Tempering Treatment Research Articles

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.

Effects of tempering temperature on the precipitation behaviors of nanoparticles and their influences on the susceptibility to hydrogen embrittlement of a Cr–Mo–V steel

This paper presents an experimental study of tempering treatment to optimize the precipitation behavior of nano-sized particles for improving the resistance to hydrogen embrittlement (HE) of an AISI 4330-type low-alloy high-strength steel. The precipitates and dislocations in the microstructure, which serve as irreversible and reversible hydrogen traps, were quantitatively investigated using TEM, X-ray diffraction and hydrogen permeation techniques. It was found that V-rich M2C precipitates of less than 2 nm size appeared when tempered at 610 °C, a tempering temperature associated with the lowest HE susceptibility of the tempered steel. Furthermore, the hydrogen could promote movement of the multiple dislocation at the low-temperature tempering process but pin the separated dislocation at higher temperature tempering process. The interaction of the dislocations (i.e., multiple dislocation or separated dislocation) with nanoprecipitates and hydrogen atoms produced the hydrogen-induced hardening/softening behavior in a hydrogen-charging environment.

2 GPa H13 steels fabricated by laser powder bed fusion and tempering: Microstructure, tensile property and strengthening mechanism

The successful manufacture of crack-free and highly dense H13 tool steel using laser powder bed fusion (LPBF) has been widely reported. Although the phases contain only martensite and some (<20 %) of residual austenite (RA), the differences in tensile properties are very large in previous studies. Here, the microstructure and tensile properties of the LPBF-fabricated H13 steels with different heat treatments were comparatively studied. Tensile strengths ranged ∼2.0–2.2 GPa for the optimal as-built and direct-tempered samples. By increasing the heat input, the RA content was reduced to 0.1 % and the microstructure contained only hierarchically fine martensite with improved tensile properties and anisotropy. Based on the full-martensitic microstructure in the optimal as-built samples, secondary hardening was achieved by direct tempering at 530–590 °C with tensile strengths of ∼2.1–2.2 GPa and improved elongations (4.93–6.43 %). The optimal direct-tempered samples yielded higher tensile strengths compared to the standard heat-treated counterparts. For the direct-tempered samples, the substantial retaining of the fine martensitic structure and high density of dislocations introduced by LPBF was the key to the excellent properties rather than the precipitates. This work elucidated the effect of the LPBF process, direct tempering, and standard heat treatment on the tensile property of H13 steel. It is concluded that process optimization for LPBF fabrication of H13 steel requires not only defect avoidance but also fine martensite and low-content RA. On this base, the LPBF-prepared H13 steel can be directly tempered to further obtain components with excellent tensile properties, which are superior to the standard heat-treated counterparts.

New White Etch Cracking resistant martensitic stainless steel for bearing applications by high temperature solution nitriding

White Etch Cracking (WEC) is a severe and unpredictable failure mode that has been frequently observed in, among others, bearings for wind energy applications. In this work a novel, patented, WEC resistant bearing steel solution is developed through high temperature solution nitriding, followed by a custom heat treatment. Conventional medium carbon, 13 wt% Cr martensitic stainless steels were subjected to the novel process to obtain a nitrogen-rich case. A series of soft annealing, austenitization, cryogenic and tempering treatments converted the nitrogen-rich region into a fine-grained case containing nano-sized precipitates. Test bearings and tribometer specimens were treated with the same sequence of treatments. These specimens were tested under two different accelerated WEC failure promoting conditions. In contrast to standard through-hardened bearing steel the nitrided specimens showed no WEC formation, not even after prolonged testing.

Effect of heat treatment on microstructure and properties of 10B21 cold-heading steel for fasteners

Fasteners are widely used in automobile, electronic and other fields, and the demand for high performance fastener materials is increasingly urgent. 10B21 mild steel has the advantages of good plasticity, obvious heat treatment effect and so on. It is used to produce fasteners below grade 9.8. In this paper, the domestic 10B21 boron steel as the research object, through quenching, tempering and other heat treatment, change its structure from ferrite to tempered martensite, in order to improve the strength and hardness.

