Influence Of Austempering Temperature Research Articles

Influence of Austempering Conditions on Hardness and Microstructure of Bainite in Low-Alloyed Steel

The influence of austempering temperature and time on the microstructure and hardness of a low-alloyed bainitic steel is investigated in the temperature range 275 °C to 375 °C for up to 24 hours. It is shown that the dislocation density and coarseness of the bainitic microstructure are affected by the austempering temperature, while only the dislocation density is significantly affected by the austempering time. The hardness of the steel is estimated based on microstructure–property relations and is in good agreement with the measured hardness. In conclusion, the decrease in dislocation density is the main reason for loss in hardness upon increasing austempering temperature and/or time for the studied temperature range.

Influence of Austempering Temperature on Microstructure and Mechanical Properties of High‐Silicon Carbide‐Free Bainitic Steel

The microstructural evolution of a novel high‐silicon carbide‐free bainitic steel at different austempering temperatures is investigated. The microstructure is evaluated by means of optical and electron microscopy, X‐ray diffraction, microhardness, and nanohardness. Results show a variation in the amount of stabilized retained austenite changing the temperature of the isothermal treatment. In particular, it is observed an increase in the retained austenite volume fraction increasing the temperature up to 350 °C, while further increase leads to a reduction. Moreover, increasing the isothermal holding temperature from 250 °C, through 300, 350, and 370 °C, a progressive bainite coarsening and an increase in the amount of stabilized carbon‐enriched retained austenite are observed. Tensile tests reveal an excellent combination of mechanical properties: mechanical strength in the range 1276–1988 MPa and total elongation 0.18–0.44.

Influence of austempering temperature on carbide free bainite development, a critical review

In this review paper, it is well established that high carbon high silicon steels on austempering result in carbide free bainite (CFB) which exhibits enhanced mechanical and tribological properties without adding any heavy alloying elements. Most of the research has been pointed out regarding the improvement of CFB steels that consists of the fine structure of bainitic ferrite laths and retained austenite (RA). In some cases, it was observed that the tensile strength of CFB steels was found similar to the commercial quenched and tempered steel alloys. Regarding other properties, it is estimated that out of the various failures that take place due to wear, 50% are caused by abrasive wear. To improve the lifetime of components, the selection of material and optimized processing techniques plays a pivotal role.

Austempered Compacted Graphite Iron — Influence of austempering temperature and time on microstructural and mechanical properties

This study investigates the effect of austempering temperature and time on the microstructural and mechanical properties of unalloyed Compacted Graphite Iron (CGI) with an initially ferritic matrix structure. The as-cast CGI samples were first austenitised at 900 °C for 60 min in a furnace, then austempered in a closed salt bath at three austempering temperatures – 275, 325, and 375 °C – for different times; 30, 60, 90, and 120 min. Tensile properties, Brinell, Vickers and Rockwell C hardness values were evaluated for the as-cast and austempered CGI ones. LOM and SEM, EBSD analysis techniques were used for microstructure and phase analysis. A mixture of acicular ferrite and retained austenite was achieved in the austempered CGI samples. In general, a decrease in austempering temperature resulted in a decrease in retained austenite content, corresponding improvements in hardness and tensile strength, and a decrease in elongation values.

Influence of Austempering Temperature and Time on the Microstructure and Mechanical Properties of Ductile Iron Weldment Using Developed Coated Electrode

Sound welded joints of ductile iron were first made by developing coated electrodes as well as weld procedure. The weldments were then austenitized at 900 °C for 2-h holding time followed by austempering at 300 and 350 °C for three different holding times (1.5, 2 and 2.5 h) at each austempering temperature. The influence of austempering temperature and time on the microstructural and mechanical properties was studied. Microstructural characterization, phase analysis, microhardness and mechanical properties were performed to understand the effect of austempering heat treatment on microstructure, austempering kinetics and mechanical properties of welded joints. In spite of significant variation in microstructures among all the three zones of DI weldment before austempering, the response of both weld metal and HAZ to austempering heat treatment similar to a base metal was noted. However, a significant variation in matrix structures (bainitic ferrite, retained austenite) as well as graphite nodules among the three zones was observed with changing the austempering temperature and holding time. Also, 100% joint efficiency of the welded joints was achieved at both 300 and 350 °C for 2-h holding time. Hardness and charpy impact toughness mostly depended on the volume fraction of retained austenite and carbon content. Based on the results of tensile and charpy impact testing, 350 °C and 2-h holding time could be considered as an optimum austempering condition for ADI weldment.

