Cu-bearing 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.

TiC-induced nanoscale Cu-rich re-precipitation mechanism under welding thermal cycles and its effect on the strength-toughness of heat affected zones

In order to solve the softening problem of welding heat affected zone (HAZ) for Cu-bearing steel caused by the dissolution of Cu-rich particles, TiC was utilized to induce the Cu-rich re-precipitation. With the peak temperature increased from 780 °C (ICHAZ) to 950 °C (FGHAZ), the size of 9R–Cu increases from 4 nm to 5 nm, accompanied with the increment of volume fraction from 0.6% to 1.0%. Phase field simulations indicate that TiC repels Cu atoms into γ-Fe matrix and promotes the formation of Cu-rich clusters. Then, Cu-rich clusters provide more nucleation sites for Cu-rich particles, which contributed to the re-precipitation of refined 9R–Cu. Due to the disappearance of coarse grain boundary Cu-rich particles and formation of fresh lath bainite, re-precipitated Cu-rich particles provided precipitation strengthening value of 237 MPa and 298 MPa without decreasing the low temperature toughness for ICHAZ and FGHAZ. The yield strength and absorbed energy at −40 °C of HAZs exceed 1000 MPa and 120J, respectively.

Enhancement resistance to microbiologically influenced stress corrosion of Cu-bearing steel against Bacillus cereus

Microorganisms are notoriously known to cause local corrosion and stress corrosion cracking (SCC), which seriously endangers the materials service safety. Cu can enhance antibacterial function of the material and reduce the vulnerability to hydrogen embrittlement (HE). However, the dilemma of how much Cu content generates the best resistance to microbiological corrosion and SCC arises. Here, we modified the Cu content in pipeline steel to obtain the best antibacterial effect to nitrate reducing bacteria Bacillus cereus and HE resistance. The findings offer a fresh perspective on how to design and prepare a steel that are both resistant to microbiological corrosion and SCC.

The Effect of Direct Quenching on the Microstructure and Mechanical Properties of NiCrMo and Cu-Bearing High-Strength Steels.

In this work, two types of 590 MPa grade steels, composed of NiCrMo steel and Cu-bearing steel, were processed using traditional offline quenching and tempering and direct quenching (DQ) and tempering. The influence of DQ on microstructural evolution and strengthening mechanisms of these two types of steel was investigated. Grain refinement and dislocation density increase were determined by controlled rolling and following the DQ process in both two types of steel. In Cu-bearing steels, the refined grains and high-density dislocation further promoted the precipitation behavior of Cu-rich particles and alloyed carbides during the tempering treatment. Compared with traditionally quenched and tempered steels, NiCrMo steels after the direct quenching and tempering (DQT) process achieved 106 MPa higher yield strength through grain refinement strengthening and dislocation strengthening, while the Cu-bearing steels after the DQT process achieved 159 MPa higher yield strength through grain refinement strengthening, dislocation strengthening, and precipitation strengthening. The contribution degree of different strengthening mechanisms was quantitatively analyzed. Grain refinement also compensated for the toughness loss caused by the increase in dislocation, leading to an impact energy of 237 J and 248 J at -84 °C for NiCrMo and Cu-bearing steels after DQT, respectively.

Precipitation mechanism of nanoscale Cu-rich particles in restrained welding conditions and its effect on the mechanical properties of HAZs

The effect of welding constraint on nanoscale Cu-rich precipitation in welding heat affected zones (HAZs) of Cu-bearing steel was studied in this work. Due to the constraint tensile stress of 150 MPa, α-Fe transformation start temperature (Ts) of CGHAZ and FGHAZ increased by 55 °C and 42 °C, respectively. The volume fraction and average size of 9R-structural Cu-rich particles in FGHAZ increased from 0.3 % to 0.8 % and from 5 nm to 8 nm, respectively. Three-dimensional phase field simulation shows that the increment of Ts promoted the precipitation of Cu-rich particles in α-Fe matrix. However, the Ts of restrained CGHAZ was too low to favor the precipitation of Cu-rich particles. The tensile strength of FGHAZ increased from 970 MPa to 1032 MPa due to the nanoscale Cu-rich precipitation strengthening.

