The heating of steel semi-products in view of hot rolling process or heat treatments is achieved at the large scale in propulsion ovens for the increase of their deformability and to improving mechanical characteristics of finite products.
The main heating defects (oxidation and decarburation, overgrown grain size of steels) represent processes of alteration of the superficial layers or the decrease of the physical and mechanical characteristics of the finished products.
This paper presents the results of experimental researches on the oxidation susceptibility, variation of the depth of the decarburized layer and the susceptibility to overheat of two ship steel grades (A36 and E36 grade), during the heating for the hot metallurgical processing of the semi-products. It is the deepening of the researches about heating behavior of naval steels with different chemical compositions

Elisabeta VASILESCU

The Annals of “Dunarea de Jos” University of Galati Fascicle IX Metallurgy and Materials Science

Directory of Open Access Journals

FA
CU
LT
AT
E
A
D
E
IN
G
IN
ER
IA MATERIALELO
R
Ş I
A
M
EDIULUI
THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE
N0. 1 – 2014, ISSN 1453 – 083X
EXPERIMENTAL RESEARCH ON HEATING BEHAVIOR OF SOME
STEELS DURING HOT METALLURGICAL PROCESSING
Elisabeta VASILESCU
„Dunarea de Jos” University of Galati
e-mail: elisabeta.vasilescu@yahoo.com
ABSTRACT
The heating of steel semi-products in view of hot rolling process or heat
treatments is achieved at the large scale in propulsion ovens for the increase of
their deformability and to improving mechanical characteristics of finite products.
The main heating defects (oxidation and decarburation, overgrown grain size
of steels) represent processes of alteration of the superficial layers or the decrease
of the physical and mechanical characteristics of the finished products.
This paper presents the results of experimental researches on the oxidation
susceptibility, variation of the depth of the decarburized layer and the
susceptibility to overheat of two ship steel grades (A36 and E36 grade),  during
the heating for the hot metallurgical processing of the semi-products. It is the
deepening of the researches about heating behavior of naval steels with different
chemical compositions.
KEYWORDS: oxidation susceptibility, decarburized layer, susceptibility to
overheat, main defects, ship steel grades, metallurgical processing
1. Introduction
The performance of obtaining products or
providing services is ensured through a primordial
factor called quality.
Maintaining performance requires continuous
quality improvement and quality assurance includes
all planned systematic actions necessary to provide
adequate confidence that a product or service satisfies
the quality requirements [15]. The quality of a steel
product is determined primarily by the properties of
the material which in turn depend on its nature, (type)
characterized by chemical composition and by
particular structure. The structure of a metal material
can be modified by thermal treatment and / or
thermomechanical, so product quality is directly
influenced and in the greatest extent through the
modification of its properties.
On steel products market quality of a product is
defined by identifying the concept with one of the
important features of the product, which is obviously
superior in comparison to similar products. A rational
use of a steel product for a given application is a
complex and schematic matter that actually means
providing steel grades that meet the maximum
strength and durability characteristics under a
minimum cost price. Capitalizing fully technological
properties of steels contributes to process in optimal
conditions the blank to obtain a finished product with
optimum features. Defined as material sizes, heat
treatment technological characteristics are expressed
quantitatively by experimentally determined values,
under conventional set, so those sizes to allow the
comparison of different metallic materials or of the
