and α-Fe matrix decreased to 0.24 and 0.21, respectively. The refinement of Cu-rich particles increased the precipitation strengthening from 46 MPa to 248 MPa.

Characterisation of Compressive Behaviour of Low-Carbon and Third Generation Advanced High Strength Steel Sheets with Freely Movable Anti-buckling Bars

Measuring the compressive behaviour of sheet materials is an important process for understanding the material behaviour and numerical simulation of metal forming. The application of side force on both surfaces of a specimen in the thickness direction is an effective way to prevent buckling when conducting compressive tests. However, the side effects of side forces (such as the biaxial stress state and non-uniform deformation) make it difficult to interpret the measured data and derive the intrinsic compressive behaviour. It is even more difficult for materials with tension–compression asymmetry such as steels that undergo transformation-induced plasticity. In this study, a novel design for a sheet compression tester was developed with freely movable anti-buckling bars on both sides of the specimen to prevent buckling during in-plane compressive loading. Tensile and compressive tests under side force were conducted for low-carbon steel using the digital image correlation method. The raw tensile and compressive stress–strain data of the low-carbon steel showed apparent flow stress asymmetry of tension and compression, originating from the biaxial and thickness effects. A finite element method-based data correction procedure was suggested and validated for the low-carbon steel. The third generation advanced high strength steels showed intrinsic tension–compression asymmetry at room temperature whereas the asymmetry was significantly reduced at 175 °C.

The influence of H2S on hydrogen absorption and sulfide stress cracking resistance of high strength low alloy carbon steel C110

The application of high strength low alloy carbon steel C110 in wet-H2S environment is limited by sulfide stress cracking (SSC). The objective of this research is to evaluate the effect of the environmental H2S content on the susceptibility to SSC. Since SSC is hydrogen induced fracture, the study focusses on: (1) evaluating the effect of H2S concentration on hydrogen absorption, (2) assessing SSC susceptibility by a novel slow strain rate tensile testing (n-NTSSRT) method under both sour and non-sour environments, (3) the correlation between absorbed hydrogen concentration and SSC susceptibility. The results show that with increasing H2S concentration, sub-surface hydrogen concentration C0 increases exponentially, while critical stress intensity factor KISSC decreases. The application of n-NTSSRT methodology criteria is determined to be 1 mol% H2S, which corresponding to a C0 value of 6.66 × 10−6 mol/cm3. When H2S concentration is higher than 1 mol%, the KISSC values should be calculated by assuming the fracture is linear elastic fracture. Otherwise, the elastoplastic fracture solution J-integral should be considered.

The Evaluation of Quenching Temperature Effect on Microstructural and Mechanical Properties of Advanced High Strength Low Carbon Steel After Quenching Partitioning Treatment

The influence of quenching temperature on microstructural and mechanical properties of low alloy steel of the following chemical composition: 0.26 C, 1.70 Mn, 1.42 Si, 1.10 Cr, 1.10 Ni, 0.94 Cu, 0.24 Mo, 0.1 V, Bal. Fe (Wt.%) was investigated after applying a quenching-partitioning (Q-P) treatment. The steel samples were isothermally quenched at 260, 280, and 300 °C, from the austenitizing temperature and then Q-P treated at 340 °C. After the Q-P treatment, the steel showed a multiphase microstructure containing bainite, martensite, and retained austenite. It was determined that the tensile strength and Charpy impact energy increased with a decrease in quenching temperature to 1415 MPa and 43 J, respectively. This effect was attributed to an increase in the volume fraction of austenite/martensite micro blocks that introduces a hard phase mixture strengthening factor and the presence of tempered martensite, which is strengthened by fine particle dispersion and moreover, a decrease in thickness of the bainitic-ferrite subunits that refine the microstructure. The fractographic examination of the Charpy tested specimens showed that the sample quenched at 260 °C contained finer and deeper dimples, which indicates that more energy was spent on the nucleation and growth of ductile fracture microvoids, thus increasing the toughness.

