Tempering Temperature Research Articles

Effect of tempering temperature and grain refinement induced by severe shot peening on the corrosion behavior of a low alloy steel

In this study, the effect of tempering temperature on the corrosion behavior of a low carbon steel (F1272) was analyzed by means of electrochemical tests: linear polarization resistance, potentyodinamic polarization and electrochemical impedance spectroscopy (EIS) in freely aerated 3.5% NaCl solution, at room temperature. The results show that corrosion resistance of the steel increases with elevating tempering temperature from 200 to 500 °C and finally, to 680 °C. Additionally, a severe shot peening (SSP) treatment was applied in the sample with the best corrosion behavior (TT680), in order to modify the grain structure. Results evidence that corrosion resistance of the TT680 sample decreases after the applied SSP treatment (10A and 5000% coverage). Corrosion behavior is discussed through the different microstructural singularities induced both the heat treatments and the SSP.

The impacts of M/A constituents decomposition and complex precipitation on mechanical properties of high-strength weathering steel subjected to tempering treatment

The impact of microstructure evolution on the mechanical properties of a typical 500 MPa-grade weathering steel produced by an identical thermo-mechanical control process and different tempering treatments at 450–650 °C were thoroughly investigated mainly using scanning electron microscopy (SEM) equip with an electron backscatter diffraction (EBSD), high-resolution transmission electron microscopy (HRTEM), and X-ray diffractometer (XRD). Results indicated that the as-rolled steel consists of granular bainitic ferrite (GBF) and a considerable amount of martensite/austenite (M/A) constituents, exhibiting unsatisfied mechanical properties. As the tempering temperature increased from 450 to 550 and 650 °C, the massive twin-type M/A constituents decomposed preferentially into carbides following the sequence of Fe3C→(Cr, Mn, Fe)3C→(Cr, Mn, Fe)3C + (Cr, Mn)23C6, with a small amount of fine lath-type M/A constituents remained. The matrix recovered with the bainitic ferrite laths merged, the dislocation density decreased and the proportion of high-angle grain boundary (HAGB) increased. Nanoscale (Ti, Nb)C and ε-Cu particles also precipitated simultaneously, leading to an increase of yield strength. The strain hardening capacity and hence the tensile strength reduced resulting from the decomposition of M/A constituents. Moreover, the impact toughness was first enhanced by tempering at 450–600 °C with the decreasing twin-type M/A constituents content and increasing HAGBs proportion, and then deteriorated by tempering at 650 °C due to the precipitation of necklace-like M23C6 carbides at the grain boundaries. An optimum mechanical property combination was achieved via tempering at 550–600 °C.

Effect of Oxide Metallurgy Technology on Mechanical Properties and Hydrogen‐Induced Cracking Susceptibility of High‐Strength Low‐Alloy Steel

The oxide metallurgy is used in the fabrication of X80 pipeline steel. The mechanical properties of X80 steel at different tempering temperatures are studied by offline heat treatment process. The hydrogen‐induced cracking (HIC) susceptibility of X80 steel with optimal mechanical properties is studied. The results show that the optimal combinations of mechanical properties are obtained for the X80 pipeline steel under the heat treatment conditions of water quenched at 900 °C and tempered at 630 °C. The yield strength of the X80 steel is 569 MPa and the impact energy is higher than 300 J at −40 °C. After deoxidation by Ti and Zr, the average size of inclusions in X80 steel is 0.23 μm. Among them, the typical spherical composite inclusions are TiOX–Al2O3–ZrO2–MnS, combined with the fine (Nb, V, Ti)C and the formation of Cu2S and Cr2O3 protective layers. X80 steel has excellent HIC resistance.

Clarify the effect of reversed austenite on the pitting corrosion resistance of super 13Cr martensitic stainless steel

The effect of reversed austenite on the pitting behavior of super 13Cr martensitic stainless steel (S13Cr MSS) was investigated. The results revealed that reversed austenite was a FCC structure with Ni enrichment after tempering process, and there were no Ni-depleted regions adjacent to it. The reversed austenite content increased with increasing tempering temperature, and the pit depth decreased, as well as the dispersion degree of the Kelvin potential distribution. The reversed austenite reduced the risk of pitting corrosion through increasing the passive film compactness, and inhibiting Cl- penetration. Accordingly, the pitting corrosion resistance was enhanced as the tempering temperature increased.

