Cu-containing Steel Research Articles

Microstructure evolution and constitutive modeling of Cu-bearing high-strength low-alloy steel during hot deformation

The microstructural evolution of austenite during hot deformation determines the mechanical properties of steel products. Consequently, industrial applications necessitate a thorough comprehension and modeling of this process. Under varied hot deformation conditions, the flow stress, microstructure evolution, and constitutive modeling of a Cu-bearing steel were examined. At various temperatures and strain rates, compression experiments are conducted, and the resulting microstructures were studied by electron backscatter diffraction (EBSD). Our results indicate that fine prior austenite grains with an average diameter of 22.1 m and a high-angle grain boundary density of 0.25 m1 were produced at a deformation temperature of 950 °C and a strain rate of 1 s−1. The dominating rotating cube components ({001}<110>) in the sample deformed at 1150 °C were gradually replaced by the γ-fiber texture component as the deformation temperature decreased. To accurately predict the flow behavior of this steel, we proposed an improved Arrhenius constitutive model that accounts for strain rate and adiabatic temperature rise. With a correlation coefficient (Rc) of 0.9936, a root mean square error (RMSE) of 4.92%, and a relative error (δ) of 6.05 MPa, our results demonstrate that this model predicts the flow stress of the experimental steel with good precision. This research contributes to the development of high-performance steel products by shedding light on the microstructural evolution and flow behavior of Cu-containing steels under hot deformation conditions.

Atomistic Simulation of the Interaction between the Σ9[110](221) Shear-Coupled Grain Boundary Motion and the Cu-rich Precipitates in α-Iron

Shear-coupled grain boundary motion (SCGBM) is an important and efficacious plasticity mechanism in the deformation of metals. In this work, a molecular dynamic (MD) simulation of the interaction between the SCGBM of Σ9[110](221) GB and Cu-rich precipitates in α-iron was carried out. The effects of the size, the temperature, and the composition of the Cu precipitates were also studied. It was found that the precipitates inhibited the GB motion significantly, and the configuration transformation from spheroid to ellipsoid was also investigated in the simulation results. The critical stress of the interaction increased with the size of the precipitates. At higher temperatures, the GB sliding event increased the critical stress of the GB motion, which was higher than that of the interaction, inducing no stress-rise stage in the stress–time curve. The critical stress of the CuNi precipitates on the SCGBM was higher than that of the pure Cu precipitates with the same size, which was one of the reasons for the outstanding strength of the high-strength low-alloy (HSLA) steels compared with the traditional Cu-containing steels.

Research on the mechanism of Cu addition on the grain boundary characteristics and toughness in CGHAZ of low carbon low alloy steel

In this study, the coarse grained heat affected zone (CGHAZ) of Cu-containing/free steels was simulated at various heat inputs by thermal simulator. A comparative study was conducted to reveal the role of Cu addition and heat input in toughness variation by microstructural observation and crystallographic analysis. The results showed that the toughness exhibited a plateau-like variation with heat input increasing, which was mainly determined by the distribution of high angle grain boundary (HAGB). Also, a considerably higher toughness was achieved in Cu-containing steel irrespective of heat input. This attributed to the grain boundary distribution and variation selection. Cu addition weakened the variation selection and promoted the formation of more Bain groups, which helped to increase the fraction of HAGB and improve the impact toughness. In addition, Cu addition resulted in a higher fraction of boundary length in V1/V2, V1/V3, V1/V5 variant pair, which was beneficial to accommodate the transformation strain and release the residual stress, leading to a higher toughness in Cu-containing steels.

