Effect Of Carbide Precipitation Research Articles

Effect of Carbide Precipitation on Hardness and Wear Resistance of H13 Steel

The carbide precipitation of H13 steel and its effect on hardness and friction and wear resistance are investigated by microstructure observation, phase analysis, and mechanical property test. Results show that the tempering hardness is mainly related to the content of secondary carbides. After solution treatment in the temperature range of 1040–1070 °C, quenching and tempering, with the increase of the solution temperature, the content of secondary carbides and hardness of H13 steel in the tempering microstructure increase first and then decrease, and both reach the maximum value when the solution temperature is 1060 °C. The change of hardness is consistent with that of the content of secondary carbides. When the solution temperature is 1040 °C, the wear mass loss of the tempered H13 steel is the least, which is 4.63 mg, indicating that its wear resistance is the best, and this is caused by the presence of more undissolved carbides in the tempering microstructure. With the increase of the solution temperature, the wear mass loss increases gradually, and the wear resistance decreases, which is mainly related to the content decrease of undissolved and secondary carbides and the content increase of residual austenite.

Effect of carbide precipitation on Coffin–Manson relationship of a polycrystalline nickel‐based superalloy

AbstractThis study explores the dual‐slope Coffin–Manson (C–M) behavior of a polycrystalline nickel‐based superalloy, EA, used in turbine engine applications with an emphasis on discerning the micro‐mechanisms responsible for it. The motivation for distinguishing the micro‐mechanisms responsible for bi‐linear C–M behavior stemmed from the earlier evolved comprehensions that state that the fatigue life estimation based on the extrapolation of any single line gives inaccurate results. Transmission electron microscopy (TEM) investigations of fatigue fractured specimens at low strain amplitudes, Δε/2, revealed that dislocations are homogeneously distributed in the γ‐channels and occasionally form networks at γ/γ′ interface. Whereas deformation is heterogeneous at high Δε/2 owing to the complex dislocation reactions. Cr23C6 carbides are precipitated during the high Δε/2 fatigue tests, which act as obstacles for dislocations. The deformation heterogeneity resulting from the dislocation–γ′ precipitate interactions and the dislocation–M23C6 carbide interactions accounts for the dual‐slope C–M behavior.

Study of the Effect of Quenching and Tempering Modes on the Strength Level of Alloyed Structural Steels Used to Produce Fasteners

The development of high-strength fasteners is required due to the modern trend of reducing the weight of engineering structures. At present, structural bolts of property classes 8.8–10.9 are widely used, and higher-strength bolts of property classes 12.9 and 14.9 are being developed. In this paper, we analyzed the possibilities and conditions for manufacturing fasteners of different strength categories from steels of seven grades, containing and not containing boron. The necessary corresponding temperature ranges of processing are determined based on the study of hot-rolled round steel. Tensile strength, yield strength, relative elongation, reduction in area, and Vickers microhardness were measured. An analysis was made of the hardenability and the influence of the holding time during tempering on the mechanical properties of the considered round steel. Using the method of scanning electron microscopy, the effect of carbide precipitation during tempering on the mechanical properties of fasteners was established.

Effect of Carbide Precipitation on “Precipitation Plasticity” and Residual Stress during Tempering

Materials with residual stress can experience irreversible plastic strains as carbides precipitate during the tempering process, thereby relaxing the residual stress. In previous studies, this plastic behavior is named “precipitation plasticity.” Although precipitation plasticity plays a key role in the relaxation of the residual stress, the micromechanism involved is not yet elucidated. Here in this study, experiments are performed on low‐carbon steel to study precipitation plasticity and the residual stress during tempering. The results show that precipitation plasticity is mainly produced by the generation of interfacial vacancies at the carbide–matrix interface and the diffusion and evolution of these vacancies under temperature and stress fields. Two precipitation plasticity regimes are observed, namely, Precipitation Plasticity I, which is associated with vacancy diffusion, and Precipitation Plasticity II, which is associated with dislocation proliferation. Precipitation Plasticity I is found to be controlled by the volume mismatch and carbide size and is the main cause of residual stress relaxation. The finer and more dispersed the carbide precipitates are, the more significant the precipitation plasticity is. Precipitation Plasticity II causes a slight increase in the residual stress, which, however, is considerably smaller than the stress relaxation corresponding to Precipitation Plasticity I.