same metallic material with different structural states
(ie values of critical points, critical transformation
speed, susceptibility to overheating, susceptibility to
deformation and rupture etc.).
Thus, susceptibility to overheating [3, 4] of
steels characterizes  kinetics of crystal growth of
austenite formed by heating slowly to a temperature
in the range of its stability. The size of the crystals
formed in the austenite steels with different chemical
compositions or with similar chemical composition
but from different batches, depends in different ways
on the temperature and duration of heating for the
austenitising. Therefore, to characterize a steel
overheating susceptibility we should determine the
grain size of austenite formed, in heating conditions
(temperature and holding time) set in a conventional
manner, for different groups of steel.
Characterization of the behavior of a metallic
material in the chemical interaction with the
environment where the heating and cooling are made
for a certain type of hot metallurgical processing
-  32  -
FA
CU
LT
AT
E
A
D
E
IN
G
IN
ER
IA MATERIALELO
R
Ş I
A
M
EDIULUI
THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE
N0. 1 – 2014, ISSN 1453 – 083X
(plastic deformation, heat treatment) is done using
thermodynamic characteristics that define the
chemical affinity of metallic material to the
components of the environmental [3]. For this
purpose, there are used the appropriate
thermodynamic characteristics as the oxygen
potential of the metal oxide, the activity of carbon,
nitrogen activity, etc., whose values depend on the
chemical composition and temperature of the metallic
material. Using the values of the chemical
characteristics of metallic materials can be selected,
chemical compositions of the media heating / cooling,
which at the temperature that the metallurgical
process in being performed exerts on the superficial
layers of metallic materials products, chemical
actions corresponding prescriptions. Given these
theoretical considerations, this paper aims to highlight
the results of laboratory scale investigations on the
susceptibility to oxidation and susceptibility to
overheating of naval steels during heating of the
products for to increase their deformability and the
heat treatment applied.
2. Materials and experimental conditions
Heating steel semi-products to hot rolling
furnaces powered (Specific conditions of the steel
Plant in Galati) aims to reduce rolling resistance to
deformation or heat treatment (normalization,
improvement) requiredby the standard product.
The main heating defects (oxidation and
decarburization of steels) are processes that destroy
superficial layers of heated material that  leading to
significant increases of the fuel consumption and
lower of the furnace productivity (increased
consumption of steel). Overcoming decarburized
layer thickness over a certain value means discarding
the material. The steel surface is oxidized more
intense as the temperature and duration of heating are
higher. Also if slabs have lower temperatures than
those required by technological they return for a new
heating. In this situation there is an increase in fuel
consumption per ton of steel [14].
Using a suitable heating technologies of the
slabs for rolling,, contributes substantially to the
reducing of energy consumption.
The rolling can be achieved with higher values
of passage reductions, the wear of subassemblies
being entered in the normal range.
By maintaining a constant temperature during
treatment  are avoided rejects and technological
limitations that arise from overheating or over
maintaining, thus reducing losses by oxidation and
respecting the scheduled quality of the treated
product.
In shipbuilding, the highest amount of material
is in the hull. The hull is made of sheets, strips, rods
and profiles with thickness of maximum 50 mm, hot
rolled weldable steels. In general, steel tables for
constructions in transportation industry (marine, rail,
land, etc.) can be obtained from the manufacturing
flow of heavy plate mill No. 1 or No. 2 of the plant
