Carbide Precipitation Research Articles

Investigating the corrosion performance of hull steel with different microstructure in a tropical marine atmosphere

The corrosion behavior of ship steel with different microstructure in a simulated tropical marine atmosphere was systematically investigated. Results show that homogeneous martensite structure obtained by water-quenching process was much more resistant to corrosion than that of ferrite-pearlite. Furthermore, the precipitation of carbide resulting from tempering process promoted the formation of corrosive microcells within the matrix and further intensified the corrosion. Rapid cooling rate led to the enrichment of chromium, which formed protective corrosion products such as FeCr2O4 and Cr(OH)3. This also facilitated the conversion of α-FeOOH and significantly enhanced the corrosion resistance.

Effects of Nb addition on resistance to hydrogen embrittlement in SA 372 steels used for hydrogen-gas storage containers

The resistance to HE of Cr–Mo low-alloy SA 372 steels fabricated by adding different amounts of Nb was investigated by slow-strain-rate tensile and H-permeation tests. NbC carbides played an important role in hindering grain boundary migration, leading to a significant grain refinement from 28.3 to 13.1 μm. The Nb-free steel exhibited a significant loss of elongation (Elloss), and its fracture surface contained several secondary cracks and quasi-cleavage facets. In the 0.08 wt%-Nb-added steel, the Elloss decreased significantly due to the facilitated precipitation of additional NbC carbides, resulting in a ductile-dimpled fracture mode. The effective H-diffusivity of Nb-added steels was lower than that of the Nb-free steel, indicating that H-diffusion was considerably hindered in the Nb-added steels by the presence of NbC precipitation as well as grain refinement. This hindered H-diffusion contributed to an improvement of the resistance to HE in SA 372 steels.

Mitigating high temperature hydrogen attack with interphase precipitation

The attack on steel by reaction with high-pressure hydrogen at elevated temperatures can jeopardise structural integrity in oil & gas industries. Following dissociation, the hydrogen penetrates the steel to react with the carbon present in the ferrite to form methane bubbles within the microstructure. This depletion of carbon in the ferrite causes the dissolution of carbides in order to maintain the ferrite-carbide equilibrium. Therefore, thermodynamically more stable carbides which cause a reduced activity of carbon improve the stability of the steel to hydrogen attack. In this work, we investigate specifically the response of the interphase precipitation of alloy carbides that form during the transformation from γ to α, on hydrogen attack. It is demonstrated quantitatively that the vanadium carbides thus produced enhance the resistance to attack when compared with data from an earlier study involving current, commercially-used steel in the petrochemical industries.

Wear and corrosion behavior of vanadium-alloyed nodular cast irons fabricated by sand-casting

Nodular cast irons have been mainly used in automobile components exposed to large forces like brake pads, suffering from abrasion against recently developed lightweight Al2O3-containing brake rotors during operation. Besides, aqueous corrosion (rain, snow, and chlorides) can cause these brake pads to wear out faster. This study examined the wear and corrosion properties of the V-alloyed nodular cast irons as a function of V content (0, 0.25, 0.5, 0.75, and 1 wt%). The samples were tested against an Al2O3 ball to simulate more severe abrasive conditions, whereas the electrochemical corrosion behavior was investigated in a 3.5 wt% NaCl solution. It was revealed that wear resistance increased with increasing V up to 0.50 wt%, but higher V caused a reduction due to the heavily branched eutectic carbide formation. Wear losses increased with the applied load, whereas sliding speed had no significant effect. The samples experienced uniform and graphitic corrosion in a 3.5 wt% NaCl environment. Increasing V improved their corrosion resistance to 0.75 wt% V due to the precipitated spherical vanadium carbides. The 1 wt% V-alloyed sample failed both wear and corrosion tests because of increased metastable eutectic carbides.

