Carbide Size Research Articles

Effect of Tempering Temperature on Microstructure and Uniformity of LP Steel Plate under HOP Process

Longitudinal profiled steel plate (LP steel plate) is a green steel product, which is widely used in steel structure fields such as ships and bridges. In this paper, the effect of Heat-treatment Online Process (HOP) on microstructure and uniformity of LP steel plate was investigated by thermal simulation test. The results show that the microstructure consists of grain boundary allotriomorphs, upper bainite, acicular ferrite and carbon-enriched austenite at 550°C. During the isothermal process, the austenite transforms into bainite, the acicular ferrite grows and coarsens, and the bainite laths gradually “fuse” to form large granular bainite. After online tempering at 650°C, the austenite transforms into ferrite, acicular ferrite and bainite undergo tempering transformation, in which the size of bainite decreases and some acicular ferrite transforms into polygonal ferrite. After tempering at different temperatures (650∼750°C), the microstructure consists of grain boundary allotriomorphs, coarsened acicular ferrite and a small amount of granular bainite. With the increase of tempering temperature, the tempering transformation degree of acicular ferrite and bainite is intensified. Elongated carbides at grain boundaries become short rods and particles, which decreases the size and aggregation of carbides. Compared with the traditional process, the difference of microstructure and hardness of LP steel plate with different thickness specifications after HOP process is reduced, and the hardness is higher, which is beneficial to improve the performance and uniformity.

Soft annealing technology applied to high chromium white cast iron

High Cr white cast iron is an alloy widely used in the field of manufacturing parts working in conditions of high wear resistance. However, the machining process for this alloy is often difficult due to its high hardness. Therefore, the objective of this study is to find out the appropriate parameters of heat treatment process to be able for softening of high Cr white cast iron with a lower hardness, ensuring the cutting process. In this study, the samples were austenitized partially and soft annealed in a resistance furnace. Optical microscope, X-ray diffractometer and field emission scanning electron microscope were used to observe and evaluate the microstructure of samples before and after heat treatment. The Rockwell hardness tester (RHT) is also used to evaluate hardness variation of samples. Research results have shown that the change of primary carbide grain size and formation of secondary carbides during heat treatment can reduce the hardness of white cast iron to the suitable range for machining.

Effect of Tempering Temperature on the Microstructure and Stress Corrosion Cracing Susceptibility of Ultra-High-Strength Mooring Steel

Mooring chain steel has been widely used for stabilizing offshore platforms and suffers from stress corrosion cracking. Herein, the microstructure difference, its relation to strength and susceptibility of stress corrosion cracking after tempered at different temperatures have been studied. Result shows increasing tempering temperature increases the proportion of low value CSL boundaries, decreases the local misorientation angle and promotes the precipitation of carbides. These factors induced the decrease of SCC susceptibility at higher tempering temperature. The resistance to SCC at 640 °C tempering temperature is about 20% higher than that of 580 °C at − 1000 mVSCE. The main strengthening mechanism of the ultra-high-strength steel is ultra-fine grain strengthening mechanism, precipitation strengthening mechanism, and dislocation strengthening mechanism. Increasing tempering temperature from 580 to 640 °C decreases the yield strength by 85 MPa, which is mainly attributed to larger carbides size.

Taguchi’s method of optimization of fracture toughness parameters of Al-SiCp composite using compact tension specimens

The objective of this work is to investigate the process parameters which influence the fracture toughness of aluminum-silicon carbide particulate composite prepared using the stir casting technique. The Taguchi’s design of experiments is conducted to analyze the process parameters. Three parameters considered are composition of material, grain size and a/W ratio. From the Taguchi’s analysis, on compact tension specimens, aluminum 6061 reinforced with 9 wt% of the silicon carbide particles composite and a/W ratio of 0.45 are considered to be optimized parameters. Taguchi's technique result shows that the increment in the a/W ratio causes decrement in the load carrying capacity of the composite. Whereas the fine grain size of silicon carbide have better toughness values. From the ANOVA outcomes it is clear that the composition and a/W ratio of the geometry has more influence on the fracture toughness than the grain size of reinforcement.

