M. Nerádová, R. Augustin, P. Kovačócy: The effect of the annealing temperature on the corrosion resistance of weld joint of AISI 310 steel - short communication

Materials Engineering - Materiálové inžinierstvo 18 (2011) 151-154

151

THE EFFECT OF THE ANNEALING TEMPERATURE

ON THE CORROSION RESISTANCE OF WELD JOINT

OF AISI 310 STEEL - SHORT COMMUNICATION Martina Nerádová1,*, Robert Augustin1, Pavel Kovačócy1

1Department of Welding, Faculty of Materials Science and Technology, Slovak University of Technology, Bottova 23, 917 24 Trnava, Slovak Republic

*corresponding author: e-mail: martina.neradova@stuba.sk

Resume

The article presents samples of weld joint of AISI 310 austenitic steel which were subjected to solution annealing at various temperature - time exposures. The objective of the experiment was to determine the annealing temperature so that the steel should not be sensitized. Tendency to intercrystalline corrosion was analysed by means of a corrosion test in 10 % oxalic acid according to ASTM A 262. At the temperatures of 1000 and 1100°C held for 15 min. the steel was not sensitized. At the temperature of 850°C the steel was sensitized, i.e. susceptible to intercrystalline corrosion.

Available online: http://fstroj.uniza.sk/PDF/2011/26-2011.pdf

Article info

Article history: Received 13 April 2011 Accepted 11 September 2011 Online 26 October 2011

Keywords: AISI 310 steel, Intercrystalline corrosion, Sensitization, Solution annealing, Weld joint, Corrosion test ASTM A 262 ISSN 1335-0803

1. Introduction

Intercrystalline /intergranular/ corrosion is a type of corrosion that attacks mainly austenitic stainless steels and it is a kind of relatively rapid and local corrosion associated with a failure of microstructure known as the precipitation of carbides. Intercrystalline corrosion occurs mainly at heat-affected zones of weld joint or after improper heat treatment. Austenitic stainless steels and alloys can be susceptible to intercrystalline corrosion not only after heat treatment with critical temperatures but also in the condition after solution annealing. Weld metals and heat-affected zones of base material are at welding exposed to the conditions that may induce the susceptibility to intercrystalline corrosion. The intensity of intercrystalline corrosion may be increased under simultaneous action of residual stresses and / or external stress the intensity of intercrystalline corrosion may be increased [1, 2, 3].

Austenitic stainless steels are the most often welded using the fusion methods of welding. Arc welding in shielding gases with non-consumable electrode (TIG) is a progressive method of fusion welding of metals and alloys [5, 6].

2. Characteristic of experimental steel

Material examined during the experiments was AISI 310 austenitic stainless steel (X6CrNiNbN25-20; 1.4952) with increased content of Cr and Ni. Its chemical composition is given in Table 1, basic mechanical properties in Table 2.

Table 1

Chemical composition of experimental steel (weight %)

C

min.

max

Cr

min.

max.

Ni

min.

max.

N

min.

max.

Si

min.

max.

Mn

min.

max.

S

min.

max.

Nb

min.

max.

P

min.

max.

-

0.11

22.8

27.2

16.85

23.2

0.14

0.36

-

1.55

-

2.04

-

0.035

0.15

0.65

-

0.035

M. Nerádová, R. Augustin, P. Kovačócy: The effect of the annealing temperature on the corrosion resistance of weld joint of AISI 310 steel - short communication

Materials Engineering - Materiálové inžinierstvo 18 (2011) 151-154

152

Table 2

Basic mechanical properties of the steel (at the temperature of 20 °C)

Rp1.0

(MPa)

Rp0,2

(MPa)

Rm

(MPa)

A

(%)

E

(103 MPa)

325 295 655-900 30 193

2.1. Experimental material

Experimental material was a tube made of AISI 31O steel with the diameter of 44.5 mm and wall thickness of 6.3 mm. One section of this material was taken. The examined section was welded using TIG technology (samples 10 to 14). Localization of samples taken from the experimental material is shown in Fig. 1.

Fig. 1. Section of experimental material welded with TIG technology and localization of taken

samples 10 to 14

2.2. Heat treatment of experimental material

Samples were subsequently subjected to heat treatment. Samples of weld joint with corresponding parameters of heat treatment (solution annealing) can be found in the table below (Table 3). The annealing itself was made in LM 212.11 VEB Elektro electric resistance furnace. Digital thermometer GMH 3230 by Greisinger Elektronic was used to determine more precisely temperature in vicinity of the samples. Table 3 shows the sample of initial material which was not subjected to any heat treatment, only to corrosion test to determine the sensitization of steel.

3. Corrosion test in oxalic acid according

to ASTM A 262

Oxalic Acid Etch Test is a rapid and non-destructive corrosion test used for preliminary evaluation of intercrystalline attack of a material, providing only qualitative estimation of the degree of attack and susceptibility of the material to intercrystalline corrosion. The samples in this test were electrolytically etched in 10 % oxalic acid, while the prescribed etching time is 90 seconds at current density of 1 A/cm2 and temperature of 20 °C. The analysed surface must be polished before the test. Final „etching“ of the sample performed by means of a light microscope facilitates the evaluation and classification of the degree of attack,. Continuity of the etched grain boundaries, usually at the magnification of 250 to 500 times, is investigated [4].

