Abstract: 4340 steel bars were austenitized at 850 °C for 1 h followed by heating at 700 °C for 90 min and quenching into a salt bath at the temperature range of 300–450 °C for 1 h to obtain dual structures with 34 vol.% fraction ferrite and various bainite morphologies. SEM studies showed that by increasing the austempering temperature, bainite morphology varies from lower to upper bainite. Tensile, impact and hardness tests revealed that increasing the austempering temperature from 300 to 400 °C leads to a reduction in yield and ultimate tensile strength, hardness, uniform and total elongation and impact energy. But in dual phase steel produced by austempering at 450 °C, yield and tensile strength and hardness increased and severe reduction in total elongation and impact energy obtained. Fractography of tensile specimens showed brittle behavior for this austempering temperature. Fatigue test results showed that fatigue limit decreases with increasing austempering temperature from 300 to 400 °C. Finally, fractography studies showed cleavage fracture at the surface of fatigue specimens austempered at 400 °C, which confirms the tendency to brittle behavior.

Abstract: An investigation was carried out to examine the influence of austempering temperature on microstructural parameters and the wear behaviour of austempered ductile iron. Ductile iron was austenitised at 900 °C for 30 min and austempered for 2 h at 260, 280, 300, 320, 350, 380 and 400 °C. Resulting microstructures were characterised through optical microscopy and X-ray diffraction. Wear test was carried out using a pin-on-disc machine with sliding speed of 289 m min−1. Coarse ausferrite microstructure exhibited higher wear rate than fine ausferrite microstructure. At high austempering temperature large amounts of austenite was instrumental in improving the wear resistance through formation of deformation induced martensite. Study of the wear surface under scanning electron microscope showed that, under dry sliding condition, wear occurred mainly due to adhesion and delamination. Wear rate was found to be dependent on the yield strength, austenite content and its carbon content.

Abstract: A new ausferritic steel with high strength and exceptionally high fracture toughness has been developed. This steel has been synthesized integrating concepts from Austempered Ductile Cast Iron (ADI) technology. The influence of the austempering temperature on the microstructure and mechanical properties of this steel at room temperature and ambient atmosphere has been examined. The effect of microstructure on the plane strain fracture toughness and on the magnetic, electrical, and thermal properties was also investigated. Compact tension and cylindrical tensile specimens prepared from the low alloy medium carbon steel with high silicon content were initially austenitized at 927 °C for 2 h and then subsequently austempered at several temperatures between 260 °C (500 F) and 400 °C (750 F) to produce different microstructures. The microstructures were characterized by X-ray diffraction, scanning electron microscopy and optical metallography. A combination of exceptionally high yield strength (1336 MPa) and a high fracture of toughness of 116 MPa√m (a value comparable to maraging steel) was obtained in this steel after austempering at 316 °C (600 F) for 2 h. Potential applications of this steel include the inexpensive fabrication of armored plates and components requiring high reliability and durability.

Abstract: In the present work, the transformation characteristics of ductile iron austempered from intercritical austenitization temperature ranges were investigated. For this purpose, an unalloyed ductile cast iron containing 3.50 wt% C, 2.63 wt% Si and 0.318 wt% Mn were intercritically austenitized (partially austenitized) at various temperatures and then rapidly transformed to a salt bath held at the 365 °C for austempering for various times to produce dual matrix structure with different ausferrite volume fractions in ferrite matrix. A microstructure map was created to illustrate the transformation of products quantitatively as a function of austempering time for a particular intercritical and austempering heat treatment temperature and time. It was demonstrated that the total volume fraction of transformed phases was approximately constant for all austempering times after rapidly transforming samples from a particular intercritical temperature to austempering temperature. It was found out that the new ferrite (It is also called epitaxial ferrite) introduced into the intercritically austenitized structure during austempering and its content was dependent on the intercritical austenitizing temperature and austempering time.

Abstract: In this study, the machinability of austempered ductile iron (ADI) having a ferritic structure was examined. For this purpose, three types of ductile iron materials (as cast, ADI-250, ADI-375) and two different types of cutting tool materials (ceramics and cermet) were used. To emphasize the role of austempering process, ductile iron (DI) specimens are first austenitized in salt bath at 900°C for 120 minutes after which they are quenched in salt bath at 250°C (ADI-250) and 375°C (ADI-375) for 120 min. Machining tests were carried out at various cutting speeds (100–500 m/min) under the constant depth of cut and feed rate. The performance of both ceramic and cermet tools were evaluated based on the workpiece surface roughness and flank wear. Wear conditions of the cutting tools were characterized by scanning electron microscope. The results point out that the lower austempering temperature results in increasing of the cutting forces, while better surface roughness is obtained. Additionally, the results indicate that the tool wear occurs mainly on the flank face. However, higher cutting speed results in chipping formation in cermet cutting tool.

