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Results in Physics 4 (2014) 127–134

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Results in Physics

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Fatigue behavior of welded austenitic stainless steel in differentenvironments

http://dx.doi.org/10.1016/j.rinp.2014.03.0052211-3797/� 2014 The Authors. Published by Elsevier B.V.This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

⇑ Corresponding author. Tel.: +234 8039140798.E-mail address: [email protected] (S.O. Aluko).

D.S. Yawas, S.Y. Aku, S.O. Aluko ⇑Mechanical Engineering Department, Ahmedu Bello University, Zaria, Nigeria

a r t i c l e i n f o a b s t r a c t

Article history:Received 10 September 2013Accepted 14 March 2014Available online 21 March 2014

Keywords:Austenitic stainless steelFatigueSeawaterHydrochloric acidWet steam

The fatigue behavior of welded austenitic stainless steel in 0.5 M hydrochloric acid and wet steam corro-sive media has been investigated. The immersion time in the corrosive media was 30 days to simulate theeffect on stainless steel structures/equipment in offshore and food processing applications and thereafterannealing heat treatment was carried out on the samples. The findings from the fatigue tests show thatseawater specimens have a lower fatigue stress of 0.5 � 10�5 N/mm2 for the heat treated sample and0.1 � 10�5 N/mm2 for the unheat-treated sample compared to the corresponding hydrochloric acid andsteam samples. The post-welding heat treatment was found to increase the mechanical properties ofthe austenitic stainless steel especially tensile strength but it reduces the transformation and thermalstresses of the samples. These findings were further corroborated by the microstructural examinationof the stainless steel specimen.

� 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-NDlicense (http://creativecommons.org/licenses/by-nc-nd/3.0/).

1. Introduction

Fatigue failure is of great importance as it is well attested to bythe large percentage of failures in machine elements. Metal fatigueis caused by repeated cycles of load. It causes progressive localizeddamage due to fluctuating stresses and strains on the material.From estimates made, over 80% of failures in machines is the resultof fatigue failure [12].

Fatigue failures occur in engineering materials whereby a mate-rial (metal) fails when subjected to repetitive dynamic or fluctuat-ing stresses/loads much lower than those required to causefractures on single applications. Loads which can cause fatigue fail-ure apart from axial can be those in shear or bending [11].

Rotating equipment uses a great deal of 300 series stainlesssteels and as a result we often experience several types of corro-sion. Stainless steel generally exhibits excellent corrosion resis-tance, but pitting can cause catastrophic failure in structuresmade of alloy [11].

Stainless steels are widely used in different industries such asthe oil and gas (onshore and offshore), pulp and paper, marine,automobile, food processing industries and for the constructionof storage tanks (www.materialsengineer.com). Stainless steels

are iron alloys which depend upon a very thin transparent passivesurface film of chromium oxide to resist corrosion [6].

Several research works have been carried out on fatigue behav-iors of stainless steel, among such works is the work done by Sololu[13], he investigated the effect of crude oil and seawater on thefatigue strength of ST 60 Mn steel. The result obtained showed thatcrude oil and saline environment (seawater) lower the fatiguestrength of ST 60 Mn steel and the kind of heat treatment givencauses further decreases in the fatigue strength. Odebisi [7] andOlubisi [8] carried out research on corrosion fatigue behavior ofST 60 Mn steel in cocoa mucilage and in cassava juice respectively.They observed that the forms of heat treatment described abovewill enhance the fatigue strength of ST 60 Mn steel in a corrosiveenvironment. Adebayo and Aremu [1] worked on corrosive andsynergistic actions of inhibitors on the fatigue properties of mildsteel. They observed that the fatigue strength of the non-corrodedspecimen is higher than that of the corroded specimen of the samebatch of mild steel. Oluwole [9] worked on the effect of heat treat-ment on the damage ratio of corroded ST 60 Mn steel. He recom-mended that manganese steels like ST 60 Mn used for oilpipelines should be heat treated by normalizing prior to use inorder to enhance the fatigue strength of this grade of steel and thusprevent oil spillage.

The objective of this work is to study the fatigue behavior ofwelded austenitic stainless steels in different corrosive media.

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Table 1Chemical composition of seawater.

Element O H Cl Na Mg S Ca K Br C

% by wt 85.84 10.82 1.94 1.08 0.13 0.091 0.04 0.04 0.0067 0.0028

Seawater having a pH value of 8 and a salinity of 3.5% [13].