Microstructural Investigations of Ni-Based Superalloys by Directional Solidification Quenching Technique.

The improvement of the mechanical properties of Ni-based superalloys is achieved in most cases by modifying the chemical composition. Besides that, the processing can be modified to optimize the as-cast microstructure with regard to the mechanical properties. In this context, the present study highlights the solidification mechanism of several Ni-based superalloys by conducting experiments using a modified, laboratory-scale Bridgman-Stockbarger furnace. In that context, the single-crystal rods are partially melted, directionally solidified and quenched sequentially. Several characterization methods are applied to further analyze the influence of the alloying elements and the variation of the withdrawal rate on the as-cast microstructure. Four stages of solidification are distinguished whereby the morphology observed in the different stages mainly depends on the cooling rate and the local concentration of the carbide forming elements. The effect of carbide precipitation and the effect on the as-cast microstructure is investigated by employing energy dispersive X-ray spectrometry (EDX) and electron backscatter diffraction (EBSD) analysis techniques. A local polycrystalline structure is observed in the single-crystal system as consequence of the influence of the carbon content and the cooling rate. The present work aims to develop strategies to suppress the formation of the polycrystalline structure to maintain the single-crystal microstructure.

Effect of thermal aging on metallurgical, tensile and impact toughness performance of electron beam welded AISI 316 SS joints

Abstract Electron beam welding was used to fabricate a fully penetrated joint of 18 mm thick AISI 316 stainless steel plates. The effects of carbide precipitation on the metallurgical and mechanical properties of the weld were evaluated after aging at 750 °C for 300 h. The optical microstructure analysis showed that the weld zone consists of skeletal, vermicular, lathy, and lacy ferrite which further transformed into carbides after thermal aging. The weld zone was weaker in terms of ultimate tensile strength as compared to the base metal, as the presence of ferrite content (varied from 8% to 2.9 %) in the weld zone. Analysis along the thickness of the welded joint revealed that the bottom of the weld bead possessed 6% higher ultimate tensile strength as compared to the top of the weld bead. The microhardness and impact toughness in as-welded specimens got increased by 12.5 % and 49.5 % respectively while traversing from top to root of the weld bead. Thermal aging promoted the formation of Cr rich carbides (Cr23C6) on the grain boundaries and reduced the delta ferrite content near to zero. Further, it led to a reduction in the impact toughness by 62 % at the bottom of WZ and increased the ductility and the microhardness of the weld bead.

Effect of Carbide Precipitation on the Evolution of Residual Stress during Tempering

The evolution of microstructure and residual stress during the tempering of 700 L low-carbon micro-alloyed steel was studied using a crack compliance method for measuring residual stress. Additionally, a non-isothermal tempering dilatation test, Vickers micro-hardness test, and transmission electron microscopy were used. The evolution of residual stress during tempering consists of two stages. The first stage coincided with cementite precipitation. Under the initial residual stress, the transformation plasticity due to cementite precipitation leads to partial relaxation of the micro-stress evoked by the austenite-to-ferrite transformation during quenching. It also caused the material surface and the core to exhibit different residual stress evolution trends. After tempering at 300 ∘ C for 30 min, the residual stress was reduced from 487 MPa to 200 MPa; however, the elastic strain energy remained unchanged. The second stage coincided with alloy carbide precipitation and Mn partitioning, but the precipitation of the alloy carbide only reduced the elastic strain energy by 8.7%. Thus, the change in activation energy was the main reason for the relaxation of residual stress at this stage. After tempering at 600 ∘ C for 30 min, the residual stress was reduced to 174 MPa, the elastic strain energy was reduced by 72.72%, and the residual stress was controlled.