Abstract: The volume fraction of high carbon austenite present in the microstructure of austempered ductile iron (ADI) is one of the important factors that influence the mechanical and physical properties of the alloy. Formation of martensite by TRIP (transformation induced plasticity) mechanism during the machining operation in which a large amount of stress is applied to the microstructure results in a decrease in machinability of austempered ductile iron which has affected the expansion of ADI in industry. In this article, the effect of depth of cut as a machining variable is assessed in an alloyed austempered ductile iron containing Cu, Ni and Mo. The measurements of mechanical properties including impact energy, tensile strength, hardness and microhardness along the cross-section of samples are reported for samples austenitized at 870 °C followed by austempering at 375, 340 and 300 °C. Results indicate that contrary to the behavior of many alloys, in austempered ductile iron, reducing the depth of cut will not improve the machinability. In the case of studied composition, cutting with depths of 0.5 and 0.1 mm had the best and worst results, respectively.

Abstract: Super Bainite Steel is described comprising between 90 % and 50 % bainite, the rest being austenite, in which excess carbon remains within the bainitic ferrite at a concentration beyond that consistent with equilibrium; there is also partial partitioning of carbon into the residual austenite. Such bainite steel has very fine bainite platelets (thickness 100nm or less). In this specification the expression "Super Bainite Steel" is used for such steel. In particular, the impact of varying the manganese content to achieve fast transformation times, and hence low manufacturing costs without the presence of expensive alloying materials is discussed. In one embodiment of the invention a Super Bainite Steel comprises in weight percent: carbon 0.6 to 1.1 %, silicon 1.5 to 2.0 %, manganese 0.5 to 1.8 %, nickel up to 3 %, chromium 1.0 to 1.5 %, molybdenum 0.2 to 0.5 %, vanadium 0.1 to 0.2 %, balance iron save for incidental impurities. In particular it was noted that excellent properties were obtained if the manganese content is about 1% by weight. Various processes for making the Super Bainite Steel are discussed, but a particularly useful process includes the step of cooling the steel from an austenite quickly enough to avoid transformation to pearlite and transforming the steel to bainite at a temperature in the range 190°C to 2500°C. The patent discusses the impact of changing the transition temperature on hardness, and conclude that the invention can provide a very hard steel (>630HV) It is also noted that suitable pearlite can be produced for cutting drilling and shaping, before final transformation to Super Bainite Steel.

Abstract: In the present investigation, the influence of austempering treatment on the microstructure and mechanical properties of silicon alloyed cast steel has been evaluated. The experimental results show that an ausferrite structure consisting of bainitic ferrite and retained austenite can be obtained by austempering the silicon alloyed cast steel at different austempering temperature. TEM observation and X-ray analysis confirmed the presence of retained austenite in the microstructure after austempering at 400 °C. The austempered steel has higher strength and ductility compared to as-cast steel. With increasing austempering temperature, the hardness and strength decreased but the percentage of elongation increased. A good combination of strength and ductility has been obtained at an austempering temperature of 400 °C.

Abstract: The influence of the thermal cycle and austempering treatment on the mechanical behavior of a 0.56C–1.43Si–0.58Mn–0.47Cr (wt%) steel has been investigated. The thermal cycle consisted of heating the steel to 800°C or 900°C, in the intercritical and austenitic region respectively, fast cooling down to 600°C or 400°C, followed by 300 s hold. After austempering the materials were cooled at different rates and then submitted to tensile testing. The total elongation of 15–20% and tensile strength of 1300–1400 MPa were reached after heating to 900°C and transformation at 400°C. The strain-induced austenite transformation to martensite during the plastic deformation (Transformation Induced Plasticity Effect) is responsible for this combination of high strength and ductility. Silicon acts to stabilize the austenite during austempering. However, the stabilized austenite can be transformed and the microstructure modified, resulting in the formation of others constituents such as bainitic ferrite, upper bainite and martensite.

Abstract: Boronizing and austempering were successively applied to a GGG-40 grade ductile iron in order to combine the advantages of both process in a single treatment. This new procedure formed a 30 μm thick boride layer on the surface with subsurface matrix structure consisted of acicular ferrite and retained austenite. Reciprocating wear tests showed that successive boronizing and austempering exhibited considerably higher wear resistance than conventional boronizing having a subsurface matrix structure consisting of ferrite and pearlite.

