Tempering Treatment Research Articles

Effect of vanadium on microstructure and mechanical properties of bainitic forging steel

This investigation attempts to thoroughly explore the effect of microalloying element V on the microstructural characteristics and mechanical properties of 20Mn2SiCrS bainitic forging steel. The results show that the cooling rate range of bainitic transformation was broadened with a 0.13% V addition and mainly a granular bainite microstructure was obtained after post-forging continuous cooling. The addition of V could refine the martensite/austenite (M/A) constituent and inhibit the formation of pro-eutectoid ferrite. Physical-chemical phase analysis revealed that only ~8.5% of the added V was in the V(C,N) precipitate in the as-forged condition, which resulted in relatively small precipitation strengthening (~40 MPa) compared with that in ferritic-pearlitic medium carbon forging steel. The addition of V can enhance the overall mechanical properties of the steel and it is concluded that the primary role of V in the as-forged bainitic forging steel is mainly to promote the formation of bainite and to refine the microstructure especially the M/A constituents as well as to resist softening of the M/A during the post-forging continuous cooling or during subsequent tempering when tempering treatment is necessary.

Microstructural evolution and dimensional stability of TiC-reinforced steel matrix composite during tempering

To improve the service reliability of components prepared by TiC-reinforced steel matrix composite material, tempering treatment was carried out to tailor the microstructure and properties of the composite. The aim of this study was to investigate the microstructure, properties, and dimensional stability of a TiC-reinforced steel matrix composite during tempering and to identify the underlying stabilizing mechanisms. We observed that the metastable retained austenite transformed into martensite and that residual stress released during tempering. The microstructure and properties of the composite reached an optimal state for a tempering time of 10 h. Furthermore, the relative dimensional change, Vickers hardness, thermal strain, and saturation magnetization of the composite were 0.0219%, 960.8 HV, 3.16 × 10−4, and 109.7 emu/g, respectively. Various stabilizing mechanisms, including retained austenite-martensite transformation and residual stress release, were observed during tempering, effectively improving the dimensional stability of TiC-reinforced steel matrix composites.

Fabrication of a High Chromium Cast Iron/Low Carbon Steel Bimetal: Diffusion Behavior and Bonding Strength

In the present study, a high chromium cast iron (HCCI) alloyed with Mo (16 wt.% Cr-6 wt.% Mo-2.4 wt.% C) with excellent wear resistance was bonded to a low carbon steel (LCS) by surface liquid-phase sintering. The bimetal was also subjected to a quenching + tempering treatment. The diffusion behavior of the atoms between the HCCI and LCS was analyzed. The bonding strength of the bimetal was investigated before and after heat treatment. The results show that the bimetal had a good bonding quality due to the uphill diffusion of C atoms. A diffusion zone with a width of approximately 37 μm and a troostite structure formed on the HCCI side by the interface. With different bonding times, there was no obvious change in the width of the diffusion zone. The shear strength of the bimetal at all holding times was reduced from a high level after heat treatment and decreased with increasing tempering temperature. The impact toughness of the bimetal substantially increased compared with that of the HCCI. After a quenching treatment, the impact toughness of the bimetal decreased, and the microhardness of the diffusion zone improved. As the tempering temperature increased, the microhardness and impact toughness decreased and increased, respectively.

Intercritical Annealing Processing and a New Type of Quenching and Partitioning Processing, Actualized by Combining Intercritical Quenching and Tempering, for Medium Manganese Lightweight Steel

The microstructure and its effects on mechanical properties of medium manganese lightweight steel are investigated under both intercritical annealing (IA) and a new type of quenching and partitioning processing, actualized by combining intercritical quenching and tempering (IQ‐TP). The result shows that the steel intercritically annealed at 800 °C exhibits a superior tensile ductility, which is related to long‐term continued transformation‐induced plasticity (TRIP) effect of austenite. Tempering has different effects on steels quenched at various temperatures. For the sample quenched at 800 °C, tempering has a negative effect on its mechanical properties due to a decrease in both volume fraction of austenite and carbon content in austenite. However, for the samples quenched at the range of 850–900 °C, the tempering heat treatment can remarkably improve mechanical properties, which is related to the improvement of austenite stability due to the partitioning of carbon from the carbon‐supersaturated primary martensite into the austenite through the simple quenching and tempering treatment. Meanwhile, the tempering treatment can dramatically promote the yield strength. One of the important reasons is carbon in the primary martensite precipitation as carbides within tempered martensite.