Effect of aging process on the microstructure, corrosion resistance and mechanical properties of stainless steel AISI 204

In this study, the microstructure thermostability, corrosion resistance, and mechanical properties of AISI204 stainless steel after aging were investigated. The microstructural analysis showed precipitation of M23C6 carbide along grain boundaries and its amount tends to increase with increasing aging time and temperature. Little effect of carbide precipitation on tensile strength where the maximum drop was at temperature 850 °C and aging time 48 h by 5.09%. At the same aging conditions, precipitation severely affected yield strength, ductility, and the microhardness. The yield strength decreased by 46% and microhardness to 210 HV. On the other hand, the ductility increased to 21% in terms of percent reduction in area. Weight loss as a result of uniform corrosion and corrosion current density were strongly dependent on aging time and temperature. Furthermore, Passivation current density showed independent behavior as the temperature increase.

Effect of Carbide Precipitation on Mechanical Properties of Si-added Middle Carbon Martensitic Steels

Effect of Carbide Precipitation on Mechanical Properties of Si-added Middle Carbon Martensitic Steels

Effect of carbide precipitation on strain-hardening behavior and deformation mechanism of metastable austenitic stainless steel after repetitive cold rolling and reversion annealing

A metastable austenitic stainless steel was repetitively cold rolled and reversely annealed. The strain-hardening behavior and deformation mechanism during tensile testing were comparatively studied for the specimens annealed at 800°C and 1000°C. Fine-grained austenite with uniformly distributed carbides was formed in the 800°C-annealed specimen, whereas coarse-grained austenite without carbides was obtained with annealing at 1000°C. Continuous strain hardening was achieved in all specimens, which could be attributed to the strain-induced martensite and deformation twining for the annealed specimens at 800 and 1000°C, respectively. The carbide precipitation promoted the formation of strain-induced martensite due to the depletion of austenite stabilizers.

Effects of carbide precipitation on the microstructural and tribological properties of Co–Cr–Mo–C medical implants after thermal treatment

In this work, the influences of heat treatments on the microstructural features and, consequently, on the mechanical and wear characteristics of Co–Cr–Mo–C alloys commonly used as hip and knee implant materials, are investigated. Specimens of Co–Cr–Mo–C alloy in the as-cast condition were solution treated at 1230 °C for 3 h, and then either were quenched in water or furnace cooled. The achieved microstructures of the heat-treated samples, characterized by fine globular and lamellar-type carbides due to the different thermal-treatment conditions, was proved to affect the material microstructural, mechanical and wear behavior. The wear behavior was evaluated by means of pin-on-disk wear tests, which showed that the wear properties are strongly affected by the carbides shape, distribution, and size. It was proved that both large carbides precipitated in as-cast alloys, and also lamellar-type carbides induced by slow cooling after solubilization caused lower wear resistance than the globular fine carbides that were dispersed in the solution-treated and water-quenched specimens. Moreover, the e-martensite, formed by the strain-induced martensitic transformation through plastic straining during the sliding of pin on disk, decreases the wear rate mainly due to the lower number of slip systems of the hexagonal structure.

Plastic instability at elevated temperatures in a TRIP-assisted steel

An experimental investigation of plastic instability in a three-phase, TRIP-assisted steel prepared with a two-step quenching and partitioning heat treatment is presented. Testing conditions explored temperatures from 293 to 623K at four quasi-static strain rates. Strain rate contours computed with stereo digital image correlation (DIC) showed propagating bands that resemble Type A Portevin–Le Châtelier (PLC) bands and are indicative of plastic instability. Negative strain rate sensitivity (nSRS), noted in the 333 to 623K range, with flow curve serrations occurring within 373–523K, suggested dynamic strain aging as the underlying mechanism for plastic instability. Band propagation speed and peak strain rate are dependent on strain rate but not temperature. Based upon the steel chemistry and band nucleation and kinetics analyses, plastic instability in the QP980 steel is attributed to C diffusion. The activation energy for band propagation is estimated to be 160±16kJ/mol, in excess of 84.1kJ/mol for C diffusion. The effect of carbide precipitation in lath martensite on plastic instability is investigated with transmission electron microscopy at selected temperatures.