Changes in water status and microstructure reveal the mechanisms by which tempering affects drying characteristics and quality attributes of medicinal chrysanthemums

To elucidate the mechanism behind the heterogeneity in the water distribution during the drying process of medicinal chrysanthemum (Imperial chrysanthemum), and thereby optimize the drying process, this study introduced an innovative approach by incorporating tempering into the drying process and evaluated the effects of hot air drying (HAD), infrared-assisted hot air drying (IR-HAD), and tempering-incorporated IR-HAD (TD+IR-HAD) on the water status, microstructure, and phytochemicals of dried chrysanthemums. Results showed a significant difference in the rate of dehydration between the central and marginal parts of chrysanthemums. The highest difference in moisture content value (1.34 g water/g dry matter) was observed between these two parts for samples subjected to 2.5 h of IR-HAD drying. Consequently, the sample subjected to 2.5 h of IR-HAD drying was selected for tempering. After the optimal tempering treatment (12 h), the samples were subjected to an additional 0.5 h of IR-HAD drying. This incorporated drying method (TD+IR-HAD) effectively reduced the drying time and energy consumption. Transverse relaxation curves and microstructural observations further confirmed that these reductions were related to the enhancement of water mobility and the formation of microchannels during tempering. As a result, chrysanthemums dried using TD+IR-HAD showed increased contents of chlorogenic acid, luteolin, total phenolic, total flavonoid, antioxidant capacity, and the number of volatile compounds compared to HAD and IR-HAD. Overall, these results highlight the potential of TD+IR-HAD as a promising drying technique for enhancing the value and applications of medicinal chrysanthemums in industrial settings.

Influence of thermomechanical processing and tempering temperature on tensile flow and work hardening behaviour of India specific reduced activation ferritic martensitic steel

In the present work, an indetailed investigation has been carried out on the effect of thermomechanical treatment (TMT) and tempering temperature on microstructural features, tensile flow characteristics and work hardening behaviour of the India specific reduced activation ferritic martensitic (INRAFM) steel. The flow and work hardening characteristics of the studied steel are described by using the Voce constitutive equation and Kocks- Mecking (K-M) approach respectively in the temperature range of 300–873 K. The steel subjected to TMT and tempering for 90 min at 1033 K shows a refined martensitic lath width, finer size (Cr/W/Fe)23C6 and (V/Ta) (C/N) precipitates with an increment in number density. Furthermore, increase in tempering temperature coarsened the refined structural features. Voce equation closely fits the flow curves at 823 K and 873 K, but shows a slight deviation at temperatures below 773 K. The parameters derived from Voce equation are fairly in good correaltion with the experimental values. The strain hardening rate (θ) vs. true stress (σ) plots portrayed stage-I and stage-III work hardening stages and their corresponding phenomena were discussed. In addition, the effect of TMT and tempering treatment on the work hardening parameters obtained from K-M approach and inter-barrier spacing of the steel were also presented in this study. The work hardening characteristics of the steel signifcantly improved upon TMT due to refinement in microstructural features. The flow stress and work hardening parameters decreases with raise in test temperature due to the dominant effect of dynamic recovery.

EBSD-data analysis of an additive manufactured maraging 300 steel submitted to different tempering and aging treatments

Maraging is a high alloy steel sensitive to the precipitation of intermetallics from a supersaturated solid solution during aging heat treatments. The precipitation phenomenon is well described in the literature, which gave rise to the alloy name regarding a martensite matrix with precipitates formed by aging treatment. Many studies have been performed to characterize this material, usually subjected to many sample preparations for transmission microscopy, which is very laborious, and few EBSD analyses. Therefore, in this work, a large study was conducted using electron backscatter diffraction (EBSD) to analyze maraging microstructures through band-contrast, kernel average misorientation (KAM), grain orientation spread (GOS), and misorientation distribution. Our results show that solubilization of the additive manufactured maraging steel resulted in a more homogeneous microstructure with new angle grain boundaries. Furthermore, tempering heat treatments relieve martensite strain, increasing band contrast values. Posterior aging presented a low impact on the results of EBSD analysis.