Microstructure gradient formation in electron-beam melting powder-bed fusion of a gamma-prime Ni-based superalloy

Microstructure gradient is formed during the additive manufacturing of Ni-based superalloy Haynes® 282® via electron-beam melting powder-bed fusion (EB-PBF) process. The precipitation of secondary phases occurs owing to EB-PBF in-situ heat treatment as consequence of high temperature powder bed pre-heating and multiple melting and re-heating thermal cycles, which can be summarised as a carbide precipitation heat treatment at 1000–1025 °C/8 h, aging between 875 and 975 °C/30 h, followed by a slow cooling step. Relatively large precipitates formed inter- and intragranularly with M3B2 boride and gamma-prime (γ') have sizes of approximately 5 μm and 110 nm, respectively, at the bottom of the build. The size of the precipitates decreases along the build direction. In the top region, the precipitate sizes of boride and γ' are 1 μm and 50 nm, respectively. MC carbide with a size of <1 μm precipitated throughout the build. A good correlation is observed in terms of the γ' size to hardness with average values of 350 HV at the bottom and 400 HV at the top. The ultimate tensile strength (UTS), yield strength (YS), and elongation (EL.) values at the bottom and top regions are 1080 ± 40 MPa, 805 ± 25 MPa, and 20 ± 5%; and 1105 ± 20 MPa, 825 ± 15 MPa, and 25 ± 5%, respectively. Overall, EB-PBF Haynes® 282® exhibits higher UTS and YS but lower EL than those of the as-received wrought alloy (950 ± MPa, 650 ± 15 MPa, and 40 ± 5%, respectively).

INFLUENCE OF TEMPERING TEMPERATURE ON THE MICROSTRUCTURE AND ULTIMATE TENSILE STRENGTH OF 28Cr3SiNiMoWV STEEL

In this research, the influences of the tempering temperature on the microstructure and ultimate tensile strength of 28Cr3SiNiMoWV steel were studied. The microstructure and ultimate tensile strength were investigated after tempering 28Cr3SiNiMoWV steel at different temperatures, ranging from 280 °C to 440 °C for 2 h. The results show that after tempering it at different temperatures, the microstructure of 28Cr3SiNiMoWV steel was tempered martensite. During the tempering process, the alloy carbides precipitated in the martensite matrix. Precipitation of alloy carbides in the microstructures of different specimens is the cause for an increase in the ultimate tensile strength. With the increasing tempering temperature, the ultimate tensile strength initially increases from 1390 MPa to 1601 MPa, and then decreases to 1466 MPa, with its maximum value at 280 °C.

Effect of laser power and heat treatment on microstructures and tensile properties of LPBF fabricated Hastelloy X superalloy

Laser powder bed fusion (LPBF) technic is suitable for manufacturing metal parts with complex shapes and internal channels. The energy input and post heat treatment have great influence on the formability, microstructure and properties of the metallic materials. In this work, Hastelloy X superalloy is fabricated by LPBF with a variation of laser power, and then post-treated by hot isostatic pressing and solution treatment. Influences of laser power and heat treatment on microstructure features of as-built sample are evaluated. The correlation among laser power, microstructure features and tensile properties of heat-treated samples are revealed. The results reveal that average grain size, aspect ratio, texture intensity increases while the proportion of high-angle grain boundaries decreases with the increase of laser power. Precipitates of Cr-rich carbides along grain boundary are observed after post heat treatment. Post-treatment promotes the twinned recrystallization, grain coarsening and texture degradation. Yield strength increases while tensile strength decreases with the increase in laser power. The higher vertical yield strength of sample with laser power of 320 W could be attributed to its larger aspect ratio and more twin boundaries. 280 W is the preferred laser power to obtain the best overall tensile properties. This study is helpful for the exploration of optimal LPBF process and post heat treatment, by which Ni-based superalloys with a good balance between strength and ductility can be produced.

INVESTIGATION OF CRYOGENIC TREATED DRILL BIT

We look into brief introduction of cryogenic treatment. Our focus throughout the report is more on cryogenic treatment of tool steel and high speed steel. In metal forming industry tools are exposed to very complex and rough surface conditions, which are the result of different effects (mechanical, thermal and chemical) and thus require well defined mechanical properties. Different approaches are followed to increase the surface properties of tool steels. The surface hardening treatments of steel has shown significant improvement of various properties including wear and fatigue resistance. Cryogenic treatment is yet another approach acknowledged by some to extend the tool life of many cutting tools. We will describe the complete procedure and investigate the effects on the metallurgical changes in the tool steel. However real mechanisms behind the better performance of tools are still in doubt. Studies in the given references on cryogenically treated tool steel shows micro structural changes in material that can influence the tool life. However little is gained from the experimental results showing involvement of carbide precipitations. Cryogenic treatments of carbides has yet to be extensively studied. In this paper drill bits are treated with cryogenic method and to predict the hardness, wear strength and other results are analysing.

