Cr Steel Research Articles

Microstructure and properties of WC–Co cemented carbide/40Cr steel joints brazed at low–temperature with Ag–Cu–In–Ti filler alloy

WC–Co cemented carbide/steel brazed at low–temperature is of significant scientific and technical interest. In this study, the interface microstructure between the filler alloy and WC–Co and 40Cr steel, the formation process of the joint microstructure, and the effect of brazing temperature on the microstructure and properties of joints were systematically studied. The filler alloy was bonded by forming a TiC reaction layer with WC–Co and 40Cr steel, which enhanced the retention of the filler layer on the joint. The microstructure of the joint was a WC–Co/TiC reaction layer/TiCo reaction layer/Cu2InTi + eutectic structure (Ag [s, s] + Ag–doped Cu7In3 + Cu4In) + Cu [s, s]/TiC reaction layer/40Cr steel. Moreover, the maximum average shear strength of the joint (brazed at 740 °C) reached 258 MPa, which is approximately 60% higher than those reported in the literature. The fracture behavior of the joint was mainly affected by the distribution of the Cu2InTi intermetallic compounds in the filler layer and the diffusion of Co from the cemented carbide.

Tribological and electric contact resistance properties of pulsed plasma duplex treatments on a low alloy steel

Low friction low cost tribology systems involve most often use of lubricants, which must be periodically refurbished and often present environmental issues. Furthermore, use of liquid lubricants is a non-starter in many critical applications.In this work, the performance of single process duplex tribo-conditioning treatments is explored. The treatments are based on pulsed low-pressure plasma treatments, where nitriding processes are complemented with the deposition of carbonaceous solid lubricating top layers. The duplex treatments are carried out sequentially in the same chamber.The study comprised, among others, exploring the use of different residual gas mixes and pulse frequencies. Roughened blasted 42CrMo4 low alloy steel (AISI 4140 equivalent) was used as substrate. Resulting surface properties were studied with nano-indentation, profilometry and contact angle measurements. Besides, tribological studies were carried out against 100Cr6 steel at different humidities. The evolution of the coefficient of friction and the electrical contact resistance (ECR) was assessed for each test, as well as the wear rates.Results showed tribological outcomes heavily dependent of ambient conditions, and ECR of the wear track surface condition, i.e. the amount of remaining coated surfaces. The use of pulsed plasmas generated comparatively softer, smoother and more hydrophobic surfaces.

The effect of boron nitride nanoparticles on 100Cr6 steel's mechanical and tribological properties after vacuum heat treatment

Various heat treatment techniques have been used to enhance the mechanical and tribological properties of the substrate material. Adding BN nanoparticles into the base matrix-bearing steel helps improve tribological properties. In the present work, three different samples of the bearing material 100Cr6 are impregnated with various wt—% of boron nitride nanoparticles. The tribological properties of the fabricated specimens have been evaluated using a pin-on-disc tribometer. The pins samples of 100Cr6 were heat treated in a vacuum at 1200 °C temperature. The samples were kept inside the furnace for 10 h. The microhardness of the prepared specimen is determined using the traverse method. The microstructure and the elemental composition of the specimens are characterized using SEM and EDAX analysis.

Effect of defocused electron beam surface Ni/VC alloying on microstructure and properties of 40Cr steel

ABSTRACT The use of alloying technology can improve the surface mechanical properties of 40Cr steel and prolong its service life. In this study, the Ni/VC surface alloying modification treatment of 40Cr steel was carried out using electron beam defocusing. The results show that after defocusing electron beam treatment, the cross-section of the specimen is composed of alloying layer, heat-affected zone and matrix. When the VC content is 80%, the maximum hardness is 1030 HV0.1, which is 4.3 times higher than that of the 40Cr matrix (240 HV0.1), and the lowest coefficient of friction (COF) is 0.395, which is 1.9 times lower than that of the matrix (0.757). The wear mechanism of the matrix is mainly severe abrasive wear, and the wear mechanisms of the three specimens are mainly slight abrasive wear, slight fatigue wear and adhesive wear.