Effect of tempering temperature on microstructure and mechanical properties of a low carbon bainitic steel treated by quenching-partitioning-tempering (QPT) process

The quenching-partitioning-tempering (QPT) treatment was carried out on a low carbon bainitic steel, and the effect of tempering temperature on the microstructure and mechanical properties of the QPT processed steel was investigated. The findings demonstrate that as the tempering temperature increases, the yield strength decreases gradually, while the tensile strength decreases first and then increases. However, the elongation exhibits a trend of increasing first and then decreasing with increasing the tempering temperature. When the tempering temperature is 340 °C, the best mechanical properties can be obtained with the yield strength of 1495 MPa, tensile strength of 1806 MPa, elongation of 17.7%, and product of strength and elongation up to 32.92 GPa%. Such excellent mechanical properties are related to the synergistic combination of tempered martensite, low carbon bainite, retained austenite and carbides.

Kekerasan Baja DC 11 Pada Perlakuan Media Quenching dan Suhu Tempering

Heat treatment is a process of renewing the metal structure by heating the specimen to a temperature below the melting point and a certain time, which is then cooled in a cooling medium to change the physical and mechanical properties. This study aims to determine the effect of quenching media and tempering temperature on the hardness value of DC 11 steel. This study used an experimental method with hardening at 990 °C and a holding time of 30 minutes with quenching media with SAE 10W-30 oil and 3.45 NaCl solution. %. After that, tempering was carried out at 250 °C, 350 °C, and 450 °C with a holding time of 2 hours. Then, the specimens were tested for hardness using the Rockwell method. Based on the results of the study, it was found that the effect with the highest hardness value was found in the quenching media with 3.45% NaCl solution and a tempering temperature of 250 °C of 49.6 HRC. The conclusion obtained is that the higher the tempering temperature, the lower the hardness value.

DIE STEEL 4Х4Н5М4Ф2 (WITHOUT FORGING TREATMENT) FOR HOT DEFORMATION OF ALUMINUM ALLOY

Purpose. Production of steel with controlled austenitic transformation during operation of the 4Х4Н5М4Ф2 grade (without forging treatment) using the technology of electroslag remelting and establishing optimal modes of heat treatment (annealing, quenching and tempering). Production of tools (matrices) from 4Х4Н5М4Ф2 steel (without forging treatment) for hot deformation of aluminum alloy at operating temperatures below the critical point A1.
 Research methods. Metallographic analysis of experimental die steels 4Х4Н5М4Ф2 (without forging treatment) and forged 4Х5МФ1С: study of metal structure; determination of specific resistance; determination of tensile strength; determination of hardness and impact strength.
 Results. The results of research on the optimization of heat treatment modes (quenching and tempering) of 4Х4Н5М4Ф2 steel (without forging treatment) are given. Adjusted chemical composition (4Х4Н5М4Ф2) and optimized mode of heat treatment of steel, which allowed to increase heat resistance up to a temperature of 650 °С. The tempering temperature of steel (475±25 °С) at which irreversible temper brittleness occurs is established. Experimental and industrial tests of steel 4Х4Н5М4Ф2 (without forging treatment) for hot deformation of AK7ч aluminum alloy are presented. It is shown that compared to forged steel H13 (an analogue of 4Х5МФ1С), which is used at one of the Chinese enterprises, the experimental steel has practically the same resistance .
 Scientific novelty. In the process of partial recrystallization (incomplete annealing at a temperature of 750±20 °C) of 4Х4Н5М4Ф2 steel (without forging treatment), a spheroidized carbide component is formed, which leads to an improvement in the mechanical processing of the workpiece for the manufacture of matrices.
 Practical value. The possibility of using steel with an adjustable austenitic transformation during operation of the 4Х4Н5М4Ф2 grade (without forging treatment) is shown for a wide range of operating temperatures of hot deformation: copper-nickel (at an operating temperature above the critical point A3) and aluminum alloy (at an operating temperature below the critical point A1) with increased service life compared to forged steel 4Х5МФ1С.

