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 object of research is a rock massif with various cross-sectional shapes of roadway. The purpose of work: computer modeling of stress-strain state and volumetric damageability in the neighbourhood of a mine roadway. The undisturbed rock massif has an initial stress-strain state (under its own weight) before a mine roadway is formed. Therefore, to determine the stress-strain state of the rock massif with the mine roadway, we must first calculate the stress state of the rock massif without the roadway and then take it into account as a pre-stressed state for the rock massif therewith. Damageability assessment of the rock massif with a mine roadway was carried out based on the obtained distributions of stresses and strains. We calculated volumetric damageability through the model of a deformed solid body with dangerous volume. Dangerous volume is a limited area where stresses or strains exceed the predetermined threshold. Calculation of dangerous volumes and integral damageability was carried out in the finite element package ANSYS. The program was written in APDL. The ratios between the existing and limiting stresses was calculated for each finite element. The elements for which this ratio exceeds unity will form a dangerous volume for the whole model. As a result, we have an array of finite elements constituting the dangerous volume and its value. The developed method for assessing damageability in the mine roadway neighbourhood takes into account various cross-sectional shapes of the mine roadway and its depth. The relevance of studying possible destruction regions using the model of a deformed solid body with dangerous volume was substantiated.
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.
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