METAL 2003
20. - 22. 5. 2003 Hradec nad Moravicí
__________________________________________________________________________________________
_
THE OXIDATION’S KINETICS OF SOME HIGH ALLOYED STEELS
Maciej Hajduga, Dariusz Jędrzejczyk
University of Bielsko-Biała, Material’s Engineering Department, Willowa 2,
43-309 Bielsko-Biała, Poland, E-mail:[email protected]
Abstract
The results of surface oxidation and decarburization of (Fe,C,Mn,Si,Cr,Ni) steels are
reported. The oxidation anneals were carried out at temperatures T= 980, 1020, 1060, 1100
°C. The aim of presented experiment was to compare typical alloyed steel behavior in the
same high temperature corrosion conditions. The estimated oxidation kinetics in connection
with later microstructure investigations and measurements of decarburized thickness layer
will allow for complex evaluation of examined steels. It follows from the experiment that
according to expectations steel H18N9S that belongs to the heat-resisting group characterizes
with greatest resistance against influence of high temperature. On special attention deserve
fact that the measurement indicate decreasing of the sample weight. This process is
systematical and with increasing of oxidation time and temperature the weight of oxidized
samples decrease.
Among the rest of materials the high resistance against the high temperature shows steel:
NC10 and SW18. Steel SK5 is situated in the middle of the range of weight increase, whereas
steel: 11G2 and ŁH15 show weight increases nearing to the greatest.
1. INTRODUCTION
The high temperature atmospheric corrosion is the most frequent example of chemical
corrosion and brings serious loses in chemical industry, power engineering, air and road
transport. The corrosion wear has essential influence on the lifetime both steel constructions
and machine elements. Atmospheric corrosion cause also the considerable loses during metals
production treatment. According to the statistical data about 1/3 of metallic materials is
withdrawn from uses in consequence of damages caused corrosion [1, 2]. Naturally part of
these materials is used again among other things as the charge materials in metallurgical
process, however about 10% of material is irrevocably lost. During the production of hot
working elements about 7% of treated material creates the scale layer and makes in this way
receiving of high quality product more difficult.
Total elimination of losses caused by corrosion is not possible. However advisable is
aspiration for it’s limitation both by suitable protection and by exact recognition of rights
ruling corrosion.
The most of papers and monographs published till now refers to the oxidation process of
the samples corresponding to semi-infinitive plane. Results of these investigations find
practical application in relation to some constructional elements and mainly to thin steel sheet.
Considering the practical application of cylindrical shape products (rods, wires), authors from
many years lead research regarding the oxidation of the cylindrical shaped samples with
diameter 3-50 mm [3-5]. It was stated among others thing that the oxidation process of the
sample with small diameter differs essentially from the oxidation of the flat samples, and it’s
kinetics could be described by exponential equation, whereas the kinetics of flat samples is
usually described by parabolic equation.
One of the methods of enlarging the steel resistance against corrosion is the proper
chemical composition choice of alloys working in corrosion circumstances. Most often
introduced alloyed elements are chromium and nickel.
1
METAL 2003
20. - 22. 5. 2003 Hradec nad Moravicí
__________________________________________________________________________________________
_
The aim of presented experiment was to compare typical alloyed steel behavior in the same
high temperature corrosion conditions. The estimated oxidation kinetics in connection with
later microstructure investigations and measurements of decarburized thickness layer will
allow on complex evaluation of examined steels.
2. THE OWN INVESTIGATIONS
The experiment was realized using cylindrical shape samples turned from typical alloyed
steel presented in table 1. The example of speciment appearance after oxidation is presented at
Fig. 1.
a)
b)
Figure 1. An example of specimens appearance after oxidation – steel SW7Mo; a – T =
9800C, t = 1000 min, b – T = 10200C, t = 1000 min.
Table 1. Chemical composition of materials used in the experiment, %.
Steel
design.
Chemical composition, %
ŁH15
C
0,79
Mn
0,2÷0,4
11G2
0,93
11,5
H18N9S
0,07
SW18
0,80
55
0,55
NC10
1,60
max.
2,0
max.
0,4
0,50÷
0,80
ab. 0,4
SW7Mo
0,79
ab. 0,30 ab. 0,25
SK5
1,06
max.
0,40
Si
0,15÷
0,35
0,4÷0,7
0,8÷1,5
max.
0,5
0,17÷
0,37
ab. 0,4
max.
0,40
P
max.
0,027
max.
0,10
max.
0,035
max.
0,03
max.
0,040
max.
0,03
max.
0,030
max.
0,03
S
max.
0,02
max.
0,030
max.
0,03
max.
0,03
max.
0,040
max.
0,03
max.
0,030
max.
0,03
Cr
1,40
17,0÷
20,0
4,0
max.
0,25
13,0
ab.
4,00
3,80÷
4,80
Ni
max.
0,3
-
Cu
max.
0,25
-
11,4
-
ab. 18%W; 1,25%V
max.
0,30
-
max.
0,30
-
ab.6,5%W; ok.
2,00%V; 5,5% Mo
16,6÷19,5%W;
max.0,40%Ni;
1,2÷1,7%V;
4,9%Co
Sample with diameter φ=30 mm and length l =20 mm after polishing were oxidized in
silite chamber furnace PKS 600/25. The experiment was conducted in four different
2
METAL 2003
20. - 22. 5. 2003 Hradec nad Moravicí
__________________________________________________________________________________________
_
temperature levels – 980, 1020, 1060 and 1100 0C. Samples were taken from the furnace one
by one after: 250, 400, 700 and 1000 min.