Cerium Addition Effect on Modification of Inclusions, Primary Carbides and Microstructure Refinement of H13 Die Steel

A comprehensive study of the Ce addition effect on microstructure, inclusions, and primary carbides in H13 steel was carried out. 3D morphology of inclusions and primary carbides was assessed by the non-aqueous electrolytic method. The addition of 0.0038 mass% Ce had no obvious refinement effect on dendritic structures in H13 steel. With Ce content increase from 0.0038 to 0.019 mass%, dendritic structures of H13 steel were refined. Al2O3 and MnS inclusions in original H13 steel promoted heterogeneous nucleation of primary carbides. Al content increased, and S content decreased with increasing Ce content. When the latter was increased from 0.0038 to 0.019 mass%, the original inclusions were modified first to Al11O18Ce and CeAlO3, then to Ce2O3, and, finally, to Ce2O2S. Numerous small-sized Ce2O2S inclusions were found in steel with 0.019 mass% Ce, which promoted nucleation of γ-Fe during solidification and contributed to the refinement of as-cast dendritic microstructures of H13 steel. Besides, Ce2O2S inclusions suppressed heterogeneous nucleation of primary carbides. The size of primary carbides decreased, and their morphology became less developed due to the finer microstructure hindering their growth. Finally, banded structures in forged Ce-bearing H13 steel were improved.

EFFECT OF SEVERE PLASTIC DEFORMATION ON RADIATION HARDENING OF T91 FERRITIC-MARTENSITIC STEEL

Effect of thermomechanical treatment on radiation hardening behavior in T91 ferritic-martensitic steel was evaluated. An applying of severe plastic deformation (SPD) by the “upsetting-extrusion” method and subsequent heat treatment led to a considerable grain refinement, crushing of martensite lamellas, reduction of MX carbides size and their more uniform distribution. Nanoindentation measurements of SPD-modified steel revealed a 1.4-fold increase in the hardness relative to the initial steel. Irradiation response of modified steel was examined after 1.4 MeV Ar+ ion irradiations in the dose range of 10…45 displacements per atom (dpa) at room temperature and 460 °C. Microstructure characterization was performed by means of transmission electron microscopy (TEM). It was found that dislocation loops and nano-sized argon bubbles dominated the damage microstructure after ion irradiation. The effects of SPD-induced transformations as well as nano-bubbles formation are discussed regarding to the hardening phenomenon observed in irradiated steel.

Effects of post-printing heat treatment on the microstructure and mechanical properties of a wire arc additive manufactured 420 martensitic stainless steel part

Abstract In this study, microstructural features and mechanical properties of a wire arc additively manufactured 420 martensitic stainless steel were investigated in as-printed and heat-treated conditions. Initial microstructural investigations on the as-printed part revealed the formation of residual δ-ferrite during the solidification process, which is known as a deleterious phase to both mechanical and corrosion performance of stainless steels. To remove the residual δ-ferrite and obtain a fully martensitic microstructure, the as-printed samples were subjected to different austenitizing temperatures of 950, 1050, 1150, and 1300 °C. Austenitizing at 1150 °C was selected as the optimum cycle due to removal of undesirable phases, such as δ-ferrite and carbides, resulting in a fully martensitic microstructure. Following the austenitizing heat treatment, the samples were tempered at different temperatures including 200, 300, 400, 500, and 600 °C. Increasing the tempering temperature was found to vary the size, morphology, and distribution of chromium carbides precipitated during the tempering process. Although, tempering at lower temperatures (200 and 300 °C) decreased the hardness due to the formation of tempered martensite and stress relieving of the structure, the intermediate temperature of 400 °C increased the hardness value by virtue of the formation of carbides at optimum size and distribution. However, tempering at 500 and 600 °C decreased the hardness as compared to 400 °C due to intergranular segregation and coarsening of carbides. The results of uniaxial tensile testing were consistent with the hardness measurements and confirmed that the tempering temperature of 400 °C led to the optimal combination of strength and ductility ascribed to the formation of fine and homogenously distributed chromium carbides embedded in a moderately tempered martensitic matrix.

