Research on Tensile Behaviour of New Structural Material MoNiCa

Abstract

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

Tribo-fatigue Behavior of Austempered Ductile Iron MoNiCa as New Structural Material for Rail-wheel System

“…For homogeneous materials such as hardened or tempered steel, the hardness is a dominant property in the tribo-fatigue system, however for austempered ductile irons with complex structure (nodular graphite, retained austenite, carbide) this dependence due to the presence of different inclusions is lower. On the other hand, formation of granular carbides in the structure of MoNiCa [6] promotes an increase of abrasion wear resistance with slightly decrease of toughness. Such a result could be explained [7] by an increase of micro hardness on and close the surface because of the strain induced transformation of retained austenite with low carbon content into martensite during the tests.…”

“…Test samples were subjected to heat treatment according to the following scheme ( Fig. 2): 1) austenization at 890 °C for 30 min; 2) quenching in salt bath, 5 s; 3) austempering at three different temperatures 270 °C, 300 °C and 330 °C; and 4) air quenching [6]. It was avoided to select higher process temperature trying to avoid worse wear performance of ADI as reported by other authors [13].…”

“…It was shown [6] that the strength of the new structural material practically reached the strength of high-strength steel. However, plasticity of MoNiCa is still much lower.…”

“…Austempering is the most widelyused heat treatment procedure to reach excellent combination of high strength, ductility, good wear resistance and tribo-fatigue behavior. So called austempered ductile irons (ADI) in addition to low manufacturing cost, fluidity, recyclability, damping capacity, and heat conductivity are much better than of some grades of alloyed cast steels, consequently they can be considered as an economical replacement for alloyed steel and other grades of cast irons [3,6,7].…”

Computer modeling of volumetric damageability in the mine roadway neighbourhood

“…Опасный объем есть ограниченная область, где напряжения или деформации превышают установленный порог. Кроме опасного объема, в качестве интегрального показателя состояния выработки может также использоваться повреждаемость опасного объема [1,[6][7][8][9][10].…”