Corrosion-Wear of ST60-Mn Steel in Cassava Juice

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Journal of Minerals & Materials Characterization & Engineering, Vol. 11, No.2 pp.153-158, 2012

1087

Corrosion-Wear of ST60-Mn Ste el in Cas sava Juice

* M. A. Bodude, W.A. Ayoola , D. E. Esezobor and, A. A. Agbeleye

Department of Metallurgical and Materials Engineering, University of Lagos, Nigeria

*Corresponding Author: [email protected]

ABSTRACT

Steels are used widely for production of machine components due to their versatility, low cost,

ease of production and modification of their properties through heat-treatment. ST60Mn Steel is

one of the common high strength steel produced in Nigeria and utilized for machine building

purposes. Components made from this materials failed by wear, corrosion or both mechanism.

The aim of this paper is to determine the influence of austempering heat-treatment on the

corrosion-wear resistance of ST60Mn steel in cassava juice. The heat-treatment was performed

by varying the austenitizing temperature, austempering temperature and time. The corrosion

wear resistance was investigated under an instrumented pin-on-disc wear testing machine with

the steel samples dipped in the cassava juice. The results obtained showed that the austempered

ST60Mn steel has a wear rate of 3.0µg/cycle. While, the un-heat-treatment sample possess

70.1µg/cycle. This is a tremendous improvement in corrosion wear rate through the

austempering heat treatment.

Keywords: Corrosion, wear, Austempering, Heat-treatment, Cassava-juice.

1. INTRODUCTION

ST60Mn Steel is a common medium carbon steel produced in Nigeria. It has strength

comparable to those of imported machine building steels and is used for the production of

components such as shafts, gears, bolts and nuts and other machine components that are

subjected to rubbing actions in a corrosive medium as well as non-corrosive medium.

Greater abrasive resistance for low bainite matrix, with the same hardness, under a pin-on-disc

test has been reported [1]. In recent time, heat treatment of steels with bainite structure ensures a

good complex of mechanical properties has been observed [2]. Evidence showed that the

154 M. A. Bodude, W.A. Ayoola Vol.11, N o.2

ST60Mn steel reliability in these applications in terms of wear characteristic is lower than its

imported counterparts [3].

The wear failures of steels depend on the intrinsic parameters such as chemical composition,

microstructure, and smoothness of the mating surfaces as well as the ex trinsic parameters like the

applied load, sliding velocity, sliding distance or number of c ycles. The failure also depends on

the service environment such as the presence of corrosive agents. The presence of liquid or solid

films on mating (rubbing) surfaces have marked influence on their wear rate has also be noted

[4]. The simultaneous actions of corrosion and wear often lead to rapid deterioration of

component. This is due to the continuous Mechanical removal of oxidized metal as a result of

which a protective layer can not be sustained.

Machine components steels are required to have a bainite microstructure. The institution of

Metallurgist [5] reported that an austempered bainitic steel consisting of two phase matrix of

mixed bainitic ferrite and retained austenite superior wear resistance. The positive mechanical

strength and corrosion re s i st ance of bain it e s tru cture dep en d on number o f factors such as b ainite

ferrite grain size, dislocation density, internal stress and carbide dispersion.

2. MATERIAL AND METHODOLOGY

The ST60Mn steel sample hot rolled 12mm diameter rod used was obtained from Osogbo Steel

rolling Mill, Osun State, Nigeria. The Steel has chemical composition: C(0.35-0.42), Si (0.20-

0.30), Mn (0.90-1.20), P(0.04), CU(0.25), S(0.04), Cr(010).

Sixty-five test specimens of 14mm length and 12mm diameter were cut from the as-received

steel samples. Five of the test specimens were retained as the as-received specimen while the

rest were su bj e cted to aus tem peri ng h ea t -tre at ment u nder di fferent aus temp ering conditions. The

steel specimens austempered using different austenitizing temperature TS(780, 820, 860 and

9000C), soaked for one hour, were quenched isothermally in salt bath containing 55% KNO3

and 45% NaNO3 at different transformation temperatures TT (340, 400, 480 and 5000C) and

transformation times tT (1, 15, 45 and 60 minut es ). The sam pl es w ere th en air cooled to ambient

temperat u re. Macro hardness test was conducted on the as-received and the austempered

specimens using the Rockwell component of Briro V.A. (0-7300) universal hardness machine.

The hardness values were read after a 1200 diamond cone indenter was pressed on the samples

with a load of 1400N for about 15 minutes. Prior to exposing samples to cassava juice, their

weights were measured on PB 153 Meltler Toledo digital weighing balance.

The cassava juice which was used as a corrosive medium was obtained by pressing a freshly

harvested and ground cassava tubers obtained from a research farm using a screw press with a

bucket underneath to collect the cassava juice that was later preserved in a refrigerator. The pH

Vol.11, No.2 Corrosion-Wear of ST60-Mn Steel 155

of the freshly extracted cassava juice was determined before and after the corrosion wear test.

