Abstract: Cr, Mo and/or Ni were added to TRIP-aided bainitic ferrite (TBF) steel (0.2% C, 1.5% Si, 1.5% Mn and 0.05% Nb ultrahigh-strength TBF steel) in order to increase its hardenability. In addition, the effects of the alloying elements on the Vickers hardness, microstructure and retained austenite characteristics of the TBF steels were investigated. When the TBF steels were austempered at temperatures between MS and Mf, the Vickers hardness increased from HV300 to HV430 with increasing hardenability. The microstructure consisted of martensite and bainitic ferrite lath structures and retained austenite phases and the volume fraction of retained austenite increased with increasing hardenability. Conversely, the carbon concentration of the retained austenite decreased with increasing hardenability. Simultaneously, the quantity of the hard blocky martensite phase (M-A constituent) with refined interlath retained austenite films increased with increasing hardenability. These characteristics are mainly caused by the delayed bainite transformation during austempering through the addition of Cr, Mo and/or Ni. The addition of Ni lowered the T0 line further. The retained austenite phases of Cr- and/or Mo-bearing TBF steels were relatively stable against straining, despite their low carbon concentrations.

Abstract: During the last few years, researchers have sought new ductile iron (DI) applications focusing on the development of mixed microstructures, such as ferritic-bainitic or ferritic-martensitic. These kinds of structures result in DI with a good combination of mechanical properties, compared to other conventional DI. The combination of properties offered by the mixed structure DI, particularly in “dual phase austempered ductile iron” (ADI) has opened new horizons for cast iron to replace steel castings and forgings in many engineering applications. This new DI has a particular microstructure composed of different amounts and morphologies of ausferrite and free ferrite.

Abstract: This work describes the steps in the study and development of the high content of C, Si, and Cr in commercial steel with a nanostructured matrix of martensite, bainite and retained austenite. Specimens of this steel were austenitized at 900 °C for 5 min and isothermally heat treated at different times (0.5, 2, 24, 48 h) and temperatures (200, 220, 270 °C). Different mechanical behavior was observed for the samples treated under different conditions due to their microstructural constitution. Specimens treated for 2 h at 200 °C showed lower yield strength of 979 MPa. On the other hand a high tensile strength of 2248 MPa was reached. The sample treated at 270 °C showed higher yield strength of 1363 MPa with the same treatment time. As for the fracture analysis, the brittle fracture mechanism was predominant for the samples treated at 200 °C, while the ductile fracture mechanism was predominant for the samples treated at 270 °C.

Abstract: Austempered ductile iron (ADI) has several advantages of replacing cast steel and forged steel in many engineering fields. A new Mn-Cu alloyed ADI with excellent mechanical properties has been developed in order to cut the cost and enlarge the application of ADI. The helical bevel gears were made of the new-developed Mn-Cu alloyed ADI. The microstructure and mechanical properties of the standard sample were investigated by optical microscope (OM), scanning electron microscope (SEM) and performance measurement. The results showed that after a series of treatments, the mechanical properties ( R m 1007.4 to 1200 MPa, A 5.2% to 8.8%, HRC 32 to HRC 35, α K 70 to 120 J/cm 2 ) of the Mn-Cu alloyed ADI standard sample could reach European standard EN1564-97/EN-CJS-1000-5. The surface hardness after helical bevel gears meshing was significantly increased due to the formation of martensite. The bench test and traffic running testing results suggested that the new Mn-Cu alloyed ADI with ultimate life and median life respectively exceeding 30 × 10 4 and 50 × 10 4 times could replace 20CrMnTi forged steel for manufacturing the EQ140 helical bevel gears.

