Analysis of the oxidation process of powders and sinters of the austenitic stainless steel
Journal of Thermal Analysis and Calorimetry
Analysis of the oxidation process of powders and sinters of the austenitic stainless steel
Karolin Mazur 0 1
Marek Hebda 0 1
0 Institute of Materials Engineering, Cracow University of Technology , Cracow , Poland
1 & Marek Hebda
Nowadays, austenitic stainless steels due to its properties are widely used in various applications. In powder metallurgy technology, one of the key factors, affecting the pressing process, the sintering phenomena and the final properties of sintered parts, is the shape and particle size of the powders. The article presents the results focused on analysis of the oxidation process of austenitic stainless steel. Powders of the same chemical composition, however of different shapes, depending on the manufacturing technique, i.e. spherical after inert gas atomization and sponge after water atomization, were investigated. Moreover, the influence of particles' size from different ranges 40-56 and 80-100 lm on the oxidation behaviour was analysed. Thermal measurements, differential scanning calorimetry and thermogravimetry, were performed by the STA 409 CD (Netzsch) advanced coupling techniques. Moreover, dilatometry technique has been used for the analysis of the influence of the size and shape of particles on the sintering process. Sinters oxidation phenomena have also been determined. Based on the obtained results, it was found that both shape and size of powders have a significant influence on the oxidation processes of powders as well as sinters of the austenitic stainless steel.
Oxidation; Stainless steel; TG/DTG/DSC
Austenitic stainless steel (SS) has excellent anti-corrosion
properties. Therefore, it is often used for the production of
parts exposed to work in extreme conditions, such as
increased temperature or harmful atmospheres. SS is
widely used in a variety of: medical, heavy industry,
precision mechanics and electronics applications, where it is
often impossible to replace it with modern materials due to
the operating conditions [
Nowadays, among the many methods of manufacturing
powder metallurgy, due to economic and ecological aspects
of production, it is one of the most intensively developed
technologies. The properties of the final products depend
on many factors. The most important is the chemical
composition and the parameters used in the subsequent
stages of the manufacturing process: mixing of powders,
forming and sintering. At each of these stages, the shape
and particle size of the powders used in the manufacturing
of the products has a significant impact [
example, the morphology of the particles plays an
important role in the process of forming, especially in die
compacting, the most popular industrial process. Generally,
powders of spherical shape compared to sponge are much
more difficult to compact. This effect has a major influence
on the reduction of the strength properties of sinter.
Another factor, apart from the shape of the particles and
their chemical composition, which has a main impact on
the compacting as well as sintering process is the particle
size. Moreover, dependent on the powder consolidation
technique, it is required that their size is: (1) strictly
defined, to a very narrow range, e.g. for MIM (metal
injection moulding) or SLM (selective laser melting)
method or (2) in a relatively wide range as for die
The aim of the presented work was to investigate the
influence of shape and size of austenitic stainless steel
particles on the oxidation process and sintering
phenomena. Moreover, the influence of particles’ size and
shape on the oxidation behaviour of sinters was also
Materials and methods
In this research, an austenitic stainless steel powder AISI
316L, supplied by Hoganas, was used. The chemical
composition specified by the manufacturer is shown in
Thermal measurements were taken with STA 409 CD
(Netzsch) advance coupling techniques (DSC/TG). Two
replicates were measured. The calorimetric curves were
recorded with a differential scanning calorimeter using an
alumina crucible, with about 20 mg of samples under a
dynamic air atmosphere (80 mL min-1). The temperature
range was from 30 to 1300 C at a heating rate of 5, 7.5, 10,
12.5, 15 C min-1. The holding time at the isothermal
temperature was kept at 60 min. An empty alumina
crucible was used as a reference. The apparatus was calibrated
using indium, tin, bismuth, zinc, aluminium, silver and
gold as a standard. The heat flow signal was calibrated by
the melting heat of the above-mentioned elements. The
DSC/TG data were analysed using Proteus software (ver.
5.2) from Netzsch. All of the presented curves were
corrected against empty runs.
Moreover, analysis of sintering behaviour using the
horizontal Netzsch 402 C dilatometer was investigated on
samples with a diameter of 5 mm and a height of 10 mm.
Green compacts were produced by uniaxial cold pressing at
600 MPa. The sintering process was performed in
highpurity (99.999%) hydrogen atmosphere with
100 mL min-1 flow rate. The heating and cooling rates
were 10 C min-1. The isothermal sintering temperature
was 1250 C. The holding time at the isothermal sintering
temperature was 30 min.
The sieve analysis was performed on a Vibratory Sieve
Shaker Analysette 3 Spartan Fritsch. The sieve size was 40,
56, 63, 71, 80, 100 and 160 lm. Measurements were taken
according to PN-EN 24497 ISO 4497.
