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Showing papers on "Tempering published in 2016"


Journal ArticleDOI
TL;DR: In this paper, the evolution of phases in modified 9Cr-1Mo P91 steel and their effects on microstructural stability and mechanical properties have been studied for specimens that were subjected to different thermal heat treatment conditions.
Abstract: To achieve high thermal efficiency, modern day thermal power plants operate at higher operating temperature and pressure which necessitates use of steels with high creep rupture strength such as modified 9Cr-1Mo steels. In the present study, the evolution of phases in modified 9Cr-1Mo P91 steel and their effects on microstructural stability and mechanical properties have been studied for specimens that were subjected to different thermal heat treatment conditions. The main focus has been to study the effect of heat treatment temperature ranging from 623 K to 1033 K (350–760 °C) on P91 steel. Further, the effect of furnace cooling, water quenching, tempering at 1273 K (1000 °C) and austenitizing on the mechanical properties and microstructure has been studied. The techniques used for material characterization were scanning electron microscopy (SEM), optical microscopy (OM) and X-ray diffraction. For low tempering temperature, i.e. 623 K (350 °C), M 23 C 6 , M 3 C, M 7 C 3, and MX precipitates have been observed with high yield strength (YS), tensile strength (UTS), hardness and low toughness. In the high temperature range, 923–1033 K (650–760 °C), fine MX, M 7 C 3 , M 23 C 6 , M 2 X, and M 3 C precipitates have been observed with low YS, UTS, hardness and high toughness. The steel tempered at 1033 K (760 °C) was observed to be having best combination of YS, UTS, hardness, toughness and ductility.

160 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of hydrogen embrittlement on martensitic advanced high-strength steels (MS-AHSS) is investigated. But, the results are limited to a few published works.
Abstract: The martensitic advanced high-strength steels (MS-AHSS) are used to create fuel-efficient, crashworthy cars. Hydrogen embrittlement (HE) is an issue with high-strength steels; thus, the interaction of hydrogen with MS-AHSS needs to be studied. There are only a few published works on the HE of MS-AHSS. The current literature indicates that the HE susceptibility of MS-AHSS is affected by (i) the strength of the steel, (ii) the applied strain rate, (iii) the concentration of hydrogen, (iv) microstructure, (v) tempering, (vi) residual stress, (vii) fabrication route, (viii) inclusions, (ix) metallic coatings, and (x) specific precipitates. Some of the unresolved issues include (i) the correlation of laboratory results to service performance, (ii) establishing the conditions or factors that lead to a certain HE response, (iii) studying the effect of stress rate on HE, and (iv) a comprehensive understanding of hydrogen trapping in MS-AHSS.

117 citations


Journal ArticleDOI
TL;DR: In this article, the effect of solutionizing temperature on microstructure and mechanical properties of CSEF P91 steel has been investigated using optical metallography and scanning electron microscopy (SEM).
Abstract: Mechanical properties of creep enhanced ferritic (CSEF) steels is affected by various parameters, the solutionizing temperature is one of them. The present work demonstrates the effect of solutionizing temperature on microstructure and mechanical properties of CSEF P91 steel. Optical metallography (OM) and Scanning electron microscopy (SEM) were carried out to study the microstructure of P91 steel in different heat treatment conditions. In order to determine the precipitates present in microstructure; X-ray analysis was performed. Moreover, the influence of solutionizing temperature on the mechanical properties (strength, hardness and impact toughness) has also been studied.