Hall-Petch relation in the fracture strength of matrix-body PDC bits

Matrix-body PDC bits endure the reactive shear force and impact damage during the rotary cutting of rock formations under downhole, making the bit blades vulnerable to premature breakage. To avoid the blade breakage, the key is to improve the fracture strength (also known as transverse rupture strength, TRS) of the matrix body of PDC bits. This work investigated the effects of size, shape, and type of tungsten carbides on fracture strength. Weibull distribution was adopted to describe the variations in the repeated TRS test results, which proved to be more appropriate than the normal distribution and could be used as an indirect indicator of the quality and performance of the matrix body. The results of this study showed that the median particle size is the predominant factor determining the TRS performance of the matrix body. Small-sized carbide particles deliver higher TRS, indicating that the fracture strength of the matrix body follows the Hall-Petch relation. Based on this finding, the fracture strength can be significantly reinforced to extend the service life of matrix-body PDC bits under harsh downhole conditions, leading to the reduction of trips and dramatic savings. However, the small-sized carbide particles are inherent lack of erosion resistance and accordingly limit their applications.

Effect of heat treatment on microstructure and mechanical properties of Fe–Cr–Ni–Co–Mo maraging stainless steel produced by selective laser melting

Abstract In the present work, a Fe–11Cr–9Ni–6Co–3Mo (wt.%) maraging stainless steel was successfully fabricated by selective laser melting (SLM). The SLM process parameters were optimized and the influence of heat treatment on microstructure and mechanical properties of the SLMed Fe–11Cr–9Ni–6Co–3Mo samples was systematically explored. The results show that the optimized laser volume energy density with the relative density ≥99.5% for the SLMed samples is 83.33–200 J/mm3. For SLMed samples, the phase analysis reveals predominantly martensite with some retained austenite, and the microstructure is characterized by the prior austenite grains and fine martensite laths. After subsequent heat treatments (solution + cryogenic cooling + aging), the microstructure results in the formation of nanosized CrMoC carbide precipitates, uniformly dispersed in the martensite laths and retained/reverted austenite. Compared with the SLMed samples, the microhardness and tensile strengths are significantly improved after subsequent heat treatments. The effects of heat treatment parameters (solution temperature, aging temperature and aging time) on mechanical properties primarily depend on the size and fraction of carbide precipitates as well as the content of retained/reverted austenite. The microhardness of 439–444 HV, yield strength of 1325–1355 MPa and ultimate strength of 1365–1374 MPa are obtained with the optimal heat treatment regime (solution treatment at 750–850 °C for 1 h + cryogenic cooling at −73 °C for 2 h + aging treatment at 450 °C for 7 h).

Influence of yttrium on purification and carbide precipitation of superalloy K4169

The effect of reactive element yttrium on purification and carbide precipitation of superalloy K4169 has been studied through vacuum induction melting. The results show that yttrium has a strong deoxidizing and desulfurizing ability, and the impurity elements of sulfur and oxygen in melting K4169 are greatly reduced to 2−5 ppm and 4−5 ppm, respectively. The metallurgical reaction product is mainly Y2O3 and yttrium containing sulfides have not been observed. With the increase of the content of yttrium from 0.005 wt.% to 0.033 wt.%, the morphology and size of MC carbides in casting are significantly influenced due to that the yttrium changes the diffusion of the carbide forming elements and solid fraction during solidification. In the alloys without yttrium, only isolated blocky or strip carbides exist, while skeleton-like carbides are observed in the alloys with yttrium. Both the average size and the number density of skeleton carbides decrease monotonously with yttrium content increasing. After yttrium increasing to 0.033 wt.%, a phase of hexagonal Ni17Y2 is observed to precipitate in the form of symbiosis with MC carbide and matrix. The addition of yttrium is not beneficial for the properties of K4169 alloys at the room temperature, which is quite related to the MC carbides with a large skeleton-like morphology through the analysis of tensile fracture.