Abstract: It is discussed the use of ADI (Austempered Ductile Iron) for gears. The gears were produced from continuous cast iron bars, heat treated for grade 3 of ASTM ADI Standard A897M06 (UTS >1200 MPa), and compared to carburized steel AISI 8620 and to induction hardened steel AISI 4140. Tests on gears were made using equipment developed at UTFPR, measuring the time for pitting and spalling on the surface of the gears. The results show very good potential of using ADI for gears, replacing induction hardened steels. The results show too that the nodule size affects the life of gears, independently of the mechanical properties of the matrix. The ADI with smallest nodules show higher life for pitting formation. It is discussed additionally the mechanisms of crack propagation under the surface of the gears, for all tested materials.

Abstract: Ductile iron can acquire enhanced thermal and mechanical properties from austempering heat treatment. The present study aims to identify the function of different cutting parameters affecting machinability and to quantify its effects. Turning was performed to test machinability according to the ISO3685-1993 (E) standard. After austenitizing at 900 C for 90 min, austempered ductile iron (ADI) specimens were quenched in a salt bath at 380 C for 90 min. The cutting force signals along three directions were measured in real time, whereas flank wear and surface roughness were measured offline. For the cutting parameters, the cutting speed and depth of cut were varied, but the feed rate was kept constant. In the flank wear tests, machining length was corresponded to tool life. In addition, in order to find out the effect of cutting parameters on surface roughness (Ra), tangential force (Ft), and flank wear (VB) during turning, response surface methodology (RSM) was utilized by using experimental data. The effect of the depth of cut on the surface roughness was negligible but considerable in the cutting forces. The increased cutting speed produced a positive effect on surface roughness. It is found that the cutting speed was the dominant factor on the surface roughness, tangential force, and flank wear. [DOI: 10.1115/1.4005805]

Abstract: Selecting a suitable manufacturing process is one way of achieving sustainability of a product by diminishing energy consumption during its production cycle and improving material efficiency. The article attempts to explore the new processing technology for direct manufacturing of lightweight austempered ductile iron (ADI) casting in a permanent mold. The new processing technology is based on the innovative integrated approach toward casting and heat-treatment process. In this technology, the ductile iron samples obtained using the permanent mold are first austenized immediately after solidification process followed by austempering heat treatment in the fluidized bed and then air cooled at room temperature to obtain ADI material. The influence of austempering time on the microstructural characteristics, mechanical properties, and strain-hardening behavior of ADI was studied. Optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) analyses were performed to correlate the mechanical properties with microstructural characteristics. It was observed that the mechanical properties of resulting ADI samples were influenced by the microstructural transformations and varied retained austenite volume fractions obtained due to different austempering time. The results indicate that the strain-hardening behavior of the ADI material is influenced by the carbon content of retained austenite.

Abstract: Intercritically austempered ductile irons hold promise for applications requiring fatigue durability, excellent castability, low production energy requirements, reduced greenhouse gas emissions, and excellent machinability. In the present study, four different ductile iron alloys, containing manganese and nickel as the primary austenite-stabilizing elements, were heat treated to obtain different quantities of austenite in the final microstructure. This article reports the microstructures and phases present in these alloys. Furthermore, lattice strains and diffraction elastic constants in various crystallographic directions and the transformation characteristics of the austenite were determined as a function of applied stress using in situ loading during neutron diffraction at the second generation Neutron Residual Stress Facility at the High Flux Isotope Reactor at Oak Ridge National Laboratory.

Abstract: The effect of reducing the austempering time on the high-cycle fatigue behavior of austempered ductile iron (ADI) has been investigated by subjecting samples to rotating bending and fatigue crack propagation tests. Starting from the same cast iron, two distinct types of ADI were austempered at the same temperature of 360 °C but for different austempering times, which resulted in two materials whose main difference was the content of carbon in austenite. The first sample was austempered for 1.5 h, while the second was austempered for only 0.6 h. The austenitizing cycle (900 °C, 1.5 h) was the same for both ADIs. Therefore, we investigated the influence of the mechanical stability of austenite in the initiation and propagation of fatigue cracking. Reducing the austempering time increased the fatigue life and did not affect the mechanical properties or the rate of fatigue crack propagation. Reducing the austempering time increased the time to fatigue crack nucleation in ADI in addition to its economic and environmental benefits.