Austempered Ductile Iron (ADI): Influence of Austempering Temperature on Microstructure, Mechanical and Wear Properties and Energy Consumption

Alloyed Ductile iron, austenitized at 840 °C for 30 min in a special sealed austempering furnace, was austempered for 30 min in molten salt mixture at 4 trial temperatures of 300 °C, 320 °C, 340 °C and 360 °C. Tensile strength, yield strength, percentage elongation and impact energy were evaluated for the as-cast and austempered samples. Microstructures were investigated using microscopy, coupled with analyzing software and a scanning electron microscopy. The specific wear of samples was tested using pin-on-disc wear testing machine. X-ray diffraction was performed to calculate the amount of retained austenite present in the ausferrite matrix. As-cast microstructure consists of ferrite and pearlite, whereas austempered ductile iron (ADI) contains a mixture of acicular ferrite and carbon enriched austenite, called “ausferrite”. Hardness and strength decreased, whereas ductility and impact strength improved with an increase in the austempering temperature. XRD analysis revealed that the increase in austempering temperature increased the retained austenite content. A decrease in wear resistance with austempering temperature was observed. Modified Quality Index (MQI) values were envisaged, incorporating tensile strength, elongation and wear resistance. MQI for samples austempered at 340 °C and 360 °C showed a better combination of properties. About an 8% reduction in energy consumption was gained when the heat treatment parameters were optimized.

Influence of austempering temperature and salt bath agitation on microstructure and mechanical properties of austempered ductile iron

The influence of austempering temperature and salt bath agitation on microstructure and mechanical properties of austempered ductile iron was studied. The as-cast specimens of ductile iron were subjected to heat treatments consisting of austenitisation at 900◦C for 1 h followed by austempering at temperatures ranging from 230 to 450◦ C in a salt bath with and without agitation. The volume fraction of retained austenite increases with increasing austempering temperature to about 395◦C and decreases at higher austempering temperatures. The austempering at lower temperatures leads to the formation of finer microstructures. The agitation of the salt bath leads to the formation of the higher volume fraction of ausferrite at the expense of the retained austenite compared to that of the specimens prepared without salt bath agitation. Vickers hardness decreases with increasing austempering temperature and increasing volume fraction of the retained austenite. Room temperature impact energy increases with increasing austempering temperature to about 395◦C and then decreases at higher temperatures. The impact energy increases with increasing volume fraction of the retained austenite. The proposed mathematical models are of industrial importance for prediction of Vickers hardness, impact energy and volume fraction of the retained austenite as functions of austempering temperature and agitation or no agitation of the salt bath.

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.

Microstructure and wear behavior of austempered high carbon high silicon steel

In the present investigation, the influence of austempering temperature and time on the microstructure and dry sliding wear behavior of high silicon steel was studied. The test specimens were initially austenitised at 900°C for 30 minutes, thereafter austempered at various temperatures 280°C, 360°C and 400°C, for varying duration from 30 to 120 minutes. These samples after austempering heat treatment were subsequently air cooled to room temperature, to generate typical ausferritic microstructures and then correlated with the wear property. The test outcomes demonstrate the slight increase in specific wear rate with increase in both austempering temperature and time. Specific wear rate was found to be minimum at an austempering temperature of 280°C, that exhibits lower bainite microstructure with high hardness, on the other hand specific wear rate was found to be slightly high at increased austempering temperatures at 360°C and 400°C, due to the upper bainite structure that offered lower hardness to the matrix. The sample austempered at 280°C for 30 minutes offered superior wear resistance when compared to other austempering conditions, mainly due to the presence of fine acicular bainitic ferrite along with stabilized retained austenite and also some martensite in the microstructure.

Microstructure and wear behavior of austempered high carbon high silicon steel

In the present investigation, the influence of austempering temperature and time on the microstructure and dry sliding wear behavior of high silicon steel was studied. The test specimens were initially austenitised at 900°C for 30 minutes, thereafter austempered at various temperatures 280°C, 360°C and 400°C, for varying duration from 30 to 120 minutes. These samples after austempering heat treatment were subsequently air cooled to room temperature, to generate typical ausferritic microstructures and then correlated with the wear property. The test outcomes demonstrate the slight increase in specific wear rate with increase in both austempering temperature and time. Specific wear rate was found to be minimum at an austempering temperature of 280°C, that exhibits lower bainite microstructure with high hardness, on the other hand specific wear rate was found to be slightly high at increased austempering temperatures at 360°C and 400°C, due to the upper bainite structure that offered lower hardness to the matrix. The sample austempered at 280°C for 30 minutes offered superior wear resistance when compared to other austempering conditions, mainly due to the presence of fine acicular bainitic ferrite along with stabilized retained austenite and also some martensite in the microstructure.

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.

An Austempering Study of Ductile Iron and the Effect of Copper Addition on the Tensile Properties of Austempered Ductile Iron

Austempered Ductile Iron (ADI) has proved to be an excellent material as it possesses attractive properties like high strength, ductility and toughness combined with good wear resistance and machinability. These properties can be achieved upon adequate heat treatment which yields optimum microstructure for a given chemical composition. In this work, an investigation has been conducted on ductile iron alloyed with Cu and austempered in a range of time and temperatures. The influence of austempering temperature, time and copper addition on tensile strength and elongation of ADI has been determined. The tensile strength was found to increase with decreasing austempering temperature, with maximum tensile strength seen in samples austempered at lower temperature, 250 °C, and for shorter time. Maximum ductility was obtained after austempering for 1.5 h. An increase in the ductility of ADI was found on copper addition

