Cr Steel Research Articles

Improving of 100Cr6 Steel Corrosion and Wear Properties in Simulated Sea Water Environment by Tungsten-Doped DLC Coating.

A progressive type of tungsten-doped DLC coating was applied to a quenched and tempered 100Cr6 steel with the aim to improve the wear and corrosion properties in simulated seawater conditions and to compare the performance to conventional DLC coating. Tungsten doping caused a shift of the corrosion potential (Ecorr) to a lower negative value of -172 mV, while the conventional DLC exhibited an Ecorr of -477 mV. In dry conditions, the W-DLC coefficient of friction is slightly higher than that of the conventional DLC (0.187 for the W-DLC vs. 0.137 for the DLC), but in cases of a saltwater environment, this difference becomes almost negligible (0.105 for the W-DLC vs. 0.076 for the DLC). The conventional DLC coating also started to show marks of deterioration when exposed to a combination of wear in a corrosive environment, while the W-DLC layer still maintained its integrity.

Three-step learning strategy for designing 15Cr ferritic steels with enhanced strength and plasticity at elevated temperature

15Cr ferrite steels are urgently required in advanced Ultra-supercritical power plants but meet design challenges in balancing excellent strength and plasticity at high temperatures. We developed a three-step learning strategy based on mutually driven machine learning and purposeful experiments to complete this multi-objective task. Compared with traditional adaptive learning and local-interpolation learning, this step-by-step modular manner provides good transparency and interpretability of the information flow, which is ensured by identifying essential factors from an exquisitely prepared composition-microstructure dataset, and learning valuable knowledge about the composition-property relationship. The requirement of only two groups of experiments indicates the low cost and high efficiency of the strategy. Performing the strategy, we found that Ti is another key element affecting the Laves phase besides Mo and W, and their effects on ultimate tensile strength (UTS) and elongation were also uncovered. Importantly, several low-cost steels free of Co were successfully designed, and the best steel exhibited 156%, 31%, and 62% higher UTS and elongation at 650 °C than the typical 9Cr, 15Cr, and 20Cr steels, respectively. Based on the advantages and success of the strategy in terms of alloy improvement, we believe the strategy suits other multi-objective design tasks in more materials systems.

Effect of retained austenite on the fatigue behavior of modified bainitic 100Cr6 steels considering local phase transformation

Since highly loaded components, such as roller bearings, tend to have relatively high lifetime scatter caused by microstructural defects, an increased defect tolerance of the material can improve the performance as well as the reliability of these highly stressed components. To increase the defect tolerance of the roller bearing steel 100Cr6, two different laboratory melts with either 1.5 wt.-% Al or 1.5 wt.-% Si in addition to the standard composition were developed. After an adapted heat treatment, both steels exhibited a bainitic microstructure with a relatively high content of retained austenite with more than 20 vol.-%. Considering the effects of the retained austenite, a defined mechanical stability is essential to avoid excessive deformation-induced transformation from the retained austenite into α′-martensite, which can lead to shape deviations in components. However, besides the increased deformability of the austenitic phase, local phase transformations in the vicinity of defects can increase the defect tolerance. The fatigue tests performed at ambient temperature (AT) and at T = 100 °C, show a higher fatigue strength of the Si-alloyed steel due to a refined microstructure and revealed for both steels a relatively high austenite stability, since no macroscopic phase transformation was observed. The high austenite stability can be explained by a relatively high carbon content of the austenitic phase. However, in contrast to the Al-alloyed steel, a decrease in the fatigue strength and in the defect tolerance due to the increased temperature were observed for the Si-alloyed steel, which indicates a more pronounced phase transformation at AT. The lower carbon content and the finer distribution of the retained austenite, when compared to the Al-alloyed steel, are supposed to be the reason. While a smaller carbon content decreases the phase stability, the refined austenite distribution results in a higher probability of retained austenite presence in the vicinity of a defect.