Table 2Chemical compositions of austenitic stainless steel.

Element C Si Mn Ni Cr Mo V Cu

% by wt 0.079 0.212 1.216 14.189 16.189 1.538 0.037 0.155

Element W As Co Al Pb Ca Zn Fe

% by wt 0.416 0.150 0.134 0.008 0.004 0.0001 0.019 64.215

Fig. 2a. Metal inert gas welding (Center for Energy and Research Institute, AhmaduBello University, Zaria).

Fig. 2b. Welded fatigue specimen.

128 D.S. Yawas et al. / Results in Physics 4 (2014) 127–134

2. Materials and methods

2.1. Materials

The corrosive media used in this study include:

0.5 M hydrochloric acid, seawater, wet steam.

The etchants used are:

5 g FeCl2, 50 ml HCl, 100 ml water (for the as-receivedsamples);and 4 g CUSO4, 20 ml HCl, 20 ml water (for the heat-treated).

2.2. Equipment

The equipment used in this study includes:

Metal analyser, lathe machine, gemco heat furnace, weighingbalance, plastic bowls, austenitic stainless steel, metal inertgas welding machine, fatigue testing machine, grinding, polish-ing and etching machines, photographic visual metallurgicalmicroscope.

2.3. Methods

2.3.1. Preparation of test fluid20.80 cm3 of HCl from a standard Winchester bottle was dis-

solved in 500 cm3 of distilled water to obtain the desired concen-tration from the Chemical Engineering Department of the

Fig. 1. Fatigue specimen (schematic diagram).

Fig. 3. Gemco Furnace (Industrial Development Centre, Zaria).

Table 3Fatigue stress of austenitic stainless steel in seawater.

Time of immersion (days) Fatigue stress � 105 (N/mm2)

Heat treated Unheat treated

5 1.5 1.210 1.3 1.015 1.2 0.920 1.0 0.625 0.9 0.430 0.5 0.1

Table 4Fatigue stress of austenitic stainless steel in 0.5 M HCl.



5 2.0 1.510 1.8 1.215 1.5 1.020 1.4 0.725 1.1 0.630 0.6 0.3

Table 5Fatigue stress of austenitic stainless steel in wet steam.



5 2.5 2.210 2.4 1.815 1.9 1.520 1.8 1.025 1.5 0.830 1.0 0.5

D.S. Yawas et al. / Results in Physics 4 (2014) 127–134 129

Ahmadu Bello University, Zaria, Nigeria and seawater solution wasobtained from the Bar Beach in Lagos State, Nigeria while the spec-imens were subjected to steam at Sunseed Nig. Ltd., Jos road, Zaria,Nigeria (see Table 1).

2.3.2. Preparation of specimenThe work material, (austenitic stainless steel rod) was pur-

chased from the steel market in Zaria, Nigeria in the form of rods

and the chemical composition was carried out at Universal SteelIkeja, Lagos, Nigeria using a spectrometer machine.

2.3.2.1. Metal analysing procedure. This was done to determine theelements present and their percentages in stainless steel. A20 mm � 30 mm piece of standard pipe samples was made. Thesurface of the sample was ground in a grinding machine to obtaina smooth surface. The sample was placed in the orifice on themachine, a pin to pin spark was impressed on the sample using asolid technique optical emissions spectrograph with 0.0001% sen-sitivity. The reading was taken from a direct computerized spec-trometer. The procedure was repeated two times and a meanvalue was obtained that revealed a straight grade, type 316 austen-itic stainless steel as shown in Table 3 below (see Table 2).

The austenitic stainless steel rods of 10 mm diameter were cutinto equal lengths and machined on the lathe machine to ASTMstandard with the ASTM code D3166-99 for a fatigue test forAVERY 7304 fatigue testing machine. The machining was done atthe production workshop of the Mechanical Engineering Depart-ment, Ahmadu Bello University, Zaria, Nigeria (see Fig. 1).

Each specimen was cut into two equal parts and then weldedtogether using MIG (metal inert gas welding) at the Centre forEnergy Research and Technology, Ahmadu Bello University, Zaria,Nigeria (see Figs. 2a and 2b).

Some specimens were retained in as-received conditions whilethe others were annealed at the Industrial Development Centre(IDC), Zaria, Nigeria.

This is in order to relieve stresses, increase softness, ductilityand toughness after welding.

