Effect of Nanoscale Cu-Riched Clusters on Strength and Impact Toughness in a Tempered Cu-Bearing HSLA Steel

The effect of Cu-riched clusters on strength and impact toughness in a tempered Cu-bearing high-strength low-alloy(HSLA)steel is investigated. With increasing the tempering temperature, it is found that the yield strength increases firstly, achieving the maximum value(~ 1053 MPa) at the tempering temperature of 450 ℃, and then decreases significantly with the rise of tempering temperature. The tempering temperature-dependent yield strength is closely related to the precipitation of Cu-riched clusters. When tempering at 450 ℃, the peak strength will be reached as the nanoscale Cu-riched clusters with small size and high number density will cause a strong precipitation strengthening(~ 492 MPa) due to the dislocation shearing mechanism. However, the Cu-riched clusters will coarsen with further increasing tempering temperature, resulting in obvious decrement of yield strength owing to the dislocation bypassing mechanism. Compared with the yield strength,the variation in impact energy displays an inverse tendency and the impact energy is only 7 J for the sample tempered at 450 ℃. The fracture mode can be well explained by the competition between the cleavage fracture strength( σ F) and “yield strength”( σ Y). Although transgranular cleavage fracture can be found in samples tempered at 450 and 550 °C, the crack propagation along the lath boundaries is prevented in the sample tempered at 550 ℃. The reason is that the number density of Cu-riched clusters at lath boundaries decreases and the segregation of Mo element at the lath boundaries is induced,which will increase the bonding energy.

Geochemical Characteristics,Genesis of Concealed Cu-rich Ore Body in the Jinchuan Deposit,Northwestern China,and Its Prospecting

The Jinchuan deposit is hosted by the olivine-rich ultramafic rock body, which is the thirdlargest magmatic sulfide Ni-Cu deposit in the world currently being exploited. Seeking new relaying resources in the deep and the border of the deposit becomes more and more important. The ore body, ore and geochemistry characteristics of the concealed Cu-rich ore body are researched. Through spatial analysis and comparison with the neighboring II1 main ore body, the mineralization rule of the concealed Cu-rich ore body is summed up. It is also implied that Cu-rich magma may exist between Nirich magma and ore pulp during liquation differentiation in deep-stage chambers, which derives from deep-mantle Hi-MgO basalt magma. It is concluded that the type of ore body has features of both magmatic liquation and late reconstruction action. It has experienced three stages： deep liquation and pulsatory injection of the Cu- and PPGE-rich magma, concentration of tectonic activation, and the later magma hydrothermal superimposition. In addition, the Pb and S isotopes indicate the magma of I6 concealed Cu-rich ore body originates predominantly from mantle; however, it is interfused by minute crust material. Finally, it is inferred that the genesis of the Cu-Ni sulfide deposit is complex and diverse, and the prospect of seeking new deep ore bodies within similar deposits is promising, especially Cu-rich ore bodies.

Study of Cu-rich phase precipitation in austenitic antibacterial stainless steel

Cu precipitation behaviors in two Cu-bearing austenitic antibacterial stainless steels,type 304 and type 317L,were systematically studied by using relatively simple methods for materials analysis,including micro-hardness,electrical resistivity,electrochemical impedance spectroscopy,X-ray diffraction and differential scanning calorimetry.The results indicated that after aging at elevated temperature,the micro-hardness, electrical resistivity,electrochemical impedance and lattice constant of the steel were all varied at different degrees due to the precipitation and growth of Cu-rich phases.The results also showed that the heat evolution during the process of Cu precipitation could be sensitively detected by means of differential scanning calorimetry,obtainning the starting temperature,peak temperature,peak area of the Cu-rich precipitation,and even the activation energy by calculation.The results confirmed that the Cu-rich phased precipitation in the Cu-bearing austenitic antibacterial stainless steel should be a thermal activation process controlled by Cu diffusion.All the materials analysis methods used in this study can be more simple and effective for application in R & D of the Cu-bearing antibacterial stainless steels.

BEHAVIOUR OF Co_5Cr_3Si_2 PHASE IN Cu-RICH ALLOYS CONTAINING Co,Cr AND Si

The major phases in the Cu-rich alloys containing Co,Cr and Si are α-Cu(a solid solution of Co,Cr and Si in Cu),χ-phase(Co_5Cr_3Si_2)and Co_2Si.In comparison with reference sample,it has been detected that the crystal structure of Co_5Cr_3Si_2 is cubic,α-Mn type with a=0.8694 nm.The melting temperature of χ-phase and the alloy are higher than that of the pure Cu,namely,1535 and 1389 K respectively.During ageing treatment,the Co_2Si phase precipitates out from α-Cu and χ-phase simultaneously,but the hardening effect is mainly contributed by the precipitation from α-Cu.