Effect of Double Austenitization and Pre-Annealing Heat Treatment on the Microstructural and Mechanical Properties of QT 41Cr4 Steel

Effect of Double Austenitization and Pre-Annealing Heat Treatment on the Microstructural and Mechanical Properties of QT 41Cr4 Steel

Investigation on high-strength low alloy 0.35Cr-1.9Ni-0.55Mo steel deposited on 20Cr substrate by wire and arc-based directed energy deposition

This article aims to observe the microstructure, mechanical properties, and interface bonding of a 0.35Cr-1.9Ni-0.55Mo alloy deposited on 20Cr steel by wire and arc-based directed energy deposition (WA-DED). For this purpose, different characterization techniques such as optical microscope, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), and high-resolution X-ray diffractometer were used to analyze microstructure, chemical composition, and phases of the deposited material. Microhardness and tensile tests were also carried out. The results show that the microstructure of the deposited material is relatively homogeneous with a slight increase in grain size from the bottom to the top of the deposited part, thus resulting in a gradually decreasing trend in microhardness, from 288±16.78 HV0.1 (in the bottom) to 256±17.04 HV0.1 (in the top). The heat-affected zone (HAZ) is the hardest (301±2.70 HV0.1), while the substrate has the lowest microhardness (203±17.64 HV0.1). The tensile strengths of deposited materials are relatively isotropic in both the horizontal direction (HD) and vertical (VD) direction: UTSVD = 1013±9.29 MPa, USTHD = 985±24.58 MPa, YS(0.2%)VD = 570±4.51 MPa, and YS(0.2%)HD = 614±19.66 MPa. The tensile strengths of interface specimens are also comparable to those of the substrate materials (e.g., 951 vs. 972 MPa in UTS), indicating an excellent metallurgical bonding between the deposited and substrate materials. The results of this work confirm the efficiency of WA-DED technique to produce high-quality components in industry

Electrochemical and molecular modelling studies of corrosion inhibition characteristics of imidazolines on 1Cr steel under sweet conditions

ABSTRACT Organic compounds like imidazoline derivatives are commonly used as corrosion inhibitors. This study characterised the corrosion inhibition properties of two forms of imidazoline, 2-Methyl-2-imidazoline (2-MI) and 2-Phenyl-2-imidazoline (2-PI), with and without the presence of mono ethylene glycol (MEG) on steel surface under CO2 corrosion condition. Electrochemical, surface characterisation and molecular modelling were used to study corrosion inhibition properties and underlying mechanisms. In the pure form, 2-PI had higher corrosion inhibition efficiency than 2-MI, likely due to stronger adsorption to the steel surface, as confirmed by molecular modelling. The addition of MEG improved the inhibitor efficiency of both 2-MI and 2-PI.

The Synergistic Effects of Boron and Impression Creep Testing during Paced Controlling of Temperature for P91 Steels

This article induces the quadruple knowledge on effects of 100 ppm (P91B) and 22 ppm (P91) boron in as‐received 9Cr steels in normalized and tempered conditions (NT) and impression crept conditions (ICC). Herein, impression creep testing is improved through paced temperature to fast evaluate creep performance. P91B performs the utmost by advancing activation energy and 30% better creep life, leading to same targeted creep life to 574 °C than P91 at 550 °C. Further, it incisively discusses variations in microstructure, precipitate size, geometrically necessary dislocations (GNDs), pseudo‐rocking curve, grain size (GS), several types of grain boundaries (GBs), effective GB energy, and elastic stiffness. Novel phenomenological mechanisms like GB hardening/softening; antithetical mechanisms; boron‐dependent mosaicity; grain refinement/fragmentation/coarsening/homogenization; interaction among various types of GBs, triggering re/degeneration of dislocations and Σ boundaries as Σ reactions; super‐continuous and geometric dynamic recrystallizations; enhanced creep immunity of like‐oriented GBs than unlike oriented GBs; primary/secondary recrystallization; specialness; boron/NT/ICC‐dependent stiffness; high stiffness is dependent on low GNDs and big GS, and vice versa are observed. The synergistic effects of [100 ppm boron in NT/ICC] and ICC in manifestation of 22/100 ppm boron are ascertained. However, dependency [proportionally and antithetically] and independency of GB character on creep‐microstructural reciprocity discourse and converse into the mathematical relationship.