Influence of Cu and Ni on the Hot Ductility of Low C Steels with Respect to the Straightening Operation When Continuous Casting

Cu-containing steels can suffer from hot shortness unless Ni is added to protect them but whether this problem also influences the straightening operation is not clear. Previous work on hot ductility has found that only when the tensile samples from Cu-containing steels are oxidised can any deleterious influence of copper be found. However, this paper shows that oxidation is not essential. It is more complex than that and, as Cu has been suggested for TRIP steels at levels up to 2.5% Cu to increase their strength and ductility, a greater understanding is required, both of hot shortness and cracking during straightening. The present paper explores the hot ductility behaviour of steels alloyed with Cu and Ni in the straightening temperature range, 700–1000 °C, when tested in air and in an argon atmosphere. Segregation of Cu to the sulphides and grain boundaries occurred allowing the formation of fine Cu2S particles at the austenite grain boundaries favouring intergranular failure and this was more pronounced under oxidising conditions and required strain. It was concluded that a Cu addition, as well as causing hot shortness at higher temperatures will also cause cracking problems in the straightening temperature range in the more sensitive to cracking grades of steel and although the problems are different they are nevertheless interrelated and provided there is sufficient Ni, both may be avoided.

Effects of Ni/Cu replacement on improvement of tensile and hydrogen-embrittlement properties in austenitic stainless steels

Effects of Ni/Cu replacement and subsequent aging treatment on tensile and hydrogen embrittlement (HE) properties were investigated in Fe-Cr-Ni austenitic stainless steels. With the Ni/Cu replacement, tensile strength and ductility were reduced in the as-annealed state by the increased stacking fault energy (SFE), whereas they were enhanced in the aged state due to the consumption of Cu in the matrix by the precipitation and resultantly lowed SFE. After the electrochemical H-charging, the H permeation depth decreased in the aged Cu-containing steels, indicating that Cu-rich precipitates effectively interfered the diffusion of H to increase the HE resistance. However, the excessive formation of Cu-rich precipitates destabilized the austenite phase, and induced the martensitic transformation. This α’-martensite preferably formed inside or at intersections of deformation twins, along with austenite grain boundaries, thereby providing H-induced crack propagation paths. These cracks caused the earlier brittle fracture and severe HE as a consequence. This result would suggest that the formation of Cu-rich precipitates by replacing expensive Ni could enhance both tensile properties and HE resistance, but a delicate control of SFE should be required to overcome the trade-off relationship of strength and HE resistance.

Effect of Cu and solid solution temperature on microstructure and mechanical properties of Fe-Mn-Al-C low-density steels

Relatively low yield strength (YS) level restricts austenitic low-density steels to some applications requiring small or no deformation than impact energy absorption. Therefore, to enhance the YS of this type of steel, this research investigates variations of microstructure and mechanical properties of two austenitic low-density steels (Fe-25Mn-10Al-1.1C-(0,0.25) Cu) with solid solution temperatures (TS, 850 °C–1050 °C). The results show that TS and Cu have significant impacts on the microstructure characteristics and mechanical properties of the two tested steels. At low TS of 850 °C, an increase of 170 MPa in YS compared with that of Cu-free steel was obtained in Cu-containing steel, which is mainly attributed to much finer grain size, more fine twins, and high dislocation density of the latter. An increase in TS caused the κ-carbides in the two steels to dissolve completely, but the austenite content in Cu-containing steel remained largely stable for the addition of Cu. As a result, the strength of the two tested steels decreased while the ductility increased, and both the strength and yield-to-tensile strength ratio of Cu-containing steel are remarkably higher than those of Cu-free steel. It is concluded that the Cu-containing steel exhibits a superior combination of YS and ductility together with a ∼17% reduction in density compared to pure iron. This study provides a promising way to further enhance the YS of austenitic low-density steels through the addition of a small amount of Cu and tailoring TS.

Susceptibility to Surface Hot Shortness of a Cu-containing Steel

The susceptibility to surface hot shortness of a Cu-containing low alloy steel has been investigated using high temperature treatment tests in air. The grain boundary oxidation of this steel is very serious after soaking at 1100°C for 60 minutes. The oxidation rate of grain boundary was faster than that of internal oxidation at 1100°C but the opposite phenomenon was occurred when the soaking temperature is 1200°C. The phenomenon has an important impact on the susceptibility to surface hot shortness of this steel.

