Tempering Treatment Research Articles

Microstructure and mechanical-property evolution of the explosive welding joint from the same RAFM steels under explosive welding and post-weld heat treatment

This study investigated the morphological evolution behaviors and the mechanical property of the weld interface during explosive welding for the flyer plate and base plate sourcing from the same reduced activation ferrite/martensitic (RAFM) steel. The relationship between fine-grain formation and the occurrence of dynamic recrystallization was analyzed based on the strain and temperature field distributions at the explosive-weld interface. Although post-weld tempering (PWT) treatment eliminated bent martensite laths, but it did not eliminate fine equiaxed grains and δ ferrite grains near the explosive-weld interface; therefore, the PWT treatment improved the mechanical properties of the explosive-weld RAFM steel joint only minimally. However, implementation of a normalizing process after the explosive welding process (“PWN” treatment) significantly eliminated the gradient structure and the residual δ ferrite grains at the explosive-weld interface of the RAFM steel joint. Based on the PWN state, the inclusion of a tempering treatment (“PWNT” treatment) promoted the uniform precipitation of M23C6 carbides, which significantly improved the tensile strengths of the explosive-weld RAFM steel specimens under both room and high temperatures. To study the influence of different microstructures on the plastic deformation behavior at the explosive-weld interface, the representative volume element (RVE) models basing on crystal plasticity finite element (CPFEM) method was constructed for different post-weld heat treatments (PWHTs). At the explosive-weld interface of the PWT-state RAFM steel joint, the plastic deformation was mainly concentrated in the δ ferrite grains, rather than in the fine equiaxed grains. In addition, only minimal deformation concentration was observed for the PWNT-state RAFM steel joint. In order to reveal the independent influence of the fine equiaxed grains at the weld interface on the mechanical properties of explosive-weld RAFM steel joint, the microstructural and mechanical distinctions between the RAFM steel joints in the N-PWT and PWNT states were investigated detailly. Finally, through optimization of the PWHT method, an explosive-weld RAFM steel (PWNT state) joint with a uniform microstructure and ideal mechanical properties was obtained.

Design and Fabrication of a Novel Commercial Baking Oven

This study presents the design and fabrication of a novel wood-fired commercial oven for baking bread. The oven design features an external combustion chamber with heating elements which comprise stainless-steel pipes filled with magnesia starting from the combustion chamber to the 3 oven compartments. Each compartment has 12 heating elements laid under a mild steel sheet metal where the dough mould and its content is placed. Heat loss due to conduction, radiation and convection was prevented by the use of a double wall in both oven and combustion chamber compartments with silica brick and fibre glass respectively, and the oven was fired with wood to bake some dough. Findings showed that maximum temperature attainable by the oven was 700°C, however, the temperature required for baking bread is between 150°C and 180°C and the time was 25 minutes, the quantity of heat generated per time using 10 kg of wood was about 15,088 KJ. Furthermore, the physical appearance of the products was examined to meet consumers’ requirement and a total of 400 bread of 180 mm × 120 mm × 80 mm dimensions can be baked at a time. With slight modifications in the oven design, this number can be improved. The oven can be fired with other types of solid biofuels and can be used for metallurgical furnace applications like annealing, tempering and other heat treatments of metals.

Effect of surface treatment on oxidation film of 55SiCr spring steel wire

Abstract In this work, the surface pretreatments of 55SiCr spring steel wire rods were conducted using shot blasting and phosphating. After drawing, the steel wire was heated at 950°C × 15 s, followed by oxidation treatment with high-temperature steam or air for 3 seconds, and tempering treatment at 520°C. The effects of different surface treatment methods on the surface oxide film of spring steel wire were studied using stereomicroscopy, SEM, EDS, and XRD. The results showed that the steel wire surface oxide film with phosphating pretreatment was thicker and easy to fall off. The thickness of the oxide film formed by phosphating pretreatment samples increased by 2.1 um (high-temperature steam) and 0.3 um (air) compared to the shot-blasting samples under different oxidation atmospheres. High-temperature steam oxidation treatment significantly increased the thickness of the oxide film by 0.65 um (shot blasting) and 2.45 um (phosphating) under different surface pretreatment conditions. The outer surface of the oxide film turned black with high-temperature steam oxidation treatment and turned yellowish brown with air oxidation treatment. By both above oxidation treatments, the oxide film showed a multilayer structure, with enrichment of Cr and Si on the inner side.