Effect of initial martensite and tempered carbide on mechanical properties of 3Cr2MnNiMo mold steel

Effect of initial martensite and tempered carbide characteristics on mechanical properties of 3Cr2MnNiMo mold steel were investigated. The results indicated that the initial martensite microstructure can be effectively adjusted by changing the quenching temperature. With the increase of quenching temperature from 760 °C to 1010 °C, the initial microstructure gradually changed from acicular ferrite + plate martensite + M7C3 carbides to lath martensite, and the grain size increased monotonically. The coarsening of the initial martensite led to the increase of tempered carbide size, and the morphology of tempered carbide gradually changed from spherical to long strip-shaped. The large-size and long strip-shaped carbides promoted the formation of micro-voids during the tensile deformation and significantly decreased the elongation. In addition, with the coarsening of the martensite microstructure, both the decrease of high-angle grain boundaries (HAGB) density and the appearance of long strip-shaped tempered carbides significantly reduced the impact absorbed energy. The fracture mechanism transformed from ductile fracture caused by micro-voids coalescence to intergranular cleavage fracture. Moreover, when the initial microstructure completely transformed into lath martensite, the yield and tensile strength remained approximately unchanged. The precipitation strengthening compensated the adverse effect of martensite coarsening.

Role of vanadium additions on tensile and cryogenic-temperature charpy impact properties in hot-rolled high-Mn austenitic steels

It is well known that the vanadium addition can effectively enhance yield strength of high manganese austenitic steel, and numerous fine VC particles can precipitate in matrix in a relatively low annealing temperature range of 600–800 °C. Unfortunately, a relatively low annealing temperature strongly deteriorates cryogenic impact toughness at -196 °C due to grain boundary segregation and precipitation. Hence, it is of significance to understand the role of vanadium additions in high manganese austenitic steel, which is a hopeful cryogenic material. It has been determined that an effective strength increment can be attained as the vanadium addition reaches 0.6 wt.%, and the double strengthened modes of precipitation strengthening and hardened structure strengthening are found due to vanadium additions in the studied Fe-24Mn-0.6C-1.9Al high manganese austenitic steel. The results show that there is a minor increase in yield strength by the vanadium addition of 0.31 wt.%, but the high vanadium addition of 0.60 wt.% can greatly enhance the yield strength by ~113 MPa, and the cryogenic toughness can still achieve a high level of 121 J. The grain refinement and solid solution strengthening effects of vanadium are rather weak, whereas the high vanadium addition strongly suppresses recrystallization and recovery. Moreover, high-density dislocations in hardened structures suppress the twinning activities, leading to sparse twins of the V-0.6 steel. Due to the sparse twins and small carbide size, the retardation effect of carbides on twinning is considered to be small. The negative effects of carbides and grain size on cryogenic toughness are relatively small compared to that of high-density dislocations in the V-0.6 steel. To summarize, the V-0.6 steel exhibits a better combination of yield strength and cryogenic toughness compared to the reported high manganese austenitic steels.

Effect of Nb Content on the Behavior of Primary Carbides in 0.4C-5Cr-1.2Mo-1V Steel

Niobium (Nb) microalloying can improve the material properties of H13 steel (0.4C-5Cr-1.2Mo-1V steel), but it also affects the natures of the primary carbides. Therefore, the effect of Nb content and cooling rate on the behavior of primary carbides in H13 steel was studied in this paper. The matrix structure was obtained by chemical etching, and then the formation location of primary carbides was identified by electron probe microanalysis (EPMA). The three-dimensional (3D) characteristics, including morphology, number density, and size, were obtained by a non-aqueous electrolysis method. The enrichment of alloying elements in the last-to-solidify region leaded to the formation of primary carbides during the solidification. The Ti4C2S2 phase precipitated first, and then the Mo-Cr-rich carbide was formed around the Ti4C2S2 phase. During the cooling process, the Ti4C2S2 phase partly transformed into Nb-rich carbide and then further partly transformed into V-rich carbide. There is a huge difference between the two-dimensional and three-dimensional morphologies of the primary carbides. As the Nb content increased, the size of last-to-solidify region decreased gradually and the size and number density of primary carbides in the 3D observation increasingly increased. However, as the decrease of the cooling rate, the size of primary carbides increased rapidly and the number density of primary carbides decreased markedly. The thermodynamic and kinetics calculation results agreed well with the experimental observations.

