Effect Of Austempering Temperature Research Articles

Ultra-Fine Bainite in Medium-Carbon High-Silicon Bainitic Steel.

The effects of austenitizing and austempering temperatures on the bainite transformation kinetics and the microstructural and mechanical properties of a medium-carbon high-silicon ultra-fine bainitic steel were investigated via dilatometric measurements, microstructural characterization and mechanical tests. It is demonstrated that the optimum austenitizing temperature exists for 0.3 wt.%C ultra-fine bainitic steel. Although the finer austenite grain at 950 °C provides more bainite nuclei site and form finer bainitic ferrite plates, the lower dislocation density in plates and the higher volume fraction of the retained austenite reduces the strength and impact toughness of ultra-fine steel. When the austenitizing temperature exceeds 1000 °C, the true thickness of bainitic ferrite plates and the volume fraction of blocky retained austenite in the bainite microstructure increase significantly with the increases in austenitizing temperature, which do harm to the plasticity and impact toughness. The effect of austempering temperature on the transformation behavior and microstructural morphology of ultra-fine bainite is greater than that of austenitizing temperature. The prior martensite, formed when the austempering temperature below Ms, can refine the bainitic ferrite plates and improve the strength and impact toughness. However, the presence of prior martensite divides the untransformed austenite and inhibits the growth of bainite sheaves, thus prolonging the finishing time of bainite transformation. In addition, prior martensite also strengthens the stability of untransformed austenite though carbon partition and enhances the volume fraction of blocky retained austenite, which reduces the plasticity of ultra-fine bainitic steel. According to the experimental results, the optimum austempering process for 0.3 wt. %C ultra-fine bainitic steel is through austenitization at 1000 °C and austempering at 340 °C.

PENGARUH TEMPERATUR AUSTEMPERING TERHADAP SIFAT MEKANIK DAN STRUKTUR MIKRO BESI COR KELABU DENGAN NIKEL 10% UNTUK KOMPONEN BOILER PLTU

Effect of austempering temperature on microstructure and mechanical properties gray cast iron with 10%wt nickel for boiler combustion application has been studied. Cast iron with the JIS FCD 45 standard with a minimum tensile strength of 414 MPa and a hardness of 187 HB is commonly used for this application. To improve its mechanical properties such as strength and hardness, austempering heat treatment usually applied. Austempering was carried out at 250°C, 300°C, 350°C, 400°C, and 450°C for 1 hour, with the same austenization temperature of 850°C for 1 hour. The highest increase in hardness was found at the austempering temperature of 250°C. The hardness was 321.80 HB or 19.30% of the initial hardness of 259.70 HB. In terms of strength, the highest increase occurred at the austempering temperature of 250°C which was 257 MPa or 31.52% of the initial strength of 176 MPa.

Effect of Austempering Temperature on Microstructure and Deformation Behavior of Selective Laser Melting 24CrNiMo-Steel

Effect of Austempering Temperature on Microstructure and Deformation Behavior of Selective Laser Melting 24CrNiMo-Steel

Effect of Austempering Temperature on Microstructure and Mechanical Properties of M50 Bearing Steel

By means of microstructure observation and mechanical property tests, the effect of austempering temperature on the bainite transformation, carbide precipitation, and the hardness, impact toughness of M50 bearing steel were studied. Results show that when the austempering temperature increases from 180 °C, 200 °C, 220 °C, 240 °C to 260 °C, the bainite content in the microstructure of the steel is 3.5%, 11.9%, 15.4%, 22.1% and 36.1% respectively. The effect of austempering temperature on bainite content is mainly related to the incubation period of bainite transformation, the driving force of bainitic ferrite nucleation and the stability of supercooled austenite. With the increase of austempering temperature, the carbide content decreases but the average carbide size generally increases in the austempered and tempered steel. When the austempering temperature increases from 180 °C to 200 °C, the hardness of the sample decreases from 62.45 HRC to 62.04 HRC, and the impact toughness of the sample increases from 144.75 kJ/m2 to the maximum value of 171.50 kJ/m2 at 200 °C. When the austempering temperature increases from 200 °C to 260 °C, the hardness and impact toughness of the steel both decrease, which is related to the weakening of the dispersion strengthening caused by the increase of carbide size, and to the increase of bainite content, the increase of bainite size, and the self-inhibited behavior of bainite transformation.

