Increasing Tempering Temperature Research Articles

Evolution of Microstructures and Mechanical Properties with Tempering Temperature in a Novel Synergistic Precipitation Strengthening Ultra-High Strength Steel

The evolution of microstructures and mechanical properties with tempering temperature of a novel 2.5 GPa grade ultra-high strength steel with synergistic precipitation strengthening was investigated. With increasing tempering temperature, the experimental steel initially progressed from ε-carbides to M3C and then to M2C, followed by further coarsening of the M2C carbides and β-NiAl. Concurrently, the martensite matrix gradually decomposed and austenitized. The ultimate tensile strength and yield strength initially increased and subsequently decreased with rising tempering temperature, reaching peak value at 460 and 470 °C, respectively. Conversely, the ductility and toughness initially decreased and then increased with rising tempering temperature, reaching a minimum at 440 °C. The increase in strength was attributed to the secondary hardening effects resulting from carbide evolution and the precipitation of β-NiAl. The subsequent decrease in strength was due to the recovery of martensite and coarsening of precipitates. The decrease in ductility and toughness was linked to the precipitation of M3C, while their subsequent increase was primarily attributed to the dissolution of M3C and an increase in the volume fraction of reverted austenite. The high dislocation density of martensite, the film of reverted austenite, nanoscale M2C carbides, and ultrafine β-NiAl obtained during tempering at 480 °C resulted in the optimal mechanical properties of the experimental steel. The strength contributions from M2C carbides and β-NiAl were 1081 and 597 MPa, respectively.

Effect of Tempering Temperature on the Aqueous Corrosion Resistance of 9Cr Series Heat-Resistant Steel

In this investigation, the aqueous corrosion resistance of 9Cr series heat-resistant steel during tempering was investigated. Optical Microscopy (OM), Scanning Electron Microscopy (SEM), and Energy Dispersive Spectrometer (EDS) were used to analyze the effect of tempering temperature on the microstructure and precipitation behavior of precipitates. The heat-resisting steel was heated to 1150 °C for 1 h, and then tempered at different temperatures between 680 °C and 760 °C for 2 h. The microstructure of the heat-resistant steel after tempering was composed of lath-tempered martensite and fine precipitates. The hardness decreased with increasing tempering temperature, ranging from HBW 261 to HBW 193. The aqueous corrosion resistance improved as the tempering temperatures increased from 680 °C to 720 °C but deteriorated at higher temperatures, such as 760 °C, which was obtained by an electrochemical corrosion performance test. The aqueous corrosion resistance was affected by the decrease in dislocation density and the decrease in Cr solution in the tempered martensite. With the increase in the tempering temperature, the aqueous corrosion potential first increases and then decreases, the self-corrosion current density first decreases and then increases, and the polarization resistance first increases and then decreases. Furthermore, the increase in corrosion resistance is attributed to the reduction in dislocation density and chromium depletion in the martensitic structure as the tempering temperature approaches 720 °C. This paper reveals the effect of tempering temperature on the corrosion resistance of 9Cr series heat-resistant steel, which is a further exploration of a known phenomenon.

The regulation of dislocation and precipitated phase improving hydrogen embrittlement resistance of pipeline steel in high pressure hydrogen environment

In this study, the hydrogen embrittlement behavior of quenched pipeline steel tempered at 550 °C to 650 °C in a high-pressure hydrogen environment was analyzed. Hydrogen permeation tests and microstructural analyses indicated that the dislocation density of the steel decreases with increasing tempering temperature, while precipitates gradually nucleate and grow. These hydrogen traps interact with hydrogen atoms, resulting in significantly higher diffusible hydrogen content in steel tempered at 550 °C compared to that tempered at 600 °C and 650 °C. Fatigue crack growth (FCG) test results show that steel tempered at 600 °C and 650 °C exhibits significantly better hydrogen embrittlement resistance than steel tempered at 550 °C. This is primarily due to the combined effect of the high hydrogen concentration, high dislocation density and low nano carbide content in the steel tempered at 550 °C, which inhibits dislocation slip and emission, leading to high crack tip stress and rapid crack propagation. In contrast, the low dislocation density and and dispersed nano carbides in steel tempered at 600 °C and 650 °C facilitate some dislocation slip and emission, result in crack tip stress relaxation and reduced crack propagation rate. Properly controlling the initial dislocation density and increasing the density of irreversible hydrogen traps can enhance the strength of materials while improving their resistance to hydrogen embrittlement.