EFFECTS OF HEAT TREATMENT ON THE IMPROVED WEAR RESISTANCE OF SHOT BLAST MACHINE BLADE MATERIAL

The blade is a component of the shot blast machine that functions as a thrower of small steel balls (steel shot). During its use, the blade undergoes impacts and friction with the steel shot, causing wear and a shortened lifespan. The material typically used for blades is white cast iron. Hence, the blade must possess good hardness and wear resistance. This study analyzed the causes of blade failure and proposed solutions in the form of hardening and tempering treatments. The tests conducted in this research included composition analysis, metallographic examination, hardness testing, and wear resistance testing. Based on the composition and hardness tests, the failure was attributed to material composition and hardness not meeting the ASTM A532 standards. The solution to this failure involves heat treatment to achieve hardness that complies with ASTM A532 standards, specifically hardening at 900°C for 40 minutes, followed by cooling with oil as the quenching medium. Then, the tempering process was carried out at 200°C, 250°C, and 300°C with holding times of 80 and 120 minutes. Post-heat treatment, the optimal hardness value, and the lowest wear rate were obtained at a tempering temperature of 300°C with a holding time of 120 minutes. The hardness value of the blade material under these conditions reached 63.8 HRC, and the wear rate was 1,21E-04 mm3.kg-1.m-1. A low wear rate indicates that the material has high wear resistance.

Effects of Tempering on Microstructure and Properties of Additive Manufacturing Cu-Bearing AISI 431 Steel.

AISI 431 martensitic stainless steels (MSS) with 2.5 wt% Cu were fabricated via laser-directed energy deposition additive manufacturing followed by single-step tempering treatment. The influences of different tempering times at 600 °C on microstructure and mechanical properties of the as-deposited 431-2.5Cu MSS have been explored and analyzed. The as-deposited MSS specimen primarily consisted of lath martensite, austenite and M23C6 carbide. After the single-step tempering treatment at 600 °C, Cu-enriched (ԑ-Cu) nano-precipitates and reverse austenite can be formed and promoted by extending the tempering treatment. The microhardness, strength and elongation can be improved with increasing the tempering time up to 1.0 h, and subsequently reduced with the tempering time prolonging to 2.0 h. Compared to 431 MSS that requires a multiple-step heat treatment for excellent performance, the 431-2.5Cu MSS specimen presented superior tensile properties after single-step tempering at 600 °C for 1.0 h in the present work. The ultimate tensile strength (UTS), yield strength (YS) and elongation (EL) of one-hour tempered MSS were 1611 MPa, 1334 MPa and 16.3%, respectively. This study provides a quantitative theoretical reference and experimental basis for realizing short-process fabrication of the Cu-bearing MSS with high strength and ductility.

Exploring W-EUROFER brazed joints: S/TEM and nanoindentation analysis following post-brazing tempering treatment

Tempering treatments are essential for restoring the hardness and microstructure of EUROFER steel when W-EUROFER joints are formed at temperatures exceeding the steel's austenitization point (890 °C). This post-brazing heat treatment can, however, alter the microstructure and thereby affect the mechanical properties. This study explores the microstructural and nanomechanical effects in the brazed area of W-EUROFER joints following this heat treatment, utilizing copper as an intermediate filler material. Using Scanning Transmission Electron Microscopy (STEM) with Energy Dispersive Spectroscopy (EDS) on FIB lamellae and nanoindentation techniques we examined the stability and phase characteristics of the post-tempered microstructure in two lamellae that covers the whole phases of the braze microstructure.The tempering process enhances copper diffusion and the growth of copper precipitates without significantly altering the joint's overall microstructure. Despite the general stress-relief effects of tempering, which typically lower mechanical properties, the diffusion phases formed during brazing maintained high hardness and modulus, indicative of a complex, element-rich composition. A reduction in mechanical properties was observed in the iron-rich phase near the W-braze interface and the EUROFER base material, aligning with the purpose of the heat treatment. However, the copper braze and tungsten base material largely retained their stability and resilience to thermal treatments.This research provides vital insights into the behavior of these material systems under thermal processing, highlighting the necessity of optimizing heat treatment parameters to preserve joint integrity in high-performance applications such as nuclear fusion reactors. The findings contribute significantly to the development of durable and reliable materials for fusion energy, emphasizing the importance of controlled tempering processes to enhance material properties.

