Ni Cr Mo Steel Research Articles

Selection of parameters of high-speed thermodeformation of Cr–Ni–Mo steel processing on the basis of imitation modeling

The temperature of the end of finishing stage, cooling rate and coil winding temperature are structure-sensitive parameters for bainite-grade steels in the production of plate less than 10 mm thick. Simulation modeling of high-speed thermo-deformation processing of Cr–Ni–Mo bainitic steel samples has been carried out in order to select the most rational technological modes in continuous hot rolling mills. The influence of strain rate and temperature as well as niobium and vanadium microalloying additives on phase transformations has been investigated.

Prediction of Microstructure Evolution in Ball Mill Liner Forging Process

The liner is affixed to the inner side of the ball mill cylinder to protect the cylinder. Through isothermal compression experiments, Arrhenius constitutive models, peak strain models, critical strain models, dynamic recrystallization dynamic models, and grain size models suitable for the forging process of Mn–Cr–Ni–Mo steel used in ball mill liners were established. By utilizing Deform software, a 3D thermo‐force‐structure coupling model for the hot forging process of ball mill liners was constructed, and the volume fraction of dynamic recrystallization and average grain size during forging was predicted. The response surface model was employed to investigate how process parameters interacted with each other and affected microstructure uniformity in ball mill liners. After optimization, the optimal parameters were determined: initial forging temperature at 1200 °C, forging speed at 30 mm s−1, and friction coefficient at 0.3. Subsequently, a hot forging experiment on ball mill liners was conducted using these optimized parameters; samples were analyzed through backscattered electron diffraction device experiments and microscopic tissue observations. Results demonstrated that microstructural changes observed during actual forging processes aligned with numerical simulation results—thus verifying both the accuracy of the Mn–Cr–Ni–Mo steel material model and numerical simulation method.

Effect of quenching-super intercritical quenching-tempering process on the evolution of microstructure and the yield ratio of Ni–Cr–Mo steel

In the present study, X-ray diffraction, electron probe microanalysis, and transmission electron microscopy, among other advanced characterization methods, were used to analyze the microstructure and mechanical properties of the 9Ni steel treated at different heat treatment conditions. The goal was to reveal the dual-optimal strengthening mechanism of “low yield ratio and ultra-cryogenic toughness” of the investigated steel. The experimental results indicated that the 9Ni steel, designed with a ''Ni–Cr–Mo'' multi-elemental composition, balanced its hardenability and corrosion resistance. After the Q-Q' (710 °C) -T process, the diffusion of Cr and Mo atoms in the steel accelerated, while the Fe displacement diffusion formed a more stable FeNi face-centered cubic structure with a lattice energy of −76.98 eV. At this stage, the microstructure of the investigated steel primarily consisted of tempered sorbite (with an average effective grain size of 13.1 μm), tempered martensite lath clusters, reversed austenite, and precipitated Cr23C6 and Mo2C particles. This composition resulted in a low yield ratio. The concentration of Ni near the lath clusters promoted the formation of the reversed austenite with a volume fraction of 10.2%, ensuring the cryogenic toughness of the investigated steel.

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.

Impact of Alloy Elements on the Adsorption and Dissociation of Gaseous Hydrogen on Surfaces of Ni–Cr–Mo Steel

In this study, the effect of alloying elements on the adsorption and dissociation behaviors of hydrogen molecules on the bcc-Fe (001) surface has been investigated using first-principles calculations. H2 molecules can easily dissociate on the hollow site, and the dissociated hydrogen atoms bond with the surrounding metal atoms. Doping Cr and Mo atoms on the surface would reduce the H2 molecule adsorption energy, which promotes the H2 molecule adsorption and dissociation. When only one or two Ni atoms doping on the surface, it improves the adsorption energies, which in turn can hinder the H2 molecule adsorption and dissociation. However, three or four Ni atoms doping on the surface is beneficial to the H2 molecule adsorption and dissociation. Thus, the nickel content in Ni–Cr–Mo steel should be reasonably controlled to improve the hydrogen embrittlement resistance of the steel.

Tooth flank fracture – An applied fatigue study of case hardened bevel gears

A material model for carburized CrNiMo steel and an advanced shear stress intensity, multiaxial fatigue criterion against surface and subsurface fatigue in bevel gears have been developed and presented in earlier publications. This study assesses the accuracy of the proposed methodology by comparing it to load-controlled bevel gear tests at varying hardening layer thicknesses. The dominant failure mode was wheel-initiated tooth flank fracture. Fractographic analysis by means of scanning electron microscopy revealed a severely elongated MgO-Al2O3 cluster in the only pinion-initiated tooth flank fracture. By correlating the calculated material utilizations and the number of cycles to failure, a reiterated lifetime factor is presented. The refined methodology is shown to be capable to differentiate between and accurately predict pitting and subsurface fatigue under well-defined test conditions.

