Byung-Hyun Shin, Dohyung Kim, Sanghyup Park, Myungwon Hwang, Junghyun Park and Wonsub Chung
The secondary phase decreased the corrosion resistance because of the segregation of Cr and Mo. Therefore, this paper aims to study the precipitation condition and the effect of…
Abstract
Purpose
The secondary phase decreased the corrosion resistance because of the segregation of Cr and Mo. Therefore, this paper aims to study the precipitation condition and the effect of secondary phase with volume fraction on corrosion behavior.
Design/methodology/approach
Secondary phase precipitated approximately from 375°C to 975°C because of saturated Cr and Mo at grain boundary by growth of austenite. Therefore, heat treatment from 800°C to 1,300°C was applied to start the precipitation of the secondary phase.
Findings
The secondary phase is precipitated at 1,020°C because of segregation by heterogeneous austenite. The growth of austenite at 1,000°C needs the time to saturate the Cr and Mo at grain boundary. When the volume fraction of austenite is 56 per cent (14 min at 1,000°C), the secondary phase is precipitated with grain boundary of austenite. The secondary phase increased the current density (corrosion rate) and decreased the passivation. That is checked to the critical pitting temperature (CPT) curves. The 1 per cent volume fraction of secondary phase decreased CPT to 60°C from 71°C.
Research limitations/implications
The precipitation of secondary phase not wants anyone. Casted super-duplex stainless steel (SDSS) of big size precipitates the secondary phase. This study worked the precipitation condition and the suppression conditions of secondary phase.
Social implications
Manufacturers need precipitation condition to make high-performance SDSS.
Originality/value
The corrosion resistance of SDSS is hard the optimization because SDSS is dual-phase stainless steel. The precipitation of the secondary phase must be controlled to optimize of the corrosion resistance of SDSS. Anyone not studied the precipitation condition of secondary phase and the effect of secondary phase with volume fraction on corrosion behavior of SDSS.
Details
Keywords
Byung-Hyun Shin, Junghyun Park, Jongbae Jeon, Sung-bo Heo and Wonsub Chung
In this study, super duplex stainless steel (SDSS) was heat-treated. The purpose of this study is to assess the effect of the cooling rate after heat treatment on the pitting…
Abstract
Purpose
In this study, super duplex stainless steel (SDSS) was heat-treated. The purpose of this study is to assess the effect of the cooling rate after heat treatment on the pitting corrosion of SDSS.
Design/methodology/approach
The heat treatment from 1,000°C to 1,300°C was applied to SDSS to check the effect of the cooling rate.
Findings
The heat treatment temperature produced a different SDSS microstructure, and the cooling rate led to the growth of austenite. The casted SDSS indicated the presence of heterogeneous austenite, and the precipitation secondary phase under 1.6 per cent precipitated to bare metal. By applying heat treatment and cooling SDSS, its corrosion resistance changes because of the change in the chemical composition. The cooling rate at 5,600 J/s has the highest critical pitting temperature (CPT) at 1,100°C, and the cooling rate at 1.6 J/s has the highest CPT at 1,200°C. Low cooling rate (0.4 J/s) made the secondary phase at all temperature range.
Research limitations/implications
The effect of secondary phase not consider because that is well known to decreasing corrosion resistance.
Practical implications
Solution annealing is taken into account to optimize the corrosion resistance. But that is not consider the cooling rate at each temperature. This study assessed the effect of the cooling rate at each temperature point.
Social implications
Manufacturers need to know the effect of the cooling rate to optimize the corrosion resistance, and this study can be applied in the industrial scene.
Originality/value
SDSS is hard the optimization because SDSS is a dual-phase stainless steel. Corrosion resistance can be optimized by controlling heat treatment temperature and the cooling rate. Anyone not studied the effect of the cooling rate at each temperature. The effect of the cooling rate should be considered to optimize the corrosion resistance.