Effects of austenitic and duplex electrodes on microstructure, mechanical properties, pitting, and galvanic corrosion re
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Reshma Sonkusare Department of Materials Science and Engineering, Indian Institute of Technology (IIT) Kanpur, Kanpur 208016, India (Received 19 February 2017; accepted 20 June 2017)
In this work, examination of joint properties of ferritic and dual-phase stainless steel dissimilar welds was carried out by using E2209 duplex and E309LMo austenitic electrodes. The results of E2209 weld showed dual-phase microstructure of ferrite and austenite in the form of grain boundary austenite, Widmanstatten and intragranular austenite, whereas E309LMo weld showed acicular ferrite in the cores of subgrain of austenite. Electron backscatter diffraction was used to study the evolution of the microstructure and micro-texture. The significant variations in the feature of weldments illustrated the presence of a very strong texture. Ferritoscope measurement revealed higher ferrite content in the E2209 weld. Tensile strength, hardness, and absorbed energy of weld metal were dominated by E2209 weld. The modified Strauss test indicated intergranular corrosion attack in the AISI 430 ferritic side heat affected zone. Higher pitting resistance showed by E2209 weld than E309LMo weld. While higher galvanic corrosion observed in the E309LMo weld and AISI 430 ferritic base metal couple.
I. INTRODUCTION
Nickel (Ni) is relatively pricey on the market, which breaching the backbone of austenitic producer and end users, therefore, the market is looking an alternative option.1 Ferritic and dual-phase (austeno-ferritic) or popularly known as duplex stainless steel (DSS) may fill the gap of this expensive alloying element. Ferritic stainless steels (FSSs) are an economically low-cost alternative of austenitic stainless steels (ASSs) and exhibit greater resistance to stress corrosion cracking (SCC) and pitting corrosion,2 it is also distinguished by higher thermal conductivity and smaller linear expansion.2 Whereas DSSs illustrate higher resistance to SCC and pitting corrosion, also shows higher strength than that of ASSs due to dualphase (austenite and ferrite) nature and higher pitting resistance equivalent number (PREN).3,4 Both FSS and DSS are preferably applied in certain environments such as chemical tankers, ocean engineering, pressure vessels, and heat exchanger pipes.5,6 In addition to these, FSS (especially 430 and 439 grades) and DSS (2205 grade) greatly used together in heat recovery steam generator (HRSG) units to avoid Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.269
dew-point corrosion.7 This may also be one of the choices, where Ni-free stainless steels are required, one such application is a TiCl4 reduction retort with Mg, where Mg has the propensity to leach away Ni from the ASS and degrading the mechanical properties.8 Since multiphase steels are in great demand and used in industries; researchers have also focused on the relation between strength, ductility, cold workability, and welding behavior of dissimilar metals for the cost flexibility.9
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