Creep damage in 9-12% Cr steel notched components: Microstructural evolution and stress state dependence

To understand the stress state dependent creep damage, following creep tests in 9–12% Cr steel notched components with different root radii, a study of associated time dependent microstructural evolution is presented in this work. Particular attention is paid to the dependence of creep damage evolution on the stress state. The average creep strain of notched component exhibits a typical three-stage characteristic (transient, steady and tertiary stages). During the transient stage, remarkable re-distribution in stress state (equivalent stress and stress triaxiality) is found. The rapid relaxation of equivalent stress near the notch root, associated with the initial coarsening of substructure would delay the nucleation or growth of cavity. By contrast, the time-dependent increase of equivalent stress combined with the relatively high stress triaxiality seems to be responsible for the higher cavity density at the center of notched component. The precipitate coarsening is heterogeneous and promoted by the high level of equivalent stress or stress triaxiality. During the steady stage, the creep damage behavior is related to the magnitude of stress state. Higher cavity density and greater reduction in hardness are mainly found in the region where both the equivalent stress and stress triaxiality are high. As a whole, both the redistribution process of stress states and their levels exhibit significant influence on microstructural evolution and creep damage behavior of notched components at elevated temperatures.

Atmospheric corrosion performance of structural steel bolts in the Wenchang marine environment, South China

The atmospheric corrosion performance of three different grades of hexagonal head structural steel bolts with distinctive surface finishes (304 stainless steel (plain), galvanized steel (Zn coated), and 40Cr steel (black coated)) was examined in this study using surface analysis and characterization techniques. The bolts were exposed in the Wenchang marine environment for two years. Results showed that a combination of factors such as alloying content, microstructure, surface finishing, and environmental conditions impacted the corrosion performance of the examined bolts. The corrosion mechanisms and patterns varied between the different bolt materials; 304SS bolts exhibited localized corrosion, while galvanized steel and 40Cr steel bolts exhibited uniform corrosion. In terms of coating performance in the marine environment, the zinc coating provided minimal protection to the underlying steel substrate when compared to the black oxide coating which failed prematurely, rendering it unsuitable for use in the marine atmosphere. Furthermore, despite the formation of a dense rust layer on the galvanized and 40Cr steel substrates after 2 years of marine atmospheric exposure, the fastener degradation was critical, suggesting that the rust layer is not beneficial in the threaded fasteners due to the high susceptibility to exfoliation that may eventually lead to thread stripping. This poses a serious risk to bolted assemblies.

Influence of laser surface treatment on the microstructure distribution, bearing capacity and impact property of 1.0C‐1.5Cr steel

A diode laser with a rectangular spot was used to perform laser surface treatment on a 1.0C‐1.5Cr steel. Based on the numerical simulation, an empirical equation was developed to predict the peak temperature, and the microstructure distribution was analyzed. The bearing capacity and impact fracture mechanisms were also studied. The results indicated that the relationship between the peak temperature and scanning rate was affected by the depth, and the peak temperature on the outer surface was approximately linear with the reciprocal of the square root of the scanning rate. The higher peak temperature leads to cementite dissolution and coarsening near the outer surface. Cementite dissolution was postponed during the laser surface treatment. The bearing capacity was a combined result of strengthening in the surface region and softening in the heat affect zone. Under a lighter contact load, laser surface treatment had no adverse effect on the bearing capacity. However, under a heavier contact load, the plastic deformation of the heat affect zone slightly decreased the bearing capacity. The impact fracture started at the outer surface of the laser-hardened layer, and propagated intergranularly near the crack source, and then propagated inward through the transgranular fracture. Owing to the stress concentration near the interface between the cementite and martensite matrix, cementite particles tend to appear along the crack propagation path. The decrease in the impact absorbed energy is attributed to the brittleness of the hardened layer and tensile residual stress, and the impact toughness can be improved by preheating.

