Abstract: The stretch-flangeability of a newly developed high-strength bainitic sheet steel which is associated with the transformation-induced plasticity (TRIP) of retained austenite, or "TRIP type bainitic steel" was investigated for the automotive applications. An excellent stretch-flangeability was completed in the steel composing of bainitic ferrite matrix and interlath retained austenite films without initial blocky martensite. In this case, the stable or carbon-enriched retained austenite films enhanced the stretch-flangeability due to the reducion of the surface damage on hole-punching and the promotion of the TRIP effect on hole-expanding. Also, uniform fine bainitic ferrite lath structure contributed to improving the stretch-flangeability due to the increased localized ductility and development of severe plastic flow.

Abstract: The influence of different amounts (10, 20, and 40%) of compressive deformation of austenite on the subsequent isothermal transformation of bainite has been investigated in FeMnSiC alloy steels. The overall transformation kinetics became slower and the final attained amount of bainite decreased in deformed austenite after the isothermal transformation was completed. The prior deformation of austenite had a strong impact on the bainitic transformation, because it created defects which hinder the growth of bainite and resulted in finer microstructure. If the recovery of deformed austenite occurred, the effect of mechanical stabilization of austenite would be mitigated. These results emphasized that the accumulated strain in austenite matrix retarded significantly the growth of bainite.

Abstract: An investigation was carried out to examine the influence of austempering time on the resultant microstructure and the room-temperature mechanical properties of an unalloyed and low manganese ductile cast iron with initially ferritic as-cast structure. The effect of austempering time on the plane strain fracture toughness of this material was also studied. Compact tension and round cylindrical tensile specimens were prepared from unalloyed ductile cast iron with low manganese content and with a ferritic as-cast (solidified) structure. These specimens were then austempered in the upper (371 °C) and lower (260 °C) bainitic temperature ranges for different time periods, ranging from 30 min. to 4 h. Microstructural features such as type of bainite and the volume fraction of ferrite and austenite and its carbon content were evaluated by X-ray diffraction to examine the influence of microstructure on the mechanical properties and fracture toughness of this material.

Abstract: Austempered ductile iron (ADI) is finding an ever increasing worldwide market in the automotive and other sectors. It offers a range of mechanical properties superior to those of other cast irons, and shows excellent economic competitiveness with steels and aluminium alloys. The aim of the present research is to develop a generic model that will enable the producers of ADI to optimise their product in terms of microstructure and mechanical properties, hence minimising the need for expensive and exhaustive experimental trials and reducing alloy development lead times.

Abstract: A new method of refining the microstructure of austempered ductile iron (ADI) by thermome chanical processing is investigated. Refinement of microstructure is effected by grain refinement of parent austenite by hot deformation in the austenitizing temperature range, before the austempering treatment. The effects of austenite deformation on the kinetics of austempering reaction and the microstructure development were studied using metallography and X-ray diffraction (XRD), at different austempering temperatures and deformations. The process window for optimum microstructure was determined in terms of the parameters involved. Deformation of 40 to 60 pct could be imparted in the temperature range 900 °C to 1025 °C, resulting in a reduction in the prior austenite grain size by 35 to 50 pct and ferrite size in ausferrite by 70 to 75 pct. The effects of austenitization temperature on the austempered microstructure were also studied.

Abstract: The growth of short fatigue cracks was investigated in an austempered ductile cast iron (wt% 3.6C, 2.5Si, 0.6Mn, 0.15Mo, 0.3Cu), austenitized at 870 °C and then austempered at 375 °C for 2 h. At stress amplitudes close to the fatigue limit endurance limit of 10 7 cycles, subcritical crack nuclei initiated at graphite nodules. The crack nucleus decelerated and arrested after propagating a short distance. The position of an arrested crack tip was characterized using an electron backscatter diffraction technique, demonstrating that short fatigue cracks in austempered ductile cast iron (ADI) can be arrested by boundaries such as those between ausferrite sheaves or packets and prior austenite grains. Refinement of the prior austenite grain size decreased the size of subcritical crack nuclei. It is proposed that the arrest and retardation of short crack nuclei are controlled by the austenite grain size and graphite nodule size. This determines the fatigue endurance limit.