Microstructure characterisation and mechanical properties of ODS Eurofer steel subject to designed heat treatments

The present work deals with oxide dispersion strengthened (ODS) Eurofer steel fabricated by powder metallurgy involving mechanical alloying and spark plasma sintering. A heat treatment route including normalising and tempering was applied to the as-produced steel, based on differential scanning calorimetry (DSC) measurement. The microstructure was characterised by scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), electrolytic extraction, X-ray diffraction (XRD) and transmission electron microscopy (TEM). Thermodynamic calculations conducted using Thermo-Calc software were used to determine the precipitation conditions. The results show that the Vickers microhardness of the sample after the designed heat treatment is more uniform compared to the as-produced condition. A dual phase and bimodal microstructure is formed in the as-produced and tempered steels. M23C6 and M6C carbides were found in the as-produced sample while only M23C6 carbides were observed in the tempered sample. The carbides dissolve and reprecipitate during the heat treatment, preferably at the grain boundaries. Nanosized Y2O3 particles were found to be homogenously distributed in the steel matrix, which is crucial for the mechanical properties. The dislocation density in the material is decreased significantly after the normalising and tempering treatment. A yield strength model was developed that includes the strengthening contributions of solid solutes, grain size, dislocation density and nanoparticles. Good agreement is obtained between the experimentally measured and theoretically calculated strength of the as-produced and tempered steels.

Improvement of the mechanical properties of Al–Mg–Si alloys with nano-scale precipitates after repetitive continuous extrusion forming and T8 tempering

Repetitive continuous extrusion forming (R-Conform) followed by T8 tempering treatment was found to be a viable approach for obtaining superior strength with high ductility in an Al–Mg–Si alloy. The evolution of mechanical properties and microstructure of the Al–Mg–Si alloy, and its mutual relationship during this novel approach were investigated. The results showed that a homogeneous and refined microstructure was formed during the R-Conform process, which improved the mechanical properties of the alloy. Concurrently, the R-Conform process caused effective dynamic strain redissolution of β″ precipitates, and the precipitation kinetics were affected by the subsequent T8 tempering process. The refined (sub)grains and induced high densities of the dislocations accelerated the formation of numerous dispersive nano-scale β″ precipitates during an additional T8 tempering treatment at a low artificial aging temperature (120°C) and a short aging time (3h). Therefore, remarkable improvements in both the tensile strength and ductility were achieved by 7 R-Conform passes and T8 tempering.

Improved hydrogen embrittlement resistance after quenching–tempering treatment for a Cr-Mo-V high strength steel

The effect of quenching-tempering (QT) treatment on the hydrogen embrittlement (HE) resistance of a reactor pressure vessel steel was studied. Decomposition of M3C/VC carbides and precipitation of M7C3 carbides were confirmed by transmission electron microscopy and atom probe tomography observations. Tensile tests showed that HE sensitivity decreased to a negligible level after QT treatment. The improvement of HE resistance was mainly attributed to the decreased number of M3C carbides which act as the reversible trapping sites for hydrogen. This was supported by the decreased concentration of reversible hydrogen as measured by thermal desorption spectroscopy. The amount of irreversible hydrogen (probably trapped at VC carbides) also decreased, which is however not considered responsible for the HE improvement.

Effect of film-like retained austenite on low temperature toughness of high strength offshore steel

Film-like retained austenite was prepared by a quenching + intercritical annealing + tempering (QIAT) heat treatment to study its effect on the low temperature toughness of high strength offshore steel. Based on the Purdy model, the flat growth mechanism of film-like retained austenite was studied and the toughening mechanism of this kind of retained austenite was revealed. The results showed that the microstructure after the QIAT heat treatment was a multi-phase structure containing tempered bainite/martensite, intercritical ferrite and film-like retained austenite. The thickness of the film-like retained austenite was only 0.1 μm. The yield strength was 716 MPa, the tensile strength was 812 MPa and the low temperature toughness at −40 °C reached 150 J. The low temperature toughness was significantly improved compared with the quenching + tempering (QT) treatment. Enrichment of Mn in the retained austenite formation region caused a surge in dissipated free energy induced by austenite interface migration, making it a one-dimensional film-like flat growth. The excellent stability of the film-like retained austenite and the large number of low-angle grain boundaries were the reasons for the excellent low temperature toughness of this offshore steel.

Study Regarding the Properties of a Knife from a Grinding Mill Obtained from Metallic Powders

In the paper is presented the analysis of tool steel used for making a knife for a mill for grinding plants. The material used for the knife is about 1% carbon and is symbolized by RWL34. To improve the properties of the material, especially the knife cut, a thermal treatment were made and was measured hardness, wear resistance and microscopic analyzes of the metal. The paper presents the values of the mechanical properties on the initial sample, on the hardening sample and on the sample subjected to a hardening and tempering treatment, as well as the graphs related to them. The next step in finalizing the analysis of the grinder mill knife is to study the behavior in operation and the possible corrections that should be made.