Effect of austempering temperature on microstructure and tribological behaviour of hypoeutectic austempered ductile iron alloyed with copper

ABSTRACT In the present work, Cu alloyed ductile iron was isothermally treated at five different temperatures (280°C, 300°C, 320°C, 350°C, and 380°C) for 1 h to obtain an ausferrite microstructure composing a very fine ferrite phase and carbon enriched austenite. Microstructural characteristics exhibited a high ultimate tensile strength of 950–1600 MPa of ADI comparable to or even stronger than forged steels. The bulk hardness was 460–288 HV10, higher than pearlite, but lower than pure martensitic. The tribological behaviour of ADI was investigated using a 10 mm pin diameter during sliding. Its friction coefficient decreased almost by half as compared with ductile iron due to its ausferritic morphology and carbon enrichment. Under oxidative and adhesive conditions, an austempered microstructure with very fine ferrite and high carbon austenite is most wear-resistant due to its adequate strength, toughness, and lubricative behaviour. Wear resistance of ADIs can be improved through tailoring microstructure through austempering.

Simultaneous increase of ultimate tensile strength and uniform elongation of 30Si2MnCrMoVE ultra-high strength steel by hot deformation direct quenching and partitioning

In order to further improve the combination of strength and ductility for 30Si2MnCrMoVE ultra-high strength steel (UHSS), a thermomechanical treatment, named deformation direct quenching and partitioning (DQ&P), was carried out on it. The microstructure evolutions and mechanical properties of 30Si2MnCrMoVE UHSS treated by DQ&P were compared with those treated by conventional off-line quenching and tempering (Q&T) through various microscopic characterization methods and uniaxial tensile tests. Moreover, the effects of austempering temperature on the microstructure evolutions and mechanical properties of the studied steel after DQ&P process were also investigated. The results show that the DQ&P samples, although lower or slightly lower yield strength, possess significantly higher ultimate tensile strength due to higher work-hardening rate caused by high density dislocations and fine dispersed carbides. Moreover, DQ&P310 sample exhibit apparently higher uniform elongation than Q&T sample despite of comparable content of retained austenite due to more prone to transformation induced plasticity (TRIP) effect. The DQ&P process can increase the ultimate tensile strength by 267 MPã423 MPa and the uniform elongation by 78%∼85%, respectively, as compared to Q&T process, which indicates that DQ&P process may be a promising thermomechanical treatment method to improve the comprehensive mechanical properties of the studied steel. The strengths and elongations of DQ&P samples do not vary monotonously with the increase of austempering temperature, which are both closely related to the content of retained austenite.

Effect of austempering temperature on high cycle fatigue behaviour in nanostructured bainitic steels

The effect of three different austempering temperatures viz. 250°C (NB250), 300°C (NB300) and 350°C (NB350) on high cycle fatigue behaviour of carbide-free nanostructured bainite was investigated. There was an increase in yield strength with a decrease in austempering temperature due to finer bainitic ferrite (BF) and its higher volume fraction compared to retained austenite (RA). However, NB350 showed significant strain hardening compared to NB250 and NB300 due to transformation induced plasticity (TRIP). This also had implications in enhancing its fatigue life at almost all stress levels compared to NB250 and NB300 inspite of having a lower yield strength and tensile strength.

