REFRACTORIES IN HEAT UNITS
STUDY OF REFRACTORY CONCRETE
BEFORE AND AFTER SERVICE IN A CEMENTATION FURNACE
V. A. Perepelitsyn,
L. V. Uzberg,
G. V. Efimova,
O. N. Yakhontova,
V. Z. Nazmutdinov,
and N. V. Ipatov
Translated from Novye Ogneupory,No.1,pp.3–6,January, 2010.
Original article submitted July 17, 2009.
Results are provided for a study of refractory concrete before and after service in a cementation furnace with
the aim of revealing reasons for rapid wear of a concrete block after four months of operation at 850 – 930°C
in an endogas atmosphere. It is established that the reason for the rapid loss of concrete strength is destruction
of the concrete matrix as a result of the chemical action of endogas. Destruction of the concrete matrix is con
nected with partial reduction of SiO
to volatile SiO in microsilica and in calcium aluminosilicates.
Keywords: mullite-corundum low-cement concrete, microsilica, cementation furnace, endogas, concrete
Cementation furnaces are a form of heating furnaces
within which chemical heat treatment is performed for steel
objects (components) in an endogas atmosphere. Endogas
contains 20% CO, 40% H
and balance N
. The furnace
working temperature is 850 – 930°C. It is assumed that the
relatively low operating temperature does not create prob
lems for the choice of refractories for lining cementation fur
naces. However the mechanism of the action of endogas on a
refractory lining is not entirely clear.
Carbon monoxide and hydrogen are potential corrosive
agents during reaction with refractories. Their corrosive ac
tivity includes reduction of refractory oxides, however these
processes occur at relatively high temperature [2, 3]. Accord
ing to data in , it is thermodynamic possible to reduce
with CO from 1100 to 1400°C, mullite from 1200 to
1500°C, and corundum from 1400 to 2000°C. Hydrogen is a
stronger reducer than CO. Dinas refractories break down at
1200°C in a hydrogen atmosphere as a result of rapid conver
sion of silica. Hydrogen breaks down mullite with formation
of corundum and silicon monoxide SiO. Corundum refrac
tories on heating to 1500 – 1700°C exhibit stable properties
in a hydrogen atmosphere .
However, the mechanism of the action of endogas on a
refractory lining of heating furnaces is different [1, 4]. As a
result of long-term laboratory studies of different refractories
in an endogas atmosphere it has been established that there is
liberation of sooty carbon by the reaction 2CO ® CO
that proceeds within the volume of porous body slowly and it
is accelerated by catalysts. The catalysts are iron and its ox
ides, contained in lining materials. If the iron oxides are
within the composition of silicate phases, then they are not
The size and uniformity of catalytic inclusions with the
refractory structure has a marked effect on refractory stabil
ity in an endogas atmosphere. It is noted that coarse inclu
sions of sooty carbon lead to breakdown of even stable
refractories, whereas fine point inclusions of sooty carbon
within the structure of highly porous lightweight refractories
are not dangerous for their integrity.
According to data in , breakdown of refractories with
deposits of sooty carbon is caused by reaction of iron and CO
with formation of carbides and oxides, that proceeds with a
significant increase in volume, heat creates stresses within a
refractory body exceeding its strength. The working layer of
a refractory lining of a cementation furnace (walls, roof) is
made from heat insulation refractories, for which the stan
content is not more than 1.6%.
Refractories and Industrial Ceramics Vol. 51, No. 1, 2010
1083-4877/10/5101-0001 © 2010 Springer Science+Business Media, Inc.
OAO VOSTIO, Ekaterinburg, Russia.
OAO VNIIMT, Ekaterinburg, Russia.
OOO NPF Chleny-Ogneupory, Naberezhnye Chleny, Tatarstan