Showing papers on "Austempering published in 1990"
TL;DR: The morphology of continuously cooled bainite in steels is examined in this article and compared with that of isothermally transformed bainites, and a classification system for bainitic microstructures is also developed.
Abstract: The morphology of continuously cooled bainite in steels is examined in this review and compared with that of isothermally transformed bainite. Some experimental observations of microstructures in continuously cooled commercial steels are also presented; these results demonstrate the presence of microstructures which are not easily defined in terms of any of the “classical” bainitic morphologies. The numerous terms created over the last 50 years to describe specific bainite morphologies have led to some confusion, and it is suggested that the commonly used terminologies do not adequately describe the full range of bainitic microstructures which are observed. A general definition for the bainite transformation is proposed. A classification system for bainitic microstructures is also developed, encompassing both isothermally transformed and continuously cooled bainites. It is suggested that primary bainite morphologies be classified as B1, B2, or B3, depending on whether the acicular ferrite is associated with (1) intralath precipitates, (2) interlath particles/films, or (3) discrete regions of retained austenite and/or secondary transformation product(e.g., martensite or pearlite), respectively. Possible ambiguities with the descriptions of autotempered martensite and Widmanstatten ferrite are also discussed, and a number of areas are identified where further work would be helpful.
261 citations
TL;DR: In this article, a Cu-Mo ductile iron was austempered at 633 K for 2 h and then laser hardened, and the sliding wear characteristics against a heat treated 52100 steel were compared with the results obtained from normalized specimens with and without laser hardening.
36 citations
TL;DR: In this paper, the sliding wear behavior of various microstructural combinations obtained by austempering ductile cast iron (3.7 wt.%, 2.54 wt., 0.45 wt.).
31 citations
TL;DR: In this article, the effects of austempering temperature and isothermal transformation time on the low-cycle fatigue (LCF) behavior in ductile irons have been studied and the fracture surfaces were observed by a scanning electron microscope in order to understand the fracture mechanism of LCF.
19 citations
TL;DR: In this article, the effect of austenitising temperature on the microstructure, mechanical properties, and dimensional stability of a spheroidal graphite iron containing copper and nickel has been investigated.
Abstract: The effect of austenitising temperature on the microstructure, mechanical properties, and dimensional stability of a spheroidal graphite iron containing copper and nickel has been investigated. It was found that as the temperature increased the amount of carbon taken into solution by the austenite increased thus reducing the driving force of the original austenite to bainitic ferrite and high carbon austenite. As a consequence, the amount of retained austenite increased, but its stability decreased. This placed an upper limit on the austenitising temperature and on the amount of retained austenite permissible. All properties other than hardness showed maximum values after austenitising at 900°C. It was also found that increasing the solution treatment temperature increased the dimensional stability.MST/1116
17 citations
Patent•
26 Oct 1990
TL;DR: An austempered ductile iron differential gear and method of manufacture is described in this article, where the gear is cast to near net shape in a vertical injection, flaskless molding machine using delayed inmould inoculation to ensure greater homogeneity of the alloy melt.
Abstract: An austempered ductile iron differential gear and method of manufacture. The gear is cast to near net shape in a vertical injection, flaskless moulding machine using delayed inmould inoculation to ensure greater homogeneity of the alloy melt. The gear casting is allowed to cool, then austenized at a temperature of 1628° F. for a period of approximately 11/2 hours, and subsequently austempered in a quench bed at a temperature of approximately 526° F. for a period of approximately four hours.
16 citations
TL;DR: In this article, a modified oil quenching (MOQ) treatment was compared with its corresponding conventional treatment, which significantly improved the notched tensile strength of the steel with slightly increased 0·2%PS and UTS.
