This paperwork shows the laboratory experiments made on X60 and X65 steels with several intercritical thermomechanical treatment application.
Two variants were used: “down-up” thermomechanical treatment with heating and rolling in the intercritical range and “up-down” thermomechanical treatment with preliminary complete austenitizing and rolling in the intercritic interval. High values of the strength characteristics and a good plasticity were gotten. A comparison was made with gotten results of the classical thermal treatment application (normalizing)

Ana DONIGA

Elisabeta VASILESCU

Miltiade ISTRATE

Silviu MACUTA

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

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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI 
FASCICLE IX METALLURGY AND MATERIALS SCIENCE, ISSN 1453 – 083X. NR 1 – 2005 
 
 
  
 
THERMOMECHANICAL PROCESSING OF MICROALLOYED 
STEELS USED FOR NAVAL AND OIL INDUSTRIES 
 
Ana DONIGA, Elisabeta VASILESCU,  
Miltiade ISTRATE, Silviu MACUTA 
 
“Dunarea de Jos” University of Galati 
e-mail: doniga.ana@ugal.ro 
 
ABSTRACT 
 
This paperwork shows the laboratory experiments made on X60 and X65 steels 
with several intercritical thermomechanical treatment application. 
Two variants were used: “down-up” thermomechanical treatment with heating 
and rolling in the intercritical range and “up-down” thermomechanical treatment 
with preliminary complete austenitizing and rolling in the intercritic interval. High 
values of the strength characteristics and a good plasticity were gotten. A 
comparison was made with gotten results of the classical thermal treatment 
application (normalizing). 
 
KEYWORDS: thermomechanical treatment, rolling, intercritic interval. 
 
 
1. Introduction 
 
 The present world conjuncture regarding the 
plate products offers and costs imposed (to keep the 
markets) the making of the new technologies of the 
processing and thermal treatments that lead to the 
diminution of the energy consumption. The siderurgy 
is placed between the industrial branches with high 
level energy consumption therefore, the aim of this 
paper-work is to settle the reduction solutions of the 
energy consumption in the final stage of the plate-
products thermal-treated.[1] 
 The study of the national and international 
standards, that establishes the manufacturing 
conditions, mechanical and technological 
characteristics of the siderurgical products made of 
the hypoeutectoid steels, showed that there are cases 
when the thermal treatment characteristics are not 
precised. In these cases first of all, and when the 
treatment characteristics are not precised, the 
researches could be achieved to settle the reducing 
ways of the energy consumption by temperature 
decrease or final thermal treatment elimination. 
 It is supposing a nonconventional 
approaching of the thermal treatment process by 
studies thoroughly regarding transformation 
mechanism and kinetics in the intercritic field of the 
structural steels and a better correlation to the 
previously stage – plastic deformation.[2] 
 In the practice of the thermal treatments the 
conservative positions are shown that imposes the 
hypoeutectoid steels to be complete austenitized to 
achieve the normalizing annealing or quenching.  
 Long time it was considered that the 
incomplete austenitizing to such steels leads to the 
fatigue strength worsening and to the transition 
temperature increase at brittle fracture. 
 For all that some domestic and abroad 
researches introduce the incomplete austenitizing for 
normalizing of the naval plates or some structural 
steels quenching and of the welded joint thermal 
influence zones for some low Carbon Ni-Mo or Ni-
Mo-V steels. 
 It was established that, by thermal treatment 
temperature reducing a certain values increase of the 
material strength and plasticity, and metal loss 
reduction due to oxidation during thermal treatment 
were gotten. 
 By study thoroughly and systematisation of 
this field research-results, a new orientation could be 
traced in the practice of the hypoeutectoid steels, 
thermal treatment, and answers better to the purposes 
for which these siderurgical products are made.      
 The thermal treatment of the steels and cast-
irons, based on the austenite getting and, subsequent, 
transformation (annealing, quenching), are made 
traditionally, with complete austenitizing (for 
hypoeutectoide steels) or incomplete austenitizing 
(for eutectoide, hypereutectoide and ledeburite 
steels).[3] 
 From austenitizing temperature point of 
view, the respective treatment of the hypoeutectoide 
steels could be considered “overcritic” (above Ac1-
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI 
FASCICLE IX METALLURGY AND MATERIALS SCIENCE, ISSN 1453 – 083X. NR 1 – 2005 
 
