This article presents the results of a set of innovative research to analyse a new structural material – steel like austempered ductile cast iron with mechanical properties similar to heat-treated steel, and with technological and exploitation characteristic close to high-strength cast iron with nodular graphite. Specific examples of its high efficiency for the manufacture of critical, mass and heavy-loaded components of modern machinery and equipment are presented. New structural material MoNiCa was tested on tension and was compared to commercial grades of austempered ductile cast irons and heat treated steels. Unconventional behaviour of examined material was observed: with tensile strength increase to almost 1600 MPa the metal became less brittle. Hardness test revealed another distinctive feature of new material that there is no linear relation between strength and hardness increase, different hardness values ~ 40 HRC or ~ 55 HRC can be achieved with the same tensile strength 1000 – 1200 MPa. Microscopic analysis demonstrated of sophisticated structure formed owing to different regimes of austempering treatment. Specific properties emerged from successful ratio of three elements Mo, Ni, and Cu (carbon equivalent), and properly chosen heat treatment modes. DOI: http://dx.doi.org/10.5755/j01.ms.25.3.23079
The influence of the austempering temperatures on the microstructure and mechanical properties of austempered ductile cast iron (ADI) was investigated. ADI is nodular graphite cast iron, which owing to higher strength and elongation, exceeds mechanical properties of conventional spheroidal graphite cast iron. Such a combination of properties is achieved by the heat treatment through austenitization, followed by austempering at different temperatures. The austenitization conditions were the same for all the samples: temperature 890 °C, duration 30 min, and quenching in a salt bath. The main focus of this research was on the influence of the austempering temperatures (270 °C, 300 °C, and 330 °C) on the microstructure evolution, elongation, toughness, and fatigue resistance of ADI modified by certain amounts of Ni, Cu, and Mo. The Vickers and Rockwell hardness decreased from 535.7 to 405.3 HV/1 (55.7 to 44.5 HRC) as the austempering temperature increased. Optical images showed the formation of graphite nodules and a matrix composed of ausferrite; the presence of these phases was confirmed by an XRD diffraction pattern. A fracture surface analysis revealed several types of the mechanisms: cleavage ductile, transgranular, and ductile dimple fracture. The stress-controlled mechanical fatigue experiments revealed that a 330 °C austempering temperature ensures the highest fatigue life of ADI.
This research presents the results of tribo-fatigue behavior of austempered ductile cast iron MoNiCa and gives a comparison with standard grades of steel and cast iron. Due to the possibility to combine the castability of cast iron and toughness of steel in one material, new structural material MoNiCa attracted attention of industry and science because of economic benefits and high performance at the different application areas. After successful former experiments the main directions of further development of research for solving relevant practical wear and fatigue problems in rail-wheel system were framed. The complex experimental studies have demonstrated that MoNiCa is consistent with heat treated steels including the rail steels: required tensile strength of rail steel ranges from 1180 MPa to 1280 MPa when rolling surface hardness have to be from 38 HRC to 44 HRC whereas new structural material showed higher tensile strength up to 1400 MPa and slightly higher hardness up to 50 HRC. Herewith the workability of frictional couple cast iron MoNiCa/steel 20MnCr5G exceeds work performance of steel/steel system by 14 %.
The unified methods of wear-fatigue tests of models of active systems, which are based on a combination of the known mechanical fatigue, friction and wear test methods, are offered. A bending fatigue test method for a uniform cylindrical specimen with a test portion diameter of 10 mm is adopted as a basic one.Introduction. Special wear-fatigue test methods have been elaborated for experimental assessment of mutual and joint influence of friction and fatigue processes on the working capacity of materials and models of active systems under complex loading conditions [1][2][3][4][5].Under laboratory conditions the wear-fatigue damage resistance is usually studied by testing small models of active systems. The tests are performed on special wear-fatigue test machines of a SI series [5][6].One of the ways of developing complex wear-fatigue test methods is to combine the known mechanical fatigue test methods with the friction and wear test methods. Figure 1 illustrates, as an example, the principle of such combination whereby a basic fatigue test method incorporates bending with rotation. Note that rotary motion is most typical of modern machines; therefore, the methods as shown in Fig. 1 are of practical importance.A similar approach enables the machines intended for wear-fatigue tests to be used for conventional tests or mechanical fatigue tests or for friction and wear testing under preset conditions. The Basic Test Schemes. A test object for mechanical fatigue tests is a structural element, for example, a cylindrical one of a given geometry (Fig. 2c). If the tests are performed in the sliding or rolling friction modes, the test object is a friction pair (Fig. 2b, c) consisting of specimen 1 and counterspecimen 2; they are also called the body and the counterbody. Note that here the specimen is always referred to as the cylindrical structural element and the counterspecimen (counterbody) as the bushing or the roller. Finally, in wear-fatigue tests the test objects are the models of active systems of two elements -1 and 2 (Fig. 2a, d).It should be mentioned that all the methods of wear-fatigue testing (Fig. 2) implemented on SI series machines are based on using a uniform smooth cylindrical specimen with a test portion diameter d r = = 2 10mm. It is identical to a standard fatigue test specimen. This provides both the consistency of tests as well as comparability of test results.Let's address the mechano-sliding fatigue test scheme (Fig. 2e). The cylindrical specimen 1 is fixed in a spindle 2 and rotates with angular speed w 1 . A vertical bending load Q (upwards or downwards) is applied to its free end. Also, a nonrotating counterspecimen 3, for example, a plate or a partial bushing, is in contact with the specimen test portion zone of diameter d =10 ìì under a contact load F N . Thus, the maximum contact and bending stresses arise simultaneously in the specimen test portion zone.Implementation of the test scheme as shown in Fig. 2e makes it possible to perform the following tests: -wear-fatigue tests for mechano-sl...