Abstract: This work studies the influence of the PVD processing parameters on the characteristics of TiN and CrN coatings deposited on ADI substrates, austempered at 360°C, with different nodule counts and surface roughnesses. Coatings were applied by arc ion plating using an industrial reactor and different sets of parameters, with BIAS voltages, arc currents, chamber pressures and substrate temperatures varying from –100 to –250 V, 60 to 65 A, 0.7 to 2.8 Pa and 280 to 450°C, respectively. The effect of the different depositions conditions on the substrates microstructure was also analyzed. The existing phases, preferred orientation, surface topography, film thickness, hardness and adhesion of each coating were determined. The retained austenite content and hardness of each substrate were computed before and after coating deposition.The results obtained indicate that the different deposition conditions and coating materials evaluated do not generate significant changes neither in the resulting topography nor in the coating adhesion, which can be related to indices between HF1 and HF2. Coating adhesion was not affected by different substrate roughnesses. The combined reduction of BIAS voltage, arc current and chamber pressure leads to a decrease of TiN growth rate and hardness, while high substrate temperatures promotes an increase in TiN and CrN growth rates. Substrate temperatures around 300°C with deposition times of up to 240 min do not promote noticeable changes on the ausferritic microstructure, while temperatures of 400°C and above translate into a clear microstructural deterioration, even for short deposition times.

Abstract: The present study attempts to tailor the size, morphology and distribution of the ferrite needles/sheaves by thermomechanical processing and develop an ultrafine ferrite + martensite duplex microstructure for enhancement of strength and toughness in SAE 52100 steel. The thermo-mechanical routine included 5% hot deformation before, during or after austenitizing at 950 °C for 15 min followed by austempering at 270 °C for 30 min and subsequent water quenching to room temperature. Optical/electron microscopy along with X-ray diffraction was used to quantitatively monitor the size, morphology and distribution of the phase or phase aggregate. Significant improvement in nanohardness, wear resistance and elastic modulus and was observed in samples subjected to thermomechanical processing, as compared to that following the same austenitizing and austempering routine without hot deformation at any stage. However, improvement in the bulk mechanical property due to the present thermo-mechanical is lower than that obtained in our earlier study comprising cold deformation prior to austenitizing and austempering.

Abstract: In austempering, the microstructural end product of the spheroidal graphite (SG) iron matrix is essentially bainite, a structure formed below the pearlite temperature range but above the martensite range. Ductile cast iron undergoes a remarkable transformation when subjected to the austempering process. Due to isothermal transformation, it produces a microstructure that is stronger and tougher than the structures resulting from conventional heat treatment process. In the present investigation, the SG iron was austempered with three different austempering temperatures (250C,300C and 350C) with varying austempering time. The sample was taken for XRD analysis to study the morphology of the matrix. It was found that both the austenite (111) and ferrite (110) lines are identified nearly in all cases. The maximum intensity of the austenite (111) line is increasing with increasing temperature but ferrite (110) line is increasing with increasing austempering time and decreasing with austempering temoerature. Hence austempering calls for very precise control of process times and temperatures.

Abstract: Provided are: a high-strength steel sheet which is improved in both elongation and local formability and thus exhibits excellent workability; and a manufacturing method thereof. The high-strength steel sheet contains C, Si, Mn, Al, P and S with the remainder including iron and unavoidable impurities, and has a metal structure which includes polygonal ferrite, bainite, tempered martensite, and retained austenite. In the metal structure, (1) the bainite has a composite microstructure including both a high-temperature-formed bainite having an average distance between adjacent regions of retained austenite and/or carbide of 1 µm or more and a low-temperature-formed bainite having an average distance between adjacent regions of retained austenite and/or carbide of less than 1 µm each identified upon observation with a scanning electron microscope; and (2) the retained austenite is present in a volume percentage of 5% or more of the entire metal structure as determined by a saturation magnetization measurement.