113 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of retained austenite stability and morphology on the hydrogen embrittlement (HE) susceptibility were investigated in a high strength steel subjected to three different heat treatments, i.e., the intercritical annealing quenching and partitioning (IAQP), quenched and partitions (QP and QT), and it was shown that the HE susceptibility increases in the following order: QT, QP and IAQP.
Abstract: The effect of retained austenite (RA) stability and morphology on the hydrogen embrittlement (HE) susceptibility were investigated in a high strength steel subjected to three different heat treatments, i.e., the intercritical annealing quenching and partitioning (IAQP), quenching and partitioning (QP) and quenching and tempering (QT). IAQP treatment results in the coexistence of blocky and filmy morphologies and both QP and QT treatments lead to only filmy RA. No martensitic transformation occurs in QT steel during deformation, while the QP and IAQP undergo the transformation with the same extent. It is shown that the HE susceptibility increases in the following order: QT, QP and IAQP. Despite of the highest strength level and the highest hydrogen diffusion rate, the QT steel is relative immune to HE, suggesting that the metastable RA which transforms to martensite during deformation is detrimental to the HE resistance. The improved resistance to HE by QP treatment compared with IAQP steel is mainly attributed to the morphology effect of RA. Massive hydrogen-induced cracking (HIC) cracks are found to initiate in the blocky RA of IAQP steel, while only isolate voids are observed in QP steel. It is thus deduced that filmy RA is less susceptible to HE than the blocky RA.

89 citations


Journal ArticleDOI
TL;DR: In this article, a unified description for hardness in martensitic steels for a wide range of carbon contents is presented, based on describing the strength contributions of lath and plate martensite, precipitates and retained austenite.

86 citations


Journal ArticleDOI
Si-Yuan Lu1, Kefu Yao1, Yun-Bo Chen, Miao-Hui Wang, Na Chen1, Xueyuan Ge 
TL;DR: In this paper, a 0.3C-13Cr martensitic stainless steel (MSS) was subjected to quenching and partitioning (Q&P) treatment.

74 citations


Journal ArticleDOI
TL;DR: Tempered martensite obtained from four different tempering modes were characterized using transmission electron microscopy, high-angle annular dark field scanning transmission electron microscope, and nanoindentation techniques as discussed by the authors.
Abstract: Tempered martensite obtained from four different tempering modes were characterized using transmission electron microscopy, high-angle annular dark field scanning transmission electron microscopy, and nanoindentation techniques. Crystallographic analysis of tempered martensite revealed that ferrite (α) and cementite (θ) obtained via furnace and Gleeble heat treatment obeyed the Isaichev orientation (or close to it) with [ 3 1 1 ] θ 0.91° from [ 1 1 1 ] α and the [ 1 12 ] α || [ 001 ] θ Bagaryatsky orientation relationship. A strict orientation relationship between ferrite and cementite could not be determined on the tempered structure extracted from the sub-critical heat affected zone of two different laser beam welded samples. Extensive recovery and reduction of boundary regions was identified on the structure tempered slowly, whereas rapidly tempered structures retained a high density of dislocation and less decomposition of the lath structure. The relationship between dislocation density and modified tempering parameter was determined and their contributions on tensile strength were evaluated.

72 citations


Journal ArticleDOI
TL;DR: In this paper, a high-strength low-alloy structural steel derived from martensitic Cu-bearing HSLA-100 is presented, where sub-nanometric-sized M2C carbides along with Cu precipitates produce higher strength steels that still meet impact toughness and ductility requirements.
Abstract: HSLA-115 is a novel high-strength low-alloy structural steel derived from martensitic Cu-bearing HSLA-100. HSLA-100 is typically used in conditions with overaged Cu precipitates, to obtain acceptable impact toughness and ductility. Present work on HSLA-115 demonstrates that incorporating sub-nanometric-sized M2C carbides along with Cu precipitates produces higher strength steels that still meet impact toughness and ductility requirements. Isothermal aging at 823 K (550 °C) precipitates M2C carbides co-located with the Cu precipitates and distributed heterogeneously at lath boundaries and dislocations. 3D atom-probe tomography is used to characterize the evolution of these precipitates at 823 K (550 °C) in terms of mean radii, number densities, and volume fractions. These results are correlated with microhardness, impact toughness, and tensile strength. The optimum combination of mechanical properties, 972 MPa yield strength, 24.8 pct elongation to failure, and 188.0 J impact toughness at 255 K (−18 °C), is attained after 3-hour aging at 823 K (550 °C). Strengthening by M2C precipitates offsets the softening due to overaging of Cu precipitates and tempering of martensitic matrix. It is shown that this extended yield strength plateau can be used as a design principle to optimize strength and toughness at the same time.