After cooling samples were exactly measured and weighted, then the scale layer was
removed and the metallographic specimens were prepared perpendicularly to the cylinder axis
to enable structure observation and micro-hardness measurement. For these research the
optical microscope NEOPHOT-2 and durometer DURIMET-20K were used.
3. RESULTS’ ANALYSIS
Because investigations relating to the micro-hardness measurements and structure analysis
are in the course of executing, the presented analysis will refers only to the oxidation kinetics
of tested materials. Data regarding internal materials’ structure, micro-hardness measurements
and estimated diffusion coefficients will be published gradually depending on the progress of
research work.
a)
Weight increase,g
increase,g
Weight
H18N9S
SW7Mo
b)
200
20 0
15
-0,2
400
600
800
1000
1100
1060
1020
980
10
-0,4
5
-0,6
0
-0,8
200
400
600 min
800
Time,
Time min
1000
Figure 2. The kinetics of oxidation of steel H18N9S and
SW7Mo
At the Fig. 2 the results of the weight
change for two extreme
materials: steel H18N9S,
in chance of which in
every oxidation temperature the weight decreasing was stated and
steel SW7Mo, which
shows the greatest weight
increase. Only in chance
of steel H18N9S the
weight decrease was
stated, the rest of materials showed systematical
weight increase. The
maximal relative weight
increase of steel SW7Mo
was about 14% (T =
1020 0C, t = 1000 min.),
considering the initial
sample weight about
114g.
The final confrontation of obtained weight
measurements is presented at Fig. 3.
Not typical – maximal weight increase of steel SW7Mo was measured at temperature 1020
C (see Fig.1). Such material behaviour could be explained by scale layer structure covering
sample oxidized at this temperature level. The observed scale was cracked and distorted.
There was no similar scale layer both in higher and lower temperature of oxidation.
It follows from presented results that according to expectations steel H18N9S that
belongs to heat-resisting group characterizes with greatest resistance against influence of high
temperature. On special attention deserve fact that the measurement indicate decreasing of the
0
3
METAL 2003
20. - 22. 5. 2003 Hradec nad Moravicí
__________________________________________________________________________________________
_
sample weight. This process is systematical and with increasing of oxidation time and
temperature the weight of oxidized samples decrease. Although differences between the initial
and final weight are not large and reach about 0.7g, which mean decreasing about 0.7%, the
stated trend shows rather, that this dependence it is not result of measuring error.
Among the rest of materials the high resistance against the high temperature corrosion
shows steel: NC10 and SW18. Steel SK5 is situated in the middle of the weight increase
range, whereas steel: 11G2 and ŁH15 show weight increases nearing to the greatest.
a)
b)
980 oC
ŁH15
11G2
H18N9S
SW18
7
5
3
55
NC10
SW7Mo
1
SK5
15
Weight increase, g
Weight increase,g
9
500
800
13
11
9
7
5
3
1
-1
200
1020 oC
17
-1
200
1100
500
800
1100
Time, min
Time, min
c)
d)
o
1060 oC
9
9
Weight increase,g
Weight increase,g
7
5
3
1
7
5
3
1
-1
200
1100 C
500
800
-1
1100
200
Time, min
500
Time, min
800
1100
Figure 3. The kinetics of oxidation the investigated alloyed steel at different temperature
level: a- 980 0C, b – 1020 0C, c – 1060 0C, d – 1100 0C.
4. CONCLUSIONS
1.
2.
Among the investigated steels the greatest resistance against influence of the high
temperature expressed by weight increase reveals steel H18N9S (in the range of
temperature 980-1100 0C, within time 250-1000min).
Unexpectedly, the relatively large weight increase (about 14% of initial value) was
measured for steel SW7Mo in oxidation temperature 1020 0C. Both in lower and
higher temperature of oxidation such surrosion was not stated.
4
METAL 2003
20. - 22. 5. 2003 Hradec nad Moravicí
__________________________________________________________________________________________
_
3.
The complex resistance estimation of examined materials against the high temperature
corrosion demands further investigation - measurements of: scale layer thickness,
decarburized layer thickness, micro-hardness of subsurface layer and X-ray microanalyze.
BIBLIOGRAPHY
1. KUčERA J., HAJDUGA M.: High-temperature and long-time oxidation of iron and
steels; Edt. PŁ Filia w Bielsku-Białej, 1998, p.88.
2. KLESNIL M., LUKAS P.: Fatigue of Metallic Materials, ACADEMIA Praha, 1992
3. HAJDUGA M., JĘDRZEJCZYK D., JURASZ Z.: Influence of Fe-samples diameter on the
process of oxidation at high temperature. METAL’99. 8th International Metallurgical
Symposium 11-13.05.1999. Ostrava Czech Republic. Proceedings V.4., pp. 33-38.
4. HAJDUGA M., JĘDRZEJCZYK D., JURASZ Z.: High temperature time dependence of Fe-C
samples oxidation. EDEM’99. International Conference on Environmental
Degradation of Engineering Materials. 19-23.09.1999. Gdańsk-Jurata. Poland.
Proceedings pp.119-127.
5. HAJDUGA M., JĘDRZEJCZYK D.: The influence of high-temperature oxidation on
decarburization, hardness and on fatigue limit in Fe-C-Cr-Mn-Si steels. KSCS 2000.
3rd Kurt Schwabe Corrosion Symposium. August 30 – September 2, 2000. Zakopane.
5