2.3.3. Post-welding heat treatmentThe samples were placed in the furnace and the furnace was

closed. The power was then switched on and the temperaturewas set at 930 �C. After attaining the set temperature, the sampleswere soaked for 2 h after which the furnace was switched off andthe samples were left to cool to room temperature in the furnaceaccording to the method of Aiyelero [3]. The samples were thenremoved from the furnace (see Fig. 3).

The respective annealed specimens were subjected to corrosionin seawater, 0.5 M hydrochloric acid and steam corrosive media for30 days.

2.3.4. Fatigue testThe duplex fatigue testing machine belongs to the class of

rotating bar fatigue testers. It provides for the determination of

Plate 1a. Micrograph of the parent as-received austenitic steel showing some non-metallic inclusion (black), alpha ferrite (white) in austenitic matrix (white background).100�.

Plate 1b. Micrograph of the weldments of the as-received austenitic steel showing some carbide inclusion (black), delta ferrite (lacy-white) in austenitic matrix (whitebackground). 100�.

Plate 2a. Micrograph of parent annealed austenitic stainless steel showing some carbide inclusion (M23C6) precipitates (black), delta ferrite (white) in austenitic matrix(white background). 100�.


alternating bending stresses and can only be used for imposingupon the specimen pure alternating bending stresses.

The fatigue testing machine applied cyclic loads to the testspecimen. Fatigue testing is a dynamic testing mode and can be

used to simulate how a component/material will behave/fail underreal life loading/stress conditions [6].

An electric motor mounted on the machine rotated the twochucks at the rotor ends. These chucks were used to hold two

Plate 2b. Micrograph of the weldments of the annealed austenitic stainless steel showing high proportions of carbide (M23C6) precipitates along the grain boundaries (black),delta ferrite (acicular-white) in austenitic matrix (white background). 100�.

Plate 3a. Micrograph of the acidic corroded parent austenitic stainless steel showing visible corrosion on the carbide (M23C6) precipitates and delta ferrite (acicular-white)but less in the austenitic matrix (white background). 100�.

Plate 3b. Micrograph of the acidic corroded weldments of the austenitic stainless steel showing high attack on the carbide (M23C6) sites (black) and sigma phase (black) butrelatively less in the austenitic matrix (white background). 100�.


specimens with the load placed on the pan weighing 22.24 Nwhich was hung on a spring mounted on the specimen throughthe roller bearing. Rotating bending was achieved as bending isvertically downward.

There are two dials with counters on the sides of the machineindicating the number of stress reversals through which each

specimen has been rotated. After placing the specimen on themachine, it was switched on and as soon as the specimens failed,the pan which carries the weight falls down, pressing a buttonwhich automatically stops the counter and the machine.

Hence the dial reading was taken at any time after the specimenfailed. The counter can record up to 1,000,000 reversals. The

Plate 4a. Micrograph of the sea water corroded parent austenitic stainless steel showing a significant visible rate of attack on the carbide (M23C6) sites (black) and delta ferrite(lacy-white) but probably no attack on the austenitic matrix (white background). 100�.

Plate 4b. Micrograph of the sea water corroded weldments of the austenitic stainless steel showing a significant attack on the carbide (M23C6) sites (black) and sigma phase(black) distributed along the austenitic matrix (white background). 100�.

Plate 5a. Micrograph of the wet steam corroded parent austenitic stainless steel showing visible high proportions of corroded carbide (M23C6) sites (black) and sigma phase(black) distributed along grain boundaries of the austenitic matrix (white background). 100�.


fatigue stress was recorded against each specimen. The results areshown in Tables 3–5.

2.3.5. MetallographyMetallography was carried out on the as-received, annealed and

corrosive specimen in the following sequence of operation:

grinding, polishing, etching in order to know the effects of varioustests on the microstructure.

The photomicrography of the specimen at the point of fractureand the parent material were taken using a photographic visualmetallurgical microscope at the Metallurgical and MaterialEngineering Department of the Ahmadu Bello University, Zaria.

The microstructural examinations are shown in Plates 1a–5b.

Plate 5b. Micrograph of the wet steam corroded weldments of the austenitic stainless steel showing visible high proportions of corroded carbide (M23C6) sites (black) andsigma phase (black) distributed along the austenitic matrix (white background). 100�.

Fig. 4. Variation of fatigue stress with exposure time of austenitic stainless steel inseawater.

