PH Stainless Steel Powder Research Articles

Development of PIM Components for Robot Surgery

In this study, the micro forcep of end-effector for robot surgery was produced by powder injection molding. The 17-4PH stainless steel powder and binder system based on a wax-polymer were mixed to fabricate the feedstock. The optimum solid loading (vol. %) was determined by the torque rheometer experiments. After injection molding, debinding and sintering were carried out, final product having small and regular patterns was produced.

Thermal Stability of the MoS2 Phase in Injection Moulded 17-4 PH Stainless Steel

In the present paper, an analysis of the stability of the MoS2 compound in 17-4 PH stainless steel matrix during the sintering of powder injection moulded samples is presented. A feedstock containing 10% vol. of the solid lubricant phase MoS 2 , mixed with 17-4 PH stainless steel powder was prepared and injected. The sintering was carried out at various temperatures ranging from 650°C to 1,300oC. The progress of the dissociation process of MoS 2 as a function of sintering temperature and the formation of new phases were analyzed via X-ray diffraction. The microstructure of the resulting material was analyzed by SEM/EDS. As expected, for temperatures above 650oC, the results confi rm the decomposition of MoS 2 and formation of others sulphides during the sintering cycle. In addition, there occurs dissolution of molybdenum resulting from MoS2 decomposition.

Microstructures and Properties of 17-4 PH Stainless Steel Fabricated by Selective Laser Melting

Objective This research examines 17-4 PH stainless steel powders produced by atomization in either argon or nitrogen atmospheres (producing martensitic (α-Fe) or mostly austenitic (γ-Fe) phase powders, respectively) and correspondingly fabricated by selective laser melting (SLM) in either a nitrogen or argon atmosphere. Methods Pre-alloyed 17-4 stainless steel powders prepared by atomization in either argon or nitrogen atmospheres were fabricated by SLM. The initial powder microstructures and phase structures were examined by light (optical) microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Prototypes fabricated by SLM were similarly characterized, and in addition transmission electron microscopy (TEM) characterization was also performed. Results Martensitic powder fabricated by SLM in nitrogen gas produced a martensitic product while pre-alloyed austenitic powder produced a primarily austenitic product. In contrast, both powders produced martensitic products when fabricated by SLM in argon gas. This unusual behavior occurred because of the rapid cooling affected by nitrogen versus argon cover gas as a consequence of a 40% greater thermal conductivity of nitrogen gas versus argon gas. SLM fabricated martensitic products exhibited HRC 30 in contrast to HRC 43 when aged at 482°C for 1 hour. Austenitic products did not exhibit age-hardening. Conclusions Using an argon cover gas, SLM-fabricated products are martensitic (and magnetic) with either an austenitic or martensitic pre-alloyed 17-4 PH stainless steel powder. Using a nitrogen cover gas, the product phase is the same as the precursor powder phase (austenitic or martensitic).

고정밀 신관 부품의 MIM 공정에 관한 연구

During the past two decades, Metal Injection Molding(MIM) has become a very competitive technology to fabricate small, precise and complex-shaped parts in large quantities. In this research, the applicability of MIM technology in the mass-production of the high precision fuze parts to save manufacturing cost was investigated. The water-atomized 17-4PH stainless steel powder, one of the best corrosion-resistant high strength materials, was injection-molded into real-shape fuze part and flat tensile specimens. The injection-molded parts were thermally debound in hydrogen gas flow without solvent extraction. Sintering of the debound parts was carried out in vacuum at temperatures ranging from <TEX>$1150^{\circ}C$</TEX> to <TEX>$1370^{\circ}C$</TEX>. The sintering behavior, mechanical properties, dimensional precision, corrosion resistance of the MIMed 17-4PH stainless parts were investigated. It was found that almost all the properties of the MIMed parts were comparable to those of the mechanically machined parts. Also, actual military field tests using both MIMed and mechanically machined fuze parts were performed as well and were found to be very successful.

Characterization of 17-4PH stainless steel powders produced by supersonic gas atomization

17-4PH stainless steel powders were prepared using a supersonic nozzle in a close-coupled gas atomization system. The characteristics of powder particles were carried out by means of a laser particle size analyzer, scanning electron microscopy (SEM), and the X-ray diffraction (XRD) technique. The results show that the mass median particle diameter is about 19.15 μm. Three main types of surface microstructures are observed in the powders: well-developed dendrite, cellular, and cellular dendrite structure. The XRD measurements show that, as the particle size decreases, the amount of fcc phase gradually decreases and that of bcc phase increases. The cooling rate is inversely related to the particle size, i.e., it decreases with an increase in particle size.

