Understanding the main relationships between the microstructure parameters controlling the strength and ductility of low temperature bainitic microstructures is of considerable importance for further development of these grades. Although the microstructure essentially consists of solely two phases, bainitic ferrite and retained austenite, the complexity of the different microstructural characteristics, the natural consequence of its unique transformation mechanisms, might not provide with one unique answer, but a set of several parameters interdependent among them. This paper will deal with some of these relationships’ microstructure properties, strength, and ductility, with special emphasis in the mechanical stability (TRIP effect) of retained austenite.

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Strengthening and mechanical stability mechanisms in nanostructured bainite

Austempered ductile iron (ADI) is a type of graphite cast iron produced by an isothermal heat treatment process. It is an alternative to traditional steel castings and forgings and even aluminum due to the exceptional mechanical properties such as high strength, good toughness and excellent machinability. In the matrix, the unique ausferritic structure consists of graphite nodules uniformly surrounded by acicular ferrite and carbon saturated austenite. In the automotive industry, ADI has been commonly applied in the manufacturing of camshafts, crankshafts, gears and engine valves. These components are frequently subjected to surface contact with relative motion and external load. Therefore, it is necessary to understand the wear behavior of ADI in order to solve the tribological issues in existing ADI applications and utilize ADI into future designs appropriately. This paper was aimed at reviewing the fabrication processes of single-step and dual-step ADIs. The corresponding microstructure and mechanical properties were also briefly discussed. The studies on wear performance of ADI and potential mechanisms have been systemically reviewed.

A review: phase transformation and wear mechanisms of single-step and dual-step austempered ductile irons

http://hj.diva-portal.org/smash/get/diva2:680982/FULLTEXT01

Characterisation and investigation of local variations in mechanical behaviour in cast aluminium using gradient solidification, Digital Image Correlation and finite element simulation

http://hj.diva-portal.org/smash/get/diva2:457629/FULLTEXT01

Incorporating predicted local mechanical behaviour of cast components into finite element simulations

Castings are produced by a manufacturing method which gives the components properties that are dependant on design, metallurgy and casting method. The wall thickness influences the resulting coarseness and type of microstructure and the material will have properties dependant on local metallurgical and thermal history. The local properties in a cast iron component can vary essentially in the casting volume, which makes it difficult to optimize the castings with good accuracy. Often simulation of stress/strain of cast products use constant material properties throughout the castings. If the microstructure is determined or predicted at a given point, it is possible to calculate the local material properties and its deformation behavior.

On Modeling and Simulation of Mechanical Properties of Cast Irons with Different Morphologies of Graphite

A numerical description relating microstructure to elastic and plastic deformation behavior would make it possible to simulate the mechanical behavior of complex cast components with tailored material properties Limited work and data, however, have been published regarding the connection between microstructure and plastic behavior of austempered ductile irons (ADIs) In the current work, the effects of austempering temperature and austempering time on the strength coefficient and the strain hardening exponent of the Hollomon equation were investigated for two ADI alloys The results show that the plastic behavior is highly dependent on the combination of austempering temperature and austempering time It was found that as the austempering temperature increases, both the strength coefficient and the strain hardening exponent initially decrease, but after reaching a minimum at the critical austempering temperature, they show a plateau or an increase The effect of the austempering time on the plastic behavior depends on the austempering temperature At low austempering temperatures, the strength coefficient and the strain hardening exponent decrease with increased austempering time, whereas at higher austempering temperatures, they show little time dependence These relations are explained by the microstructural transformations that take place during the austempering heat treatment

/pdf/effect-of-austempering-on-plastic-behavior-of-some-24n6h38wdx.pdf

Dan Larsson

Papers

Effect of Austempering on Plastic Behavior of Some Austempered Ductile Iron Alloys

Modelling the plastic deformation behaviour of cast irons