US20130105047A1 - Method for manufacturing mechanical components made of particularly wear-resistant austempered spheroidal cast iron - Google Patents

Method for manufacturing mechanical components made of particularly wear-resistant austempered spheroidal cast iron Download PDF

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Publication number
US20130105047A1
US20130105047A1 US13/805,310 US201113805310A US2013105047A1 US 20130105047 A1 US20130105047 A1 US 20130105047A1 US 201113805310 A US201113805310 A US 201113805310A US 2013105047 A1 US2013105047 A1 US 2013105047A1
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comprised
cast iron
mechanical components
casting
percentage
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Franco ZANARDI
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ZANARDI FONDERIE SpA
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ZANARDI FONDERIE SpA
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D5/00—Heat treatments of cast-iron
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/34—Methods of heating
    • C21D1/44—Methods of heating in heat-treatment baths
    • C21D1/46—Salt baths
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/08—Making cast-iron alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C37/00—Cast-iron alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C37/00—Cast-iron alloys
    • C22C37/04—Cast-iron alloys containing spheroidal graphite

Definitions

  • the present invention relates to a method for manufacturing mechanical components made of particularly wear-resistant austempered spheroidal cast iron.
  • austempered spheroidal cast irons of various types and having different structures are known and are used in particular for manufacturing various types of mechanical components.
  • the thermal treatment required in order to obtain this type of cast iron consists of a treatment of complete austenitization, with holding of the component at a temperature higher than the upper austenitization limit temperature (usually designated by A c3 ) followed by quenching in a molten salt bath.
  • a c3 the upper austenitization limit temperature
  • ausferritic structure is composed of acicular ferrite and austenite. This particular structure gives the material high mechanical characteristics. Since it is essential to prevent the forming of pearlite during cooling, it is necessary to alloy the material with alloying elements, such as nickel and/or molybdenum.
  • the cited international standard ISO 17804 : 2005 defines, in Annex A, “Abrasion-resistant grades of ausferritic spheroidal graphite cast iron”, grades ISO17804/JS/HBW400 and ISO17804/JS/HBW450. These are the two recommended grades for applications that require high resistance to wear.
  • the maximum contribution to wear-resistance is given by the high proportion of acicular ferrite in the matrix and by its hardness.
  • FIG. 5 taken from “Section IV Ductile Iron Databook for Design Engineers” (http://www.ductile.org/didata/Section4), shows schematically the Dorazil curve (the topmost chart).
  • the curve represents the volumetric fraction of stabilized austenite as a function of the time elapsed from the moment when the material is immersed in the austempering bath.
  • the horizontal portion which represents the maximum of this curve, corresponds to the maximum stability of the austenite as a consequence of its progressive enrichment with carbon. Accordingly, the Brinell hardness of the material also reaches its minimum value, since the transformation into martensite of an important volume fraction of the matrix subjected to the hardness test is avoided.
  • first stage The part of the transformation process from the beginning to the attainment of the cited condition of maximum stability of the austenite is termed first stage, since an excessive extension of the holding of the material in the austempering bath would cause an unwanted decomposition of the austenite, stabilized by the carbon enrichment, into acicular ferrite and carbides, a possible part of the transformation process known as second stage.
  • the condition of maximum stability of the austenite is necessary in order to manage the process in controlled and repetitive conditions. It is also known that the optimum time, with respect to this requirement, of permanence in the thermal bath in order to reach the condition of maximum stability of the carbon-enriched austenite depends essentially on the thickness of the casting, on the austenitization temperature, on the isothermal quenching temperature, and on the content of silicon, manganese and other elements with strong segregation, such as molybdenum.
  • This comparative chart shows the advantageous behavior, in wear resistance, of ADI cast irons with respect to the materials with which they have been compared.
  • the wear resistance values offered by ADI cast irons advantageous in many applications in which it has been possible to avoid the induction quenching of cast irons and/or steels, the nitriding of cast irons and/or steels, the cementation of steels, such as for example:
  • ADI cast irons are insufficient and it is necessary to resort to other families of abrasion-resistant cast irons.
  • These materials besides being penalized by the cost associated with a high content of carbide-forming alloying elements (these are in fact ledeburitic white cast irons in which the carbon is predominantly in a form that is combined with iron), are even more limited in use due to their fragility, which is a consequence of the ledeburitic white structure.
  • wear-resistant steels which, as is known, are characterized by a foundry process that is more complex and expensive than the typical one of cast iron foundry.
  • CADI cast irons make it possible indeed to obtain mechanical components that are particularly wear-resistant, on the other hand they are more fragile than normally required in many applications and are also difficult to obtain.
  • the chart shown in FIG. 2 taken from “Agricultural Applications of Austempered Cast Irons” by Kathy L. Hayrynen PhD FASM, Tim Dorn, John R. Keough PE, Vasko Popovski PE, Steven Sumner, Anon Rimmel PhD, illustrates the improvement of the resistance to wear/abrasion of CADI cast irons, compared with abrasion-resistant cast irons, which increases as the carbide content rises.
  • the aim of the present invention is to provide a new method for manufacturing austempered spheroidal cast iron that makes it possible to obtain a material that has an optimum wear-resistance and at the same time a sufficient resilience.
  • FIG. 1 is a comparative chart of the wear resistance of various metallic materials, including various ADI cast irons and various types of hardened and tempered spheroidal cast irons and steels;