Abstract: The low temperature mechanical properties of 0·4C–Cr–Mo–Ni steel can be improved significantly by thefollowing treatments. Modified oil quenching (MOQ): interrupt quenching at 573 K just below the martensitic transformation temperature followed by short time tempering at 673 K (up-quenching) before oil quenching and subsequently 473 K tempering (after conventional 1133 K austenitisation). Modified austempering (MA): the same up-quenching treatment followed by austempering at 673 K and subsequently water cooling. Each modified treatment was compared with its corresponding conventional treatment. The MOQ treatment significantly improved the notched tensile strength of the steel with slightly increased 0·2%PS and UTS, owing to an increase infracture ductility over the temperature range 123–203 K and also improved the Charpy impact energy of the steel over the temperature range 203–373 K. As a result of the MA treatment, the 0·2%PS and UTS and the notched tensile strength were developed remarkably wi...
12 citations
TL;DR: In this paper, as-cast and heat-treated materials of spheroidal graphite cast iron from room temperature to 500°C were used for axial load fatigue tests.
10 citations
Patent•
1 Feb 1990
TL;DR: In this article, the title cast iron in which matrix structure is regulated to the mixed one of bainite and residual astenite by casting low alloy ductile cast iron having specific compsn.
Abstract: PURPOSE:To manufacture the title cast iron in which matrix structure is regulated to the mixed one of bainite and residual astenite by casting low alloy ductile cast iron having specific compsn. and thereafter subjecting it to austempering heat treatment. CONSTITUTION:The parts such as a bolt and a nut for connecting by low alloy ductile cast iron contg., by weight, 3.4 to 3.8% C, 2.4 to 3.0% Si, 0.2 to 0.6% Mn and =10% elongation.
7 citations
01 Dec 1990-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the hardness, ultimate tensile strength and dynamic elastic modulus are presented for a commercially available unalloyed compacted iron (C.E. 4.31) and correlated with different matrix microstructures (as-cast, ferritized, normalized and austempered).
Abstract: Austempered cast irons have been the subject of much attention in recent years because of their excellent mechanical properties. The hardness, ultimate tensile strength and dynamic elastic modulus are presented for a commercially available unalloyed compacted iron (C.E. 4.31) and correlated with different matrix microstructures (as-cast, ferritized, normalized and austempered). For this study, two isothermal temperatures for the austempering treatment were chosen: 400°C and 300°C. The influence of a ferritizing treatment prior to normalizing and austempering has been evaluated, the results indicating that no advantages are obtained with this additional treatment. The influence of microstructure on properties and on the resulting fracture surfaces in tensile tests are discussed.
5 citations
Patent•
8 Jun 1990
TL;DR: In this paper, shot peening is applied to a cast iron member to improve surface hardness and the formation of residual compressive stress in the surface part, by which the ferrous member remarkably improved in fatigue strength can be obtained.
Abstract: PURPOSE:To manufacture a ferrous member excellent in fatigue strength by subjecting a cast iron member to austempering treatment under specific conditions, heating a part requiring fatigue strength under specific conditions, and then applying shot peening to the above part. CONSTITUTION:Austempering treatment is applied to a cast iron member to form a structure containing >=30% retained austenite, by which high strength and high toughness as the whole cast iron member are obtained. Subsequently, only the part requiring fatigue strength is heated up to 420-650 deg.C, by which retained austenite in the vicinity of the surface of the above part is decomposed into cementite and ferrite and surface strength is increased. Further, shot peening is applied to the above part to improve surface hardness and the formation of residual compressive stress in the surface part. By this method, the ferrous member remarkably improved in fatigue strength can be obtained.
1 Jan 1990
TL;DR: In this article, the effects of varying austempering parameters on the response of S.G. cast iron to plasma nitriding and nitrocarburizing was studied, and the results were explained by the different distributions of cementite arising when the differently austempered micro-structures were tempered on heating to the nit riding temperature.