Effect of austempering temperature on corrosion evolution during immersion of high carbon nano-structured bainitic steel in aqueous chloride environment

Nano-structured bainitic (NSB) steels have a dual-phase structure comprising carbon-rich retained austenite (RA) and bainitic ferrite (BF). These steels exhibit high strength as well as sufficient ductility and damage tolerance and hence can find potential application in marine areas. However, a systematic study of the corrosion behavior is required to assess the reliability and longevity of these steels for the above applications. The role of austempering temperature (250 and 350 °C: specimens NB250 and NB350, respectively) and in turn the microstructural constituents on the corrosion response in aqueous chloride environment has been studied using immersion tests at different intervals of time (10, 20 and 30 days). Characterization of corrosion products has been done using microscopy and multiple spectroscopy techniques to reveal the attack mechanism and corroded layer composition. The corrosion rate, measured using weight loss experiments, decreases with a reduction in austempering temperature of the specimens and with an increase in immersion duration. Cross-sectional imaging of the corroded regions shows highly non-uniform but deeper penetration of corrosion with an increase in austempering temperature. In contrast, specimen transformed at the lowest temperature showed uniform and shallow penetration of corrosion. The corroded layer formed over NB350 after 10 days mostly comprised of oxyhydroxides but oxides took predominance after 30 days. However, NB250 showed mostly oxyhydroxides on the surface after 10 as well as 30 days. Hence, decreasing the austempering temperature while transforming austenite to nano-bainite not only provides higher strength but also greater corrosion resistance in saline environments.

Effect of austempering temperature on microstructure and mechanical properties of ductile cast iron modified by niobium

Abstract Owing to their exceptional physical, mechanical, and technological properties, ductile cast irons have been increasingly used, especially in automotive industries. Alloying elements and heat treatment routes can increase the strength of ductile irons. In this work, the effects of austempering temperature and time on the microstructure and mechanical properties of a ductile cast iron modified by 0.35% Nb have been studied. Two austempering temperatures of 320 °C and 360 °C for a holding time of 15, 30, 60, and 90 min were applied. The niobium addition was found to be effective in homogenizing the size and distribution of graphite nodules, maintaining the degree of nodularization above 90%, favoring pearlite refining, increasing the volume fraction of pearlite, forming niobium carbides in dispersed blocks in the matrix and graphite nodules, increasing both the yield and tensile strength, and reducing the elongation. Both the niobium addition and austempering temperature improved the yield and tensile strength but decreased the elongation compared to those of the reference ductile iron. The best combination of strength and ductility was observed at an austempering time of 60 min. The effect of austempering temperature on the microstructure and tensile mechanical properties of tested irons was found to be crucial.

Effect of austempering temperature and manganese content on the impact energy of austempered ductile iron

Austempered ductile iron (ADI) is a revolutionary material that has the ability to replace some of the commonly used steel forgings. ADI is being used in wide range of products because of the avail...

The Effects of Austempering Temperature and Time on Mechanical Properties of Ductile Cast Iron Grade FCD450

The purpose of the study was to inspect microstructure, mechanical properties and impact toughness of ductile cast iron grade FCD450 produced by austempering process. The study focused on austempering parameter, which effected impact toughness of material at low temperature. The FCD450 was initially temperature austenized at 885°C (1625˚F) for 2 hours. Austempering was carried out at three different temperatures of 271°C (520˚F), 313°C (560˚F) and 357°C (675˚F). The austempering temperature were varied at 1.5, 2.5 and 3.5 hours. X-ray diffraction was showed that the austempered ductile cast iron (ADI) microstructure consists of austenite and ferrite. The results showed that when austempered at 357°C (675˚F) for 2.5 hours has highest hardness and impact energy at low temperature. The dimple ductile fracture of ADI fracture surfaces was revealed by scanning electron microscope (SEM).

Effect of Austempering Temperature on the Microstructure and Retained Austenite of Cast Bainitic Steel Used for Frogs in Railway Crossovers

Effect of Austempering Temperature on the Microstructure and Retained Austenite of Cast Bainitic Steel Used for Frogs in Railway Crossovers

Mechanical properties and wear resistance of ultrafine bainitic steel under low austempering temperature

The mechanical properties and wear resistance of the ultrafine bainitic steel austempered at various temperatures were investigated. Scanning electron microscopy (SEM) and X-ray diffraction were used to analyze the microstructure. The worn surfaces were observed via laser scanning confocal microscopy and SEM. Results indicated that, under low austempering temperatures, the mechanical properties differed, and the wear resistance remained basically unchanged. The tensile strength of the samples was above 1800 MPa, but only one sample austempered at 230°C had an elongation of more than 10%. The weight loss of samples was approximately linear with the cycles of wear and nonlinear with the loads. The samples showed little difference in wear resistance at different isothermal temperatures, whereas the thickness of their deformed layers varied greatly. The results are related to the initial hardness of the sample and the stability of the retained austenite. Meanwhile, the experimental results showed that the effect of austempering temperature on the wear resistance of ultrafine bainitic steel can be neglected under low applied loads and low austempering temperature.

