An Internal State Variable Model for the Low Temperature Tempering of Low Alloy Steels

An internal state variable (ISV) framework is used to predict the rate and degree of strain relaxation associated with the stage I, low temperature tempering of martensite. A single variable tracks the change in volume between the tempered an untempered structures. The rate at which this occurs is taken to be a function of martensite fraction, temperature, degree of tempering, and carbon concentration. Experimental dilatometty data is used to both fit and validate the model.

Application of the Controllable Quenching Technology to the Quenching and tempering Workpieces

In order to obtain the desired mechanical properties of quenching and tempering workpieces, as well as reduce the cracking tendency and distortion, a program of controllable quenching was established. Furthermore, a computer-aided quenching system (CAQ) was also developed. The application samples of the CAQ system showed satisfactory results.

Mathematical Model for Tempering Time Effect on Quenched Steel Based on Hollomon Parameter

Through the differentiating and integrating process, a mathematical model for tempering time effect on quenched steel was derived based on the attribute of state function and the general equation of Hollomon parameter, which correlates the tempering hardness with the tempering time at different tempering temperature. Using the established model, the linear relationship between the tempering hardness and the tempering time in logarithm was proved theoretically, and the tempering hardness for various tempering time was reduced to the measurement and calculation of a hardness experiment tempered for 1 h at different tempering temperatures. Moreover, the hardness of steel 42CrMo and T8Mn tempered for various times at 200-600℃ was calculated using this method. The predicted results are in good agreement with those of the available experiments.

Research on the Numerical Simulation of the Tempering Process of Steel

In this paper, the kinetics and creeping behavior in the tempering of were experimentally investigated in detail with two kinds of large-forging steel. The martensitic and bainitic transformations were expressed as functions of the tempering parameter. The kinetics of phase transformation of the retained austenite was described by the Avrami equation. Based on the elastoplastic-creeping theory, the constitutive relations for steel tempering process were obtained, and an FEM code was developed. The program was verified with the tempering process of a cylindrical specimen, and the quenching-tempering process of a turbine rotator was analyzed.

STUDY ON THE STRUCTURE AND PROPERTIES OF HIGH CHROMIUM WHITE CAST IRON AND ITS TEMPERING STANDARD

The structure and properties of high chromium white cast iron in different treatment states were studied. Using X ray diffraction method, observing their metallograph and measuring their microhardness, the phases involved in the iron were determined. The notch toughness, macrohardness and the fractograph of the samples are compared and their performance was determined, which mainly depends on the matrix structure. Relatively good comprehensive properties can be obtained in the tempering state. Improvements have been made on the commonly used tempering standard. Tempering for a short period at low temperature can improve the materials′ service performance obviously.

Influence of nitrogen-alloying on the tempering properties of the martensitic stainless steel 00Cr13Ni4Mo

The mechanical and corrosive properties of 00Cr13Ni4Mo （S13 -4N） were tested and compared with those of 00Cr13Ni6Mo （S13 -6）. The effects of nitrogen on the properties of the steels were analyzed. The results of the tensile and corrosion tests show the strength,the ductility,and the pitting corrosion resistance of S13 -4N are higher, lower and poorer than those of S13 -6 respectively, when tempered at a temperature below 550 ℃and vice versa when the tempering temperature is higher than 550℃. The results of the X-ray diffraction （XRD） and the electron backscattered diffraction （EBSD） analyses reveal that inversed austenite appears at 550℃ and the amount of it peaks at 600 ℃ with the best ductility. And the total amount of the inversed austenite in S13 -6 is more than that in S13 -4N in different forms. Nitrogen performs better in terms of stabilizing inversed austenite while nickel is more favorable for forming inversed austenite, the amount and stability of which affect the ductility remarkably. The reason for the embrittlement of S13 -4N at 450℃ can be the result of carbide and nitride precipitating at grain boundaries.