Influence of niobium microalloying on the thermal stability of medium-carbon carbide-free bainitic steel

This paper investigates the influence of niobium on the thermal stability of ultra-fine bainite microstructures and their mechanical properties by means of an isothermal transformation at 340 °C, followed by tempering in the range of 200–700 °C for two medium-carbon, carbide-free bainitic steels with and without 0.018 wt. % Nb. The results reveal that ultra-fine bainite microstructures, especially film-like retained austenite, is refined, and the average carbon content of retained austenite is also improved as a result of the addition of Nb element. Both of the bainitic steels in this paper exhibit good thermal stability at low temperatures (≤400 °C) and precipitation hardening arising from carbide precipitation following tempering at 500 °C. The precipitation strengthening compensates for the decrease in strength induced by the decrement in the dislocation density and coarsening of the bainitic ferrite plates during tempering process. M23C6- and MC-type carbides are precipitated in Nb-free and Nb steels, respectively, when the tempering temperature exceeds 400 °C. The further coarsening of the carbides and bainitic ferrite plates, and the decrement in the dislocation density in the latter, relate to the decrease in the mechanical properties for both of the tested bainitic steels following tempering at 500 and 600 °C. Compared to those in the bainitic steel without Nb, the larger size and superior thermal stability of MC-type carbides results in greater strength and elongation of the bainitic steel containing 0.018 wt. % of the Nb element, but does harm to its impact toughness after tempering at 700 °C.

Sliding wear behavior of cold-sprayed Ni-WC composite coatings: Influence OF WC content

Metal Matrix Composites reinforced with WC particles and Co or Ni as matrices are well-known for their unique combination of hardness, toughness, and thus superior wear performance. Previous studies showed that the structure of the coating including carbide size and content, and morphology as well as matrix/binder microstructure must be carefully tailored to achieve desirable wear properties. In this study, Ni–WCNi composite coatings were deposited using the cold spray. Agglomerated WCNi powders and spherical Ni powders were used as feedstock materials. It was found that Ni–WCNi coatings can be tailored to contain 13-54 vol% WC and display a varied hardness ranging between 225 and 550 HV1. A higher concentration of WC in initial feedstock led to more compaction of WCNi particles in coatings, the lower mean free path between WC particles, and harder coatings. The sliding wear behavior of coatings was studied with a sliding speed of 3 mm/s under normal loads of 5 and 12 N. Coatings with higher WC fill ratios were found to be more wear-resistant than coatings with less or no WC. This is related to the uniform distribution of WC particles with the lower mean free path that minimized adhesive wear at the initial stages of wear and helped to develop a higher coverage of protective mechanically mixed layers. However, the protective role of mechanically mixed layers was reduced at higher load, caused by subsurface crack propagation at WC particle interfaces, and was related to strain accumulation in highly compacted WC coatings. A qualitative comparison of coating cohesion strengths was performed using scratch tests on the polished cross-section of coatings and correlated to wear properties.

