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Al-Khwarizmi 
Engineering 

Journal 
 

Al-Khwarizmi Engineering Journal, Vol. 17, No. 1, March, (2021) 
P. P. 20- 33 

 

 
Influence of Aging Heat Treatment on Pitting Corrosion Resistance of 

Martensitic Stainless Steel 
 

Abdullah Dhayea Assi  
Middle Technical University/ Institute of Technology - Baghdad/ Baghdad/ Iraq 

Email: drabdullah_dhayea@mtu.edu.iq 

 
(Received 19 June 2019; accepted 9 December 2020) 

https://doi.org/10.22153/kej.2021.12.003 
 
 

Abstract 
        

This research aim to study the influence of aging heat treatment on the pitting corrosion resistance of martensitic 
stainless steel (MSS), where a number of martensitic stainless steel specimens were subjected to solution treatment at 
1100 oC for one hour followed by water quenching then aging in the temperatures range (500-750) oC for different 
holding times (1, 5, 10, 15 & 20) hr. Accelerated chemical corrosion test and immersion chemical corrosion test were 
performed on samples after heat treatment. The results of the research showed that the pitting corrosion resistance is 
significantly affected by the aging temperature. where samples that aged at 500 °C have the highest rate of corrosion 
due to an increase in the ratio of the Delta ferrite (δ-ferrite) and very soft precipitates from other phases of 
heterogeneous form in the basic martensitic phase; which leads to increase corrosion rate. From the other side, the aged   
samples in the temperature range (550–650) °C have the smaller rate of corrosion, this is due to the high volumetric 
ratio of remaining austenite. The aged samples at temperatures above 650 °C shows a medium corrosion rate. It was 
also found that the type of pits results from both the chemical corrosion tests and their shape were not related to the 
ferrite type and the carbides present in the microstructure.   

 
Keywords: Martensitic, Stainless Steel, thermal aging, pitting corrosion resistance. 
 
 
1. Introduction 

 
The need to use steels at medium operating 

temperatures and high ratios of tensile strength to 
the weight led to develop one type of stainless 
steel which have corrosion resistance and 
hardened by precipitation, the martensitic type. 
These types of stainless steel have proven their 
efficiency in applications with chemical corrosion 
resistance, such as oil, marine and nuclear 
applications, as they are exposed to corrosive 
media. The chemical corrosion resistivity of 
martensitic stainless steel which has corrosion 
resistance and hardened by precipitation is better 
than other martensitic types and can be compared 
with austenitic stainless steels in most media. 
Therefore, it widely used in military and non-
military equipment, and completely preferred 

compared with immersed and refractory 
martensitic steels [1]. 
       Electrochemical studies of chemical 
corrosion of stainless steel have shown that the 
chemical composition and microstructure of these 
steels are important factors in determining 
chemical corrosion behavior. As well as, the 
chromium content of stainless steel is important in 
order to obtain and maintain good chemical 
corrosion resistance under certain operating 
conditions. If the chromium content is low at the 
granule boundary, the steel will be vulnerable to 
attack and corrosion among the granules even if 
there is high chromium content in the basic 
freezing solution. On the other side, if chromium-
rich carbides are concentrated on the grain 
boundaries, there will be a shortage of chromium 
in the vicinity of the boundary and the carbides 



Abdullah Dhayea Assi                      Al-Khwarizmi Engineering Journal, Vol. 17, No. 1, P.P. 20- 33 (2021) 
 

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will begin to settle there. This will corrupt the 
chemical corrosion resistance in these areas and 
will result in granule local corrosion [2]. 

The study of the chemical wear behavior of 
stainless steel that can be quickly deposited and 
frozen shows that it is produced in the form of 
chrome-rich and molybdenum-rich carbide on the 
boundary of grains, which can be the cause of the 
high susceptibility of these alloys to pitting 
corrosion [3]. 

The heat treatment of stainless steels helps to 
produce changes in the physical state, mechanical 
properties, residual stress levels, and in restoring 
maximum chemical corrosion resistance when 
these properties are adversely affected by various 
manufacturing or heating processes. An 
acceptable combination of resistance to chemical 
corrosion with optimum mechanical properties 
can be obtained by appropriate choice of heat 
treatment. In general, any improvement in the 
mechanical properties of steels by rapid cooling 
and revision will inevitably associated with 
increased chemical corrosion [4]. 

