The role of microstructure in predicting corrosion resistance of austenitic stainless steel welded joints

Dissertant

Atawi, Umar A.

Thesis advisor

Abbas, Muna Khudayr

University

University of Technology

Faculty

-

Department

Department of Production Engineering and Metallurgy

University Country

Iraq

Degree

Master

Degree Date

2011

English Abstract

-Austenitic stainless steelsare used in a wide range of applications like chemical, petrochemical, medical and kitchen equipmentbecauseof their good mechanical properties and excellent corrosion resistance.Most of austenitic stainless steel products are fabricated by welding process.

This process leads to change the mechanical properties and corrosion resistance because of the high temperatures during this process and the concomitant of changing in solidification and cooling rates.

The present study focuses on the effect of welding parameters on corrosion resistance of austenitic stainless steel weld metal.

Variation in welding parameters lead to several microstructures varying in formed phases, distribution of phases, microsegregation, grains size, etc.

Plates of two types of austenitic stainless steel were chosen (AISI 304 with thickness of 4mm and 316 with thickness of 5mm) and weldedby different welding currents and filler metals.

Five magnitudes of welding current (100, 125, 150, 175 and 200 A)were applied to weld the samples of thetwo types of austenitic stainless steelby using Gas Tungsten Arc Welding (GTAW) process with two kinds of filler metals for each stainless steel base metal (E308 and E347 for stainless steel AISI 304, E316 and E316L for stainless steel AISI 316).

The microstructure examinations were achieved for the twenty samples of this work.

Also, the microhardness and delta – ferrite (FN) were measured for the samples.

The electrochemical corrosion in seawater solution (3.5% NaCl) at constant temperature (25°C) was appliedusing electrochemical polarizationmethod to study the corrosion behavior and predict localized corrosion of the welded samples.

The results of microstructure examination show the equiaxed fine grains at the center of weld metal.

The shape of the grains was changed to the columnar grains in direction perpendicular to the interface between weld metal and heat affected zone.

The microhardness distribution results show that the higher value is at the center of weld metal and began to decrease away from weld metal center toward the heat affected zone and base metal in both sides of weld.

Delta – ferrite number results were varied according to variation in welding current and filler metal.

The highest value of (FN 8.6) was obtainedin the sample which was welded by welding current of 150A with filler metal of E347 for stainless steel AISI 304, while the highest value of (FN 10.2) was obtained in the sample which was welded by welding current of 150 A with filler metal of E316L for stainless steel AISI 316.

The lowest value of (FN 6.8) was obtained to the sample which welded by welding current of 200A with filler metal of E308 for stainless steel AISI 304, while the lowest value of (FN 8.6) was obtained in the sample which was welded by welding current of 100 A with filler metal of E316 for stainless steel AISI 316.

The electrochemical polarization results show two kinds of corrosion behavior; first when Eprotappears below Epass, that means the corrosion occurs quickly before the metal reaches the passivation stage, this case is moredangerous than the second one which shows that Eprotshows upper Epass which means that the corrosion occurs late.

The best result of corrosion behavior was recorded to the sample that was welded by welding current of 175 A with filler metal of E347 for stainless steel AISI 304.

For the stainless steel AISI 316, the best results were recorded to the sample that was welded by welding current of 200 A with filler metal of E316 and all the samples that were welded with filler metal of E316L.

Main Subjects

Materials Science , Minerals

Topics

• Stainless steel

• APA
• MLA
• AMA

Language

English

Data Type

Arab Theses

Record ID

BIM-305312