Effect of heat treatment on microstructure and mechanical properties of duplex stainless steel

Abstract

Nowadays DSS products are obtained by different processes e.g., casting, forging, rolling etc. The microstructure and mechanical properties of the manufactured product strongly depend on the specific process. Present study aims to study the structural and associated mechanical property changes after the deformation and heat treatment. Thermomechanical processing, which combines both deformation and heat treatment is very effective for microstructure control and various treatments have been developed to improve the mechanical properties without sacrifice of corrosion resistance. However, thermomechanical treatment is still lacking in the field of stainless steel as compared to low and high alloyed carbon steels and hence it is attempted for the improvement of mechanical properties of materials. Attempts have also been made to study the effect of cold rolling prior to heat treatment on the investigated stainless steel. EXPERIMENTAL PROCEDUREThe duplex stainless steel was obtained as cast form with approximately 50 mm square cross section. Then the material was homogenised at 1200 o C for 120 minutes in a resistancereheating furnace. The homogenised ingots were forged into bars of 12.5 mm u 12.5 mm section with a reduction ratio of 1:16 using a pneumatic hammer of 1.0-ton capacity. The forged bars were soaked at 1200 o C and hot rolled in a laboratory scale two -high rolling mill (10 HP) with 750 o C finish rolling temperatures (FRT) down to a thickness of approximately 6 mm in three passes (Fig. 1). The FRT for the steel was fixed at 750 o C with an aim to incorporate approximately 10% deformation as was feasible under the experimental facility. After completion of rolling, samples were cooled in air. The chemical composition of the investigated steel is shown in Table 1. The material was heat treated in different schedules as described in Table 2.To study the microstructures, the samples were subjected to the standard grinding and polishing techniques before etching. The steel sample was etched using aqua regia solution (75% HCl and 25% HNO 3 mixture) 6 . Properly etched samples were examined under the ZEISS (Axiovert 40 MAT) optical microscope at different magnifications and representative photomicrographs were presented. Quantitative metallographic studies were also done using image -analysis technique in order to describe the microstructures. Microstructures have been quantified by the OLYSIA -m3 soft imaging system developed by Olympus. ABSTRACTPresent study concerns the effect of deformation and heat treatment on the microstructure and mechanical properties of a duplex stainless steel. While hot rolling causes the coarse distribution of the constituent phases (ferrite and austenite), 50% cold rolling results into the elongated and splintered two -phase structure. Supersaturated ferrite structure established by water quenching from 1300°C results into the strengthening due to the formation of fine dispersed austenite precipitates within ferrite grain after isothermal heat treatment (1000°C, 0.5 hour). Duplex s...

Advanced Mechanical Strength in Post Heat Treated SLM 2507 at Room and High Temperature Promoted by Hard/Ductile Sigma Precipitates

“…The microhardness of the heat treated SLM 2507 was around 400 Hv, which is twice as high as casted duplex material [26] and comparable with as-built SLM 2507 duplex material reported earlier [9]. Considering the fact that the heat treatment relieves the residual stresses of as-built SLM 2507, the high microhardness is possibly due to the presence of hard phase such as sigma/Khi phases in the material (which is not present in as-built SLM 2507).…”

“…The measured relative density of the heat treated SLM 250 (99%) suggests that the low elongation of 1.8% is not only due to the flaws in the material but also due to the presence of intermetallic phases rich in Cr and Mo; sigma phase [24]. As seen from Table 1, the tensile strength of the heat treated SLM 2507 is higher than as-casted and solution treated duplex stainless steel [26] and heat treated SLM duplex 2205 material [25]. Fracture surface micrographs in Figure 1b,c shows cleavage fracture without any sign of ductile fracture.…”

“…Furthermore, secondary phases, sigma and Khi, are identified. The sigma and Khi phase quantification is approximated to 16 [9] 1320 MPa 8% 450 Hv Post heat treated SLM 2205 [25] 750 MPa 20% -Heat treated conventional duplex [26] 649 MPa 34% 227 Hv As Casted duplex [26] 660 MPa 29% 235 Hv…”

Corrosion Behavior Difference in Initial Period for Hot-Rolled and Cold-Rolled 2205 Duplex Stainless Steels

“…The 2205 duplex stainless steels (DSS), with excellent corrosion performance, as well as good mechanical properties, have been used as engineering alloys for many years and provide wide applications in many industrial fields, especially in aggressive environments [1][2][3][4][5][6]. The effects of microstructural modifications of 2205 DSS on their mechanical and corrosion resistance were intensively investigated in the past.…”

The Difference of Corrosion Behavior in Initial Period for the Hot-Rolled and Cold-Rolled 2205 Duplex Stainless Steel

“…The 2205 duplex stainless steels (DSS), with excellent corrosion performance as well as good mechanical property, have been an important class of engineering alloys for many years and provide wide applications in many industrial fields, especially in the aggressive environment [1][2][3][4][5][6].…”