Genome-wide characterization of graft-transmissible mRNA-coding P450 genes of cucumber(Cucumis sativus L.)

P450(cytochrome P450)is a supergene family,which is involved in various metabolic pathways in plants.Based on previous study,we found some of cucumber P450 mRNAs were systemic mobile in cucumber/pumpkin grafts.However,the reason that why P450 mRNAs were endorsed as signaling,and what specific motif(s)did they harbored is not clear yet.Here,we first identified 221 CsaP450 genes in cucumber genomewide level.Combining with graft-transmissiblemRNAs datasets in cucumber,we elucidated 15mobile-CsaP450-coding genes,of which 5 and 10 belonged to A-type and non-A type respectively.Compared with Arabidopsis and pumpkin(Cucubit moschata)graft-induced-transmissible P450 mRNAs,a phylogenetic treewas constructed and divided into eight clans by usingmultiple-sequence alignment.Gene ontology(GO)enrichment and Kyoto Encyclopedia of Genes and Genomes(KEGG)annotations indicated that the expression patterns of the mobile-mRNA-coding CsaP450 genes in different tissues of cucumber was specifically enriched in oxidoreductase activity and secondary metabolic pathways.The structures and motifs of these 15 mobile-mRNA-coding CsaP450 genes and their types of regulatory elements told that the proportion of CU-rich motifs was higher than nonmobile-mRNA-coding CsaP450 genes.The integrated analysis of mobility direction and mRNA abundance of 15 mobilemRNA-coding CsaP450 genes allowed to conclude that there was rarely relationship between them.The study provided a new insight into the relationship between the motifs and functional characterization of mobile-mRNA-coding P450 genes of cucumber in genome-wide levels.

Effect of annealing treatment on microstructures and properties of austenite-based Fe-28Mn-9Al-0.8C lightweight steel with addition of Cu

The mechanical properties of an austenite-based Fe-Mn-Al-C lightweight steel were improved by co-precipitation of nanoscale Cu-rich and κ-carbide particles.The Fe-28Mn-9Al-0.8C-(0,3)Cu (wt.%) strips were near-rapidly solidified and annealed in the temperature range from 500 ℃ to 700 ℃.The microstructure evolution and mechanical properties of the steel under different annealing processes were studied.Microstructural analysis reveals that nanoscale κ-carbides and Cu-rich particles precipitate in the austenite and ferrite of the steel in this annealing temperature range.Co-precipitation of nanoscale Cu-rich particles and κ-carbides provides an obvious increment in the yield strength.At the annealing temperature of 600 ℃,both the yield strength and ultimate tensile strength of Fe-28Mn-9Al-0.8C-3Cu (wt.%) steel strip are the highest.The total elongation is 25%,which is obviously higher than that of Cu-free steel strips,for the addition of Cu reduces the large sized κ-carbides precipitated along austenite/ferrite interfaces.When the annealing temperature rises to 700 ℃,the strength and ductility of the two steel strips deteriorate due to the formation of massive intergranular κ-carbides precipitated along austenite/ferrite interfaces.It can be concluded that a proper co-precipitation of Cu-rich particles and κ-carbides would improve the properties of austenite-based Fe-Mn-Al-C steel.

Nanometer Stripe Microstructure of Supersaturated Solid Solution in Fe-Cu Alloy

Strengthening due to precipitation of Cu in the a-Fe matrix is an important phenomenon utilized in the design of HSLA steels. In the present work, the microstructure of supersaturated solid solution in Fe-1.18%Cu binary alloy was investigated by means of high resolution electron microscopy. The results indicated that the solid solution was heterogeneous, there were lots of Cu atom clusters, which consisted of diffractive stripe microstructure similar to twin crystal. Orientation deviation was observed between two （110）o planes in diffractive stripes, which results in light and shade contrast. Furthermore, formation mechanisms of the nanometre stripe microstructure were discussed in terms of the interaction of Cu and Fe atoms in the Fe-Cu binary alloys.

