Materials Sciences and Applicatio ns, 2010, 1, 323-328
doi:10.4236/msa.2010.16047 Published Online December 2010 (http://www.scirp.org/journal/msa)
323
Mechanical Characteristics of Superaustenitic
Stainless Steel Type 30Cr25Ni32Mo3 at Elevated
Temperatures
Gholam Reza Ebrahimi1, Hamid Keshmiri2, Hadi Arabshahi3
1Metallurgy and Materials Engineering Department, Sabzavar Tarbiat Moallem University, Sabzevar, Iran; 2Esfarayen Industrial
Complex, Esfarayen, Iran; 3Physics Department, Ferdowsi University of Mashahd, Mashahd, Iran.
Received October 26th, 2010; revised November 17th, 2010; accepted December 3rd, 2010.
ABSTRACT
In making tubes of corrosion resistant and hardly deformed steels and alloys, the pilger rolling method is used for hot
rolling of final thick-walled tubes or mother tubes of large diameters (above 300 mm) and small quan tities of othe r size
tubes when no oth er, more efficient tube rollin g or extrusion equipmen t is available. To cla rify individ ual parameters of
the production process and make choice of the deformation-and-temperature parameters, mechanical properties of the
alloy type 30Cr25Ni32Mo3 Superaustenitic Stainless Steel at various temperatures were studied. The tests have been
performed using sa mples taken from the forged 400 mm diameter billet to determine strength and p lastic properties of
the billet metal at various temperatures and its macro- and microstructure. Th e test results will be used in the choice of
optimum condition s of preheating of the billets and hot rollin g of tubes. On the who le, it should be stated that as-forged
alloy 30Cr25Ni32Mo3 features a favorable combination of strength and plastic properties in the hot-working tempera-
ture range of 1075-1200˚C.
Keywords: Superaustenitic Stainless Steel, Hot Deformation, Mechanical Properties, Micro structure Evaluation
1. Introduction
The superaustenitic grades of stainless steels provide
excellent corrosion resistance as well as high strength
levels [1]. As the austenitic steels are characterized by
their low Stacking Fault Energy (SFE) [2], the dominant
restoration processes during and after hot Deformation
are therefore dynamic and Metadynamic Recrystalliza-
tions (DRX and MDRX), respectively [3-7]. For the last
two decades intensive studies have been down on the
changes of austenitic microstructure and mechanical
properties in steels with hot working conditions. Several
thermomechanical processing technologies such as con-
trolled rolling controlled cooling and direct quenching
were developed through these studies. Some research
have been done to determine the best plasticity tempera-
ture range using the thermomechanical processing such
as hot compression and hot torsion tests in steels[8-12].
However, metallurgical studies are scarcely performed to
characterize hot working behavior of superaustenitic
stainless steels. In this research, mechanical properties
accompanying with microstructural evaluation of the
alloy type 30Cr25Ni32Mo3 Superaustenitic Stainless
Steel at various temperatures were studied. For this pur-
pose tensile and torsion tests at various temperatures
from 800˚C up to 1180˚C and 1000˚C up to 1200˚C have
been done respectively.
2. Experimental Procedures
The material used for virtually all the experiments in this
work was a 30Cr25Ni32Mo3 super austenitic stainless
steel obtained from a cross-section of the forged 400 mm
diameter billet produced by EICO, IRAN. The chemical
composition and as received microstructure of this steel
are given in Table 1 and Figure 1 respectively. Me-
chanical properties at room temperature in as-received
condition are given in Table 2. In tensile tests at room
temperature, two types of specimens were used: conven-
tional cylindrical specimens (type 3) and special fil-
let-neck specimens (type 4) designed for testing hardly
deformed materials. A minor scatter of property readings
was observed: the fillet-neck specimens had strength (Rm;
Rp0.2) levels somewhat lower and plastic property (А; В)

Mechanical Characteristics of Superaustenitic Stainless Steel Type 30Cr25Ni32Mo3 at Elevated Temperatures 324
Table1. Chemical composition of the material used. (Wt %)
C Cr Ni Mo Mn P S
0.025 28.00 33.00 3.50 0.60 0.0280.0015
20µm
Figure 1. Microstructure of 30Cr25Ni32Mo3 in the as-re-
ceived condition.
