GMAW Cold Wire Technology for Adjusting the Ferrite–Austenite Ratio of Wire and Arc Additive Manufactured Duplex Stainless Steel Components

Abstract

The use of commercially available filler metals for wire and arc additive manufacturing (WAAM) of duplex stainless steel components results in a microstructure with a very low ferrite content. The ferrite–austenite ratio in the duplex stainless steel weld metal depends on both the cooling rate and particularly on the chemical composition. However, the research and testing of special filler metals for additive deposition welding using wire and arc processes is time-consuming and expensive. This paper describes a method that uses an additional cold wire feed in the gas metal arc welding (GMAW) process to selectively vary the alloy composition and thus the microstructure of duplex stainless steel weld metal. By mixing different filler metals, a reduction of the nickel equivalent and hence an increase in the ferrite content in additively manufactured duplex stainless steel specimens was achieved. The homogeneous mixing of electrode and cold wire was verified by energy dispersive spectroscopy (EDS). Furthermore, the addition of cold wire resulted in a significant increase in sample height while the sample width remained approximately the same.

Additive Manufacturing with Superduplex Stainless Steel Wire by CMT Process

“…It was reported [26] that the ferrite content in subsequently deposited layers is reduced along with hardness compared to the support plate. Stützer et al [27] used a new approach for estimation of ferrite (α)/austenite (γ) balance with different wires and CMT technology and achieved a balance of 50%/50% of austenite and ferrite with good mechanical and corrosion properties.…”

Wire Arc Additive Manufacturing of Stainless Steels: A Review

“…Their microstructure features and mechanical properties are quite different after WAAM. Stützer et al found that mixing different filler metals can reduce the nickel equivalent and increase the ferrite content in GMAW duplex stainless steel specimens [89]. Moreover, appropriate process parameters can help to achieve a high-quality WAAM structure.…”

“…Other factors also have specific effects on phase balance, including material composition [105] and heat treatments [91]. For instance, in the investigation of adjusting the ferrite-austenite ratio of WAAM duplex stainless steel components, Stützer et al [89] mixed two different filler metals to decrease the nickel equivalent, thus increased the ferrite content in the specimens. The sample fabricated with 100% of the filler metal G 22 9 3 (see Figure 7a) contains large austenitic side plates.…”

“…For duplex stainless steels, the ratio of austenite to ferrite phase crucially affects the properties in strength and corrosion resistance [107]. The high content of austenite and the formation of secondary austenite can significantly lower corrosion resistance and strength of stainless steel [89].…”

“…It is feasible to control the microstructure, such as promoting the nucleation and growth of precipitates in δ-ferrite, which can influence the mechanical properties [91], by controlling the process parameters. Modifying the material compositions, such as using double wires [89], is another effective approach to achieve desirable final microstructures. Post heat treatments also can significantly influence and change the final microstructure.…”