Prakt. Met. Sonderband 52 (2018) 97
ANNEALING OF NANOSTRUCTURED CARBIDE FREE BAINITE
ney
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rity Peter Kirbis 2, Ivan Anzel?, Tomaz Irgoli¢?, Tatjana Vecko Pirtovsek’, Mihael Bruncko?
Azenung Von 1. Metal Ravne d.d. KoroSka cesta 14, 2390 Ravne na KoroSkem, Slovenia
hor 2. University of Maribor, Faculty of Mechanical Engineering, Smetanova 17, 2000
OSphorsäure Maribor, Slovenia
of Wird und
Pf ABSTRACT
Welche Two experimental high Al nanostructured bainitic steels have been annealed in order to
obtain a microstructure suitable for machining. It was observed that the microstructural
development is heavily dependent upon the ration of C and carbide forming elements
(Mn, Cr, Mo), whereby the balance shifts from cementite towards graphite. The annealed
microstructures are exceptionally fine and provide superior machinability characteristics.
(derdände
"UM GmbH; INTRODUCTION
Machinability can be thought of as the ability of a given machining operation to achieve
Sonderbände the pre-set quality requirements for a given work material while keeping a pre-defined
UM GmbH, level of process efficiency [1]. As such it can be regarded as a system property,
depending on many variables ranging from the tool material, edge geometry, cutting fluid
Azan, and the characteristics of the work piece. It is sometimes argued that the tool material is
the dominating factor determining machinability [2]. However once a certain industrial
"und practice becomes established it is of interest to optimize the properties of the work pieces.
The ideal material for machining operations shall be brittle which is the basis of a model
which describes a reasonable correlation between machinability and the specific damage
energy, defined as the area under the real damage curve [3]:
Er = | de,
0
When these two criteria are considered the ideal materials would be extremely fine
grained, with negligible work hardening in particularly at high strain rates, therefore
Nanograined materials come to mind. In order to truly exploit them it is also necessary to
reduce their hardness and increase the thermal stability. In addition to microstructure the
cutting behavior is also dependent on various metallurgical factors, most notably the
presence of hard inclusions and carbides. The chip formation is also influenced by their
shape and spaceal distribution, whereby the later can be altered via heat treatment,
whereas the total amount is determined by the chemical composition.
The introduction of embittering particles is commonly accomplished via alloying additions
of S, P, Se and similar elements which form inclusions and thereby promote the formation
and breakage of chips [4]. The presence of such inclusions however adversely affects
the mechanical properties of heat treated high strength steels, therefore this approach is
limited to less demanding applications. There is a continuous effort in the development of
annealed steel microstructures that could ease machining operations preferably without
2