Analysis of the Effect of Tempering Temperature on the Formation of Microstructure and Hardness Values in SKD11 Steel

SKD11 steel is a tool steel material. SKD11 steel must have strong and tough mechanical properties. So to improve the quality and ability of SKD11 steel to accept external loads and forces, it is necessary to heat treatment. The heat treatment carried out in this research is hardening and hardening – tempering. The hardening process is carried out by heating SKD11 steel at austenitic temperature of 950 °C and holding time of 30 minutes. Then fast cooling (quenching) with water cooling media. As for the hardening – tempering process with temperature variations of 400 °C, 500 °C, 600 °C and a holding time of 60 minutes. In the as-quenching process the microstructure formed is martensite and residual austenite which cannot be transformed. Increasing the tempering temperature affects the martensite formed into tempered martensite consisting of ferrite and cementite carbide. In addition, with increasing tempering temperature the volume of carbide distribution will decrease and have a smoother shape. As the volume of carbide distribution decreases and the ferrite structure becomes more consistent, the ductility of the steel will increase and the hardness will decrease. The hardness value of SKD11 steel with hardening of 950 °C is 61.5 HRc. While the steel with hardening - tempering at a temperature of 400 °C = 57.3 HRc, 500 °C = 56.3 HRc, and 600 °C = 49,5 HRc. Increasing the tempering temperature will increase the ductility and decrease the hardenability on SKD11.

Changes of Dark Couverture Chocolate Hardness During Storage Tempered Using Automatic Tempering Machine with Tank and Tempering Temperature as Variables

Couverture chocolate is highly demanded by consumers. Dark couverture chocolate is known as chocolate with high proportion of cocoa. There are several parameters that need to be considered to ensure the quality of this chocolate. One of the important chocolate qualities is hardness. In chocolate making, which is affected by the tempering process. Generally, the tempering process is carried out manually or automatically. Manual tempering is done by hand and is difficult to control the process temperature. Therefore, an automatic tempering machine was chosen in this study by controlling the tank and tempering temperatures. The purpose of the research was to optimize the combined effect between tank temperatures and tempering temperatures of the automatic tempering machine on the chocolate hardness parameter. Different ranges of the tank and tempering temperatures were applied to the chocolate mass processed in the machine. Chocolate hardness during storage was in the range 12.27 to 20.19 N/mm2 in 45oC tank and 32.5oC tempering temperature. The optimum of the tank and tempering temperatures were 45oC-32.5oC (A), 48oC-32.5oC (B), and 50oC-31.5oC (C) which resulted in different k values and glossy appearances. The k values for A, B, and C were -0.00195; -0.0024; and -0.0031, respectively. While the determination coefficients for A, B, and C were 0.8970; 0.8887; and 0.9013, respectively.

Structural and wear assessment of H11 die steel as a function of tempering temperature

H11 steel is widely used in helicopter landing gears and dies for extrusion and forging. The property of H11 steel can be enhanced by several types of heat treatments for a long life span and improved design accuracy. In the present work, an attempt is made to study the effect of the tempering cycle on the two-body abrasive wear behavior. The structural characterization of hardened and tempered specimens was carried out using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Two body abrasive wear tests were carried out using silicon carbide abrasive with a systematic and simultaneous variation of test parameters. The different tempering temperatures used in the present investigation are 200 °C, 400 °C and 600 °C. The result showed that the wear mechanism like (ploughing and micro-cutting) in each condition was dominated by the types of phases present in the material and their morphology. The wear debris was flaky and ductile. There was the presence of a small amount of SiC particles from the abrasive wear paper in wear debris for high load (40 N) wear tests. The wear debris particles were relatively finer in as-quenched condition and low tempering temperature (200 °C), while those were large for samples tempered at 400, 600 °C and fully annealed condition. The wear debris analysis through micrographs and iron oxide particles were not detected in XRD patterns.

