Showing papers on "Austempering published in 1985"
TL;DR: In this paper, the effect of bainite on the mechanical properties of a commercial Japanese 0.40 pct C-Ni-Cr-Mo high strength steel (AISI 4340 type) has been systematically made.
Abstract: A study has been systematically made of the effect of bainite on the mechanical properties of a commercial Japanese 0.40 pct C-Ni-Cr-Mo high strength steel (AISI 4340 type) having a mixed structure of martensite and bainite. Isothermal transformation of lower bainite at 593 K, which appeared in acicular form and partitioned prior austenite grains, in association with tempered marprovided provided a better combination of strength and fracture ductility, improving true notch tensile strength (TNTS) and fracture appearance transition temperature (FATT) in Charpy impact tests. This occurred regardless of the volume fraction of lower bainite present and/or the tempering conditions employed to create a difference in strength between the two phases. Upper bainite which was isothermally transformed at 673 K appeared as masses that filled prior austenite grains and had a very detrimental effect on the strength and fracture ductility of the steel. Significant damage occurred to TNTS and FATT, irrespective of the volume fraction of upper bainite present and/or the tempering conditions employed when the upper bainite was associated with tempered martensite. However, when the above two types of bainite appeared in the same size, shape, and distribution within tempered martensite approximately equalized to the strength of the bainite, a similar trend or a marked similarity was observed between the tensile properties of the mixed structures and the volume fraction of bainite. From the above results, it is assumed that the mechanical properties of high strength steels having a mixed structure of martensite and bainite are affected more strongly by the size, shape, and distribution of bainite within martensite than by the difference in strength between martensite and bainite or by the type of mixed bainite present. The remarkable effects of the size, shape, and distribution of bainite within martensite on the mechanical properties of the steel are briefly discussed in terms of the modified law of mixtures, metallographic examinations, and the analyses of stress-strain diagrams.
117 citations
Journal Article•
TL;DR: Transformation bainitique dans la fonte a graphite spheroidal. Variation des proprietes en fonction de la temperature du traitement d'austempering.
Abstract: Transformation bainitique dans la fonte a graphite spheroidal. Variation des proprietes en fonction de la temperature du traitement d'austempering
38 citations
TL;DR: In this paper, the authors discuss the possibility of achieving austempered ductile iron (ADI) properties in the foundry, but the cost of adding the elaborate heat-treating facilities required for austempering is high.
Abstract: In a general sense austempered ductile iron (ADI) is a new class of ductile iron that is twice as tough as standard grades of ductile iron at the same strength level. ADI has excellent toughness and wear resistance and has been shown to have superior fatigue properties as well. The unique microstructure developed by austempering ductile iron provides these remarkable engineering properties. This heat treatment is an extra step in the manufacturing process that adds direct and indirect costs. The current capacity of heat-treatment facilities capable of austempering is limited. There is interest in achieving austempered ductile iron (ADI) properties in the foundry, but the cost of adding the elaborate heat-treating facilities required for austempering is high. Acicular irons, where-by high strengths are achieved by transformation on continuous cooling of alloyed irons through the bainitic transformation region, provide one alternative; however, the high ductility and toughness associated with ADI are generally absent in acicular irons. Another alternative is to employ controlled cooling that closely approximates the thermal schedule for austempering. Controlled cooling can be applied either following a hot shakeout or normalizing treatment. This has been done in a laboratory environment. The results of this study will be discussed, and suggestions for pursuit of this technology are given in view of current and emerging foundry processing technologies.
26 citations
21 citations
TL;DR: In this paper, the authors studied the influence of the size of the solidification cells on the evolution of the bainite reaction in a homogeneous matrix after isothermal holding in the range of temperatures 350 to 450 °C.
Abstract: Alloy segregation at the solidification cell boundaries can have a very important influence upon the kinetics of the bainite reaction. The two stages usually observed in a homogeneous matrix after isothermal holding in the range of temperatures 350 to 450 °C can be described as follows: 1 -γ→ (α) + (γ); 2-(α) + (γ) → α + silicocarbides. These reactions are functions of the elements in solution in the matrix. For this reason, segregated elements affect very sensitively the evolution of the two basic reactions. The solidification cell boundaries are often not completely transformed to bainite, which explains the presence of martensite observed in these areas. The influence of the size of the solidification cells has also been studied. The austenitization conditions are also very important. At the opposite extreme, the bainitic reaction of the matrix located along the graphite interface evolves more quickly than that observed in the matrix or at the cell boundaries.
