Tempering Treatment Research Articles

Effect of different quenching holding times on microstructure, texture and electrical resistivity of NiCrAlFe alloy

Quenching treatment can provide microstructure for subsequent tempering treatment in the production process of NiCrAlFe precision resistance alloy. However, the recrystallization texture formed during quenching will be inherited into the tempered alloy, causing anisotropy of resistance and affecting the final performance of precision resistors. In order to investigate the evolution of the texture and its influence on the anisotropy of resistance, the effect of various quenching holding times on the alloy were studied. The results indicate that certain rolling deformation texture is gradually transformed into recrystallization texture and the texture intensity decreases significantly during the holding process. At the same time, the formation of a large number of twins promotes the formation of Brass-R {111}<112> texture at twin boundaries. The electrical resistivity of the alloy changes from 1.360 μΩ·m to 1.427 μΩ·m, and it shows an increasing trend with the holding time. The large number of supersaturated vacancies generated by quenching is the main reason for the increase in alloy electrical resistivity, but there is no correlation between the orientation density of texture and the electrical resistivity, however the type and intensity of textures exhibit significant influence on the anisotropy of the electrical resistivity. The electrical resistivity of direction rolling, direction 45°, and direction 65° are mainly influenced by Goss {110}<001> texture, Goss {110}<001> texture and Brass-R {111}<112> texture, and S {123}<634> texture and R {124}<211> texture, respectively.

Effect of quenching and tempering treatments on microstructure and mechanical properties of 300M ultra-high strength steel fabricated by laser powder bed fusion

To achieve high-performance 300 M steel parts through the Laser Powder Bed Fusion (LPBF) additive manufacturing process, post-heat treatments are indispensable. Herein, the effects of quenching and tempering treatments on the microstructure and mechanical properties of LPBF-fabricated 300M ultra-high strength steel were investigated, and the relevant strengthening and toughening mechanisms were analyzed. The microstructure of quenched samples primarily consisted of quenched martensite with minor amounts of bainite and some grain boundary allotriomorphic ferrite. The quenched samples presented significantly higher strength than the 300M forgings, primarily attributed to the contributions of solid solution strengthening, grain boundary strengthening and dislocation strengthening. After following tempering treatment, the microstructure of LPBF-fabricated samples mainly consisted of tempered martensite with minor amounts of bainite and residual austenite. Compared to the quenched samples, the tempered samples exhibited a decrease in strength while demonstrating a significant increase in ductility. The samples treated with the optimal heat treatment process (900 °C/1 h/Oil Cooling for quenching + two times of 300 °C/2 h/Air Cooling for tempering) demonstrated a remarkable strength–ductility balance, with a yield strength (YS) of 1834 MPa, an ultimate tensile strength (UTS) of 2099 MPa, and an elongation (EL) of 10.2%, which are all beyond or comparable to those of 300M forgings.

Effects of tempering treatment on structural evolution and electrochemical properties of laser cladded NiAlCrZrMo medium–entropy alloy coating by DFT calculation

A NiAlCrZrMo medium–entropy alloy (MEA) coating with solid solution was fabricated by laser cladding, which was evolved to high–entropy alloy (HEA) structure by tempering treatment for the improvement of corrosion resistance. The effects of tempering treatment on the structural evolution and electrochemical properties of obtained MEA coatings were comparatively investigated, and the corrosion mechanism was discussed with the density functional theory (DFT) calculation. The results show that the MEA structure of original MEA coating is evolved to HEA structure of tempered MEA coating by tempering treatment, which is composed of AlNi2Ti and Cr phases. The charge transfer resistance of tempered MEA coating is increased by ∼140 times compared with the original MEA coating, in which the diffusion of electrons is held back by its HEA structure. Moreover, the tempered MEA coating possesses higher electrochemical resistance compared with the original MEA coating, which is attributed to the AlNi2Ti phase of tempered MEA coating decreasing the corrosion tendency by the effect of high–entropy evolution.