Fig. 5. Variation of fatigue stress with exposure time of austenitic stainless steel in0.5 M HCl.

Fig. 6. Variation of fatigue stress with exposure time of austenitic stainless steel inwet steam.

Fig. 7. Variation of fatigue stress with exposure time of heat treated austeniticstainless steel in seawater, 0.5 M HCl and wet steam.


3. Results and discussion

3.1. Results

The results of the study are shown in Tables 3–5 and Figs. 4–8and Plates 1a–5b.

Fig. 8. Variation of fatigue stress with exposure time of unheat-treated austeniticstainless steel in seawater, 0.5 M HCl and wet steam.


3.2. Effects of corrosive media

The graphs of the fatigue stress against the immersion time forboth the heat-treated and unheat-treated samples are plotted inthe table below (see Figs. 4–8).

3.3. Discussions

3.3.1. Fatigue strength of austenitic stainless steelFigs. 4–8 show variations of the fatigue strength with exposure

time for austenitic stainless steel in the different media used.The graphs show that fatigue strength decreases as the expo-

sure time increases. Fatigue has to do with initiation and propaga-tion of cracks and flaws at the weldment and there is formation ofchromium carbide precipitates in the corrosive media whichassumes the anodic and cathodic sites, because of the formationof cracks, which in turn reduces the fatigue strength. And thewet steam specimens have greater strength to failure followedby the specimen corroded in hydrochloric acid and lastly the spec-imen corroded in seawater. Also, where corrosion fatigue is a con-cern, materials with inherent corrosion resistance are betterchoices than those with just high fatigue strengths, but poorer cor-rosion resistance. Stainless steels can therefore be considered inpreference to high strength alloy steels for corrosive environmentservice. It is however, to be noted that as corrosion is time depen-dant, high fluctuating stress rates may however result in fatiguefailure before corrosion damage occurs.

This revealed that stainless steel suffers greater corrosion inseawater due to the attack of chloride ions, this invariably reducesthe fatigue strength, which is in agreement with the findings of Ili-yasu [4], Omotade [10] and Afolabi [2].

3.3.2. MicrostructurePlates 1–5 show the microstructures of as-received specimen,

heat treated specimen, seawater corroded specimen, acidic speci-men and wet steam corroded specimen for both the base materialand weldments of austenitic stainless steel.

The microstructure of the parent as-received austenitic stain-less steel reveals alpha ferrite (white) in austenitic matrix whilethe weldment reveals delta ferrite (lacy-white) in austeniticmatrix. Also, the microstructure of the media used gives

predominantly carbide (M23C6) precipitates in the austeniticmatrix while the weldment reveals high proportions of carbideprecipitates along the grain boundaries.

Where the M23 represents the carbide complexes that areformed. This research is in agreement with earlier researches byRajasekhar [12], Zhang et al. [14] and Lakshminarayanan et al. [5].

4. Conclusion

The following conclusions can be drawn from the results of thestudy undertaken on the effects of seawater, 0.5 M hydrochloricacid and wet steam corrosive media on the fatigue strength andmicrostructures of welded and heat treated austenitic stainlesssteel:

The fatigue strength was found to decrease with an increase inexposure time and steam corroded specimen has greater resis-tance to fatigue failure than other media used.The microstructure of the parent as-received austenitic stain-less steel reveals alpha ferrite (white) in the austenitic matrixwhile the weldment reveals delta ferrite (lacy-white) in theaustenitic matrix. Also, the microstructure of the media usedgives predominantly carbide (M23C6) precipitates in the austen-itic matrix while the weldment reveals high proportions of car-bide precipitates along the grain boundaries.

References

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[14] Zhang YM, Pan C, Male AT. Welding of austenitic stainless steel using doublesided arc welding process. J Mater Sci Technol 2001;17:1279–84.

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Fatigue behavior of welded austenitic stainless steel in different environments1 Introduction2 Materials and methods2.1 Materials2.2 Equipment2.3 Methods2.3.1 Preparation of test fluid2.3.2 Preparation of specimen2.3.2.1 Metal analysing procedure

2.3.3 Post-welding heat treatment2.3.4 Fatigue test2.3.5 Metallography

3 Results and discussion3.1 Results3.2 Effects of corrosive media3.3 Discussions3.3.1 Fatigue strength of austenitic stainless steel3.3.2 Microstructure

4 ConclusionReferences

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