EFFECTS OF A Cu ADDITION ON THE CORROSION RESISTANCE OF LOW-ALLOY PRE-HARDENED PLASTIC MOLD STEEL

The influence of Cu on the corrosion performance of low-alloy Cu-bearing pre-hardened plastic mold steel was investigated and compared with non-Cu-bearing mold steel using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), salt-spray tests and electrochemical impedance spectroscopy (EIS). The results reveal that the formed rust layer is composed of α-FeOOH, β-FeOOH, γ-FeOOH, Fe3O4 and large amounts of amorphous compounds. The corrosion product in the early stages of corrosion is loose and porous but becomes denser and more tightly bound to the steel matrix in the later stages, and the corrosion rate of Cu-bearing steel decreases with the increasing corrosion time. With a further Cu addition, the free-corrosion potential of Cu-bearing steel increases and, consequently, the electrochemical impedance, the capacitive single semicircular arc on the impedance spectra and the charge transfer resistance are also significantly enhanced. Therefore, Cu effectively enhances the corrosion resistance of pre-hardened mold steel, prolonging its service life and ensuring a high quality and shape fidelity of molded plastic products.

Effect of arsenic on the high temperature oxidation and hot shortness behaviour of copper-bearing steel

To understand the disadvantages caused by As in Cu-bearing steels during hot working processes, high temperature oxidation and surface hot shortness characteristics were systematically investigated using thermogravimetry (TG), optical microscopy (OM), scanning electron microscopy (SEM) and Gleeble-3800 thermal/mechanical simulation system. Analyses of TG curves and the oxide scale morphologies showed that the oxidation kinetics for all steels obeyed the initial linear oxidation law and the later parabolic oxidation law at 950–1050 °C, while the kinetics presented two different stages of the linear oxidation law at 1100 and 1150 °C due to oxide scale separation. Increasing the As content from 0 to 0.15 wt.% decreased the oxidation activation energy and accelerated the oxidation degree of Cu-bearing steel. Cu + As enrichment indicated that an increase in As content induced the precipitation of a more hazardous Cu-rich liquid phase along grain boundaries by decreasing the solubility of Cu in austenite and the melting point of the Cu phase at 1050 °C. Furthermore, the degree of Cu + As enrichment became more serious with an increase in the oxidation temperature from 1000 to 1050 °C, and then decreased because of occlusion and faster back diffusion of Cu + As into the matrix at 1100 and 1150 °C. The hot compression results agreed well with the enrichment behaviour of Cu + As obtained from investigations of isothermal oxidation.

First-principles study on effect of alloying elements on heterogeneous nucleation of reverse austenite on Cu precipitation

The mechanical properties of ultra-high strength martensite steel strongly depend on the shape, size and content of the reversed austenite. In general, the plasticity and toughness of the materials can be improved effectively by increasing the content of the reversed austenite. After aging treatment of Cu-bearing as-quenched steel with martensitic microstructure, Cu particles precipitate at the boundary of martensitic structure and act as heterogeneous nucleation sites to promote the nucleation of reversed austenite. In order to explore the effects of different alloying elements on heterogeneous nucleation of reversed austenite on Cu particles, the effects of &lt;i&gt;X&lt;/i&gt; (&lt;i&gt;X&lt;/i&gt; = Cr, Al, Mo, W, Ni, Co, Mn) on the interfacial properties of Cu/&lt;i&gt;γ&lt;/i&gt;-Fe are studied via first-principles method. The adhesion work, interfacial energy and electronic structure of the interfaces before and after the replacement of Cu and Fe atoms at Cu/&lt;i&gt;γ&lt;/i&gt;-Fe boundaries are calculated. The results show that when the alloying elements replace Cu atoms at the Cu/&lt;i&gt;γ&lt;/i&gt;-Fe interface, strong &lt;i&gt;X&lt;/i&gt;—Fe covalent bond forms at the Cu/&lt;i&gt;γ&lt;/i&gt;-Fe interface, the adhesion work increases and the interfacial energy decreases, and thus improve the heterogeneous nucleation capability of reverted &lt;i&gt;γ&lt;/i&gt;-Fe on Cu particles. When Fe atoms at the interface are replaced, the stability of the interface changes little, and the bonding between the doped atoms and the neighboring atoms is weak.

A Comparison Study on the Strengthening and Toughening Mechanism between Cu-Bearing Age-Hardening Steel and NiCrMoV Steel.