Characterization of the mechanical properties and microstructural evolution of martensitic steel in repeated tempering cycles

The purpose of this study was to understand the behavior of martensitic H13 steel in accordance with the microstructural evolution, mechanical properties and wear in repeated tempering cycles. The microstructures were characterized by axio image observer microscope, scanning electron microscope (SEM), x-ray diffraction (XRD). Uniaxial tensile test, charpy v-notch impact test, rockwell hardness test and wear test were conducted to analyze the changes in mechanical properties, impact properties, hardness and wear in repeated tempering cycles. The specimen prepared were subjected to the hardening at 1030 °C for 20 minutes, oil quenched and subjected to repeated tempering cycles at 570 °C for 2hrs holding time each. The mechanical properties recorded indicates that the maximum ultimate tensile strength obtained was at double tempering due to secondary hardening effect i.e., alloy carbides precipitation offering strength to the matrix and corresponding wear was found to be minimum. The annealed specimen revealed bainitic microstructure and with hardening and repeated tempering cycles, fine needle like structure and carbides was observed in microstructure and retained austenite was converted into martensite and martensite was converted into tempered martensite. Carbide size and martensite lath distribution controls the strength and fracture rate.

Tailoring the microstructure and mechanical properties of (CrMnFeCoNi)100-xCx high-entropy alloys: Machine learning, experimental validation, and mathematical modeling

As a common thermomechanical treatment route, “cold rolling and annealing” is widely used for the processing and grain refinement of interstitial-containing high-entropy alloys (HEAs). The interrelationship between the parameters of this process, the content of interstitial elements, and their interactions are outstanding challenges and areas of open discussion. Accordingly, the data-driven machine learning approach is a favorable choice for tuning the microstructure and mechanical properties, which needs to be systematically investigated. In the present work, these subjects were addressed in terms of correlating the thermomechanical processing parameters and chemical composition with the recrystallization and grain growth behaviors, grain size, carbide precipitation, and the resulting tensile yield stress for the model (CrMnFeCoNi)100-xCx HEAs. For this purpose, machine learning models based on adaptive neuro-fuzzy inference system (ANFIS), backpropagation artificial neural network (BP-ANN), and support network machine (SVM), as well as mathematical relationships and equations for the contribution of each strengthening mechanism were proposed and verified by extensive experimental work, which shed light on the design and prediction of the microstructure and properties of HEAs.

Superior mechanical properties of M35 high-speed steel obtained by controlling carbide precipitation and distribution via electropulsing treatment

Carbide precipitation and distribution always significantly affect the mechanical properties of High-speed Steel (HSS). Thus, the effect of electropulsing treatment (EPT) on the microstructure and mechanical properties of M35 HSS was investigated in this paper. The results show that the electropulsing austenitising then quenched, followed by electropulsing tempered (EQ + ET) samples, showed a 2.3% increase in Rockwell hardness, a 9.7% increase in the bending strength, and the impact toughness increased by 10.3% compared with the conventional heat treatment (CQ + CT) samples. The superior mechanical properties were attributed to the reduction of retained austenite (RA), the uniform distribution of the carbide, and the refinement of the prior austenite grains. Under the action of the current, Ms increased in response to various combinations of alloying elements, thereby reducing the content of RA. Compared to conventional heat treatments, the electropulsing treatment provides additional Gibbs free energy, as well as a large number of dislocations generated by the thermo-compressive stresses, which increase the carbide nucleation sites, resulting in a large number of small-sized carbides precipitating and uniformly distributed in the matrix. The fracture morphology indicates that micro-cracks arise between the carbide and martensite, and the larger carbide provides a preferential path for crack initiation.