Таble 2. Меchanical properties of the forged metal.
Specimen
type
Rm
(MPa)
Rp0.2
(MPa)
Elongation,
А %
Reduction of
area, В%
type 3 583 292 45,5 63
type 4 579 289 46 64
levels higher than conventional specimens but this dif-
ference was inessential.
The standard tensile test specimens according to
ASTM A370 and special torsion samples (D = 8 mm)
were prepared in longitudinal direction of forged billets.
Before testing, all the specimens subjected to solid solu-
tion heat treatment at 1250˚C soaked for 15 minutes fol-
lowed by cooling to the hot deformation temperature at a
rate of 10˚Cs-1. Before deformation, the specimens were
held for 3 min at the deformation temperature to elimi-
nate the thermal gradients as well as to ensure the uni-
form temperature of specimens. The tensile tests were
then carried out at the temperatures between 800˚C and
1180˚C and between 1000˚C and 1250˚C at constant
strain rate of 1 s-1 for torsion test. To preserve the micro-
structure, the samples were immediately quenched after
hot deformation. The process of hot deformation test is
shown schematically in Figure 2.
Temperature
10˚Cs
-1
1250˚C
3min
Temperature
5˚Cs
-1
Figure 2. Thermal and thermomechanical cycles imposed on
samples in this research.
After hot deformation testing, the torsion specimens
were cut along the longitudinal axis for electrochemical
polishing. Following this, the specimens were electroli-
tically etched in oxalic acid to reveal the microstructures.
In order to follow the microstructural changes through
hot deformation, the structure of samples were studied
using both optical and scanning electron microscopy.
3. Results and Discussion
3.1. Hot Tensile Tests
Tensile test results for alloy 30Cr25Ni32Мo3 in the range
of at 20 to 1180˚C are shown graphically in Figure 3.
Analysis of Figure 3(a) shows that as the test tem-
perature increases, tensile strength and yield strength of
alloy 30Cr25Ni32Мo3 decrease gradually and plastic
properties (percent elongation and reduction of area)
increase as well.
3.2. Hot Torsion Tests
Because of a lower plasticity of corrosion-resistant aus-
tenitic steels and alloys, it is of high importance to know
the temperature range of plasticity of the studied material
during its hot working. In order to determine the tem-
perature range of an optimum plasticity of alloy 30Cr25Ni
32Mo3, the method of hot torsion of special specimens
was used to determine the material plasticity at the hot
working temperatures. The number of torsions (n) and the
torsion moment (Mtor) at which the specimen fracture
occurs are important indices of the material plasticity.
Such indices are usually determined for various metal
preheat temperatures.
This test method has been developed at State Enterprise
“Ya. Ye. Osada Scientific Reseasrch Tubе Institute” (SE
“NITI”), Dnipropetrovsk, Ukraine, for mastering the
technology of manufacture of tubes of hardly deformed
steels and alloys and has been widely adopted in Ukrain-
ian pipe and tube industry.
The tests were carried out with the use of special 8 mm
diameter cylindrical specimens. The hot torsion test re-
sults are shown in Figure 4.
Alloy 30Cr25Ni32Mo3 reaches its maximum plasticity
at test temperature of 1200˚C and retains it up to 1250˚C.
But it should be pointed out that minimal values of torque
(MSKR) characterizing deformation resistance of alloy
30Cr25Ni32Mo3 are observed within the temperature
range of 1100-1175˚C.
3.3. Microstructural Observations
The results of metallographic analysis of hot-torsion test
specimens have shown that structure inhomogeneity re-
mained in various specimens at 1050˚C. In a specimen
fractured after 8.5 turns, grain variation was observed

Mechanical Characteristics of Superaustenitic Stainless Steel Type 30Cr25Ni32Mo3 at Elevated Temperatures 325
75080085090095010001050 1100 1150 1200
20
40
60
80
100
120
140
160
180
800 850 900950 1000 10501100
60
80
100
120
140
160
180
200
220
240
Tensile strength (Mpa)
260
Temperature (˚C)
yield strength (Mpa)
750 800 850 900 950 1000105011001150
Temperature (˚C)
(a) (b)
25
30
35
40
45
50
55
60
65
1200
7508008509009501000 1050 1100 11501200
40
50
60
70
80
90
100
Temperature (˚C)
Elongatio
n
(%)
Temperature (˚C)
1000 10501100 1150 12001250
0
Reduction of area (%)
(c) (d)
Figure 3. Tensile properties of alloy 30Cr25Ni32Мo3 at elevated temperatures. (a) Tensile strength, (b) Yield strength, (c)
Percentage elongation, (d) Reduction of area.