from Galati.
As mentioned, this paper is a development of
previous experimental research [14] on the behavior
at heating of the steel plate products for ships. It is
planned to study the heating behavior of semi-
finished steel, fine grained E36 in comparison with
steel grade A36 (table 1). The author wished to study
especially the heating behavior of flat steel products
E36 given the results of the author's previous
research, which demonstrated the possibility of
performing the specific heat treatment (normalizing,
annealing, etc.) with heating at lower temperatures
(termical treatment with heating in the intercritical
range of steel), with the important advantage of
reducing susceptibility to oxidation and overheating.
Generally, constructions and naval parts are
subject to the rules and specifications RNR or
International Ship Register. The standard 8326-86
covers hot rolled steel sheets, with thickness between
4 mm and 60 mm used in welded naval constructions,
primarily for bearing structure elements of river and
sea vessels of different dimensions: small, medium
and heavy sizes which are manufactured in
accordance with the Romanian Naval Register. Under
this standard, the tables for shipbuilding are classified
into: normal strength steel sheets with minimum yield
strength value of 235 N/mm2 and high strength sheet
steel with minimum yield strength value of 315
N/mm2. The table below shows the chemical
composition of steel samples under study.
Table 1. Chemical composition of the steels studied
Chemical composition (%)Steel
Grade C Mn Si S P Cr Ni Mo Al Cu Nb V/Ti
E36 0.15 1.40 0.30 0.020 0.018 - - - 0.043 - - -
A36 0.17 1.45 0.27 0.017 0.029 - - - 0.033 - 0.031 0.021
-  33  -
FA
CU
LT
AT
E
A
D
E
IN
G
IN
ER
IA MATERIALELO
R
Ş I
A
M
EDIULUI
THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE
N0. 1 – 2014, ISSN 1453 – 083X
Rectangular samples with dimensions of
10x10x50mm were machined and then
metallographically prepared until mirror gloss. After
degreasing in alcohol the samples were kept in
desiccator for weighing.
Fig. 1. Machined samples
Experiments were performed in the laboratory
in electric furnaces with forced bars.
The samples were heated at temperatures:
900°C, 1000° C, 1100° C, 1200° C with holding
times of: 1 hour, 2 hours, 3 hours, 5 hours, 8 hours, in
the oxidation atmosphere of the furnace.
Placing in the oven was made on a special
holder that allowed exposure to the oxidant
environment of all sample surfaces.
After oxidation the samples were subjected to
mechanical removal of the corrosion products and
were reweighted. Losses of weight were determined
at oxidation temperatures and durations of
maintenance experienced. The oxidation rate was also
determined on each sample according to the
experimental thermic regime (working temperature
and holding time). In order to study the structural
changes, the samples were cut. Sectional area of
10x10 mm size was metallographic prepared.
The microstructure was revealed by chemical
attack: 2% nital and X100 magnification.
It has been measured the depth of the
decarburized layer and it was determined the
granulation score of the microstructure and
Widmannstatten structure, by comparing with the
standard images.
Next we proceeded to the processing of the
experimental data. To facilitate interpretation and to
elucidate the behavior at heating of the two brands of
steel, graphs were plotted which easily illustrate the
objective of the experiments.
3. Experimental results
Table 2. The loss of mass from the oxidation of steel samples depending on the heating regime
Heating
temperature Holding time
Average mass loss
A 36
Average mass loss
E 36
[0C] [h] [g/m2]
1 4.68 30.45
3 22.08 34.46
5 23.37 32.44
8 - 29.50
900
3 - 100.07
1 25.45 32.99
3 48.51 94.481000
5 69.93 80.35
1 29.44 97.47
3 69.31 94.161100
5 73.20 194.31
1200 1 - 61.70
-  34  -
FA
CU
LT
AT
E
A
D
E
IN
G
IN
ER
IA MATERIALELO
R
Ş I
A
M
EDIULUI
THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE
N0. 1 – 2014, ISSN 1453 – 083X
0
20
40
60
80
0 1 2 3 4 5 6