19 citations
Patent•
23 Dec 1985TL;DR: In this paper, a method for forming a ferrous alloy melt consisting essentially of by weight, 3-4% carbon, 2.0-3.0% silicon, 0.1-0.9% manganese, up to 0.002% sulphur up to 1% contaminants or impurities, 0-0,4% molybdenum, and the reminder essentially iron, the melt being subjected to a graphite modifying agent in an amount and for a period of time effective to form either ductile or semiductile iron upon solidification
Abstract: A method is disclosed which comprises: (a) forming a ferrous alloy melt consisting essentially of by weight, 3-4% carbon, 2.0-3.0% silicon, 0.1-0.9% manganese, up to 0.02% phosphorus, up to 0.002% sulphur, up to 1% contaminants or impurities, 0-0.4% molybdenum, 0-3.0% nickel or copper, and the reminder essentially iron, the melt being subjected to a graphite modifying agent in an amount and for a period of time effective to form either ductile or semiductile iron upon solidification; (b) heat treating the solidification of said melt by austempering to form a matrix consisting substantially of high carbon austenite and ferrite and a cell boundary having unreacted low carbon austenite; (c) heating said austempered iron to a pearlite forming temperature (1200°-1300° F.) and holding (2-5 minutes) at said temperature to permit the unreacted low carbon austenite to form pearlite; and (d) cooling said heat treated iron to room temperature.
11 citations
Patent•
12 Jan 1985
TL;DR: In this article, the authors proposed a combined austempering method of a specifically composed middle and high carbon steel by stabilizing positively residual austenite to obtain a heat-treated steel provided with high strength, excellent ductility and toughness.
Abstract: PURPOSE:To obtain a heat-treated steel provided with high strength, excellent ductility and toughness in a combined austempering method of a specifically composed middle and high carbon steel by stabilizing positively residual austenite. CONSTITUTION:A middle and high carbon steel contg., by weight, 0.40-1.10% C and 0.8-2.7% Si among the elements in the steel is held at a temp. region of the Ac3 point -Ac3 point of said steel +150 deg.C to austenitize the steel. The steel is then hardened from said temp. region to a temp. region of the Ms point -M80% point of the steel. The steel is thereafter heated from the state in which >=20vol% untransformed austenite is maintained to a temp. region of 300- 450 deg.C so that the tempering of martensite and the bainite transformation of the untransformed austenite is effected. The steel is at the same time cooled to an ordinary temp. by regulating the holding time in said heating temp. region in such a way that the residual amt. of the austenite stable at an ordinary temp. attains >=5vol%. The bainite transformation is interrupted by such regulation. The steel in which the three phases, martensite, bainite and residual austenite, coexist, is thus obtd.
9 citations
Patent•
5 Sep 1985TL;DR: In this article, a method for forming a surface hardenable cast iron article by development of metastable retained austenite in the cell boundary of a ductile or semiductile cast iron was disclosed.
Abstract: A method is disclosed for forming a surface hardenable cast iron article by development of metastable retained austenite in the cell boundary of a ductile or semiductile cast iron. The method comprises (a) controlling the solidification of a cast iron melt to extend the eutectic arrest time to 4-12 minutes, the melt having by weight percent a carbon equivalent (carbon plus one-third silicon) equal to 4.3-5.0, manganese 0.55-1.2, nickel 0.5-3.0, and the remainder essentially iron, the melt having been treated to form cell boundaries in the solidified iron with a high proportion of the manganese being segregated in the cell boundaries; (b) subjecting the solidified cast iron to an austempering heat treatment to permit the segregated manganese in the cell boundaries to form metastable retained austenite; and (c) terminating the heat treatment prior to the conversion of the metastable austenite to a stable microstructure. To obtain the benefits of wear resistance, the method further comprises using the heat treated cast iron by stressing a surface region thereof and transforming the microstructure of such surface region to martensite.
8 citations
Patent•
12 Jun 1985
TL;DR: In this paper, a mixed structure consisting of semi-austenite, bainite and martensite is formed by surface working, which is then carried out by cutting, shot peening or other method to cause martensitic transformation.
Abstract: PURPOSE:To manufacture spheroidal graphite cast iron with high strength and toughness by austempering spheroidal graphite cast iron and forming a mixed structure consisting of semi-austenite, bainite and martensite by surface working. CONSTITUTION:Spheroidal graphite cast iron is austempered by heating at 800- 950 deg.C austenitizing temp. for 0.5-3hr and quenching to 350-450 deg.C. By the austempering, a mixed structure consisting of about 10-70vol% residual semi- austenite which causes martensitic transformation by working and the balance bainite or bainite and martensite is formed. Surface working is then carried out by cutting, shot peening or other method to cause martensitic transformation. Part of the structure is converted into martensite, the residual compressive stress is increased, and the fatigue strength is remarkably improved by work hardening, thus obtaining spheroidal graphite cast iron with high strength and toughness.
