Microstructure, Mechanical and Electrochemical Evaluation of Dissimilar low Ni SS and 304 SS using Different Filler Materials

Ankur V Bansod,Awanikumar P Patil,Sourabh Shukla,Jagesvar Verma

doi:10.1590/1980-5373-mr-2017-0203

Abstract

This study investigates the effect of dissimilar metal welding of low nickel stainless steel (SS) and 304 SS employing tungsten inert gas (TIG) welding process by using three different filler materials (316L, 308L and 310 SS). Microstructural, mechanical properties and corrosion behavior in 3.5% NaCl solution was studied. The microstructural investigation revealed the formation of δ-ferrite and γ-austenite in the weld (welded by 316L and 308L filler). The Higher δ-ferrite content was found more in 316L weld zone. Whereas samples welded by 310 SS filler showed the columnar structure in the weld zone. Relatively wider heat affected zone (HAZ) was measured on Cr-Mn SS side as compared to 304 SS side. Impact fracture surface of all the welded samples exhibited dimple appearance. Corrosion studies showed better pitting corrosion resistance in 316L SS welded sample due to the beneficial effect of δ-ferrite and also the addition of molybdenum (Mo). Electrochemical impedance spectroscopy (EIS) revealed higher polarization resistance (Rp) in 316L SS as compared to other fillers. Galvanic current density was found to be higher in Cr-Mn SS as compared to 304 SS when coupled with different welded samples.

Highlights

Austenitic stainless steels (ASS’s) are being utilized in most of the industrial domains such as piping, pressure vessels and structural sectors
More width of heat affected zone (HAZ) was observed in Cr-Mn SS side as compared to 304 SS, which may be due to the higher thermal conductivity of Cr-Mn SS 5
More δ-ferrite was observed in 316 L SS as compared to other welds (308 L SS and 310 SS)

Summary

Introduction

Austenitic stainless steels (ASS’s) are being utilized in most of the industrial domains such as piping, pressure vessels and structural sectors. These steels are extensively used due to their excellent mechanical properties, non-magnetic and high corrosion resistance owing to its austenitic phase present in the matrix 1,2. The ASS’s constitute 18% chromium (Cr) and 8% nickel (Ni) (i.e. 300 series SS) in the alloying element which provides better corrosion resistance due to its ability to form a passive film (mainly Cr2O3) over the surface 3,4. Ni is added in this SS’s to stabilize the austenitic structure, enlarge the γ phase and helps in the corrosion resistance to some extent 5. The addition of Mn in the 200 series SS has reduced the consumption of Ni as the prime alloying element in SS . 6,7,8

Methods

Results

Conclusion