Effect of Cryogenic Treatments on Hardness, Fracture Toughness, and Wear Properties of Vanadis 6 Tool Steel.

The ability of cryogenic treatment to improve tool steel performance is well established; however, the selection of optimal heat treatment is pivotal for cost reduction and extended tool life. This investigation delves into the influence of distinct cryogenic and tempering treatments on the hardness, fracture toughness, and tribological properties of Vanadis 6 tool steel. Emphasis was given to comprehending wear mechanisms, wear mode identification, volume loss estimation, and detailed characterization of worn surfaces through scanning electron microscopy coupled with energy dispersive spectroscopy and confocal microscopy. The findings reveal an 8-9% increase and a 3% decrease in hardness with cryogenic treatment compared to conventional treatment when tempered at 170 °C and 530 °C, respectively. Cryotreated specimens exhibit an average of 15% improved fracture toughness after tempering at 530 °C compared to conventional treatment. Notably, cryogenic treatment at -140 °C emerges as the optimum temperature for enhanced wear performance in both low- and high-temperature tempering scenarios. The identified wear mechanisms range from tribo-oxidative at lower contacting conditions to severe delaminative wear at intense contacting conditions. These results align with microstructural features, emphasizing the optimal combination of reduced retained austenite and the highest carbide population density observed in -140 °C cryogenically treated steel.

Simultaneous Enhancement of Strength and Sulfide Stress Cracking Resistance of Hot-Rolled Pressure Vessel Steel Q345 via a Quenching and Tempering Treatment.

Sulfide stress cracking (SSC) failure is a main concern for the pressure vessel steel Q345 used in harsh sour oil and gas environments containing hydrogen sulfide (H2S). Methods used to improve the strength of steel usually decrease their SSC resistance. In this work, a quenching and tempering (Q&T) processing method is proposed to provide higher strength combined with better SSC resistance for hot-rolled Q345 pressure vessel steel. Compared to the initial hot-rolled plates having a yield strength (YS) of ~372 MPa, the Q&T counterparts had a YS of ~463 MPa, achieving a remarkable improvement in the strength level. Meanwhile, there was a resulting SSC failure in the initial hot-rolled plates, which was not present in the Q&T counterparts. The SSC failure was not only determined by the strength. The carbon-rich zone, residual stress, and sensitive hardness in the banded structure largely determined the susceptibility to SSC failure. The mechanism of the property amelioration might be ascribed to microstructural modification by the Q&T processing. This work provides an approach to develop improved strength grades of SSC-resistant pressure vessel steels.

Effect of austenitisation and tempering treatments on the mechanical properties of advanced high strength spring steel SAE 9254

In response to increasingly stringent global regulations within the automotive industry, there is a growing demand for lightweight yet high-strength steel suspension coil springs. This study undertakes a comprehensive examination of the critical factors influencing the mechanical properties of SAE 9254, a well-established spring material, in its quenched and tempered (QT) state. The primary objective is to optimise its strength and ductility, especially in high-performance applications with an emphasis on lightweight design. The investigation encompasses a detailed exploration of the effects of varying austenitisation temperature (AT) and austenitisation time (At) on the microstructure and mechanical properties of the steel. Of particular interest is the study of tempering temperatures ranging between 300°C and 350°C to elucidate the mechanisms responsible for enhancing the steel's strength. Notably, the findings highlight dislocation density as the primary factor driving the strengthening of martensitic spring steel. Furthermore, the pivotal role of austenite grain size before quenching becomes evident, influencing toughness, ductility, martensite block size, and the percentage of retained austenite (γR). This study provides valuable insights into optimising the mechanical properties of SAE 9254 spring steel for high-performance applications, achieving ultimate tensile strengths (UTS) exceeding 2100 MPa and a reduction in area (RoA) exceeding 30%. Notably, the properties attained for this grade are comparable to those achieved with microalloying additions. Consequently, this research underscores the significance of controlling austenite grain size and dislocation density as critical factors for tailoring the properties of martensitic steels, positioning them as competitive materials, particularly in the pursuit of lightweight design.

