Aspetti metallurgici e caratteristiche meccaniche in getti realizzati ...
Aspetti metallurgici e caratteristiche meccaniche in getti realizzati ...
Aspetti metallurgici e caratteristiche meccaniche in getti realizzati ...
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ACCIAIO<br />
EXPERIMENTATION AND MODELLING OF THE ANNEALING<br />
PROCESS PERFORMED IN A HYDROGEN BELL<br />
KEYWORDS:<br />
Steel, steel-mak<strong>in</strong>g, anneal<strong>in</strong>g, model<strong>in</strong>g,<br />
processes, hydrogen bell<br />
The anneal<strong>in</strong>g performed <strong>in</strong> hydrogen bell furnace can represent<br />
a good alternative with respect to the other anneal<strong>in</strong>g<br />
process structured to reach high productivity rate, because<br />
it can grant a good cleanl<strong>in</strong>ess and homogeneous<br />
treatment. This is a technique known for several years, but<br />
<strong>in</strong> this study a new version, named HICON-H2, has been<br />
taken <strong>in</strong>to account. The efficient heat transmission is assured<br />
by the high convection devices rotat<strong>in</strong>g at 75 Hz and the<br />
atmosphere is completely satured by 100% H2 dur<strong>in</strong>g the<br />
anneal<strong>in</strong>g period. This atmosphere permits a satisfactory<br />
cleanl<strong>in</strong>ess of the surface which also decreases the time of<br />
the anneal<strong>in</strong>g process.<br />
The annela<strong>in</strong>g cycles of SAE1006 (tab.1) featured by different<br />
parameters has been observed (table 2). The positive<br />
ABSTRACT<br />
convection has been proved by the little scatter of the hardness<br />
and ductility data among the different coils (table 3)<br />
and with<strong>in</strong> any s<strong>in</strong>gle coil (table 4). The gra<strong>in</strong> size has been<br />
measured for each coil (table 5) and then it has been related<br />
to the anneal<strong>in</strong>g parameters after the def<strong>in</strong>ition of the construction<br />
of a mathematical model based on the f<strong>in</strong>ite different<br />
method to treat the heat transmission <strong>in</strong> order to def<strong>in</strong>e<br />
the thermal transmission modality. To def<strong>in</strong>e the convective<br />
heat transmission coefficients the thermocouples have been<br />
placed with<strong>in</strong> the coils (fig.1) dur<strong>in</strong>g the anneal<strong>in</strong>g period<br />
and then the heat transmission coefficients have been def<strong>in</strong>ed<br />
<strong>in</strong> order to fit the experimental results (fig.6). This permits<br />
to simulate correctly the anneal<strong>in</strong>g process and by the<br />
use of a method recently proposed to describe the static recrystallization.<br />
the average gra<strong>in</strong> size of the annelaed gra<strong>in</strong><br />
has been related to the characteristic parameters of the annela<strong>in</strong>g<br />
cycle, giv<strong>in</strong>g good results. So the comb<strong>in</strong>ed use of<br />
the ricrystallization model and the determ<strong>in</strong>ed heat convection<br />
can allow a good design<strong>in</strong>g of the annela<strong>in</strong>g process<br />
with great sav<strong>in</strong>gs of money produced avoid<strong>in</strong>g the expensive<br />
trial and error procedure.<br />
4/2004 Memorie<br />
la metallurgia italiana 35