Systematic study of radiation-induced segregation in neutron-irradiated FeCrAl alloys

This work systematically reports grain boundary radiation-induced segregation (RIS), and insights into RIS mechanisms, in FeCrAl alloys. Recently, FeCrAl alloys have received significant attention as direct replacement accident tolerant fuel (ATF) claddings for light water cooled nuclear reactors, because of their corrosion and high-temperature oxidation resistance characteristics. One degradation method not studied in detail is RIS, which could sufficiently alter grain boundary chemistry, potentially compromising the superior aqueous corrosion resistance. This study focuses on candidate ATF FeCrAl alloys C06M, C35M, C36M, and C37M that are neutron irradiated to 1.8 displacements per atom (dpa) at 357°C. Grain boundary Cr enrichment and Al depletion are observed in all irradiated alloys that span the 10-13 wt.% Cr and 5-6 wt.% Al composition space. Fe will either enrich or deplete at grain boundaries to balance the grain boundary composition. The Cr enrichment is attributed to interstitial diffusion, consistent with that in body centric cubic 9-12 wt.% Cr steels. The depletion of Al occurs through the same mechanisms as α−α′ phase partitioning previously observed in FeCrAl alloys. This study underscores the need for FeCrAl alloy design to consider RIS implications on corrosion and oxidation susceptibility.

Microstructure and properties of graphene reinforced co-based composite coating by laser cladding

Graphene (Gr)-reinforced Co-based (Co50) composite coatings were prepared on 40Cr steel substrates by laser cladding technology. The effects of different amounts of Gr addition on the microstructure and mechanical properties of the coating were studied. The addition of a proper amount of Gr can improve the comprehensive properties of the coating, and most of the Gr forms carbides, such as Cr23C6 and Cr7C3, under the action of laser irradiation. The addition of Gr can significantly refine the grains and evenly distribute them. When the addition of Gr is 3 wt%, the average grain size in the coating is the smallest, which is 5.7 μm, and the highest microhardness reaches 777.5 HV0.2, which is an increase of 270.2 % compared with that of the substrate. The unmelted Gr remains dispersed in the coating, which can improve lubrication and reduce friction. The average friction coefficient and wear volume are decreased to 0.335 and 4.26 × 107 μm3, which are approximately 54.2 % and 28.0 % of those of the substrate, respectively.

Microstructure, Tensile, and Fatigue Properties of Large-Scale Austenitic Lightweight Steel.

High-Mn lightweight steel, Fe-0.9C-29Mn-8Al, was manufactured using steelmaking, ingot-making, forging, and rolling processes. After the final rolling process, a typical austenite single phase was observed on all sides of the thick plate. The microstructural changes after annealing and aging heat-treatments were observed, using optical and transmission electron microscopy. The annealed coupon exhibited a typical austenite single phase, including annealing twins in several grains; the average grain size was 153 μm. After aging heat treatment, κ-carbide was observed within the grains and on the grain boundaries. Additionally, the effect of aging heat treatment on the mechanical properties was analyzed, using a tensile test. The fine κ-carbide that precipitated within the grains in the aged coupon improved the 0.2% offset yield and the tensile stresses, as compared to the as-annealed coupon. To estimate the applicability of high-Mn lightweight steel for low-pressure (LP) steam turbine blades, a low-cycle fatigue (LCF) test was carried out at room temperature. At a total strain amplitude of 0.5 to 1.2%, the LCF life of high-Mn lightweight steel was approximately three times that of 12% Cr steel, which is used in commercial LP steam turbine blades. The LCF behavior of high-Mn lightweight steel followed the Coffin-Manson equation. The LCF life enhancement in the high-Mn lightweight steel results from the planar dislocation gliding behavior.

Thermo-Mechanical Processing as Method Decreasing Delta-Ferrite and Improving the Impact Toughness of the Novel 12% Cr Steels with Low N and High B Contents.

The universal thermo-mechanical processing including the interim long-term annealing together with forging for three 12% Cr martensitic steels with different alloying. This thermo-mechanical processing remarkably increases the impact toughness of these steels in wide temperature ranges and reduces the ductile-brittle transition temperature by 10-20 K. There is a 25 °C impact toughness of all 12% Cr steels subjected to the thermo-mechanical processing exceeds 60 J cm-2. Such an increment in impact toughness is accompanied with the significant changes in the structures of all 12% Cr steels with different alloying. The common feature for all 12% Cr steels subjected to the thermo-mechanical processing is found to be a noticeable decrease in delta-ferrite amount. In the steels containing Ta, the decrease in the mean size of prior austenite grains by 20-26% was revealed. For the 12% Cr steels with ultra-low N content, the thermo-mechanical processing provides the changes in the dispersion of M23C6 carbides and MX carbonitrides.