The general corrosion behavior of sintered 17-
4 PH stainless steel processed under different 
processing conditions in dilute sulfuric acid 
solution at 25 °C was studied by open-circuit 
potential measurement and potentiodynamic 
polarization technique. The results showed that 
the precipitation-hardening treatment could 
significantly improve the corrosion resistance of 
the sintered 17-4 PH stainless steel in studied 
environment.  It can be concluded that the highest 
corrosion resistance in 0.5 M H2SO4 solution 
exhibits 17-4 PH after solution treatment at 1040 
°C followed by aging at 480 °C [5]. 

Pitting corrosion properties were investigated 
in 0.6M NaCl electrolyte with sulfate additions by 

Potentiodynamic Polarization (PP). Hardness, 
tensile and yield strength of the UNS S46500 
steel after lower aging temperature, 510ºC 
(H950), are higher than the ones found in the 
538ºC (H1000) aged steel. This result is explained 
by microstructure, X-ray diffraction and Thermo-
Calc analysis, which indicated the presence of 
austenite, chi phase and probably Ni3Ti 
precipitates finely and uniform distributed 
throughout the martensite matrix [6]. 

The aim of this research is to study the 
influences of aging heat treatment and the 
resultant phases on the pitting corrosion resistance 
of martensitic stainless steel through accelerated 
chemical corrosion as well as immersion chemical 
corrosion tests that have to be performed on 
samples after aging heat treatment. This is due to 
the necessary need for this type of stainless steel 
in various applications.  
 
2. Experimental Work 
2.1.  Materials 

  
The materials used in this research are 

martensitic stainless  steel sheets hardened by 
precipitation hardening that was pre-exposed by 
the manufacturer to the normalizing process at a 
temperature of 924 °C, then cooled in the air and 
exposed to aging process at 600 °C. It finally 
cooled in the air to room temperature. The 
chemical analysis of the used steel was obtained 
by the spectroscopy device (Model Spector Max-
X). Table (1) shows the chemical composition of 
this steel and Steel grade 420SS [7] . 
 

Table 1, 
The chemical composition of the used stainless-steel. 

  
 
2.2. Heat Treatment 
 

The previous sheets were cut into 32 samples 
with dimensions of (10 × 5 mm) for each sample, 
and then subjected to the following heat 
treatments: 
1- Solution treatment at 1100 °C for one hour, 
then immersed in water. 

2- Aging at temperatures 500, 550, 600, 650, 700,  
and 750 °C for five hours, and then cooled by air 
3- Aging at two temperatures 500 and 650 °C 
during different times 1, 5, 10, 15, and 20 hours. 
The samples were heated using two electric 
furnaces as shown in Figure (1a), the first for the 
dissolution treatment and the second for the aging 
process .  

Element 

% 

C Cr Ni Mo Si Mn S P Ti Fe 

Standard 
[7]  

0.07 15-17 3-5 0.5-2 0.25-0.5 0.5-1 0.002 0.01-0.04 0.45 Bal. 

Measured  0.05 15.5 5.6 0.80 0.3 0.70 0.002 0.02 0.4 Bal.



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Fig. 1a. Two Electric Furnaces for heat treatment. 
 
 
2.3. Chemical Corrosion Test (dynamic 
voltage or acceleration test) 

 
Chemical corrosion testing or acceleration 

testing is an effective widely used method in 
estimating the chemical corrosion in aqueous 
media by passing a current into the electrode 
using an inert electrode.  The degree of 
polarization is determined by measuring the 
sample voltage, while the rate of electrode 
reaction is measured from the density of the cell 
current that it directly transits to a chemical 
corrosion rate measured in mm/year. The anode 
and cathode polarization diagrams of electrodes 
(samples) exposed to a 6% FeCl3 solution are 
plotted and the electrode area is 0.5 cm2. These 
diagrams are obtained using PS6 device connected 
with a computer. The voltage range was found in 
all tests from - 200 to +1000 mV, and the scan 
rate was set to 0.5 mV/s. This test was carried out 

at room temperature at the Ministry of Science 
and Technology / Department of Materials as 
shown in Figure (1b). 

 

 
 
Fig. 1b. The Chemical Corrosion Test. 