 
  
Ac3 interval), and for the other steels “intercritic” (in 
Ac1-Accem critic interval). 
 By heating, in the balance condition of a 
hypoeutectoide steel, in A1-A3 interval, its 
microstructure, pearlitic-ferrite initially, will become 
austenite-ferrite. Carbon concentration of the 
austenite and austenite ratio, as well, will depend on 
steel carbon content and heating temperature. The 
highest possibiliyties of controlable variation of such 
characteristics, the steels with extend A1-A3 range 
present, those with 0,10 – 0,30%C, respectively. [4] 
Moreover, the fact should be specified that 
the studies balance situation could be achieved on the 
other ways as: by steel heating in the austenite field 
(total austenitizing) and by show cooling up to a 
temperature placed in A3-A1 interval (fig.1). 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
This kind of the treatments were named 
intercritical thermal treatments and are used for 
thermal influenced zone recovery from electroslag 
welding of some Ni-Mo or Ni-Mo-V steels (with low 
carbon) and dual-phase steels, as well.  
The latest paper-works of speciality show 
that the intercritical thermal treatment could be used 
for some hypoeutectoide steel, as well, those with 
high Ni content, carbon-steel, and low alloyed steels 
for naval constructions.[5] 
 
 
 
 2. Laboratory experiments  
 
 Having in view the importance of the naval-
plates from the total production of S.C.ISPAT-
SIDEX Galati, it is considered that the reduction of 
the energy consumption will be important using the 
intercritic conditions. Combining the thermal 
treatment with a plastic deformation in the intercritic 
field, an intercritic thermal mechanical treatment was 
achieved. For experiments X65 steel test pieces were 
used having the following characteristics (mentioned 
in table no.1 and 2) 
 
Table 1. Chemical characteristics of X65 steel (%). 
 
C Mn Si V Al Ni Mo Ti Nb 
0,1 1,53 0,26 0,03 0,07 0,01 0,003 0,02 0,04 
 
 
Table 2. The imposed mechanical characteristics steel grade. 
 
Steel  Rm,min  [N/mm2] 
Rp0.2,min  
[N/mm2] 
A,min  
[%] 
KV, min  
[J] 
X65 413 331 22 27 
 
 
The intercritic thermo-mechanical treatment 
was used by the direct heating in the intercritic + 
deformation field (down-up) and deformation in 
intercritic condition after a preliminary austenitizing 
(up-down) - fig.2. 
A2 
A1 
t
a b 
T
Figure 1. Practical ways of an intercritic 
treatment for an hypoeutectoide steel: 
      a) heating from the ambient 
temperature in A3-A1 interval (down-up) 
      b) preliminary austenitizing and 
precooling in A3-A1 interval (up-down) 
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI 
FASCICLE IX METALLURGY AND MATERIALS SCIENCE, ISSN 1453 – 083X. NR 1 – 2005 
 
 
  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
In the laboratory conditions the 
thermomechanic treatment consisted of: 
 - heating in the austenitic or intercritic 
conditions; 
 - one passing rolling with a ε = 30% and 
20% reduction degree on the laboratory rolling mill 
having barrell diameter of  D = 129mm;  
 - the rolling was achieved in the intercritic 
field (temperature of 8500C and 8000C) 
for both treatments: “down-up” and “up-down”; 
- the cooling after rolling was made in air or 
water. 
On the test specimen, thus gotten, the 
mechanical characteristics and structure was 
determined. The results are shown in table 3. 
 