Achieving 1.7 GPa Considerable Ductility High-Strength Low-Alloy Steel Using Hot-Rolling and Tempering Processes.

To achieve a balanced combination of high strength and high plasticity in high-strength low-alloy (HSLA) steel through a hot-rolling process, post-heat treatment is essential. The effects of post-roll air cooling and oil quenching and subsequent tempering treatment on the microstructure and mechanical properties of HSLA steels were investigated, and the relevant strengthening and toughening mechanisms were analyzed. The microstructure after hot rolling consists of fine martensite and/or bainite with a high density of internal dislocations and lattice defects. Grain boundary strengthening and dislocation strengthening are the main strengthening mechanisms. After tempering, the specimens' microstructures are dominated by tempered martensite, with fine carbides precipitated inside. The oil-quenched and tempered specimens exhibit tempering performance, with a yield strength (YS) of 1410.5 MPa, an ultimate tensile strength (UTS) of 1758.6 MPa, and an elongation of 15.02%, which realizes the optimization of the comprehensive performance of HSLA steel.

Effect of zirconium addition on microstructural characteristics and nano-mechanical properties of P9 steel

Micro-alloying in steels has significant effects on microstructure and its properties. The main objective of the work is to understand the influence of zirconium (Zr) addition to P9 ferritic/martensitic (F/M) steel on phase stability, microstructure, and nanomechanical properties. The alloy compositions in this study were designed using thermodynamic calculations, based on which steels with Zr concentration in the range of 0.05–2 wt.% were synthesized using vacuum arc melting. The cast alloy was subjected to thermo-mechanical treatments followed by austenitization and tempering treatments. Zr concentration of the steel was found to influence the nature of secondary phases formed, which were quantified through detailed synchrotron X-ray diffraction (XRD) analysis and also characterised extensively using electron microscopy techniques. Detailed structural analysis of the Fe23Zr6 phase using aberration corrected transmission electron microscopy is reported for the first time. The nano-mechanical properties of the heat-treated steels were evaluated using instrumented indentation tests at room temperature with a sphero-conical indenter. A systematic variation in hardness and yield strength with Zr content of P9 steel was observed, which is correlated to the microstructural changes. The P9 F/M steel with optimum concentration of Zr, with better mechanical properties is proposed through this structure-property correlation study.

Effect of dislocation density on microstructure and mechanical properties of cold-rolled medium Mn steel

This study investigated the effect of dislocation density on microstructural transformation and mechanical properties of Fe-7.23Mn-4.42Al-0.09C-1.99Si (wt.%) steel. By the tempering treatment, the dislocation density was reduced. The effect of of dislocation density on the plasticity of the steel was analyzed. The dislocation density was reduced from 2.3 × 10−16 m−2 to 1.6 10−16m−2 by tempering. Reducing dislocation density in the metastable austenite resulted in a higher metastable austenite transformation rate. And the low dislocation density steels exhibited a longer strain length during tensile deformation. It was obvserved that the dislocation density of the test steel decreased by 30% after tempering, the austenite transformation rate increased to 53.3%, and tensile strength and elongation increased to 1010 MPa and 44% respectively.

Improved passivation performance of selective laser melted Inconel 718 alloy via tempering treatment

The passivation performance of the selective laser melted Inconel 718 alloy after tempering treatments was investigated, and the underlying mechanism for the improved passivation film protectiveness was explored. The dislocation reversion and the mitigated segregation of Nb, Mo and Ti at Laves and δ phases decreased the storage energy of lattice distortion were critical factors for the formation of more protective passivation film in chloride-containing solutions. The film formation rate increased after tempering, presenting the increased electric field strength and the decreased dissolution rate accordingly, as well as for the point defect diffusion coefficient and the oxygen vacancy flux therein.