Abstract: A new processing method was investigated for improving the strength and elongation of austempered ductile iron (ADI) by grain refinement of parent austenite using thermomechanical treatment. The material was deformed at the austenitization temperature by single and multipass rolling before the austempering treatment. The effects of the amount of deformation, austenitization temperature, austempering temperatures, reaustenitization, and secondary deformation on the tensile properties were studied. The properties obtained using the method were compared with those of the ASTM standards. The effect of deformation on the graphite shape was also studied. Tensile strength/yield strength/elongation values were found to increase with increasing austenite deformation up to 40% and then to start decreasing. Tensile strength/yield strength and elongation values of 1700 MPa/1300 MPa/5% and 1350 MPa/920 MPa/15% can be achieved with this method in the ranges of variables studied.

Abstract: The present study investigated the effect of austempering temperature and austempering time on the microstructure and mechanical properties of low alloyed Ni-Mo-Cu ductile iron. The effect of austempering parameters and alloying additions on the austemperability of treated ductile iron has been estimated, too. Specimens were austenitised at 900°C for 120 min, then austempered for 10, 30, 60, 120, 240 and 360 min at 300, 350 and 400°C respectively, and examined by light and scanning electron microscopy. The structure consisted of bainitic ferrite containing retained austenite, the amount of which increased, and the carbon content of which decreased, with increasing austempering temperature. The carbon content of austenite has been evaluated by measuring the lattice parameter by X-ray diffraction. After short periods of austempering time in iron, the carbon content of the retained austenite decreases and on subsequent cooling to room temperature it transforms to martensite. The volume fractions of retained austenite, bainitic ferrite, martensite and austenite carbon content was correlated with microstructural changes and mechanical properties. Optimum properties are obtained at intermediate austempering periods (120-240 min) when both the amount of retained austenite and austenite carbon content are maximum.

Abstract: Austempered ductile iron (ADI) is gradually replacing many fabricated and forged steel components in engineering applications. One of its advantages is the combination of good castability, machinability, and mechanical properties with significant savings in cost and weight compared with equivalent steel components. A problem in the production of ADI is the use of expensive and dangerously reactive magnesium as a graphite nodulariser. There is a need to find cheaper, safer, and equally effective substitutes. Results of an investigation of the effectiveness of a multiple calcium–magnesium based master alloy nodulariser and the properties of the ductile iron and ADI produced are reported. Up to 96% nodularity could be obtained using a special Ca–CaC2–Mg master alloy, compared with 98% using magnesium alone. The mechanical properties were also comparable.

Abstract: The very little plastic deformation exhibited in the fracturing of flake graphite (FG) and compacted graphite (CG) cast irons qualified them as brittle materials. The fatigue pre-cracking of these brittle material in KIC plane strain fracture toughness testing is a difficult task. Opposed to this static toughness KIC, the dynamic toughness obtained by impact testing does not have such problems. Since the stress–strain behavior of brittle material is essentially linear and the fracture appearance of the specimens after impact testing must largely be flat without shear-lip, these conditions also satisfy the linear-elastic requirement in KIC testing. Thus, it is of interest to find out if there’s any linear relationship existed between these two toughness properties of brittle material. Annealing, normalizing, and austempering heat treatment were applied to FG and CG irons to alter their matrix structures so as to obtain a range of static (KIC) and dynamic (impact) toughness values. A third toughness, calculated by integrating the area under the load versus CGD (Clip Gage Displacement) curve in KIC testing, was termed ‘calculated toughness’ and was also listed for comparison purposes. It was found, among dynamic impact toughness (X), static KIC (Y), and calculated toughness (Z), linear relationships exist for flake graphite cast iron as: Y=4.02X−0.81 Z=1.75X+2.99 and for compacted graphite cast iron as: Y=0.86X+20.2 Z=0.77X+4.77.