Table 3. The experimental conditions of the intercritical treatments 
 
           Mechanical characteristics 
No. 
exp. 
Experimental variants of  TT/TTM ε 
[%] 
Rm 
[N/mm2] 
Rp0,2 
[N/mm2] 
A5 
[%] HB 
1 Heating to 920o  C + cooling air (normalizing) 30 546 368 29 278 
2 Heating to 920o→cooling 850o+ rolling→ water 30 804 764 22 292 
3 Heating to 920o→ cooling 850o+ rolling → air 30 637 579 29 191 
4 
Heating to 920o→ cooling 800o + rolling → 
water  30 803 753 20 285 
5 Heating to 920o→ cooling 800o+ rolling → air 30 577 412 26 174 
6 Heating to 850o→rolling→ water 20 834 685 26 292 
7 Heating to 850o→rolling → air 20 686 566 32 202 
8 Heating to 800o→rolling→ water 30 1027 852 20 329 
9 Heating to 800o→rolling → air 30 651 498 20 215 
10 Heating to 800o→rolling→ water 20 933 756 20 315 
11 Heating to 800o→rolling → air 20 651 498 20 215 
12 Heating to 920o→cooling 850o+ rolling→ water 20 880 696 20 301 
13 Heating to 920o→ cooling 850o+ rolling → air 20 636 526 26 148 
    600 
       700 
    800 
    900 
       1000 
Te
m
pe
ra
tu
re
  o
C
 920 
oC 
Time , min
( Ac3 )
( Ac1 )
850 oC 
30 min
    600 
       700 
    800 
    900 
       1000 
Te
m
pe
ra
tu
re
  o
C
 
Time , min
 ( Ac3 )
( Ac1 )
850 oC 
30 min 
Figure 2. Intercritical thermo-
mechanical treatments 
 
 
a –  down-up;   
 
 
 
 
 
 
 
 
 
 
 
 
 
 
b – up-down 
 
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI 
FASCICLE IX METALLURGY AND MATERIALS SCIENCE, ISSN 1453 – 083X. NR 1 – 2005 
 
 
  
3. Results and discussions 
 
 First experiment consisted in a clasic 
normalizing treatment for results comparison (table 3, 
regime 1). 
 Second experiments group consisted of “up-
down” treatments where working conditions were 
different by the cooling way and deformation degree: 
- austenitizing temperature T = 9200C; 
- cooling at 8500C; 
- rolling with ε1 = 30% and ε2 = 20%; 
- cooling water and air. 
It is remarked that Rm and Rp0,2 mechanical 
characteristics values exceded the values provided by 
the norms (table 2). In turn, the elongation is not 
framing, in all cases, in the values required by the 
norms. 
Deformation degree didn’t influence 
appreciably the mechanical characteristics. 
In case of such treatment the best results are 
gotten in domains 3 and 5 (table 3) with austenitizing 
temperature T = 9200C, cooling 8500C, rolling ε1 = 
30% and air cooling. The water cooling results the 
low elongation values. The structure are shown in 
fig.3a and 3b. 
The third group of the experiments consisted 
of “down-up” treatment thus: 
- heating at 8500C and 8000C; 
- rolling at these temperature; 
- air or water cooling; 
- deformation degree ε1 = 30% and ε2 = 
20%. 
The best results were gotten in the domains 6 
and 7 (table 3) with heating at 8500C, rolling with ε2 
= 20% and air / water cooling. 
High values are gotten for both Rm and Rp0,2 
and elongation as well (32% to the min 22% provided 
by norms).  
The structures are shown in fig.3c and 3d. 
 