Tailoring cementite precipitation and mechanical properties of quenched and tempered steel by nickel partitioning between cementite and ferrite

Abstract The effect of Ni on the evolutions of cementite and mechanical properties in quenched and tempered Cr–Ni–Mo steel was investigated. The results of tensile and Charpy impact tests showed that an increase in the Ni content was more effective in improving the low-temperature impact toughness than in increasing yield and tensile strengths. Experimental observations revealed that Ni was beneficial to cementite refinement but had almost no impact on refining the sizes of both the quenched martensite structure and tempered effective grain size. Further, energy dispersive spectrometry (EDS) and thermodynamic studies on cementite and adjacent ferrite indicated that Ni partitioning resulted in the formation of a Ni-rich layer at the ferrite/cementite interface and thereby retarded cementite growth. In order to clarify the different effects of Ni on the impact toughness and yield and tensile strengths, the role of cementite refinement in strengthening and toughening mechanisms was analyzed in detail.

Fatigue of carburised CrNiMo steel: Testing and modelling concept

AbstractIn this study, a testing and modelling concept is presented, aimed at estimating the local fatigue properties of carburised CrNiMo steel, covering the fatigue limit under axial and torsional loading at various mean stresses. Aimed at predicting the bulk material properties, all specimens were ultrasonic shot‐peened prior to testing. Fractographic analyses were conducted on all specimens using scanning electron microscopy to define the type, size and chemical composition of crack initiation‐related discontinuities. An iteration of the FKM guideline is presented, relying on the external notch concept to explain the effect of large internal notches on the mean stress sensitivity.

Predicting the Fracture of Large Forgings with a Heterogeneous Structure

The possibility of predicting the fracture of large forgings made of a heat-hardenable Cr–Ni–Mo steel with a different-scale structure is estimated.

Stress Relaxation Behavior of Cavitation-Processed Cr–Mo Steel and Ni–Cr–Mo Steel

Cr–Mo steel and Ni–Cr–Mo steel have higher strength and hardness than carbon steel, and they are occasionally used in harsh environments where high temperatures and high pressures are simultaneously applied in an oxidizing gas atmosphere. In general, in order to improve the fatigue strength of a material, it is important to impart compressive residual stress to the material surface to improve crack resistance and corrosion resistance. Conventionally, the most famous technique for imparting compressive residual stress by surface modification of a material is shot peening processing. However, in shot peening processing, there is concern that particles adhere to the surface of the material or the surface of the material becomes rough. Therefore, in this study high temperature and high-pressure cavitation was applied and the material surface was processed at the time of collapse. A theoretical and experimental study on a new processing method giving compressive residual stress was carried out. In the present study, we will report stress relaxation behavior due to the heat of cavitation in processed Cr–Mo steel and Ni–Cr–Mo steel.

Evaluation of Microstructure due to Addition of Carbon in Ni–Cr–Mo Steel Mechanically Through Surface Mechanochemical Case Carburizing Treatment (SMCT)

Mechanochemical reaction of Fe–C is achieved in Ni–Cr–Mo steel during surface mechanochemical case carburizing treatment (SMCT) at room temperature. Gradient nano-carbide layers are formed in the surface and near surface up to few microns. The Ni–Cr–Mo steel was treated for 15, 30, 45 and 60 min, respectively, to find out the alteration in microstructure. The surface and cross-sectional microstructures were investigated by Olympus optical microscope (Japan), 6390-A scanning electron microscope and JEOL F-2100 transmission electron microscope (TEM). It is observed that mechanical alloying of carbon in iron lattice is achieved and surface carbon concentration increased from 0.17 to 0.8 wt% with 1 hour of SMCT operation time. The mechanochemical reaction between Fe and C produces Fe3C (cementite) in the surface and undersurface up to 500–800 microns along with nano-particulate on the surface and near surface in 1-hour operation time. It is observed that the carbide cell blocks (CB) and geometrically necessary boundaries (GNB) are produced due to severe plastic deformation created by SMCT operation.