5 citations
Patent•
13 Jun 1985
TL;DR: In this paper, a casting of spheroidal graphite cast iron having restricted Ni, Cu and Mo contents is taken out of a casting mold and heated to the austenitizing temp. The resulting casting is then cooled to the point W 400°C by forced air cooling and allowed to cool.
Abstract: PURPOSE: To easily produce a high strength casting of spheroidal graphite cast iron by taking a casting of spheroidal graphite cast iron having restricted Ni, Cu and Mo contents out of a casting mold, heating the casting to the austenitizing temp., and cooling it to a specified temp. by forced air cooling. CONSTITUTION: Molten spheroidal graphite cast iron contg. 0.5W2.0wt% Ni, 1.0W3.0wt% Cu and 0.3W2.0wt% Mo is poured into a casting mold. The resulting casting is taken out of the mold and heated to the austenitizing temp. The casting is then cooled to the Ms point W 400°C by forced air cooling and allowed to cool. Thus, the matrix structure of the casting is easily converted into a bainite structure without using an austempering furnace, so the strength of the casting of spheroidal graphite cast iron is increased. COPYRIGHT: (C)1986,JPO&Japio
4 citations
Patent•
11 Apr 1985
TL;DR: In this paper, a low alloy steel member is carbonitrided at 850-880 deg.C to increase the C content of the surface layer to 0.75-1.00%.
Abstract: PURPOSE:To provide superior wear resistance to a low alloy steel having a specified composition by carbonitriding the surface of the steel and austempering it to form a martensite structure in the surface layer. CONSTITUTION:A low alloy steel member contg. 0.55-0.65% C, <0.50% Si, 0.40-1.30% Mn, <4.00% Ni, 0.55-1.30% Cr and <0.70% Mo is carbonitrided at 850-880 deg.C to increase the C content of the surface layer to 0.75-1.00% and the N content to 0.15-0.40%. The member is austempered by putting in a cooling medium at a high temp. such as a salt bath at 230-260 deg.C, and it is held for such a time that transformation to bainite is caused in most of the member and is not caused in the surface layer. The held member is rapidly cooled or air- cooled. A martensite structure with high hardness is formed in the surface layer, and superior wear resistance is provided to the layer.
Patent•
26 Jul 1985TL;DR: In this paper, a method for making compacted graphite cast iron of improved strength and hardness while retaining excellent thermal conductivity, low shrinkage, and excellent damping characteristics was disclosed.
Abstract: A method is disclosed for making compacted graphite cast iron of improved strength and hardness while retaining excellent thermal conductivity, low shrinkage, and excellent damping characteristics. A ferrous alloy is melted consisting essentially of, by weight, 3-4% C, 2-3% Si, .2-.7% Mn, 25-.4 Mo, .5-3.0% Ni, up to .002% sulfur, up to .02% phosphorus, and impurities or contaminants up to 1.0%, with the remainder being essentially iron. The melt is subjected to a graphite modifying agent to form compacted graphite upon solidification. The solidified casting is heat treated by austempering and quenching to produce an iron having a matrix of bainite and austenite.
Patent•
17 Jun 1985
TL;DR: In this paper, a high strength spheroidal graphite cast iron for austempering is obtd. by adding one or more among prescribed amounts of Mo, Ni, Cu and Mn to a specified basic composition consisting of C, Si, Mg and Fe.
Abstract: PURPOSE:To obtain the titled cast iron which can be austempered at a low cost by direct holding at constant temp. in a cooling stage after casting by adding one or more among prescribed amounts of Mo, Ni, Cu and Mn to a specified basic composition consisting of C, Si, Mg and Fe. CONSTITUTION:This high strength spheroidal graphite cast iron for austempering is obtd. by adding one or more among <=0.5wt% Mo, <=1.0wt% Ni, <=1.5wt% Cu and <=1.5wt% Mn to conventional spheroidal graphite cast iron having a composition consisting of 3.0-4.5wt% C, 1.5-3.0wt% Si, 0.02-0.10wt% Mg and the balance Fe so as to enable bainitic transformation even at a low cooling rate. Accordingly, this spheroidal graphite cast iron can be austempered at a low energy cost with the potential heat of a casting by direct holding at constant temp. in a cooling stage after casting.
TL;DR: In this paper, several alloys of Ductile cast iron containing various amounts of manganese, molybdenum, and nickel were austempered in the temperature range 316° to 427 °C.
Abstract: Several Alloys of Ductile Cast Iron containing various amounts of manganese, molybdenum, and nickel were austempered in the temperature range 316° to 427 °C. The rate and morphology of ferrite platelet formation (bainite reaction) were studied by optical metallography, x-ray diffraction, and hardness measurements. Austenitizing temperature, austempering temperature, and deformation by rolling were used as variables to control the kinetics of ferrite formation, stage I of the austempering reaction.