Processing of a new high strength high toughness steel with duplex microstructure (Ferrite + Austenite)

In this investigation a new third generation advanced high strength steel (AHSS) has been developed. This steel was synthesized by austempering of a low carbon and low alloy steel with high silicon content. The influence of austempering temperature on the microstructure and the mechanical properties including the fracture toughness of this steel was also examined. Compact tension and cylindrical tensile specimens were prepared from a low carbon low alloy steel and were initially austenitized at 927°C for 2h and then austempered in the temperature range between 371°C and 399°C to produce different microstructures. The microstructures were characterized by X-ray diffraction, scanning electron microscopy and optical metallography. Test results show that the austempering heat treatment has resulted in a microstructure consisting of very fine scale bainitic ferrite and austenite. A combination of very high tensile strength of 1388MPa and fracture toughness of 105MPa√m was obtained after austempering at 371°C.

Influence of austempering temperature on the mechanical properties of a low carbon low alloy steel

In this investigation, a new low alloy and low carbon steel with exceptionally high strength and high fracture toughness has been developed. The effect of austempering temperature on the microstructure and mechanical properties of this new steel was examined. The influence of the microstructure on the mechanical properties and the fracture toughness of this steel was also studied. Test results show that the austempering produces a unique microstructure consisting of bainitic ferrite and austenite in this steel. There were significant improvement in mechanical properties and fracture toughness as a result of austempering heat treatments. The mechanical properties as well as the fracture toughness were found to decrease as the austempering temperature increases. On the other hand, the strain hardening rate of steel increases at higher austempering temperature. A linear relationship was observed between strain hardening exponent and the austenitic carbon content.

Influence of Alloying Elements on the Bainitic Transformation of Ductile Iron

Alloying elements may be added to ductile iron to improve mechanical properties or prevent pearlitic transformation during austempering process. On the other hand, the segregation of alloying elements during solidification changes the kinetics of austempering process which in turn bainitic transformation would be function of local concentration of alloying elements. In this research, kinetics of the first stage of bainitic transformation in ductile iron has been studied by the means of comparing the bainitic transformation in steels with the same composition similar to the alloyed ductile iron matrix after austempering treatment. According to the results of dilatometry tests, the effect of Si and Mn in steel samples on the incubation time of bainitic transformation was obtained. Also, the influence of austempering temperature on "S-shape" curve has been investigated by means of dilatometry data.

The Influence of Austempering Temperature on the Wear Resistance of Ductile Iron under Two Different Tribosystems

This paper reports the results obtained in a research conducted to evaluate austempered ductile iron (ADI) as a wear resistant material for the production of machine parts processed at intermediate and high austempering temperatures (Ta). Severe abrasion in actual service performance trials and low stress abrasion laboratory tests (ASTM G-65) were carried out along with microstructural characterization by optical microscopy and X-ray diffraction. The results derived show that ADI yields excellent abrasion resistance under the operating conditions resulting from the field tests when Ta is raised. Nevertheless, ADI show an opposite trend under the low stress abrasion conditions imposed by the dry sand/rubber wheel abrasion apparatus (ASTM G-65). The presence of a metastable and ductile ausferrite phase (reacted and unreacted austenite+ferrite) in ADI microstructure appears to be the most relevant factor influencing the performance observed. In addition to a high deformation capability detected at the wear surfaces, an austenite to martensite transformation took place as determined by X-ray diffraction. These two factors combined make the ausferritic microstructure overcome hardness reduction when the austempering temperature is raised, improving or sustaining the resistance to severe abrasive wear but, at the same time, increasing impact toughness.

Fracture toughness of a high carbon and high silicon steel

A high carbon and high silicon (HCHS) steel containing about 1% carbon and 2.5% silicon has been developed. This steel has been synthesized using concepts from austempered ductile cast iron (ADI) technology. The influence of austempering temperature on the microstructure and the mechanical properties of this steel in room temperature and ambient atmosphere was examined. The influence of microstructure on the plane strain fracture toughness of this HCHS steel was also investigated. Compact tension and round cylindrical specimens were prepared from this steel. These specimens were then austenitized at 927°C for 2 h and then austempered at several temperatures between 260 and 399°C for a fixed time period of 2 h to produce different microstructures. The microstructures were characterized by X-ray diffraction and optical metallography and correlated to the mechanical properties. The test results showed that the maximum fracture toughness is obtained in this steel with a upper bainitic microstructure when the microstructure contains about 35% austenite and the carbon content in the austenite is about 2%. The retained austenite and its carbon contents increased with austempering temperature, reaching a peak value at 385°C and then retained austenite decreased with increasing temperature. The carbon content of the austenite also showed a similar behavior. The fracture toughness was found to depend on the parameter ( X γ C γ/ d) 1/2 where X γ is the volume fraction of the austenite, C γ is the carbon content of austenite and d is the mean free path of dislocation motion in ferrite.

Influence of austempering temperature on fracture toughness in bainitic nodular cast iron

Etude du mecanisme de rupture sur differentes microstructures de fonte bainitique. Correlation entre la tenacite et la surface de rupture