Abstract: Warm deformation tests were performed using a kind of tubby heater. The microstructures and mechanical properties of an Fe-C-Mn-Si multiphase steel resulting from different warm deformation temperatures were investigated by using LOM (light optical microscopy), SEM and XRD. The results indicated that the microstructure containing polygonal ferrite, granular bainite and a significant amount of the stable retained austenite can be obtained through hot deformation and subsequent austempering. Warm deformation temperature affects the mechanical properties of the hot rolled TRIP steels. Ultimate tensile strength balance reached maximum (881 MPa) when the specimen was deformed at 250°C, and the total elongation and strength-ductility reached maximum (38% and 28614 MPa · %, respectively) at deforming temperature of 100°C. Martensite could nucleate when austenite was deformed above M3, because mechanical driving force compensates the decrease of chemical driving force. The TRIP effect occurs in the Fe-C-Mn-Si multiphase steel at deforming temperature ranging from 15 to 350°C. The results of the effects of warm deformation on the mechanical properties of the Fe-C-Mn-Si multiphase steel can provide theoretical basis for the applications and the warm working of the hot rolled TRIP sheet steels in industrial manufacturing.

Abstract: Two types of ductile iron has been taken for the present investigation. Both austempering time and temperature are considered as the main variables for structure property correlation of Austempered Ductile Iron. The two types of spheroidal graphite iron (differ by copper percentage) were austempered at four differing austempering temperatures viz. 250oC, 300oC, 350oC and 400oC for 60min, 90 min and 120 min respectively. The effect of austempering variables on the mechanical properties of spheroidal graphite iron was investigated as a function of austempering time and temperature. The cooling rate and the quenching techniques followed in the present study plays an important role for the property development of spheroidal graphite iron. The tensile properties have been correlated with the graphite morphology for both grades of ADI. SEM micrographs have been taken from fracture surfaces of the tensile specimen under different austempering conditions. It has been found from the result that ADI having the alloying element (copper) achieved significant mechanical properties as compared to ADI without having copper throughout the different austempering processes adopted in this study.

Abstract: Materials such as dual phase (DP) steels, transformation induced plasticity (TRIP) steels and dual phase ductile irons are produced by intercritical heat treatments. These materials can provide significant weight savings in the automotive industry. The goal of this dissertation is to study intercritical heat treatments in ductile iron and steel to optimize the production parameters. Three different aspects were addressed.First, common steels were intercritically austenitized and austempered (intercritically austempered) under a variety conditions. The results showed that common grade steels that were intercritically austempered exhibited tensile properties in the same range as DP and TRIP steels.The second study consisted of determining the effect of heat treatment conditions on the tensile properties of intercritically austenitized, quenched and tempered ductile iron (IAQ&TDI). The results showed that (1) ultimate tensile strength (UTS) and yield strength (YS) were determined by the volume fraction of martensite, (2) tempering improved the elongation 1.7-2.5 times with only a slight decrease in strength, (3) the carbon in austenite formed during the intercritical heat treatment of ductile iron with a ferritic-pearlitic matrix came from the carbon available in the matrix and that carbon diffusion from the graphite nodules was restricted, and (4) limited segregation of substitutional elements occurred during intercritical austenitizing.Finally, intercritically austempered ductile iron (IADI) alloyed with different amounts of manganese and nickel was produced. Tensile properties and microstructure were determined. Also, the stability of the austenite during deformation and the lattice strains of the ferrite and the austenite phases were determined using x-ray diffraction (XRD) and neutron diffraction. The results indicated that: 1) high manganese concentrations produced materials with large blocky, low carbon austenite particles at the intercellular boundaries which decreased the elongation of the materials and transformed to mar-tensite during deformation at low strains. 2) Nickel and nickel-manganese alloys formed a combination of blocky and plate-like austenite particles, which were more stable during deformation and either transformed to martensite after yielding or did not transform at all.%%%%PhD%%%%1 online resource (xvi, 113 p.) :ill. (some col.)%%%%%%%%Materials Science and Engineering%%%%Engineering%%%%Austenite stability Ductile Iron Intercritical austenitizing Intercritical heat treatments Neutron diffraction Steel%%%%UNRESTRICTED

