Cavitation Erosion Resistance of Stainless Steel

8/3/2019 Cavitation Erosion Resistance of Stainless Steel

http://slidepdf.com/reader/full/cavitation-erosion-resistance-of-stainless-steel 1/9

Considerations upon the cavitation erosion resistance of stainless steel with variable

chromium and nickel content

This article has been downloaded from IOPscience. Please scroll down to see the full text article.

2010 IOP Conf. Ser.: Earth Environ. Sci. 12 012036

(http://iopscience.iop.org/1755-1315/12/1/012036)

Download details:

IP Address: 97.67.68.66

The article was downloaded on 30/12/2010 at 15:38

Please note that terms and conditions apply.

View the table of contents for this issue, or go to the journal homepage for more

ome Search Collections Journals About Contact us My IOPscience

http://iopscience.iop.org/page/terms

http://iopscience.iop.org/1755-1315/12/1

http://iopscience.iop.org/1755-1315

http://iopscience.iop.org/

http://iopscience.iop.org/search

http://iopscience.iop.org/collections

http://iopscience.iop.org/journals

http://iopscience.iop.org/page/aboutioppublishing

http://iopscience.iop.org/contact

http://iopscience.iop.org/myiopscience

http://iopscience.iop.org/myiopscience

http://iopscience.iop.org/contact

http://iopscience.iop.org/page/aboutioppublishing

http://iopscience.iop.org/journals

http://iopscience.iop.org/collections

http://iopscience.iop.org/search

http://iopscience.iop.org/

http://iopscience.iop.org/1755-1315

http://iopscience.iop.org/1755-1315/12/1

http://iopscience.iop.org/page/terms



Considerations upon the cavitation erosion resistance of stainless steel with variable Chromium and Nickel content

A Karabenciov1, A D Jurchela

1, I Bordeaşu

1, M Popoviciu

2, N Birău

1and

A Lustyan1

1Department of Hydraulic Machinery, “Politehnica” University of Timisoara, Bv. Mihai

Viteazu, no. 1, Timisoara, 300222, Romania2Academy of Romanian Scientists, Timisoara Branch

E-mail: [email protected]

Abstract. Paper presents results of experimental investigations regarding the cavitation erosionof eight different stainless steels with constant carbon content (0.1 %). Four of them haveconstant chromium (12%) and variable nickel content. The other four have constant nickel (10%) and variable chromium content. Using the images of the eroded specimens, the parametersMDPR and MDP as well as the characteristic curves, the influence of chemical and structural

modifications, upon the cavitation erosion, are put into evidence. The investigated steels,manufactured through casting, maintain the general composition of the materials with goodcavitation erosion qualities. The experimental researches were carried out in TimisoaraHydraulic Machinery Laboratory on a magnetostrictive facility, taking into account the ASTMG32-2008 Standards [10].

1. Introduction

Cavitation erosion is one of the causes, which raises the maintenance costs in Hydraulic Power Plants. This phenomenon is present in all hydraulic systems and machinery (i.e. hydraulic turbines, pumps, propellers, etc.).For a long time, scientists and engineers tried to control this problem by optimizing the design of components indanger or by employing new materials with a good cavitation erosion resistance. Numerous investigations wereconducted in researching the mechanism of cavitation erosion and correlating the cavitation erosion behavior with the materials microstructure and mechanical properties. In general, the cavitation erosion resistance of austenitic and martensitic stainless steels is better than that of ferrite stainless steels.

This paper analyze the cavitation erosion resistance of eight stainless steels: four stainless steels withconstant content of chromium (≈12%) and variable nickel content, and four stainless steels with constant contentof nickel (≈10%) and variable chromium content.

2. Experimental procedure

2.1 Studied materials

This paper presents researches conducted upon eight stainless steels, with constant carbon content. Four of them have a constant nickel content of ≈10% and variable chromium content, and the other four have a constantchromium content of ≈12% and variable nickel content. All the steels were obtained by casting small samples, atSC. Prod SRL Bucharest. The cavitation erosion tests were conducted without using additional heat treatmentson the studied specimens. Simple notations were used for the materials studied in the paper, aiming to simplifytheir identification A1-A4 constant nickel, A5-A8 constant chromium.

Table 1 shows the main alloying elements for the eight stainless steels that were subjected to cavitation

erosion. The chemical compositions were determined at the Bucharest Polytechnic CEMS Laboratory(Laboratory for Researches and Survey of Special Materials), using the Fe-30-M program. The mechanical

characteristics (Table 2) and the microstructure were also determined in the same laboratory.