Local Hydrogen Measurements in Multi-Phase Steel C60E by Means of Electrochemical Microcapillary Cell Technique

By utilizing hydrogen as an eco-friendly energy source, many metals are exposed to gaseous (pressurized) hydrogen. High-strength steels with an ultimate tensile strength of 800 MPa and above are especially susceptible to hydrogen-induced fracturing, also referred to as hydrogen embrittlement (HE). Both the microstructure and phase fractions within the steel, as well as lattice distortion, carbide precipitation, residual stress, etc., significantly affect the susceptibility to HE. Among others, one important cause for this observation is found in the locally varying hydrogen solubility within different microstructural phases such as martensite, bainite, pearlite, and ferrite. Both a thorough understanding of the HE mechanisms and taking countermeasures in the form of alloying design require an accurate analysis of local diffusive hydrogen concentrations within the material. Thermal analysis methods such as Thermal Desorption Mass Spectrometry only display an integral hydrogen concentration throughout the whole sample volume. To analyze the local diffusive hydrogen concentration, novel measuring techniques with a high special resolution must therefore be utilized. The current research presents first-of-its-kind hydrogen analyses by means of the electrochemical microcapillary cell. Using a 10 µm tip opening diameter allows for conducting local diffusive hydrogen measurements within individual grains of multi-phase carbon steel C60E (1.1221). The results confirm that hydrogen is distributed heterogeneously within multi-phase steels. Considering the individual phase fractions and the respective local diffusive hydrogen concentrations, a total diffusive hydrogen concentration can be calculated. The obtained value is in good agreement with reference thermal hydrogen analyses. Our results suggest that electrochemical microcapillary cell measurements offer great potential for further studies, which will provide a better understanding of HE and local hydrogen accumulation.

Effect of cooling medium on the κ carbide precipitation behavior, microstructure and impact properties of FeMnAlC low-density steel

The effect of four different cooling mediums, namely ice brine, water, oil, and air on the κ carbide precipitation behavior, microstructure, and impact properties of FeMnAlC low-density steel is thoroughly investigated by using OM (Optical Microscope), SEM (Scanning Electron Microscope), TEM (Transmission Electron Microscope), XRD (X-Ray Diffraction), VSM (Vibrating Sample Magnetometer), Rockwell hardness tester and in conjunction with low-temperature impact experiments. The results indicate that after cooling with different mediums, the austenite structure exhibits a mixed crystalline phenomenon and has a significant presence of twins. The average grain size of austenite increases as the cooling rate decreases, with the largest size observed in air-cooled conditions. Concurrently, the volume fraction and size of intragranular κ carbides gradually increase with a decreasing cooling rate. This phenomenon contributes to an increase in Rockwell hardness, with the highest value recorded in the air-cooled state at 36.8 HRC. Furthermore, the impact toughness initially increases and then decreases as the cooling rate decreases. Notably, water cooling demonstrates the highest impact energy at 68 J. The formation of intergranular κ carbides in oil and air-cooled conditions is identified as the primary reason for the decline in impact toughness.

Improved creep‐fatigue and remnant tensile/creep properties of 321 stainless steel by self‐healing coating

AbstractAISI 321 steels used as intake valves in turbines are frequently subjected to creep‐fatigue (C‐F) exposure during service. Improving C‐F resistance and assessing remnant creep/tensile properties are therefore required for their safe service. In this work, the self‐healing coating consisting of Al2O3‐13TiO2 layer, TiC layer, and NiCrAlY layer was prepared for 321 steel. The effects of such self‐healing coating on the C‐F and remnant creep/tensile properties were studied. The results showed that the initial hardening phenomena of the studied steel during C‐F exposure was mainly attributed to the dislocation strengthening and a certain level of carbides precipitation strengthening, while the subsequent softening behaviors were resulted from dynamic recovery and coarsening of carbides. Moreover, as compared to other coatings, the self‐healing coating is able to improve the mechanical properties of steels due to dislocation strengthening, precipitation strengthening, and the self‐healing behavior resulting from the reaction between the TiC layer and oxygen.

Mechanical characteristics and stretch-bend failure analysis on ultra high frequency pulsed gas tungsten arc welded thin FSS 409/430 dissimilar joints