71 citations


Journal ArticleDOI
TL;DR: In this paper, the influence of hydrogen on dual-phase (DP), transformation-induced plasticity (TRIP), and twinning-induced Plasticity (TWIP) steels was reviewed.
Abstract: The literature is reviewed regarding the influence of hydrogen on dual-phase (DP), transformation-induced plasticity (TRIP), and twinning-induced plasticity (TWIP) steels. Hydrogen influences DP steels by decreasing ductility while strengths are largely unaffected. TRIP steels may be susceptible to hydrogen embrittlement (HE) as indicated by the loss of ductility and some brittle fracture features. The literature on the influence of hydrogen on TWIP steels was inconsistent. Some researchers found no significant influence of hydrogen on TWIP steel properties and fully ductile fractures, whereas others found a significant loss of ductility and strength due to hydrogen and some brittle features. Possible countermeasures for HE are tempering for DP and TRIP steels and aluminum alloying for TWIP steels

70 citations


Journal ArticleDOI
Wenbin Gao1, Dongpo Wang1, Fangjie Cheng1, Xinjie Di1, Caiyan Deng1, Wei Xu 
TL;DR: In this paper, the microstructure evolution of the reheated columnar region and coarse grain heat affected zone (CGHAZ) is discussed to explain the beneficial effect of temper bead.

69 citations


Journal ArticleDOI
TL;DR: In this paper, a composite of 35CrMo high-strength steel matrix reinforced with TiC reinforcement has been produced by conventional powder metallurgy (PM) and the sintering temperature and process for heating treatment were discussed.
Abstract: The composite of 35CrMo high-strength steel matrix reinforced with TiC reinforcement (50 wt.%) has been produced by conventional powder metallurgy (PM). The sintering temperature and process for heating treatment were discussed. The scanning electron microscopy (SEM) revealed the morphology and distribution of the reinforcement phase. Density, hardness, and transverse rupture strength (TRS) of the samples were analyzed. The results showed that the optimal sintering process for the composite is sintering at 1430 °C for 1 h and heat treatment process is annealing at 850 °C/30 min, quenching at 880 °C/30 min and then tempering at 560 °C/60 min. The composite after heat treatment has excellent mechanical properties with a relative density of 99.7%, hardness of 65 HRC, TRS of 1850 ± 20 MPa, respectively, and will be used as refractory moulds, cold work moulds and some gaskets, etc.

Journal ArticleDOI
TL;DR: In this article, different microstructures and their mixtures have been obtained through various heat treatment processes, and the correlations between misorientation, grain size, microscopic fracture propagation and toughness have been studied in detail using electron backscatter diffraction.
Abstract: The uniformity of toughness along thickness direction has long been the critical problem for producing ultra-heavy steel plate. To clarify the rule and mechanism of the influence of microstructures on toughness, different microstructures and their mixtures have been obtained through various heat treatment processes. The microstructures and substructures were characterized by means of optical microscope and transmission electron microscope. Furthermore, the correlations between misorientation, grain size, microscopic fracture propagation and toughness have been studied in detail using electron backscatter diffraction. Results suggest that after tempering, lath bainite can achieve better toughness property than martensite, whereas granular bainite is detrimental for toughness. Note that firstly generated lath bainite can effectively refine subsequent martensitic packets and blocks, and increase barriers for fracture propagation. Compared with single-phase martensite microstructure, the mixture of martensite+bainite obtains finer substructure and more percentage of large misorientation, which are favorable for hindering the propagation of microcrack, meanwhile it is an ideal microstructural type to achieve the optimal combination of toughness and strength. Besides, functional mechanism of packet boundaries and block boundaries for hindering crack propagation is different, as it is more difficult for crack propagation to bridge between different lattice planes than between different crystallographic orientations.