Study on the influence of heat treatment process on the microstructure and hardness of carburized layer of 20CrMoH steel

Abstract In this paper, the effects of different carburizing quenching processes and tempering processes on the depth of the hardened layer and microstructure of 20CrMoH were studied by means of hardness analysis and SEM microstructure analysis. The results show that: when the quenching temperatures in the range of 820-880 °C, it has little effect on the depth of the hardened layer. And the hardness value at the same depth is at a considerable level, which is not affected by the quenching temperature. When the tempering temperature range is 150-280 °C, the tempering temperature has a great influence on the depth of hardened layer. And with the gradual increase of tempering temperature, the depth of hardened layer decreases gradually. Also the hardness value at the same depth from the edge shows a monotonous decreasing trend with the gradual increase of tempering temperature.

Study of bainite and martensite tempering in a medium C high Si steel. microstructural disparities and equilibrium convergence

This study investigates the tempering behavior of bainite and martensite in a medium carbon, high silicon steel, with a focus on the microstructural evolution and the attainment of equilibrium, over a temperature range of 200–650 °C. The dissimilarities between the characteristics of the two initial microstructures, both comprising a C-saturated tetragonal ferrite matrix and retained austenite, are reflected in the differences observed in their evolution towards equilibrium as the tempering temperature increases. Therefore, while retained austenite plays a pivotal role in the bainitic microstructure, in the martensitic microstructure it is the ferritic matrix, which is highly dislocated and enriched in carbon, that plays a determinant role. The findings demonstrate that while both bainite and martensite can converge towards the same equilibrium state upon high-temperature tempering (600–650 °C), the pathway to this convergence is markedly different, with bainite exhibiting a slower transformation rate. This path to equilibrium has been characterised by means of high-resolution dilatometry, scanning electron microscopy and detailed X-ray diffraction analysis. This has provided a dynamic and detailed picture of the most relevant microstructural changes and tempering mechanisms in high silicon steels. It has also provided a foundation for tailoring heat treatment processes to optimise the mechanical properties of advanced bainitic and martensitic steels.

Effect of heat treatment processes on the microstructure and mechanical properties of 00Cr13Ni5Mo super martensitic stainless steel (SMSS)

The effects of quenching and tempering temperatures on the microstructure and mechanical properties of super martensitic stainless steel (SMSS) 00Cr13Ni5Mo were studied. The SMSS after heat treatment is composed of martensite (α phase) and a small amount of austenite. When the quenching temperature is 930 °C, with the increase of tempering temperature, the enrichment of Ni in martensite leads to the formation of reverse austenite, the content of martensite phase decreases from 84.9 % to 80.0 %, and the average grain size increases from 23.23 μm to 27.07 μm. When tempering at 580 °C, the content of martensite phase decreases from 80.0 % to 83.7 % with the increase of quenching temperature. The average grain size increased from 25.23 μm to 35.01 μm. When the quenching temperature is 930 °C, the hardness and yield strength of SMSS decrease, and the hardness and yield strength are the highest at 530 °C, which are 275 HV and 873 MPa. The plasticity increases first and then decreases, and the plasticity is the best at 580 °C. The elongation and reduction of area were 22.87% and 71.41%. These changes in mechanical properties are mainly related to the content of martensite and reversed austenite in the microstructure. The tensile strength and elongation of SMSS under different process conditions were compared. The results show that when the quenching temperature is 930 °C and the tempering temperature is 580 °C, the comprehensive performance of SMSS is the best, reaching 18700 MPa•%. This value is 31% higher than that of forgings. Finally, the formation mechanism of reversed austenite was discussed, and the strengthening model of SMSS 00Cr13Ni5Mo was established.