ANALYSIS OF STRENGTH OF A FORK OF THE FORKLIFT BY NUMERICAL METHODS

Forklift is an industrial power truck, commonly called forklifts or lift trucks, then usually have two forks the can be trial power truck used forklifting and transport materials. Fork-lifts, to this day, the fork strength of a forklift under load still seems to be one of the biggest issues. Fork’s related structural design and detail have a significant impact on the overall performance and reliability of a forklift. In this work, static analyses of a fork forklift were performed using Finite Element Method, on the free software FreeCAD, a multidisciplinary software application that is the result of a long-term active collaboration between develop-ers and users. Open science hardware is cheaper, easier to maintain, and more accessible to more people. In this paper, by calculating the maximum normal stress of the section, the force situation and allowable stress of the fork are analyzed. The fork is made of structural material is 40Cr steel. The output values of the static study consist in establishing the distri-bution of equivalent unitary stresses (stress state) according to the von Mises criterion. The maximum stress of the structure is 128 MPa, which is does not exceed the allowable. Then in order to enhance the structural strength of the weak part, the measures of gradually in-creasing the fillet radius of the fork root were proposed, and the radius were selected as 35mm and 45mm, the weight of the forklift load was still 0,5t. Numerical experiments have shown that by increasing the radius from 25 to 45 mm, stresses decrease by 1.1...1.15 times, which is consistent with the theory of basic mechanics that stress concentration can easily lead to fatigue failure of the structure. Both numerical calculations and visual analysis showed consistency, with stress concentrations observed at the fork neck, demonstrating the accuracy of the established finite element model.

Microstructural Characterization of Novel ZrO2 Dispersion-Strengthened 9Cr Steel by Spark Plasma Sintering

Technologically important Oxide Dispersion-Strengthened steels are synthesized using ZrO2 as a dispersion strengthener instead of conventionally used Y2O3. Powder metallurgical route followed by spark plasma sintering is adopted for synthesizing the material. Detailed microstructural characterization revealed a fine-grained microstructure with finer dispersoids in as-sintered and normalized condition. The stable microstructure is found to be retained even after subjecting the samples at 973 K for as long as 1000 h for long-term thermal aging trials, indicating at a possible superiority of this material over the conventional Oxide Dispersion-Strengthened steels. The yield strength is calculated by making use of microstructural parameters and predictive models, both of which shown a good agreement. Mechanical property analysis through hardness measurements was correlated with microstructural observations and compared with the conventional Oxide Dispersion-Strengthened steels. The collective results indicate ZrO2 as a potential alternate dispersoid for strengthening steel and future scope for vast exploration.

Scale-Invariant Geometries Arising from the Interaction Between a 9%Cr Steel and Molten Nitrate Salt

Scale-Invariant Geometries Arising from the Interaction Between a 9%Cr Steel and Molten Nitrate Salt

Investigation on grinding-induced cracking mechanism of 40Cr steel camshaft

The generation of grinding cracks during the grinding process will adversely affect the service performance of the workpiece and even cause the workpiece to be scrapped. However, the microscopic formation mechanism of grinding cracks is still unclear at present. In this regard, the morphologies of grinding cracks on the surface of the cam were characterized, and the initiation and propagation behaviors of grinding cracks were analyzed from the perspectives of element composition, micro-structure and surface work hardening. Based on the experimental results and analysis, the generation mechanism of grinding cracks is clarified, and measures to prevent the grinding cracks are proposed.

