Effect of quenching and tempering processes on properties and microstructure of G115 steel

The novel martensitic heat-resistant steel G115 was designed for thick-section boiler components of ultra-supercritical(USC) power plants at 630-650 ℃.The impact of the quenching and tempering processes on the properties and microstructure of G115 steel was explored.The samples that were quenched and tempered twice had a higher tensile strength at room temperature and 650 ℃,and the impact energy was significantly improved.The strength and impact energy increased in proportion to the increase in the first quenching temperature.The microstructure differences between the single and double quenched and tempered samples were examined using metallographic microscopy and scanning electron microscopy.The grain size of the double quenched and tempered samples was finer than that of the single quenched and tempered samples, and the tempered martensite lath is more visible, as are the carbides and other precipitates, which are finer and more uniformly distributed.As the first quenching temperature increased, the grains became coarser but more uniform.

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.

Analysis of Quenching Resistor Effect to Improve Stability of TIA Circuit for APD-A Secondary Publication

In this paper,since the Avalanche Photo Diode(APD)for Light-to-Voltage LTV conversion uses a high voltage in the operating range unlike other Photo Diodes(PD),the quenching resistor must be connected in series to prevent overcurrent when using the Transimpedance Amplifier(TIA).In such a case,quenching resistance may affect the transfer function of the TIA circuit,resulting in serious stability.Therefore,in this paper,by analyzing the effect of APD quenching resistance on the voltage and current loop transfer function of TIA,we proposed a loop analysis and a method for determining the quenching resistance value to improve stability.A TIA circuit with quenching resistance was designed by the proposed method and its operational stability was verified through simulation and chip fabrication.

Discussion on the Free Quenching Heat Treatment Process of Automotive Leaf Springs

Free quenching of automotive leaf springs is a new technology that has gradually started to be applied in the industry in China in recent years.Only a few manufacturers are applying it in the industry.Through more than half a year of on-site practice,the changes in the hot forming of spring plates before free quenching have been explored,and finally a heat treatment process that meets the production requirements of our company has been developed,achieving normal production.

Influence of two distinct quenching end-temperatures on phase development and mechanical properties in QP980 steel

Bainite microstructures have become increasingly attractive for the development of advanced high-strength steel owing to their balanced strength-plasticity properties.In this study, the final microstructure and mechanical properties of a quenching and partitioning(QP) steel sample after two distinct QP processes were analyzed.The results reveal that martensite transformation after quenching resulted in a lathed morphology with higher yield strength and hole expansion ratio.In contrast, bainite transformation after quenching resulted in the formation of a blocky microstructure composed of bainitic ferrite retained austenite and nanoscale precipitates during the subsequent phase transformation at a higher temperature.This kind of final microstructure is beneficial to the elongation of QP steel but detrimental to the hole expansion ratio.

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.

Analysis of microstructure and performance of temper bead welded joints for SA508-3 steel by Quenching and Tempering mode

The HAZ microstructure and performance of Quenching and Tempering mode temper bead welding and general welded joints which were made on SA508-3 steel of 60 mm thickness were compared in this article. The result shows that tempering sorbite which has excellent overall performance was obtained in both modes. The microstructure of Quenching and Tempering mode welded joints got more fine grain. Even though the hardness of tempering bead welded joints is higher than the general one,it still meets the standards which is lower than 350 HV. The impact absorbing energy of each district of tempering bead welded joints HAZ reached 170 J,which is equal to general one.

Cold extrusion deformation behavior of medium carbon steel after quenching and tempering

By taking 40Cr as a specific object, cold extrusion deformation behavior of medium carbon steel after quenching and tempering was studied by experimental works. The influence of deformation extent (10%-50%), cone angle of die (90 °-120 °), hardness after quenching and tempering (HRC21-29) and lubricated condition on the forming load was analyzed. The results show that there is no central bursting and micro crack in the inner of the extruded specimen, and the forming quality is good. The double-peak phenomenon takes place at the front-end of the specimen; the double-peak index increases with deformation extent, and larger deformation can avoid the double-peak phenomenon. The deformation extent is the most important influencing factor, and the lubricated condition almost has no influence, which means that the phosphate coating plus soap process is still a proper lubrication method for cold extrusion of medium carbon steel after quenching and tempering. By investigating the microscopic structure before and after deformation, the initial equiaxed grain is elongated in the extrusion direction, and this feature is more significant at the front-end of specimen.