Abstract: The effects of varying austempering parameters on the response of S.G. cast iron to plasma nitriding and nitrocarburizing was studied. The ideal austempered microstructure of bainite and austenite yielded poor compound layers and the shallowest case depth. A microstructure consisting wholly of bainite obtained by austempering at too high a temperature yielded the best surface-engineered product. Adding carburizing potential to the plasma reduced the thickness of compound layers and case depth. The results were explained by the different distributions of cementite arising when the differently austempered microstructures were tempered on heating to the nitriding temperature. It is concluded that S.G. iron destined to be plasma nitrided should be austempered at higher than normal temperatures, and that nitriding should be preferred to nitrocarburizing.
Patent•
9 Jan 1990
TL;DR: In this paper, shot peening treatment is applied to practically the whole surface of the cast member to induce martensitic structure in the surface layer, by which a metallic structure having the desired high hardness is formed.
Abstract: PURPOSE:To improve machinability in machining by applying shot peening treatment to the whole surface of an austempered cast member and then subjecting only the part to be machined to tempering treatment at a specific temp. CONSTITUTION:A cast member made of spheroidal graphite cast iron or cast steel is subjected to austempering treatment, by which a matrix structure as a whole is formed into a mixed structure of bainite and retained austenite to improve strength and toughness. Subsequently, shot peening treatment is applied to practically the whole surface of the cast member to induce martensitic structure in the surface layer, by which a metallic structure having the desired high hardness is formed. Then, only the part to be machined of the cast member is subjected to tempering treatment at 250-400 deg.C and the above martensitic structure in the surface layer is decomposed into troostite structure of low hardness. By this method, machining can be applied to the required part easily without influencing the internal matrix structure of the cast member.
Patent•
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19 Apr 1990
TL;DR: In this paper, an outer ring made of high-strength nodular graphite cast iron and the inner ring 2 of flake graphite composite cast iron are integrated by fitting, and the integrated material is austempered into austenite at 850-950 deg.C and then into bainite at 220-350 deg C.
Abstract: PURPOSE:To obtain the title gear excellent in strength and vibration damping ability by integrating an outer ring made of nodular graphite cast iron on the tooth side and an inner ring made of flake graphite cast iron on the shaft hole side by fitting, and then austempering the integrated material under specified conditions. CONSTITUTION:The gear is composed of the outer ring 1 and the inner ring 2, and a tooth 3 is provided to the periphery of the outer ring 1 and the shaft hole 4 to the inner periphery of the inner ring 2. The outer ring 1 is made of high-strength nodular graphite cast iron, and the inner ring 2 is made of the flake graphite cast iron having excellent vibration damping ability. The outer ring 1 and the inner ring 2 are integrated by fitting, and the integrated material is austempered into austenite at 850-950 deg.C and then into bainite at 220-350 deg.C. By this method, a gear wherein the strength and vibration damping ability are appropriately balanced is obtained. Furthermore, a mixed structure of bainite and residual austenite is obtained by the austempering, the interface between both structures contributes to the improvement of the vibration damping ability, and the vibration damping ability of the nodular graphite cast iron and the strength of the flake graphite cast iron are improved.
Patent•
31 Jul 1990
TL;DR: In this paper, lost pattern casting was used to form a carburized layer on the surface of the cast article, which was then hardened by heat treatment, and a cast article having high resistance to fatigue was obtained.
Abstract: PURPOSE:To save energy in austempering and to reduce the treating time by taking out a cast article from a casting mold when the article is cooled to a specified temp., soaking the article in a prepared austenitizing furnace, then quenching the article in a thermostatic bath, and holding the article at a specified temp. CONSTITUTION:Cast iron is cast, and the cast article is taken out from a casting mold when the article is cooled to 400-900 deg.C in the course of solidification. The article is soaked in the prepared austenitizing furnace, then immediately quenched in the thermostatic bath, and held for a specified time to allow the isothermal transformation to proceed. The cast steel is cast by the lost pattern casting method to form a carburized layer on the surface of the cast article. The carburized layer is hardened by heat treatment. By this method, a cast article having high resistance to fatigue is obtained.
