This study presents results of experimental tests on quality of dissimilar welded joints between 316L austenitic and 2304 lean duplex stainless steels, welded without ceramic backing. Fiber laser ...welded butt joints at a thickness of 8 mm were subjected to non-destructive testing (visual and penetrant), destructive testing (static tensile test, bending test, and microhardness measurements) and structure observations (macro- and microscopic examinations, SEM, element distribution characteristics, and ferrite content measurements). Non-destructive tests and metallographic examinations showed that the welded joints meet the acceptance criteria for B level in accordance with EN ISO 13919–1 standard. Also the results of the destructive tests confirmed the high quality of the joints: specimens were fractured in base material with lower strength—316L austenitic stainless steel and a 180° bending angle was obtained confirming the high plasticity of the joints. Microscopic examination, SEM and EDS analysis showed the distribution of alloying elements in joints. The microhardness of the autogenous weld metal was higher by about 20 HV0.2 than that of the lean duplex steel. Ferrite content in the root was about 37% higher than in the face of the weld. The Schaeffler phase diagram was used to predict the phase composition of the welded joints and sufficient compliance with the magnetic method was found. The presented procedure can be used for welding of 316L–2304 stainless steels dissimilar welded joints of 8 mm thickness without ceramic backing.
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Metal components produced via selective laser melting (SLM) additive manufacturing (AM) can offer comparable and sometimes superior mechanical properties to those of bulk materials. ...Selection of the appropriate process parameters (e.g. laser power, build direction, scan hatch spacing) plays a fundamental role in determining final properties. For this reason, microstructure, defect formation and mechanical properties of AISI 316L components are investigated in this paper according to the process parameters used for their fabrication. A first experimental campaign establishes process parameters guaranteeing a density greater than 98%. Samples for microstructural and mechanical characterization are then produced based on these results, varying laser power from 100W to 150W, hatch space from 0.05mm to 0.07mm and orientation from 45° to 90°. A MYSINT100 SLM machine with laser power up to 150W and spot diameter of 50μm is employed for all experiments. The presented results establish a correlation between the process parameters and the resulting microstructure and mechanical properties of SLM 316L specimens.
The austenitic steel AISI 316L has recently become one of the most popular alloys for laser powder bed fusion as it shows good mechanical properties along with sufficient corrosion resistance. For ...duplex stainless steels the LPBF process does not seem to be as attractive as a solution annealing treatment is required to attain the desired austenite and ferrite microstructure. The goal of this study is to identify a chemical composition that shows enhanced corrosion resistance and tensile strength compared to AISI 316L without requiring a post-process heat treatment like the conventional duplex stainless steels. Based on thermodynamic simulations powder mixtures of austenitic stainless steel AISI 316L and duplex stainless steel AISI 318LN in three mixing ratios have been processed. The influence of the chemical composition and LPBF processing parameters on the resulting microstructure are investigated by light optical microscopy and electron backscatter diffraction. Tensile tests were conducted and polarization curves recorded to evaluate the potential of the most promising alloy. 30 wt.-% of AISI 318LN added to AISI 316L lead to an austenite/ferrite microstructure in the as-built condition. The phase fractions vary with the LPBF processing parameters. The strength as well as corrosion resistance of this new alloy is superior to that of pure AISI 316L, while the ductility is lower.
Stainless steels represent a quite interesting material family, both from a scientific and commercial point of view, following to their excellent combination in terms of strength and ductility ...together with corrosion resistance. Thanks to such properties, stainless steels have been indispensable for the technological progress during the last century and their annual consumption increased faster than other materials. They find application in all these fields requiring good corrosion resistance together with ability to be worked into complex geometries. Despite to their diffusion as a consolidated materials, many research fields are active regarding the possibility to increase stainless steels mechanical properties and corrosion resistance by grain refinement or by alloying by interstitial elements. At the same time innovations are coming from the manufacturing process of such a family of materials, also including the possibility to manufacture them starting from metals powder for 3D printing. The Special Issue scope embraces interdisciplinary work covering physical metallurgy and processes, reporting about experimental and theoretical progress concerning microstructural evolution during processing, microstructure-properties relations, applications including automotive, energy and structural.
A dissimilar autogenous laser welded joint of AISI 430F (X12CrMoS17) martensitic stainless steel and AISI 304 (X5CrNi18-10) austenitic stainless steel was manufactured. The welded joint was examined ...by non-destructive visual testing and destructive testing by macro- and microscopic examination and hardness measurements. With reference to the ISO 13919-1 standard the welded joint was characterized by C level, due to the gas pores detected. Microscopic observations of AISI 430F steel revealed a mixture of ferrite and carbides with many type II sulfide inclusions. Detailed analysis showed that they were Cr-rich manganese sulfides. AISI 304 steel was characterized by the expected austenitic microstructure with banded δ-ferrite. Martensitic microstructure with fine, globular sulfide inclusions was observed in the weld metal. The hardness in the heat-affected zone was increased in the martensitic steel in relation to the base metal and decreased in the austenitic steel. The hardness range in the weld metal, caused by chemical inhomogeneity, was 184–416 HV0.3.
During the process of selective laser melting (SLM), spatter is generated with a negative impact on the performance of parts. Two types of spatter have been identified: droplet spatter, produced by ...the tearing of molten metal and powder spatter, formed when non-molten metallic powder particles around the molten pool are blown away, both arising as a result of the impact of metallic vapor. Single-track experiments were performed in order to observe spatter behaviors by using a high-speed camera. The influence of energy input on the spatter behavior was investigated by employing 316L stainless steel powder. Results indicate that energy input affects the size, scattering state and jetting height of spatter. Energy dispersive spectroscope analyses show that oxygen contents increase in spatter and SLM parts. X-ray diffraction analyses show that diffraction peaks of austenite and ferrite are considerably lower than those in 316L powder owing to the generation of iron oxides (Fe+2Fe2+3O4). Comparative tensile testing results show that although both groups of specimens manufactured with fresh and contaminated powders are mainly characterized by ductile fracture, the tensile properties of the latter are far inferior to those of the former, owing to a greater quantity of inclusions.