Effect of heat treatment on notch toughness of powdered tool steels M390 and M398

This paper deals with the possibilities of heat treatment of a pair of tool steels, produced by the powder metallurgy. The investigated steels named M390 and M398 belong to the group of high-alloy chromium steels used in the plastics industry in the production of screws for injection moulding machine unit. The steels were heat treated using quenching or quenching with deep freezing to achieve a homogeneous martensitic structure. Subsequently, the pair of steels was tempered twice in the temperature range from 200°C to 600°C. The given samples were experimentally tested for hardness and notch toughness using a Charpy hammer. The results compared the values of hardness and notch toughness depending on the tempering temperature. Selected fractures were observed using SEM microscopy.

Establishing the influence of structure parameters of steel on their abrasive wear resistance

We studied carbon steels (from technical iron to Y8) and low-alloy steel 65G. The grades of these steels are regulated by GOST 8559-75. To create different structures in the studied steels, the samples were subjected to heat treatment. The processing modes were selected in such a way as to ensure the study of the effect on wear resistance of one structural parameter of steel with the relative stability of other parameters. The relationships between the parameters of the structure of heat-treated steels and their abrasive wear resistance are established. At all temperatures of the final tempering of hardened steel, there is a direct relationship between its structure parameters (the number of elements in a solid solution, the density of dislocations, the size of cementite particles and the intercementite distance) and wear resistance when sliding friction against loose abrasive particles. A computer program has been developed to select the chemical composition of the steel grade and methods of thermal hardening in order to ensure the required wear resistance.

Effects of thermal treatment on the mechanical and electromagnetic properties of 9Cr-1Mo steel

This paper presents the effects of thermal treatment conditions on the mechanical properties of 9Cr-1Mo steel. Each sample was normalized at 1,040 °C for 1 h prior to tempering at different temperatures for 2 hours. Three levels of tempering conditions, 600, 650, and 700 °C, were tested in this study. After treatment, the metallurgical structures of the samples were observed and characterized by optical microscope (OM), scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS) and X-ray diffraction (XRD). Hardness and static tensile of the samples at room and elevated temperatures were also measured and analyzed. Non-destructive testing (NDT) associated with the eddy current method was employed to detect the microstructural changes of samples. The results revealed that the lath martensitic structure, lath boundaries, coarse precipitates, and prior austenite grain boundaries were found at grain boundaries and inside the matrix region. The average size of the particle and area fraction of carbide precipitates decreased with tempering temperature increases from 600 − 650 °C. The true yield stress and true ultimate tensile stress decreased while true strain increased when the tempering process was applied after the normalization. In addition, the use of the eddy current method at 100 kHz with proper conductivity could more accurately detect the microstructural changes of 9Cr-1Mo steel specimens than using the phase angle approach. The correlation coefficient of conductivity and true ultimate tensile strength was found to be 0.9459, indicating a high correlation between them.

Structure Flexibility of Alpha-galactosidase from a Marine Psychrophilic Yeast, Glaciozyma antarctica PI12

Factors that contribute to maintaining the flexibility or stability of an enzyme structure may depend on the composition of each amino acid with different characteristics, providing a purpose and bonding features within the structure. Based on this assumption, a study using homology modeling and a comparative study to observe different structure behaviors of an enzyme at an extremely low temperature (psychrophile) against temperate (mesophile) and high temperature (thermophile) was performed. The subject, a-galactosidase from Glaciozyma antarctica as a marine psychrophilic candidate was chosen against a-galactosidase from Trichoderma reesei (mesophile) and Ramsonia emersonii (thermophile). This enzyme catalyzes the hydrolysis of a-1-6 linked terminal galactosyl residues which can be found in a wide range of the organism. The ability of G. antarctica to grow in extremely cold temperatures rendered the question that the enzyme must have special characteristics to adapt to the cold condition. Based on the homology modeling and molecular dynamics study, a comparison of the structure of G. antarctica a-galactosidase enzymes with its homolog from the mesophilic and thermophilic fungi showed that G. antarctica a-galactosidase enzyme confers its flexibility by the increased number of small amino acids with reduced charges, more loops, a fewer number of hydrogen and disulfide bonds in its structure. Furthermore, a-galactosidase has potential for commercialization in bleach paper and the baking industry also a treatment for bloating and Fabry disease.