The morphology of the particles was observed by the
JEOL JSM-5510LV scanning electron microscope.
Microanalysis was performed by the application of an
energy-dispersive spectrometer (EDS) IXRF Systems
Model 500 Digital Processing.
The phase identification was performed by an X-ray
diffraction apparatus D2 Phaser analyser manufactured by
Bruker (anode: copper; step of measurement: 0.02 ; 8 s per
step). Diffraction data processing was carried out by EVA
software. The phases were identified with PDF2 database.
Results and discussion
Figure 1 shows representative powder particle shapes that
depend only on the manufacturing method used. The
spheroidal particles identified in the article with symbol A
are characteristic for the atomization process, a stream of
molten steel, by an inert gas (Fig. 1a). On the other hand,
the spongy particles designated as B are obtained after the
water atomization process (Fig. 1b). The influence of the
method of production on the shape of particles is well
known and independent of the chemical composition of the
materials produced [
14, 16, 17
]. The particle size
distribution of powders A and B used in the studies is presented
in Table 2. Based on the obtained results, it was found that
the largest percentage share, regardless of the shape of
powders, was fractions in the range 40–56 and 80–100 lm.
Since the particles from these fractions were the largest
volume fraction and they differed from each other in size
twice, they were selected for analysing the effect of particle
size and shape on the oxidation process (Table 3).
Figure 2 shows the TG changes recorded during the
oxidation of powders, depending on: (1) the size and shape
of the austenitic stainless steel particles and (2) the heating
rate. The onset and endset values determined from the
curves are presented as summary graphs in Fig. 3. Based
on the obtained results, it was found that regardless of the
type of particles, a single-step oxidation process of the
powders was observed. It always started at temperatures
above 1060 C. It has also been observed that the onset of
oxidation occurred at a temperature lower by about 60 C
for spongy-shaped powders compared to the results
obtained for spheroidal powder. This effect was
independent of particle size and heating rate. In addition, the
increase in the particle size of the powder increased the
temperature at which the oxidation process started. This
effect was occurred at a temperature by about 10 C higher
for the spongy powder as compared to the spheroidal one.
Also, as the heating rate increased, the temperature at
which the oxidation started was increasing.
Mass of samples as a result of oxidation process
increased in the range from 37 to 43%. In general, for
spheroidal particles, a larger mass growth was recorded
than for spongy-shaped particles of similar size. The
smallest mass increase was recorded for 80–100 lm and
Fig. 1 Shapes of 316L
austenitic stainless steel
particles a spheroidal, b spongy
spongy shape, while the largest for spheroidal particles in
the range 40–56 lm.
Based on the DTG curves, the temperatures at which the
oxidation process was characterized by the most violent
waveforms were determined. These values were both
dependent on the size and shape of the powder particles, as
shown in Fig. 4. For heating rates above 5 C min-1 and
spongy powder of 80–100 lm, the maximum oxidation
intensity occurred at about 1180 ± 5 C. However, for the
powders of the same size but the spherical shape, the
extreme DTG effect was observed at about 1210 ± 10 C.
Analogous effects occur for a particle size of range
40–56 lm, but the difference between maximum of DTG
peak due to the shape of the particles was then about 10 C.
Figure 5 presents collected DSC curves recorded for all
analysed samples. Regardless of the size and shape of the
investigated powders, during their heating, one intense
exothermal effect was observed. This phenomenon is
related to the oxidation process occurring in the materials.
The exothermic peaks that occur in the high temperature
(above 1100 C) are possibly related to the oxides
formation, which correlates the beginning of the increase in the
total mass in the TG curves (Fig. 2).
Similarly as with the TG measurements, it was found
that with the increase in the heating rate, the start and end
of the exothermic effect were shifted to a higher
temperature range. It has also been observed that the energy
released during spheroidal particle oxidation is always
greater by more than 1.5 times compared to the values
recorded during the spongy-shaped particle analyses
Ozawa–Flynn–Wall (OFW) isoconversional methods
were carried out to calculate, by performing TG analysis at
different heating rates, the activation energy of austenitic
stainless steel oxidation process. The activation energy
values of spherical powder were almost double as high
compared to the values obtained for the spongy particles
The results of DSC, TG and the calculated activation
energy values clearly demonstrate a higher resistance to
oxidation process of spheroidal than spongy particles.
However, upon activation, their oxidation process is much
more violent and involves a larger share of spheroidal than
spongy powder particles.