Refining single-crystalline epsilon iron oxide nanorods via low-temperature aging

Refinement of ε-Fe2O3 phase in ε-Fe2O3/SiO2 composite powder is an urgent need in terms of its practical applications in high-density magnetic storage media. In this work, two types of refinement routes were employed for this purpose. It was found that short-time tempering treatment was not an ideal route for the refinement, because ε-Fe2O3 nanorods were ruptured to nanoparticles with an extremely wide size distribution, and their low coercivity of merely 1.0 kOe was not desirable for expected applications. By contrast, low-temperature aging route facilitated the formation of uniform ε-Fe2O3 nanorods with a length of about 200 nm and a width of about 40 nm. Because of their narrow size distribution and high crystallinity, these nanorods possessed large coercivity around 19 kOe, pronounced remanent squareness and prominent thermomagnetic behaviors, making them fairly desirable for further applications in magnetically-relevant field.

Effect of Heat Treatment on Microstructure and Mechanical Properties of API X90 Pipeline Steel Welded Joints

In this work, X90 pipeline steel was welded by shielded metal arc welding with root and submerged arc welding with calk and cap. After that, the joint was tempered at 550 °C and 600 °C. Subsequently, the microstructure and mechanical properties were investigated by optical microscope, scanning electron microscope (SEM) and Vickers hardness tester. The fracture surface of welded joint was analyzed by SEM. The experiments show that: After high-temperature tempering treatment, the Widmanstatten structure disappears in coarse-grained region. The number of lath martensite in the original structure of the welded joint decreases, and the quantity of granular bainite increases. The acicular ferrite disappears gradually and the polygonal ferrite grains increase, and the M/A island components decompose into fine grains with the increase in tempering temperature. The mechanical properties of the joints also change and the hardness rises because of the disappearance of Widmanstatten structure improves after heat treatment, and yield strength and tensile strength of the specimens have the lowest values after tempering at 550 °C. After tempering at 600 °C, the hardness decreases and strength–ductility reaches 11,571 MPa%. The tensile fracture of 600 °C sample presents delamination and ductile fracture. Through comparative analysis, it can be concluded that the plasticity and toughness of multilayer welded joints after tempering at 600 °C is improved, and they have better comprehensive mechanical properties.

Microstructure and mechanical properties of an Al-Zn-Cu-Mg alloy processed by hot forming processes followed by heat treatments

An investigation was conducted to determine the microstructure and tensile properties of an Al-Zn-Cu-Mg alloy processed by spray formed then hot forming processes (forging and extrusion at 703 K). Hot formed samples were solution treatment (743 K/1.5 h) and followed by different heat treatments; T6 aging treatment (393 K/24 h), T74 tempering treatment (393 K for 6 h followed by 433 K for 12 h) and T73 tempering treatment (393 K for 8 h followed by 433 K for 24 h) conditions. The results show that during the T6 aging treatment the number of precipitates is increased which are mainly of η′ and η. The high number of fine percipitates is leading to an enhancement of the tensile strengths and the ductility. The tensile yield strength of T6 and T74 heat treatments are decreasing gradually to different degrees with increasing the testing temperatures up to 473 K and drops dramatically after 473 K. The tensile yield strength (YS) of the T73 tempering treatment sample decreases dramatically after temperature 373 K. The coarse precipitates after T73 tempering treatment were unable to pin grain boundary and dislocation movement during the tensile testing at 373 K. The Precipitates start to dissolve during T73 tempering treatment forming new fine η′ and G.P. zones phases inside the η phase.

Influence of Intercritical Heating on the Microstructure and Mechanical Properties of Al‐Rich Quenching–Partitioning–Tempering Steel

The microstructure and mechanical properties with traditional and intercritical heating and quenching–partitioning–tempering (referred as Q–P–T and I&Q–P–T, respectively) treatment for the Al‐rich steel are revealed through optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD), electron probe microanalysis (EPMA), and tensile testing. Results indicate that the multiphase microstructures of the Q–P–T and I&Q–P–T‐treated steel consist of martensite (M), ferrite (F), and retained austenite (RA). Meanwhile, the I&Q–P–T‐treated steel has much more ferrite and relatively less RA than those of the Q–P–T‐treated one. During tensile testing, more RA with optimized stability transforms to martensite in the I&Q–P–T‐treated specimen, which leads to a more pronounced transformation‐induced plasticity (TRIP) effect. Thus, with more ferrite and a remarkable TRIP effect, the elongation and product of strength–elongation of the I&Q–P–T steel are higher than those of the Q–P–T‐treated one.