At the beginning point of scanning track, the laser starts to strike the powder bed, the molten pool has not yet been formed, and vaporization is weak, therefore, the glare is weak.
When the laser beam moves to the middle point of scanning track, the molten pool reaches a dynamic equilibrium state, hence the glare gets steady.
When laser beam moves to the end point of scanning track, the moving laser beam slows down, the powders absorb more energy, vaporization in molten pool is enhanced, thus the glare becomes intenser dramatically. Display omitted
•Dynamic process of spatter behavior during SLM was captured by high-speed camera.•Energy input affects the size, scattering state and jetting height of spatter.•Spatter and SLM part are very sensitive to the oxygen content.•Spatter significantly reduces the mechanical properties of SLM part.
Additive manufacturing as a new processing technique can produce unique microstructure that is difficult to achieve using conventional techniques. In this study, we have investigated the creep ...behavior of 316 L stainless steel produced by a laser powder bed fusion process at temperatures of 550, 600 and 650 °C and stresses between 175 and 300 MPa. We found that additively-manufactured 316 L stainless steel had a higher stress dependence of the minimum creep rate than conventionally-made Type 316 SS, which could be attributed to the dislocation cell structure resulting from the printing process. The dislocation cell structure was unstable under creep, evolving into a uniform dislocation structure under the test conditions. While internal porosity in AM 316 L SS may serve as nucleation sites of creep voids and may be responsible for a relatively lower creep life, additively-manufactured 316 SS did not show inferior creep ductility when compared with conventionally-made 316 SS. The creep life of AM 316 L SS could be improved by stabilizing dislocation cell structure and/or reducing internal porosity through an optimized additive manufacturing process.
In the present study, electron beam welding (EBW) was used to join reduced-activation ferritic-martensitic (RAFM) steel to 316L stainless steel. Microstructural evolution and mechanical property ...variation in the heat-affected zone (HAZ) and weld metal (WM) during the post weld heat treatment (PWHT) was investigated. The results suggested that the hardness of RAFM-HAZ decreased with increased PWHT temperature, while the hardness of WM decreased to minimum at 620 ℃ and then increased at higher PWHT temperatures. This was consistent with strength variation in the WM during PWHTs. Microstructural observations and corresponding phase diagram calculation indicated that blending of two types of base metals increased nickel content of WM, enlarged the two phase-region and lowered A1 (start of transformation of ferrite to austenite) point of WM, as compared with similar ferritic-martensitic steel weld joint. Thus, reversed austenite transformation and subsequent martensite transformation occurred in WM of sample subjected to higher temperature heat treatment, while there was no transformation in the HAZ. This effect explained the changes in hardness and strength of WM corresponding to PWHT. The optimized properties of both HAZ and WM in the dissimilar weld joint were obtained by a two-step post weld heat treatment.
•A summary of reference I-profile column tests and numerical results is provided.•Finite element models are developed to study minor and major flexural buckling.•A parametric study on ferritic, ...austenitic and duplex stainless steel is presented.•The reliability of Eurocode and two different CSM buckling approaches are assessed.•Recommendations are made for the buckling curves for both axis flexural buckling.
This paper studies the buckling behaviour and design of welded I-section stainless steel columns. Experimental and numerical structural performance data together with the design methods for stainless steel welded I-section columns available in the literature have been collated and reviewed. A numerical modelling programme including validation and parametric studies has been carried out to supplement the literature experimental and numerical data for the assessment of the existing codified and literature proposed flexural buckling design formulations for stainless steel welded I-section columns. Columns of austenitic, duplex and ferritic stainless steel grades undergoing major axis and minor axis flexural buckling have been investigated. From comparisons with the EN 1993–1-4 (EC3) flexural buckling capacity predictions, it was found that (1) for the austenitic welded I-section columns, the EC3 buckling curve (α = 0.76 and λ¯0 = 0.2) is suitable for both axes, (2) for the duplex and ferritic grades, the EC3 buckling curve (α = 0.76 and λ¯0 = 0.2) is conservative, and a higher buckling curve with (i) α = 0.49 and λ¯0 = 0.2 for both axes or (ii) α = 0.49 and λ¯0 = 0.2 for minor axis and α = 0.34 and λ¯0 = 0.2 for major axis may be adopted. In addition, comparisons with the recently proposed Continuous Strength Method showed marginally improved strength predictions but with slightly higher scatter.
•Passivation of 2507 steel in local occlusive environment of seawater is studied.•The HFM and PDM are compared to obtain point defect diffusivity.•Passive current is increased in acidified seawater ...by increasing φf/s, DO, and ND..•Acidification increases oxidized Cr, Fe(II) and hydroxides inside the passive film.•Transpassivation leads to increase in oxidized Fe, Cr2O3, and formation of pores.
Passivation and film chemistry of 2507 super duplex stainless steel in modified artificial seawater (ASW) are investigated. Removal of dissolved oxygen decreases the electric field strength and point defect diffusivity of the passive film. Passive current density in acidified ASW is higher than that in aerated ASW due to increased potential drop across film/solution interface, donor density and point defect diffusivity. The content of oxidized Cr, Fe(II) and hydroxides increases and film thickness reduces with acidification. In acidified ASW, passive film become denser from pre-passivation to passivation region and pores form accompanied with the increase of oxidized Fe after transpassivation.
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