Sintered Duplex Stainless Steels Research Articles

Studies on Mechanical Properties of Hot-Forged Duplex Stainless Steels Sintered in Hydrogen Atmosphere

Duplex stainless steels DSS X and DSS Y were made ready from pre-alloyed powders such as 310L, 304L and 430L using powder metallurgy route. Elemental powders such as chromium, nickel and molybdenum were also added with pre-alloyed stainless steel powders in appropriate proportions. A pair of unlike powder preforms of DSS with the geometry of 30 mm diameter and 12 mm height was compacted in universal testing machine at a pressure level of 550 MPa ± 10 MPa and followed sintering at 1350 °C in hydrogen atmosphere. Sintered compacts underwent forging operation at a temperature of 1150 °C followed by water-quenching. Forged-cum-sintered duplex stainless steels were analyzed for microstructural studies, density parameters, hardness measurement and tensile properties and wear. The microstructure of the sintered duplex stainless steels exposed the austenite and ferrite phases and showed surely the presence of duplex structure. Forged density was in the range of 95 to 96 percent of its theoretical density. DSS X exhibited the highest tensile strength of 748 MPa and hardness of 62 HRA in the forged condition. The wear resistance of DSS X was better than that of DSS Y. DSS X showed higher ferrite content in sintered and forged conditions. Fractographs of both DSS X and DSS Y have undergone ductile mode of failure.

Analysis of the interface and mechanical properties of field-assisted sintered duplex stainless steels

The development of duplex stainless steels produced by powder metallurgy represents an interesting alternative to conventional fabrication routes, since typical routes imply a strict control of composition and temperature during the processing path in order to avoid undesirable brittle phases. This work proposes a sintering route, designated as field-assisted hot pressing technique, in which an alternating current is applied to consolidate duplex stainless steels with different initial austenite percentages, always higher than ferrite. In all the cases, a thin and hard planar interface composed by two different microconstituents is generated between austenite and ferrite, growing inside the ferritic phase. The good mechanical properties achieved by these field-assisted sintered duplex stainless steels, in terms of nanohardness, elastic modulus, yield strength, ultimate tensile stress and ductility, establish these steels as promising candidates to be introduced in the market.

Characterization of the Cr3C2-NiAl coatings on sintered duplex stainless steels

Characterization of the Cr3C2-NiAl coatings on sintered duplex stainless steels

Fatigue Behaviour of Sintered Duplex Stainless Steel

The stainless steel despite of tradition of use over the 100 years are steel interesting in terms of metallurgical improvement and development of new products. Stainless steel products undergo intensive development, especially for duplex stainless steel grades manufacture be conventional casting method and metal forming processes, thus, influences an increase in the interest of those materials by alternative technologies of metal forming, which is powder metallurgy. The powder metallurgy and manufacturing processes of metal powders and sintered components production undergoing rapid development. This trend applies also for sintered duplex stainless steels. The paper investigates fatigue behaviours of vacuum sintered duplex stainless steel produced by mixing in appropriate proportions powders of ferritic and austenitic stainless steel and elemental alloying powders and then sinter hardening in a vacuum. The mechanical properties of studied steel were evaluated in terms of tensile strength, hardness, toughness, plasticity. Fatigue tests were carried out in symmetric plane bending at stress ratio R= – 1 with frequency of about 24Hz. Fatigue crack propagation micromechanisms were investigated by means of a scanning electron microscope fracture surface analysis.

Microstructural study of duplex stainless steels obtained by powder injection molding

This experimental work is focused on the study of microstructural evolution during sintering of duplex stainless steels (DSS) obtained by powder injection molding (PIM). Ferritic 430L and austenitic 316L stainless steel powders were previously premixed in a 50/50volume ratio and afterward they were sintered in low vacuum at different temperatures for 1h. Microstructural analysis of sintered samples was conducted by means of scanning electron microscopy (SEM) and a compositional analysis of the alloying elements along different phases was performed by energy dispersive analysis of X-rays (EDS). Phase transformations were evaluated by X-ray diffraction (XRD) experiments, and the magnetic phase content was measured with a ferritoscope. The intensity of the main austenite diffraction peak decreases as sintering temperature increases to finally disappear in the sample sintered at 1100°C. This destabilization of the austenite is probably related to a high Nickel diffusion detected from austenite to ferrite particles. Moreover, electron backscatter diffraction (EBSD) data were collected to quantify microstructural properties. Several EBSD pattern maps were acquired in order to define the amount of austenite phase. Due to the advantages of this technique a 0.5% of austenite could be detected after sintering at 1200°C. After sintering process, the austenite content in sintered duplex stainless steels obtained through this processing route was lower than expected. Finally, Bain mechanism was proposed as an explanation to this phase transformation takes place. EBSD technique has been proved to be the most suitable to monitor the microstructure of sintered DSS.