The role of powder atomisation route on the microstructure and mechanical properties of hot isostatically pressed Inconel 625

Abstract The powder's characteristics and its purity can greatly influence the properties of nickel (Ni)-base superalloys parts produced by near net-shape powder metallurgy hot isostatic pressing (NNS PM HIP) manufacturing process. In this study, Inconel 625 (IN625) powders produced using four different atomisation routes, argon, nitrogen, plasma and water atomisation (AGA, NGA, PA, WA, respectively) were investigated. The first section of this study is focused on the determination of powder characteristics which includes chemical composition, particle size distribution (PSD), tap density and powder's cross-section analysis, whereas the second section is about hot isostatic pressing (HIPping) of the four powder types and to assess the impact of the powder characteristics on the microstructure-property development after HIPping. To gain an understanding of the surface chemistry of the powders, X-ray photoelectron spectroscopy (XPS) analysis were carried out on the surface of the four powders. The latter analysis highlighted fundamental differences on the powder's surface, especially the differences in the surface and near-surface distribution of the alloying elements i.e. C, O, Cr, Mo and Nb present in the alloy chemistry. The micrographs of the four IN625 hot isostatically pressed (HIPped) powders revealed a fully dense microstructure with the presence of prior particle boundaries (PPBs). The atomisation route greatly impacted the nature and amount of PPBs, as well as on the fractions and sizes of oxides, carbides, oxycarbides and oxycarbonitrides precipitates. WA showed the most severe presence of PPBs, followed by NGA, AGA and lastly PA. The powder quality has a greater impact on the mechanical properties of as-HIPped materials, especially on ductility. Overall, PA HIPped IN625 possessed the optimum balance between tensile strength, ductility and Charpy impact properties once compared to the others and match the properties to wrought IN625 material.

Microstructure and mechanical properties of LBW and EBW weld joints of CLF-1 steel: A comparative analysis

This study was focused on welding joints of reduced-activation ferritic/martensitic (RAFM) CLF-1 steel medium-to-thick plates produced via laser beam welding (LBW) and electron beam welding (EBW). Such joints were used in the ITER project, in particular, in the back plate mockup of Helium Cooled Ceramic Breeder Test Blanket System developed in China in 2015. The microstructural evolutions and the mechanical properties of fusion zones (FZs), weld zones (WZs), and heat-affected zones (HAZs) of LBW and EBW joints were analyzed and compared using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Moreover, the microstructural differences between the two types of joints and their effect on the impact properties were discussed. Results showed that the well-formed welds without defects, such as pores, incomplete fusion, and cracks, could be obtained via LBW and EBW. Different heat inputs led to the differences in the grain size gradients, the boundary angles, the content of carbides, and the distribution of dislocations. Despite obvious differences in morphology among FZ, WZ, and HAZ, both types of joints exhibited excellent tensile properties and impact toughness. The tensile strengths of the LBW and EBW joints were 633 and 634 MPa at room temperature, respectively, versus 370 and 366 MPa at 550 °C. The mean impact-absorbing energy values of LBW and EBW joints were 251 and 284 J. The further analysis revealed that the low δ-ferrite content, small effective grain size, large grain size gradient, high grain boundary angle, diminutive size of M23C6 carbides, high-Ta content in MX carbides and low dislocation density led to high impact toughness of the LBW joint, while the microstructure of EBW joint failed to show the improvement of impact toughness, and the extraordinary impact toughness could be attributed to the high scattering band.

Effect of heat treatment on microstructural evolution and properties of cemented carbides (WC-17Co) reinforced with 3% volume hexagonal-boron nitride (h-BN) and processed by selective laser sintering (SLS)

