Influence of Heat Treatment on Structure and Durometric Properties of Coatings Obtained by Surfacing with CSR-04СR27NI7MO3CU2Т Cast Rods

The effect of heat treatment modes on the structure and durometric properties of coatings obtained by surfacing with CSR-04СR27NI7MO3CU2Т cast rods, is considered. It is found that the temperature of 800°С and soaking time of 5 hours are optimal to increase the deposited metal hardness. It is shown that such a phenomenon results from the formation of the austenitic structure hardened by the precipitates of the σ-phase (FeCr), chromium carbides (Cr3C2) and titanium carbides (TiC). The heat treatment modes proposed can be applied in the wear-resistant surfacing technology of chemical equipment parts.

Creep Resistance of S304H Austenitic Steel Processed by High-Pressure Sliding

Sheets of coarse-grained S304H austenitic steel were processed by high-pressure sliding (HPS) at room temperature and a ultrafine-grained microstructure with a mean grain size of about 0.14 µm was prepared. The microstructure changes and creep behavior of coarse-grained and HPS-processed steel were investigated at 500–700 °C under the application of different loads. It was found that the processing of S304H steel led to a significant improvement in creep strength at 500 °C. However, a further increase in creep temperature to 600 °C and 700 °C led to the deterioration of creep behavior of HPS-processed steel. The microstructure results suggest that the creep behavior of HPS-processed steel is associated with the thermal stability of the SPD-processed microstructure. The recrystallization, grain growth, the coarsening of precipitates led to a reduction in creep strength of the HPS-processed state. It was also observed that in the HPS-processed microstructure the fast formation of σ-phase occurs. The σ-phase was already formed during slight grain coarsening at 600 °C and its formation was enhanced after recrystallization at 700 °C.

Effect of Annealing Temperature on the Microstructure and Mechanical Properties of High-Pressure Torsion-Produced 316LN Stainless Steel

316LN stainless steel is a prospective structural material for the nuclear and medical instruments industries. Severe plastic deformation (SPD) combined with annealing possesses have been used to create materials with excellent mechanical properties. In the present work, a series of ultrafine-grained (UFG) 316LN steels were produced by high-pressure torsion (HPT) and a subsequent annealing process. The effects of annealing temperature on grain recrystallization and precipitation were investigated. Recrystallized UFG 316LN steels can be achieved after annealing at high temperature. The σ phase generates, at grain boundaries, at an annealing temperature range of 750–850 °C. The dislocations induced by recrystallized grain boundaries and strain-induced nanotwins are beneficial for enhancing ductility. Moreover, microcracks are easy to nucleate at the σ phase and the γ-austenite interface, causing unexpected rapid fractures.

Identification of Inhomogeneous Temperature on Stainless Steel using Statistical Analysis

Corrosion in stainless steel, abbreviated as SS, is still an exciting topic to study. Even though SS is a corrosion resistance material, this property will be degraded when exposed to high temperatures for a long time because of σ phase, such as a Fe-Cr compound, formation. The presence of this phase can be observed using a special chemical etchant solution that will give five specific colours to this phase: light brown, dark brown, bluish brown, light blue, and dark blue. In this study, the specimen sample is from ASTM A297. Furthermore, the metallography process is carried out to obtain microstructure images that describe the σ phase. Here, two grains were taken as objects to discretize with one of them was around the specimen sample center and the other was close to the boundary with the environment. The discretization resulted in a 2 x 5 frequency table, called contingency table, that is analysed by the independence χ2-test. The contingency table is also represented geometrically in cartesian. The study shows that two grains were not independent. The grain which was around the specimen sample center contained many σ phases dominated by light blue colour (43%). In other words, the prolonged heating did not give homogeneous corrosion level.

Aging precipitation behavior of σ phase in 22Cr15Ni3.5Cu austenitic stainless steel

σ phase is one of the main precipitates affecting the toughness of austenitic stainless steel, V-notch impact test, SEM, EDS and TEM analysis were conducted on the newly developed 22Cr15Ni3.5Cu stainless steel after 650°C aging. Precipitation mechanism of σ phase and its effect on the toughness of the material were analyzed. The test results show that toughness of the material decreases to 25.6J after 300h aging, σ phase started to precipitate along the grain boundary after 500h aging, and in the crystal after 1000h aging. The precipitation spacing is about 100 nm, forming a gradually increasing size from crystal to grain boundary. As the precipitation time 500h of σ phase was later than the critical aging time of ductile brittle transition, it can be inferred from the test result that σ phase is not the main precipitation phase affecting the toughness of 22Cr15Ni3.5Cu.

Effect of Al Content on Phase Compositions of FeNiCoCrMo0.5Alx High Entropy Alloy

The FeCoNiCrMo0.5Alx system with x up to 2.13 was analyzed from the point of view of evolution of the phase composition and microstructure. Cast samples were synthesized by induction melting and analyzed by X-ray diffraction, energy dispersive spectroscopy, scanning electron microscopy, and Vickers microhardness test methods. Phase compositions of these alloys in dependance on Al concentration consist of FCC solid solution, σ-phase, NiAl-based B2 phase, and BCC solid solution enriched with Mo and Cr. Phase formation principles were studied. Al dissolves in a FeCoNiCrMo0.5 FCC solid solution up to 8 at.%.; at higher concentrations, Al attracts Ni, removing it from FCC solid solution and forming the B2 phase. Despite Al not participating in σ-phase formation, an increase in Al concentration to about 20 at.% leads to a growth in the σ-phase fraction. The increase in the σ-phase was caused by an increase in the amount of B2 because the solubility of σ-forming Mo and Cr in B2 was less than that in the FCC solution. A further increase in Al concentration led to an excess of Mo and Cr in the solution, which formed a disordered BCC solid solution. The hardness of the alloys attained the maximum of 630 HV at 22 and 32 at.% Al.