Effect of chemical composition and sintering conditions on the mechanical properties of sintered duplex stainless steels

Abstract Duplex stainless steels were obtained through powder metallurgy technology from austenitic AISI 316L and ferritic AISI 430L powders mixed in different amounts to obtain ratios of austenite/ferrite of 25/75, 50/50 and 75/25. Prepared powder mixes were compacted at 650 or 750 MPa and sintered in N 2 –H 2 atmosphere (95%-5%) at several sintering conditions and with three sintering cooling rates (furnace, gas and water). Mechanical properties were evaluated using tensile testing and macro–microhardness. The cooling rate was the main factor affecting the microstructure. A full microstructural study for the three cooling rates has been performed. The mechanical behaviour was a function of the cooling rate and the chemical composition. For furnace cooling, the sample with 75/25 of austenite/ferrite powders showed the best result. A hardening effect for the water cooling process was observed with the duplex stainless steels.

Microstructure and mechanical properties of duplex stainless steels sintered in different atmospheres

Present investigation is aimed at developing duplex stainless steels through powder metallurgy route and study the effect of sintering atmospheres on density, mechanical properties and microstructures. Duplex stainless steel composition was prepared from the mixture of 316L and 430L alloyed powders. The powders were mixed in a pot mill for 12 h and compacted at a pressure of 560 MPa. The green compacts were sintered at 1350°C in four different atmospheres such as nitrogen, argon, hydrogen and partial vacuum. Sintered duplex stainless steels were subjected to density measurement, metallography examinations and tensile testing. Duplex stainless steel sintered in partial vacuum showed highest densification of 96% theoretical, tensile strength and ferrite content, when compared with stainless steels sintered in other three atmospheres. Microstructure of stainless steels sintered in argon, hydrogen and partial vacuum showed the bi-phase structure. SEM fractographs of the stainless steels sintered in partial vacuum and hydrogen revealed completely ductile mode of failure.

Stainless Steels Sintered Form the Mixture of Prealloyed Stainless Steel and Alloying Element Powders

The aim of the presented paper is to describe the sintered duplex stainless steels manufactured in sinter-hardening process and their structural and mechanical properties. Duplex stainless steels were obtained through powder metallurgy starting from austenitic 316L or ferritic 410L prealloyed base powders by controlled addition of alloying elements powder. Prepared mixes were compacted at 700MPa and sintered in a vacuum furnace with argon backfilling at temperature of 1240°C for 1h. After sintering different cooling cycles were applied: rapid cooling (6°C/s) using nitrogen under pressure and slow cooling (0.1°C/s) with furnace in argon atmosphere. Produced sintered duplex stainless steels were studied by scanning and optical microscopy and EDS chemical analysis of microstructure components as well as X-ray analysis. Mechanical properties were studied through tensile and three-point bending tests and Charpy impact test. It was demonstrated that austenitic-ferritic microstructures with regular arrangement of both phases and absence of precipitates can be obtained with properly designed powder mix composition as well as sintering cycle with rapid cooling rate. Produced sintered duplex steels show good mechanical properties which depend on austenite/ferrite ratio in the microstructure and elements partitioning (Cr/Ni) between phases. The optimal mechanical properties were obtained for compositions based on ferritic 410L powder where the balanced distribution of α and γ is present and the tensile strength can reach value about 500MPa with 16% of elongation and impact energy about 120J. The precipitations of hard intermetallic σ-FeCr phase take place when sintering with slow cooling cycle what cause substantial decrease of plastic properties, including reduce of elongation to 7% and in particular decrease of impact energy to 68 J.