Thermomechanical Processing for Improved Mechanical Properties of HT9 Steels.

Thermomechanical processing (TMP) of ferritic-martensitic (FM) steels, such as HT9 (Fe-12Cr-1MoWV) steels, involves normalizing, quenching, and tempering to create a microstructure of fine ferritic/martensitic laths with carbide precipitates. HT9 steels are used in fast reactor core components due to their high-temperature strength and resistance to irradiation damage. However, traditional TMP methods for these steels often result in performance limitations under irradiation, including embrittlement at low temperatures (<~430 °C), insufficient strength and toughness at higher temperatures (>500 °C), and void swelling after high-dose irradiation (>200 dpa). This research aimed to enhance both fracture toughness and strength at high temperatures by creating a quenched and tempered martensitic structure with ultrafine laths and precipitates through rapid quenching and unconventional tempering. Mechanical testing revealed significant variations in strength and fracture toughness depending on the processing route, particularly the tempering conditions. Tailored TMP approaches, combining rapid quenching with limited tempering, elevated strength to levels comparable to nano-oxide strengthened ferritic alloys while preserving fracture toughness. For optimal properties in high-Cr steels for future reactor applications, this study recommends a modified tempering treatment, i.e., post-quench annealing at 500 °C or 600 °C for 1 h, possibly followed by a brief tempering at a slightly higher temperature.

Effects of plasma‐activated water and mild heating on Escherichia coli inactivation during wheat tempering and flour quality

AbstractBackground and ObjectivesHeat treatment, as a pathogen reduction step, could compromise flour quality. Plasma‐activated water (PAW) is a novel pathogen reduction treatment for foods. Combining these treatments could improve pathogen inactivation during wheat tempering and maintain flour quality. This study evaluated the effects of PAW and mild heating on Escherichia coli inactivation during wheat tempering and wheat flour quality.FindingsE. coli was inoculated into wheat grains at 6.0 ± 0.1 log CFU/g. A 5‐log reduction was achieved after 6 h of tempering with PAW and heating (55°C), whereas 12 h were needed when using heating and deionized water (DI). Tempering with DI (control) and PAW alone only produced a 1‐log reduction after 24 h. The PAW and PAW + heat tempering treatments produced flours with comparable yield, physicochemical, dough rheology, and bread characteristics compared to the control treatment.ConclusionMild heating and PAW tempering demonstrated a synergistic effect as it produced greater E. coli reductions at shorter tempering times compared to the individual treatments. The hurdle approach used in this study did not compromise flour quality.Significance and NoveltyThe demonstrated hurdle approach can be a viable pathogen mitigation step in wheat milling which could help improve food safety of wheat‐based foods.

Strength and toughness balance in 7 %Ni steel by formation epsilon martensite, retained austenite and Low matrix strain

In the current study, 7 wt.%Ni alloy steel was prepared, hot rolled, and heat treated according to popular quenching, lamellarization, and tempering treatments. The inter-critical lamellarization temperature was varied and the microstructure-property correlation was evaluated in each stage of heat treatment to understand the metallurgical aspects. Optical and detailed electron microscopic techniques were used to characterize and quantify the microstructures. Mechanical responses under uniaxial and impact loading were also recorded for all the studied samples. Tempered martensite with blocky and lamellar morphology, along with retained austenite and ɛ-martensite, were observed in the microstructures after the above-mentioned heat treatment. The lamellarization at 700 ℃ leads to a more uniform distribution of alloying elements and, therefore, promotes the formation of finer retained austenite with uniform distribution, compared to 650 °C lamellarization temperature. The presence of lower matrix strain and uniformly distributed fine retained austenite provides the highest toughness with moderate strength in the 700 °C samples. ɛ-martensite is expected to provide the necessary strength to balance the softening arising due to tempered martensite and retained austenite. Moreover, the uniformly distributed fine and filmy-shaped retained austenite provides thermal stability, and arrests crack propagation, enhancing toughness. The XRD results after impact toughness show that the γ-ε-α transformation takes place during the -196 °C temperature, and during impact toughness testing, ε-α transformations also provide the toughening in the Ni-700+590 sample.