Journal ArticleDOI
TL;DR: In this paper, the effect of retained austenite on the hydrogen embrittlement of a medium carbon quenching and partitioning steel was investigated by comparison to a traditional quenched and tempering steel with an identical chemical composition.
Abstract: The effect of retained austenite on the hydrogen embrittlement of a medium carbon quenching and partitioning steel was investigated by comparison to a traditional quenching and tempering steel with an identical chemical composition. Electrochemical precharging reduces the plasticity, including the elongation and reduction in area, of both steels, and the embrittlement phenomenon is more severe in the quenching and tempering steel based on a slow strain rate tensile test. As a result, the ultimate tensile strength decreases, as well. The fracture mode was dominated by intergranular features in the areas containing hydrogen, suggesting the weakening of boundary cohesion. Retained austenite, which retards diffusion and increases the solubility of hydrogen, is stable under the attack of hydrogen, contributing to the high hydrogen embrittlement resistance of quenching and partitioning steel. Refining the microstructure further improves plasticity due to the lower hydrogen content per area. In general, the quenching and partitioning steel with a refined microstructure exhibits the lowest hydrogen embrittlement susceptibility.

Journal ArticleDOI
TL;DR: The microstructure and mechanical properties of laser solid formed (LSFed) 300M steel with tempering treatment was investigated in this paper, where the size of the martensite lath and blocks changed little with increase of the tempering temperature.

Journal ArticleDOI
TL;DR: In this article, the hydrogen induced ductility loss of three FeCMo alloys is evaluated and correlated with the hydrogen interaction of the Mo2C precipitates, and two thermal treatments are applied to compare two main conditions; i.e., an as-quenched and a quenched-and tempered state in which Mo 2C particles have precipitated.

Journal ArticleDOI
TL;DR: In this paper, the impact of tempering on the stability of retained austenite (RA) in obtaining excellent combination of strength and toughness in an ultrahigh-strength low carbon air-cooled bainitic rail steels was elucidated.
Abstract: We elucidate here the impact of tempering on the stability of retained austenite (RA) in obtaining excellent combination of strength and toughness in an ultrahigh-strength low carbon air-cooled bainitic rail steels. The microstructure of rail steels comprises of bainite, martensite and martensite/austenite (M/A) constituents. The bainitic rail steels exhibit excellent strength and toughness combination after tempering at 280 °C (ultimate tensile strength: 1388 MPa; total elongation: 16%; U-notch impact toughness at 20 °C: 130 J/cm2). The filmy RA in the tempered microstructure has high mechanical stability, which ensures retention of superior mechanical properties of bainitic steels. The study underscores stability of filmy retained austenite obtained via tempering is the underlying reason for superior mechanical properties.

Journal ArticleDOI
TL;DR: In this article, the fracture toughness, hardness and nanohardness, flexural strength, fracture toughness and wear resistance of Vanadis 6 ledeburitic steel have been characterized.
Abstract: Vanadis 6 ledeburitic steel manufactured by powder metallurgy of rapidly solidified particles was conventionally quenched and subzero-treated at temperatures of −90 and −196 °C for 4 and 10 h, respectively, followed by standard double-tempering to a secondary hardening peak at 530 °C for 2 h. Besides quantification of standard microstructural features by using examination by scanning electron microscopy and X-ray diffraction analysis, the fracture toughness, hardness and nanohardness, flexural strength, fracture toughness, and wear resistance have been characterized. The obtained results indicate the following: (i) The microstructure of the material consists of tempered martensite and eutectic, secondary, and small globular carbides. Retained austenite is completely eliminated by application of the given heat-treatment schedules. (ii) The amount of small globular carbides is significantly increased by subzero treatments; the lower the temperature (or the longer the duration) of subzero treatment, the higher the content of these carbides. (iii) The hardness of the material is influenced slightly negatively by subzero treatments followed by tempering in the normal secondary hardening temperature range. (iv) There is no negative impact of the given treatment schedules on either toughness or fracture toughness of the steel. (v) When a hardened ball bearing is used as a counterpart, wear resistance is improved by subzero treatments despite the slightly lower hardness of the examined tool steel.