Optimizing Tempering Parameters to Enhance Precipitation Behavior and Impact Toughness in High-Nickel Steel

This study explores the effects of tempering on the precipitation behavior and impact toughness of high-nickel steel. The specimens underwent double quenching at 870 °C and 770 °C, followed by tempering at various temperatures. Advanced characterization techniques including optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to elucidate precipitation phenomena. Additionally, electron backscatter diffraction (EBSD) was employed to assess the misorientation distribution after tempering. Charpy impact tests were performed on specimens tempered at different temperatures to evaluate their toughness. The findings reveal that with increasing tempering temperature, the fraction of low-angle grain boundaries decreases, which correlates positively with enhanced impact toughness. The results demonstrate that tempering at 580 °C optimizes the material’s microstructure, achieving an impact toughness value of approximately 163 J.

The effect of tempering temperature on microstructure and corrosion resistance of M390 powder metallurgical martensitic stainless steel

The corrosion resistance of M390 powder metallurgical martensitic stainless steel with different tempering temperatures was investigated by potentiodynamic polarization measurements, salt spray tests, and microstructural analyses utilizing scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The tempering temperature had no significant effect on the size and volume fraction of carbides. The corrosion resistance of M390 steel gradually deteriorated with increasing tempering temperature, and a loss passivation (LOP) effect was observed when tempered at 450 °C, 500 °C, and 550 °C. Transmission electron microscopy (TEM) analysis showed that the width of the Cr-depleted zones around the undissolved M7C3 carbides increased with increasing tempering temperature, while the Cr content in these zones decreased, which was the main reason for the deterioration of corrosion resistance. This study offers valuable insights into optimizing the tempering process to improve the corrosion resistance of M390 steel for practical applications.

Hydrogen embrittlement of a V+Nb-microalloyed medium-carbon bolt steel subjected to different tempering temperatures

The effect of different tempering temperatures on the hydrogen embrittlement (HE) resistance of a V + Nb-microalloyed medium-carbon bolt steel was studied by slow strain rate tensile testing and hydrogen thermal analysis. The HE resistance represented by notch tensile strength σbN of hydrogen-charged specimens increases with increasing tempering temperature Ttem, and the σbN of the in situ hydrogen-charged sample is considerably lower than that of the pre-hydrogen-charged sample. Both the diffusible hydrogen content Cdiff and hydrogen-trapping capability of the precipitates show a significant increase-decrease change trend with Ttemp. The ratio of Cdiff primarily trapped by nanoscale V-rich MC precipitates increases linearly with increasing Ttemp. The control of V-rich MC through suitable increasing Ttemp is vital for obtaining the best HE resistance although at the cost of decreased strength. It is thus suggested that a compromise between strength and HE resistance should be considered for the practical application of this type of steel.

Effect of isothermal tempering time and temperature on microstructure and hardness of 3Cr5Mo2SiVN hot-work die steel

In this work, the effect of isothermal tempering time and temperature on microstructure and hardness of 3Cr5Mo2SiVN hot-work die steel was studied. The results indicated that with the increase of isothermal tempering time and temperature, the hardness significantly decreased, which corresponded to the microstructural recovery including the transformation of high angle grain boundaries (HAGBs), the precipitation and coarsening of precipitates, the annihilation and rearrangement of dislocations, the formation and coarsening of sub-grains, and the coarsening and coalescence of laths. The driving force of grain boundary transformation was provided by the dislocation- and heat-induced boundary migration. The increased density of HAGBs was induced by the coalescence of low-angle lath boundaries and low-angle sub-boundaries that continuously absorbed dislocations. In addition, the formation and coarsening of sub-grains were the results of dislocation rearrangement with dislocation cells acting as the core. Moreover, the V-rich M(C, N), Fe-rich M3C, (Fe, Cr)-rich M7C3 and M23C6 formed by the desolvation of alloying elements exhibited an obvious coarsening, decreasing the pinning effect of dislocations and then resulting in the hardness loss. This study offered a systematically revelation into the softening mechanism of hot-work die steel.

In depth analysis of the passive film on martensitic tool alloy: Effect of tempering temperature

Effect of tempering temperature on the composition of the passive film of a martensitic tool alloy was studied by synchrotron-based hard/soft X-ray photoelectron spectroscopy and electrochemical analyses. The contents of Cr and Mo in the passive film are affected by precipitation of tempering carbides. Increase of tempering temperature from 200 to 525°C leads to enhanced formation of Cr/Mo-rich tempering carbides and Cr depletion. Tempering at 525°C results in a Cr content < 11 at% in the underlying metallic layer and formation of a Cr-deficient defective passive film, and thus loss of passivity for the tool alloy in corrosive conditions.