Influence of tempering treatments on mechanical properties and hydrogen embrittlement of 13 wt% Cr martensitic stainless steel

The influence of tempering treatments on mechanical properties and hydrogen embrittlement (HE) of 13 wt% Cr martensitic stainless steel (MSS) have been investigated by Charpy impact tests and slow strain rate tensile (SSRT) tests followed by fracture surface examination. The austenitized and quenched specimens were tempered at 300, 550 and 700 °C for 2.5 h. The MSS tempered at 550 °C showed brittle intergranular (IG) fracture after impact tests indicating its susceptibility to temper embrittlement. The experimental results showed that the 13 wt% Cr MSS is sensitive to HE. The as-quenched condition showed cracking during hydrogen pre-charging itself. Hydrogen pre-charging duration increased the susceptibility to HE of tempered MSS. The maximum HE susceptibility was observed for specimen tempered at 550 °C with a drastic reduction in strength and strain to failure. Tempering at 300 and 550 °C showed brittle IG fracture with hydrogen pre-charging in SSRT tests whereas increased IG region with ductile dimples was observed for specimen tempered at 700 °C with increase of pre-charging duration. The reason for maximum susceptibility to HE of specimen tempered at 550 °C is due to synergistic interaction of hydrogen and impurities segregated at prior austenitic grain boundaries.

Effect of welding techniques on the microstructure and mechanical properties of reduced activation ferritic-martensitic (RAFM) steel weld joints

Reduced Activation Ferritic-Martensitic steels (RAFM) are chosen as the candidate material for structural components in fusion reactors. Gas Tungsten Arc (GTA) welding is one of the candidate process for fabricating the structural components made of RAFM steel. A variant of GTA welding process called as Activated Tungsten Inert Gas (A-TIG) welding has been reported to overcome the limitations of GTA welding and enhance creep rupture life in F–M steels. In the present work, 10 mm thick RAFM steel is welded by conventional TIG and A-TIG welding processes and the effect of welding techniques on the microstructure and mechanical properties are compared. Post Weld Heat Treatment (PWHT) conditions are optimized in A-TIG weld joint to get improvement in impact toughness values. TEM investigation on weld metals revealed that the martensite lath and prior austenitic grain boundaries are decorated with M23C6 precipitates and the lath size was in the range of 0.3 -0.4 μm. Very fine MX precipitates are seen in intra martensite laths and very fine sub grain formation was observed after tempering treatment. Hardness and strength properties are higher for A-TIG weld joint while ductility is similar for both the weld joints. An impact toughness of 155 J was obtained in the A-TIG weld joint on full size sample.

Strengthening Mechanism and Thermal Stability of Spray Formed H13 Steel

The aim of this work is to study the strengthening mechanism and thermal stability of spray formed H13 steel. The microstructure and hardness of spray formed H13 steels are investigated by electron microscopy, transmission electron microscopy and hardness measurementscanning. The calculated results demonstrate that tensile strength, impact energy and hardness values of sprayed-formed H13 steel are higher than that of as-cast H13 steel when the tempering temperature is 600 °C after quenched at 1050 °C. Compared with as-cast H13 steels, tempered spray-formed H13 steels possess supernal high-temperature temper resistant stability. The chemical composition of the carbides in spray-formed steels is V and Cr rich spherical carbides are hardly influenced by the tempering treatment.

Pengaruh Perlakuan Panas Terhadap Struktur Mikro, Kekerasan dan Ketahanan Oksidasi Suhu Tinggi Pada Baja Tahan Karat Martensitik 13Cr3Mo3Ni-Cor

Tulisan ini memaparkan pengaruh perlakuan panas terhadap struktur mikro, kekerasan dan ketahanan oksidasi suhu tinggi pada baja tahan karat martensitik 13Cr3Mo3Ni-cor. Tujuan penelitian ini adalah untuk meningkatkan kualitas baja tersebut melalui proses perlakuan panas terhadap struktur mikro, kekerasan dan ketahanan oksidasi temperatur tinggi. Proses pembuatan baja tahan karat 13Cr3Mo3Ni-cor dilakukan menggunakan proses peleburan induksi dan pengecoran sedangkan perlakuan panas yang dialami oleh baja tersebut antara lain austenisasi, tempering tunggal dan tempering ganda. Proses austenisasi dilakukan pada temperatur 1020°C selama 4 jam dan didinginkan diair kemudian dilanjutkan proses tempering 650°C selama 2 jam dan didinginkan di udara dan kemudian dilanjutkan proses tempering ganda 550°C selama 2 jam dan didinginkan di udara.Pengujian struktur mikro, kekerasan dan uji oksidasi temperatur tinggi 400-700 °C dilakukan pada masing-masing baja dengan perlakuan panas yang berbeda. Kemudian, hasil eksperimen baja temper ganda dibandingkan dengan baja kontrol, baja austenisasi dan baja temper tunggal. Perlakuan panas temper ganda menghasilkan dampak positif terhadap ketahanan baja tahan karat martensitik 13Cr3Mo3Ni-cor di lingkungan suhu tinggi.