Microstructural manifestation and kinetics of dynamic transformation in a W-modified 9%Cr steel

Dynamic transformation (DT) of austenite to ferrite is shown to occur in a W-containing 9%Cr steel during hot deformation across a wide range of strain rates. A new facet of DT, namely its dependency on process kinetics, is revealed by examining work-hardening rate and strain rate. The kinetics of DT is associated with competing processes of dislocation immobilisation and remobilisation, both of which have a complex dependence on strain rate. The microstructural manifestation of DT-ferrite is examined and contrasted with that of conventional ferrite on the basis on morphology. This contrast arises from different modes of transformation and resultant differences in crystallography. DT is placed in the practical context of thermo-mechanical processing by addressing issues of process control and stability.

Numerical simulation and correlation research of multi-track overlapping laser quenching process for 40Cr steel

Laser quenching has a short process cycle and high production efficiency, and it plays an important role in automobile, ship, machinery manufacturing, and other fields. The surface hardness of 40Cr steel laser quenching parts is uneven by unreasonable set on the quenching overlap zone. This will affect the microstructure of the quenched layer, resulting in cracking, corrosion during service, and other hazards that ultimately reduce reliability. Numerical simulations provide an effective way to quantitatively reveal the transient evolution of the multi-field coupling between temperature field, stress field, and phase transition field in quenching, which directly determines the extent of the overlap zone and quenching properties. The quenched phase transition layer profile is predicted to effectively determine the extent of the secondary tempering softening zone and solve the bottleneck problem of uneven surface hardness in quenching. The innovation of this paper is to establish a multi-field coupled numerical model of the 40Cr steel multi-track laser quenching process. The transient quenching temperature, phase transition hardening, and stress distribution were numerically calculated, and the size of the tempering zone under different overlapping rates was evaluated, revealing the internal coupling mechanism and correlation between multi-fields during the laser quenching. The quenching temperature, microstructure, and hardness distribution of 40Cr steel were tested by an infrared thermometer, Axio Vert A1 Zeiss microscope, Thermo ScientificTM Apreo scanning electron microscope, and Q10M microhardness tester, which verified the effectiveness of numerical simulation. The research can provide an important theoretical basis for optimizing quenching process parameters in production.

Study on corrosion resistance mechanism of Cr-containing steel in simulated oilfield produced fluid

In view of the CO2 corrosion environment of oil and gas fields, the corrosion behavior of 5Cr, 9Cr and 13Cr steels was studied by high temperature and high pressure weight loss test and electrochemical test with J55 material as comparison. Scanning electron microscopy (SEM) analysed the morphology of corrosion products. The corrosion resistance mechanism of Cr-containing steel was analyzed from the perspective of structural stability by first-principles. The results show that the uniform corrosion rate of Cr-containing alloy steel is lower than that of J55 steel, and the CO2 corrosion resistance of the material increases with the increase of Cr content. With the increase of temperature, the self-corrosion current density of different Cr-containing steels gradually increases, the pitting potential of 9Cr and 13Cr gradually decreases, and the pitting resistance decreases. The electrochemical corrosion kinetic resistance of Cr-containing steel increases under long-term immersion corrosion. Molecular dynamics and first-principles calculations show that the corrosion product preferentially formed by Fe is FeCO3, and the corrosion product preferentially formed by Cr is Cr(OH)3. On the surface of the iron matrix, Cr(OH)3 is more easily adsorbed on the surface of the iron matrix, thereby protecting the matrix from corrosion resistance.

Microstructure Characteristics of the Compound Layer Cracked during Grinding on QPQ‐Treated Cr‐Containing Steel Shafts

Cr‐containing structural steels with quench‐polish‐quench (QPQ)‐treated surfaces are noticed having higher grinding cracking tendency compared to plain carbon steels. Herein, the compound layers of QPQ‐treated shafts produced from 20Cr and 40Cr steels by performing XRD, SEM, EDS, and microindentation measurements are investigated. The differences between the compound layers on the shafts with and without cracks are compared in morphology and element distribution. It is revealed that the basic reason of grinding cracking is the imperfect compound layer with serious porosities. The formation of serious porosities is mainly due to the inhibition of the outward diffusion of the nitrogen molecules from the nitride layer. Stronger nitride‐forming element Cr is considered to strengthen this inhibition.