Cu-bearing age-hardening steel has significant potential in shipbuilding applications due to its excellent weldability as compared to conventional NiCrMoV steel. Not much research has been carried out to analyze the differences in the mechanisms of strength and toughness between Cu-bearing age-hardening and NiCrMoV steel. Both steels were heat treated under the same conditions: they were austenized at 900 °C and then quenched to room temperature, followed by tempering at 630 °C for 2 h. The uniaxial tensile test reveals that the Cu-bearing age-hardening steel exhibits relatively lower strength but larger plasticity than NiCrMoV steel. The lower contents of Carbon and other alloying elements is one of possible reasons for these differences in mechanical properties. Transmission Electron Microscope observations show that two types of precipitates, Cr carbides and Cu-rich particles, exist in tempered Cu-bearing age-hardening steel. Cu-rich particles with sizes of 20–40 nm can inhibit the dislocation motion during deformation, which then results in dislocation pile ups and multiplication; this makes up the strength loss of Cu-bearing age-hardening steel and simultaneously improves its plasticity.

Effects of Ti and Cu Addition on Inclusion Modification and Corrosion Behavior in Simulated Coarse-Grained Heat-Affected Zone of Low-Alloy Steels.

In this paper, the effects of Ti and Cu addition on inclusion modification and corrosion behavior in the simulated coarse-grained heat-affected zone (CGHAZ) of low-alloy steels were investigated by using in-situ scanning vibration electrode technique (SVET), scanning electron microscope/energy-dispersive X-ray spectroscopy (SEM/EDS), and electrochemical workstation. The results demonstrated that the complex inclusions formed in Cu-bearing steel were (Ti, Al, Mn)-Ox-MnS, which was similar to that in base steel. Hence, localized corrosion was initiated by the dissolution of MnS. However, the main inclusions in Ti-bearing steels were modified into TiN-Al2O3/TiN, and the localized corrosion was initiated by the dissolution of high deformation region at inclusion/matrix interface. With increased interface density of inclusions in steels, the corrosion rate increased in the following order: Base steel ≈ Cu-bearing steel < Ti-bearing steel. Owing to the existence of Cu-enriched rust layer, the Cu-bearing steel shows a similar corrosion resistance with base steel.

Refinement of Cu-M2C precipitates and improvement of strength and toughness by Ti microalloying in a Cu-bearing steel

The present work aims to unravel the effect of Ti microalloying on the refinement of co-precipitated nanoscale Cu and M2C carbides, and thereby the improvement of both strength and toughness of an ultrahigh-strength Fe-0.05C-1.3Cu steel. The co-precipitated Cu and M2C carbides in Ti-free and Ti-containing steels was characterized after quenching and aging treatment via atom probe tomography (APT), and their contribution to the yield strength was quantified. APT results show that after being aged at 550 °C for 1 h, nanoscale Cu particles and M2C carbides co-precipitated. And, the density of finer Cu was found to be higher in the Ti-containing steel than that in the Ti-free steel which can produce more nucleation sites for M2C carbides precipitation. After being aged at 550 °C for 1 h, the Ti-containing steel had a yield strength as high as 1055 MPa, and an impact toughness of 132 J at −40 °C, which was an improvement of 61 MPa and 27 J, respectively, in comparison to the Ti-free steel. The higher-density M2C carbides were found to contribute to precipitation strengthening enhancement. The co-precipitation strengthening contribution from the Cu-M2C precipitates of the Ti-containing steel was calculated to be 69 MPa higher than that of the Ti-free steel. This is similar to the difference of 61 MPa from the experiment. The high toughness of Ti-containing steel is attributed to a higher density of high angle grain boundaries and a smaller prior austenite grain size by deflecting crack propagation.

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.

Cu Precipitation Behaviors and Microscopic Mechanical Characteristics of a Novel Ultra-Low Carbon Steel.

