austenite as white areas depicting the interdendritic regions. a 
For these reasons, maraging steels must go through homogenization A 
heat treatment. This homogenization not only promotes a better ageing Lo 
response but also improves toughness (8-11) Le 
2. EXPERIMENTAL PROCEDURE a 
An experimental heat of 18%Ni 1900MPa maraging steel was induction en 
melted undervacuum with the following composition : C=0.007%;Si=0.03%; en 
Mn=0.03%;Ni=18.15%;C0=9.01%;M0=4.97%;T1=0.70%;AR1=0.07%;P=0.007%; I 
S=0.003%. A 140x140mm square section ingot of about 47kg was cast, 
and hammer forged at 1180°C to a 90x90mm billet. Six specimens were oe 
taken from the central region of this billet with relation to its 
thickness and length. Only one of these specimens remained in the 
as-forged condition and the other five were homogenized at 1197°C for Se 
1.5 ,10,25,35 and 50 hours respectively, and air cooled. Under these Se 
conditions, the six specimens were examined through optical So 
metallography, X-ray diffractometry and electron microprobe. Then, Le 
all specimens were aged at 480°C/3h and examined by optical “i 
metallography and X-ray diffractometry. we 
For metallographic tests the following etchants were used: 10%Nital, Dackets 
4%Nital,10gFeCl;+30mLHC1+120mLH,0 and electrolytic 10% Chromic acid. EE 
In the as~forged + aged condition the volumetric fraction of Ta 
austenite was assessed by means of quantitative metallography in 
accordance with the ASTM E562 standard (12) 120 random fields were Howe 
counted using the 100-points grid and magnification 200x. The pa 
microstructures were observed through a Zeiss ICM 405 optical So 
microscope. RE 
X-ray diffractometry was done to determine the austenite content by Eh 
using a Rigaku-Strainflex MSF2M parallel beam X-ray diffractometer. as sh 
The integrated intensities of the (220)y and (211)a reflections were Pl 
used for the calculations of the austenite content. EN 
The microsegregation degree of nickel,molybdenum and titanium was ” Ihr 
assessed semi-quantitatively using a Jeol Superprobe 733 electron : 
microprobe WDS. For each element, 100 X-ray intensities were 
recorded along the lines perpendicular to the microsegregation 
Prakt. Met. Sonderbd. 21 (1990) 
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