Sinterizazio-atmosferaren eragina M graduko (ASP 30 ... - Euskara

Fracture toughness tests performed on these T grade steels gas
sintered(16,19-21), quenched and tempered have shown K, 0 values similar to
vacuum sintered high speed steels .
In the present work the vacuum sintering behaviours of two Px30
steels, one of them rich in sulphur(Px30S free-machining grade), are compared with
sintering in the gas mixture N 2-H2CH 4 to see if sintering in an atmosphere rich in
nitrogen has also effect on M grade high speed steels, other than M2 . The effect of
an addition of 0 .2% elemental carbon to these two steels is also studied . After
sintering, the carbon, oxygen and nitrogen content are analyzed together with the
microstructure characterized by the austenite content, initial grain size and the
composition, size and volume fraction of the primary carbides . Sintering in the gas
atmosphere will allow cost saving due to the low temperature sintering, and
improvement in microstructure, mechanical properties and performance in service
and offers the prospect of significant competitive advantage to manufacturers of tool
and wear parts .
EXPERIMENTAL PROCEDURE
Vacuum annealed, water atomized Px30 and Px30S powders were
bought from Powdrex Limited, Tonbridge, U .K. The -ccr_nposition_and sieve analysis
of the powders provided by the . . . manufacturer are given in Tables I and II
respectively . Additions of 0 .2 weight % of elemental carbon in the form of graphite,
15 µm mean size, were made and appropiate amounts of dry powders and graphite
mixed for a period of 4 hours .
Compacts of 16 mm diameter, weighing 4 g were cold compacted
uniaxially at a pressure of 500 MPa, the walls being lubricated . This resulted in a
green density of 5 .4x 10 3 and 5 .6x 10 3 kgm -3 for the Px30 and Px30S steels
respectively. These values are equivalent to 65.9% TD for Px30 and 68 .3% TD for
Px30S . The compacts were sintered either in a flowing atmosphere composed of
90% volume N29%H 2-1 %CH 4 or in vacuum . In this second case the vacuum was
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