Samples of weld joint were marked with numbers 10, 11, 12, 13 and 14 – Fig. 1. Samples 11 to 14 according to Tab. 3 were subjected to solution annealing. The initial condition of the material is sample No. 10 - Tab.3 which was not subjected to solution annealing. Microstructures after the corrosion test are illustrated and described in the following pictures (Fig. 2 to Fig. 6).

Tab. 3

Annealing parameters of weld joint AISI 310

Designation

of samples

Annealing

temperature

(°C)

Annealing

time

(min.)

13 1100 15

14 1000 15

12 850 1

11 850 5

Designation of

samples

Initial condition of the

material

10 Weld joint

Fig. 2 documents the fusion line of initial weld joint (sample 10). The microstructure of the base material shows STEP structure, which means that the steel is not

M. Nerádová, R. Augustin, P. Kovačócy: The effect of the annealing temperature on the corrosion resistance of weld joint of AISI 310 steel - short communication

Materials Engineering - Materiálové inžinierstvo 18 (2011) 151-154

153

sensitized and thus is not susceptible to the attack for intercrystalline corrosion.

Fig. 2. Microstructure of initial weld joint - sample

10 (Parent material STEP structure)

Fig. 3 and Fig. 4 documents sample 11 and sample 12 respectively. It is possible to see a DITCH structure in both pictures where the grain boundaries are surrounded with a ditch after etching. This means that the steel is sensitized and susceptible to intercrystalline corrosion.

Fig. 5 and Fig. 6 document sample 14 exposed at 1000 °C/15min and sample 13 exposed at 1100 °C/15min respectively, where the structure of the base material is STEP type, it is not sensitized and thus not susceptible to intercrystalline corrosion.

Fig. 3. Microstructure of sample 11 exposed at

850 °C/5min (Parent material DITCH structure)

Fig. 4. Microstructure of sample 12 exposed at 850 °C/5min (Parent material DITCH structure)

Fig. 5. Microstructure of sample 14 exposed at

1000 °C/15min (Parent material STEP structure)

Fig. 6. Microstructure of sample 13 exposed at 1100 °C/15min (Parent material STEP structure)

HAZ-FZ interface – (heat affected zone – fusion zone interface)

40 µµµµm Parent material

* HAZ-FZ

interface

Weld metal

40 µµµµm

Weld metal

Parent material

* HAZ-FZ

interface

40 µµµµm

Weld metal

Parent material

* HAZ-FZ

interface

40 µµµµm

Weld metal

Parent material

* HAZ-FZ

interface

40 µµµµm

Weld metal

Parent material

* HAZ-FZ

interface

M. Nerádová, R. Augustin, P. Kovačócy: The effect of the annealing temperature on the corrosion resistance of weld joint of AISI 310 steel - short communication

Materials Engineering - Materiálové inžinierstvo 18 (2011) 151-154

154

Table 5 shows the results after the corrosion test according to ASTM A 262 . The sample of initial material that was not subjected to solution annealing showes STEP structure after the corrosion test. Samples 13 and 14 have STEP structure, which means that they are not sensitized. Samples 11 and 12 have clearly delineated DITCH grain boundaries, which means that they are sensitized and susceptible to intercrystalline corrosion.

4. Conclusions

The purpose of the weld joint corrosion test was to determine the proper temperature of solution annealing in order to prevent corrosion. Susceptibility to intercrystalline corrosion was not confirmed at annealing within the temperature (time exposures) of 1000 and 1100 °C for the period of 15 min.

Sensitization occurred at the temperatue of 850°C already after the first minute of annealing, which means that it is susceptible to intercrystalline corrosion.

Based on the above mentioned results it can be claimed that weld joint at the temperatures of 1000 and 1100 °C is not susceptible to corrosion.

Acknowledgements

The contribution was prepared under the

support of GA VEGA MŠ SR and SAV project

No. 1/0842/09

References

[1] V. Číhal: Korozivzdorné oceli a slitiny.

ACADEMIA, Praha 1999

[2] V. Číhal: Medzikrystalová koroze ocelí a slitin.

STNL, Praha 1984.

[3] J. Janovec, M. Dománková, P. Grgáč, F.

Gömöry, M. Kusý: Progresívne materiály

a technológie. AlumniPress, Trnava 2008

[4] T. Kuníková: Štúdium kinetiky precipitácie fáz

na hraniciach zŕn v austenitickej oceli s nízkym

obsahom interstícií (Study of kinetics of phase

precipitation at grain boundaries in austenitic

steel with low interstitial content) [PhD Thesis],

STU Trnava 2004 (in Slovak)

[5] Z. Lipa: Priemyselné technológie a výrobné

zariadenia (Industrial technologies and

production equipments). STU, Bratislava 2003

(in Slovak)

[6] V. Országh, P. Országh: Zváranie TIG ocelí a

neželezných kovov (Welding of the TIG steels

and nonferrous mettals). SAV, Bratislava 1998

(in Slovak)