Effect of quenching and tempering on microstructure and corrosion resistance of aerospace-bearing steel

CSS-42L steel is not only highly competitive for aerospace bearing applications but also for core components such as gears and shafts used in high-temperature or corrosive environments. This puts higher requirements on its microstructure, mechanical properties, and corrosion resistance. In this paper, CSS-42L steel was subjected to quenching, cryogenic and tempering treatments to study the effects of different heat treatments on the microstructure, hardness, and corrosion resistance of CSS-42L steel. It was found that the microstructure of the specimen after quenching contained martensite, a large amount of residual austenite, and trace amounts of fine carbides, and its hardness and corrosion resistance were improved. The residual austenite in the tempered sample underwent almost complete decomposition and transformed into fine martensite, and numerous finely dispersed and uniformly distributed carbides were precipitated, its hardness was further increased to 578.6 Hv concerning the quenched specimen, but concurrently exhibited a decrease in corrosion resistance. CSS-42L steel can be hardened by quenching, cryogenic and tempering to obtain martensite, but fine martensite reduces corrosion resistance. Since the amount of martensite or residual austenite affects the mechanical properties and corrosion resistance of CSS-42L bearing steel, the ratio of martensite and residual austenite needs to be adjusted to obtain optimum mechanical properties and corrosion resistance.

Numerical Simulation of Reversed Austenite Evolution during Intercritical Tempering of Low-Carbon Martensitic Stainless Steel.

Since the formation of reversed austenite during critical tempering treatment is an important factor affecting the mechanical properties of 13Cr4Ni martensitic stainless steel, a detailed study of the content and morphology of reversed austenite in heat treatment is needed. In this study, the variation curves of a reversed austenite volume fraction with holding time at different tempering temperatures were measured by in situ X-ray diffraction (XRD), and the reversed austenite and carbides of each process were evaluated by transmission electron microscopy (TEM). The austenite content shows a parabolic change with the increase in the tempering temperature; the maximum can reach a peak of about 6.8% at 610 °C, and drops to 0% at 660 °C. It also shows a parabolic change with the extension of the holding time, reaching a maximum of about 9.2% at 5 h of holding time, and a decreasing trend at 10 h of holding time, about 6.8%. The results show that the precipitation of carbides in the microstructure causes elemental segregation at grain boundaries and inside, which is one of the main factors affecting the thermal stability of reversed austenite formation. The kinetic process of reversed austenite during the tempering process was simulated using the JMAK model and the KM model, which can describe the trend of reversed austenite content during the tempering process. Combining the two models, a mathematical model for the room-temperature reversed austenite content under different processes was obtained, and this can predict the room-temperature austenite content.

The Effect of Direct Quenching on the Microstructure and Mechanical Properties of NiCrMo and Cu-Bearing High-Strength Steels.

In this work, two types of 590 MPa grade steels, composed of NiCrMo steel and Cu-bearing steel, were processed using traditional offline quenching and tempering and direct quenching (DQ) and tempering. The influence of DQ on microstructural evolution and strengthening mechanisms of these two types of steel was investigated. Grain refinement and dislocation density increase were determined by controlled rolling and following the DQ process in both two types of steel. In Cu-bearing steels, the refined grains and high-density dislocation further promoted the precipitation behavior of Cu-rich particles and alloyed carbides during the tempering treatment. Compared with traditionally quenched and tempered steels, NiCrMo steels after the direct quenching and tempering (DQT) process achieved 106 MPa higher yield strength through grain refinement strengthening and dislocation strengthening, while the Cu-bearing steels after the DQT process achieved 159 MPa higher yield strength through grain refinement strengthening, dislocation strengthening, and precipitation strengthening. The contribution degree of different strengthening mechanisms was quantitatively analyzed. Grain refinement also compensated for the toughness loss caused by the increase in dislocation, leading to an impact energy of 237 J and 248 J at -84 °C for NiCrMo and Cu-bearing steels after DQT, respectively.