 

2.4. Pitting Chemical Corrosion Test 
(Immersion Test) 
        

The pitting chemical corrosion resistance was 
measured according to ASTM G48 for pitting test 
by using a ferric chloride (FeCl3) as immersion 
solution with a concentration of 6% prepared by 
dissolving 100 g of aqueous ferric chloride (FeCl3. 
6H2O) in 900 ml distilled water . 
The test was carried out in the following manner: 
1- The samples are firstly weighed  
2- The samples are immersed in the previous 
solution for 72 hours.  
3- The samples are removed from the solution and 
washed with distilled water to remove dissolved 
oxides that have formed on the surface of the 
samples, 
4- The samples are weighed again. 
5-   The weight loss is calculated by the difference 
between the two weights.  
        Finally, the samples are examined under a 
microscope at 50 times magnification and the 
pitting spots formed on the surface of the samples 
are captured according to the previous 
specification with changing the immersion 
solution after each immersion and existing process 
of samples.The corrosion rate can be calculated by 
equation (1) [Reference]:  

Where:  
3650 W

CR
A d t




 
                           …(1) 

CR: Corrosion rate (mm / year) 
W: Weight loss = Initial Weight - Final 
Weight in (grams) 
A: Sample exposed surface area (cm2) 



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d: Tested material density (gm / cm3) 
t: Immersion time (day) 
 
2.5. Microstructure Test 

 
The microstructures of the heat-treated 

samples that were subjected to chemical 
corrosion tests have been examined by using an 
OLYMPOS optical microscope. Samples were 
prepared for microscopic examination of 
sharpening, polishing and smoothing with Fry 
solution for smoothing consisting of (5g from 
CuCl2 copper chloride) + (40 mL from HCl) + 
(30 mL from methyl alcohol) and 30 mL of 

water. The phases and microscopic components, 
such as the martensitic matrix and the Delta 
ferrite phase, were identified using an optical 
microscope, since the martensitic floor appeared 
in the form of plates, while the Delta type ferrite 
appeared in small quantities in the form of 
longitudinal white ribs, and no presence of 
austenite was found in this sample, as indicated 
by in Figure (2). 

The volumetric ratios for the Austenite were 
determined using XRD diffraction technique 
according to the method described in ASTM 
E975-95 . 

 

 
 

Fig. 2. The microstructure of soluble treated samples at a temperature of 1100 °C (50X). 
 

  
3. Results  
3.1 Effect of aging process on austenite 
volumetric ratios 
 

Figure (3) shows the effect of aging 
temperature on the austenite volumetric 
percentages. It was found that by increasing the 

aging temperature, the austenite volumetric ratios 
gradually increase, and the maximum value of the 
austenite volumetric ratios occurs at a 
temperature of 650 °C. After that, a gradual 
decrease was occurred down to temperature of 
750 °C. 

 

 

Fig. 3. Effect of four hours aging temperature on volumetric ratio for austenite. 



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24 

The effect of aging time on the austenite 
volumetric percentages at 500 and 650 ° C aging 
is shown in figure (4). No significant change in 
the residual austenite volumetric percentages at 

500 °C was noticed. While at aging temperature 
of 650 °C increases the amount of austenite was 
significantly increased from 20% to 55%; by 
increasing the aging time from 1 to 20 hours. 

 

 

Fig. 4. Effect of aging time on the austenite volumetric percentage at two aging temperatures. 
 
 
3.2 The Effect of Aging Process on the 
Microstructure 
 

The microscopic structure of heat-treated 
samples at different aging temperatures and times 
were shown in Figures (5 to 11). All microscopic 
structures consist mainly of low carbon 
martensitic and variable percentages of ferrite 
delta type, which sometimes present in the form 
of Longitudinal ribs. The fundamental change in 
the microscopic structure with increasing aging 
temperature and time was the decomposition of 
martensitic associated with the appearance of 
austenite. The volumetric ratio of the austenite 
was increased by increasing the aging temperature 
up to 650 °C. 

The microstructure of the aging samples at a 
temperature of 500 °C and a time of 4 hours was 
shown in Figure (5). The form of elongated 
carrots, Martensitic slices and also austenitic 
elongated granules, which arise between the 
Martensitic slices within the former austenitic 
granules, leading to the variation of the 
microscopic structure.  