Volume fraction of retained austenite in 1.2842 tool steel as a function of tempering temperature

Untransformed austenite during quenching process is known as retained austeinite. The quantitative determination of the retained austenite is of great importance to the steel mechanical properties. Its percentage has a large effect on the mechanical properties and service life of components. The amount of retained austenite in through-hardened tool steels should be kept at its optimum level in order to minimize size change, and increase service life. In this study, the influence of tempering temperature on the amount of retained austenite was evaluated by using X-ray diffraction phase analyses. It was seen that tempering at low temperatures resulted in small amount of retained austenite for the studied steel.

Effect of Intercritical Temperature on the Microstructure and Mechanical Properties of a Ferritic-Martensitic Dual-Phase Low-Alloy Steel with Varying Nickel Content.

Dual-phase low-alloy steels combine a soft ferrite phase with a hard martensite phase to create desirable properties in terms of strength and ductility. Nickel additions to dual-phase low-alloy steels can increase the yield strength further and lower the transformation temperatures, allowing for microstructure refining. Determining the correct intercritical annealing temperature as a function of nickel content is paramount, as it defines the microstructure ratio between ferrite and martensite. Likewise, quantifying the influence of nickel on the intercritical temperature and its synergistic effect with the microstructure ratio on mechanical properties is vital to designing dual-phase steels suitable for corrosive oil and gas services as well as hydrogen transport and storage applications. In this work, we used a microstructural design to develop intercritical annealing heat treatments to obtain dual-phase ferritic-martensitic low-alloy steels. The intercritical annealing and tempering temperatures and times were targeted to achieve three different martensite volume fractions as a function of nickel content, with a nominal content varying between 0, 1, and 3-wt% Ni. Mechanical properties were characterized using tensile testing and microhardness measurements. Additionally, the microstructure was studied using scanning electron microscopy coupled with electron backscatter diffraction analysis. Tensile strength increased with increasing martensite ratio and nickel content, with a further grain refinement effect found in the 3-wt% Ni steel. The optimal heat treatment parameters for oil and gas and hydrogen transport applications are discussed.

Ralstonia solanacearum Facing Spread-Determining Climatic Temperatures, Sustained Starvation, and Naturally Induced Resuscitation of Viable but Non-Culturable Cells in Environmental Water.

Ralstonia solanacearum is a bacterial phytopathogen affecting staple crops, originally from tropical and subtropical areas, whose ability to survive in temperate environments is of concern under global warming. In this study, two R. solanacearum strains from either cold or warm habitats were stressed by simultaneous exposure to natural oligotrophy at low (4 °C), temperate (14 °C), or warm (24 °C) temperatures in environmental water. At 4 °C, the effect of temperature was higher than that of oligotrophy, since R. solanacearum went into a viable but non-culturable (VBNC) state, which proved to be dependent on water nutrient contents. Resuscitation was demonstrated in vitro and in planta. At 14 °C and 24 °C, the effect of oligotrophy was higher than that of temperature on R. solanacearum populations, displaying starvation-survival responses and morphological changes which were stronger at 24 °C. In tomato plants, starved, cold-induced VBNC, and/or resuscitated cells maintained virulence. The strains behaved similarly regardless of their cold or warm areas of origin. This work firstly describes the natural nutrient availability of environmental water favoring R. solanacearum survival, adaptations, and resuscitation in conditions that can be found in natural settings. These findings will contribute to anticipate the ability of R. solanacearum to spread, establish, and induce disease in new geographical and climatic areas.

