Abstract
Super duplex stainless steel (SDSS) weld metal microstructures, covering the complete temperature range from ambient to liquidus, were produced by arc heat treatment for 1 and 10 min. Temperature modeling and thermodynamic calculations complemented microstructural studies, hardness mapping and sensitization testing. After 1 min, intermetallics such as sigma and chi phase had precipitated, resulting in moderate sensitization at 720–840 °C. After 10 min, larger amounts of intermetallics resulted in hardness up to 400 HV0.5 and more severe sensitization at 580–920 °C. Coarse and fine secondary austenite precipitated at high and low temperatures, respectively: The finer secondary austenite was more detrimental to corrosion resistance due to its lower content of Cr, Mo, and N as predicted by thermodynamic calculations. Increased hardness and etching response suggest that 475 °C embrittlement had occurred after 10 min. Results are summarized as time-temperature-precipitation and property diagrams for hardness and sensitization.
Highlights
Super duplex stainless steels (SDSS), with a microstructure consisting of approximately equal amounts of ferrite and austenite, present an excellent combination of toughness andThe original version of this article was revised: Tables 4-6 have been displayed erroneously
This study aims at complementing current knowledge by characterizing the microstructure, sensitization behavior, and hardness of a SDSS weld metal, for all temperatures from ambient to liquidus, after heat treatment for 1 and 10 min
The fusion zone is fully ferritic in both samples whereas a graded microstructure, as revealed by variations in the etching response, was formed in the region heat affected by the arc heat treatment
Summary
Super duplex stainless steels (SDSS), with a microstructure consisting of approximately equal amounts of ferrite and austenite, present an excellent combination of toughness andThe original version of this article was revised: Tables 4-6 have been displayed erroneously. A large imbalance in ferrite/austenite ratio and/or the precipitation of unwanted secondary phases such as nitrides, intermetallics, and sometimes secondary austenite may result in the degradation of properties [5, 6]. This is typically due to excessive heating and reheating during fabrication and processing, such as cutting, heat treatment, and welding [7]. To avoid the formation of nitrides and an unacceptably high ferrite content during welding, filler metals overalloyed in Ni, shielding and backing gases with N-additions, and/or higher heat input are recommended to promote austenite formation [8]. Knowledge about allowable combinations of times, temperatures, and cooling and heating rates to avoid detrimental changes of the microstructure is essential for efficient fabrication and processing
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