Figure (6) shows the microscopic image of the 
aging specimens at 500 °C for one hour. The 
typical low-carbon slice martensitic structure is 
shown in the former austenitic granule. The 
transformation of martensitic to austenite becomes 
more pronounced by increasing the aging 
temperature and time. At temperature aging of 
550 °C for 5 hours the same microstructure as 
shown in Figure (7) where a high number of 

longitudinal grounded austenite were pronounced. 
This decomposition of martensitic becomes more 
pronounced at temperatures of (550 and 600 °C) 
as shown in Figures (7 and 8) below .   In this case 
the austenite volumetric percentage was about 
20% as shown from previous Figure (3).  

After the aging temperature of 600 °C for 5 
hours, the microstructure is almost identical to 
that of the previous 550 °C as shown in Figure 
(8), but the residual austenite volume increases to 
about 30%. 

 

 
 

Fig. 5. Microstructure of aging specimens at 
temperature 500 ° C and aging time 5 hrs 200 X . 
 



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Fig. 6. Microstructure of aging samples at 550 oC 
for 1 hour (200X). 
 

 
 
Fig. 7. Microstructure of aging samples at a 
temperature of 550 oC for 5 hours (100X). 
 

 
 

Fig. 8. Microstructure of aging samples at a 
temperature of 600 °C for 5 hours (200X). 
 

 
The maximum residual austenite value of 32% 

is shown in the sample treated at 650 ° C for 5 
hours as shown in Figure (9). The microstructure 
seems to be as equal axes granules, which can be 
seen inside these soft needle-shaped 
microstructures. Examination of this structure at 

High magnification showed that the residual 
austenite granules are elongated, and their 
volumetric ratio increased with the aging time 
from 1 to 20 hours as shown in Figure (10). The 
former austenitic granules are dark in color and 
others are light in color and larger in size. 
 

 
 

Fig. 9. Microstructure of aging samples at 650 oC 
for 5 hours (200X). 
 

 
 

Fig. 10. Microstructure of aging samples at 650 oC 
for 16 hours (1000X). 
 

The microstructure of the aging samples at a 
temperature of 700 °C for 5 hours is shown in 
Figure (11). In this figure the ribs of ferrite delta 
type are shown and adjacent to them are often 
bright white elongated granules and others with 
almost equal axes. These granules are for the 
residual austenite which has been converted to 
non-aging martensitic. 
 



Abdullah Dhayea Assi                      Al-Khwarizmi Engineering Journal, Vol. 17, No. 1, P.P. 20- 33 (2021) 
 

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Fig. 11. Microstructure of aging samples at 700 oC 
for 4 hours (500X) 
 
 
3.3 Effect of aging process on chemical 
corrosion rate (dynamic voltage and 
immersion tests) 
 

       Figure (12) shows the effect of 5-hours aging 
temperatures on the chemical corrosion rate (with 
6% iron chloride acceleration test) and immersion 
test, as it appears from this form the following 
points: 
1. The chemical corrosion rate is increasing 
sharply in the aging temperature range from (500 
to 550) °C. 
2 - The largest value of the rate of chemical 
corrosion is about 2.5 mm / year; when aging to a 
temperature of 550 °C. 
3. The chemical corrosion rate decreases steeply 
when aging in a temperature range of (550 to 600) 
°C 
4 - The minimum value of the rate of chemical 
corrosion about 0.2 mm / year that produced at 
aging range of (550 to 650) °C. 
5. The rate of chemical corrosion increases again, 
gradually, when aging after the previous field. 
 
 

 

 

Fig. 12. Effect of 5-hour aging temperature on chemical corrosion rate due to acceleration test (dynamic voltage 
test) and immersion test . 
 

 
Figure (13) shows the effect of aging time on 

the chemical corrosion rate; at 550 and 650 ° C 
aging temperatures, when aging at a temperature 
equal to 550 °C, the initial phase of chemical 
corrosion increases from 1 to 5 hours. The 
maximum value of the chemical corrosion rate 

was at an aging time of 5 hours, after which the 
rate of chemical corrosion gradually decreases. 
When aging at a temperature equal to 650 °C, the 
chemical corrosion rate gradually increases with 
the aging time and the increase rate is much 
faster after aging time of 10 hours. 



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Fig. 13. Effect of aging time on the chemical corrosion rate of aging samples at an aging temperature of (500 and 
650) °C from the accelerometer test (dynamic voltage test). 
 