Effect of finish rolling temperature on microstructure and mechanical properties of X80 pipeline steel by on-line quenching

A Ti–V microalloyed X80 seamless pipeline steel was prepared using on-line quenching and off-line tempering technology. The influence of finish rolling temperatures (FRTs∼950 °C and 900 °C) and tempering temperatures (600°C–700 °C) on microstructure and mechanical properties was investigated. Fully recrystallized austenite was formed at 950 °C FRT, but partially at 900 °C FRT. The quenched microstructure consisted of lath bainite, granular bainite, cementite and TiC precipitates. With the decrease in FRT, more granular bainite and strain-induced TiC precipitates were obtained in the quenched microstructure. The original quenched structure significantly impacted the subsequently tempered microstructure. The tempered microstructure was composed of polygonal ferrite, tempered bainitic laths, cementite and (Ti, V)C precipitates. As FRT decreased, the tempered microstructure exhibited more polygonal ferrite, smaller grain size and better precipitation characteristics of (Ti, V)C precipitates, simultaneously improving the strength and impact toughness. An ideal combination of the yield strength (∼632 MPa), tensile strength (∼707 MPa), impact value (∼249 J at −20 °C) and shear-fracture area (∼97% at −20 °C) was achieved at 900 °C FRT and 680 °C tempering temperature, which satisfied the API requirements of X80 pipe. Therefore, 900 °C FRT and 680 °C tempering temperature were suitable process parameters for on-line quenching technology to produce X80 seamless pipeline steel.

Influence of Partitioning Effects on the Retained Austenite Content and Properties of Martensitic Stainless Steel

The effect of a quenching and partitioning (Q&P) heat treatment with a quenching temperature (TQ) range from 20 to 190 °C is investigated for two martensitic stainless tool steels X40Cr14 and “X25CrN13”, focusing on microstructural evolution, hardness, and toughness. The influence on the retained austenite (RA) content, when replacing part of carbon with nitrogen, is of core interest. The amount of RA is analyzed by X‐ray diffraction and is additionally proved with electron backscatter diffraction, and the RA content is thermodynamically calculated. Subsequently, the effect of the microstructure on toughness and hardness is investigated. For both steels, the toughness maximum is reached in the region of the RA maximum. The “X25CrN13” attains higher toughness at higher RA contents. Higher RA contents do not benefit X40Cr14. Furthermore, the effect of double tempering at higher tempering temperatures after Q&P on the steels is investigated. Besides RA contents and hardness, dilatometer curves are used to evaluate the formation of fresh martensite in the microstructure. The secondary hardness maximum of “X25CrN13” is reached at 500 °C and that of X40Cr14 is at 480 °C. For double tempering temperature at 520 °C, TQ has little effect on toughness, and “X25CrN13” shows better values.

Effect of Cu on the Microstructure and Mechanical Properties of a Low-Carbon Martensitic Stainless Steel.

Reversed austenite is of vital importance in low-carbon martensitic stainless steel because it improves impact toughness. However, a proper amount of reversed austenite is obtained by tempering at a critical temperature, which reduces the strength of the steel. Therefore, how to improve strength-toughness matching is an important problem. Copper (Cu) is an effective strengthening element in steels. However, there is little in-depth discussion on the role of Cu on the microstructure and mechanical properties of low-carbon martensite steel. In this work, the effect of different Cu content on the reversed austenite formation, tensile strength, and impact toughness of a low-carbon martensitic stainless steel (0Cr13Ni4Mo) was systematically investigated through use of a transmission electron microscope (TEM), transmission Kikuchi diffraction (TKD), atom probe tomography (APT), and other characterization methods and mechanical property tests. The results showed that the addition of Cu decreased the phase transition temperatures of martensite and austenite and increased the volume fraction of the reversed austenite. APT results indicated that Cu-rich clusters first formed with alloying elements such as ferrum (Fe) and nickel (Ni) and then grew to be precipitates through rejection of the alloying elements. The Ni atoms diffused towards the interface between the precipitates and the martensite matrix, which provided heterogeneous nucleation sites for the reversed austenite. Cu precipitations strengthened tensile strength during tempering. However, it generated temper brittleness in the steel at a tempering temperature of 450 °C, resulting in the impact energy of the 3Cu-steel being only 7 J. A good combination with higher tensile strength (863 MPa) and ductility (192 J) was obtained when tempering at 600 °C in the presence of Cu-rich precipitates and a sufficient volume fraction of the reversed austenite. The results provide guidance for the design of steels with reversed austenite and Cu and promote the development of high-strength and high-toughness steels.