Microstructural characterization and layer stability of low-temperature carburized AISI 304L and AISI 904L austenitic stainless steel

Carbon stabilized expanded austenite (S-phase) is prepared by commercial low-temperature carburizing process(LTC) on austenitic stainless steels AISI 304L and AISI 904L. The current paper deals with the material response to LTC and thermal stability of the formed metastable structure. The aim is to investigate the influence of the alloy composition and surface finishing as well as thermal annealing on the microstructure, phase constituents andhardness of the modified layer by means of combined analysis techniques. It has been found that the formationof expanded austenite is accompanied by H\ue4gg carbides on as-carburized 304L. However, the highly alloyed 904Lexhibits mainly S-phase with larger degree of lattice expansion after carburizing. S-phase has proven to be morestable in 904L, whereas residual and/or induced ferrite/martensite in 304L makes the formation of S-phase less favourable. LTC induces significant enhancement of surface hardness, more effectively on 904L.The hardening mechanism is discussed. In order to evaluate the phase evolution and stability of the expanded austenite at elevated temperatures, annealing has been performed in vacuum at temperature of 600\ub0C for 150 hours.The decomposition of S-phase and the related microstructure evolution give rise to reduced hardening effect and declined corrosion resistance in both S-phase layer and the region below

Microstructural characterization and layer stability of low-temperature carburized AISI 304L and AISI 904L austenitic stainless steel

Carbon stabilized expanded austenite (S-phase) is prepared by commercial low-temperature carburizing process(LTC) on austenitic stainless steels AISI 304L and AISI 904L. The current paper deals with the material response to LTC and thermal stability of the formed metastable structure. The aim is to investigate the influence of the alloy composition and surface finishing as well as thermal annealing on the microstructure, phase constituents andhardness of the modified layer by means of combined analysis techniques. It has been found that the formationof expanded austenite is accompanied by H\ue4gg carbides on as-carburized 304L. However, the highly alloyed 904Lexhibits mainly S-phase with larger degree of lattice expansion after carburizing. S-phase has proven to be morestable in 904L, whereas residual and/or induced ferrite/martensite in 304L makes the formation of S-phase less favourable. LTC induces significant enhancement of surface hardness, more effectively on 904L.The hardening mechanism is discussed. In order to evaluate the phase evolution and stability of the expanded austenite at elevated temperatures, annealing has been performed in vacuum at temperature of 600\ub0C for 150 hours.The decomposition of S-phase and the related microstructure evolution give rise to reduced hardening effect and declined corrosion resistance in both S-phase layer and the region below

On the Effect of Slight Variations of Si, Mn, and Ti on Inclusions Properties, Microstructure, and Mechanical Properties of YS460 C-Mn Steel Welds

This study investigates the effects of slight variations in the average Ti, Mn, and Si weld metal contents, obtained by properly designing different rutile-based flux-cored wires, on the all-weld metal microstructure, intragranular inclusions, and mechanical properties. The compositional changes have been restricted to max 15% variation approximately; in particular, the Ti, Mn, and Si levels have been changed, respectively, in the range 340\u2013400 ppm, 1.28\u20131.38 wt.%, and 0.35\u20130.42 wt.%. Metallographic and image analysis techniques have been used to quantitatively examine the microstructural changes, and the results have emphasized how even such slight variation on Ti, Mn, and Si contents can lead to representative microstructural changes. The volume fraction of the inclusions increases from about 0.8 to 1.0% and their size from 520 nm up to 710 nm. Furthermore, higher acicular ferrite content is observed, i.e., from 66 to 81 vol.%. By the point of view of mechanical properties, the microstructural changes have improved both the tensile strength, with a 5% increase, and the Charpy impact toughness that increases up to 17 J (roughly 20%) at 12 60 \ub0C temperature. Nucleation and growth mechanisms of intragranular inclusions and weld microstructure are then proposed, and correlations with mechanical properties evolution are identified and discussed

Microstructural characterization and layer stability of low-temperature carburized AISI 304L and AISI 904L austenitic stainless steel

Carbon stabilized expanded austenite (S-phase) is prepared by commercial low-temperature carburizing process (LTC) on austenitic stainless steels AISI 304L and AISI 904L. The current paper deals with the material response to LTC and thermal stability of the formed metastable structure. The aim is to investigate the influence of the alloy composition and surface finishing as well as thermal annealing on the microstructure, phase constituents and hardness of the modified layer by means of combined analysis techniques. It has been found that the formation of expanded austenite is accompanied by H\ue4gg carbides on as-carburized 304L. However, the highly alloyed 904L exhibits mainly S-phase with larger degree of lattice expansion after carburizing. S-phase has proven to be more stable in 904L, whereas residual and/or induced ferrite/martensite in 304L makes the formation of S-phase less favourable. LTC induced significant enhancement of surface hardness, more effectively on 904L. The hardening mechanism is discussed. In order to evaluate the phase evolution and stability of the expanded austenite at elevated temperatures, annealing was performed in vacuum at temperature of 600\ub0C for 150 hours. The decomposition of S-phase and the related microstructure evolution give rise to reduced hardening effect and declined corrosion resistance in both S-phase layer and the region below

Flow Boiling Heat Transfer of R1234yf on a Microparticle Coated Copper Surface

This paper presents some preliminary experimental measurements collected during flow boiling heat transfer of low-GWP refrigerant R1234yf on a microparticle coated surface obtained via cold spray, a simple and non-expensive technique. The specific surface engineering was obtained by depositing a 100 \u3bcm thick pure copper coating on a smooth copper plate 200 mm long and 10 mm wide. The coating was deposited via High Pressure Cold Spray (HPCS) starting from a feedstock of pure copper particles with average size of 20 \u3bcm. The experimental measurements, carried out at the department of Industrial Engineering of the University of Padova, refer to a heat flux equal to 50 kW m-2, at a constant saturation temperature of 30 \ub0C; the refrigerant mass velocity was varied between 30 and 200 kg m-2 s-1, while the vapour quality varied from 0.2 to 0.95

Different cold spray deposition strategies : single and multi layers to repair aluminium alloy components

Cold spraying is increasingly being used for reconstruction or repair of damaged aluminium alloy components, especially in the aviation industry. Both thin (<0.5 mm) and thick (up to 1 cm) coatings are necessary to achieve dimensional recovery of such components. Thin and above all thick coatings can be deposited in a single pass (single layer) or in several passes (multi-pass), resulting in different thermal and stress effects in the component and the coating itself. The thermal input, the amount and type of residual stresses and the porosity affect various characteristics such as adhesion, crack propagation and mechanical properties of the coating. In this study, two sets (single- and multi-pass) of aluminium alloy (AA6061) coatings with different thicknesses (0.5 mm to 2 mm) were deposited onto AA6061 substrates and compared using metallographic and fractographic analyses, four-point bending testing, residual stress analysis and Vickers microhardness indentation. Finally, the coating adhesion and cohesion were measured using the standard ASTM-C633 adhesion test and tubular coating tensile test. This study demonstrates that the single-layer strategy results in greater adhesion and lower porosity, while multilayer coatings have higher elastic modulus. Independent of the strategy, the compressive residual stress decreases as a function of coating thickness.Peer reviewed: YesNRC publication: Ye