Production and aging of highly porous 17-4 PH stainless steel

This study describes production of highly porous 17-4 PH stainless steel for biomedical implant applications by space holder-sintering technique. 17-4 PH stainless steel powders were mixed with space holder and then compacted. For designing pore properties, both spherical and irregular shaped carbamide with different particle size ranges were used as space holder and removed by water leaching. Porous 17-4 PH steel specimens were sintered at 1,260 °C for 40 min. Boron was used as a liquid phase sintering additive. In addition, sintered specimens were aged in order to increase mechanical properties. Specimens were austenitized at 1,050 °C and then quenched. Quenched specimens were aged at times of 1–6 h at temperatures between 450 and 570 °C. The pore size and shape of the 17-4 PH stainless steel foams replicated the initial size and shape of the carbamide particles. This suggests that pore properties can be designed by using proper size, shape and content of space holder.

The use of artificial neural network for prediction of grain size of 17-4 pH stainless steel powders

This study is aimed to deals with artificial neural network (ANN) approach for prediction grain size (GS) of 17 - 4 pH stainless steel powders. Experimental data which were obtained from experimental studies in a laboratory environment have been used for this modeling. Using some of the experimental data for training and testing an ANN for GS was developed. In these systems, output parameters GS has been determined using input parameters including environment, time, speed, ball diameter, ball ratio, and material. When experimental data and results obtained from ANN were compared by regression analysis in Matlab, it was determined that both groups of data are consistent. The correlation coefficient between estimated GS values and experimental data obtained are 0.99 for traing and 0.98 for testing respectively. The correlation coefficient is closely to 1. This coefficient shows that there is a strong relationship between these data. Also, the accuracy rate was 98.97% for GS. As a result, it has been shown that designed ANN can be used reliably in powder metallurgic industry and engineering. Keywords: Artificial neural network, mechanical milling, garin size.

Experimental investigation into selective laser melting of austenitic and martensitic stainless steel powder mixtures

Selective laser melting (SLM) is a novel additive layer manufacturing method that has been used to directly consolidate a wide range of metallic powders to form net-shape metallic parts for various engineering applications. It is capable of processing steel powders in a range of grades and also allowing the creation of custom alloys by consolidating the mixed powders of two or more grades. This study investigates the effects of varying the ratio of austenitic and martensitic powder mixtures on the laser consolidation of steel parts. Specimens were fabricated by SLM processing from 316L austenitic and 17-4PH martensitic stainless steel powder mixtures with varying composition ratios. Mechanical and magnetic properties of the specimens were assessed by micro-hardness testing and comparison of ‘magnetic adherence’ forces. The composition ratios of the mixed powders have been found to influence the laser consolidation mechanisms and the resulting microstructures in the specimens. The microstructures play an important role in altering the micro-hardness and the magnetic properties of the specimens and determining a definite relationship between these two properties. The results of this study prove that a new stainless steel grade can be produced via the SLM process to have tailored mechanical and magnetic properties.

Microstructural and mechanical properties of injection moulded gas and water atomised 17-4 PH stainless steel powder

This paper describes the microstructural and mechanical properties of injection moulded 17-4 PH stainless steel gas and water atomised powder. Gas and water atomised stainless steel powders were injection moulded with wax based binder. The critical powder loading for injection moulding were 62·5 and 55 vol.-% for gas and water atomised powders respectively. Binder debinding was performed using solvent and thermal method. After dedinding the samples were sintered at different temperatures for 1 h in pure H2. Metallographic studies were conducted to determine to extend densification and the corresponding microstructural changes. The results show that gas atomised powder could be sintered to a maximum (98·7%) of theoretical density, and water atomised powder could be sintered to a maximum (97·08%) of theoretical density. Maximum tensile strength was obtained for gas atomised powder sintered at 1350°C. The tensile strength of the water atomised powder sintered at the same temperature was lower owing to higher porosity. Finally, mechanical tests show that the water atomised powder has lower mechanical properties than gas atomised powder.

Effects of surfactant on properties of MIM feedstock

Effects of the surfactant for improving the properties of MIM feedstock were investigated. Feedstocks were prepared by 17-4PH stainless steel(SS) powder and paraffin wax-based binder containing different contents of stearic acid(SA) as the surfactant. The viscosity of the feedstock decreases significantly when the SA is added. Besides, the wetting angle of the binder against the 17-4PH SS powder decreases greatly and the critical solid loading increases with the adding of the SA. Fourier transformation infrared spectroscopy(FTIR) analysis was used to prove the interaction between the SA and the 17-4PH SS powder. Chemical bonding is found on the surface of 17-4PH SS powder after mixing and it helps a lot to enhance the interacting force between the binder and the powder. Then an adsorbing model was adopted to estimate the least content of the surfactant that formed a monolayer adsorption on the mono-sized spherical powder (with smooth surface). The least content of the surfactant is calculated to be 0.19%. Whereas, the experiments indicate that about 5% is the optimal value to improve the properties of the feedstock. The reason may come from two aspects: firstly, the powders used in current experiment are not all mono-sized spheres and the coarse surface of the powder has a great effect on the adsorptive capacity of the powder; secondly, multilayer adsorption is likely to occur on the powder surface, which will also increase the adsorptive capacity.