Figure 6 shows dimensional changes of samples
recorded during sintering. The obtained results demonstrate the
significant influence of the size and shape of austenitic
stainless steel powders on the sintering process. It was
observed that for the spongy particles, the dominance of
the diffusion mechanism of matter transport over the
thermal expansion of the material occurred at about
953 C. In contrast, the same effect for the spheroidal
particles began at a temperature above about 144 C. The
particle size did not affect significantly to this
Heating rate/°C min–1
direct consequence of the poorer consolidation of
spheroidal powders than the irregular ones. These effects also
significantly affect the resistance of sinters to oxidation at
elevated temperatures. For samples made from spongy
powders, which were more densified during sintering and
thus characterized by lower porosity, during the oxidation
process, a smaller mass growth was recorded than for
sintered powders made from spheroidal particles (Fig. 7). It
has also been observed that the sintered samples oxidation
process was two-stage, unlike the one-step oxidation
mechanism of powders. The first stage of the oxidation
process for all investigated sinterings was in the
temperature range of 690–1015 C. As a consequence, the sample
mass increased by approximately 4%. The second stage
followed immediately after the first one. The end of the
second stage was when the cooling step from the
isothermal annealing temperature at 1250 C started. The total
mass growth of the sintered material was 19% lower than
the value recorded during the oxidation of powders. This
effect was independent of the type of analysed samples.
The oxidized outer surface has the character of an
adherent coating, however, with numerous cracks (Fig. 8),
which are a consequence of the increase in temperature and
different coefficients of thermal expansion of the formed
oxides and steel. It was found that regardless of the size
and shape of the powder particles and the applied
compaction pressures, the oxidized outer surface of sinters has
a similar morphology. Furthermore, observed surface
morphology of oxides layer allows to explain recorded
A, 40–56 μm
A, 80–100 μm
B, 40–56 μm
B, 80–100 μm
Fig. 6 Dilatometric curves of austenitic stainless steel depending on
the size and shape of the powder particles
effect of inflection of TG curves, occurring at a
temperature of about 1000 C. The cracking of the layer of oxides
formed on the surface of the sample allows further internal
oxidation of the sinters.
The XRD (Fig. 9) and the global EDS (Fig. 8) analyses
indicate the formation of haematite (Fe2O3) and magnetite
(Fe3O4) in the oxidized surface. The oxidation of Fe
explains the increase in samples mass recorded on TG
curves (Figs. 2 and 7) and the exothermic effect on the
DSC curves (Fig. 5). The formation of haematite on steel
may proceed according to the reaction: 4Fe ? 3O2 =
2Fe2O3, while the magnetite may create according to the
reaction: Fe ? 4Fe2O3 = 3Fe3O4. Based on the literature,
it can be stated that in the first stage of oxidation, less
stable Fe2O3 oxides form on the surface of the sample. On
the other hand, higher temperatures can induce chromium
oxides (Cr2O3), solid solution of chromium–iron oxide
(Cr,Fe)2O3 or chromite spinel phases [
chromium can replace iron in the Fe2O3-type oxide [
Based on the obtained results, it was found that both shape
and size of powders have a significant influence on the
oxidation processes of powders as well as sinters of the
austenitic stainless steel. The initial oxidation temperature
of spongy powders, regardless of size, was always lower
than for spheroidal particles. Moreover, when the size of
powder particles decreases, their oxidation occurs at a
lower temperature, regardless of shape. These effects were
independent of the applied heating rates. Dilatometric
investigations have shown that for spheroidal powders the
dominance of the diffusion mechanism of matter transport
over the thermal expansion of the material occurs at a
higher temperature than that of the spongy particles. In
addition, it has been shown that the shape of the powder
particles is important for the oxidation resistance of
austenitic sinters. It has also been observed that the process of
oxidation of powders occurs in one step, while the sinters
oxidize into two stages. This effect is related to the
densification of the material and necessity of the cracking of
the layer of oxides formed on the surface of the sinters
which allows further internal oxidation of the sample. This
is also confirmed by the fact that sinters made of spongy
particles were characterized by a smaller mass growth
compared to sintered spheroidal powders. It was also
observed that the oxidation of powders is much larger than
for the sinters.
Acknowledgements This study was supported by the statutory
activity of the Institute of Materials Engineering, Cracow University
Open Access This article is distributed under the terms of the
Creative Commons Attribution 4.0 International License (http://crea
tivecommons.org/licenses/by/4.0/), which permits unrestricted use,
distribution, and reproduction in any medium, provided you give
appropriate credit to the original author(s) and the source, provide a
link to the Creative Commons license, and indicate if changes were
1. Amel-Farzad H , Peivandi MT , Yusof-Sani SMR . In-body corrosion fatigue failure of a stainless steel orthopaedic implant with a rare collection of different damage mechanisms . Eng Fail Anal . 2007 ; 14 : 1205 - 17 .