Abstract: The invention discloses a carbide-containing austempered ductile iron plowshare, which uses austempered ductile iron as a raw material, wherein the ductile iron comprises the following chemical components in percentage by weight: 3.40 to 3.80 percent of C, 2.20 to 2.80 percent of Si, 0.20 to 0.50 percent of Mn, less than or equal to 0.03 percent of P, less than or equal to 0.02 percent of S, 0.03 to 0.04 percent of Mg, 0.01 to 0.02 percent of Re, 0.25 to 0.5 percent of Cr, and the balance of Fe; the graphite metallurgical structure in the ductile iron is characterized by a spheroidization rate of above grade-2, a graphite size of above grade-6 and a graphite quantity of more than 100 per square millimeters. The matrix of the ductile iron is martensite and lower bainite and residual austenite and carbide, wherein the carbide is less than 2 weight percent. The carbide-containing austempered ductile iron plowshare has the advantages of improving the conventional process for finely casting plowshares by using low alloy steel in the past, having a service life which is more than three times as long as that of the low alloy steel plowshares and a price as low as two thirds of that of the low alloy steel plowshares and greatly reducing agricultural production cost.

Abstract: In the present work were evaluated the microstructural changes and mechanical properties exhibited by ductile iron when it was heat treated in the intercritical region (α+γ) and then austempered at 375◦C. For this purpose, ductile iron specimens were heated to the austenitizing temperature in the range of 780 to 830◦C for 90 minutes and then austempered at 375◦C for 60 minutes. This treatment was aimed to induce a duplex structure constitued of pro-eutectoid ferrite and ausferrite. A comparison of the properties exhibited by the heat treated ductile iron with conventionally processed ductile irons austenitized at 860◦C, indicated that the material strength was not significantly modified. However, the impact strength and elongation show appreciable improvements. The enhanced in both properties of the heat treated ductile iron with and without alloying elements (1Ni-0.24Mo) was related to the presence of a duplex matrix. In particular, the best results of impact strength were found when the ductile irons were heat treated in the intercritical region between 800 830◦C and austempered at 375◦C. Impact strength of 130 145 J and 100 140 J were obtained for unalloyed and alloyed ductile iron, respectively. These results are comparable with fully ferrite structure (intercritical heating at 780◦C) and higher than totally ausferrite structure (austenitizing at 860◦C).

Abstract: In order to produce formed steel parts in a simple process, said parts having high strength and good residual elongation at break, according to the invention a primary steel material is provided which (in % by weight) comprises C: 0.02 - 0.6%, Mn: 0.5 - 2.0%, Al: 0.01 - 0.06%, Si: max. 0.4%, Cr: max. 1.2%, P: max. 0.035%, S: max. 0.035%, and optionally one or more of the elements of the "Ti, Cu, B, Mo, Ni, N" group, with the proviso that Ti: max. 0.05%, Cu: max. 0.01%, B: 0.0008 - 0.005%, Mo: max. 0.3%, Ni: max. 0.4%, N: max. 0.01%, and the remainder as iron and inevitable contamination. The primary material is heated through at a heating temperature (TA) ranging between the AcI and Ac3 temperature such that at best incomplete austenitization of the primary material takes place, is placed into a press-form tool and formed therein into the formed steel part. The formed steel part is then heated to a bainite forming temperature (TB), which is above the martensite starting temperature (Ms), however below the perlite transformation temperature of the steel from which the primary material is produced in each case. After cooling, it is maintained for an austempering period (tB) at the bainite forming temperature (TB) in a substantially isothermic manner until the formed steel part has produced a structure comprising predominantly ferrite and bainite, the martensite content thereof being < 5%, wherein residual austenite contents of ≤ 10% may be present. After the end of the austempering period (tB), the formed steel part is brought to room temperature. ..

Abstract: The effect of austempering temperature on the microstructure and properties of a high chromium white cast iron was investigated with the Rietveld refinement method. The result shows that the upper bainite exists in the sample austempered at 623 K and the martensite, lower bainite, M7C3, and retained austenite exist in the samples austempered at 563 K and 593 K. The relative content of the retained austenite increases with increasing the austempering temperature from 563 K to 623 K. The higher hardness, impact toughness and impact abrasive wear resistance can be obtained for the specimen austempered at 593 K.

Abstract: Boronizing and austempering were successively applied to a GGG-40 grade ductile iron in order to combine the advantages of both process in a single treatment. This new procedure formed a 30 μm thick boride layer on the surface with subsurface matrix structure consisted of acicular ferrite and retained austenite. Reciprocating wear tests showed that successive boronizing and austempering exhibited considerably higher wear resistance than conventional boronizing having a subsurface matrix structure consisting of ferrite and pearlite.