Abstract: A threaded steel coupling with an exterior coating and interior case and threads, wherein the coupling body consists primarily of bainite and the interior case and threads consist primarily of a mixture of martensite and bainite. Also provided is a method of fabrication, including selective carburization of the interior threaded portion of the steel coupling forming the case and austempering.

Abstract: Recent research has reported that austempered ductile irons (ADI) suffer a marked embrittlement when the material is tested in tension with its surface in contact with water. The objective of this ...

Abstract: The invention relates to a method for austempering steel parts according to which the steel parts are firstly austenitized and are subsequently quenched to a starting temperature (T2) which is higher than the martensite starting temperature (TM) of the steel parts. Afterwards, a first isothermal storage of the steel parts is firstly carried out at starting temperature (T2) and over a first period (Δtiso, 1). A second isothermal storage of the steel parts is then carried out over a second period (Δtiso, 2) and at a finishing temperature (T3) that is higher than the starting temperature (T2). The inventive method is especially suited for rapidly austempering steel parts which makes it possible to obtain a pure bainite structure and to adjust the core hardness of the obtained steel parts by altering the starting temperature (T2), the finishing temperature (T3), the duration of the first period (Δtiso, 1) and the duration of the second period (Δtiso, 2).

Abstract: Microstructural changes during the austempering heat treatment of alloyed ductile iron are described. The effect of heat treatment cycle and casting structure on mechanical properties of Austempered Ductile Iron, ADI, of composition 3.52%C, 2.64%Si, 0.25%Mo, 0.25%Cu, 0.67%Mn are studied. Comparison of EDX analysis with mechanical properties show that the optimised properties for an ADI are achieved when an ausferritic structure of high carbon austenite and ferritic plates with minimum martensite and carbides is formed. Processing Window is the period of austempering time over which the structure is fully ausferritic The results show that for a high Mn DI, single austempering process does not provide a fully ausferntic structure and usually further austempering process, double or stepped austempering process, is required. The experimental results demonstrate that such an ADI still might satisfy the ASTM standard with careful control over austempering parameters. This study confirms that some casting features like low nodules count and preferential segregation of alloying elements narrow the processing window This study also shows that the microstructural defects like microporosity and poor modularity have a detrimental effect on properties of ADI.

Abstract: PROBLEM TO BE SOLVED: To produce a steel sheet having a soft structure in the shipping stage of a steel maker, and in which tensile strength(TS) is controlled to >=1800 N/mm2 and tensile strength(TS)×elongation(El) is controlled to >=18×104 N/mm2% by heat treatment after working at a customer SOLUTION: This high carbon thin steel sheet has a steel compsn contg 045 to 075% C, 005 to 05% Si, 005 to 100% Mn, 00020 to 00080% N also so as to satisfy (Mn+Cr+Mo+ Ni): 08 to 20%, and the balance substantial Fe with inevitable impurities, having a ferrite+spheroidized cementite structure and moreover having 180 to 280 Vickers hardness Hv, and after austempering, bainite, tempered martensite and 1 to 20 vol% residual austenite are formed

Abstract: The effects the leading factors bearing on fatigue limits were investigated with three kinds of ductile iron specimens various microstructures. As a result of examination, the fatigue limits in relationship to hardness and tensile strength, the expected higher improvement for fatigue limits in the case of the high strength specimens that experienced austempering treatment are not observed in comparison with the specimens treated with stress relief treatment. The estimated maximum defect size is one of the important parameters in predicting and evaluating fatigue limits for three different heat-treated ductile cast irons. Also, a quantitative relationship can be established between the fatigue limit and maximum defect size. Moreover, it is possible to explain the difference in fatigue limits in the three ductile cast irons by application of the rates of non-propagating crack which connects the adjacent graphite nodules before it stops.