Effect of Pre-Deformation Enhanced Thermal Aging on Precipitation and Microhardness of a Reactor Pressure Vessel Steel

Microstructure evolution in neutron irradiated Reactor Pressure Vessel （RPV） steels was experimentally simulated through an improved degradation procedure in this study. The degradation procedure includes austenitizing at 1 150℃ and water quench, deformation 10% and 30% respectively, and then thermal aging at 500℃ for different period of time. The microstructure of the specimens was analyzed in details using transmission electron microscopy （TEM）. The micro-hardness test results showed that all the hardness curves of undeformed, 10% pre-deformed and 30% pre-deformed specimens have two micro-hardness peaks with the first peak value corresponding to different thermal aging time of 1 hour, 5 hours and 10 hours, respectively. It was revealed that the hardness curves were influenced by the precipitation of Cu-rich precipitates （CRPs） and carbides, deposition of martensite and work hardening.

EFFECT OF COPPER ADDITION ON MECHANICAL PROPERTIES OF 4Cr16Mo

Experiments conducted to determine the effect of copper addition on the machinability of plastic mold steel, 4Cr16Mo, were presented. The machinability of mold steel 4Cr16Mo was visibly improved by adding Cu. The top wear of 4Cr16Mo with copper was less than that without copper. The Cu-rich phase had the effect of a lubricant and the heat conductivity, which reduced cutting-tool wear, improved machinability, and increased the service life of the cutting-tool. Increasing of copper addition decreased the hot-working character of 4Cr16Mo. The optimal hot-working parameters for 4Cr16Mo with copper were determined by the tensile test and the compression test. The rate of deformation should be adopted as 0.6 s-1. The heating-up temperature, initial forging temperature, and terminal forging temperature were 1200℃, 1150℃, and 950℃, respectively.

Effects of Al and Ni on copper-rich phases in the scale/steel interface after high-temperature oxidation of copper-containing steel

A study was conducted on the formation of a Cu-rich phase at the scale/steel interface of Cu-containing steel by high-temperature oxidation with varying amounts of A1 and Ni. Both A1 and Ni were found to help decrease the amount of the Cu-rich phase at the interface. Analysis of the effects by these elements was conducted in terms of the melting point of the Cu-rich phase, the solid solubility of Cu in austenite, the rate of oxidation, and the amount of Cu-rich phase occlusions in scales. Because of selective oxidation,in which A1 and Ni are oxidized more and less preferentially than Fe, respectively, A1 was weakly concentrated at the interface whereas Ni was more heavily concentrated in it. Thus, A1 exerted no effect on the melting point of the Cu-rich phase, whereas Ni raised its melting point. A1, which was applied at contents of less than 2.0%, decreased the solubility of Cu in austenite but this effect weakened at the interface during oxidation. By contrast,Ni increased the solubility of Cu, and this effect was strengthened with oxidation. Both A1 and Ni promoted internal oxidation and the formation of occlusions.

Effect of Cu Content on Aging Precipitation Behaviors of Cu-Rich Phase in Fe-Cr-Ni Alloy

The precipitation characteristics and effect on strengthening mechanism of Cu-rich phases during short-time and long-time aging for Super 304H steels with different Cu content were investigated using X-ray diffraction （XRD）, scanning electron microscope （SEM） and transmission electron microscope （TEM）. The results show that the size of Cu-rich phase particles increases, the interspace of Cu-rich phase particles decreases and the density of Curich phases increases with the increase of Cu content during short-time aging （approximately 800 h） at 650℃ for Super 304H steels. During long-time aging （more than 2 000 h） at 650 ℃, Cu-rich phase precipitates sufficiently and the strengthening effect of Cu-rich phase is preferable in Super 304H steel containing Cu of 4%. The strengthening effect of Cu-rich phase in Super 304H steels containing Cu of 2.2% or 5% is weaker than that with Cu of 4% during long-time aging （more than 2 000 h）.

Strengthening effect of Cu-rich phase precipitation in 18Cr9Ni3CuNbN austenitic heat-resisting steel

The Cu-containing austenitic heat-resistant steel 18Cr9Ni3CuNbN, which is being used as superheater and reheater tube material for modern ultra-super-critical （USC） power plants all over the world, has been investigated at 650 ℃ long time aging till 10 000 h. SEM, TEM and 3DAP （three dimensional atom probe） have been used to follow microstructural changes with mechanical property variations. Experimental results show that Cu-rich phase and MX precipitate in the grains as well as M 23 C 6 precipitates at grain boundaries are the main precipitation strengthening phases in this steel. Among them Cu-rich phase is the most important strengthening phase. Homogeneous distribution of very fine nano-size Cu-rich phase has been formed at very early stage of 650 ℃ aging （less than 1 h）. Cu atoms gradually concentrate to Cu-rich particles and the other elements （such as Fe, Cr, Ni etc） diffuse away from Curich particles to γ-matrix with the increasing of aging time at 650 ？ C. The growth rate of Cu-rich phase at 650 ℃ long time aging is very slow and the average diameters of Cu-rich phase have been determined by TEM method. Cu-rich phase keeps in about 30 nm till 650 ℃ aging for 10 000 h. It shows that nano-size Cu-rich phase precipitation strengthening can be kept for long time aging at 650 ℃ because of its excellent stability at high temperatures. According to structure stability study and mechanical properties determination results the Cu-rich phase precipitation sequence and its strengthening mechanism model have been suggested and discussed.