Phenonmenon of Cu Segregation in Cu-containing steel During Soaking at 1150 ℃

Phenonmenon of Cu Segregation in Cu-containing steel During Soaking at 1150 ℃

Improving the Toughness of the Weld-Heat-Affected Zone of Cu-Containing Low-Alloy Steel for Offshore Applications by Optimizing Chemical Composition

Abstract Copper-containing low-alloy steel based on the ASTM A707 5L grade is widely used for structural parts of offshore wells. However, it is difficult to stably obtain good weld joint toughness. With this background, this paper focuses on the metallurgical factors controlling the heat-affected zone (HAZ) toughness of A707 modified steel. Potential factors considered are the grain size, the martensite–austenite constituent (M-A), and precipitates. Thus, the purpose was to clarify the effect of M-A and precipitates on HAZ toughness. Furthermore, Cu, Si, and Mn contents, which affect M-A and precipitates generations, were focused on and tried to improve HAZ toughness by optimizing their contents in ASTM A707 steel. The weld test results showed that the toughness of an intercritically coarsened grain HAZ (ICRCGHAZ) was remarkably lower than that of the other heat cycle pattern due to the formation of M-A. It is, therefore, essentially important to suppress the formation of M-A in order to improve toughness in the HAZ of the steel. Therefore, the chemical composition was optimized in an effort to improve HAZ toughness. Copper had no negative influence on the HAZ toughness. It was found that when the Mn and Si contents of the steel decreased, the area fraction of M-A decreased. Consequently, the ICRCG HAZ toughness is improved because the toughness increases with the decrease in the area fraction of M-A. The recommended amounts of Cu, Mn, and Si to ensure HAZ toughness are more than 1.0 wt%, less than 0.6 wt%, and less than 0.1 wt%, respectively.

Favourable modulation of osteoblast cellular activity on Cu-containing austenitic stainless steel and comparison with the Cu-free counterpart

ABSTRACT In the present study, we describe the favorable modulation of osteoblast functions on Cu-containing austenitic stainless steel in comparison to the Cu-free steel. A series of biological experiments were conducted to understand the determining role of Cu in stainless steel on cellular activity. The study clearly demonstrated that cell attachment, proliferation, and cell-material interactions were significantly enhanced in the presence of Cu. The % area covered by cells increased from 13.4% to 17.8% on Cu-free steel and 17.7% to 25.2% on Cu-containing steel after 2 h and 24 h of incubation, respectively. Similarly, the cell density increased from ~3845 cells/cm2 to ~5481 cells/cm2 on Cu-free steel and ~4990 cells/cm2 to ~8590 cells/cm2 on Cu-containing steel after 2 h and 24 h of incubation, respectively. It is underscored that copper can be added to biomedical alloys from the perspective of cellular functions.

Understanding the Role of Copper Addition in Low-Temperature Toughness of Low-Carbon, High-Strength Steel

In this work, the effect of Cu addition on the microstructure and mechanical properties, in particular, low-temperature toughness, of low-carbon, high-strength steel was investigated. Steels with Cu concentrations varying from 1 to 2.5 wt pct in the place of carbon were prepared and then subjected to the two-step intercritical heat treatment. A mixed microstructure consisting of intercritical ferrite, tempered martensite, and retained austenite was obtained. There was an increased amount of retained austenite in the steels with Cu contents ranging from 0.23 to 2.5 wt pct. Therefore, Cu addition was beneficial for the stabilization of retained austenite. This phenomenon can be attributed to the enrichment of Cu in austenite and the increased driving force of reversed transformation caused by reduction in the T0 temperature (the temperature at which fcc austenite and bcc ferrite of identical composition have equal free energy). Furthermore, nanoscaled Cu precipitates were dispersed in the microstructure of Cu-containing steels. The combined effect of retained austenite and Cu precipitates could be the reason for excellent low-temperature toughness without loss in strength, which is featured by the impact energy of more than 120 J at 153 K (– 120 °C) for the Cu-containing steels. In addition to the deformation-induced transformation of retained austenite, bcc Cu precipitates act as misfit centers to improve the low-temperature toughness by enhancing the dislocation mobility and decreasing the ductile-to-brittle transformation temperature (DBTT).