THE RELATION BETWEEN THE TEMPERING EFFECTS AND THE INTRINSIC COERCIVITY OF SINTERED SmCo5 ALLOY AT 750℃

The relation between the tempering effects of sinterd SmCo^(5)alloy at 750℃and its intrinsic coercivity(i^(Hc))has been studied by the use of photoelectron energy spectrum.X-ray diffraction and high-voltage electron microscope.The result is that the cause of iHc dropping seriously for sintered SmCo_(5)alloy tempered at 750 t is not the eutectoid decomposition of SmCo_(5)and the increase of oxygen.In fact,iHcdropping is caused by that some defect-rich regions in Sm_(2)Co_(17)decomposed form SmC0_(5)from nucleation centers in reversed magnetization course.

Effects of Rare Earths on the Tempering Transformation Kinetics of High Carbon Steel

Effect of rare earth metals (REM) on tempering process and decomposition kinetics of martensite and retained austenite of high carbon steel were investigated by DSC technique,based on the non-isothermal kinetic theory.The result shows that the addition of REM in high carbon steel increases the decomposition temperatures of martensite and retained austenite,decreases the thennal effect values,elevates the activity energies and changes the transformation mechanism.

Variation microstructure and properties of X80 pipeline steel in the rapid induction tempering process

A self-developed electromagnetic induction-heating device was used to investigate the variation in the microstructure and properties of X80 pipeline steel in the rapid induction tempering process at different process parameters. The effects of the tempering condition on toughness, microstructure, size and distribution of precipitates of X80 pipeline steel were observed using a metallographic microscopy and scanning electron microscopy. Compared with the samples prepared via traditional tempering techniques, results show that the samples prepared via rapid induction tempering had improved performances. When the heating temperature is 590 ℃, at a holding time of 90 s,it was found that acicular ferrite was refined, carbonite precipitation was small, and precipitates were evenly distributed in the matrix. The low-temperature impact energy, also known as the impact absorption energy, at -40 ℃ was found to be 430.5 J for the rapid induction tempering samples and 323.2 J for the traditionally tempered sample. The low-temperature impact energy at -60 ℃ was found to be 351.3 J for the rapid induction tempered sample and 312.1 J for the tradition tempering sample.

Effects of low-temperature tempering on the microstructure and precipitating evolution of newly developed high-strength microalloyed steel

The effect of tempering temperature on the microstrocture and precipitating evolution and the resultant mechanical properties of newly developed high-strength microalloyed steel plate was investigated by optical microscopy （OM） and transmission electron microscopy （TEM）. The steel mainly consists of fine lath martensite and lower bainite. The width of the martensitic laths in as-hot-rolled state is about 120 nm,and increases from 120 nm to 150 nm and 180 nm after tempering at 200 ℃ and 250℃ for 2 h respectively with no change in its morphology. Of special interest is the phenomenon that both tensile strength and impact toughness of the steel plate decrease with the increase of the tempering temperature, which might be attributed to the combination of lath martensite broadening and the coarsening of needle-like carbides located on the boundaries of lath martensite and within bainitic ferrite. It is suggested that the existence of the complex carbonitride larger than 100 nm in bainitic ferrite is one of the reasons.

The effect of different cooling and tempering conditions on the strength and toughness of SA533B steel

The microstmcture and mechanical properties of SA533B low-alloy steel were investigated under different cooling and tempering conditions. Steel plates cooled at 40℃/s and 25℃/min,exibited microstructures of auto-tempered martensite and bainite, respectively. During tempering, the strength of steels quenched at the two different cooling rates decreased continuously with an increase in the tempering parameter, which is defined by T （20 ＋ log t）, where T is the temperature and t is the holding time. However, the rate of change of the strength scales with the degree to which the virgin microstructure deviates from equilibrium. The strength of the martensitic steel decreased faster and finally obtained a value close to that of the bainitic steel. The ductility and toughness gradually improved during tempering, passed through a maximum value, and finally diminished. The level of maximum toughness was also found to depend on the cooling rates of SA533B steel. The high cooling rate with a microstructure of auto-tempered martensite exhibited a larger toughness and a lower ductile-brittle transition temperature than the low cooling rate with a microstructure of bainite, because the former had finer precipitated cementite particles at quenching and a slower coarsing rate during tempering.