FE Modelling and Prediction of Macrosegregation Patterns in Large Size Steel Ingots: Influence of Filling Rate

In the present work, the influence of filling rate on macrosegregation in a 40-Metric Ton (MT) ingot of a high-strength low-carbon steel was studied using finite element (FE) simulation. The modelling of the filling and solidification processes were realized with a two-phase (liquid-solid) multiscale 3D model. The liquid flow induced by the pouring jet, the thermosolutal convection, and the thermomechanical deformation of the solid phase were taken into consideration. Two filling rates were examined, representing the upper and lower manufacturing limits for casting of large size ingots made of high strength steels for applications in energy and transportation industries. The evolution of solute transport, as well as its associated phenomena throughout the filling and cooling stages, were also investigated. It was found that increasing the filling rate reduced macrosegregation intensity in the upper section, along the centerline and in the mid-radius regions of the ingot. The results were analyzed in the framework of heat and mass transfer theories, liquid flow dynamics, and macrosegregation formation mechanisms.

The effect of H2S and NaCl concentration on hydrogen permeation in high strength low alloy carbon steel C110

ABSTRACT The sulphide stress cracking of high strength low alloy (HSLA) carbon steel C110 is related to the hydrogen absorption process. The objective of this research is to evaluate the effect of adsorbed H2S and Cl− on hydrogen permeation in C110, by studying the responses of hydrogen permeation current and characteristic inductance under environment with different H2S activities and NaCl concentrations using electrochemical methods, including hydrogen permeation method and electrochemical impedance spectroscopy (EIS). The hydrogen permeation current measured in Devanathan–Stachurski cell suggests that the enhance effect of the adsorbed H2S on the hydrogen absorption follows an adsorption isotherm behaviour as a function of H2S activity in solution. The inductive response of EIS under different H2S activities shows consistency with hydrogen permeation results. The EIS results also indicate that the coverage of H2S was suppressed by Cl−. A good correlation about the effect of adsorbed Cl− is found between inductive response and hydrogen permeation current.

Parametric and Metallurgical Investigation of Modified 3D AM 80 HD Steel for Wire and Arc Additive Manufacturing

Wire and arc additive manufacturing (WAAM) is an advanced 3D printing method for metallic materials on the foundation of traditional arc welding processes. WAAM is regarded as a proper way to manufacture large-dimensional metallic parts with the combination of high deposition rate and low cost. In this research, a specifically designed and manufactured low carbon high strength steel (Grade 3D AM 80 HD) wire, equivalent to a composition of AWS ER 110S-1 wire, was deposited using WAAM to print a muti-beads wall aiming to explore its feasibility for heavily loaded marine applications. A parametric investigation was proceeded to find the optimal deposition voltage and overlap ratio. A vertical position compensation method was adopted to optimize the step-up distance for welding torch between neighboring layers. Microstructure of the deposited component was characterized and also indicated by Thermal-Calc Software, followed by the measurement of hardness and prediction of tensile strength. Furthermore, a comparison of tensile strength of the WAAMed 3D AM 80 HD wall, 3D AM 80 HD wire, AWS ER 110S-1 wire, and a WAAMed wall produced by wire manufacturer (Voestalpine Böhler Welding Corporation) was conducted.

The Local Texture Analysis of Structural Inhomogeneities in Low-Carbon High-Strength Steel after Direct Quenching

The Local Texture Analysis of Structural Inhomogeneities in Low-Carbon High-Strength Steel after Direct Quenching

Growth behavior and kinetics of austenite grain in low-carbon high-strength steel with copper

A low-carbon high-strength steel with copper has better antibiological corrosion property, more widely used in large marine projects and ships. In this study, an austenite grain growth model of a low-carbon ship plate steel with 1.6Cu was established by using Sellars equation at 900 °C–1200 °C and different holding times (30–120 min) to reveal its kinetics. The pinning effect of grain boundary precipitates was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and a quantitative relationship between the solid solution and precipitation behavior of copper bearing precipitates in experimental steel and austenite grain growth was analyzed. The experimental results show that the austenite grains grow slowly, and the grains are fine grains when the heating temperature is below 1000 °C and the transition temperature of rapid grain coarsening is 1000 °C. The relative error of dynamic model can be controlled within 8.5%. During heat treatment, Cu atoms are segregated at the grain boundary to form a copper-rich region, providing a coating effect on the carbide and grain boundary and hindering the growth of grains. With the increase in temperature, the diffusion rate of copper atoms increases, and the precipitates containing copper are rapidly dissolved into austenite. Therefore, the pinning effect is weakened, and the austenite grains grow rapidly.