Time, [h]
T= 900 C
T=1000 C
T=1100 C
A
ve
ra
ge
 w
ei
gh
t l
os
s 
[g
/m
2]
Fig. 2. Mass losses at the oxidation of grade A36
0
50
100
150
200
250
0 1 2 3 4 5 6 7 8 9 10
T=900 C
T-1000C
T=1100
Series4
Time, [h]
A
ve
ra
ge
 w
ei
gh
t l
os
s 
[g
/m
2]
Fig. 3. Mass losses at the oxidation of grade E36
0
20
40
60
80
100
120
800 900 1000 1100 1200 1300
Temperature, [ C]
A 36
E36
A
ve
ra
ge
 w
ei
gh
t l
os
s 
[g
/m
2]
Fig. 4. Variation of mass losses with the temperature, on 3 hour duration, at grades A36 and E36
-  35  -
FA
CU
LT
AT
E
A
D
E
IN
G
IN
ER
IA MATERIALELO
R
Ş I
A
M
EDIULUI
THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE
N0. 1 – 2014, ISSN 1453 – 083X
Table 3. The speed of oxidation of the steel samples according to the heating regime
Heating
temperature Holding time
Average speed of
oxidation
A 36
Average speed of
oxidation
E 36
[0C] [h] [g/m2h]
1 4.68 15.23
3 7.36 11.55
5 4.67 6.49900
8 - 3.69
1 25.45 32.99
3 16.17 31.491000
5 13.99 16.07
1 29.44 97.47
3 23.10 47.081100
5 - 38.86
1 61.701200 3 33.36
0
5
10
15
20
25
30
35
0 1 2 3 4 5 6
Time, [h]
T=900C
T=1000C
T=1100
A
ve
ra
ge
 s
pe
ed
 o
f o
xi
da
tio
n,
 [g
/m
2h
]
Fig. 5. Average speed of oxidation of the A36 steel samples according to the heating regime
0
20
40
60
80
100
120
0 1 2 3 4 5 6 7 8 9
Time, [h]
T=900C
T=1000C
T=1100C
T=1200
A
ve
ra
ge
 s
pe
ed
 o
f o
xi
da
tio
n,
 [g
/m
2h
]
Fig. 6. Average speed of oxidation of the E36 steel samples according to the heating regime
-  36  -
FA
CU
LT
AT
E
A
D
E
IN
G
IN
ER
IA MATERIALELO
R
Ş I
A
M
EDIULUI
THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE
N0. 1 – 2014, ISSN 1453 – 083X
Fig. 7. Variation of the depth of the decarburized layer with the maintenance duration and heating
temperature for the grade A36
0
0,1
0,2
0,3
0,4
0,5
0,6
0 1 2 3 4 5 6 7 8 9
T=900C
T=1000C
T=1100C
T=1200C
Th
ic
hn
es
s 
de
ca
rb
ur
at
ed
  l
ay
er
 [m
m
]
Time, [h]
Fig. 8. Variation of the depth of the decarburized layer with the maintenance duration and heating
temperature for the grade E36
0
0,05
0,1
0,15
0,2
0,25
0,3
0,35
0,4
0 1 2 3 4 5 6
Time, [h]
A 36
E 36
Th
ic
hn
es
s 
de
ca
rb
ur
at
ed
  l
ay
er
 [m
m
]
Fig. 9. Variation of the depth of the decarburized layer with the maintenance duration at 1100°C
for the grades A36 and E36
-  37  -
FA
CU
LT
AT
E
A
D
E
IN
G
IN
ER
IA MATERIALELO
R
Ş I
A
M
EDIULUI
THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE
N0. 1 – 2014, ISSN 1453 – 083X
Below there is presented the graphic variation
of the depth of decarburization measured on the
studied steel samples according to the experimental
heating regime.
The microscopical aspects on the structural
changes of the heated steel samples taken from
shipbuilding plates
Steels analyzed and presented in Table 1 are
additionally deoxidized with aluminum and present a
medium to fine granulation.
Fig. 10. Rolled State (X100, natal 3%), sample from shipbuilding steel A36, thickness 16 mm,
ferrite and pearlite grains scoring 8-9, forming alternative rows score 4
To observe the growing trend of austenitic grain
together with increasing temperature and duration of
maintenance, in the laboratory it was simulated the
hot metallurgical processing through performing the
heating of the samples at different temperatures and
durations. The results for the A 36 steel highlight the
growth of the austenitic grain for the next thermic
regimes experimented: temperature of 880°C and
930°C and maintaing time of 2, 3, and 5min/mm.
Fig. 11. Wd structure score 3-4, A36 samples subjected to heating regime:
temperature 880°C / 3.0 min / mm holding time
-  38  -
FA
CU
LT
AT
E
A
D
E
IN
G
IN
ER
IA MATERIALELO
R
Ş I
A
M
EDIULUI
THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE
N0. 1 – 2014, ISSN 1453 – 083X
Fig. 12. Wd structure score 3-4 A36 samples subjected to heating regime:
temperature 930°C / 3.0 min / mm holding time
Fig. 13. Wd structure score 4 A36 samples subjected to heating regime:
temperature 880°C / 5.0 min / mm holding time
Fig. 14. Wd structure score 4 A36 samples subjected to heating regime:
temperature 930°C / 5.0 min / mm holding time
-  39  -
FA
CU
LT
AT
E
A
D
E
IN
G
IN
ER
IA MATERIALELO
R
Ş I
A
M
EDIULUI
THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE
N0. 1 – 2014, ISSN 1453 – 083X
4. Conclusions
The analysis of the oxidized samples
revealed the presence of a porous oxide layer that
detaches easily from the surface by rubbing, and a
bright appearance coating, adhering to the surface,
which is removed only by hot etching. The weight
loss by oxidation / unit area, due to the formation of
porous oxide, non-stick, it is negligible at 900˚C and
increases with the temperature in the range of 900-
1100˚C, for both steel grades studied. At a
temperature of 1200˚C, the weight loss recorded for
quality E36 is lower than at the temperature of
1100˚C, fact explained by the formation of adhesive
oxide in larger quantities.
Of the two steel grades considered, at least
in the temperature range 900-1100˚C, the oxidation
process was more intense at E36 brand. The speed of
oxidation increases with increasing temperature,
higher in the first stage of oxidation, for 1 hour, and
then decreases with the lasting period, being
maximum at temperature of 1100˚C. Oxidation rate is
also higher for steel E36. The depth of the
decarburized layer increases with higher temperature
(as a result of increased diffusion processes) and is
less influenced by the duration of maintaining the
temperature at 900°C. The influence of the
maintenance period on the decarburization process is
accentuated when the temperature rises.
Quality steel E36 exhibited higher
decarburization tendency compared with to that of
A36 steel, a conclusion that allows the adoption of
appropriate technological solutions to hot
metallurgical processing of products belonging to this
quality of steel.
References
[1]. Adrian M. - Tehnologia laminării, Editura Didactică și
pedagogică, București 1977.
[2]. Cheşa, I., Laşcu, N.S., Nedelcu, C., Rizescu, C., Teodorescu,
M. - Alegerea şi utilizarea oţelurilor, Editura Tehnică Bucureşti
1984.
[3]. Dulămiţă T., Florian E. - Tratamente termice si
termochimice, EDP Bucureşti 1982.
[4]. Gadea S., Petrescu M. - Metalurgie fizica și studiul metalelor,
vol I; II; III, Editura Didactică și pedagogică, București, 1979;
1981; 1983.
[5]. Geru, N. - Metalurgie fizică, Editura Didactică şi Pedagogică,
Bucureşti, 1982.
[6]. Gheorghiu-Dobre, A., Nocivin, A - Introducere in Stiinta
Materialelor, Editura Matrix, 1998.
[7]. Mantea St., Dulamita T. - Teoria și practica tratamentelor
termice, Editura Tehnica, București, 1966.
[8]. * * * - Manualul inginerului metalurg, Editura Tehnică,
Bucureşti, 1978.
[9]. Popescu N. Dumitrescu C. - Tratamente termice si prelucrari
la cald, Editura Didactică și pedagogică, Bucuresti, 1983.
[10]. Schumann H. - Metalurgie fizică, Editura Tehnică,
Bucureşti, 1962.
[11]. Shackelford F. J. - Introduction to materials science for
engineers, Macmillan Publishing Company, New York, 1991.
[12]. Tripsa, I. - Metalurgia oțelului, Editura Didactică și
pedagogică, București, 1972.
[13]. Truşculescu M. - Studiul metalelor, Editura Didactică şi
Pedagogică, Bucureşti, 1977.
[14]. Vasilescu, E., Levcovici, S. M. - Experimental Researches
Concerning the Oxidation Resistance and Ovearheat Susceptibility
of Certain Ship Plates, The Annals of Dunarea de Jos of Galati,
Fascicle IX Metallurgy and Materials Science, ISSN 1453-083X,
2002.
[15]. Vasilescu, E., Vasilescu, I. - Calitatea produselor din oţeluri
microaliate prelucrate prin procedee termice neconvenţionale, Ed.
AGIR Bucuresti 2010.
[16]. Ilut, S., E. Vasilescu - „Studii şi cercetări privind
susceptibilitatea la oxidare a produselor plate din oţel naval”
lucrare de licenta, Galati 2011.
-  40  -


Experimental Research on Heating Behavior of Some Steels During Hot Metallurgical Processing

https://www.gup.ugal.ro/ugaljournals/index.php/mms/article/download/2644/2320

Experimental Research on Heating Behavior of Some Steels During Hot Metallurgical Processing

Abstract

Similar works

Full text

Available Versions

Directory of Open Access Journals