Effect of low-temperature tempering on the mechanical properties of cold-rolled martensitic steel

Cold-rolled martensitic steel is an important type of advanced high-strength steel for automobile production.With martensite as its primary microstructure constituent, martensitic steel possesses exceptional high strength despite its low alloy content.As the strength of cold-rolled martensitic steel increases, the martensite and carbon content also increases, leading to a decrease in bending properties and toughness.In this paper, the effect of various tempering parameters on the bending property and impact toughness of a quenched cold-rolled martensitic steel sheet was studied.It is found that after quenching, the ductility and impact toughness of the experimental steel are improved using low-temperature heat treatment.The optimal tempering conditions for ductility and toughness are analyzed.

Effect of tempering on the properties and microstructure of 00Cr13Ni5Mo

In this study,normalized 00 Cr13 Ni5 Mo low-carbon martensitic stainless steel was tempered at temperatures ranging between 500-700 ℃ for 8 h and its mechanical properties were determined. The results show that the mechanical properties vary with a variation in the tempering temperature. Samples tempered at 650 ℃exhibited a good combination of properties and a low yield ratio. Scanning electron microscopy observations and Xray diffraction analysis revealed that the tempering process involved carbide precipitation,austenitic inversion,and quenching,and the properties of materials changed with a change in the tempering temperature.

Thermal Tempering Does Not Impact Rainbow Trout and Brown Trout Survival

Hatchery-reared fish are frequently adjusted (tempered) to the higher water temperatures present in the water bodies where they are to be stocked. This study was undertaken to determine the necessity of such tempering practices. This study used rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta) reared at 11.2°C. The first two trials for each species were designed to simultaneously determine the upper incipient lethal temperature and 100% lethal temperature over a 14-day period. The third trial for each species evaluated the effects of an exaggerated 12-hour tempering regime on fish survival after placement in elevated water temperatures. After transfer from a water temperature of 11.2°C, no rainbow trout survived at 26°C, and only 50% survived at 25°C. No brown trout survived at 22°C and only 50% at 20°C. Survival of rainbow trout was not improved by the 12-hour tempering regime where water temperatures were slowly increased from 11.2°C to either 25°C or 26°C. Similarly, tempering did not improve brown trout survival at either 20°C or 22°C. These results suggest that tempering is not needed when hatchery-reared trout are reared and stocked at the water temperatures within the range of those used in this study.

Thermal Tempering Does Not Increase the Survival of Eyed Salmonid Eggs

Eyed salmonid eggs can be subjected to large temperature swings during development, particularly when shipped in ice-filled containers from broodstock facilities to production hatcheries. This study examined the effect of thermal tempering on the survival of brown trout Salmo trutta and rainbow trout Oncorhynchus mykiss eyed eggs to hatch. Eyed eggs at 1°C were either directly placed in 11°C water or allowed to thermally temper from 1°C to 11°C gradually over an hour. In addition, each of the tempering treatments occurred either with or without a 10-minute iodophor disinfection treatment. Tempering had no significant effect on survival-to-hatch in either species (85% - 97%). However, survival was significantly lower in rainbow trout eggs subjected to iodine disinfection (73% - 75%) compared to non-disinfected eggs (91% - 97%), likely because of the close proximity to hatch. The results of this study indicate that slowly raising the temperature (thermal tempering) of brown trout and rainbow trout eyed eggs is unnecessary. Additionally, iodine disinfection of eyed salmonid eggs in close proximity to hatching should be avoided.

Instrumented oscillographic study on impact toughness of an axle steel DZ2 with different tempering temperatures

Compared with the conventional Charpy impact test method,the oscillographic impact test can help in the behavioral analysis of materials during the fracture process.In this study,the trade-off relationship between the strength and toughness of a DZ2 axle steel at various tempering temperatures and the cause of the improvement in impact toughness was evaluated.The tempering process dramatically influenced carbide precipitation behavior,which resulted in different aspect ratios of carbides.Impact toughness improved along with the rise in tempering temperature mainly due to the increase in energy required in impact crack propagation.The characteristics of the impact crack propagation process were studied through a comprehensive analysis of stress distribution,oscilloscopic impact statistics,fracture morphology,and carbide morphology.The poor impact toughness of low-tempering-temperature specimens was attributed to the increased number of stress concentration points caused by carbide morphology in the small plastic zone during the propagation process,which resulted in a mixed distribution of brittle and ductile fractures on the fracture surface.

