Hot Rolled Duplex Stainless Steel Research Articles

Influence of cold and hot rolling on the corrosion behaviour of duplex stainless steels in mine water environment

This study examined the corrosion behaviour of cold and hot rolled duplex stainless steel materials in mine water. Both gravimetric and electrochemical methods (potentiodynamic polarisation and open circuit potential) were adopted to monitor the corrosion of the alloys. Microscopy analyses were used to understand the degradation phenomena. In comparison, cold-rolled stainless steels displayed better resistance than hot-rolled materials under the tested conditions. The mine water pH was in the range that could lead to passivation of the sample and hence, the environmental impact was not aggressive enough to create many inferences. The surface deteriorations for cold and hot rolled steel materials were therefore not severe in both SEM (Scanning Electron Microscope) and OM (Optical Microscope) analysis results.

Phenomenological Model Describing the Formation of Peeling Defects on Hot-Rolled Duplex Stainless Steel 2205

The chemical composition, morphology, and microstructure of peeling defects formed on the surface of sheets from steel 2205 under hot rolling are studied. The microstructure of the surface is analyzed using scanning electron and light microscopy. The zones affected are shown to contain nonmetallic inclusions of types Al2O3 and CaO – SiO2 – Al2O3 – MgO in the form of streak precipitates and to have an unfavorable content of austenite, which causes decrease in the ductility of the area. The results obtained are used to derive a five-stage phenomenological model of formation of such defects.

Rietveld and Impedance Analysis of Cold and Hot Rolled Duplex and Lean Duplex Steels for Application in Paper and Pulp Industry

In this study, X-Ray Diffraction (XRD) and Rietveld Refinement were performed to identify and quantify the ferrite and austenite phase of cold and hot rolled duplex stainless steels (UNS S31803) and lean duplex stainless steels (UNS S32304). Electrochemical impedance spectroscopy (EIS) was applied to evaluate the chemical behavior of duplex and lean duplex stainless steels in white, green, and black liquors of paper and pulp industry. Rietveld analysis results showed a higher austenite content than the standard limit for duplex steels in the hot rolled condition. The hot rolling condition plays a major role in improving corrosion resistance in white liquor mainly for the lean duplex steel.

Delaminations by Cleavage Cracking in Duplex Stainless Steels at Sub-zero Temperatures

Impact toughness testing was conducted on 10 and 30 mm plates of 2205 together with a 30 mm plate of LDX 2101® duplex stainless steel (DSS). The testing temperatures were between 153 K (−120 °C) and room temperature. Interrupted fracture toughness tests of the 10 mm plate and a 50 mm plate of 2205 were also performed. The conclusion from the fractographic investigation was that the delaminations that occur in hot-rolled DSSs were cleavage fractures. The toughness anisotropy can be explained by the cleavage fracture and the appearance of the microstructure. The result from the interrupted fracture toughness test revealed that the delaminations initiated prior to the maximum force plateau and propagated ahead of the stable crack growth during testing. Estimated upper limit for the fracture delamination initiation toughness at sub-zero temperatures for the 2205 base metal according to the crack-tip opening displacement method was 28 to 61 μm for the 10 mm plate, 70 to 106 μm for the 30 mm plate and below 100 μm for the 50 mm plate.

Effect of microstructural anisotropy on stress corrosion cracking of hot rolled duplex stainless steels

Anisotropy in stress corrosion cracking of lean grade UNS S32101 and standard grade UNS S32205 hot rolled duplex stainless steels was evaluated in this study. Microstructures were characterised with stereology methods in three orthogonal orientations to quantify anisotropy in phase distribution. Constant extension rate tests were conducted in an autoclave at 2×10−6 s−1 in chloride containing alkaline sulphide solution at 170°C. The maximum crack lengths and average crack densities were measured for the rolling longitudinal and transverse longitudinal orientations after stress corrosion cracking tests. Results indicate that stress corrosion crack initiation and growth are a strong function of the microstructure in each orientation. Maximum crack length and average crack density were maximum for the rolling longitudinal orientation. Crack initiation and growth were favoured along the transverse direction. Chlorides enhanced anisotropy in crack growth behaviour by facilitating crack initiation and crack coalescence along phase boundaries, which lead to more severe stress corrosion cracking in the alkaline sulphide environments that were studied.

Influence of Texture on the Mechanical Properties of Hot Rolled Duplex Stainless Steels

This paper reports an investigation of bulk and micro texture in the as cast condition and in hot rolled conditions (50 and 75% thickness reduction) of nitrogen alloyed duplex stainless steel. Bulk texture measurements were carried out using orientation-imaging microscopy (OIM). The micro texture measurements were carried out using electron backscattered diffraction (EBSD) system for the dual phases; ferrite (alpha) and austenite (gamma). The amount of alpha fiber formation for each reduction is reported under the conditions of before heat treatment (BHT) and after heat treatment (AHT). Individual texture components for both 50 and 75% reduction under the condition of BHT and AHT are also reported. The results reveal that there is a definite improvement in the mechanical properties after reducing the specimen thickness to 75% by hot rolling, followed by heat treatment (solutionizing). This improvement in the mechanical property is correlated with the volume of low angle grain boundaries (EBSD analysis) and with the cleavage facets (SEM analysis).