Abstract: A non-austempered spheroidal graphite cast iron obtained without austempering, and having a tensile strength of 650 to 850 MPa and an elongation of 7.0 to 14.5%, wherein a fatigue limit of its V-notched material is at least 290 MPa, the spheroidal graphite cast iron having well-balanced mechanical properties of a tensile strength and elongation and being highly strong and tenacious with improved tensile strength and elongation.

Abstract: The effect of a modified austemper coupled with interrupted quenching (IQ Aus) on the bending fatigue properties of Fe-0.6C-0.5Si-0.8Mn steel has been studied to determine the validity of using IQ Aus steel in possible environmentally conscious material applications. The bending fatigue stress of steel can be improved by IQ Aus: conventional austenitization at 1133 K followed by interrupted quenching a 533 K and then austempering at 673 K for a required time followed by subsequent water quenching and 473 K tempering. The IQ Aus steel had a triple structure consisting of carbide-free upper bainite, 26 vol.% retained austenite and 10 vol.% tempered martensite. Compared to the conventional austemper (Con Aus), the IQ Aus increased the bending fatigue limit stress. Compared to the quench and temper (QT), the IQ Aus showed a significantly decreased fatigue notch factor while there was little difference between the fatigue limit stress of both steels. The results are described and discussed in terms of fractography, etc.

Abstract: Microstructure, hardness and wear characteristics were studied for: (1) Austempered SG-iron (ADI); and (2) low alloyed SG-iron. Comparison has been made between the properties of these two types and that of conventional SG-iron. The present ADI samples were produced by austenitising at 1203K, for 3.6 ks and austempered at 773K for 1.8 ks. The second type was prepared by adding low percentages of Ni, Cr, Mn and Mo to SG-iron. The microstructure of ADI consists of upper bainite and retained austenite, while the low alloyed SG-iron showed the graphite nodules to be surrounded by ferrite, pearlite, and iron carbides. Macrohardness study showed a maximum value for low alloyed SG-iron, and a minimum for conventional SG-iron, and hardness of ADI is intermediate between the two irons. The wear properties were determined using pin on ring machine, under dry sliding conditions at room temperature. The variation of wear rate with sliding distance, at variable loads and speeds were studied. The wear mechanisms were investigated by means of subsurface observations with an optical microscope. Microhardness test was used to study the change in the matrix strength with distance from the worn surface due to plastic deformation. Mild wear was observed for a wide range of sliding distances in the ADI. On the other hand, its range in low alloyed SG-iron was very narrow and most of the curves of mass loss revealed severe wear.

Abstract: A new type of wear resistant high silicon cast steel was developed Scanning electron microscopy was used to reveal the microstructure in of the austempering process detail Tensile tests, impact tests and hardness tests were performed for different austempering combinations The results show that a pure ausferrite structure that consists of bainitic ferrite and carbon riched retained austenite can be obtained by austempering treatment of high silicon cast steel over a large temperature range (240～400℃) No carbide would precipitate in the structure It was also found that a dual phase structure with high strength, good toughness and high hardness can be obtained after austempering at 280～360℃ The ausferrite structure has excellent properties including excellent work hardening

Abstract: The modified austempering was applied on the ductile cast iron (DCI) to enhance its mechanical properties. This treatment named ausquenching consists of short time austempering, direct water quenching and light tempering. In this combined heat treatment, the first austempering process takes much effect on the tensile property and toughness of ausquenched DCI (AQDI). AQDI shows higher 0.2% proof stress, tensile strength and fracture toughness than the austempered DCI (ADI) at the temperature range of upper bainite. AQDI has a complex structure of bainitic-ferrite, light tempered martensite and retained austenite. For the purpose of quantitative evaluation on the compound matrix of the martensite and the bainitic-ferrite, the X-ray diffraction profiles of α-Fe were analyzed by the curve fitting technique using Pseudo-Voight function. The profile was able to separate into two parts by the difference of carbon content. From these results, it was possible to estimate appropriate each phase fraction of the complex structure.