 
3.4  Effect of aging process on voltage 
        

Figure (14) shows the effect of increasing the 
aging temperature on the voltage; at an aging time 
of 5 hours, this figure shows the following : 
 The voltage decreases gradually by increasing 

the aging temperature in the range from (500 to 

650) °C, and produces the lowest voltage when 
aging at 650 °C. 

 The voltage increases significantly by 
increasing the temperature in the field from 
(650 to 750) °C. 

 
 
 
 

 
 

Fig. 14. Effect of aging temperature for 5 hours on voltage . 
 
 

The effect of aging time on voltage is shown in 
Figure (15) at (500 and 650) °C. An increase in 
voltage is observed at each aging temperature, 
starting from an equal aging time to one hour, and 
the rate of increase is much faster at an aging 
temperature of 500 °C, and the maximum value of 
the voltage is produced by aging for 10 hours; this 

is at all the two temperature ranges of aging. On 
the other hand, the voltage decreases gradually 
when the aging time increases above 10 hours and 
after (15) hours the rate of decrease is slower. The 
aging sample at a temperature of 500 °C had a 
higher voltage than the aging sample at a 
temperature of 

 



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Fig. 15. Effect of aging time on voltage at two aging temperatures . 
 

 
3.5 Effect of aging process on chemical 
corrosion rate (immersion test): 

 
       The changes in the chemical corrosion rate 
resulting from this test are shown in Figure (16). 
By changing the corrosion time of samples at the 
aging temperatures of (500 and 650) ° C, the 
changes in the rate of chemical corrosion by 
changing the aging time are similar to those 
resulting from the previous test (the accelerated 
test), but the values of the chemical corrosion rate 
are higher in this case. 

The results can be studied and divided into two 
types: 
1. The chemical corrosion rate of aging samples 
increases at 500 °C, in the first stage of the 
scheme from the time of aging 1 to 5 hours and 
the maximum value of the chemical corrosion rate 
occurs when aging for 5 hours, after which time 
the chemical corrosion rate gradually decreases 
with Increased aging time. 
2. The rate of chemical corrosion gradually 
increases with the aging time of the aging samples 
at 650 °C, and the rate of increase is faster after 
aging time of 15 hours . 

 
 

 
 

Fig. 16. Effect of aging time on chemical corrosion rate of aging samples at 500 and 650 °C aging temperatures. 
 

 

3.6. Click forms in aging samples at 
different time temperatures 
        

Figures (17) to (19) show microscopic images 
of aging samples at different aging temperatures 
and times tested by accelerated testing. From 
these images it can be seen that there is a deep 
and large mortise on the surface of the aging 
sample at a temperature of 550 ° C as shown in 

Figure (17b), which corresponds to the high 
chemical corrosion rate previously measured. 

When the sample is released at a temperature 
of 600 °C, the clicking is smaller and deeper than 
the rest of the sample as shown in Figure (17c), 
while the size of the tap formed on the surface of 
the aging sample at 750 °C is larger than that 
formed on the sample surface. The aging is 550 



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°C,  but remains smaller than the aging sample at 
500 °C, as shown in Figure (17f). 

An increase in the aging time with the aging 
temperature constant at 500 °C indicates that there 
is a clear decrease in the flick size after being 
tested by acceleration method as shown in Figure 
(18), and the smallest flick size after aging is 

formed within a period of 20 hours as evident 
from Figure (18e).    Conversely, by increasing the 
aging time at 650 ° C there is a noticeable 
increase in the size of the flick as shown in Figure 
(18), and the larger flick size is formed in the 
sample that was released at 20 hours as shown in 
Figure (18k). 

 

 
 
Fig. 17. Microscopic images of aging samples for 4 hours at different aging temperatures. (a, g) 500, (b, h) 550, 
(c, i) 600, (d, j) 650, (e, k) 700, (f, l) 750 °C, where (a, b, c, d, e, f, acceleration test) and (g, h, i, j, k, l, immersion 
test). 

        
Fig. 18. Microscopic images of aging samples during different aging times;(a) 1hr, (b) 5hr, (c) 10hr, (d) 15hr, 
(e) 20hr: acceleration test where (a, b, c, d, e) at 500 °C and (f, g, h, i, k) at 650 °C. 

 
 

Figure (19) shows the microscopic images of 
the aging samples at different temperatures and 
aging times. This is after being tested by 
immersion method, noting that there is almost no 
difference in the form of clicking and its size 

after aging at different temperatures and aging 
times; this is when compared to the pictures of 
the samples tested with the previously explained 
acceleration test as shown in Figure (18). 