Patent•
7 Feb 1990
TL;DR: The spheroidal graphite cast iron obtd. by this method can be formed into a high strength material combining excellent strength and elongation by subjecting it to austempering treatment.
Abstract: PURPOSE:To manufacture the title cast iron having excellent toughness by austempering treatment by incorporating specific ratios of C, Si, Mn, S, P, Cu, Sb and Mg into Fe. CONSTITUTION:The spheroidal graphite cast iron contg., as chemical components, by weight, 3.0 to 4.0% C, 2.0 to 3.0% Si, 0.4 to 0.6% Mn, <=0.02% S, <=0.06% P, 0.4 to 0.8% Cu, 0.01 to 0.03% Sb, 0.03 to 0.06% Mg and the balance Fe with inevitable impurities is prepd. The spheroidal graphite cast iron obtd. by this method can be formed into a high strength material combining excellent strength and elongation by subjecting it to austempering treatment.
Journal Article•
TL;DR: In this paper, the influence of deformation of austenite at 300 o C on the kinetics of bainite formation, the structure and mechanical properties of steel 60KhNS2M was investigated.
Abstract: An investigation is made of the influence of deformation of austenite at 300 o C on the kinetics of bainite formation, the structure and mechanical properties of steel 60KhNS2M. The method of electron diffraction microscopy is used to show that, as a result of the formation of deformation twins in the austenite, the grouping of α-crystals of bainite is changed and their size diminishes, as does the size of the regions of retained austenite, causing an improvement in the mechanical properties of the steel with bainitic-austenitic structure. Further cold rolling by 5-7% results in the formation of the largest regions of retained austenite of the lightning-shaped groups of martensite crystals
Patent•
20 Jul 1990
TL;DR: In this article, a roll tire supporting a cylindrical metal mold of a device for centrifugally forming a Hume pipe is manufactured by forming the matrix structure of a spheroidal graphite cast iron stock into a mixed structure of bainite, retained austenite, and Spheroid al graphite by means of austempering treatment where the stock as it is, after rough working, or after finish working is heated and held at 800-900 degC for 05-3hr, rapidly cooled down to 200-400 degC, and held for >=
Abstract: PURPOSE:To manufacture the roll tire excellent in wear resistance by forming the matrix structure of a stock made of spheroidal graphite cast iron into a mixed structure of bainite, retained austenite, and spheroidal graphite by means of austempering treatment CONSTITUTION:A roll tire 11 supporting a cylindrical metal mold 12 of a device for centrifugally forming a Hume pipe 13 is manufactured by forming the matrix structure of a spheroidal graphite cast iron stock into a mixed structure of bainite, retained austenite, and spheroidal graphite by means of austempering treatment where the stock as it is, after rough working, or after finish working is heated and held at 800-900 degC for 05-3hr, rapidly cooled down to 200-400 degC, and held for >=05hr By this method, the roll tire 11 having particularly superior wear resistance can be obtained, and further, replacing time can be shortened and manufacturing costs in forming the Hume pipe can be remarkably reduced
1 Nov 1990
TL;DR: In this article, the results of varying prior austenite grain size on strength and toughness and the strength-toughness relationship for the martensite/bainite mixture that may produce the highest toughness are presented.
Abstract: : A mixed martensite/bainite microstructure in the high strength-low alloy steel (ASTM A723 pressure vessel steel) can be obtained by quenching from the austenitizing temperature to below M sub s, but above M sub f, and isothermally holding. As the supercooled austenite cools below M sub s, some martensite is formed and the isothermal hold results in the remainder of the untransformed austenite transforming to bainite. The resulting microstructure may be very fine depending on the prior austenite grain size. Since the martensite is formed first, the supercooled austenite between the martensite needles transforms to bainite during the isothermal hold. The resultant lamellar structure can result in remarkable fracture toughness with quite high strength (K sub Ic of 255 MP a sq m and ultimate tensile strength of 1200 MPa). In this report, the results of varying prior austenite grain size on strength and toughness and the strength-toughness relationship for the martensite/bainite mixture that may produce the highest toughness are presented.
