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

achieved) .
The addition of 0.2% elemental carbon (producing an increase in the
carbon content of the compacts in both steels) activates the sintering process and
the optimum densification is reached at lower temperatures, 10K and 15K for
vacuum sintering in Px30 and Px30S steels respectively and 30K and 20K for Px30
and Px30S steels respectively during sintering in the gas atmosphere .
An important increase in the amount of N in the gas sintered samples
is observed with values ranging from 0 .71-0.76% for Px30 steel to 0 .44-0 .45% for
Px30S steel . These values are around two orders of magnitude higher than in the
vacuum sintered samples, 0 .012 for Px30 steel and 0 .007-0 .008 for Px30S steel . This
increase in the concentration of N has in both steels an important effect by
decreasing the optimum sintering temperatures : 50K and 30K for Px30 steel with and
without 0 .2% carbon addition respectively and 30K and 25K for Px30S steel with and
without carbon addition respectively .
Small decreases in the carbon content are generally observed after
sintering, being vacuum sintering more efficient than gas sintering in decreasing the
original concentration of oxygen .
Figs .3 a and b show the microstructures of specimens sintered at the
optimum temperature for Px30 and Px30+0 .2%C respectively, vacuum sintered . The
presence of products of the decomposition of austenite are clearly apparent mainly
surrounding the primary carbides and inside the original grains of austenite . Some
amount of retained austenite is also present. The primary carbides are mainly MC
and M.C. The carbides present in the grain boundaries are fundamentaly type
massive MC (> 4 Mm ) . For atmosphere sintering (Figs . 3 c and d), the
incorporation of nitrogen to the steel, as shown in Table III, produces some
important modification in the microstructure . In first place a significant increase in
retained austenite is observed and in second place the type MC carbides change to
MX carbonitrides of smaller size, as shown in Figs .3 c and d . It is also clearly
apparent the refining of the austenitic grain sizes in the specimens sintered in the
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