Effect of tempering temperature on microstructure and mechanical properties of 4Cr13VTi steel

To optimize the tempering process of 40Cr13VTi steel containing V and Ti, the effect of tempering temperature on microstructure, precipitation, and properties of 40Cr13VTi stainless steel has been studied. Optical microscope (OM), scanning electron microscopy (SEM), and energy dispersive spectrometer (EDS) were used to analyze microstructure and precipitates. Tensile, impact, and hardness testing tests were performed to test the mechanical properties of 40Cr13VTi martensitic stainless steel. The research results indicate that as the increase of tempering temperature, the carbides precipitated gradually increase, and the shape gradually changes from particle to flake, which is consistent with the direction of the original martensite flat surface, and most of them concentrate at the martensite boundary. When the tempering temperature is 350°C, 40Cr13VTi martensitic stainless steel obtains the best comprehensive properties, strength, impact toughness (IT), and hardness which are 1360 MPa, 1717 MPa, 8.5 J/cm2, and 45.1 HRC respectively.

The Effect of Tempering Temperature on Microstructure and Wear Behavior of Tungsten and Boron Alloyed Ni-Hard 4 White Cast Irons

AbstractThis study investigates the effect of tempering temperature on the microstructure and wear resistance of high-alloy white cast iron (Ni-Hard 4) with 1.15% W and 0.5% B additions. Specimens were austenitized at 850 °C for 5 h, quenched in air, and tempered at temperatures between 250 and 650 °C for 4 h. Equilibrium and non-equilibrium thermodynamic calculations were performed using Thermo-Calc software. After the microstructural investigations, hardness testing was carried out. A pin-on-disk tribometer was used to conduct wear tests under dry sliding conditions. Microstructure and worn surfaces were examined using light and scanning electron microscopes. The results showed that increasing tempering temperature resulted in a higher volume fraction of carbides. It was found that tempering at 550 °C for four hours increases resistance to wear giving the lowest measured values of weight loss and wear rate. Accordingly, tempering allows the precipitation of fine carbides in the martensitic matrix which may increase wear resistance.

Unveiling nano-scale chemical inhomogeneity in surface oxide films formed on V- and N-containing martensite stainless steel by synchrotron X-ray photoelectron emission spectroscopy/microscopy and microscopic X-ray absorption spectroscopy

Nano-scale chemical inhomogeneity in surface oxide films formed on a V- and N-containing martensite stainless steel and tempering heating induced changes are investigated by a combination of synchrotron- based hard X-ray Photoelectron emission spectroscopy (HAXPES) and microscopy (HAXPEEM) as well as microscopic X-ray absorption spectroscopy (µ-XAS) techniques. The results reveal the inhomogeneity in the oxide films on the micron-sized Cr2N- and VN-type particles, while the inhomogeneity on the martensite matrix phase exists due to localised formation of nano-sized tempering nitride particles at 600 °C. The oxide film formed on Cr2N-type particles is rich in Cr2O3 compared with that on the martensite matrix and VN-type particles. With the increase of tempering temperature, Cr2O3 formation is faster for the oxidation of Cr in the martensite matrix than the oxidation of Cr nitride-rich particles.

Investigating the wear resistance of high-chromium cast irons A532-class III-type A against high-energy abrasive particles

Regarding the widespread use of high chromium cast irons in manufacturing various industrial and mineral-processing parts such as liners, slurry pumps, and grinding balls, increasing erosion resistance is the key factor to enhance their performance. This research investigated three different chemical compositions of high chromium irons (in the eutectic and hypoeutectic range). Austenite destabilization process was conducted at two temperatures of 1060°C and 970°C followed by air cooling and then tempering at the range of 250°C to 400°C for 4 h. Erosion and bending tests were carried out on samples with optimal heat treatment conditions. Results show that the hardness of specimens heat-treated at 970°C, and also the low-carbon hypoeutectic specimens destabilized at 1060°C, increased by increasing tempering temperature over 300°C, which can be related to the formation of a higher volume fraction of M23C6 carbides. The best erosion resistance was observed in the low-carbon hypoeutectic specimen destabilized at 1060°C and tempered at 300°C. In addition, samples with higher erosion resistance exhibit lower bending strength. Finally, it was found that the principal wear mechanism was the occurrence of plastic deformation, and detachment of carbides from the surface before having an effective role in reducing wear.