Numerical simulation research of dimension variation in heavy plate during quenching and tempering process

The dimension variation of B610E steel during the quenching and tempering process was simulated by ABAQUS,the coefficient of heat transfer during quenching was verified by the buried thermocouple test and the trend of the dimension variation during the quenching process was also calculated by ABAQUS. It was shown by the comparison of simulated results and industrially measured results that only the simulation of thickness and width variation was accurate, while length variation needed further simulation. Besides, the dimension variation trend was identical with the measured results.

EFFECTS OF RARE EARTH METALS ON MICROSTRUCTURAL TRANSFORMATION OF LOW OR MEDIUM CARBON Si-Mn-V STEELS DURING QUENCHING AND TEMPERING

The microstruetural transformation of steels:20SiMn2V,20SiMn2VRE,40SiMn2V and 40SiMn2VRE during quenching and tempering have been examined by TEM,X-ray diffraction and dilatometer.It was shown that the addition of rare earth metals not only can refine the austenite grains of the low or medium carbon steels and packet of lath martensite and lath size,lower the M_s temperature,but can also raise the relative percentage of disloca- tion substructure of martensite in medium carbon steel,but there is little effect on volume frac- tion and thermal stability of retained austenite quenching and tempering structure of low or medium carbon steels.The rare earth metals may remarkably inhibit the decomposition of low carbon martensite during low temperature tempering,retard the precipitation of cementite plates in lath grains and delay the spheroidization of carbides.They may also restrain obvious- ly the precipitation and spheroidization of cementite in medium carbon martensite during high temperature tempering.

Microstructure and Mechanical Properties of 50SiMnNiNb Steel by a Novel Quenching-Partitioning-Austempering Heat Treatment

For the purpose of reducing weight of steel parts, save raw materials and keep or even improve safety standards, the development of advanced high strength steels is increasingly demanded in the automotive industry and engineering applications. We have proposed a novel heat treatment （quenching-partitioning-austempering treatment, Q-P-A） to obtain steel parts with high strength and good ductility. The Q-P-A process is intended to produce microstructure consisted of carbon-depleted martensite, carbon-enriched retained austenite and nanostructured bainite. Quenching（Q） treatment fabricates mixed microstructure of carbon-supersaturated martensite and certain amounts of untransformed austenite. Partitioning（P） thermal treatment accomplishes fully diffusing of carbon from the supersaturated martensite phase to the untransformed austenite phase and enriching the amount of carbon in untransformed austenite. Further low-temperature austempering（A） process induces incredible thin bainite from the carbon-enriched untransformed austenite. A study of the microstructure and mechanical properties of 50SiMnNiNb steel subjected to the novel Q-P-A treatment is presented. Microstructure is assessed by optical microscope（OM）, field emission scanning electron microscope（FESEM） and transmission electron microscope（TEM）, and the corresponding mechanical properties are measured. The experimental results indicate that attractive mechanical properties of steels during the Q-P-A process are attributed to the complex multi-phase structure. Slender plates of bainite with 20-40 nm thick are generated in the medium carbon steel. Meanwhile, with increasing of the volume fraction of nanostructured bainite, yield strength of steel parts is increased with little degradation of ultimate tensile strength. In this paper, a novel quenching-partitioning-austempering heat treatment is proposed, and the attractive mechanical properties of steels are obtained during the Q-P-A process.