Abstract: The in-situ X-ray diffraction observations of the bainitic transformation of high silicon cast steel were performed using the high temperature X-ray diffraction technique. The volume fraction and carbon content of austenite depend on the transformation temperature. The experimental result has shown that the volume fraction of austenite ceases to a constant value which indicate that the transformation is almost finished after holding for about 1000 s. Asymmetry diffraction peaks are obtained for samples at the early stage of transformation due to a heterogeneous distribution of carbon in different regions of austenite and thus exists two types of austenite: low-carbon austenite (γLC) and the high-carbon austenite (γHC). The volume fraction of bulk austenite with low carbon decreases greatly at the early stage of transformation and then tends towards zero. The lattice parameter of both low-carbon and high-carbon austenite increases with the holding time due to the carbon partition from the supersaturated ferrite to the austenite. The experimental results supports that the bainite growth is by a diffusionless mechanism when austempering temperature is in the lower bainite transformation temperature range.

Abstract: In this paper the analysis of thin walled castings made of ductile iron is considered. It is shown that thin wall austempered ductile iron can be obtained by means of short-term heat treatment of thin wall castings without addition of alloying elements. Metallographic examinations of 2 mm thin walled castings along with casting with thicker wall thickness (20x28 mm) after different austempring conditions are presented. It has been proved that short-term heat treatment amounted 20 minutes of austenitizing at 880 o C followed by holding at 400 o C for 5 minutes causes ausferrite matrix in 2 mm wall thickness castings, while casting with thicker wall thickness remain untransformed and martensite is still present in a matrix. Finally there are shown that thin wall ductile iron is an excellent base material for austempering heat treatments. As a result high mechanical properties received in thin wall plates made of austempered ductile iron.

Abstract: This study utilized electroless nickel (EN) and cathodic arc evaporation (CAE) technologies, with the known advantage of low processing temperature (EN = 90 °C and CAE = 230 °C), to treat the austempered ductile iron (ADI) substrate. The eligibility of applying the EN and CAE–CrTiAlN duplex coatings on ADI, along with the coating properties, such as structure, roughness, and adhesion, were evaluated and analyzed. Moreover, polarization and immersion tests were performed to further understand the effects of the coatings on the corrosion resistance of ADI. The results showed that the unique microstructure of ADI did not deteriorate after EN and CAE treatments. With regard to corrosion resistance, the duplex coated specimens performed better than did the uncoated and monolithic EN or CrTiAlN coated ones in 3.5 wt.% NaCl and 10 vol.% H 2 SO 4 aqueous solutions.

Abstract: 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.

Abstract: Bainitizing is used in today's industry when high toughness of steel components is required in combination with high hardness values. Compared to martensite, the main advantages of bainite ...

Abstract: We investigated the effects of austempering and subzero treatment on the damping capacity in austempered ductile cast iron. The damping capacity of austempered ductile cast iron was rapidly increased by the austempering treatment, although it was not affected by the austempering temperature or time. After subjecting the austempered ductile cast iron to subzero treatment, the austenite was transformed into martensite, and the volume fraction of the martensite increased as the subzero treatment temperature decreased. The subzero treatment sharply increased the damping capacity of the austempered ductile cast iron. However, the damping capacity gradually increased as the subzero treatment temperature decreased. By increasing the subzero treatment time, the damping capacity rapidly increased until the subzero treatment time reached 30 min, after which it increased gradually. By increasing the volume fraction of the martensite, the damping capacity was rapidly increased until the volume fraction was 5%, beyond which it increased gradually.

Abstract: The invention relates to an austempering bainite spheroidal graphite cast iron and application thereof The compositions by weight percent of the austempering bainite spheroidal graphite cast iron are 350 to 38 percent of carbon, 22 to 27 percent of silicon, 02 to 05 percent of manganese, less than or equal to 007 percent of phosphor, less than or equal to 003 percent of sulfur, 003 to 006 percent of magnesium, 001 to 004 percent of rhenium, 045 to 075 percent of copper, and the balance being iron The austempering bainite spheroidal graphite cast iron is used as a fitting part of a pump or a fitting part of a pulling machine The austempering bainite spheroidal graphite cast iron has the advantages that: firstly, the austempering bainite spheroidal graphite cast iron has superior comprehensive performance, is easy to manufacture and has low cost; secondly, the austempering bainite spheroidal graphite cast iron has long service life, low manufacturing cost, superior corrosion resistance and abrasion resistance, and good strength, plasticity and toughness; and thirdly, the industrial production of the austempering bainite spheroidal graphite cast iron on pump products, particularly the application of the austempering bainite spheroidal graphite cast iron on marine pump products and mine pump products and the application of the austempering bainite spheroidal graphite cast iron as the fitting part of the pulling machine effectively improve the product performance in the two industries and can bring about significant economic benefit