Migration of Dislocation Boundaries in a Modified P911 3%Co Heat Resistant Steel during Tempering, Ageing and Creep

Effect of carbide precipitation on pinning force and migration mechanism of boundaries of martensite laths was considered in a 3%Co modified P911. The dimensions of second phase precipitations, martensite laths and dislocation densities were measured by means of transmission electron microscopy. The pinning forces retarding the motion of the lath boundaries, that arise from M(C,N) nanoscale precipitations and M23C6 particles were evaluated by using different models. The pinning pressure evaluated by taking into account a non-uniform distribution of M23C6 particles was high enough to stabilize the lath martensite structure during tempering and long term ageing. On the other hand, significant coarsening of martensite laths occurred in neck portions of samples subjected to long-term creep tests. Additional effects from dislocation density and applied stress on the motion of lath boundaries are considered in some details.

New Model for the Overall Transformation Kinetics of Bainite. Part 2: Validation

A new model for the overall kinetics of the bainite transformation has been validated experimentally. The new model, presented in the 1st part of this work, is based in the displacive mechanism for bainite transformation. Thus, the bainite transformation kinetics of three medium carbon-high silicon steels has been studied. Results show that the model, which does not consider the effect of carbide precipitation in the bainite kinetics, predicts with a high degree of agreement the time evolution of bainitic ferrite volume fraction, even when lower bainite is present at the microstructure. Data from two additional medium carbon-high silicon steels, frequently reported in the literature, have been also used for reinforcing the validation, obtaining, again, a high agreement between the kinetic results for bainite transformation predicted by the model and those obtained experimentally. (doi:10.2320/matertrans.47.2473) In the first part of this study, a new model for the kinetics of the bainite transformation has been proposed. The model is based on the displacive mechanism for bainite transforma- tion. An important characteristic of this new model is the complete separation between the kinetics of both nucleation events of bainitic ferrite subunits, in austenite grain bounda- ries and at subunits previously formed. This distinction is based in a geometrical conception of the development of the transformation and has led to the elimination of the autocatalysis factor, an obscure parameter used in former kinetics models. The model correctly predicts the effect of carbon and other alloying elements such manganese and cobalt on the transformation kinetics, as it was shown in the first part of this work. The precipitation of cementite between the subunits of bainitic ferrite during bainitic transformation can be sup- pressed by alloying the steel with about 1.5 mass% silicon, which has very low solubility in cementite and greatly retards its growth from austenite. 1-3) The carbon that is rejected from the bainitic ferrite enriches the residual austenite, thereby stabilising it down to room temperature. Consequently, an isothermal transformation in the range of the bainite trans- formation leads to a microstructure consisting of bainitic ferrite separated by carbon-enriched regions of austenite. Since the cementite precipitation between the plates of bainitic ferrite plates has not been considered in the modelling, steels with high silicon content are most adequate for the validation of the proposed model. However, cementite precipitation within bainitic ferrite plates (lower bainite), that can occur even in high silicon steels, has not been considered in the model. In this sense, the study of lower bainite kinetics is interesting in order to evaluate the reliability of the model predictions in the event of lower bainite formation. It has been shown in the 1st part of the study that if no other reaction interacts with the successive nucleation and growth of subunits of bainitic ferrite, the incomplete reaction phenomenon, by means of the T 0 0 curve, provides a method for the estimation of the maximum volume fraction of bainitic ferrite that can be formed, at a given temperature, in a steel, vbmax. Considering a steel with a nominal carbon content �

Effects of carbide precipitation on the strength and Charpy impact properties of low carbon Mn–Ni–Mo bainitic steels

The effects of carbide precipitation on the strength and Charpy impact properties of tempered bainitic Mn–Ni–Mo steels have been investigated. An attempt has also been made to modify the microstructure of the steels in order to improve the Charpy properties, by controlling the alloy composition being guided by thermodynamic calculations of phase equilibria. Coarse rod type or agglomerated spherical type cementite particles in inter-lath region were considered to be mostly detrimental to Charpy impact properties. By reducing the precipitation of cementite through decreasing carbon content and/or by substituting it into fine M 2C carbides through increasing the molybdenum content, DBTT could be lowered significantly. Further decrease of DBTT could be achieved by substituting part of manganese content by nickel. Yield strength of tested alloys could be maintained at the level of a reference 0.2 wt% carbon alloy in spite of the significant reduction in carbon content, mainly by the increase in the precipitation of fine M 2C type carbides with increased molybdenum content.