Influence of the addition of Cr in the microstructure and in the phase transformation temperatures of Cu–Al–Be–Nb–Ni alloys

Cu–Al–Be polycrystalline SMAs modified with the addition of inoculants show improved ductility, which accredits them for technological applications. However, when the composition of these inoculants exceeds the solubility limit in the β matrix phase, precipitates occur which probably decrease the Be and/or Al content in the matrix, thus causing a change in the phase transformation temperatures. Thus, alloys that do not reach the desired phase transformation temperature need to be discarded and further processing must be performed, thereby generating additional costs in the alloy preparation process. In this sense, the main objective of this work is to investigate the influence of Cr addition on Cu–Al–Be–Nb–Ni alloys, with proportional variation of Cr and Be elements in CrBe2 ratio, alloy grain refinement and temperatures of phase transformation. Additionally, the influence of the solubility temperature of the austenite, during tempering treatment, on the phase transition temperatures of these alloys was verified. The results obtained showed that the compensation of the Be content, added in CrBe2 ratio, were efficient to maintain transformation temperatures close to the alloy without addition of Cr. It was also observed a considerable efficiency of the heat treatments in the reversion of the transition temperatures, being possible to obtain variations around 50 °C after application of the heat treatment. In this way, it is concluded that the compensation of the Be content and modifications in the solubilization temperature is efficient in the process of control of the phase transitions.

Formation and evolution of layered structure in dissimilar welded joints between ferritic-martensitic steel and 316L stainless steel with fillers

Dissimilar high-energy beam (HEB) welding is necessary in many industrial applications. Different composition of heat-affected zone (HAZ) and weld metal (WM) lead to variation in mechanical properties within the dissimilar joint, which determines the performance of the welded structure. In the present study, appropriate filler material was used during electron beam welding (EBW) to obtain a reliable dissimilar joint between reduced-activation ferritic-martensitic (RAFM) steel and 316 L austenitic stainless steel. It was observed that the layered structure occurred in the weld metal with 310S filler (310S-WM), which had the inferior resistance to thermal disturbance, leading to severe hardening of 310S-WM after one-step tempering treatment. To further ameliorate the joint inhomogeneity, two-step heat treatment processes were imposed to the joints and optimized. δ-ferrite in the layered structure transformed into γ-phase in the first-step normalizing and remained stable during cooling. In the second-step of tempering, tempered martensite was obtained in the HAZ of the RAFM steel, while the microstructure of 310S-WM was not affected. Thus, the optimized properties for HAZ and 310S-WM in dissimilar welded joint was both obtained by a two-step heat treatment. The creep failure position of two dissimilar joints both occurred in CLAM-BM.

Effect of Cryogenic Treatment on Mechanical Properties of AISI 4340 and AISI 4140 Steel

From last epoch till to date, AISI 4340 and AISI 4140 have been widely used in different engineering applications. These applications include bolt, screws, gears, drive shafts, crane shaft and piston rods for engines due to its upright mechanical properties, cost-effective and easily available in market. In present work, deep cryogenic treatment effect on the mechanical properties of AISI 4340 and AISI 4140 have been studied. Present work was carried out at laboratory scale and can be extended for mass production. Our work is simple, straight forward safe and economical. In our work, samples were heat treated in simple muffle furnace and followed by cryogenic treatment in liquid nitrogen. Before cryogenic treatment, all samples were normalized at 860°C to obtain homogenized micro structure. Samples were also compared conventionally heat treatment with quenched in oil quenchant. Experimental results showed that after cryogenic treatment with tempering treatment, one could easily increase the tensile strength, impact toughness and hardness. Advanced optical microscopy (IMM 901) and SEM (Scanning Electron Microscopy), FIT Quanta 200 methods have also been deployed to reveal and interpret the internal structure of samples. It was found from micro structure that cryogenic treated sample increases the impact strength, hardness and tensile strength as compared conventional heat treated quenching approaches.