Effect of austempering temperature on microstructure of ausferrite in austempered ductile iron

ABSTRACTThe effect of austempering temperature on the microstructure of ausferrite in austempered ductile iron was investigated. The results show that the grain sizes of retained austenite and acicular bainitic ferrite both become larger with the increase of austempering temperature. As the austempering temperature is 240°C, the crystallographic relationship between ferrite and austenite in ausferrite follows Greninger-Troiano relation. However, Nishiyama–Wassermann relation and Greninger-Troiano relation both appear in ausferrite austempered at 300°C. At this temperature, the point-to-point misorientations of individual ferrite needle austempered at 300°C are less than 1°, being less than those at 240°C. This means the ferrite needles at 300°C contain fewer defects. However, some poles of ferrite needles obviously deviate from their ideal positions, which mainly comes from some ends of ferrite needles.

Analysis of grey relational method of the effects on machinability performance on austempered vermicular graphite cast irons

In this study, vermicular graphite cast iron samples were operationalized to Austempering process in two different temperatures (315 and 375 °C) and three different waiting periods (60, 120 and 180 min). According to the selected cutting tools and cutting parameters, the effect of Austempering temperature and waiting period on the lifetime of the tools was investigated. The tests were conducted on a CNC milling machine by using coated cementite carbide cutting tools. The tests on tool wear were done in dry conditions, in a cutting speed of 120 m/min, a pitch rate of 0.15 mm/dev, and a depth of cut of 1 mm. Tool wear, cutting forces and average surface roughness rates of milled surfaces; which were occurred during the milling process, were analyzed by using grey relation method. It is observed that an increase of Austempering temperature leads to an improvement between 2.15 and 2.85 times in the lifetime of tools. By using grey relational analysis, the highest cutting performance was obtained with the sample with the temperature of 375 °C, and a waiting period of 120 min.

Effects of austempering temperature on bainitic microstructure and mechanical properties of a high-C high-Si steel

High tensile strength of ~ 1550 MPa, uniform elongation of ~ 30%, and impact energy of ~ 80 J were achieved in a high-C high-Si bainitic steel, by austempering around the nose-tip temperature of the time–temperature–transformation (TTT) diagram. This bainitic microstructure revealed multiple lengths of nanobainite plates and various sizes and shapes of retained austenite. Its bainite transformation during austempering and microstructure evolution during tensile deformation were discussed in depth. Results demonstrated that large blocks of retained austenite (with inhomogeneous carbon distribution) transformed partly and gradually to multiple martensite grains as strain increases, due to the strong effect of carbon on mechanical stability of retained austenite. Ductile long nanobainite plates (~ 0.13 at% C) suppressed the propagation of microcracks, because of stress relief effect ahead of the current microcracks.

Effects of austempering temperature on microstructure and surface residual stress of carbidic austempered ductile iron (CADI) grinding balls

The effects of austempering temperature on microstructure and surface residual stress of carbidic austempered ductile iron (CADI) grinding balls were systematically investigated in this work. The microstructures were oberserved by optical metallography and analyized by X-ray diffraction. The surface residual stress measured by the cutting method is mainly composed of thermal stress and phase transformation stress. The thermal stress in grinding balls was determined by ANSYS simulation technique, and the surface phase transformation stress was obtained by subtracting the simulated surface thermal stress from the measured surface residual stress. Results show that all microstructures consist of ausferrite, white-bright zones (mixture of martensite and austenite), nodular graphite, and carbides. The distribution of ausferrite shows uniform. With the increase of austempering temperature, the volume fraction and carbon content of austenite increase, whereas the amount of white-bright zone decreases. In addition, the surface residual stress increases with the increase of austempering temperature. Only the tension exists at the austempering temperature of 200 °C, and the pressure exists at the austempering temperature of 220–260 °C. The thermal stress changes from the tension on the inside with the radius of 0–35 mm to the pressure on the outside with the radius of 35–62.5 mm, and the stress balance state presents at the radius of 35 mm. It is also found that the transformation stress is related to the content of carbon-rich austenite, and will reduce by 5.03 MPa accompanied with 1vol.% increase of the austenite. The thermal compressive stress and the transformation tensile stress on the surface both decrease with the increase of the austempering temperature.