The results of an experimental study of damage for the structural material MoNiCa (it is high-strength cast iron VCHTG – patent of the Republic of Belarus № 15617) on sliding friction and mechano-sliding fatigue are analyzed in the report. Tests of the mechanical system shaft (a sample with a working part diameter of 10 mm made of 0.45 % carbon steel) - an insert (a prismatic counter sample with a cross section of 10 ´ 10 mm made of MoNiCa) were carried out. The kinetics of the change in average wear at 8 local points along the perimeter of the dangerous area of the sample is given for contact loads FN from 20 to 92 N of the mechanical system under study with MoNiCa inserts without heat treatment and with heat treatment. The test results of the system under study are also presented in the form of sliding friction and mechano-sliding fatigue curves in coordinates of the contact load FN – the number of cycles N until the limit state.
The influence of the austempering temperatures on the microstructure and mechanical properties of austempered ductile cast iron (ADI) was investigated. ADI is nodular graphite cast iron, which owing to higher strength and elongation exceeds mechanical properties of conventional spheroidal graphite cast iron. Such a combination of properties is achieved by the heat treatment through austenitization, followed by austempering at different temperatures. The austenitization conditions were the same for all the samples: temperature 890°C, duration 30min, and quenching in a salt bath. The main focus of this research was on the influence of the austempering temperatures (270°C, 300°C, and 330 C) on the microstructure evolution, elongation, toughness and fatigue resistance of ADI modified by certain amount of Ni, Cu, and Mo. The Vickers and Rockwell hardness decreased from 535.7 to 405.3HV/1 (55.7 to 44.5HRC) as the austempering temperature increased. Optical images showed the formation of graphite nodules and matrix composed of ausferrite; the presence of these phases was confirmed by an XRD diffraction pattern. A fracture surface analysis revealed several types of the mechanisms: cleavage ductile, transgranular and ductile dimple fracture. The stress-controlled mechanical fatigue experiments revealed that a 330°C austempering temperature ensures the highest fatigue life of ADI.
This research paper combines investigation of mechanical properties of austempered ductile cast iron (ADI) and comparison with standard grades of steel and cast iron. Due to the special features of both materialscatsability from cast iron, and toughness from steel, ADI attracts an attention of industry and science because of economic benefits and high performance at the different application areas. Austempered ductile iron was tested on tension where unconventional behaviour was observed: with the increase of tensile strength almost to 1600 MPa the metal became less brittle. Hardness test revealed absence of linear relation between strength and hardness, different hardness values ~ 40 HRC or ~ 55 HRC can be reached with the same tensile strength 1000 -1200 MPa. After successful tensile tests the main direction of further studies was solving relevant practical wear and fatigue problems in rail-wheel system. The complex practical studies demonstrated that ADI is consistent with heat treated steels including the rail steels: required tensile strength of rail steel ranges from 1180 MPa to 1280 MPa when rolling surface hardness is expected to be in the range of 38 HRC -44 HRC, whereas tensile strength of ADI was higher, up to 1400 MPa, and hardness slightly higher than of steel, 50 HRC. Herewith the workability of frictional couple cast iron/steel 20MnCr5G exceeded work performance of steel/steel system by 14 %. Specific properties emerged from successful ratio of three elements Mo, Ni, and Cu, and properly chosen austenitization schedule.
Contact interaction in a wheel-rail pair and its corresponding stress-strain state for various combinations of materials of this pair and the weights of passenger and freight cars were considered. The materials under study were steel and high-strength cast iron based structural material MoNiCa with strength and wear-fatigue characteristics close to steel ones.The load on each wheel was: 53.9 and 294.3 kN for an empty and loaded freight car, 146.8 kN and 230.5 kN for an empty and loaded passenger car. The bottom surface of the rail was rigidly fixed.Young's modules were adopted as follows: 200 GPa for steel and 165 for MoNiCa. The results of finite element calculations of the three-dimensional stress-strain state showed that the largest von Mises stresses of 613.08 MPa occur in the wheel (steel)-rail (steel) pair of the loaded freight car. For all types of loading, the lowest stresses (15.8 % – 16.7 % less than in the steel-steel pair) are observed in the wheel (MoNiCa)-rail (MoNiCa) pair. This indicates the appropriateness of using MoNiCa for the manufacturing elements of the wheel-rail system.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.