2
4
6
8
10
12
14
16
18
Temperature (˚C)
100010501100 1150 12001250
4
Torsion number (n)
20
6
8
10
12
14
16
18
20
22
Temperature (˚C)
Torque (N.m)
24
(a) (b)
Figure 4. The test results of hot torsion of specimens made of alloys 30Cr25Ni32Mo3. (a) Torsion number, (b) Torque.

Mechanical Characteristics of Superaustenitic Stainless Steel Type 30Cr25Ni32Mo3 at Elevated Temperatures 326
(Figure 5(a)). In a specimen fractured after 34 turns,
fine-grained and homogeneous structure with twin boun-
daries (Figure 5(b)) was present. Such condition of the
alloy structure has influenced the test results.
As the test temperature grows, a significant coarsening
of austenite grains (Figures 7(a-c)) and redistribution of
alloying elements between the phases and the solid solu-
tion occur which explains the higher number of torsion
turns.
To reveal probable fusion of the grain boundaries in
the structure of metal of the investigated of alloy 30Cr-
25Ni32Mo3, quenching of the specimens heated to
1200˚C was done first (Figure 8). Next, structure of the
specimens torsion-tested at 1230˚C (Figure 7(b)) and
1250˚C (Figure 7(c)) was examined.
50µm
Structure examination of the specimens heated to 1200
-1250˚C has shown coarsening of austenite grains and
presence of twin low-energy boundaries and phases in
the structure.
No grain boundary fusion in metal of alloy 30Cr25-
Ni32Mo3 was revealed.
50µm
(a)
50µm
(b)
Figure 5. Microstructure of the specimens made of alloy
30Cr25Ni32Mo3 after hot torsion tests at 1050˚C. (a) Num-
ber of torsions 8.5, (b) Number of torsions 34.
(a)
50µm
(b)
Figure 6. Microstructure of the specimens made of alloy
30Cr25Ni32Mo3 after hot torsion tests at (a) 1100˚C, (b)
1150˚C.
4. Conclusions
1) As the test temperature increases, tensile strength
and yield strength of alloy 30Cr25Ni32Мo3 de-
crease gradually and plastic properties (percent
elongation and reduction of area) increase as well.
2) Alloy 30Cr25Ni32Mo3 reaches its maximum plas-
ticity at test temperature of 1200˚C and retains it up
to 1250˚C. But it should be pointed out that minimal
values of torque (MSKR) characterizing deformation
resistance of alloy 30Cr25Ni32Mo3 are observed
within the temperature range of 1100-1175˚C.
3) The results of metallographic analysis of hot-torsion
test specimens have shown that structure inhomoge-
neity remained in various specimens at 1050˚C. In a
specimen fractured after 8.5 turns, grain variation
was observed. In a specimen fractured after 34 turns,
fine-grained and homogeneous structure with twin
boundaries was present.
4) As the test temperature grows, a significant coars-
ening of austenite grains and redistribution of alloy-

Mechanical Characteristics of Superaustenitic Stainless Steel Type 30Cr25Ni32Mo3 at Elevated Temperatures 327
ing elements between the phases and the solid solu-
tion occur which explains the higher number of tor-
sion turns.
5) Structure examination of the specimens heated to
1200-1250˚C has shown coarsening of austenite
grains and presence of twin low-energy boundaries
and phases in the structure.
6) No grain boundary fusion in metal of alloy 30Cr25
Ni32Mo3 was revealed.
200µm
50µm
(a)
50µm
(b)
50µm
(c)
Figure 7. Microstructure of the specimens made of alloy
30Cr25Ni32Mo3 after hot torsion tests at (a) 1200˚C, (b)
1230˚C, (c) 1250˚C.
(a)
50µm
(b)
Figure 8. Microstructure of the specimens made of alloy
30Cr25Ni32Mo3 after quenching at 1200˚C from a separate
heating: (а) General view, (b) Phase precipitates.
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