Journal ArticleDOI
TL;DR: In this paper, the evolution of microstructures and mechanical properties of T91 steel were investigated in detail, and transition carbides were identified in water quenched T91 steels.

Journal ArticleDOI
TL;DR: In this paper, a Gleeble-3500 thermal simulator was used to simulate the welding thermal cycles of all of the sub-zones of the heat-affected zone (HAZ) of laser-welded specimens of DP1000 steel.

Journal ArticleDOI
TL;DR: In this article, the authors explored the relationship between the microstructure and low temperature toughness of weld metal obtained from a real multi-pass weld joint (up to 55mm) by submerged arc welding, which was developed for high strength (yield strength over 550 MPa) and heavy wall pipe fitting applications with composition of 0.1% C, 2.0% Mn and other micro-alloys.
Abstract: In this study, we explore the relationship between the microstructure and low temperature toughness of weld metal obtained from a real multi-pass weld joint (up to 55 mm) by submerged arc welding, which was developed for high strength (yield strength over 550 MPa) and heavy wall pipe fitting applications with composition of 0.1 wt% C, 2.0 wt% Mn and other micro-alloys. The study indicated that the necklace-type coarse martensite–austenite (M–A) constituent formed in the interlayer heat affected zone (IHAZ) of weld metal was responsible for low impact energy of 39 J at −40 °C. To enhance the toughness, conventional tempering and new intercritical heat treatment were designed. The results suggested that there was insignificant effect on toughness through conventional tempering, but obvious improvement through combination of quenching plus intercritical annealing and tempering. The impact energy was increased to ~98 J. The microstructure that benefit toughness primarily comprised of intercritical lath-like ferrite or acicular-type ferrite, bainite/martensite, and fine acicular retained austenite, with average size of ~0.3 μm. Retained austenite with volume fraction of ~6% was formed by the enrichment of Mn and Ni in reversed austenite during intercritical tempering process.

Journal ArticleDOI
TL;DR: In this article, a commercial dual phase (DP) 980 steel at 250°C and 400°C for 60 min each was treated with tempering, and the results showed that tempering significantly reduced martensite yield strength, while it slightly reduced the ferrite yield strength.
Abstract: Tempering treatment is conducted on a commercial dual phase (DP) 980 steel at 250 °C and 400 °C for 60 min each. Ferrite and martensite grains are distinguished using electron backscatter diffraction (EBSD) and scanning probe microscopy (SPM), and the martensite volume fractions (MVF) are determined based on the image quality (IQ) map. Indentation tests combined with a newly developed inverse method are used to obtain the individual phase flow properties in each sample. The results show that, i) tempering significantly reduces martensite yield strength, while it slightly reduces the ferrite yield strength; ii) tempering temperature has a more significant influence on the work hardening exponent of ferrite than that of martensite. As a validation, a simple rule-of-mixtures is used to verify the above-predicted individual phase flow stresses with the experimentally obtained overall true stress vs. true strain curves.

Journal ArticleDOI
TL;DR: In this paper, the microstructural evolution and deformation behavior in two hot-rolled Fe-6Mn-3Al-0.2C and Fe-8.5mn-750 steel was studied and a combination of mechanical properties including total elongation (TEL) of 39.3%, ultimate tensile strength (UTS) of 1112 MPa and UTS×TEL of 43.7 GPa% were obtained in 8.5Mn.
Abstract: We have studied here the microstructural evolution and deformation behavior in two hot-rolled Fe-6Mn-3Al-0.2C (6Mn steel) and Fe-8.5Mn-3Al-0.2C (8.5Mn steel) transformation induced plasticity (TRIP) steels. Excellent combination of mechanical properties including total elongation (TEL) of 39.3%, ultimate tensile strength (UTS) of 1112 MPa and UTS×TEL of 43.7 GPa% were obtained in 8.5Mn steel subjected to intercritical hardening at 750 °C and tempering at 200 °C. The increase in the Mn-content in the experimental steel led to increase in the volume fraction of austenite and change in austenite morphology. Non-uniform Mn distribution in austenite with varied morphology resulted in different degree of austenite stability and led to discontinuous TRIP effect, contributing to the best combination of mechanical properties in 8.5Mn-750 steel.