Effect of tempering temperature on stress corrosion resistance of a low alloy high strength steel with high vanadium content

The stress corrosion resistance of a low alloy high strength steel with high vanadium content, tempered at different temperatures, was examined by electrochemical measurements and slow strain rate tensile test under different environments. Combined with scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM), the results show that three different tempering temperatures had an influence on the microstructure of this steel as well as its electrochemical behavior and stress corrosion sensitivity. With the increase of tempering temperature, the ferrite grains coarsened, the average dislocation density lowered as well as the number of vanadium carbide also decreased, though the size of vanadium carbide increased. However, the interface distortion between vanadium carbide and matrix exacerbated, resulting in the increase of the local dislocation density. Therefore, the corrosion potential and impedance decreased, meantime, the stress corrosion sensitivity aggravated.

Influence of Tempering Temperature on Mechanical and Rotational Bending Fatigue Properties of 40CrNi2MoE Steel.

In order to examine the mechanical properties and rotational bending fatigue performance of 40CrNi2MoE steel subsequent to tempering at varying temperatures, the steel specimen was subjected to tempering within the range of 400~460 °C. SEM, EBSD, and TEM were used to analyze the microstructure as well as precipitates. The strain hardening law was studied using the modified Crussard-Jaoult method. Investigations were undertaken to reveal the rotational bending fatigue life with respect to the tempering temperature. The findings indicate that the strength and fatigue life of the examined steels exhibit a decline as the tempering temperature increases, with the primary factor affecting this trend being the alteration in dislocation density. No notable impact on the fatigue fracture morphology exerted by tempering temperature was found within the range of the experiment. The C-J model analysis reveals that the work-hardening behavior of the trial steels is influenced by dislocations and the second phase.

Microstructure evolution and enhanced cryogenic toughness of laser welded dissimilar SA645/AISI304L joints via intercritical tempering

In this study, we explored the impact of intercritical tempering on the microstructural evolution and mechanical properties of dissimilar welds formed through laser welding between 5%Ni steel (SA645) and austenitic stainless steel (AISI304L). Upon tempering at 500 °C, reversed austenite manifested within the weld metal. The volume proportion of reversed austenite in weld metal at room temperature increased first, exhibiting a maximum (∼10%) at ∼600 °C, and then decreased with increasing tempering temperature, which was associated with the diminished stability of austenite. Due to the change in tempering temperatures, two distinct types of reversed austenite were present, with one being located at the high-angle grain boundaries and the other within the martensite blocks. As the tempering temperature increased, the weld metal hardness decreased, reaching a minimum of ∼306 HV at 600 °C, and then increased. The dislocation density within the martensite matrix and the quantity of reversed austenite are the crucial factors to determine the hardness of weld metal. The cryogenic impact toughness of weld metal increased at first and then decreased as the tempering temperature increased. The maximum of ∼40 J for the cryogenic impact toughness was obtained when tempering at 600 °C. The low-temperature impact toughness of the weld metal was determined by the synergy of the TRIP effect of reversed austenite, the compatible deformation capability of dual-phase structure, and the crack propagation behavior.

Heat Treatment Process, Microstructure, and Mechanical Properties of Spring Steel with Ultra-High Strength and Toughness

In this research, a new type of spring steel with ultra-high strength and toughness was designed, and its mechanical properties and microstructure under different heat treatment processes were studied. The results show that the optimal heat treatment process for the steel is oil quenching at 890 °C for 40 min, followed by tempering at 400 °C for 1 h. Its mechanical properties have an optimal combination of 1865MPa tensile strength, a yield strength of 1662 MPa, an elongation of 11.5%, a cross-sectional shrinkage of 51.5%, and a Charpy impact energy of 43.7 J at room temperature. With increasing austenitizing temperature, the austenite grain size increases, the martensite lath becomes thicker, and the strength decreases. With increasing tempering temperature, the lath boundary of martensite becomes blurred, the strength decreases, and the plasticity improves. In addition, it was found that during tempering at higher temperature (450 °C), large particle inclusions and secondary cracks appeared in the fractured surface, and a large number of carbides precipitated, leading to the brittleness of tempered martensite.

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.