TL;DR: In this paper, the authors examined the performance of gears made of spheroidal graphite cast iron, which has recently attracted attention as a new material for gears and found that the life of the gear is largely affected by the feed of the hob, and the life is longer at small feed.
Abstract: This paper discusses the hobbing of gears made of austempered spheroidal graphite cast iron, which has recently attracted attention as a new material for gears. This iron has many advantages, such as the properties of casting parts of complicated forms easily and a high strength equivalent to that of steel, and is also an economical material. However, this cast iron is hobbed before austempering heat treatment at present, because the hobbing of the teeth of a hardened gear blank is considered to be very difficult. Yet, if the cutting of a hardened gear blank is possible, the cost will be lower because the gear can be used without performing a finishing operation on the tooth surface to remove the distortion caused by heat treatment. The following conclusions are obtained. (1) The life of the hob appears to be largely affected by the feed of the hob, and the life is longer at small feed. The influence of cutting speed is also large, as in the case of hobbed alloy steel. (2) It is observed that the teeth with greatest wear are concentrated in one area of the hob. (3) The accuracy of hobbed ADI is very good.
Patent•
22 Jun 1990
TL;DR: In this article, the spheroidal graphite cast iron parts having a structure consisting of 30-60vol.% retained austenite and the balance bainite are ion-nitrided at a low temperature of ≤ 420 deg.C to form hardened surface layers and the surfaces of the cast iron part are shot-peened to produce high residual compressive stress in the surface parts.
Abstract: PURPOSE:To manufacture cast iron parts having superior fatigue strength and nearly free from surface roughness by austempering cast iron parts, ion-nitriding the resulting spheroidal graphite cast iron parts at a specified temp. and shot- peening the surfaces of the parts. CONSTITUTION:Raw material for cast iron is melted and cast in casting molds to manufacture cast iron parts. These parts are anstempered and the resulting spheroidal graphite cast iron parts having a structure consisting of 30-60vol.% retained austenite and the balance bainite are ion-nitrided at a low temp. of <=420 deg.C to form hardened surface layers and the surfaces of the cast iron parts are shot-peened to produce high residual compressive stress in the surface parts. Cast iron parts having considerably improved fatigue strength and nearly free from surface roughness are manufactured.
Patent•
12 Apr 1990
TL;DR: In this paper, the spheroidal graphite cast iron castings are subjected to austempering treatment to form the structure from bainite, >= 36.6vol.
Abstract: PURPOSE:To obtain the title castings, in a structure of castings after subjected to austempering treatment, by limiting the content of stably retained austenite and the average area in the crowded range of lumpy retained austenite. CONSTITUTION:Spheroidal graphite cast iron castings are subjected to austempering treatment to form the structure from bainite, >=36.6vol.% stably retained austenite and lumpy retained austenite having average area in the close range. The above spheroidal graphite cast iron castings can be obtd. by adding Mo to the molten metal of cast iron having prescribed compsn., subjecting it to gravity die casting into cast iron having about 250 to 300 pieces/mm graphite grain number and thereafter subjecting it to prescribed austempering treatment. At this time, casting conditions, conditions in austempering treatment or the like are controlled to form into the above compsn. In this way, the spheroidal graphite cast iron castings having excellent machinability can be obtd.
Patent•
2 May 1990
TL;DR: In this paper, the outside periphery of a shaft member is fitted with an annular member made of carburized steel and applying austempering treatment to the above while keeping the above in the fitted state.