The effect of carbide precipitation on the hydrogen-enhanced fracture behavior of alloy 690

Alloy 690 is susceptible to hydrogen embrittlement where hydrogen reduces the ductility and causes the fracture morphology to change to predominantly intergranular. The role of carbide precipitation in the embrittlement behavior is not well defined. The objective of this work is to understand the effect of intergranular carbide precipitation on the hydrogen embrittlement of alloy 690. The work reported herein used tensile and compact-tension specimens in both the solution-annealed condition (minimal grain-boundary carbide precipitation) and in the solution-annealed condition followed by an aging treatment to precipitate grain-boundary carbides. By performing the mechanical tests on materials in both uncharged and hydrogen-charged conditions, it was possible to evaluate the degree of embrittlement as a function of the carbide precipitation. It is shown that the embrittlement due to hydrogen increased as the material was aged to allow grain-boundary carbide precipitation. It is proposed that the increase in embrittlement was caused by increased hydrogen at the carbide/matrix interface due to the trapping and increased stresses at the precipitate interface, which developed from strain incompatibility of the precipitate with the matrix. It is further shown that increasing the hydrostatic stress increased the tendency for intergranular fracture, as is consistent with other nickelbase alloys.

Nondestructive evaluation of steels using acoustic and magnetic Barkhausen signals—I. Effect of carbide precipitation and hardness : 37267 Kameda, J.; Ranjan, R. Acta Metallurgica, Vol. 35, No. 7, pp. 1515–1526 (Jul. 1987)

Nondestructive evaluation of steels using acoustic and magnetic Barkhausen signals—I. Effect of carbide precipitation and hardness : 37267 Kameda, J.; Ranjan, R. Acta Metallurgica, Vol. 35, No. 7, pp. 1515–1526 (Jul. 1987)

Effect of carbide precipitation on the creep behavior of Alloy 800HT in the Temperature Range 700 ° to 900 °

The creep behavior of alloy 800HT was studied at 700 °, 800 °, and 900 ° under stresses ranging from 30 to 170 MPa. Samples that were tested in the as-quenched condition after solution treatment exhibited longer creep life than those that were overaged before testing. This difference in creep life was found to increase at lower creep stresses at a given temperature. This phenomenon is attributed to the precipitation of M23C6carbides during the early stages of creep, which strengthen the material by exerting threshold stresses on moving dislocations and thereby reducing the creep rate. A model is developed to describe the influence of carbide precipitation during creep on the behavior of the material under different creep temperatures and stresses. Comparison with the experimental results shows that the model gives accurate predictions of the creep behavior of the material in the range of stresses and temperatures used in the present study. In addition to its predictive value, the model is useful in understanding the factors that affect the creep behavior of materials when precipitation of hard phases is taking place during creep. The strengthening effect of particle precipitation during creep, as represented by the value of the threshold stress, is shown to be a complex function of the supersaturation of the matrix, the applied creep stress, and the test temperature.

Creep and creep rate curves of a 10cr-30mn austenitic steel during carbide precipitation

The effect of carbide precipitation on creep and creep rate curves was investigated for 10Cr-30Mn austenitic steel containing 0.003 to 0.55 wt pct carbon. After solution annealing, the specimens were subjected to creep testing at 873 K for up to 30 Ms (8300 hours). In the low-carbon steels containing below 0.1 wt pct carbon, where carbide precipitation scarcely occurred, the decrease in creep rate with time in the transient creep region was described by log έ = A - (1/3) log t, where A is a constant depending on stress and carbon concentration. On the other hand, in the high-carbon steels containing above 0.2 wt pct carbon, where extensive precipitation of M23C6 occurred, the creep rate decreased significantly at long times above 3 to 5 ks (1 hour), deviating from the preceding equation for the low-carbon steels. The Johnson-Mehl equation with the time exponent n = 2/3 provided a reasonable approximation for the significant decrease in creep rate at long times. This resulted from a stress-induced precipitation of M23C6 on dislocation lines produced by creep deformation. The rate constant of the Johnson-Mehl equation depended on carbon concentration but not on stress levels examined.

Ni-30Cr合金の高温クリープ抵抗に及ぼす粒界に沿った転位上析出の効果

Ni-30Cr合金の高温クリープ抵抗に及ぼす粒界に沿った転位上析出の効果