An investigation into the effect of experimental parameters on powder grain size of the mechanically milled 17-4 PH stainless steel powders

In this study, a Szegvari type vertical mechanical alloying/milling attritor was designed and constructed for research purposes. By using this attritor, optimum processing parameters such as milling time, milling speed (rpm), diameter and the amount of the milling balls, milling atmosphere and raw material properties were determined when mechanical milling of gas and water atomised 17-4 PH stainless steel powders. After milling, powder size analyses and microscopic studies were carried out for the characterisation of as-received and milled powders. It was observed from the results of the present investigation that for 17-4 PH stainless steel powders, optimum properties were obtained when milling was carried out at 500 rpm in an inert atmosphere by using 250 g of 10 mm diameter balls.

An Investigation on Elongation-Porosity Relation in Sintered 17-4 PH Stainless Steel

In the present study, powder injection molding (PIM) process, in which the porosity of sintered parts can be easily controlled, has been employed to produce specimens with the various porosities from the initial stage of sintering and to the stage of nearly full density. A series of tensile tests has been conducted on these specimens at room temperature to elucidate the effect of a wide range of porosity. The material used in this study was 17-4 PH stainless steel, which is the precipitation hardenable stainless steel containing 4% of Cu and well known to show high strength and the high corrosion resistance at the same time. The 17-4 PH stainless steel powders used in this study were produced by the high-pressure water atomization method. Based on the results of tensile tests on the specimens with the various porosity, a new approach to predict the elongation of sintered materials has been carried out and a new framework combining neck growth model and ideal pore model has been established.

Effect of powder loading on metal injection molding stainless steels

Powder loading is one of the most critical factors which has important influence on metal injection molding processes. Using the gas atomized spherical 17-4 PH stainless steel powder and the binder of 65% PW + 30% EVA + 5% SA, four kinds of feedstocks were prepared at the powder loading of 60, 64, 68 and 72%, respectively. The effects of the powder loading on the feedstock rheological properties, the compact distortion and tolerance control as well as mechanical properties and microstructures were investigated. It is proved that 68% powder loading is the optimal one. The feedstock with 68% powder loading can be injection molded with a comparatively low viscosity on a relatively wide temperature range, and it is best to get quick powder re-packing and binder molecule orientation during injection molding. From the standpoint of compact shape retention and dimension tolerance control, the optimal powder loading of 68% is also the best. Furthermore, the compact of 68% powder loading is easy to get sinter densification and has superior mechanical properties and microstructures.

Dry sliding wear in injection molded 17-4 PH stainless steel powder with nickel boride additions

Dry sliding wear behavior of injection molded 17-4 PH stainless steel powder with nickel boride additions has been studied on a pin-on-disc wear tester using an alloy steel pin and disc of hardness 63 HRC. The PIM alloys in the as sintered as well as in the precipitate-hardened conditions were investigated for their wear behavior. Wear rate was found to be initially decreased with the increasing nickel boride amount. Optical microscopy and XRD analysis were preformed to characterize the basic microstructures for all samples. SEM observations of the worn surfaces revealed plastics deformations with delamination of surface layers by subsurface cracks as the mechanism in the as sintered and precipitate-hardened conditions.

An investigation on the sintering behavior of 316L and 17-4PH stainless steel powders for graded composites

This paper presents the densification and microstructure of bilayer structures made from 316L and 17-4PH stainless steels powders during sintering. The requirements for such objects could be magnetic properties at one area of the part and non-magnetic properties at another area of the object. A pressureless solid state sintering method in conjunction with a powder layering technique was used. The sintering was carried out at temperatures ranging from 1100 to 1340 °C for 120 min in hydrogen and vacuum atmospheres. Non-isothermal sintering behavior was also examined by dilatometric analysis. It was found that the strain rate of 17-4PH stainless steel powder is higher than that of 316L during the course of sintering. This induces mismatch strain between two layers that can be harmful for the co-sintering process. The amount of strain incompatibility is noticeably higher in vacuum sintering compared to hydrogen sintering. It has also been shown that the mismatch strain induces biaxial stresses during sintering, affecting the densification rate of the bilayer. An enhanced densification rate compared to the individual layers was noticed, particularly during vacuum sintering. A narrow interlayer diffusion boundary with high volume fraction of ferrite phase was realized.