We studied the effect of Cu addition on the hardness of ultra-low carbon steels heat treated with different cooling rates using thermal simulation techniques. The microstructural evolution, Cu precipitation behaviors, variations of Vickers hardness and nano-hardness are comparatively studied for Cu-free and Cu-bearing steels. The microstructure transforms from ferritic structure to ferritic + bainitic structure as a function of cooling rate for the two steels. Interphase precipitation occurs in association with the formation of ferritic structure at slower cooling rates of 0.05 and 0.2 °C/s. Coarsening of Cu precipitates occurs at 0.05 °C/s, leading to lower precipitation strengthening. As the cooling rate increases to 0.2 °C/s, the interphase and dispersive precipitation strengthening effects are increased by 63.9 and 50.0 MPa, respectively. Cu precipitation is partially constrained at cooling rate of 5 °C/s, resulting in poor nano-hardness and Young’s Modulus. In comparison with Cu-free steel, the peak Vickers hardness, nano-hardness and Young’s Modulus are increased by 56 HV, 0.61 GPa and 55.5 GPa at a cooling rate of 0.2 °C/s, respectively. These values are apparently higher than those of Cu-free steel, indicating that Cu addition in steels can effectively strengthen the matrix.

On the role of Cu addition in toughness improvement of coarse grained heat affected zone in a low carbon high strength steel

In this article, the coarse grained heat affected zone (CGHAZ) of a low carbon high strength steel was simulated at two heat inputs on a Gleeble-3800 thermo-mechanical simulator. A comparative study was conducted to reveal the role of Cu addition in toughness improvement by microstructure characterization and Charpy impact test. Microstructure observation suggested that there is no observable difference in the microstructure and prior austenite grain size between Cu-free steel and Cu-bearing steel, but a higher density of high-angle grain boundary (HAGB) was obtained in Cu-bearing steel with 50 kJ/cm. This was intrinsically associated with the configuration of three Bain groups from the aspect of crystallography. The optimum configuration can be achieved by adjusting transformation driving force, cooling rate and nucleation characteristics during martensite/bainite transformation. In this study, Cu addition played a determining role in increasing transformation driving force at high cooling rate, and altering the diffusion kinetics of alloying elements at low cooling rate. Accordingly, the density of HAGB can be optimized to be beneficial for high toughness in CGHAZ. Therefore, the optimum toughness was obtained in Cu-bearing steel with heat input of 50 kJ/cm, which was featured by the impact energy of ~ 198 J at − 40 °C.

Synergetic utilization of copper slag and ferruginous manganese ore via co-reduction followed by magnetic separation process

Attempts to economically and effectively treat copper slag (CS) and ferruginous manganese ore(FMO) using the traditional direct reduction–magnetic separation process have faced many challenges, such as low levels of metal recovery, poor cost-effectiveness and the need for a high proportion of additives. This paper proposes an eco-friendly process to synchronously utilise copper slag and ferruginous manganese ore by co-reduction followed by a magnetic-separation process to solve those problems. In the process, MnO2 within FMO acted as a catalyst to promote the reduction of fayalite and copper sulphide contained in CS, and thus improve the metallisation rate of Fe and Cu. Meanwhile, CS, possessing the low melting point, can enables more liquid phase generation and improve the growth of alloy particle, which is beneficial for the full liberation of Fe–Cu alloy. Under the optimum conditions, A crude Fe–Cu alloy powder containing 88.83% Fe and 1.07% Cu was prepared, which can be used in an electronic furnace to produce Cu-bearing steels. A high recovery of 85.89% Fe and 87.74% Cu can be obtained using this process, thereby confirming its efficiency. Additionally, Mn contained in the ferromanganese ore was enriched into the magnetic tailing in the form of low-valence manganese (II) oxides, which can be easily extracted by acid leaching. Moreover, the mechanism involved in the co-reduction of CS and FMO was investigated by XRD, SHTT and SEM-EDS techniques, which further confirmed the complementary advantages about an organic integration of CS and FMO can realise the efficient beneficiation of the valuable metals from them.

High-resolution Transmission Electron Microscopy Characterization of the Structure of Cu Precipitate in a Thermal-aged Multicomponent Steel

High-dispersed nanoscale Cu precipitates often contribute to extremely high strength due to precipitation hardening, and whereas usually lead to degraded toughness for especially ferritic steels. Hence, it is important to understand the formation behaviors of the Cu precipitates. High-resolution transmission electron microscopy (TEM) is utilized to investigate the structure of Cu precipitates thermally formed in a high-strength low-alloy (HSLA) steel. The Cu precipitates were generally formed from solid solution and at the crystallographic defects such as martensite lath boundaries and dislocations. The Cu precipitates in the same aging condition have various structure of BCC, 9R and FCC, and the structural evolution does not greatly correlate with the actual sizes. The presence of different structures in an individual Cu precipitate is observed, which reflects the structural transformation occurring locally to relax the strain energy. The multiply additions in the steel possibly make the Cu precipitation more complex compared to the binary or the ternary Fe–Cu alloys with Ni or Mn additions. This research gives constructive suggestions on alloying design of Cu-bearing alloy steels.

