Abstract
A novel high C high Si carbide free bainitic steel was developed for the production of cold work tools, knives, and rolls, requiring high hardness, toughness, as well as abrasive/adhesive wear resistance and resistance to galling at low costs. The steel was tribologically tested in dry sliding conditions under abrasive and adhesive wear mode, facilitated by using alumina and bearing steel ball as a counter-material, respectively. It was determined that carbide dissolution occurs under high contact pressures, thereby enriching the surrounding matrix with carbon and locally increasing the retained austenite content. The high retained austenite at the sliding interface increases the steels work hardening capacity and promotes superior wear resistance when compared to much more alloyed cold work tool steel, such as AISI D2. The steel has a high resistance to galling as determined by sliding against a soft steel bar due to its chemical composition.
Highlights
The wear resistance of tool steels depends upon the microstructure, including the spacing, size, and type of hard particles, as well as the ability of the matrix to absorb energy, all defining steel hardness and toughness [1].Carbide-free bainitic microstructures are known to exhibit superior combination of mechanical and wear resistant properties
This is provided by the very fine scale of bainitic ferrite plates that are embedded within a matrix of retained austenite and a stress/strain induced transformation of the retained austenite phase into very hard untempered martensite
Phase transformation gives rise to work hardening, which is known as the transformation-induced plasticity effect [2]
Summary
The wear resistance of tool steels depends upon the microstructure, including the spacing, size, and type of hard particles, as well as the ability of the matrix to absorb energy, all defining steel hardness and toughness [1]. Refined pearlite has a greater flow stress and work hardening rate, while finer cementite is able to accommodate more deformation prior to fracture [6] In this sense it is not important how the retained austenite was stabilized, due to the effect of Si or Al [7], thermally [8] or mechanically, provided the resulting toughness is sufficient to prevent the initiation and propagation of cracks from the surface. This was well illustrated in a study where the wear resistance of carbide free lower bainite, martensite, and pearlite in the same super bainite steel was practically the same [9]. A KAB steel, which fulfils the above description, has been developed and its resistance to abrasive and adhesive wear evaluated and compared to conventional D2-type tool steel in the current work
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