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

T15 the oversintering necessary for the appearance of a continuous M6C eutectic
carbide increases from 15-20K for vacuum sintering to 50-55K for atmosphere
sintering .
Fig. 10 shows the evolution of hardness with the tempering
temperature for triple tempering of one hour and half after austenitization at two
different temperatures (1150 and 1175 ° C) of T42 * steel, for specimens sintered in
the gas atmosphere. Some data found in the literature for vacuum sintered T42 (3) is
also included . It is observed that the maximum hardness is reached at temperatures
higher than 550°C, being the actual hardness higher than 1040 and 1000 HV50 for
austenitizations at 1150 and 1175 ° C respectively . Fig. 11 compares the hardness
after triple one hour tempering for atmosphere and vacuum sintered specimens . It is
clearly apparent that the maximum of hardness for atmosphere sintered specimens
is reached at higher temperatures (575°C) than for vacuum sintered specimens
(525°C) .
Fig . 12 shows the hardness (HV10), also after triple tempering of 1 hour
duration, versus the tempering temperature for Px30 steel sintered in vacuum and in
the gas atmosphere and for two austenitizing temperatures . It is clearly apparent in
first place that the hardness in the as-quenched condition is lower for the gas
sintered material, due to the presence of a higher amount of retained austenite . The
peak hardness for the material gas sintered occurs at higher temperatures (575'C)
and with higher values of hardness (1000 HV) than for vacuum sintered material, in
which the peak occurs at 500°C and with a hardness value < 950 HV . It is observed
also negligible differences in hardness due to the use of different austenitizing
temperatures both- in atmosphere sintered specimens (1200--and- 1-2-20°C) and in
vacuum sintered specimens (1230 and 1250°C) .
Fig . 13 shows the variation of fracture toughness with hardness for the
three steels . A clear decrease of toughness with increasing hardness is observed .
Within the experimental scatter, all the data can be reasonably fitted to a straight line
of equation,
KI c =-4,5 .10-2 * (HV)+56,4 Ec .1
(*) These values were obtained by Mr . B . Ógel at the Department of Materials of the University of
Bradford