Journal ArticleDOI
TL;DR: In this article, the effect of tempering temperature on microstructure and mechanical properties was studied in a low-nitrogen, high-boron, 9%Cr steel and the results showed that mild tempering has no distinct effect on mechanical properties.
Abstract: The effect of tempering temperature on microstructure and mechanical properties was studied in a low-nitrogen, high-boron, 9%Cr steel. After normalizing and low-temperature tempering, cementite platelets precipitated within the martensitic matrix. This phase transformation has no distinct effect on mechanical properties. After tempering at 500 °C, M23C6 carbides appeared in the form of layers and particles with irregular shapes along the high-angle boundaries. Approximately, 6% of the retained austenite was observed after normalizing, which reduced to 2% after tempering at 550 °C. This is accompanied by reduction in toughness from 40 J/cm2 to 8.5 J/cm2. Further increase of the tempering temperature led to spheroidization and coagulation of M23C6 particles that is followed by a significant increase in toughness to 250 J/cm2 at 750 °C. Three-phase separations of M(C,N) carbonitrides to particles enriched with V, Nb and Ti were detected after high-temperature tempering.

Journal ArticleDOI
TL;DR: In this article, the effect of varying tempering time on microstructure revealed increase in size of precipitates, amount of precipitate and grain size, compared to particle size.
Abstract: Present paper describes the microstructural and mechanical properties of creep strength enhanced Cr–Mo P91 steel subjected to a regime of tempering time 720–3000 h. Study on the effect of varying tempering time on microstructure revealed increase in size of precipitates, amount of precipitates and grain size. It was also observed that compared to particle size, effect of tempering time was more pronounced on the grain size. The various phases that formed in the tempered P91 steel were analyzed by X-ray diffraction. Yield strength and tensile strength were observed to be decreasing with increase in tempering time. Increase in duration of tempering time led to decrease in impact toughness of P91 specimens possibly due to cracking of secondary phase particles during straining and decohesion at precipitates and matrix interface. The tempering time also observed to be affecting the hardness of P91 steel but less pronounced compared to the yield strength and tensile strength. Tensile fracture and impact toughness fracture surfaces were studied by using scanning electron microscope. The fracture surface of tempered P91 tensile specimens indicated increased dimples and presence of fewer cleavage facets. The fracture surface of P91impact toughness specimens exhibited both inter lath-decohesion and ductile dimple tearing.

Journal ArticleDOI
TL;DR: In this paper, the authors studied the mechanical properties and deformation behavior of two hot-rolled 0.2C-1.5Al-8.5Mn-Fe steels, subjected to an optimized quenching and tempering (Q&T) treatment.
Abstract: Mechanical properties and deformation behavior have been studied in two hot-rolled 0.2C-1.5Al-8.5Mn-Fe (1.5Al steel) and 0.2C-3Al-8.5Mn-Fe (3Al steel) transformation induced plasticity (TRIP) steels, subjected to an optimized quenching and tempering (Q&T) treatment. The study indicated that 1.5Al steel was characterized by excellent combination of ultimate tensile strength (UTS) of 1373 MPa, tensile elongation (TE) of 31.8%, and UTS×TE of 43.6 GPa%, where the superior mechanical properties are mainly attributed to the discontinuous TRIP effect. In contrast, 3Al steel indicated lower UTS, but higher TE of 34.5%, which resulted from the discontinuous TRIP effect and the cooperative deformation of δ-ferrite. The discontinuous TRIP effect is a consequence of varying degree of stability of austenite, which results from different austenite grain size, non-uniform C-content and Mn-distribution in lath-like austenite and blocky austenite.