Comparative Analysis of Tribological Behavior of 45 Steel under Intensive Quenching-High-Temperature Tempering and Queenching-Tempering Process

The intensive quenching process compared to traditional methods results in a lower quenching cracking tendency. The comprehensive mechanical properties of an intensive quenching workpiece has good advantages. In order to improve the performance and product quality of a 45 steel workpiece, the hardening–tempering treatment used in the traditional quenching process is replaced by an intensive quenching process. This study investigates the tribological properties of 45 steel and their differences and connection under the intensive quenching and high-temperature tempering process in comparison to when under the traditional hardening–tempering process. Both intensive quenching and tempering and hardening–tempering workpieces are composed of carburized particles and ferrite. Compared with hardening–tempering workpieces, intensive quenching and high-temperature tempering workpieces have a finer and more uniform microstructure and higher hardness, impact toughness, and yield strength. Wear tests show that intensive quenchingand tempered specimens have better wear resistance. At the same frequency, the coefficient of friction and relative wear rate of the intensive quenching and tempering specimens were lower than those of the hardening–tempering treatment, and the wear surface was flatter. The wear morphology shows that the main wear mechanisms of the intensive quenching and tempering workpieces and those of hardening–tempering are abrasive and adhesive wear, and that the main wear mechanism changes from adhesive wear to abrasive wear as the frequency increases.

The Effect of Cryogenic Treatment on W360 and E38K Hot Work Tool Steels

The present study examines the impact of cryogenic treatment (CT) on W360 and E38K hot work tool steels used in forging dies, subjected to conventional heat (HT) and CTs followed by double tempering treatment. Results reveal that CT facilitates the transformation of retained austenite from 4.9% and 2.5% for W360 and E38K steels, respectively, into martensite to an undetectable limit. Also, when compared to HT, CT at −180 °C results in about 3 times higher amount of the carbide precipitation for both steel types. In contrast, a slight increment in the hardness values with decreasing treatment temperature is observed. Notch impact test results indicate higher impact energy with lower CT temperatures, particularly notable in W360 steel. Although both steel types exhibit almost similar impact energy values at room temperature, E38K steel has ≈100% higher energy at 350 °C. DCT‐treated samples show improved wear resistance at lower cryogenic temperatures. Cryotreated W360 steel displays nearly 25% less wear rate than cryotreated E38K steel. The study underscores the suitability of W360 and E38K steels for hot work applications, with CT enhancing their mechanical and microstructural performance, particularly in W360 steel due to its higher carbide density.

Microstructure and Mechanical Properties of Laser Direct Energy Deposited Martensitic Stainless Steel 410.

The aim of this work is to study the phase transformations, microstructures, and mechanical properties of martensitic stainless steel (MSS) 410 deposits produced by laser powder-directed energy deposition (LP-DED) additive manufacturing. The LP-DED MSS 410 deposits underwent post-heat treatment, which included austenitizing at 980 °C for 3 h, followed by different tempering treatments at the temperatures of 250, 600, and 750 °C for 5 h, respectively. The analyses of phase transformations and microstructural evolutions of LP-DED MSS 410 were carried out using X-ray diffraction, SEM-EDS, and EBSD. Vickers hardness and tensile strength properties were also measured to analyze the effects of the different tempering heat treatments. It revealed that the as-built MSS 410 has very fine lath martensite, high hardness of about 480 HV1.0, and tensile strength of about 1280 MPa, but elongation was much lower than the post-heat-treated ones. Precipitations of chromium carbide (Cr23C6) were most commonly observed at the grain boundaries and the entire matrix at the tempering temperatures of 600 °C and 750 °C. In general, the tensile strength decreased from 1381 MPa to 688 MPa as tempering temperatures increased to 750 °C from 250 °C. Additionally, as the tempering temperature increased, the chromium carbide and tempered martensite structures became coarser.

Improving the Mechanical Properties of Hot Rolled Low-Carbon Copper-Containing Steel by Adjusting Quenching Roll Speed.