Application of Artificial Neural Network to the Prediction of Tensile Properties in High-Strength Low-Carbon Bainitic Steels

An artificial neural network (ANN) model was designed to predict the tensile properties in high-strength, low-carbon bainitic steels with a focus on the fraction of constituents such as PF (polygonal ferrite), AF (acicular ferrite), GB (granular bainite), and BF (bainitic ferrite). The input parameters of the model were the fraction of constituents, while the output parameters of the model were composed of the yield strength, yield-to-tensile ratio, and uniform elongation. The ANN model to predict the tensile properties exhibited a higher accuracy than the multi linear regression (MLR) model. According to the average index of the relative importance for the input parameters, the yield strength, yield-to-tensile ratio, and uniform elongation could be effectively improved by increasing the fraction of AF, bainitic microstructures (AF, GB, and BF), and PF, respectively, in terms of the work hardening and dislocation slip behavior depending on their microstructural characteristics such as grain size and dislocation density. The ANN model is expected to provide a clearer understanding of the complex relationships between constituent fraction and tensile properties in high-strength, low-carbon bainitic steels.

Microstructure, Mechanical Properties, and Galvanic Corrosion of 10CrNi3MoV Fabricated by Wire Arc Additive Manufacturing

Wire arc additive manufacturing (WAAM) technology is widely used in the fields of aerospace, shipbuilding, and automobile industry due to the advantages of fast forming speed, high material utilization and low production cost. WAAM is extremely sensitive to parameters, and different processes and materials produce different deposition effects and properties. Therefore, it is of great significance to study the WAAM formability of various materials. Herein, the microstructure, mechanical properties, and galvanic corrosion behavior of the low-carbon high-strength steel (10CrNi3MoV) fabricated by cold metal transfer (CMT) WAAM technology were investigated. The single-channel multilayer deposition parts were prepared by reciprocating deposition, and the forming parts were divided into six zones by observing the different positions of the structure: matrix, heat-affected zone, remelting zone, initial deposition zone, interlayer zone, and interlayer bonding zone. Electron backscattered diffraction (EBSD) analysis showed that the amount of recrystallization and substructure in the deposition layer had no obvious change, and the texture phenomenon was the most obvious in the initial deposition zone of the pole map reaction. The texture phenomenon gradually weakened with the increase of the deposition layers. The microhardness from the matrix to the deposition stable zone was tested. The hardness of the matrix changed smoothly, that of the heat-affected zone was the largest, and that of the deposition layer was 221–282 HV0.2. The tensile properties were tested in different directions and angles, and the yield strength and tensile strength of the deposited layer were more than 550 MPa and 760 MPa, respectively. The galvanic corrosion behavior between the deposited layer and the matrix was investigated, and the polarization curve showed that the corrosion potential of the deposited layer was lower than that of the matrix, and the corrosion current density of the deposited layer was higher than that of the matrix.

Comprehensive Analysis of the Microstructure and Mechanical Properties of Friction-Stir-Welded Low-Carbon High-Strength Steels with Tensile Strengths Ranging from 590 MPa to 1.5 GPa

High-strength steels are being increasingly employed in the automotive industry, requiring efficient welding processes. This study analyzed the materials and mechanical properties of high-strength automotive steels with strengths ranging from 590 MPa to 1500 MPa, subjected to friction stir welding (FSW), which is a solid-phase welding process. The high-strength steels were hardened by a high fraction of martensite, and the welds were composed of a recrystallized zone (RZ), a partially recrystallized zone (PRZ), a tempered zone (TZ), and an unaffected base metal (BM). The RZ exhibited a higher hardness than the BM and was fully martensitic when the BM strength was 980 MPa or higher. When the BM strength was 780 MPa or higher, the PRZ and TZ softened owing to tempered martensitic formation and were the fracture locations in the tensile test, whereas BM fracture occurred in the tensile test of the 590 MPa steel weld. The joint strength, determined by the hardness and width of the softened zone, increased and then saturated with an increase in the BM strength. From the results, we can conclude that the thermal history and size of the PRZ and TZ should be controlled to enhance the joint strength of automotive steels.