The Mechanical and Stretch-Bend Failure studies on Ultra High Frequency Pulsed Gas Tungsten Arc Welded dissimilar joints of AISI409-AISI430 Ferritic Stainless Steels were conducted. Welding was conducted with 5 ultra high frequencies (50 Hz, 150 Hz, 250 Hz, 350 Hz, 450 Hz). Mechanical characteristics evaluation on the joints included tensile strength, microhardness variations across the welds and creep. Microstructural and metallurgical investigations included weld cross section evaluation, comparing grain variations in high, medium and low thermal heat affected zones, weld zones and base material region. Stretch bend failure studies included studies on angular distortion, fracture limit strain, and coefficient of friction. Tests revealed that joints welded at 350 Hz was better, compared to other joints. Dissimilar AISI409-AISI430 joint fabricated at 350 Hz exhibited 267 ± 3 MPa as yield and 409 ± 6 MPa and as ultimate tensile strength. Its creep fracture duration was 72.7 min (highest among the joints). Microstructural studies revealed grain growth, partially coarse and partially fine grains in heat affected zones. Depending on the difference in grain sizes, on both sides of the welds, heat affected regions were identified as three distinct zones. In AISI430 side; high temperature austenitic, martensitic, delta ferrites and in AISI409 side; needle like martensitic structures, mixture of ferritic-austenitic, δ-ferrite with carbide precipitation were found in high, medium and low thermal heat affected zones, respectively. On increasing the ultra high frequency pulses, angular distortion increased, fractures changed from tensile/shear type to mixed type. In shear bend tests, on increasing the ratio of radius: thickness, fracture limit strain on outer surface, across sheet thickness, due to stretching increased.

Precipitation and Transformation of Carbides during Tempering of 7Cr14 Martensitic Stainless Steel

The precipitation and transformation of carbides in steel are gaining more interest since they are closely related to the properties of steel. Herein, the precipitation and transformation of carbides during tempering of the 7Cr14 martensitic stainless steel subjected to high‐temperature solution treatment (HTST) are investigated. The results indicate that the precipitation of M3C (300–333 °C) and M23C6 (612–645 °C) carbides occurs during tempering of the HTST steel. The effective precipitation activation energies of M3C and M23C6 carbides are 120 ± 7 and 272 ± 13 kJ mol−1, respectively. The precipitation processes of M3C and M23C6 carbides are dominated by C and Cr atomic diffusion, respectively. Moreover, it is found that two transformation processes occur during tempering with increasing temperature, namely, M3C carbides dissolve in the matrix and then M23C6 carbides precipitate along the boundaries of martensitic laths, and the plate‐like M3C carbides decompose into several globular or rod‐like M23C6 carbides that arrange in a chain‐like morphology.

Intergranular Corrosion in X39CrMo17-1 – A Review

Abstract The aim of this contribution is to review cases of repeated snap ring failures in large gas turbine engine service due to intergranular attack, or intergranular corrosion, IGC, and to shed some light on metallurgical aspects of the wet corrosion resistance of the subject high-alloy martensitic stainless chromium steel X39CrMo17-1, DIN 1.4122. It is important to note that only snap rings, a.k.a. retaining rings for bores or Seeger rings, were affected by those failures, namely fractures resulting from intergranular attack (IGA, Kornzerfall). It was determined that the metallurgical root cause of failure was sensitization, resulting from secondary chromium carbide precipitation at grain boundaries (GB), and the ensuing chromium depletion in narrow bands adjacent to the GB, which rendered the matrix there sensitive to selective corrosion (the chromium content in these narrow seams, measuring only a few 10 nm in width, drops below the corrosion resistance threshold of ca. 10.5 %). Snap rings, as the name suggests, require a certain “snappiness” to serve their purpose. It is because of this requirement that all snap rings that experienced failures in the field were heat treated per DIN EN 10088-2, providing for a low tempering temperature of max. 250 °C, leading to a relatively high hardness of ca. 580 HV 10, providing said “snappiness”. It turned out that the microstructure resulting from this heat treatment (H/T) is sensitized, rendering the material sensitive to IGA. To the knowledge of the authors, no other components made of this martensitic stainless chromium steel are given this H/T, but rather a high-temperature tempering of 650 °C–750 °C per DIN EN 10088-3, producing a lower hardness in the order of ca. 300 HV 10 and largely a lack of “snappiness”, the latter being not required by those non-snap ring applications. Metallurgically, it became clear that high-temperature tempering per DIN EN 10088-3 eliminates sensitization by “backfill” diffusion of chromium from the non-depleted matrix into formerly depleted regions next to GB. It was therefore decided in the authors’ organization to eliminate X39CrMo17-1 per DIN EN 10088-2 as a possible material selection. The metallurgical investigations described in this contribution corroborate and support this decision.