Crystal Structure Evolution of the Cu-rich Nano Precipitates from bcc to 9R in Reactor Pressure Vessel Model Steel

The crystal structure evolution of the Cu-rich nano precipitates from bcc to 9R during thermal aging was studied in nuclear reactor pressure vessel （RPV） model steels. The specimens, contained higher copper and nickel contents than commercially available one, were heated at 890 ~C for 0.5 h and then water quenched followed by tempering at 0（50 ~C for I0 h and aging at 400 ~C for 1000 h. It was observed that bcc and 9R orthogonal structure, as well as 9R orthogonal and 9R monoclinic structure, coexist in a single Cu-rich nano precipitate. Further analyses pointed out that Cu-rich nano precipitates of bcc structure were not stable, it may preferentially transform to 9R orthogonal structure and then to 9R monoclinic structure. This results showed that the crystal structure evolution of the Cu-rich nano precipitates was complex.

Compositional Variants of Cu-rich Precipitate in Thermally Aged Ferritic Steel

Atom probe tomography was utilized to investigate Cu precipitation in a high-strength low-alloy steel isothermally aged at 500℃ for 1, 4, 16, and 64 h after water-quenching from 900℃. With prolonged aging time, the Curich precipitates（CRPs） increased in size and decreased in number density, and gradually evolved from spheroidal to elliptical in morphology. The small CRPs were rich in a high amount of Fe and a certain amount of Ni and Mn at their early nucleation stage. The large CRPs with increased size due to extensive aging contained less Fe and more Cu at their later growth stage. Additionally, Ni and Mn were both readily to segregate at the CRP/matrix heterophase interfaces, and Mn was higher in content than Ni in the precipitate interior especially when the CRPs were large in size.

Ni-Based Metallic Glass Composites Containing Cu-Rich Crystalline Nanospheres

In this work, a quaternary Ni-Cu-Nb-Ta system has been designed to obtain composite microstructure with sphericalcrystalline Cu-rich particles embedded in amorphous Ni-rich matrix. The alloy samples were prepared by using single-roller melting-spinning method. The microstructure and thermal properties of the as-quenched alloy samples were char-acterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, anddifferential scanning calorimetry. It shows that the spherical crystalline Cu-rich particles are embedded in the amorphousNi-rich matrix. The average size of the Cu-rich particles is strongly dependent upon the Cu content. The effect of the alloycomposition on the behavior of liquid-liquid phase separation and microstructure evolution was discussed. The phaseformation in the Ni-based metallic glass matrix composite was analyzed.

Effect of Cu-Rich Phase Precipitation on the Microstructure and Mechanical Properties of CoCrNiCux Medium-Entropy Alloys Prepared via Laser Directed Energy Deposition

CoCrNiCux(x=0.16,0.33,0.75,and 1)without macro-segregation medium-entropy alloys(MEAs)was prepared using laser directed energy deposition(LDED).The microstructure and mechanical properties of CoCrNiCux alloys with increasing Cu content were investigated.The results indicate that a single matrix phase changes into a dual-phase structure and the tensile fracture behaviors convert from brittle to plastic pattern with increasing Cu content in CoCrNiCux alloys.In addition,the tensile strength of CoCrNiCux alloys increased from 148 to 820 MPa,and the ductility increased from 1 to 11%with increasing Cu content.The nano-precipitated particles had a mean size of approximately 20 nm in the Cu-rich phase area,and a large number of neatly arranged misfit dislocations were observed at the interface between the two phases due to Cu-rich phase precipitation in the CoCrNiCu alloy.These misfit dislocations hinder the movement of dislocations during tensile deformation,as observed through transmission electron microscopy.This allows the CoCrNiCu alloy to reach the largest tensile strength and plasticity,and a new strengthening mechanism was achieved for the CoCrNiCu alloy.Moreover,twins were observed in the matrix phase after tensile fracture.Simultaneously,the dual-phase structure with different elastic moduli coordinated with each other during the deformation process,significantly improving the plasticity and strength of the CoCrNiCu alloy.