Microstructural Damage Mapping on Heat-Resistant Steel Due to High-Temperature Fatigue

This study aims to develop a damage map based on microstructure due to high-temperature fatigue load. To start with, Ni–Cr–Mo steel was used. The tensile and fatigue properties of it were investigated. The tests were performed at 750 °C. Microscopic evaluation after deformation revealed a variation of the damage mechanism, which was compared with damage map developed computationally. The dislocation activities that typically were homogeneously distributed at room temperature were localized near grain boundaries at elevated temperatures, similar to that of creep damage. A strong particle-dislocation interaction, usually called interfacial pinning, was observed and hereby mapped. Additional microstructural evolution such as the transformation of structure into coarse equiaxed grains and the carbide coarsening was also observed. A change in fracture mechanism from trans-granular at room temperature to intergranular fracture at elevated temperature similar to creep damage was also verified. The heart of this research was the ability to relate the finite element model that simulates both the equivalent stress and temperature distributions to the real experiment. Based on this estimation, the damage level was developed. Microstructural mapping corresponding to the damage level was subsequently made based on the experiment. It was concluded that the mapping was possible and this research could be thought as the embryo for the better understanding in damage theory bridging metallurgical approach to conventional approach using mesomechanics.

Free-Cutting Cr–Ni–Mo Steel

The paper presents theoretical and practical study of formation of non-metallic inclusions in a medium-carbon free-cutting structural steel. FactSage software package was used for thermodynamic modelling of inclusion behaviour. Formation temperature and the amount of aluminium oxides, boron nitrides, manganese sulphides and aluminium nitrides were calculated. Inclusions in the steel form in the sequence Al2O3 > BN > MnS > AlN. The object of practical research was a cast billet of A38KhGMAR grade steel. It was melted in a laboratory induction furnace; boron and nitrogen were introduced after deoxidation of the melt with primary aluminium. Quality analysis included determination of chemical composition, macro-and microstructure, type and shape of non-metallic inclusions. Fine and uniformly distributed boron nitride inclusions were obtained throughout the metal matrix; their distribution was studied both qualitatively and quantitatively. Beside isolated particles, boron nitrides are also presented as a component of complex inclusions with manganese sulphides. Inclusion morphology is mostly spherical. The size of BN inclusions varies from 0.41 to 7.23 μm.

Relation between the Nonuniformity of the Properties and the Structure of Large Forgings

Heterogeneous different-scale structures in large forgings made of a heat-hardenable Cr–Ni–Mo steel are compared. The effect of heterogeneity on the properties of the metal is evaluated.

Fatigue of Thin, Oligo-Crystalline Wires Made of X2 CrNiMo 18-15-3

For a variety of applications, such as in miniaturized machines, tools for minimal invasive surgery, or coronary stents, microscale components are used. For all these components, their dimensions are far below the size of conventional test specimens, and thus the grain size can approach the dimension of the cross section in these microscale components. According to experimental results, large differences in the mechanical behavior of the material occur between single- and polycrystalline test specimens. Therefore, oligo-crystalline microstructures are defined as a transition between single- and polycrystal. To investigate and understand the fundamental impact of oligo-crystalline microstructures on the mechanical behavior of the material, thin wires made of the austenitic CrNiMo steel 316LVM were fatigued. The choice of the material is justified, because it is one of the most frequently-used materials for coronary stents, and only a small amount of research has been done on oligo-crystalline microstructures of this material. Solution were annealed and 10% cold drawn oligo-crystalline wires were compared. The cold drawn wires exhibit an endurance limit of 450 MPa, which is significantly higher compared to solution annealed oligo-crystalline wires (250 MPa). Electron backscattering diffraction (EBSD) measurements of the fatigued wires show massive grain rotations, which lead to orientation changes within the grains. Sometimes, the deformation of a whole structure is concentrated on just one or only very few grains, with a particularly high Schmid factor (>0.44).

Development of a new stainless austenitic CrMnNi steel using TRIP/TWIP effect for a high cold formability

AbstractA new austenitic stainless CrMnNi steel with a high cold formability coupled with high strength was developed. The cold formability is based on the distinct transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP). Thereby a maximum of strain is reached nearby room temperature. Using the TRIP/TWIP effect of CrMnNi steel a cost‐ and energy‐efficient production of thin sheets is enabled by a reduced number of interstage annealing. Thin sheets with thicknesses from 0.1 mm till 1.25 mm were cold‐rolled industrially and there properties compared to conventional CrNi steel 1.4301 (AISI 304) and CrNiMo steel 1.4404 (AISI 316 L).Plate and lamellae heat exchangers of CrMnNi thin sheets were produced under industrial conditions. The form stability of the plate heat exchangers was increased by 47 % and the component failure pressure raised by 45 % at room temperature. Based on its high strength it is suggested to apply the new austenitic CrMnNi steel in lightweight constructions. Although the nickel content was reduced by 50 % to 65 % compared to conventional steels 1.4301 and 1.4404 the corrosion resistance of the CrMnNi steel is comparable with conventional CrNiMo steel 1.4404.