Characterisation of mechanically milled 17-4 PH gas atomized stainless steel powders

A laboratory scale Szegvari type vertical mechanical alloying (MA)/mechanical milling (MM) attritor for research purposes was designed and constructed at Gazi University. By using this attritor, optimum processing parameters such as milling time, milling speed (rev/min), diameter and the amount of milling balls, milling atmosphere were determined when MM’ing of gas atomized 17-4PH stainless steel powders were carried out. After the milling, powder size analyses and microscopic studies (optical and SEM) were utilized for characterization of the as-received and milled powders. It was observed from the results of the present investigation that for 17-4PH stainless steel (SS) powders, optimum properties were obtained when mechanical milling at Gazi University attritor was carried out at 500 rev/min in Ar gas by using 250 g of 10 mm diameter hardened chromium steel balls. It was also observed that MM time has a profound influence on the characteristics (such as particle size, shape and distribution) of MM’ed 17-4 PH gas atomized SS powders depending on the two competing mechanisms, namely, the rate of welding and the rate of fracturing.

Sintering of a boron-doped injection moulded 17-4PH stanless steel

Powder injection molding (PIM) is an attractive process to produce complex, near-net shaped components. The process overcomes the shape limitation of traditional powder compaction, the cost of machining, the productivity limits of isostatic pressing and slip casting, and the defect and tolerance limitations of conventional casting. Over 50% of the injection molded and sintered components are made from stainless steel composition [1–3]. The alloy 17-4 PH stainless steel powders—a precipitation-hardening martensitic stainless steel, shaped and processed via injection molding can achieve high complexity of part geometrical with mechanical and corrosion properties, similar or superior to wrought material. Due to its high strength and good corrosion resistance 17-4 PH has widespread applications, especially in medical, automotive, military, and aerospace instruments [4–6]. Earlier investigations on PM or PIM 17-4 PH focused on the effect of powder characteristics, sintering atmosphere, sintering temperature, sintering time, heat treatment, residual carbon content on microstructure, corresponding microstructural characterization, mechanical and corrosion properties [4–6]. In several investigations boron as a sintering additive has been used to achieve higher sintered density in stainless steels at lower sintering temperatures [7–9]. As a consequence, a noticeable improvement in the mechanical properties is obtained. Boron can be added either in its elemental form (both amorphous and crystalline) or as a compound (for example, Fe2B, BN, NiB, and CrB). A small particle size of the additive is desirable to obtain a uniform dispersion. Boron additions increase hardenability in steels, increase strength (via increase in sintered density), improve grain boundary cohesive strength, enhance corrosion resistance, and improve ductility [7, 9]. The aim of this study is to investigate the effect of added boron on the sintering behavior and final properties of powder injection molded 17-4 PH stainless steel. In this research, gas atomized 17-4 PH stainless steel powders (Fe-16.2Cr-4.6Ni-4.6Cu-0.54Mn0.30Nb-0.30Si-0.095Mo-0.038C-0.026P-0.002S) provided by Osprey Metals Ltd. were used. It has particle size distribution of D10 = 3.25 μm, D50 = 10.65

Microstructures and mechanical properties of injection molded 17-4PH stainless steel powder with nickel boride additions

This paper describes the sintering of an injection molded 17-4 PH stainless steel with additions of nickel boride (NiB), with the aim of producing high mechanical properties. Boron is evaluated as the best sintering enhancing element in terms of densifying the iron-based materials by formation the liquid phase. Sintered density and mechanical properties were increased with the increased amount of NiB while sintering time and temperature were decreased. Sintering to full density and highest mechanical properties were obtained with the addition of 1 wt% NiB at 1280∘C for 45 min. The formation of borides caused the increase of mechanical properties. This material may therefore find a wider technological application, because of its improved mechanical properties.

Influence of nickel boride additions on sintering behaviors of injection moulded 17-4 PH stainless steel powder

Abstract Effect of nickel boride additions on sintering behavior of injection molded 17-4 PH stainless powder. With increases nickel boride amount, sintering time and temperature, relative density and mechanical properties of specimens increase. Sintering to full density was obtained with the addition of 1 wt.% NiB at 1280 °C for 45 min.

Effect of FeB additions on sintering characteristics of injection moulded 17-4PH stainless steel powder

High density sintering of precipitation hardening stainless steel such as 17-4 PH involves a combination of relatively high temperature (>1350°C) and extended sintering time. In this study, the effect of addition of FeB on sintering characteristics of 17-4 PH stainless steel was investigated. Addition of boron is promoted to get highly dense sintered steels. The amount of boron plays a role in determining the sintered microstructure and properties. With the increased amount of FeB sintered density and tensile strength increase while sintering time and temperature decrease.