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Fig. 19. Microscopic images of aging samples during different aging times  ;(a) 1hr, (b) 5hr, (c) 10hr, (d) 
15hr, (e) 20hr: immersion test where (a, b, c, d, e) at 500 °C and (f, g, h, i, k ) at 650 °C. 
 
 

4. Discuss the Results 
4.1 The relationship between the aging 
process and the microstructure . 
 

No residual austenite was observed in this 
type of stainless steel and rapidly cooled, 
probably because of the low residual austenite 
ratio of less than 2%; therefore, it did not appear 
in the microstructure and was not determined by 
X-ray diffraction . 

The remaining austenite (quasi-slice austenite) 
may appear in areas where the returning austenite 
was formed after hemolytic treatment, so a 
double needle-shaped microscopic structure 
consisting of low-carbon martensitic and 
recovered austenite may be formed in each 
martensitic slice [8]. It is known that in some 
types of martensitic stainless steel can be 
converted to austenite after aging at an aging 
temperature equal to or above 500 ° C [9].  The 
remaining austenite ratios were found to increase 
with the aging temperature and time up to 650 ° 
C, as shown in Figures (3 and 4).   It was also 
found that the amount of austenite was increased 
at the expense of martensitic by increasing the 
aging time above five hours at a temperature of 
650 ° C; this means that the amount of 
martensitic converted to austenite remaining 
during the heating process at 650 ° C increased 
with the aging time.    The volumetric ratio of the 
austenite after aging process decreases at 700 °C 
or above compared to the aging process at a 
temperature range of 500-650 °C as shown in 
Figure (3); this means that the remaining part of 

the austenite formed at these temperatures turned 
again into an aging martensitic. Aging at this 
temperature may have resulted in the deposition 
of chromium carbides Cr23C6 and titanium 
carbides (TiC) that consume carbon and 
depletion from martensitic and residual austenite 
[9]. This makes the austenite less stable and leads 
to the conversion of part of the remaining 
austenite to martensitic during cooling from 700 
– 750°C to room temperature. After the rapid 
cooling process in the water, the microscopic 
structure of this sample consists of slices of 
martensitic and ferrite in the form of longitudinal 
ribs. 

The formation of high-density slice 
martensitic in this hardened stainless steel can be 
justified by precipitation at high temperature 
starting temperature of the martensitic conversion 
of Ms = 120-150 °C as well as low carbon 
content in this steel, as it has been well proven 
that for various types of steels. The starting 
temperature of the martensitic transition and the 
ratio of carbon are the two most important factors 
that influence the structure and partial structure 
of Martensitic - and, in general, the martensitic 
with a slice structure is associated with a partial 
structure with a high intensity of dislocations 
[10].    It was found that aging samples were very 
deeply affected by the chemical smoothing 
solution as shown in Figures (5 to 11). This is 
due to the appearance of residual austenite 
among the martensitic segments .  Exposure to the 
aging process at 500 ° C leads to a microscopic 
structure in which the martensitic bundles 



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31 

dissipate or dissolve clearly. The residual 
austenite appearance and increased quantity 
between the martensitic slices up to a 
temperature of 650 ° C reduces the slide width 
from about 3 microns to 0.5 microns. The 
microscopic structure after aging at 700 °C for 5 
hours appears to consist of equal-dimensional 
granules (axes) as shown in figure (11). This may 
be due to the different range of transitions from 
chilled martensitic to residual austenite and 
martensitic no aging, as well as carbides in 
different granules. These differences make the 
boundaries of the martensitic bundles can be 
resolved and dissipated. 
 
4.2 The relationship between 
microstructure and chemical corrosion 
behavior 
 

Chemical corrosion behavior has been 
affected by the aging time and its temperature, as 
well as by the amount of remaining austenite and 
ferrite type Delta, and also by the deposition of 
molybdenum and chromium carbides. 