Optimization of Laser Shock Process Parameters for 40Cr Steel

Laser shock peening (LSP) process parameters have an important influence on the strengthening effect. In this study, theoretical calculations were used to determine a suitable range of stress wave peaks (5.09 GPa–6.36 GPa) for laser shocking, which consider the material properties of alloy steel 40Cr. In addition to theoretical calculations, the finite element numerical simulation of a single-point laser shock was also performed. The residual stresses of specimens under different shock pressure waves were simulated, and then the optimal pulse width was determined as 20 ns and the optimal pulse energy was determined as 10 J. Finally, the influences of different pulse energies on the microhardness, residual stress, microstructure, and shock-affected layer thickness of metallic materials were comprehensively investigated through experiments, and the optimization of the laser shock energy was proved to be 10 J. An optimized combination of parameters of a single-point laser shock for 40Cr was obtained, in which the spot diameter was 3 mm, the pulse width was 20 ns, and the pulse energy was 10 J. The study has implications for the selection of LSP process parameters for alloy steels.

Micromechanical Properties of Reactive HiTUS TiNbVTaZrHf–N Coatings on Different Substrates

Abstract High entropy ceramic coatings, including multicomponent transition metal nitrides called also high entropy nitrides (HEN), are usually deposited using reactive arc and/or DC magnetron (co)sputtering. High Target Utilization Sputtering (HiTUS) was not applied in HEN systems up to now. Subsequently, the mechanical properties of HEN coatings prepared by HiTUS are also not known. The transition metals from the 4th and 5th group of the periodic table (Ti, Zr, Hf, Nb, V, and Ta) are strong nitride formers which would be the most suitable for HEN coating systems and therefore, investigation of their properties would be of significant interest. However, the nanoindentation measurements on thin coatings always produce „composite“ values involving the contribution from the substrate. The separation of the coating properties from composite values requires upgraded analytical approaches different from standard Oliver & Pharr analysis. Thus, the aim work is to investigate the structure, hardness, and elastic modulus of TiZrHfNbVTa–xN coatings with different nitrogen stoichiometry deposited by reactive HiTUS using both CSM for bulk and CSM for thin films methods and to compare the results obtained on 4 different substrates (Si wafer, sapphire, 100Cr6 steel, and Ti6Al4V alloy). The subsequent results showed systematic differences in the calculated mechanical properties depending on the substrate properties both in CSM and CSMTF modes. Stiffer substrates always resulted in the overestimations of the calculated hardness and indentation modulus compared to softer substrates with lower Young’s modulus and the differences were in the range of around 10 %. Obviously, better theoretical models for the calculations of true coating properties are required.

Effect of beam current of scanning electron beam on surface alloy layer of 20Cr steel

• The cross-sectional of the sample is composed of three parts: alloy layer, heat-affected zone and matrix. • The effect of beam current on the properties of alloy layer was studied. • A surface alloying method combining scanning electron beam and plasma thermal spraying is proposed. Scanning electron beam surface alloying can effectively improve the surface quality. In this paper, plasma thermal spraying technology and scanning electron beam technology are used to treat the surface of 20Cr steel. The effect of beam current on the microstructure, microhardness and wear resistance of alloy layer was studied. The results show that after alloying treatment, the cross-sectional structure of the sample is composed of three parts, the alloy layer, the heat-affected zone and the matrix. The microstructure of the alloy layer is acicular martensite, Fe-Ni solid solution, WC particles and a small amount of retained austenite. The microstructure of the heat-affected zone is mainly acicular martensite and lath martensite, the matrix structure is ferrite and pearlite. When the beam current reaches 12 mA, the surface hardness of the sample reaches the maximum (867HV), and the wear loss reaches the minimum (4.3 mg).

Comparison of 3%-Cr steel and carbon steel corrosion behavior as well tubing materials in CO2–H2S environment

This study provides two case studies involving carbon steel and 3%-Cr steel exposed to a CO2–H2S environment with a moderate scaling index. The carbon steel tubing show shows pitting and severe corrosion, whereas the 3% chromium steel tubes are undamaged. XRD results showed that the chromium-rich layer did not alter scaling on both tubes. Investigations using SEM and EDS reveal the formation of a dense and compact layer in the 3%-Cr steel, which serves to resist corrosion. In contrast, carbon steel has a porous structure and is easily detachable due to wall shear stress caused by slug movement. In 3%-Cr steel, the EDS analysis reveals a compact layer with a significant number of chromium, which is an indication of a Cr-rich iron oxide layer. Potentiodynamic polarization shows that the anodic curve is shifting, which means that the rate of corrosion is slowing down. This study shows that 3% Cr steel is a good choice for a mixed CO2–H2S environment with a high total dissolved solid (TDS).