  • FIG. 2 is a chart, similar to the previous one, in which the behavior of an ADI cast iron and of CADI cast irons with different percentages of carbides are compared with abrasion-resistant cast irons;
  • FIG. 3 is a perspective view of a hammer subjected to a method according to the invention.
  • FIG. 4 is a micrograph at 500 magnifications of a component subjected to a method according to the invention.
  • FIG. 5 is a schematic diagram showing the effect of austempering time on the amount and stability of austenite and the hardness of ADI;
  • FIG. 6 is a plot of a time/temperature curve of a thermal treatment for interrupted quenching in a salt bath related to the method according to the invention.
  • the present invention relates to a method for manufacturing spheroidal cast iron mechanical components such as, for example, armors for stone mills and for the cement industry, screw conveyors for the cement industry, hammers for stone mills, lamination rollers for clays and mechanical components in general.
  • the method entails the following steps:
  • critical rate is understood as the minimum cooling rate required to prevent pearlitic transformation.
  • interrupted quenching in salt bath is understood to be a temperating process (as shown in FIG. 6 ) that has a cooling step at a rate that is higher than the critical rate and stops at a temperature higher than that at the beginning of the martensitic transformation MS, followed by a holding period at this temperature for the time sufficient to start the reaction but insufficient to complete it; finally, rapid cooling to ambient temperature is performed.
  • interrupted quenching in salt bath in practice is interrupted twice: a first time because during the quick cooling step one stops at the isothermal holding temperature, which is higher than MS, the second time because we interrupt the reaction at isothermal temperature at a time that is very early with respect to the condition of maximum stability of carbon-enriched austenite.
  • the method according to the invention provides for limiting, during the step for producing the casting, the forming of disperse primary carbons (Fe 3 C) in a percentage by volume of less than 5% of the volume.
  • the step that consists in limiting the forming of disperse primary carbons (Fe 3 C) comprises a process of post-inoculation in the step for pouring the casting into the die.
  • the casting of the spheroidal cast iron mechanical component subjected to the method according to the invention has a nickel content by weight comprised between 0% and 3% and a copper content by weight comprised between 0% and 1.2%.
  • the casting of the spheroidal cast iron mechanical component subjected to the method according to the invention can have a silicon content by weight comprised between 1.5% and 2.5%.
  • the casting of the spheroidal cast iron mechanical component subjected to the method according to the invention has a molybdenum content by weight comprised between 0.4% and 1%.
  • the temperature used preferably to perform the isothermal step of interrupted quenching is comprised between 290° C. and 310° C.
  • thermal interrupted quenching treatment designates a cooling with a rate that is higher than the critical one (minimum cooling rate required to prevent pearlitic transformation), keeping the casting at a higher isothermal temperature than the temperature of martensitic transformation MS; the holding at this temperature has a duration sufficient to make the ausferritic reaction start at the edges of the spheroids and is interrupted at such a stage as to obtain the desired proportion of metastable austenite.
  • Control of the process is possible thanks to the conspicuous slowing of the reaction, caused by the relatively high ratio of high-segregation alloying elements.
  • the temperature at which the mechanical components are held, as mentioned, during the austenitization step is higher than the temperature technically identified as A c3 , or temperature of complete austenitization for the time necessary to obtain a fully austenitic structure. This can be obtained by choosing a temperature higher than 850° C. and lower than 910° C. and, advantageously, according to the carbon and silicon content, comprised between 880° C. and 900° C.
  • Such temperatures are indicative for cast irons having a carbon content of approximately 3.5% and a silicon content of approximately 2%, but, obviously, may vary according to the percentages of these elements in the casting to be subjected to the thermal treatment.
  • the holding time of the mechanical component at the austenitization temperature A c3 is comprised between 90 minutes and 210 minutes, preferably between 120 minutes and 180 minutes.
  • the isothermal holding step has a duration comprised between 10 minutes and 30 minutes.
  • the method according to the invention is based essentially on the addition of a high ratio of high-segregation alloying elements, such as manganese and molybdenum.
  • a high ratio of high-segregation alloying elements such as manganese and molybdenum.
  • a hammer was provided by casting with a weight of approximately 1.74 kg, using cast iron with a predominantly pearlitic matrix (pearlite in a percentage higher than 80%) having a carbon percentage equal to 3.47%, a silicon percentage equal to 2.08%, a manganese percentage equal to 1.07% and a molybdenum percentage equal to 0.94%.
  • pearlite in a percentage higher than 80%
  • the component was brought to a complete austenitization temperature (higher than A c3 ) equal to 890° C. and was held at this temperature for 120 minutes.
  • the components made of austempered spheroidal cast iron according to the invention have always shown, for an equal hardness, a higher resistance to abrasive wear (by approximately 10-15%) than traditional austempered cast irons and Q&T steels.
  • the dimensions may be any according to the requirements, although it has been found that the method according to the invention is particularly effective for treating components with dimensions up to 100 mm.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Articles (AREA)
  • Mushroom Cultivation (AREA)
US13/805,310 2010-06-18 2011-06-17 Method for manufacturing mechanical components made of particularly wear-resistant austempered spheroidal cast iron Abandoned US20130105047A1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
ITVR2010A000124 2010-06-18
ITVR2010A000124A IT1400634B1 (it) 2010-06-18 2010-06-18 Procedimento per la produzione di componenti meccanici in ghisa sferoidale austemperata particolarmente resistente all'usura.
PCT/EP2011/060166 WO2011157840A1 (fr) 2010-06-18 2011-06-17 Procédé de fabrication d'éléments mécaniques constitués de fonte de fer sphéroïdale bainitée particulièrement résistante à l'usure