In the manufacturing and mining industries, cemented carbides (WC-Co) are desired due to their extraordinary properties such as high strength, good wear resistance and high fracture toughness. Moreover, due to design limitations, such as intricate shapes of parts manufactured using conventional powder metallurgy, metal-3D printing is being sought after for better processing and fabrication of parts with complex shapes and geometries. In this study, a cemented carbide (WC-Co) reinforced with 3% Hexagonal-Boron Nitride (h-BN) was processed using selective laser sintering and heat treated to understand the effect of the elemental composition and post-processing heat treatment on the microstructural evolution and mechanical integrity of processed parts. Generally, the as-printed WC-Co-hBN sample had distinct polyangular WC carbides with sizes between 8 μm to 18 μm, W-C-Co matrix and large areas of fused eta phases (40% area fraction). X-ray diffraction analysis revealed that beside the major hexagonal WC phases, the h-BN breaks down to form minor phases such as CoWB, Co5.47N together with W3Co3C, W3Co3N, W9Co3C4 phases. Post-processing heat treatment at 400 °C resulted in the evolution of well-defined WC carbides and eta phases including reduced W-C-Co matrix when compared with the as-printed samples. X-ray diffraction analysis showed the disappearance of the W3Co3N and W3Co3C4 phases coupled coalescence and coarsening of the WC phases and the minor W9Co3C4, CoWB and Co5.47N phases. However, post-processing at 600 °C resulted in the breakdown of the coarsened WC carbides (~10 μm to 12 μm), evolution of more eta phases (63% area fraction) and more W3Co3C phases when compared with the as-printed sample. Nevertheless, post-processing at 800 °C resulted in extensive depletion of the W-C-Co matrix and the growth of irregular WC carbides and eta phases. At 1000 °C, the relative sizes of the WC carbides were smaller but well-defined and closely packed including large volume fractions of the eta phase when compared with the samples at 800 °C. Also, the h-BN phase appeared, for the first time, in this sample with high characteristic peaks. An inverse correlation was observed with the heat treatment on the residual stresses. Thus, the heat treatment aided in relieving the residual stresses in the heat-treated samples. The as-printed sample recorded the highest average hardness value of 4200 HV which is approximately 200% higher than the SLS printed WC-17Co. The as-printed sample had the highest fracture toughness (7.5 MPa√m) whiles the 600 °C had the lowest fracture toughness. Additionally, the wear properties of the W-C-Co-hBN samples were significantly higher with the 1000 °C having the best wear properties. In general, the h-BN reinforcement in this study demonstrated an improvement and stability in the mechanical properties of fabricated parts even up to 1000 °C.

Effect of isothermal temper embrittlement and subsequent hydrogen embrittlement on tensile properties of 2.25Cr–1Mo–0.25V base metal and welded metal

2.25Cr–1Mo–0.25V base metal (BM) and welded metal (WM) with different temper embrittlement states were obtained by isothermal temper embrittlement test. The ductile–brittle transition temperature and the carbide size of temper embrittled 2.25Cr–1Mo–0.25V BM and WM increased with the isothermal tempering time. The increase in temper embrittlement time leads to a decrease in yield strength (YS) and ultimate tensile strength (UTS). Hydrogen embrittlement (HE) can decrease the ductility and increase YS and UTS of the material. The hydrogen embrittlement sensitivity and microstructure analysis both show a combined effect of HE and temper embrittlement. The deeper the temper embrittlement, the more sensitive the material to HE. When the hydrogen content in the material is low, the WM is less susceptible to HE due to its welding defects.

Effect of centrifugal casting temperature on the microstructure and properties of ZTAP/HCCI matrix composites

In the centrifugal casting process, the casting temperature parameters affected the microstructure characteristics, and the performance of the materials was greatly significant. ZTA (ZrO2 reinforced Al2O3) particles reinforced HCCI (High chromium cast iron) matrix composites with honeycomb structure were obtained by centrifugal casting. With the increased casting temperature (1450 °C, 1500 °C, 1550 °C, and 1600 °C), the austenite equivalent diameter size was 43.5 μm, 34.8 μm, 33.1 μm, 22.3 μm respective in the compound area and 58.3 μm, 63.1 μm, 65.2 μm, 71.5 μm respective in substrate area. The average size of eutectic carbides in the compound area decreased from 5.7 μm to 2.5 μm with the casting temperature increased. Meanwhile, the lattice constants of austenite and carbide increased with the increased temperature. The hardness of the composites increased by 4 ∼ 6HRC with a change in casting temperature. The results of three-body abrasive wear under high-stress static load conditions showed that the wear volume loss of the composites reduced with the temperature increased and the wear resistance was 1.4 times at 1600 °C than that at 1450 °C.