Influence of plastic deformation and Cu addition on corrosion of carbon steel in acidic aqueous solution

The influence of plastic deformation and Cu on corrosion of carbon steel was investigated. The results showed that plastic deformation promotes the corrosion of Cu-free steel, but this effect was missing in the case of Cu-containing steel. The mechanism by which plastic deformation influences the corrosion properties is discussed based on polarization curves and surface analysis. It is probable that although the dislocations increased by plastic deformation can promote the hydrogen evolution reaction, a Cu-enriched layer formed on the steel surface becomes a barrier to hydrogen permeation, so that plastic deformation doesn’t have an effect on corrosion in Cu-containing steel.

The effect of copper addition on the corrosion resistance of cast duplex stainless steel

In this study, the effects of the addition of 3.01% Cu on the corrosion behaviour of cast duplex stainless steel aged for 1h at different temperatures between 450 and 600°C was investigated by electrochemical tests in 0.6M NaCl, 0.3M H2SO4 and 0.6M NaCl+0.3M H2SO4. A short ageing time increases the hardness and mechanical resistance of the Cu-containing steel by precipitation hardening. Potentiodynamic polarization and electrochemical impedance spectroscopy results show that the effect of Cu addition depends on the media studied. In addition, critical pitting temperature (CPT) measurements revealed that steel with 3.01% Cu has a lower pitting corrosion resistance. On the other hand, for both steels, the short time ageing caused a slight increase in CPT values.

Effect of Nb and Cu on the microstructure and hardness of quenching–partitioning–tempering dual-phase steels

ABSTRACTThe effect of Nb and Cu on the microstructure and hardness of quenching–partitioning–tempering (Q–P–T) dual-phase steels was investigated. Nanostructured martensite and retained austenite were obtained when the steels were treated with a Q–P–T process. The hardness, volume fraction of retained austenite and final carbon content in austenite of the Nb + Cu-containing steel were higher than the Nb-containing steel. This was attributed to the promotion of Nb precipitation by the addition of Cu.

Influence of Cu Addition on Microstructure and Mechanical Properties of Fe-0.08C-1Mn-2.5Ni Steel

In addition to precipitation strengthening effect as Cu precipitates in steel, Cu-containing steel is generally believed to have ability to resist corrosion. However, there are some issues, e.g. strengthening mechanism and appropriate copper content, remaining to be clarified. In this presentation, an offshore platform steel Fe-0.08C-1Mn-2.5Ni was used as experimental materials and the emphasis was put on the comparative study of Cu-addition in terms of microstructural evolution and mechanical properties by using microstructural characterization and mechanical properties measurement. The continuous cooling transformation behavior of the two Cu-containing steels with varying contents was first compared. The Cu-containing precipitates were then determined by transmission electron microscopy (TEM) in the hot rolled steel plate after quenching and tempering. Finally, the effect of Cu-addition on precipitation strengthening and low temperature toughness was discussed considering the interaction of Cu precipitates with dislocation and martensite microstructure.

Role of copper on Laves phase morphology in 9-12%Cr steels

In this work the Laves phase was found to appear in two different morphologies, namely granular shapes and in an elongated shape. No difference in crystallography could be detected between these morphologies. The Laves phase was only observed in its elongated form in Cu-containing steels, where it was the primary morphology present after short term ageing. After long term ageing, the elongated Laves phase was replaced by the granular morphology. It is speculated that Cu precipitates act as nucleation sites for the elongated Laves phase, resulting in an unstable orientation relationship with the matrix, an in the meta-stable elongated morphology of Laves phase precipitates.