Study of Deformation Phenomena in TRIP/TWIP Steels by Acoustic Emission and Scanning Electron Microscopy

Modern metastable steels with TRIP/TWIP effects have a unique set of physical-mechanical properties. They combine both high-strength and high-plasticity characteristics, which is governed by processes activated during deformation, namely, twinning, the formation of stacking faults, and martensitic transformations. To study the behavior of these phenomena in CrMnNi TRIP/TWIP steels and stainless CrNiMo steel, which does not have these effects in the temperature range under study, we used the method of acoustic emission and modern methods of signal processing, including the cluster analysis of spectral-density functions. The results of this study have been compared with a detailed microstructural analysis performed with a scanning electron microscope using electron backscatter diffraction (EBSD).

Hydrogen Embrittlement of Ultrafine-Grained Austenitic Stainless Steels

Abstract The effect of electrochemical hydrogen-charging on tensile properties, mechanisms of plastic deformation and fracture micromechanisms was studied using two ultrafine-grained (UFG) Cr-Ni austenitic stainless steels. UFG austenitic structures with an average subgrain size of 200 nm for CrNiMo (316L-type) and 520 nm for CrNiTi (321-type) steel were produced using hot-to-warm ABC-pressing. Hydrogen-charging up to 100 hours weakly influences stages of plastic flow, strength properties and elongation of the UFG steels. TEM analysis testifies to hydrogen-assisted partial annihilation and rearrangement of dislocations into dislocation tangles, and to hydrogen-induced variation in ratio of low- and high-angle misorientations in UFG structure of both steels. Hydrogen-alloying promotes mechanical twinning and deformation-induced γ ® e martensitic transformation in the UFG steels under tension. Ultrafine-grained CrNiTi steel with lower stacking fault energy (SFE) is more susceptible to mechanical twinning and deformation-induced γ ® e martensitic transformation in comparison with CrNiMo steel with higher SFE. The micromechanism of the fracture in hydrogen-assisted surface layers of the steels is compositional, grain-size and hydrogen content dependent characteristic. The present results demonstrate that the steels with UFG structure possess higher resistance to hydrogen embrittlement compared to coarse-grained analogues.

Mechanical Properties of a Ni–Cr–Mo Steel Subjected to Room Temperature Carburizing Using Surface Mechano-Chemical Carburizing Treatment (SMCT)

Surface mechano-chemical carburizing treatment (SMCT) is a modified version of surface mechanical attrition treatment and it is one of the cutting-edge technologies for producing hard nano-crystalline surface in metallic materials. In the present study, a case carburized surface layer is achieved in 1.75 Ni–Cr–Mo steel at room temperature using SMCT. Activated charcoal powder is continuously fed during the process so as to achieve the carbon diffusion into the surface layer. The SMCT process has been carried out for different periods say 15, 30, 45 and 60 min respectively. The microstructure and surface chemical composition is investigated by using TEM and XRF analysis. The mechanical properties such as yield strength (YS), ultimate tensile strength (UTS), fracture toughness and surface hardness of SMCT samples have been investigated using universal testing machine, Plain strain fracture toughness test and Microvickers hardness test respectively. The surface carbon content has been found to increase linearly and grain size reduces continuously with processing time. A 60 min SMCT samples reveal 0.8% C and about 10 nm grains over the surface. The SMCT samples show significant improvement in mechanical properties. The surface hardness increases from 180 HV0.1 to ~ 878 HV0.1 by 60 min of treatment. About 55% increment in the YS and 30% increment in UTS is achieved by 60 min of SMCT. It is also interesting to note that the fracture toughness of the samples enhances from 24 to 47 MPa $$ \sqrt m $$ after 60 min of SMCT.

Comprehensive analysis of fractures, microstructure, and physical and mechanical properties for the evaluation of the crack resistance of medium-carbon Cr–Ni–Mo steel

The crack resistance of the 38CrNi3MoV (34NiCrMoV14—5. 35NiCrMoV12—5) tempered steel (at various tempering temperatures) has been estimated based on a comprehensive study of the steel fractures, microstructure, physical, and mechanical properties. Stress-intensity factor K 1C at the apex of the crack is growing continuously with an increase in the tempering temperature from 200 to 620°C. This indicates that K 1C is a structural-sensitive parameter, which depends on the steel microstructure and submicrostructure, the fracture mechanism that occurs under these structural conditions, the internal stress level, and the existence of microdefects and microcracks. The linear correlation dependence is found between the coefficient K 1C and the transverse velocity V transv. The obtained results reveal that the acoustic method can be used to quickly and efficiently estimate the crack resistance of the thermostrengthened steel without the recourse to labor-consuming mechanical tests and computations of the K 1C value.