The role of Cr content on the corrosion resistance of carbon steel and low-Cr steels in the CO2-saturated brine

The selection of appropriate materials for the transportation pipelines is of vital importance to ensure the safety operation in Carbon Capture, Utilisation and Storage (CCUS). To clarify the effects of Cr content in steel on the resistance against general and localised corrosion, electrochemistry methods combined with pH measurements and various surface analysis techniques were implemented on X65, 1Cr, 3Cr and 5Cr steel samples in a CO2-saturated solution at 60 °C and pH 6.6 during 192 h of immersion. Additionally, thermodynamic and kinetic analyses of the formation of the corrosion products on carbon steel and low-Cr steels were performed. The results show that the general corrosion resistance increased with rising Cr content without the presence of significant corrosion products formation. However, with the formation and development of the corrosion products, the general corrosion resistance reduced with the increase in Cr content. The formation of the compact crystalline FeCO3 on X65 and 1Cr steel surfaces offered superior general corrosion protection, while cannot provide enough localised corrosion protection. By contrast, the double-structural corrosion product layers on 3Cr and 5Cr steels notably suppressed the localised corrosion, but providing poor protection against general corrosion over long immersion periods. This study reveals the contributions of Cr content on general and localised corrosion resistance at various periods, providing references for material selection and evaluation in CO2 environments relevant for CCUS.

Tribological Study of Simply and Duplex-Coated CrN-X42Cr13 Tribosystems under Dry Sliding Wear and Progressive Loading Scratching

CrN coatings are widely used in the industry due to their excellent mechanical features and outstanding wear and corrosion resistance. Using scratch and ball-on-disk wear tests, the current study deals with the tribological characterisation of CrN coatings deposited onto an X42Cr13 plastic mould tool steel. Two surface conditions of the secondary-hardened substrate are compared—the plasma nitrided (duplex treated) and the un-nitrided (simply coated) states. The appropriate combination of secondary hardening providing the maximum toughness and the high-temperature nitriding of this high Cr steel is a great challenge due to the nitrogen-diffusion-inhibiting effect of Cr. The beneficial effect of the applied duplex treatment is proven by the 34% improvement of the adhesion strength and the 43% lower wear rate of the investigated duplex coatings. Detailed morphological analyses give insight into the characteristic damage mechanisms controlling the coating failure processes during scratching and wearing. For the simply CrN-coated sample, a new type of scratch damage mechanism, named “SAS-wings”, is identified, providing useful information in predicting the final failure of the coating. The tribological results obtained on tribosystems with the investigated high Cr steel/CrN constituents represent a novelty in the given field.

Formation of delta-ferrite and its effect on impact toughness of GTAW weld metals in a 12 wt-% Cr steel

This research focused on the formation of the δ-phase and the corresponding effect on the impact toughness in a GTAW weld metal of a 12%Cr F/M steel. Two kinds of δ-phase were identified: one located at the prior austenitic grain boundaries (PAGBs) (called δPAGB) and the other was in the inter-dendritic region (called δinter). The δinter implied that the peritectic transition that occurred at the final stage of solidification in the DSC test, was suppressed in the welding process. A preheating treatment at 95°C decreased optimally the δ-phase fraction and thereby decrease the ductile-brittle transition temperature (DBTT). However, excessive preheating at higher temperatures enhanced the fraction of the δinter by promoting the micro-segregation and thus increased the DBTT.

Experimental study on steam oxidation resistance at 600 °C of Inconel 625 coatings deposited by HVOF and laser cladding

Inconel 625 (IN625) coatings were deposited by High-Velocity Oxy-fuel (HVOF) and laser cladding, on a 10.50–12%Cr steel to improve its oxidation resistance. Both as-deposited coatings exhibited a γ-Ni-Cr matrix and two protective oxides (Cr2O3 and NiCr2O4). In addition, laser cladding as-deposited coatings also presented precipitates A2B-type Laves phases due to the dilution effect from laser cladding technique. Coated and uncoated steel were oxidized under isothermal conditions at 600 °C for 2000 h and subsequently analyzed using gravimetry, SEM-EDS and XRD techniques. The application of IN625 coatings revealed a weight gain ten times lower than that registered for the uncoated steel, this improvement being mainly due to the presence of protective and stable Cr2O3 and NiCr2O4 oxides. Additionally, the XRD analysis showed that the initial Laves phases present in the laser cladding coating, were re-dissolved and transformed in δ-Ni3Nb compound suggesting that that the temperature and exposure time are enough to induce this transformation.