Effect of precipitation-induced element partitioning during tempering on mechanical properties of hot-rolled 3Mn steel after intercritical annealing

This work explores the carbide evolution behavior and mechanical property evolution mechanisms of intercritical-annealed 3Mn steel during the tempering process by comparing different tempering times (5/10/20 min). The results showed that the elongation of 3Mn steel increased from 19.5% to 26.5% after tempering while maintaining a tensile strength above 1250 MPa. It is also found that carbide precipitation during tempering is first followed by dissolution. The mechanical properties exhibited abnormal degradation at tempering for 10 min, with a tensile strength of 1265 MPa and a total elongation of 16.0%. However, the optimal mechanical properties were achieved at tempering for 20 min, with a tensile strength of 1286 MPa and a total elongation of 26.5%. During the initial stage of tempering, a transformation occurs from M3C to stable M7C3, with the presence of numerous dislocations and grain boundaries promoting the precipitation and growth of abundant carbides. This leads to a reduction in the C and Mn content in the matrix, consequently decreasing the austenite content and stability, resulting in the transformation of austenite to the BCC phase during tempering instead of cooling. The decreased austenite content and stability lead to reduced ductility. Subsequently, dislocations were annihilated during tempering, suppressing carbide precipitation, and the over-precipitated carbides dissolved under thermodynamic driving force, leading to an increase in C and Mn content in the remaining austenite, thus enhancing its stability. The precipitation and dissolution of carbides during tempering, along with the partitioning of elements between carbides and austenite, strengthen austenite stability and improve mechanical properties.

Oxidation behavior and corrosion properties of 2-GPa grade Co-reduced ultrahigh-strength stainless steel

This study investigated the oxidation behavior and corrosion resistance of 2-GPa grade ultrahigh-strength stainless steel. Results revealed that the addition of V to Co-reduced FerriumS53 (7Co1V) accelerated the precipitation of MC carbide during aging, while inhibiting the precipitation of Cr-rich M23C6 carbide. A significant amount of Cr was predicted in the microstructure of the alloys, and this microstructure increased the partitioning of Cr to the alloy surface and provided enhanced resistance against corrosion pitting. These findings suggest that the addition of V into Co-reduced stainless secondary hardening steels can enhance their oxidation and corrosion resistance without compromising their mechanical properties.

Tailoring the microstructure and mechanical properties of laser metal-deposited Hastelloy X superalloy sheets via post heat-treatment

Nickel-based superalloys are subject to severe microsegregation and exhibit anisotropic properties during laser metal deposition (LMD), which restricts their wide application in the aerospace field. Thus, post heat-treatments must be investigated to further regulate the microstructure and mechanical properties of such components. The aim is to provide a comprehensive understanding of the effects of double-stage aging (DA) and solution plus double-stage aging (SDA) heat treatments on microstructure and mechanical properties of Hastelloy X superalloy sheets fabricated via LMD. The effects of DA and SDA heat treatments on the density, residual stress, phase composition, carbides precipitation behavior, dislocation structure, grain structure, and mechanical properties of the sheets were studied and in comparison with the as-deposited (AD) samples. The results showed that the DA heat treatment yielded a significant amount of lamellar and granular phases in the interdendrites and grain boundaries, whereas the anisotropic microstructure between the transverse and vertical planes was similar to that observed in the AD samples. These phases are mainly composed of Laves phase and carbides. However, the needle-like carbide phase was dispersedly precipitated within the grains and at grain boundaries, and exhibited full recrystallization and reduced dislocation density after SDA heat treatment. Consequently, the SDA samples presented superior strength-ductility balance to those of the AD and DA samples with irregularly shaped Laves phase and carbides owing to microstructural changes. For instance, the SDA heat treatment improved the ultimate tensile strength and fracture elongation of the vertical samples by up to 10.9% and 30.7%, respectively, whereas the microhardness decreased by 13.3% compared to the AD samples. The compressive residual stress of 98 MPa and tensile residual stress of 147 MPa were also observed on the surfaces of the SDA and AD samples, respectively. In addition, the SDA samples exhibited an almost isotropic tensile behavior in the vertical and horizontal directions as the epitaxially grown columnar grains transforms into equiaxed grains, as well as exhibited a prominent overall crystallographic texture. The effect of DA and SDA heat treatments on the mechanical properties were analyzed on the basis of stress–strain curves, hardening behavior, and multiple strengthening mechanisms.