2. Brooks EK , Brooks RP , Ehrensberger MT . Effects of simulated inflammation on the corrosion of 316L stainless steel . Mater Sci Eng C . 2017 ; 71 : 200 - 5 .
3. Kurgan N , Varol R . Mechanical properties of P/M 316L stainless steel materials . Powder Technol . 2010 ; 201 : 242 - 7 .
4. Skałon ´ M, Hebda M , Sulikowska K , Kazior J . Influence of FeNiMnSiB master alloy on the structure and mechanical properties of P/M AISI 316L . Mater Des . 2016 ; 108 : 462 - 9 .
5. Qi Q , Liu Y , Wang L , Zhang H , Huang J , Huang Z. One new route to optimize the oxidation resistance of TiC/hastelloy (Nibased alloy) composites applied for intermediate temperature solid oxide fuel cell interconnect by increasing graphite particle size . J Power Sources . 2017 ; 362 : 57 - 63 .
6. Cho Seungchan , Jo Ilguk, Kim Heebong, Kwon Hyuk-Tae, Lee Sang-Kwan, Lee Sang-Bok. Effect of TiC addition on surface oxidation behavior of SKD11 tool steel composites . Appl Surf Sci . 2017 ; 415 : 155 - 60 .
7. Changcong W , Kezhi L , Xiaohong S , Qinchuan H , Caixia H . High-temperature oxidation behavior of plasma-sprayed ZrO2 modified LaMo-Si composite coatings . Mater Des . 2017 ; 128 : 20 - 33 .
8. Yi W , Jianhui Y , Dezhi W. High temperature oxidation and microstructure of MoSi2/MoB composite coating for Mo substrate . Int J Refract Met Hard Mater . 2017 ; 68 : 60 - 4 .
9. Klar E , Samal PK . Powder metallurgy stainless steels: processing, microstructures, and properties . Materials Park: ASM International; 2007 .
10. Ertugrul O , Park HS , Onel K , Willert-Porada M . Effect of particle size and heating rate in microwave sintering of 316L stainless steel . Powder Technol . 2014 ; 253 : 703 - 9 .
11. Menapace C , Cipolloni G , Hebda M , Ischia G . Spark plasma sintering behaviour of copper powders having different particle sizes and oxygen contents . Powder Technol . 2016 ; 291 : 170 - 7 .
12. Sotomayor ME , Varez A , Levenfeld B . Influence of powder particle size distribution on rheological properties of 316L powder injection moulding feedstocks . Powder Technol . 2010 ; 200 : 30 - 6 .
13. Quanli J , Haijun Z , Suping L , Xiaolin J . Effect of particle size on oxidation of silicon carbide powders . Ceram Int . 2007 ; 33 : 309 - 13 .
14. Hausnerova B , Mukund BN , Sanetrnik D. Rheological properties of gas and water atomized 17-4PH stainless steel MIM feedstocks: effect of powder shape and size . Powder Technol . 2017 ; 312 : 152 - 8 .
15. Liverani E , Toschi S , Ceschini L , Fortunato A . Effect of selective laser melting (SLM) process parameters on microstructure and mechanical properties of 316L austenitic stainless steel . J Mater Process Technol . 2017 ; 249 : 255 - 63 .
16. Zhang L , Chen X , Li D , Chen Ch , Qu X , He X , Li Z . A comparative investigation on MIM418 superalloy fabricated using gas- and water-atomized powders . Powder Technol . 2015 ; 286 : 798 - 806 .
17. Mostafaei A , Hughes ET , Hilla C , Stevens EL , Chmielus M. Data on the densification during sintering of binder jet printed samples made from water- and gas-atomized alloy 625 powders . Data Brief . 2017 ; 10 : 116 - 21 .
18. Huntz AM , Reckmann A , Haut C , Severac C , Herbst M , Resnde FCT. Sabioni ACS . Oxidation of AISI 304 and AISI 439 stainless steel . Mater Sci Eng A . 2007 ; 447 : 266 - 76 .
19. Guillamet R , Lopitaux J , Hannoyer B , Lenglet M. Oxidation of stainless steels (AISI 304 and 316) at high temperature. Influence on the metallic substratum . J Phys IV . 1993 ; 3 : 349 - 56 .
20. Mukherjee A , Jain U , Dey GK . Oxidation studies of Indian reduced activation ferritic martensitic steel . J Therm Anal Calorim . 2017 ; 128 : 819 - 24 .
21. Hebda M , Ga˛dek S , Miernik K , Kazior J . Effect of the cooling rate on the phase transformation of Astaloy CrL powders modified with SiC addition . Adv Powder Technol . 2014 ; 25 ( 2 ): 543 - 50 .