1



Table 1 Chemical composition of the investigated steels (Mass, %)

Alloy

Chemical composition, %

C Cr Ni Mn Si Mo W V Ti Nb Fe

A1 0,119 6,48 10,06 3,06 1,45 0,095 0,0070 0,345 0,83 0,0040 75,912

A2 0,115 10,62 10,08 2,62 1,72 0,037 0,007 0,043 0,017 0,04 73,166

A3 0,097 17,91 9,97 2,45 1,55 0,100 0,037 0,069 0,64 0,035 65,9458

A4 0,118 23,86 10,09 2,89 2,32 0,038 0,0070 0,071 0,85 0,41 58,218

A5 0,121 12,08 0,50 1,36 1,55 0,185 0,058 1,20 0,075 0,087 82,5

A6 0,114 12,02 2,15 1,36 1,35 0,050 0,025 0,097 0,257 0,034 81,7

A7 0,112 12,07 5,95 1,67 1,79 0,031 0,016 0,047 0,047 0,031 76,9

A8 0,105 12,02 10,28 2,62 1,72 0,037 0,0070 0,043 0,017 0,040 72,1

Table 2 Mechanical properties of the investigated steels

Alloy

Property

Rm [N/mm2 ] R p0,2 [N/mm

2 ] HRC

A1 1550 1120 48

A2 1450 1020 45

A3 1335 934 38

A4 1280 901 30

A5 1450 1020 44

A6 1336 935.2 40

A7 1540 1083 46

A8 835 626 25

2.2 Test deviceCavitation erosion tests were conducted on a magnetostrictive vibratory apparatus with nickel tube T1 [3], [6],

belonging to the Hydraulic Machinery Laboratory of the “Politehnica” University of Timisoara.The running parameters of the vibratory facility are:

− vibratory double amplitude: 94 μm

− specimen’s oscillation frequency: 7000 ± 3% Hz

− electrical power of the ultrasound generator: 500 W

− immersion depth of the specimen’s active surface = 3 ÷ 5 mm

− specimen’s diameter D = 14 mm

− total duration of cavitation attack = 165 minute

Tap water was used as the testing environment. During the tests, the water temperature was maintained at 20 ± 1 0C. The choice of tap water is justified by the fact that there properties are similar to those of river water, usedin running hydraulic turbines.

Before the beginning of the tests, the test specimens (Fig. 1) were cleaned and weighed. The tests were stoppedat regular time intervals for the cleaning, drying and weighing of the specimens.

Fig.1. Shape and dimensions of test specimen

2



3. Experimental results

The figure presented below, show the curves mass loss against time. Comparing the slopes of the curves inFigures 2a and 2b, we can see that alloy A7 presents the lowest mass loss, followed by alloys A5 and A1. Thehighest mass loss was recorded for the alloys A4 and A8.

a) b)Fig.2 Variation of the eroded mass against the attack time for specimens with constant nickel content (a) and

for specimens with constant chromium content (b)

The erosion rates of the tested alloys are shown in Fig.3. The erosion rate tends to remain stable after 90

minutes of cavitation. Unlike the other alloys, the stabilization after 60 minutes occurs for alloy A7 and after 135minutes for alloy A8.

a) b)Fig.3 Variation of the erosion speed against the attack time for specimens with constant nickel content (a) and

for specimens with constant chromium content (b)

3



Figure 4 points out that the alloy A7, with 6% Ni and 12% Cr, has the highest cavitation erosion rate, while thelowest cavitation erosion resistance was recorded for the alloy A8, with 10% Ni and 12% Cr. The cavitationerosion resistance increases with the increase in chromium content (Fig. 4a).

From the diagram presented in Fig. 5 it can be seen that manganese, silicon and titanium have greater influence

on the cavitation erosion resistance in comparison with molybdenum, niobium and vanadium. For the alloys A5to A8, a slightly higher influence of vanadium on the cavitation erosion resistance occurs.

a) b)Fig. 4 Variation of cavitation erosion resistance with the chromium content (a) and with the nickel content (b).

a) c)

4



b)

Fig. 5 The influence of the main alloying elements:

a) on the cavitation erosion resistance for specimens with constant Ni content; b) on the maximum erosion depth for specimens with constant Ni content;c) on the cavitation erosion resistance for specimens with constant Cr content;d) on the maximum erosion depth for specimens with constant Cr content.