COUPLED NUMERICAL SIMULATION ON COLD ROLLER'S TEMPERATURE FIFLD-PHASE TRANSFORMATION - STRESS FIELD DURING ITS QUENCHING PSOCESS

Complicated changns occur inside the steel parts during quenching process. The abruptly changed boundary conditions make the temperature field,micro - structure and stress field change dramatically in very short time, and these variables take a contact interactions in the whole process. In this paper, a three dimensional non - linear mathematical model for queeching process has been founded and the numerical simulation on temperature field,microstructre and stress field has been realized.In the FEM analysis, the incremental iteration method is used to deal with such complicated nonlinear as boundary nonlinear, physical property nonlinear,transformation nonlinear etc.The effect of stress on transformation kinetics has been considered in the calculation of microstructure. In the stress field anal- ysis,a thermo- elasto - plastic model has been founded, which considers such factors as transforma- tion strain,transformation plastic strain, themal strain and the effect of temperature and transforma- tion on mechanical propertier etc. The transient temperature field, microstructure distribution and stress field of the roller on any time can be displayed vividly,and the cooling curve and the changes of stress on any position can also be given.

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.

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.

Effects of quenching temperature on microstructure and mechanical properties of H13 mandrel steel

Optical microscope, stereomicroscope, scanning electronic microscope （SEM） and mechanical property testing were used to research the effects of different quenching temperatures on the microstructure and mechanical properties of the H13 mandrel steel. The results indicate that following an increase in the quenching ,the degree of alloying is enhanced due to the carbides dissolving gradually in austenite, which improves the hardenability of the specimens, as well as their room and high-temperature strength. At the same time, the fracture toughness increases due to the increment of the martensite number and the interparticle distance of impact toughness. Optimal performance Consequently,the service life of the H13 the carbides. However, extremely coarse grain and martensite can decrease the can be obtained after quenching at 1 060℃ and double tempering at 620℃mandrel steel is extended significantly.

Changes in the thermodynamic properties of alkaline granite after cyclic quenching following high temperature action

During the development of hot dry rock,the research on thermal fatigue damage caused by thermal shock of cold and heat cycles is the basis that ensures the long-term utilization of geothermal resources,but there are not enough relevant studies at present.Based on this,the thermal damage tests of granite at different temperatures(250,350,450°C)and quenching cycles(1,5,10,15 cycles)were carried out.Preliminary reveals the damage mechanism and heat transfer law of the quenching cycle effect on hot dry rock.The results show that with the increase of temperature and cycles,the uneven thermal expansion of minerals and the thermal shock caused by quenching promote the crack development of granite,resulting in the decrease of P-wave velocity,thermal conductivity and uniaxial compressive strength of granite.Meanwhile,the COMSOL was used to simulate the heat transfer of hot dry rock under different heat treatment conditions.It concluded that the increase in the number of quenching cycles reduced the heat transfer capacity of the granite,especially more than 10 quenching cycles,which also reflects that the thermal fatigue damage leads to a longer time for the temperature recovery of the hot dry rock mass.In addition,the three-dimensional nonlinear fitting relationship among thermal conductivity,temperature and cycle number was established for the first time,which can better reveal the change rule of thermal conductivity after quenching thermal fatigue effect of hot dry rock.The research results provide theoretical support for hot dry rock reservoir reconstruction and production efficiency evaluation.

Characterization of γ′ precipitates in a nickel base superalloy quenching from aging temperature at different rates

The characteristics of γ′ precipitates in a superalloy quenched from 1050°C at different rates were investigated using field emission scanning electron microscope（FESEM）.When quenched from 1050°C, the size of primary aging γ′ precipitates has a small increase in the specimens that experienced iced-brine-quenching, oil-quenching, and air-cooling-quenching conditions and a drastic increase in the specimen that experienced a furnace-cooling-quenching condition.The cooling γ′ precipitates have unimodal distributions after quenching at the air-cooling rate and bimodal distributions after quenching at the furnace-cooling rate, but there are not these distributions in the specimens that experienced iced-brine-quenching and oil-quenching conditions.When aging at 760°C, the size of primary aging γ′ precipitates appears unaffected in the specimens that experienced iced-brine-quenching, oil-quenching, and air-cooling-quenching conditions.However, it has a drastic increase in the specimen that experienced a furnace-cooling-quenching condition, and it is interesting that the bigger cooling γ′ precipitates have a coalescence and octodendritic shape.The microhardness study indicates that the hardness has no variation in the specimens that experienced iced-brine-quenching, oil-quenching, and air-cooling-quenching conditions and has a drastic decrease in the specimens that experienced a furnace-cooling-quenching condition and obtains the minimum microhardness value 390.8 HV.