The corrosion wear test was carried out by dipping the samples in t he cas sav a ju ice i ns id e th e pin

on disc wear rig and running the machine for 2000 c ycles under an applied load of 500 g. After

each run (i.e. 2000 cycles) the sample was removed, washed, dried and weighed.

3. RESULTS AND DISCUSSION

Figure 1 illustrates the effect of di fferent aus teniti zing temperatures on the w ear-rate of ST60Mn

steel solution quenched at 3400C at various quenching time. Generally, the figure shows that

there is a decreas e in the wear rate as the austentizing temperature increas es from 780 0C until at

about 8200C and above when the wear rate increases with increasing austenitizing temperature.

This behaviour may be attributed to formation of homogeneous austenite at 8200C and above.

Conversely at below 8200C non-homogeneous austenite is formed. Transformation of non-

homogeneous austenite gives a mixture of pearlite and bainite while austenite at temperatures

above 8200C attributes to formation of a low strength bainite due to grain growth effect hence,

such structure possess high wear rate as shown in Figure 1.

740 760 780 800 820 840 860 880 900 920 940

100

120

140

Temperatur e (oC)

Wear Rate (ug/cycle)

1 m in

15 m in

45 m in

60 m in

Figure 1. The Effect of Austenitizing Temperature on the Wear-Rate of ST60Mn Steel

Transformed at 340ºC at various Intervals

Figure 2 depicts the effect of transformation temperature on the wear rate of ST60Mn steel

which was earlier aus t enitized at 8200C and solution quenched at different temperatures and

maintained at varying different time. It is evident from figure 2 that wears rate increases with

increase in transformation temperature.

156 M. A. Bodude, W.A. Ayoola Vol.11, N o.2

300350 400 450 500 550 600

Transfor m at ion Tem perature ( oC)

Wear Rate (ug/ Cycle)

1 mi n

15 mi n

45 mi n

60 mi n

Figure 2. The Effect of Transformation Temperature on the Wear-Rate of ST60Mn Steel

Austenitized at 820ºC at varying Time

Figure 3 shows the influence of transformation time on the wear rate of ST60Mn steel

austeni tiz ed at different temperatures and transformed at 3400C. Figure 3 shows that the wear

rate incr eas es wi t h i ncrea s e in tran sfo rmat i on t ime . This behaviour ma y be linked to the fact that

bainite formation involves carbon diffusion and ferrite shift type reactions which are time

dependent.

010 20 30 40 50 60

Tr ansformation Time (min)

Wear Rate (ug/ C ycle)

Figure 3. The Effect of Transformation on the Wear-Rate of ST60Mn Steel Austenitized at

Different Temperature and transformed at 340ºC

Vol.11, No.2 Corrosion-Wear of ST60-Mn Steel 157

Table 1 shows the hardness values of samples austenitiz ed at 8200C and transformed at varying

temperature and time. From the table it could be seen that austempering heat-treatment has

positive impact on the hardness value of the steel when compared with that of the as received

whose hardness value is 9.5 HRC.

TABLE 1. Hardness value of specimen austenitised at 8200c

TRANSFORMATON

TEMPERATUR

T;C.

TRANSFORMATION

TIME

TI.

HARDNESS VALUE

HRC.

340

56.0

340

53.5

340

53.0

340

51.0

400

32.5

400

31.0

400

30.0

400

28.0

450

38.4

450

38.2

450

37.5

450

34.5

500

25.0

500

24.0

500

23.5

500

21.3

4. CONCLUSION

From the outcome of the analysis of results obtained on the ST60Mn steel, the following

conclusions could be made.

1. Austempering heat-tr eatmen t is an effective technique for improving the corrosive wear

resistance of ST60Mn steel .

2. Corrosion wear rate as well as hardness values are dependent on the austenitizing

temperature , transformation temperature and time.

3 Austempering heat-treatment is capable of improving the structural integrity of ST60Mn steel

in cassava juice

158 M. A. Bodude, W.A. Ayoola Vol.11, N o.2

REFERENCES

1. Zum -G ah r K. H., (1982): Relation between abrasive wear rate and the microstructure of

metals, proceedings of the International Conference on wear of Materials, Reston.

2. Kaleten, A. Y; Lyzhkov, A. G. (2007): Alloying and heat treatment of steels with baintic

structure. Metal Science and Heat-treatment. Vol. November 10 pp. 731 – 735.

3. Umorus, L.E.; A. O. Akinola and M. O. Adeoye (2006): Corrosion-wear. Journal of

Applied Sciences Research Vol. 2. No. 9 pp. 529 – 532.

4. Williams, K. (2000): Plant Engineering Hardbook 2nd ed. McGr aw – Hill Book Cop y pp. 5 –

44.

5. Institution of Metallurgists (1984): Development for future foundry property. The

metallurgists and Material s Technologists, Vol. 16 No. 9 pp. 433.