For all tested materials (constant nickel content and constant chromium content), the cavitation erosionresistance increases with the surface hardness as can be seen in Fig. 6a and 6b.

a) b)Fig. 6 Variation of cavitation erosion resistance with the surface hardness of the specimens with

constant nickel content (a) and with constant chromium content (b).

Cavitation erosion resistance is in inverse ratio to the increase of mechanical resistance characteristics

(ultimate strength R m and yield limit Rp0,2 ) (Fig. 7).

5



a b

Fig. 7 Variation of cavitation erosion resistance with ultimate strength R m and yield limit Rp0,2 for specimens with constant nickel content (a) and constant chromium content (b).

Table 3 Erosion speed and maximum depth penetration

Alloy Microstructure Erosion speed

(mg/min)

MDPmax

(µm)A1 68 % martensite - 32% austenite 0.1 97.36

A2 100 % austenite 0.15 136.4

A3 98 % austenite - 2 % ferrite 0.16 228.8

A4 81% austenite - 19 % ferrite 0.17 331.1

A5 75% martensite - 25 % ferrite 0.09 63.28

A6 90 % martensite - 10 % ferrite 0.17 204.4

A7 60 % austenite - 40 % martensite 0.04 53.55

A8 100 % austenite 0.23 331.1

The microstructure of the eight alloys was determined using the Schäffler diagram and can be seen in Table 3.

The examination of the eroded surfaces on the scanning electron microscope (Fig. 8) reveals the following:

− Alloys A7, A5 and A1 show an even degradation of the material and a maximum depth penetrationsmaller than 100 μm (Table 3);

− Alloys A8, A4 show an uneven degradation of the eroded surface with aspects of brittle fracture, and amaximum depth penetration higher than 300 μm (Table 3).

A1 A2

6



A3 A4

A5 A6

A7 A8

Fig. 8 Specimens structure obtained with the scanning electron microscope (SEM), after the final time of

cavitation (x100)

4. Conclusion

The distribution range of the erosion speed curves is higher for the alloys with variable nickel contentcompared to the range for the alloys with variable chromium content.

The nature and the proportion of the alloying elements have a major effect on the cavitation erosion

resistance.The cavitation erosion resistance tends to rise exponentially with the hardness of the exposed surface, as long

as the surface does not become brittle.The cavitation erosion resistance tends to decrease with the increase of the mechanical characteristics (R m şi

Rp0,2).

The presence of martensite in the microstructure of alloys A7, A5 and A1 leads to a higher cavitation erosionresistance resulting in an even degradation.

7



Acknowledgments

The present work has been supported from the National University Research Council Grant (CNCSIS) PNII,

ID 34/77/2007 (Models Development for the Evaluation of Materials Behavior to Cavitation)

References

[1] Anton I 1984 Cavitatia vol I (Editura Academiei RSR, Bucuresti)[2] Anton I 1985 Cavitatia Vol II (Editura Academiei RSR, Bucuresti)[3] Bordeaşu I 2006 Eroziunea cavita ţ ional ă a materialelor (Editura Politehnica, Timişoara)[4] Mitelea I 1999 Ş tiin ţ a materialelor în construc ţ ia de ma şini (Editura Sudura, Timişoara)[5] Bordeaşu I, Karabenciov A, Jurchela A, Bădăr ău R, Bălăşoiu V, Mitelea I and Ghimban B Considerations

on the Influence of Nickel on the Cavitation Damage to Stainless Steels with 0,1% Carbon content andConstant Chromium Content Metalurgia International XIV 5-8

[6] Jurchela A, Karabenciov A and Bir ău N 2009 Study of Stainless Steels Cavitation Erosion with 0.1 %Charbon and 10 % Nickel Machine Design Monograpf University of Novi Sad 421-26

[7] Bordeasu I, Anton L E, Baya A and Jurchela A The Necessity of Considering Cavitation Erosion aMechanic Phenomena Against Chemical Corrosion DAAAM 2008 145-46

[8] Bordeasu I, Ghimban B, Popoviciu M O, Bălăşoiu V, Bir ău N and Karabenciov A The Damage of Austenite-Ferrite Stainless Steels by Cavitation Erosion DAAAM 2008 147-48

[9] Standard Method of Vibratory Cavitation Erosion Test 2008 ASTM (Standard G32)[10] Proiect de Cercetare Exploratorie (CNCSIS-PN II) ID-34/2007 Dezvoltarea de modele pentru evaluarea

comport ării materialelor la eroziunea prin cavita ţ ie

8

Documents

Cavitation Erosion Resistance of Stainless Steel