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EP (1) EP2582856B1 (fr)
IT (1) IT1400634B1 (fr)
WO (1) WO2011157840A1 (fr)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104831024A (zh) * 2015-05-11 2015-08-12 柳州金盾机械有限公司 一种奥铁体球墨铸铁磨球等温淬火热处理工艺
CN105018711A (zh) * 2015-08-05 2015-11-04 人本集团有限公司 一种灰铸铁ht250轴承套圈热处理工艺
CN109852886A (zh) * 2019-03-25 2019-06-07 山东润源实业有限公司 一种高强度高韧性的球墨铸铁、曲轴及其制备方法
US11441204B2 (en) * 2018-12-11 2022-09-13 Hyundai Motor Company Method of manufacturing cam piece for continuously variable valve duration and cam piece manufactured therefrom
CN115216585A (zh) * 2022-07-29 2022-10-21 宁国市华丰耐磨材料有限公司 一种细化cadi磨球石墨球粒径的工艺方法

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2993575B1 (fr) * 2012-07-23 2016-07-22 Ferry Capitain Alliage, piece et procede de fabrication correspondants
ITUB20152456A1 (it) * 2015-07-24 2017-01-24 Zanardi Fond S P A Procedimento per la produzione di componenti meccanici in ghisa lamellare o vermiculare.
CN110484676B (zh) 2019-09-26 2021-05-11 天润曲轴股份有限公司 球墨铸铁中硅量的添加控制方法、球墨铸铁的铸造方法、铸件

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US20080145645A1 (en) * 2006-12-15 2008-06-19 The Dexter Company As-cast carbidic ductile iron

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US20040112479A1 (en) * 2002-09-04 2004-06-17 Druschitz Alan Peter Machinable austempered cast iron article having improved machinability, fatigue performance, and resistance to environmental cracking and a method of making the same
US20080145645A1 (en) * 2006-12-15 2008-06-19 The Dexter Company As-cast carbidic ductile iron

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Aravind Vadiraj, G. Balachandran, M. Kamaraj, B. Gopalakrishna, K. Prabhakara Rao, Studies on mechanical and wear properties of alloyed hypereutectic gray cast irons in the as-cast pearlitic and austempered conditions, Materials & Design, Volume 31, Issue 2, February 2010, Pages 951-955, ISSN 0261-3069, http://dx.doi.org/10.1016/j.matdes.2009.07.03 *
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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104831024A (zh) * 2015-05-11 2015-08-12 柳州金盾机械有限公司 一种奥铁体球墨铸铁磨球等温淬火热处理工艺
CN105018711A (zh) * 2015-08-05 2015-11-04 人本集团有限公司 一种灰铸铁ht250轴承套圈热处理工艺
US11441204B2 (en) * 2018-12-11 2022-09-13 Hyundai Motor Company Method of manufacturing cam piece for continuously variable valve duration and cam piece manufactured therefrom
CN109852886A (zh) * 2019-03-25 2019-06-07 山东润源实业有限公司 一种高强度高韧性的球墨铸铁、曲轴及其制备方法
CN115216585A (zh) * 2022-07-29 2022-10-21 宁国市华丰耐磨材料有限公司 一种细化cadi磨球石墨球粒径的工艺方法

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EP2582856A1 (fr) 2013-04-24
WO2011157840A1 (fr) 2011-12-22
EP2582856B1 (fr) 2016-04-06
ITVR20100124A1 (it) 2011-12-19
IT1400634B1 (it) 2013-06-14

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