The Importance of MnS Inclusions on Hot Shortness of Cu-Containing Steels

A novel approach on the problem of hot cracks in Cu-containing steels is proposed to prevent the hot shortness. Cu-containing steels have been hot tensile tested to failure in argon or vacuum at different cooling rates and temperatures, followed by Scanning Electron Microscopy. EDX analysis both in fractures and cross section show that inclusions are very important in causing the Cu concentration. Although CuS precipitates slightly deteriorate the hot ductility between the Ae3 and Ar3 temperatures, the Cu concentration around inclusions can highly contribute to hot shortness by the formation of Cu-containing liquid phase. Laboratory results combine with thermodynamic calculations show that a Cu-containing liquid associated with inclusions at ≈1200 °C is clearly the cause of the hot shortness. A distinction of hot ductility and hot shortness is proposed, concerning to their very different cracking mechanisms. The interpretation of the hot tensile test for each testing condition and temperature range is discussed. It is concluded that the oxidation is not the principal cause of the increase of Cu concentration, so its importance is relative in the laboratory assessment of hot cracking. Consequently, inclusions cannot be ignored in assessing and preventing the hot shortness, and commercial implications are drawn from the results.

Effect of Cu addition on microstructure and impact toughness in the simulated coarse-grained heat-affected zone of high-strength low-alloy steels

The effects of Cu content on microstructure and impact toughness in the simulated coarse-grained heat-affected zone (CGHAZ) of high-strength low-alloy steels were investigated. It has been observed that the microstructure in the simulated CGHAZ of Cu-free steel is dominated by a small proportion of acicular ferrite and predominantly bainite with martensite–austenite constituent. Whereas, in the 0.45 and 1.01% Cu-containing steels, the acicular ferrite increased significantly due to the effective nucleation on intragranular inclusions with outer layer of MnS and CuS. The formation of acicular ferrite is attributed to superior high heat-affected zone impact toughness in the 0.45% Cu-containing steel. Furthermore, the increasing martensite–austenite constituent and ε-Cu precipitates in the simulated CGHAZ of 1.01% Cu-containing steel caused degradation in impact toughness.

Effect of immersion time in a modified green death solution on the rust layer of Cu-containing low-alloy steel

The corrosion resistance of low-alloy steel containing 0.35 wt% copper, as a function of immersion time in a modified green death solution, was investigated using electrochemical methods and surface analysis. After 30 min of immersion, the steel surface was covered with a Cu-enriched film. Improvement of the film properties and increases in the corrosion resistance were realized for the immersion time up to 6 h due to the development of the Cu-enriched layer. However, the Cu particle was formed in the Cu-enriched layer for the immersion time beyond 6 h. Since the formation of the Cu particle generated a Cu-depletion region, micro-galvanic corrosion between the Cu particle and the Cu-depletion region lead to the localized film breakdown on the surface film. The localized film breakdown, which decreased the corrosion properties of the Cu-containing steel, was accelerated by the continuous formation of Cu particles in the rust layer.

Synthesis, X-ray structure and theoretical study of benzazole thioether and its zinc complex as corrosion inhibitors for steel in acidic medium

A ligand, 2-((benzo[d]thiazol-2-ylthio)methyl)-1H-benzo[d]imidazole, and its zinc complex have been synthesized. The structure of these compounds have been determined by spectroscopic techniques and single crystal X-ray diffraction. The corrosion inhibition study of these compounds for steel in 0.5 M H2SO4 medium has also been investigated using potentiodynamic polarization and EIS techniques. The quantum calculations were applied to investigate the relationship between the electronic properties and the corrosion inhibition efficiency of the two benzazoles derivatives. Surface analysis (XRF) indicated that the rust layer formed on the Cu-containing steels was enriched with Cu compounds. Polarization curves revealed that both inhibitors acted as a mixed-type inhibitor.