Optimization of Temperature Field by Differentiating Number of Circumferential Control Zones in Local Post Weld Heat Treatment on 9%Cr Heat-Resistant Steel Pipe

Abstract This paper reports the optimal use of control zones to achieve required uniformity of temperature distribution in local postweld heat treatment of welds in 9% Cr heat-resistant large pipe system. In this research, local post weld heat treatment tests on temperature distribution with different control zones were carried out on 9%Cr steel pipes (OD 710 mm × 35 mm and OD 575 mm × 35 mm), which was further used for the development of the thermal analysis of the postweld heat treatment model via abaqus. The research results revealed (1) the effect of number of control zone on the uniformity of temperature distribution; (2) the effect of size of pipe diameter on the circumferential temperature and the through-thickness temperature gradients. This article discusses the possible reasons for the temperature difference at various positions of the pipe caused by the air flow inside the pipe with different control zones. Based on the obtained results, a practical method was designed for the selection the number of circumferential control zones on 9%Cr heat-resistant steel pipeline according to the required degree of temperature distribution uniformity. This paper contributes to the specific knowledge and the generic methodology.

Tribological properties of Laser Powder Bed Fused AlSi10Mg: Experimental study and statistical analysis

This study deals with the experimental analysis of the tribological properties of AlSi10Mg alloy components manufactured by Laser Powder Bed Fusion (LPBF). The influence of the LPBF parameters and building orientation was investigated for density, roughness, hardness, and wearing properties, as weight loss, wear volume, and friction coefficient. The tribological characterization was carried out by means of Ball on Plate Tests, using both 100Cr6 steel and alumina balls as counterpart. Then, the Analysis of Variance (ANOVA) allowed to verify the significance of process parameters, counterpart material and test area. The experimental results highlight the anisotropic effect of the process parameters on the performance of the manufactured samples for all the response variables. Tribological tests performed with steel ball showed an adhesive wear phenomenon, while the alumina ball an adhesive one. No remarkable differences were detected for varying the test area along the building direction. Finally, the analysis of the wear tests at increasing distance showed a progressive increase in the friction coefficient and a corresponding reduction in the wear rate for both counterpart materials.

Effect of a Small Amount of Cr and Mo on Aqueous CO2 Corrosion of Low-Alloyed Steel and Formation of Protective FeCO3 in Near-Saturation Conditions

The effect of a small amount (1 wt%) of Cr or Mo on aqueous CO2 corrosion of low-alloyed steel and the formation of protective FeCO3 corrosion product layers was investigated under controlled water chemistry conditions, where the bulk saturation value of FeCO3 was maintained at near-saturated condition. Changes in CO2 corrosion rate with exposure time were monitored by linear polarization resisitance measurements. The surface morphology and the composition of the corrosion product layers were analyzed by scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, and transmission electron microscopy. Results showed that the emergence of a continuous Fe3C layer created favorable conditions at the surface of nonalloyed steel (containing no Cr and Mo) for semiprotective FeCO3 to form even though the bulk saturation value of FeCO3 was maintained at near-saturated condition. However, semiprotective FeCO3 was not observed on the surface of 1% Cr steel and 1% Mo steel, but rather discontinuous and porous corrosion product layer was formed. Due to the hydrolysis reactions of Cr3+ and Mo3+, and the discontinuous structure of the corrosion product layers, the surface conditions for 1% Cr steel and 1% Mo steel were not favorable for the formation of FeCO3 under the experimental conditions of this study.

Anodizing by Electrochemical Oxidation (ECO) of the Laser Powder Bed Fusion-processed A357 aluminium alloy: microstructural characterization and dry sliding behaviour

Considering the increasing interest for Al alloys in the packaging industry, where component lightweighting allows higher process efficiency, as well as the increasing use of additively manufactured parts, which may not show a satisfactory tribological behaviour in the as-built condition, anodising by Electrochemical Oxidation (ECO) and Plasma Electrolytic Oxidation (PEO) was applied to as-built A357 (AlSi7Mg0.6) produced by Laser Powder Bed Fusion (LPBF). ECO allowed to compensate surface and surface-connected defects in LPBF A357 and produced a thicker, less-defective anodic oxide than PEO, providing higher wear resistance whilst maintaining a lower Coefficient of Friction (COF) in dry sliding tests against 100Cr6 steel. Polishing before ECO only resulted in negligible friction and wear improvements, even if it improved the compactness of the anodic oxide.