Correlations Between Plant Biomass and Soil Respiration in a Leymus chinensis Community in the Xilin River Basin of Inner Mongolia

This paper reports on two years of measurement of soil respiration and canopy-root biomass in a Leymus chinensis community in the Xilin River basin of Inner Mongolia. Correlations between components of plant biomass and soil respiration rates were examined. From respiration data based on CO2 uptake by NaOH and corresponding root biomass values for each run of 10 plots, a linear regression of CO2 evolution rates on root dry weights has been achieved for every ten days. By applying the approach of extrapolating the regressive line to zero root biomass, the proportion of the total soil respiration flux that is attributable to live root respiration was estimated to be about 27% on average, ranging from 14% to 39% in the growing season in 1998. There were no evident relations between the total canopy biomass or root biomass and CO2 evolution rates, but a significant exponential relation did exist between tire live-canopy biomass and CO2 evolution rates.

Altitudinal Range of Black-and-white Snub-nosed Monkeys (Rhinopithecus bieti ) at Baima Snow Mountain, China

Faeces were counted along horizontal, 5.0m wide strips at altitude intervals of 100m to examine the altitudinal ranging pattern of a band of black-and-white snub-nosed monkeys （Rhinopithecus bieti） at Nanren （99°04′E, 28°34′N, Baima Snow Mountain Nature Reverse, Yunnan, China） at four areas in each season between 2000-2001. Faeces were also counted along vertical, 2.5 m wide strips in one subvalley and on one subridge in each area. Monkeys used an altitudinal range of 3500-4300m, but preferred occupying the upper forest belt between 3900 and 4200m asl year-round, being at the highest altitude in summer, the lowest altitude in spring, and middle altitudes between autumn and winter （lower in winter than autumn）. Moreover, there were secondary peaks of lower altitude use （3700m） in spring and winter. In addition, more faeces were distributed in subvalleys than on subridges in winter, this suggests that monkeys tend to spend more time in subvalleys where there is less wind and fluctuating temperatures. The significant correlation between faecal density and lichen load might indicate that altitudinal distribution of food resources may act as an important factor affecting the monkeys＇ range. The monkeys might migrate to lower altitudes to eat young sprouts and leaves in spring, and to shelter from snowstorms in winter, possibly resulting in the secondary peaks at lower altitudes.

Effects of freeze-thaw on soil nitrogen and phosphorus availability at the Keerqin Sandy Lands,China

A laboratory simulated freeze-thaw was conducted to determine the effects of freeze-thaw on soil nutrient availability in temperate semi-arid regions. Soil samples were collected from sandy soils （0-20 cm） of three typical ecosystems （grassland, Mongolian pine plantation and poplar plantation） in southeastern Keerqin Sandy Lands of China and subjected to freeze-thaw treatment （-12℃ for 10 days, then r 20℃ for 10 days） or incubated at constant temperature （20℃ for 20 days）. Concentrations of the soil NO3^--N, NH4^＋-N, NaHCO3 extractable inorganic P （LPi） and microbial biomass P （MBP） were determined on three occasions： at the start of the incubation, immediate post-thawing and at the 10th day post-thawing. The results showed that soil net nitrification and N mineralization rates at three sites were negatively affected by freeze-thaw treatment, and decreased by 50%-85% as compared to the control, of which the greatest decline occurred in the soil collected from poplar plantation. In contrast, the concentration of soil NH4^＋-N, NaHCO3 extractable inorganic P （LPi） and microbial biomass P were insignificantly influenced by freeze-thaw except that LPi and NH4^＋-N showed a slight increase immediate post-thawing. The effects of freeze-thaw on soil N transformation were related to soil biological processes and the relatively constant available P was ascribed to severe soil aridity.

Self tempering effect of near eutectic Al-Si casting with different wall thickness solidified and cooled in permanent die

In order to study the self tempering effect on the solidification of Al-Si alloy, a setup was designed to conduct experiments. The characters of β phases in different thicknesses of Al-Si samples were investigated. The results show that the size distributions of β phases obey the logarithmic normal distribution. The Brinell hardness tests were also carried out. The tested hardness results show that the hardness distribution of the casting cooled in water is evener than that cooled in air, and its averaged value is higher than that cooled in air.