Improvement in low-temperature toughness of Fe-6.5Mn-0.08C Medium-Mn steel by multi-step heat treatment

In this study, a novel multi-step heat treatment method, including intercritical annealing and tempering, is proposed to improve the low-temperature toughness of Fe-6.5Mn-0.08C medium-manganese (Mn) steel. The effects of the subsequent tempering treatment on the microstructural evolution and low-temperature toughness of medium-Mn steel were investigated and compared with those of a single intercritical annealing treatment. Medium-Mn steel subjected to intercritical annealing exhibited a duplex microstructure composed of martensite and nanolaminate-retained austenite. The subsequent tempering treatment after intercritical annealing generated a more homogenous distribution of retained austenite, together with an increase in the volume fraction of the retained austenite. The uniformly distributed retained austenite prevented Mn segregation at prior austenite grain boundaries, and the high fraction of retained austenite effectively inhibited crack propagation, leading to an improvement in the low-temperature toughness. In addition, the subsequent tempered medium-Mn steel contained a considerable amount of retained austenite, which could transform into martensite during the impact test, resulting in an impact fracture morphology that changed from cleavage facets to dimples at low temperatures.

Boosting Mechanical Properties of W6Mo5Cr4V2 Alloy Fabricated by Directed Energy Deposition Through Tempering Heat Treatment

The utilization of laser‐directed energy deposition (DED) for fabricating alloys offers the potential to customize their mechanical and physical properties, surpassing traditional casting limitations. Herein, a DED‐adopted flat‐top laser is applied in producing W6Mo5Cr4V2 alloy, a material widely used in mold making, double‐screw production, and crushing roller manufacturing. To minimize its residual stress and potential defects, and enhance the performance of the deposited sample, it undergoes tempering heat treatment at 560 °C for 1 h. According to the analysis results, the deposited W6Mo5Cr4V2 alloy is predominantly composed of martensite, carbide, and a minor amount of retained austenite. Upon tempering, the retained austenite transforms into martensite, effectively reinforcing the properties of the W6Mo5Cr4V2 alloy by precipitating secondary carbides. Furthermore, the microhardness value of the alloy increases by 12% after tempering heat treatment. Both adhesive and abrasive wear are observed during the friction and wear process, resulting in a 10% reduction in friction coefficient, thereby significantly improving the wear resistance of the W6Mo5Cr4V2 alloy. The average tensile strength of the heat‐treated W6Mo5Cr4V2 sample is 762.34 MPa, which is higher than the deposited sample's 646.6 MPa. Notably, the tensile fracture displays typical brittle characteristics.

Evaluation of post weld heat treatments and susceptibility to sulfide stress corrosion cracking of simulated HAZ in forged supermartensitic stainless steel UNS S41427

Supermartensitic stainless steels (SSMSs) with 12–13%Cr, 5%Ni, 2%Mo and microadditions were developed to casings, tubullars and mandrels used in the oil and gas off-shore production. These materials have great resistance to aqueous medium containing large amounts of CO2 and can withstand high temperatures and large amounts of chloride as well. However, SMSSs have a limited resistance to H2S containing solutions, and may fail due to sulfide stress cracking (SSC). This limit is even lower for forged and welded components that used in mandrels. Recent studies have been developed to find an operational envelope for safe use of SMSSs in sour production systems. The present study shows the results of slow strain rate testing (SSRT) of a forged V-alloyed SMSS submited to thermal simulation in Gleeble machine to produce a coarse grain heat affected zone (HAZ). The microstructure of the HAZ is characterized by fresh martensite, intergranular delta ferrite and fine precipitates which increase the hardness to a level above the maximum limit for sulfide stress corrosion cracking. The effects of two post weld heat treatments (PWHT) on the mechanical properties and susceptibility SSC were evaluated. Single and double tempering treatments provoked the decrease of hardness and the increase of ductility parameters. However, specimens representative of the HAZ, base metal, and HAZ with single and double tempering presented high SSC susceptibility parameters in SSRT in saline solution (200,000 ppm NaCl) with 1.0 psia of H2S partial pressure, and pH 4.5.