Local texture analysis of structure non-uniformity in low carbon high-strength steel after direct quenching

The direct quenching of high-strength steels after hot rolling, which enables discard of the reheating operation, is economically efficient but necessitates a careful analysis of corresponding structural features. In particular, this treatment sometimes results in extended domains of coarse bainite decreasing the fracture toughness of steel. To reveal dependence of such effects on ausforming conditions, local textures of the parent γ-phase have been reconstructed from EBSD orientation data with allowance for the inter-phase orientation relationship. According to the obtained results, the unfavorable structural non-uniformity appears in the direct quenching due to excessive work hardening of austenite at the finish rolling stage; however, the structure and properties of steel can be improved by the reheating and subsequent quenching.

On the Microstructural Strengthening and Toughening of Heat-Affected Zone in a Low-Carbon High-Strength Cu-Bearing Steel

In this article, the influence of simulated thermal cycles for the heat-affected zone (HAZ) on the microstructural evolution and mechanical properties in a low-carbon high-strength Cu-bearing steel was investigated by microstructural characterization and mechanical tests. The results showed that the microstructure of the coarse-grained heat-affected zone (CGHAZ) and the fine-grained heat-affected zone (FGHAZ) was mainly comprised of lath martensite, and a mixed microstructure consisting of intercritical ferrite, tempered martensite and retained austenite occurred in the intercritically heat-affected zone (ICHAZ) and the subcritically heat-affected zone (SCHAZ). Also, 8–11% retained austenite and more or less Cu precipitates were observed in the simulated HAZs except for CGHAZ. Charpy impact test indicated that the optimum toughness was obtained in FGHAZ, which was not only associated with grain refinement, but also correlated with deformation-induced transformation of the retained austenite, variant configuration as interleaved type and a relatively weak variant selection. The toughness of ICHAZ and SCHAZ exhibited a slight downtrend due to the presence of Cu precipitates. The CGHAZ has the lowest toughness in the simulated HAZs, which was attributed to grain coarsening and heavy variant selection. In addition, the contribution of Cu precipitates to yield strength in simulated HAZs was estimated based on Russell–Brown model. It demonstrated an inverse variation trend to toughness.

Strengthening and toughening mechanism of a Cu-bearing high-strength low-alloy steel with refined tempered martensite/bainite (M/B) matrix and minor inter-critical ferrite

The microstructure–mechanical property relationship of a Cu-bearing low-carbon high-strength low-alloy steel, subjected to a novel multistage heat treatment including quenching (Q), lamellarization (L) and tempering (T), is presented. Yield strength of 989.5 MPa and average toughness at − 80 °C of 41 J were obtained in this steel after quenching and tempering (QT) heat treatments. Specimen QLT gained a little lower yield strength (982.5 MPa), but greatly enhanced average toughness at − 80 °C (137 J). To further clarify the strengthening and toughening mechanisms in specimen QLT, parameters of microstructural characteristic and crack propagation process were compared and analyzed for specimens Q, QL, QT and QLT. The microstructure of tempered martensite/bainite (M/B) in specimen QT changed to refined tempered M/B matrix mixed with minor IF (inter-critical ferrite) in specimen QLT. Cu-rich precipitates existed in tempered M/B for both specimens QT and QLT, as well as in IF. Compared with QT, adding a lamellarization step before tempering made the effective grains of specimen QLT refined and also led to coarser Cu-rich precipitates in tempered M/B matrix. The weaker strengthening effect of coarser Cu-rich precipitates should be a key reason for the slightly lower yield strength in specimen QLT than in specimen QT. No austenite was found in all specimens Q, QL, QT and QLT. Specimen QLT showed purely ductile fracture mode at − 80 °C due to the refined effective grains. The greatly improved toughness is mainly attributed to the enhanced energy of crack propagation. The combination of refined microstructure, softened matrix and deformation of minor ‘soft’ IF during crack propagation led to the most superior toughness of specimen QLT among all specimens.

Структура та фізико-механічні властивості високоміцної низьковуглецевої сталі Alform 620M за імітації термічних циклів зварювання

Структура та фізико-механічні властивості високоміцної низьковуглецевої сталі Alform 620M за імітації термічних циклів зварювання