Aging-treated samples at 500 °C have 
maximum chemical corrosion rate values as 
shown in Figure (12). This could be due to the 
presence of delta-type ferrite in the form of 
longitudinal ribs and the deposition of very small 
precipitates found to be molybdenum carbides 
(Mo2C) [11]. 
After aging for 15 hours at 500 ° C, these carbides 
may begin to disintegrate and this leads to a 
decrease in the rate of chemical corrosion as 
shown in Figures. (13 and16). Aging samples at 
550 °C have the lowest corrosion rate values as 
shown in Figure (12), and this can be due to the 
high volumetric ratio of the austenite [12]. The 
resulting high rate of chemical corrosion after 
aging for 20 hours at 650 °C can be attributed to 
the beginning or growth of Cr23C6 chromium 
carbide. After aging at temperatures above 650 ° 
C, carbides of Cr23C6 type can become dominant, 
dominant and heterogeneous deposits in the 
martensitic floor that leads to an increase in the 
rate of chemical corrosion. 

Aging in a range of (700 to 750) °C for 5 hours 
may precipitate Cr23C6 carbides at the grain 
boundary as chromium atoms leave to form 
chromium-rich carbides. If these chromium-rich 
carbides are concentrated on the grain boundaries, 
there will be a decrease in the chromium content 
in the vicinity where the carbides begin to settle, 
forming the depletion areas of the chromium. The 
grains became more dangerous in their resistance 

to chemical corrosion [12].   The large flick size of 
aging samples at 500 °C as shown in Figures 
(17b), (18) and (19b) indicates that these samples 
are more susceptible to fovea corrosion, which 
may be due to the formation of molybdenum 
carbides and the presence of delta type ferrite. It 
can be concluded that aging samples at 500 ° C 
for 5 hours are less predisposition than other 
samples, due to the small click size as indicated 
by doubt (17c,i) and can be due to high volumetric 
percentages it remains the result of the dissolution 
and disintegration of martensitic. The formation of 
chromium carbides of type Cr23C6 in aging 
samples at 750 ° C has led to a second increase in 
the volume of clicking formed on the surface of 
aging samples at this temperature. 

 
 

5. Conclusions 
 

The main conclusions drawn from this research 
are the following : 
1. The microscopic structure in rapidly cooled 

samples consists of slices of martensitic and 
longitudinal ribs of delta-ferrite and no 
residual austenite exists. 

2. The remaining austenite begins to appear in 
the microstructure after aging at 500 ° C, and 
its volumetric ratios increase to its highest 
value after aging at 650 ° C. 

3. The residual austenite volumes decrease from 
32% to 20% by increasing the aging 
temperature from 650 to 750 °C. A portion of 
the remaining austenite is converted into an 
uncharacterized martensitic; this is cooled 
from 750 °C . 

4. The chemical corrosion test was found to 
have three critical temperatures: 

 High corrosion rate at 500 °C due to the 
presence of Delta -ferrite and Mo2C carbides. 

 Low corrosion rate at 500-650 ° C, due to 
high volumes of residual or anatomic . 

 Average corrosion rate at 750 ° C as a result 
of deposition of chromium carbides and 
titanium in a small amount. 

5. The aging temperature range from 500 to 650 
° C produced minimum localized corrosion 
that can be attributed to the high volumetric 
percentages of residual austenite. 

 
 
 
 
 
 



Abdullah Dhayea Assi                      Al-Khwarizmi Engineering Journal, Vol. 17, No. 1, P.P. 20- 33 (2021) 
 

32 

6. References 
 

[1] B. Tzaneva, “Effect Of pH on the Corrosion 
Behaviour Of High Nitrogen Stanless Steel in 
Chloride Medium,” Journal of Chemical 
Technology and Metallurgy, 48, 4, 2013, pp 
383390.   

[2] R. C. Newman, “Understanding the Corrosion 
of Stainless Steel,” Corrosion, Vol. 57, No.12, 
Dec. 2001, pp1030-1041.  

[3] K. Ajay, S. Chaudhary and A. Sharma., 
“Electrochemical Studies of Stainless Steel 
Corrosion in Peroxide Solutions”, Portugaliae 
Electrochimica Acta, 2012, 30(2), 99-109. 

[4] J. Tian, W. Wang and M. Babar, “A New 
Maraging Stainless Steel with Excellent 
Strength–Toughness–Corrosion Synergy”, 
Materials 2017, 10, 1293; 
doi:10.3390/ma10111293 

[5] A. Nykiel and J. Kazior, “Effect of Aging 
Temperature on Corrosion Behavior of 
Sintered 17-4 PH Stainless Steel in Dilute 
Sulfuric Acid Solution”, Journal of Materials 
Engineering and Performance (JMEPEG), 
Published online 15 June 2017.   