Abstract: Abrasion wear rates of conventional and two-step austempered ductile cast iron (ADI) were investigated. Conventional austempering and two-step austempering processes were carried out at 280, 300, and 320°C. Microstructures revealed that higher austemperig temperature resulted in coarser ausferrite and higher volume fractions of blocky retained austenite. The ausferrite in two-step austempered ADI was slightly coarser comparing to the coventional ADI since the temperature was raised by 30°C during austempering. Two-body abrasion wear rates of ADIs were studied using a Suga abrasion wear tester. It was found wear rates of the two-step ADI become significantly lower than those of the conventional ADI, especially when the austempering was carried out at low temperature, i.e. 280°C. Such behavior was due to the strong influence of high carbon concentration in retained austenite eventhough the ausferrite matrix was coarser.

Abstract: The integrated modeling and simulation of the casting and heat treatment processes for producing austempered ductile iron (ADI) castings is presented. The focus is on describing different models to simulate the austenitization, quenching and austempering steps during ADI heat treatment. The starting point for the heat treatment simulation is the simulated microstructure after solidification and cooling. The austenitization model considers the transformation of the initial ferrite-pearlite matrix into austenite as well as the dissolution of graphite in austenite to attain a uniform carbon distribution. The quenching model is based on measured CCT diagrams. Measurements have been carried out to obtain these diagrams for different alloys with varying Cu, Ni and Mo contents. The austempering model includes nucleation and growth kinetics of the ADI matrix. The model of ADI nucleation is based on experimental measurements made for varied Cu, Ni, Mo contents and austempering temperatures. The ADI kinetic model uses a diffusion controlled approach to model the growth. The models have been integrated in a tool for casting process simulation. Results are shown for the optimization of the heat treatment process of a planetary carrier casting.

Abstract: An isothermally hardened iron with vermicular graphite represents a new group of heat-treated cast irons, which follows already proven and for its excellent properties widely used isothermally hardened iron with globular, respectively lamellar graphite (ADI – Austempered Ductile Iron, AGI – Austempered Grey Iron). This paper deals with the study of properties and the potential of application of this material in engineering. Use of isothermal heat treatment in the current production of vermicular cast iron provides a significant improvement of utility properties of manufactured parts, with minimal interference to the existing production

Abstract: Austempered ductile cast iron (ADI) has emerged as a major engineering material in recent years because of its many attractive properties. In this investigation, the influence of a step-down austempering process on the microstructure and mechanical properties including fracture toughness of an unalloyed ductile cast iron was examined. Compact tension and cylindrical tensile specimens were prepared from unalloyed nodular cast iron as per ASTM standards and were subjected to conventional as well as step-down austempering process at three different austempering temperatures. The microstructure and mechanical properties of these samples were evaluated and compared. Test results show that both the step-down and conventional austempering process resulted in very similar microstructure and mechanical properties in unalloyed ADI. The fracture toughness of the material was found to be influenced by both ferritic cell size (d) and the austenitic carbon ( ). . γ

Abstract: A method of making an austempered ductile iron article is disclosed. The method includes providing a melt of a ductile iron alloy composition. The method also includes casting the melt into a mold to form a casting. The method further includes cooling the casting to an austempering temperature by circulating a coolant through the mold; wherein cooling comprises solidifying the melt and forming a ductile iron article. Still further, the method includes heating the casting to maintain the austempering temperature for an interval sufficient to form an austempered ductile iron article that comprises a microstructure comprising ausferrite.