Journal ArticleDOI
TL;DR: In this article, the effect of large-size M 23 C 6 type carbides on the low-temperature toughness of 10Cr12Ni3Mo2VN was studied using heat treatment and microscopic microstructure analysis.

Journal ArticleDOI
TL;DR: In this article, a laser hardening temperatures/oxidation coupled model is applied for the first time to the case of an overlapping process, extending its capabilities to take into account the tempering of the second track over the martensite of the first one.

Journal ArticleDOI
TL;DR: In this article, an advanced double quenching and tempering heat treatment based laser surface modification process of dual-phase spring steel was proposed, which induced a large and high magnitude compressive residual stress with good thermal stability.
Abstract: The present work proposes an advanced double quenching and tempering heat treatment based laser surface modification process of dual-phase spring steel. Multiple laser peening without coating process utilized the decarburized surface as the protective layer for the further cold working process. The electron backscattering diffraction analysis on crystallographic orientation of individual grains and phase map exhibits a perfect dual-phase steel. Also, the high resolution transmission electron microscopic study explains the high strain induced microstructural grain refinement features and plastic deformation behaviors. The laser peening technique taking an advantage that it induces a large and high magnitude compressive residual stress with good thermal stability. The micro and nano-hardness profile provides better surface and sub-surface mechanical properties. The controlled average surface roughness is achieved in this course of work. The stress-strain characteristics on tensile properties are analyzed through the pre-fatigued specimens. The fully reversed high cycle fatigue test indicates that the current laser peening has substantially improves the fatigue life of the specimens.

Journal ArticleDOI
TL;DR: In this paper, a multiphase microstructure composed of nano-scaled bainite, martensite, undissolved spherical carbides and retained austenite was obtained on the top surface of carburizing 23Cr2Ni2Si1Mo steel after low-temperature austempered at 200°C.
Abstract: A multiphase microstructure composed of nano-scaled bainite, martensite, undissolved spherical carbides and retained austenite was obtained on the top surface of carburizing 23Cr2Ni2Si1Mo steel after low-temperature austempered at 200 °C, with a dual-phase microstructure of fine martensite lath and carbon-enriched retained austenite in the center of steel. As compared with the conventional oil quenching and tempering (OQ) state, the low-temperature austempering specimens showed a higher surface residual compressive stress and a thicker residual compressive stress layer, and the wear resistance of the top surface of specimens austempered for 4 h, 8 h and 24 h was increased 40%, 58% and 12%, respectively. Moreover, the impact toughness of the center of these austempered specimens is also improved 20.8–33.3% as compared with that of the OQ specimen. Then, it can be deduced that applying the low-temperature austempering treatment for manufacturing carburizing-steel part is beneficial to improving its service performance for the better stress condition, higher wear resistance and higher interior toughness.

Journal ArticleDOI
TL;DR: In this article, the effect of thermal tempering of aluminum alloy on microstructure and mechanical properties of AZ31-O Mg and Al 6061-T6 diffusion bonding was investigated.
Abstract: The objective of this study is to investigate the effect of the types thermal tempering of aluminum alloy on microstructure and mechanical properties of AZ31-O Mg and Al 6061-T6 diffusion bonding. Using Optical Microscope (OM) and Scanning Electron Microscopes (SEM) equipped with EDS analysis and line scan the interfaces of joints were evaluated. The XRD analysis was carried out to characterize phase constitution near the interface zone. The mechanical properties of joints were measured using Vickers micro-hardness and shear strength. According to the results in bonding of AZ31-Mg/Al-6061-O, in less plastic deformation in magnesium alloy, diffusion rate of most magnesium atoms occurred to aluminum alloy and formation of diffusion zone with minimum micro-hardness (140 HV) and maximum shear strength (32 MPa) compared to Al 6061-T6/Mg-AZ31 bonding. Evaluation of fracture surfaces indicates an occurrence of failure from the brittle intermetallic phases.