Corrosion behaviour of duplex stainless steels sintered in nitrogen

Duplex stainless steels obtained through powder metallurgy (PM) technology from austenitic AISI 316L and ferritic AISI 430L powders were mixed on different amounts to obtain biphasic structures with austenite/ferrite ratio of 50/50, 65/35 and 85/15. Prepared mixes of powders have been compacted at 750 MPa and sintered in N 2–H 2 (95% and 5%) at 1250 °C for 1 h. Corrosion behaviour, using electrochemical techniques such as anodic polarization measurement, cyclic anodic polarization scan and electrochemical potentio-kinetic reactivation test and double loop electrochemical potentio-kinetic reactivation double loop test were evaluated. For duplex stainless steels, when austenite/ferrite ratio increases the corrosion potential shifts to more noble potential and passive current density decreases. The beneficial effect of annealing solution heat treatment on corrosion behaviour was established and was compared with corrosion behaviour of vacuum sintered duplex stainless steels. The results were correlated with the microstructural features.

Corrosion resistance of sintered duplex stainless steels in the salt fog spray test

This paper presents corrosion resistance results in salt fog spray test of duplex stainless steels obtained through powder metallurgy starting from austenitic X2CrNiMo 17-12-2, martensitic X6Cr13 powders by controlled addition of alloying elements in the right quantity to obtain the chemical composition of the structure similar to biphasic one. In the preparations of mixtures the Schaffler's diagram was taken into consideration. The prepared mixtures of powders have been sintered in a vacuum furnace with argon backfilling. After sintering two different cooling cycles were applied: rapid cooling with an average cooling rate of 245 °C/min using nitrogen under pressure 0.6 MPa and slow cooling with furnace with an average cooling rate of 5 °C/min in argon atmosphere. The corrosion properties have been studied through salt fog spray test which is applied by the automotive industry end-users because it reproduces the behaviour of a material in front of the environmental corrosion with feasibility. According to the achieved results, it was confirmed that the applied sintering method as well as powder mixtures preparation allows for manufacturing the sintered duplex steels with good corrosion properties in chloride environment.

Corrosion behavior of vacuum sintered duplex stainless steels

Abstract This work presents corrosion resistance results of duplex stainless steels obtained through powder metallurgy starting from austenitic X2CrNiMo17-12-2 (AISI 316L), martensitic X6Cr13 (AISI 410) powders by controlled addition of alloying elements in the right quantity to obtain the chemical composition of the structure similar to biphasic one. In the mixes preparations the Schaffler's diagram was taken into consideration. Prepared mixes of powders have been sintered in a vacuum furnace with argon backfilling. After sintering rapid cooling was applied using nitrogen under pressure. Produced duplex stainless steels have been studied by SEM with EDS and light optical microscopy and X-rays analysis to determine obtained structures. Corrosion properties have been studied through electrochemical methods in 1 M NaCl.

Sintered Duplex Stainless Steels Corrosion Properties

This work presents mechanical properties and corrosion resistance of duplex stainless steels obtained through powder metallurgy starting from austenitic X2CrNiMo17-12-2 (AISI 316L), martensitic X6Cr13 (AISI 410L) powders by controlled addition of alloying elements in the proper quantity to obtain the chemical composition of the structure similar to biphasic one. In the mixes preparations the Schaffler’s diagram was taken into consideration. Prepared mixes of powders have been sintered in a vacuum furnace with argon backfilling. After sintering rapid cooling was applied using nitrogen. Produced duplex stainless steels have been studied by SEM with EDS and light optical microscopy (LOM) and X-rays analysis to determine obtained structures. Corrosion properties have been studied through electrochemical methods in 1M NaCl.