This paper presents a comprehensive study of the impact of quenching roll speed on enhancing the low-temperature toughness of a low-carbon copper-containing steel. The microstructure characteristics, such as the prior austenite grains, and the distribution and volume fraction of precipitates, are observed using optical microscopy, scanning electron microscopy, transmission electron microscopy, and small-angle scattering X-ray. The results show that a decrease in the quenching roller speed (2 m/min) contributes to the achievement of more excellent low-temperature toughness (the average value is 232 J), although the prior austenite grains exhibit a relatively larger size in this case. The tempering treatment results in the precipitation of a large amount of 9R-type Cu-rich particles, regardless of the quenching roller speed. Reducing the quenching roller speed contributes to the increase in the volume fraction of Cu-rich particles, which is considered to be the main factor contributing to the achievement of excellent low-temperature toughness.

Simple route to produce excellent mechanical properties of 9Mn steel with heterostructure induced by pre-existing austenite with sub-rapid solidification

Medium-Mn steels have garnered significant interest due to their unique combination of high strength and exceptional ductility. However, a high Mn content inevitably causes the macro-segregation of Mn, which can significantly compromise the mechanical properties. This study effectively prevented the formation of Mn macro-segregation by employing the sub-rapid solidification. It resulted in the distribution of Mn micro-segregation bands within dendritic gaps in Fe-9Mn-2Si-0.5Al-0.1C steel. Mn micro-segregation bands results in a high proportion of pre-existing austenite (γpre) with small size and suitable stability in the as-cast strip, forming a lamellar structure with alternating distribution of lath martensite and austenite on the micrometer scale. The as-cast strip necessitates only basic simple hot rolling control without the need for any tempering treatment to achieve excellent mechanical properties comparable to conventional lengthy processes (ultimate tensile strength (UTS) of 1762 MPa, total elongation (TE) of 20 %, and product of strength and elongation (PSE) up to 35 GPa%). Utilizing this structure as a foundation, a simple austenite reverse tempering (ART) treatment can lead to additional enhancements in comprehensive mechanical characteristics with the UTS of 1529 MPa, TE of 25 % and PSE of 38 GPa%.

Effect of microstructure on wear resistance during high temperature carburization heat treatment of heavy-duty gear steel

To shorten the production cycle of heavy-duty gear steel and ensure its wear resistance, high temperature carburization, two high-temperature tempering, quenching, subzero treatment, and low-temperature tempering treatments were performed on 18Cr2Ni4WA steel in this work. The effect of surface precipitation phases and retained austenite on wear resistance after different heat treatments was studied throughout the process. The results show that an increase in the volume fraction (Vcar) and size (Dcar) of undissolved carbides and a decrease in the volume fraction of retained austenite (Vr) are beneficial to wear resistance. The Vcar increases from 3.4 % to 6.3 %, and the Dcar increases from 152 nm to 161 nm. The undissolved carbides are mainly cementite. The carbon content of retained austenite decreases from 1.02 % to 0.79 %, and Vr decreases from 40.6 % to 4.8 %. In addition, the microstrain increases from 0.386 % to 0.458 %, and the wear rate decreases from 0.49 × 10−8 mm3·N−1·mm−1 to 0.46 × 10−8 mm3·N−1·mm−1. The improvement in wear resistance is mainly attributed to solid solution strengthening of carbon atoms and precipitation strengthening of undissolved carbides.

Effect of Cryogenic Heat Treatment on Multiple Tempered D-2 Tool Steel

The present day scenario in the manufacturing sector demands high productivity and the life of cutting tools plays a major role in increasing productivity. The freezing of metals has been acknowledged, for many decades, as an effective method for increasing" wear life" and decreasing residual stress in tool steels. Wear test using pin-on-disc machine was used to investigate the effect of multiple tempering after cryogenic treatment of D-2 tool steel. Conventional quenching (1010◦C) and tempering (515◦C) treatments were given along with intermediate cryogenic treatment (−196◦C). Specimens were subjected to wear tests on pin-on-disc machine in dry sliding condition for sliding distance of 6000 m at 6 kg load and for sliding speed of 3.0 m/s. Hardness data, microstructures, wear loss and Microstructure analys is analysis of worn surface throw light on the underlying metallurgical mechanism responsible in improving wear resistance property of the D-2 tool steel