[6] C. H. Beraldo, José Wilmar Calderón-
Hernández, Rodrigo Magnabosco and Neusa 
Alonso-Falleiros, “Effect of Aging Heat 
Treatment H950 and H1000 on Mechanical 
and Pitting Corrosion Properties of UNS 
S46500 Stainless Steel”, Materials Research. 
2019; 22(1).  

[7] AZO-Material, the state of scientific marketing 
survey, " Martensitic Stainless Steel, 
Applications", November 1, 2018. 

[8] H. Nakagawa, T. Miyazaki and H. Yokota, 
“Effect of Aging Temperature on the 
Microstructure and Mechanical Properties of 
1.8Cu-7.3Ni-15.9Cr-1.2Mo-low C, 
N,Martensitic Precipitation Hardening 
Stainless Steel,” Journal of Materials and 
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[9] P. Anja and k. Axel, “Local Corrosion of 
Martensitic Stainless Steels during Exposure to 
Saline Aquifer Water and CO2 Environment”, 
International Journal of Chemical Engineering 
and Applications, Vol. 9, No. 1, February 
2018. 

[10] D. Deng,” Microstructural Study of 17-4PH 
Stainless Steel after Plasma-Transferred Arc 
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[11] Z. De-ning., “Influence of Tempering Process 
on Mechanical Properties of 00Cr13Ni4Mo 
Super Martensitic Stainless Steel” J. of Iron 
and Steel Research, International. 17(8), 2010, 
pp 50-54.  

[12] B. Qin., “Effect of Tempering Temperature on 
Properties of 00Cr16Ni5Mo Stainless Steel”, 
Materials Characterization, 59, 2008, pp 1096-
1100.   
 
 

 
 
 

 
 
 

 

 

 

       

 
 
 
 
 
 
 
 
 



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33 

 
 

  

المقاوم للصدأ  مقاومة التآكل الكيميائي النقري للفوالذ  تاثير التعتيق الحراري على  دراسة 
  المارتنسيتي 

  
  دهللا ضايع عاصيعب

  بغداد  –بغداد/ العراق  –الجامعة التقنية الوسطى / معهد تكنولوجيا 
  drabdullah_dhayea@mtu.edu.iq  البريد االلكتروني:

  
  
  

  
  

  الخالصة 
 

عينات    اذ عرضتدراسة تأثير  المعالجة الحرارية بالتعتيق في  مقاومة التآكل الكيميائي  النقري للفـوالذ المارتنسيتي المقاوم للصدأ،    تم البحث    في هذا  
حرارة   درجـة  عنـد  انحاللية  معالجة  إلى  للصدأ  المقاوم  المارتنسيتي  الفوالذ  إلى    1100من  سخنت  ثم  ومن  بالماء  وغطست  ساعة   مدة  مئوية  درجة  درجة 

) ساعة. اجري اختبار التآكل الكيميائي المسرع واختبار التآكل الكيميائي بالغمر  20-1) درجة مئوية لمدد إبقاء متنوعة ( 750- 500حرارة ضمن المجـال ( 
أن العينات المعتقة عند درجة  على العينات بعد المعالجة الحرارية . بينت نتائج  البحث تأثر مقاومة التآكل النقري تأثرًا كبيرًا بدرجة حرارة التعتيق، ِإِْذ وجد 

فرايت) وترسبات ناعمة جدًا من أطوار أخرى بشكل  - δعظم معدل تآكل الذي قد يكون بسبب زيادة نسبة فرايت نوع دلتا (درجة مئوية تملك ا   550حرارة  
درجة  )  650–550غيـر متجانس فـي الطـور األساسـي المارتنسيتي؛ مما يؤدي إلى زيادة معدل التآكل، في حين العينات المعتقة في مجال درجة حـرارة (

درجة   650عدل تآكل أصغر، ويعزى ذلك إلى النسبة الحجمية المرتفعة لألوستنيت المتبقي . وتبدي العينات المعتقة عند درجة حرارة أعلى من  مئوية لها قيم م
نوع الفريت  بشكل  يتعلق  ال  وشكلها  الكيميائي  التآكل  اختباري  كال  عن   الناتجة  النقر  نوع  أن  كذلك  ووجد  متوسطا.  تآٍكٍل  معد ََل  والكربيدات دلت  مئوية   ا 

  الموجودة في البنية المجهرية.