Enhancing tribological performance in PM Vanadis 6 steel through optimization of cryogenic and tempering treatment

Vanadis 6, which gained popularity for industrial applications due to increased strength and wear resistance, benefited from cryogenic treatment. This study investigated the influence of cryogenic and tempering treatments on the tribological properties of Vanadis 6 cold-work tool steel, crucial for cost-effective and durable tooling. Dry sliding wear experiments using Taguchi design under varying loads and sliding velocities revealed that cryogenic treatment at − 140 °C followed by 170 °C tempering resulted in the lowest wear rate, friction coefficient, smoothest worn surfaces, and the highest transition load. Microstructural analysis supported these findings, indicating reduced retained austenite and increased carbide count in cryogenically processed steel at − 140 °C.

Effect of Tempering on Corrosion Properties of Mold Steel

Proper heat treatment of mold steel is an effective way to improve its mechanical properties, but there are currently few research reports on the effect of heat treatment on the corrosion performance of mold steel. In this paper, the corrosion resistance of 3Cr17NiMoV mold steel after 500 °C tempering treatment was analyzed using Zeiss microscope, scanning electron microscope, laser confocal microscopy, 3.5 wt.% NaCl solution immersion experiment, electrochemical testing, and other research methods. The results show that after 500 °C tempering treatment, the microstructure of 3Cr17NiMoV mold steel is transformed from martensite to tempered sorbite, the inclusion is still Al2O3, and its size do not change significantly. After 500 °C tempering treatment, the corrosion rate of the sample increased from 9.56 mm/a to 12.75 mm/a, the area and depth of the pitting pits correspondingly increased from 1280.64 μm2 and 1.083 μm to 2115.08 μm2 and 1.818 μm, respectively. And the corrosion current density of the sample increases from 3.09×10−6 A/cm2 to 4.56×10−6 A/cm2. After 500 °C tempering treatment, the corrosion resistance of 3Cr17NiMoV mold steel was slightly reduced, so in engineering practice, it is necessary to carefully design heat treatment processes to balance mechanical properties and corrosion resistance.

Effect of heat treatment on microstructure and properties of bimetallic band saw blade

Quenching and tempering treatment experimentswere conducted on the bimetallic band saw blades,and theeffect of quenching and tempering processes on the microstructure and properties of the band saw blades were studied. The results indicate that with increasing quenching temperature, the solid solution strengthening effect of the tooth tip improves the quenching hardness, but the high quenching temperature leads to martensitic coarser of the tooth back, which results in a significant decrease in the hardness. Moreover, with the increase in tempering temperature, the martensite in the microstructure of the tooth tip and tooth back was transformed into tempered trootensite and sortensite, and the primary and secondary carbides in the tooth tip became coarser, which led to the reduction of tempering hardness, and the fatigue properties changed too.

Microstructural evolution and mechanical properties of an additively manufactured high-strength steel

In this study, the microstructural evolution and mechanical properties of a new type of steel fabricated by selective laser melting (SLM) with subsequent tempering treatment were discussed. The as-built sample consisted of cellular structures, lath martensite accompanied by carbides and little residual austenite. After tempering at 560℃ for 2 h, the matrix transformed from the supersaturated martensite to the tempered lath martensite, followed by residual austenite complete dissolution and more carbides precipitation. The as-built sample showed a high strength (yield strength:1335 ± 10 MPa, ultimate tensile strength:1555 ± 2 MPa) and a considerable ductility (elongation to failture:7.7 ± 1.4 %). The outstanding strength was attributed to fine grains and high number density of dislocations. A superior mechanical properties, including the yield strength of 1762 ± 25 MPa, ultimate tensile strength of 1850 ± 39 MPa and elongation of 5.6 ± 0.8 % have been achieved in the SLMed steel after tempering. The as-built sample exhibits a higher uniform elongation (∼7.0 %) compared with tempered 560℃ sample(∼2.6 %), which may be attributed to its excellent work hardening behavior.