4. Conclusions 
 
- All the experiment variants of the 
thermomechanical treatment lead to the increase of 
the mechanical characteristics values of the strength 
(Rm, Rp0,2) and some of them to the improvement of 
the plasticity characteristics (Ar %);  
 - The experiments variants of the 
thermomechanical treatment with water cooling after 
deformation result the high values for strength 
characteristics (over 2 times higher than “rolled” 
condition) but determinate the elongation decrease 
even under 20% (smaller than “rolled” condition); 
 - The experiment variants of the 
thermomechanical treatment with air cooling after 
plastic deformation result the mechanical 
characteristics improvement both: strength and 
plasticity: 
 Rm = 577 ÷ 686 N/mm2; 
 Rp0.2 = 412 ÷ 566 N/mm2; 
 A5 = 20 ÷ 29 %, frecvent 26 %. 
 Studying the possibility of the 
thermomechanical treatment with air cooling after 
plastic deformation the following remarks are mode: 
- regarding the heating way: “up-down” or 
“down-up”, the variants with preliminary 
austenitizing result the highest values of the plasticity 
characteristics A5 = 26 – 29% when mechanical 
characteristics are kept at high values:  
(Rm = 577 ÷ 637 N/mm2; Rp0.2 = 412 ÷ 579 N/mm2 ). 
 In the frame of these experiment variants could be 
seen that the deformation degree, ε, in limits of 
20…30% hasn’t an important influence on the 
characteristics. 
 - the experiment variants of the 
thermomechanical treatment without preliminary 
austenitizing (“down-up”) determinate a decrease of 
the elongation from 26% to 20% even though the 
mechanical characteristics of strength are high, with 
remark that the deformation degree from 20% to 30% 
doesn't influence meaning fully: 
 - regarding the plastic deformation 
temperature established between intercritic interval of 
the studied steel could be remarked:   
 a) in the experiment variant with preliminary 
austenitizing and deformation at 8500C having 
deformation degree ε = 30%, a good assembly of 
mechanical characteristics is achieved (Rm = 637 
N/mm2; Rp0.2 = 579 N/mm2; A5 = 29%) in 
comparaison to the temperature of 8000C (Rm = 577 
N/mm2; Rp0.2 = 412 N/mm2; A5 = 26%); 
 b) the experiment variant without 
preliminary austenitizing (“down-up”), also, 
demonstrated that temperature of 8500C leads to the 
good results of the characteristics indifferent to the 
deformation degree. 
 In conclusion, the experiment results show 
that X65 microalloyed steel is sensitive to the 
mechanical processing and the value of the 
mechanical characteristics are modified to the rolled 
condition or to the conventional thermal treatment but 
the optimum experiment variants that lead to the 
establishing of the technological conditions in 
keeping with the studied steel grade are characterized 
by the following parameters: 
 1) preliminary austenitizing at 9200C; 
 2) plastic deformation temperature 8500C; 
 3) deformation degree about 30%; 
4) air cooling after deformation. 
 
 
 
 
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI 
FASCICLE IX METALLURGY AND MATERIALS SCIENCE, ISSN 1453 – 083X. NR 1 – 2005 
 
 
  
    
 
    
 
    
 
    
 
 
References 
 
[1] Leger J.  - Etudes  des traitements  intercritiques  (A1-A3) des 
aciers  hypoeutectoides Mem. Scient. Met LXVII,  nr. 5 , 1971 
[2]  Vasilescu E.  - Tratamente termice si termochimice (note de 
curs). 
[3] Nicolae Popescu s.a  - Tratamente termice neconvenţionale 
(Bucureşti, Editura Tehnică 1990). 
[4]  Suzana Gâdea şi Maria Petrescu  - Metalurgie fizică si 
studiul metalelor (Bucureşti, E.D.P. 1983) 
[5] Doniga A., Vasilescu E. - Bazele tratamentelor termomecanice 
E.D.P. 2004. 
 
Figure 3. Specimen microstructure with 
 intercritic thermomechanical treatment  
(table 3) (x 500 magn., Nital etch 2%) 
 
 
a) regime 3; 
b) regime 5 
 
 
 
 
 
 
 
 
 
 
 
 
c) regime 6 
 
 
 
 
 
 
 
 
 
 
 
d) regime 7 
- 79 -


Thermomechanical Processing of Microalloyed Steels Used for Naval and Oil Industries

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Thermomechanical Processing of Microalloyed Steels Used for Naval and Oil Industries

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