Tribological behavior of different doped ta-C coatings for slip-rolling contacts with high hertzian contact pressure

PurposeThe curved and tribologically highly stressed surfaces of bearing components pose a major challenge for steel alloys or tribological resistant coatings like tetrahedral amorphous carbon (ta-C) coatings which in particular have an increased risk of delamination due to the significantly increased residual stresses. A possibility to prevent coating failure is the use of dopants while maintaining or even increasing tribological properties. This study aims to compare the tribological behavior of several doped diamond-like-carbon coatings with an undoped ta-C coating under varying slip conditions and Hertzian pressure up to 1800 MPa.Design/methodology/approachFor this purpose, the tribological behavior was studied using of a ball-on-disc tribometer and a two-disc test rig under mixed/boundary conditions. The tests were conducted with coated specimens against uncoated 100Cr6 steel. Additionally, the influence of lubrication additives was studied due to the use of two fully formulated PAO-based oils, one without and one with molybdenum containing additives. The friction was measured in situ, and the wear was analyzed trough laser scanning microscopy and tactile measurement.FindingsIt was shown that the use of doped ta-C coatings exhibited a tendency for a more favorable tribological behavior compared to undoped ta-C coatings, with no general dependence on the lubricants used. The use of the most suitable coatings reduced the wear of the steel counter-body considerably.Originality/valueTo the best of the authors’ knowledge, this is the first approach of testing the tribological behavior of these doped ta-C coatings, developed for friction efficiency, in dependency on lubrication additives under the given load collective. The approach is relevant to determine whether the friction reduction and the wear inhibition of these coatings are suitable for higher contact pressures and load cycles.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-11-2022-0336/

Newly developed high-strength martensitic stainless steel for the sniper rifle barrel with high shooting accuracy

With the increasing requirements for the shooting accuracy of the sniper rifle, steel combined with excellent high-temperature strength, low-temperature toughness, and extraordinary corrosion resistance is desirable for the barrel material of the sniper rifle with high accuracy and a long lifespan. In this study, martensitic stainless steel 2Cr11Ni2Mo2WV (MPS700A) was developed by introducing Mo, W, and V into the currently used 2Cr13 steel. The 600 °C tensile tests demonstrated that the ultimate tensile strength of MPS700A reached 767 MPa, which was 46.4 and 97.2 % higher than those of 2Cr13 and 30SiMn2MoV, respectively. Meanwhile, the −40 °C impact toughness of MPS700A reached 88 ± 4 J/cm2, which was 20.5% higher than that of 2Cr13 and comparable to that of 30SiMn2MoV. The intralath precipitation of ellipsoidal M2C nano carbides was observed in MPS700A after tempering, which followed a Dyson orientation relationship (OR) of (01¯12)M2C//(200)α with the martensitic matrix. After deformation at 600 °C, such a Dyson orientation relationship (OR) was maintained, and the M2C in MPS700A exhibited higher thermal stability than the M3C in 2Cr13, which hinders the dislocation movement and contributes to the higher strength of MPS700A at 600 °C. The fine martensitic laths and homogeneously dispersed M2C nano carbides also contributed to the higher impact toughness of MPS700A than that of 2Cr13. Additionally, the salt spray test indicated that the mass loss of MPS700A was 1.72 ± 0.24 g m−2 at 72 h, which was 95.6% lower than that of Cr-plated 30SiMn2MoV and comparable to that of 2Cr13. Based on these results, we demonstrate that MPS700A exhibits high strength up to 600 °C, excellent impact toughness at low temperatures, and outstanding corrosion resistance, making it a promising gun barrel material for sniper rifles with long lifespans and high shooting accuracy.