Microstructure and Properties of the LDEDed Cu-Bearing Martensitic Stainless Steel After a Single-Step Tempering Treatment

Microstructure and Properties of the LDEDed Cu-Bearing Martensitic Stainless Steel After a Single-Step Tempering Treatment

Impact of Ultra-Flash Tempering Treatment on the Microstructure and Mechanical Properties of High-Strength Carbon Steel

A novel high-frequency induction technology was successfully developed to carry out ultra-flash tempering treatment (UFTT) of high-strength carbon steel (HS-CS) with a heating rate of 1000 °C/s. The as-received HS-CS is a fully martensitic structure with low toughness. UFTT strategy at various temperatures is proposed to produce a tempered martensitic lath structure with promoting carbide precipitates in this structure. Microstructure evolution during UFTT was characterized using secondary electron imaging and electron backscatter diffraction technique in a scanning electron microscope. Micro-indentation hardness tests were measured through the cross-section of the steel to analyze the impact extent of UFTT. The mechanical properties were measured by uniaxial tensile tests. The results revealed that UFTT at various temperatures (550-650 °C) significantly affected the microstructure and the mechanical strength of the steel. A fully tempered martensitic microstructure with various types of carbide precipitates was promoted. Although, the microhardness and tensile strength of flash-tempered steel decreased owing to the breakdown of lath and dislocation structure in the achieved microstructure by UFTT. Hence, it is expected that the promoted microstructure during UFTT in the tested steel will result in a superior strength-toughness synergy. Based on the achieved results, the UFTT technique provides an alternative route for the conventional processing to tailor the microstructure of microalloyed HS-CS, consequently, optimizing the mechanical performance. Meanwhile, Economically, it is a cost-effective route to manufacture advanced high-strength steel.

Microstructural Investigation and Impact Strength of Sinter-Hardened PM Steels: Influence of Ni Content and Tempering Temperature

This study analyzed the influence of tempering treatment temperature on the microstructural and mechanical behavior of two different powder metallurgy steels containing 0 wt. % Ni and 4 wt. % Ni. The evolution of the microstructure and the macro- and microhardness of the microstructural constituents resulting from tempering treatments conducted on the sinter-hardened materials at temperatures ranging from 160 °C to 300 °C were investigated. The role of the tempering conditions in the impact behavior was assessed using Charpy tests on V-notched and unnotched samples, tempered at 180 °C, 220 °C and 280 °C. The observed macrohardness reduction with increasing tempering temperature was related to martensite transformations. At high tempering temperatures, the remarkable loss in impact energy values was attributed to microfracture modes. The contribution of Ni-rich austenite areas in enhancing impact strength was detected.

Acidic water tempering and heat treatment, a hurdle approach to reduce wheat Salmonella load during tempering and its effects on flour quality

The cultivation and processing of wheat render it susceptible to microbial contamination from varied sources. Hence, pathogens such as Salmonella can contaminate wheat grains, which poses a food safety risk in wheat-based products. This risk is displayed by the incidence of foodborne illness outbreaks linked to Salmonella-contaminated wheat flour and flour-based products. The purpose of this study was to assess the effectiveness of combining acidic water and heat treatment in reducing the Salmonella load of hard red spring (HRS) wheat grains during tempering. Effective treatments were then evaluated for their effects on wheat flour quality. Tempering with sodium bisulfate (SBS), lactic acid (LA), and citric acid (CA) at 15% w/v alone reduced (p < 0.001) wheat Salmonella load by 3.15, 3.23, and 2.91 log CFU/g, respectively. Heat treatment (55 °C) reduced (p < 0.001) wheat Salmonellaload by 4.1 log CFU/g after 24 h of tempering. Combining both tempering and heat treatments resulted in a greater reduction in Salmonella load as non-detectable levels (<2 log CFU/g) of Salmonella in the wheat grains were obtained after 12 h of tempering with LA (15%) + heat. A similar result were achieved for both SBS (15%) + heat and CA (15%) + heat treatments after 18 h of tempering. Applying the combined treatments in HRS wheat grains resulted in comparable wheat flour baking (volume, texture, and crumb structure) and physicochemical properties (rheology and composition) relative to the control (tempering with water alone). The results from this study has the potential to be utilized for developing more effective methods for improving the food safety of wheat flour against Salmonella contamination.