Abstract: PURPOSE:To easily manufacture a metallic fitted member free from noise emission during operation by fitting the outside periphery of a shaft member made of ductile cast iron with an annular member made of carburized steel and applying austempering treatment to the above while keeping the above in the fitted state mentioned above. CONSTITUTION:A shaft member 2, such as camshaft, is formed of ductile cast iron material. On the other hand, an annular member 3, such as drive gear, is formed of steel material to which carburizing treatment alone is previously applied. The outside periphery of a mating part 2a of the above shaft member 2 is fitted with the above annular member 3. Subsequently, austempering treatment is applied to the above while keeping the above-mentioned fitted state, by which the structure of the shaft member 2 is formed into a mixed structure of bainite and retained austenite and simultaneously hardening is applied to the carburized layer of the annular member 3. The coefficient of linear expansion of the ductile cast iron material with the above structure is higher than that of the steel material. Accordingly, in the resulting metallic fitted member 1, the widening of the clearance between the shaft member 2 and the annular member 3 due to high temp. can be prevented and also the emission of noises during operation can be prevented.
Patent•
8 Jun 1990
TL;DR: In this paper, an undercoat layer 2 under the Ni-P plating layer 1 is formed into a structure in which upper bainite and retained austenite exist as a mixture.
Abstract: PURPOSE:To manufacture a member having extremely high wear resistance by subjecting austempering treatment to a cast iron member, applying Ni-P plating to a part requiring wear resistance, and then partially heating the above plating layer and its undercoat layer alone at a specific temp. CONSTITUTION:When austempering treatment is applied to a cast iron member and then Ni-P plating is applied to a part requiring wear resistance, an undercoat layer 2 under the Ni-P plating layer 1 is formed into a structure in which upper bainite and retained austenite exist as a mixture. When the above Ni-P plating layer 1 and its undercoat layer 2 alone are partially heated next up to 420-650 deg.C, the undercoat layer 2 is formed into a structure constituted. of an upper undercoat layer 2a in which high-hardness cementite and ferrite exist as a mixture and a lower undercoat layer 2b in which upper bainite and undercompsed retained austenite exist as a mixture. By this method, hardness in the vicinity of the surface of the undercoat layer can be increased, and wear resistance can be improved.
TL;DR: In this paper, the formation of bainite is discussed in terms of the temperature difference (undercooling) between the austenitizing temperature and austempering temperature, and the subsequent development of the phases present to bainitic is related to the carbon concentration gradient caused by compacted graphite acting as a sink for carbon.
Abstract: Samples of unalloyed compacted graphite cast iron (CGI) have been thermally treated to obtain a bainitic structure. Heat treatments consisting of various holding times at two different austenitizing temperatures and two different austempering temperatures have been carried out followed by metallographic observations of the resultant structures by scanning electron microscopy (SEM). The formation of bainite is discussed in terms of the temperature difference (undercooling) between the austenitizing temperature and austempering temperature, and the subsequent development of the phases present to bainite is related to the carbon concentration gradient caused by compacted graphite acting as a sink for carbon. This favors the final stages of the transformation. A hypothesis for the bainitic transformation mechanism in CGI's is thus proposed.
TL;DR: In this paper, a comparative study of the affects of graphite morphology and matrix structure on mechanical properties was carried out on spheroidal, compacted and flake graphite irons by a short austenitizing plus austempering treatment.
Abstract: A comparative study of the affects of graphite morphology and matrix structure on mechanical properties was carried out on spheroidal, compacted and flake graphite irons by a short austenitizing plus austempering treatment. Transformation kinetic data showed that compacted graphite iron had the fastest, spheroidal graphite iron the second and flake graphite iron the slowest austenitizing rate. In spheroidal and compacted graphite irons the strength increased, while ductility decreased, with increasing the amount of bainite in matrix due to prolonging austenitizing time. On the other hand, the increase of bainite structure in the matrix had no significant affect on the mechanical properties of flake graphite iron. Fractographic examinations showed that the fracture surface of spheroidal graphite iron changed from a ductile mode to a brittle mode when its matrix changed from ferrite to bainite dominant. The flake graphite iron ruptured with brittle mode no matter what matrix it had. Compacted graphite iron exhibited an intermediate type of fracture surface. With a short austenitizing plus austempering treatment, the mechanical properties of spheroidal and compacted graphite irons could be improved and extended to a very wide range.