Phase precipitation and corrosion properties of copper-bearing ferritic stainless steels by annealing process

The effects of different annealing processes on the phase precipitation behavior and corrosion properties of copper-bearing 430 ferritic stainless steel were systematically investigated.The shape,quantity and distribution of copper-rich precipitates by different annealing processes were characterized by scanning electron microscopy,transmission electron microscopy,backscatter electron and backscatter diffraction.The pitting resistance behavior in simulated physiological saline envi-ronments(0.9 wt.%NaCl)was investigated using electrochemical workstation and X-ray photoelectron spectroscopy.The results showed that the copper-rich phase prepared by repeated rolling and annealing gradually changed from long needle-like to short thick rod-like and granular,whose distribution tended to be uniform and diffusive,and the number of copper-rich phases increased.After solution/antibacterial annealing process,the size and density of the copper-rich phase increase,resulting in a discontinuity of the passivation film on the stainless steel,which reduces the pitting resistance to some extent.The refinement mechanism revealed that pre-deformation brings about a modification in both precipitation mechanism and growth kinetics of epsilon copper.

Effect of heat treatment on corrosion resistance and antibacterial ability of 0Cr15Ni5Cu3Mo carbon steel

Before and after heat treatment,0Cr15Ni5Cu3MoN stainless steel(SS)samples were immersed in sulfate-reducing bacteria(SRB)environment to study the effect of heat treatment on the antimicrobial properties of Cu-containing stainless steel.The effect of heat treatment on the corrosion resistance and antibacterial ability of 0Cr15Ni5Cu3MoN SS was studied by scanning electron microscopy,transmission electron microscopy,laser scanning confocal microscopy,and electrochemistry.The results show that 0Cr15Cu3 SS has better antibacterial properties with fewer bacteria adsorbed on the surface after heat treatment,and its corrosion resistance is significantly improved.Interestingly,on the 7th day of immersion,the corrosion resistance of the heat-treated stainless steel was lower than that of the rolled stainless steel.This was due to the fact that the rolled samples were protected by biofilm at this time,while the surface bacteria on the heat-treated samples died,resulting in the exposure of the substrate surface and thus reducing the corrosion resistance of the heat-treated samples.Thus,because of the strong bactericidal properties of the heat-treated Cu-containing stainless steel,the corrosion resistance of the samples suddenly decreases in the middle stage of corrosion,and this discovery provides a new view to study the corrosion process of Cu-containing stainless steel in the SRB environment.

Microbial corrosion resistance of a novel Cu-bearing pipeline steel

Microbiologically influenced corrosion(MIC) is becoming a serious problem for buried pipelines. Developing environmentally friendly strategies for MIC control is increasingly urgent in oil/gas pipeline industry.Copper(Cu) in steels can not only provide aging precipitation strengthening, but also kill bacterium,offering a special biofunction to steels. Based on the chemical composition of traditional X80 pipeline steel, two Cu-bearing pipeline steels(1% Cu and 2% Cu) were fabricated in this study. The microstructure,mechanical properties and antibacterial property against sulphate-reducing bacteria(SRB) and Pseudomonas aeruginosa(P. aeruginosa) were studied. It was found that the novel pipeline steel alloyed by 1%Cu exhibited acicular ferrite microstructure with nano-sized Cu-rich precipitates distribution in the matrix, resulting in better mechanical properties than the traditional X80 steel, and showed good MIC resistance as well. The pitting corrosion resistance of 1% Cu steel in as-aged condition was significantly better than that of X80 steel. A possible antibacterial mechanism of the Cu-bearing pipeline steel was proposed.

Cu-assisted austenite reversion and enhanced TRIP effect in maraging stainless steels

Control of the formation and stability of reverted austenite is critical in achieving a favorable combination of strength,ductility,and toughness in high-strength steels.In this work,the effects of Cu precipitation on the austenite reversion and mechanical properties of maraging stainless steels were investigated by atom probe tomography,transmission electron microscopy,and mechanical tests.Our results indicate that Cu accelerates the austenite reversion kinetics in two manners:first,Cu,as an austenite stabilizer,increases the equilibrium austenite fraction and hence enhances the chemical driving force for the austenite formation,and second,Cu-rich nanoprecipitates promote the austenite reversion by serving as heterogeneous nucleation sites and providing Ni-enriched chemical conditions through interfacial segregation.In addition,the Cu precipitation hardening compensates the strength drop induced by the formation of soft reverted austenite.During tensile deformation,the metastable reverted austenite transforms to martensite,which substantially improves the ductility and toughness through a transformation-induced plasticity(TRIP)effect.The Cu-added maraging stainless steel exhibits a superior combination of a yield strength of~1.3 GPa,an elongation of~15%,and an impact toughness of~58 J.