Computer aided materials design of PM duplex stainless steels

The purpose of this paper is to describe the sintered duplex stainless steels manufactured in sinter-hardening process and its use in the field of stainless steels and, moreover, to calculate the powder mix composition using computer software. In the presented paper, duplex stainless steels were obtained through powder metallurgy starting from austenitic or ferritic base powders by controlled addition of alloying elements powder. In the studies, besides the preparation of powder mixes, computer software based on Schaeffler's diagram was studied. It has been demonstrated that austenitic-ferritic microstructures with regular arrangement of both phases and absence of precipitates can be obtained with properly designed powder mix composition and sintering cycle. Applied producing method and used sintering cycle as well as developed computer software proves advantageous in the case of obtained microstructures also working with cycles easy to be introduced in industries. [Received 15 March 2007; Accepted 10 July 2007]

Mechanical and oxidation properties of high density sintered duplex stainless steels obtained from mix of water and gas atomised powders

High density powder metallurgy duplex stainless steels have been obtained by mixing water andgas atomised powders. AISI 434L water atomised ferritic powders were mixed with differentpercentages (up to 50%) of AISI 316L gas atomised powders. The mixtures were then compactedby uniaxial pressing and vacuum sintered at three temperatures. Physical and mechanicalproperties were measured, showing the positive influence of small size austenitic powders indensity and strength. Best materials were submitted to oxidation tests at 800 and 900°C. Massgains during high temperature exposure have been dramatically reduced by the addition of gasatomised powders. Characterisation of the scales through scanning electron microscopy andX-ray diffraction has shown that the mixtures mainly comprise chromia, although other oxideshave been detected.

Properties of Vacuum Sintered Duplex Stainless Steels

This work presents the possibility of obtaining duplex stainless steels through powder metallurgy technology starting from austenitic X2CrNiMo17-12-2, martensitic X6Cr13 powders by controlled addition of alloying elements, such as Cr, Ni, Mo, Cu in the right quantity to obtain the chemical composition of the structure similar to biphasic one. Moreover the ferritic stainless steel X6Cr17 has been mixed to austenitic stainless steel in the ratio of 50%-50% in order to exam the deriving structure after sintering. In the studies behind the preparation of mixes, Schaffler’s diagram was taken into consideration. Prepared mixes of powders have been compacted at 800 MPa and sintered in a vacuum furnace with argon backfilling at 1260°C for 1 hour; after sintering rapid cooling has been applied in N2.

Properties of vacuum sintered duplex stainless steels

This work presents the possibility of obtaining duplex stainless steels through powder metallurgy technology starting from austenitic X2CrNiMo 17-2-2, martensitic X6Cr13 powders by controlled addition of alloying elements, such as chromium, nickel, molybdenum and copper in the right quantity to obtain the chemical composition of the structure similar to biphasic one. In the studies behind the preparation of mixes, Schaffler's diagram was taken into consideration. Prepared mixes of powders have been compacted at 800 MPa and sintered in a vacuum furnace with argon backfilling at 1260 °C for 1 h; after sintering rapid cooling has been applied in N 2, with an average cooling rate of 650 °C/min. Produced duplex stainless steels has been studied by SEM with EDS a light optical microscopy (LOM) and X-ray analysis to determine obtained structures. Mechanical properties such as tensile strength, impact energy, hardness and wear rate were evaluated.

Activated sintering of P/M duplex stainless steel powders

Boron alloyed duplex stainless steels have been obtained by sintering the mixture of austenitic and ferritic stainless steels powders, and their mechanical properties have been studied in comparison to the boron free sintered duplex stainless steels. Boron activates sintering and enhances densification, closing the residual porosity and increasing ductility with respect to the boron free sintered duplex stainless steels.

Effect of nitrogen on sintered duplex stainless steels

In this paper, the authors have studied the effects of the different sintering atmospheres (vacuum, nitrogen-hydrogen, and dissociate ammonia) on 50A-50F duplex stainless steels, fabricated by the powder metallurgy process.The DSS sintered in atmosphere of N2-H2 exhibit a tensile strength of at least 500 MPa with an elongation to fracture smaller than 2%. The presence of nitrides was the main cause of the deterioration in the corrosion resistance.

Corrosion resistance and properties of sintered duplex stainless steels : M. Rosso, A, Grande. (Torino Polytechnic, Torino, Italy)

Corrosion resistance and properties of sintered duplex stainless steels : M. Rosso, A, Grande. (Torino Polytechnic, Torino, Italy)

Mechanical and corrosion properties of sintered duplex stainless steels

Mechanical and corrosion properties of sintered duplex stainless steels