Effect of austempering temperature on microstructure and properties of austempered ductile iron

The influence of austempering temperature on microstructure and properties of Austempered Ductile Iron were studied in this paper. The purpose was to improve comprehensive performance of Austempered Ductile Iron for adapting to slurry pump transflux parts. The nodularisation grade of graphite was 2-3 magnitude and the size of graphite was 6-7 magnitude. After austempered at different temperatures for 120 min, the microstructure mainly consisted of acicular ferrite, retained austenite and spheroidal graphite. With increasing austempering temperature, tensile strength improved firstly and then decreased, impact toughness increased, the wear resistance became worse, and the corrosion resistance increased. When the heat treatment process was 900°C × 90 min + 250°C × 120 min, the comprehensive performance was better (tensile strength: 1710 MPa, elongation: 2%, impact toughness: 40 J/cm2, Brinell hardness: 467 HBW, wear weightlessness rate: 0.17 mg/m) than the requirements in ASTM A897-06.

Effect of austempering temperature on microstructure and properties of austempered ductile iron

The influence of austempering temperature on microstructure and properties of Austempered Ductile Iron were studied in this paper. The purpose was to improve comprehensive performance of Austempered Ductile Iron for adapting to slurry pump transflux parts. The nodularisation grade of graphite was 2-3 magnitude and the size of graphite was 6-7 magnitude. After austempered at different temperatures for 120 min, the microstructure mainly consisted of acicular ferrite, retained austenite and spheroidal graphite. With increasing austempering temperature, tensile strength improved firstly and then decreased, impact toughness increased, the wear resistance became worse, and the corrosion resistance increased. When the heat treatment process was 900°C × 90 min + 250°C × 120 min, the comprehensive performance was better (tensile strength: 1710 MPa, elongation: 2%, impact toughness: 40 J/cm2, Brinell hardness: 467 HBW, wear weightlessness rate: 0.17 mg/m) than the requirements in ASTM A897-06.

Structure-properties relationship in TRIP type bainitic ferrite steel austempered at different temperatures

BackgroundAttractive properties of TRIP-type bainitic ferrite (TBF) steel ascribe to its unique microstructure of lath structure bainitic ferrite matrix and interlath retained austenite films. This work is concerned with obtaining ultra high-strength hot forged TBF steel with high elongation and excellent strength-elongation balance.MethodsThe effect of austempering temperature on the microstructure along with its retained austenite characteristics and tensile properties of a hot forged TBF steel was studied. A detailed investigation correlating the steel structure and its tensile properties was carried out.ResultsTensile strength ranging from 1058 to 1552 MPa was achieved when the hot forged steel was austempered at (325 - 475 °C).ConclusionsUltra high tensile strength of 1058 MPa, large total elongation of 29% and excellent strength-elongation balance of 30 GPa % were attained when the steel was austempered at 425 °C. The large total elongation of this steel is mainly due to the uniform fine lath structure matrix and the pronounced TRIP effect of a large amount of retained austenite films which prevents a rapid decrease of strain hardening rate at low strain and leads to a relatively high strain hardening at high strain level. Rapid transformation of blocky retained austenite at low strain in the hot forged TBF steel austempered at higher temperatures results in a rapid increase of initial strain hardening. In addition, the coarse microstructure that contains large blocks of retained austenite / martensite and the insufficient numbers of bainitic ferrite lathes and retained austenite films deteriorate the total elongation and the strength-elongation balance of the TBF austempered at 475 °C.