Finite Differential Method Simulation on Temperature Field in Process of Laser Quenching

Laser Quenching is one of main contents in laser heat treatment. At present, computer simulation on cooling course of laser quenching is the main research field and the foundation of calculating inner thermal stresses in object. It also provides theoretical basis for optimizing and controlling the course of laser quenching technology. In this paper, the difference between finite element method and finite differential method, which are two methods to calculate the laser quenching temperature field and calculation precision are studied. The unstable temperature field is solved and the configure and time are discretizcd simultaneously. About time discrete, two kinds of differential pattern are discussed. Compared the calculation results with measurement values, it shows that the differential method adopting in the paper is feasible and the calculation precision and calculation velocity can be increased to use variable step-size about time. Also, the result testifies that different calculation methods can be employed in case of variable application situation and calculation precision.

Effect of quenching temperature on the microstructure of Si-containing steel during quenching and partitioning

This study aims to investigate the effect of the 1-step quenching and partitioning （Q＆P） process on the microstructure and the resulting Vicker＇ s hardness of 0.3C-1.5Si-1.5Mn steel by using in-situ dilatometry ,optical microscopy （ OM ）, scanning electron microscopy （ SEM ）, X-ray diffractometry （ XRD ）, and Vicker ＇ s hardness measurement. Systematic analyses indicate that the microstructure of the specimens quenched and partitioned at 150℃ ,200 ℃ ,250℃ ,and 300℃ mainly comprises lath martensite and retained austenite. The dilatometry curve of the specimen partitioned at 150℃ is presumably ascribed to the formation of isothermal martensite. In the early stages of partitioning at 200℃,the nearly unchanged dilatation curve is closely related to the synergistic effect of isothermal martensite formation and transitional epsilon carbide precipitation. In the later stages of partitioning at 200 ℃ ,the slight increase in the dilatation curve is due to the continuous isothermal martensite formation. With further increase in partitioning temperature to 250℃, the dilatation increases gradually up to 3600 s, which is related to carbon partitioning and lower bainite formation. Partitioning at a higher temperature of 300 ℃ causes a rapid increase in the dilatation curve during the initial stages, which subsequently levels off upon prolonging the partitioning time. This is mainly attributed to the rapid diffusion of carbon from athermal martensite to retained austenite and continuous formation of lower bainite.

Numerical Simulation of Stress Field in Physical Tempering Process of Flat Soda Lime Silica Glass

Based on the analysis of different theory for glass tempering process,the“structural theory”with stress relaxation and structural relaxation effects was selected to investigate the tempering of flat glass quantificationally.The geometrical model with small size and non-homogeneous mesh were considered to build the finite element models according to the characteristics of stress field.The tempering process of flat glass with12 mm thickness was calculated with the verified finite element model.The transient and permanent stress of the central area,edge and corner end of the flat glass are obtained and analyzed.From the calculation results of basic case,the transient tensile stress at the upper surface of the central area,the center point of edge,the edge of edge,the edge of corner were 14.30,18.94,40.76 and 34.75 MPa,respectively.The transient tensile stress at these points were dangerous to promote the glass to break during the tempering.In addition,the point at the diagonal line of symmetry plane in the thickness direction,which is 14 mm from corner,has the maximum permanent tensile stress about 70.01 MPa in the flat glass after tempering.Thus,it is indicated that the corner is the weakest region in the tempered glass.