Effect of Ni and Cu Addition on Corrosion Behaviors of Pre-Oxidized Ultra-Strong Steel for Automotive Applications

The incomplete elimination of oxide scale formed during the normalizing process can result in severe degradation of the surface and mechanical properties of ultra-strong steels. This study revealed that the formation of oxide scale was highly dependent upon the alloying elements Ni and Cu. Ni-bearing steel showed a much higher oxidation rate, resulting in much thicker scale than Cu-bearing steel. Uneven scale/steel interfaces and oxide penetration along the grain boundary of the steel were clearly observed in the Ni-bearing steel. The difference in the solid solubility limit of Ni and Cu to austenite could lead to the enrichment of Ni and precipitation of Cu at scale/steel interfaces in the two types of steels, respectively. This resulted in the different structure and properties of the oxide scales, which influenced the subsequent corrosion behavior in chloride containing conditions. Linear polarization resistance measurements showed that the addition of Ni and Cu to the steel had a beneficial influence on the corrosion resistance, by suppressing the anodic dissolution and cathodic reduction reactions of Ni and Cu-bearing steels, respectively. This study provided a proposed mechanism for the difference in corrosion behaviors between the two types of steel. Key words: nickel, copper, steel, oxidation scale, corrosion

Hydrogen-Induced Cracking Resistance of Novel Cu-Bearing Pipeline Steels

Hydrogen-Induced Cracking Resistance of Novel Cu-Bearing Pipeline Steels

Aging characteristics and strengthening behavior of a low-carbon medium-Mn Cu-bearing steel

We describe here the aging characteristics and strengthening behavior of a low-carbon medium-Mn Cu precipitation-strengthened steel. Atom probe tomography (APT) was employed to characterize the evolution of Cu-rich precipitates in terms of mean radius, number density and volume fraction. Aging at 500 °C and 550 °C for 1 h resulted in substantial coherent body-centered cubic (bcc) Cu-rich precipitates with mean radius of 1.35 and 2.59 nm, respectively. The precipitation strengthening mechanism for these two aging conditions was shearing mechanism and the corresponding strengthening contribution was ~ 266 and ~ 312 MPa, respectively. Here, coherency strengthening and modulus strengthening played a major role, while the contribution of chemical strengthening was relatively small. With increased aging temperature to 600 °C, the precipitates grew and coarsened to elongated shape with incoherent face-centered cubic (fcc) structure, and the strengthening mechanism was Orowan mechanism with a contribution of ~ 232 MPa. Increasing the aging temperature also facilitated the formation of retained austenite, which was of great benefit to plasticity without pronounced deterioration on precipitation strengthening. Ultra-high yield strength of 1020 MPa with superior total elongation of 25.8% was obtained in the sample aged at 600 °C for 1 h. The excellent mechanical properties derived from the combination of precipitation strengthening by Cu-rich precipitates and plasticity effect of retained austenite can be considered as a design principle to simultaneously optimize strength and ductility.

Quantitative analysis of microstructure and impact toughness in the simulated coarse-grained heat-affected zone of Cu-bearing steels

ABSTRACTBecause of 0.32% Cu addition, the inclusion is modified from Al-Ti oxide covered with layer of MnS in Cu-free steel to Al-Ti oxide with shell of (Mn,Cu)S in Cu-bearing steel. The quantitative result reveals that the frequency of inclusion effectively for acicular ferrite nucleation, fraction of acicular ferrite and high angle grain boundary in the simulated coarse-grained heat-affected zone (CGHAZ) of Cu-bearing steel are higher than that of Cu-free steel, respectively. Therefore, the high density of acicular ferrite microstructures in CGHAZ of Cu-bearing steel with smaller crystallographic grain size has superior impact toughness than that in Cu-free steel.