Fatigue crack growth behavior of selective laser melted martensitic stainless steel

This study investigated the fatigue crack growth (FCG) behavior of selectively laser-melted AISI 420 martensitic stainless steel built in two directions. The effect of tempering treatment at 400 °C was considered. In both as-built and tempered conditions, the parallel orientation exhibited lower fatigue crack growth rates (FCGRs) than the perpendicular orientation, indicating an anisotropic FCG behavior. Tempering treatment moderately reduced the anisotropy of FCG behavior, as the difference in FCGR between the two build orientations decreased in the tempered state. The anisotropic FCG behavior was attributed to the interaction between the crack path and the elongated cellular structure. Tempered martensite had a greater influence on the FCGR of the perpendicular group over the parallel group in tempered state.

Obtaining Excellent Mechanical Properties in an Ultrahigh-Strength Stainless Bearing Steel via Solution Treatment

A novel versatile ultrahigh-strength stainless bearing steel was prepared by first solution treating the steel at temperatures between 1000 °C and 1100 °C for 1 h, followed by performing cryogenic treatment at −73 °C for 2 h, and tempering at 500 °C for 2 h, with the cryogenic and tempering treatments being repeated twice. The microstructures were characterized using multiscale techniques, and the mechanical properties were investigated using tensile testing, as well as via Rockwell hardness and impact toughness measurements. Tensile strength was found to be independent of solution temperature, with a value of about 1800 MPa. In contrast, yield strength decreased from 1530 MPa to 1033 MPa with increasing solution temperature, while tensile elongation increased from 15.3% to 20.5%. This resulted in an excellent combined product of tensile strength and elongation for steels initially treated at 1080 °C and 1100 °C, with values of 33.9 GPa·% and 37.0 GPa·%, respectively. Furthermore, the steels showed excellent impact toughness, increasing from 37.0 J to 86.2 J with increasing solution temperature. The microstructural and mechanical investigations reveal that the excellent mechanical properties and impact toughness are related to three factors, namely (i) a transformation-induced plasticity effect, mainly attributed to a high volume fraction of retained austenite, (ii) a high strengthening capacity arising from a high dislocation density, and (iii) a synergistic effect due to cobalt additions and the nanoprecipitation of M2C and M6C carbides.

The Evolution of a Microstructure during Tempering and Its Influence on the Mechanical Properties of AerMet 100 Steel

In order to provide guidance for furthering the balance of strength and toughness of AerMet 100 steel through tempering treatment, the effects of the tempering time on microstructure and mechanical properties are investigated. The microstructure evolution, especially M2C precipitates and austenite in AerMet 100 tempered at 482 °C for 1~20 h, was characterized, and its influences on the mechanical properties were studied. The tensile strength decreases gradually, the yield strength increases first and then decreases, and the fracture toughness KIC increases gradually with an increasing tempering time. The strength and toughness matching of AerMet 100 steel is achieved by tempering at 482 °C for 5~7 h. Without considering the martensitic size effect, the influence of the dislocation density on the tensile strength is more significant during tempering at 482 °C. The precipitation strengthening mechanism plays a dominant role in the yield strength when tempering for 5 h or less, and the combined influence of carbide coarsening and a sharp decrease in the dislocation density resulted in a significant decrease in tensile strength when tempering for 8 h or more. The fracture toughness KIC is primarily influenced by the reverted austenite, so that KIC increases gradually with the prolongation of the tempering time. However, a significant decrease in the dislocation density resulting from long-term tempering has a certain impact on KIC, giving rise to a decrease in the rising amplitude in KIC after tempering for 8 h or more.