Simulation of pressure effects on hot isostatic pressing of stainless steel powder

To investigate the effects of pressure on the hot isostatic pressing(HIP) process of a stainless steel powder,density distribution and deformation of the powder at four different applied pressure levels were predicted and compared by using finite element method(FEM).Constitutive relations of porous compacts during HIP process were derived based on the yield criterion of porous metal materials.Thermo-mechanical coupling calculations were carried out by the MSC.Marc.Densification mechanisms were studied through evolutions of relative density,equivalent plastic strain and equivalent viscoplastic strain rate for compacts.The simulation results were also compared with experimental data.The results show that the densification rate and final density of compacts increase dramatically with the increase in the applied pressure level when it is below 100 MPa during HIP process,and the creep for compacts evolves into steady stage with the improvement of density.

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 prn. 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.

Warm compacting behavior of stainless steel powders

The warm compacting behaviors of four different kinds of stainless steel powders,304L,316L,410L and 430L,were studied. The results show that warm compaction can be applied to stainless steel powders. The green densities and strengths of compacts obtained through warm compaction are generally higher than those obtai ned through cold compaction. The compacting behaviors in warm compaction and col d compaction are similar. Under the compacting pressure of 700 MPa,the warm co mpacted densities are 0.100.22 g/cm^3 higher than the cold compacted o nes,and the green strengths are 11.5%50% higher. The optimal warm compa cting temperature is 100110 ℃. In the die wall lubricated warm compact ion,the optimum internal lubricant content is 0.2%.

Investigation on Rapidly Solidified T15 High Speed Steel Powder and Its Bulk Microcrystalline Material

Authors produced rapidly solidified T15 high speed steel powders by high pressure(5~ 6MPa) N_a atomization and liquid N_2 cooling,observed and analyzed the morphology and structure of the powders;at the same time,prepared bulk microcrystalline T15 high speed steel materials by hot extruding or HIPing and hot rolling of the powders,observed and measured the microstructure and performance of the bulk materials.It was shown that rapid solidification may change the solidification characteristics and structure of T15 high speed steel powder and improve the qualities and properties of T15 high speed steel materials.

The Research for Surface Properties of Steel Slag Powder and High-Temperature Rheological Properties of Asphalt Mortar

In order to evaluate the feasibility of steel slag powder as filler,the coating properties of steel slag and limestone aggregate were compared by water boiling test,the micro morphology difierences between steel slag powder and mineral powder(limestone powder)were compared by scanning electron microscope(SEM),and the high-temperature rheological properties of asphalt mortar with difierent ratio of filler quality to asphalt quality(F/A)and difierent substitution rates of mineral powder(S/F)were studied by dynamic shear rheological test.The results show that the surface microstructure of steel slag powder is more abundant than that of mineral powder,and the adhesion of steel slag to asphalt is better than that of limestone.At the same temperature,the lower the ratio of S/F is,the greater the rutting factor and complex modulus will be.In addition,the complex modulus and rutting factor of the asphalt mortar increase with the increase of F/A,and the filler type and F/A have a negligible efiect on the phase angle.

Possibility of utilizing water-atomized Fe-Ni-Mo steel powder as base materials for warm compaction process

Water atomized Fe Ni Mo steel powder, was utilized as base powder for designing powder mixtures for warm pressing. The warm pressing and sintering behaviours of the powder mixtures were studied. The results show that, compared with the pressing at room temperature, the green density gain by warm pressing is within a range of 0.10 0.19 g/cm 3 and reduction in spring back is 30% 40% of the ambient, and maximum green density of 7.32 g/cm 3 at 735 MPa is obtained as the graphite mass fraction is 0.8%. It was found that sintered densities of the compacts were reduced slightly due to releasing of elastic stress stored in the compacts during sintering. The warm pressing of steel powders gives evidence for substituting the traditional double pressing and double sintering process.

Effect of Fine Steel Slag Powder on the Early Hydration Process of Portland Cement

Hydration heat evolution, non-evaporative water, setting time and SEM tests were peorormed to investigate the effect of fine steel slag powder on the hydration process of Portland cement and its mechanism. The results show that the effect of fine steel slag powder on the hydration process of Portland cement is closely related to its chemical composition, mineral phases, fineness, etc. Fine steel slag powder retards the hydration of portland cement at early age. The major reason for this phenomenon is the relative high content of MgO , MnO2, P2O5 in steel slag, and MgO solid solved in C3 S contained in steel slag.

Preparation of Reactive Powder Concrete Using Fly Ash and Steel Slag Powder

To decrease the cement and SF content of RPC by using ultra-fine fly ash （UFFA） and steel slag powder （SS）, the effect of these mineral admixtures on compressive strength of RPC were investigated. The experimental results indicate that the utilization of UFFA and SS in RPC is feasible and has prominent mechanical performance. The microstructure analysis （SEM and TG-DTG-DSC） demonstrated that the excellent mechanical properties of RPC containing SS and UFFA were mainly attributed to the sequential hydration filling effect of the compound system.

Experimental Research of Concrete with Steel Slag Powder and Zeolite Powder

In order to increase use ratio of steel slag solid waste,the concrete containing steel slag powder and zeolite powder as admixtures was prepared by using the orthogonal test method.The effects of water-binder ratio,sand ratio,steel slag powder content and zeolite powder on working properties,mechanical strength and chloride ion permeability of the concrete was studied.It was found that the early strength of the concrete had a decrease with the mixing of steel slag and zeolite powders,but its later strength approached to pure concrete.Moreover,the physical filling and pozzolanic activity of the admixtures increased the density of the concrete,resulting in the improvement of the durability of the concrete by the migration speed of Cl−reducing.The optimum mix ratio of C40 steel slag powder-zeolite powder concrete is obtained,and which had the slump of 220 mm,the 3 d,7 d and 28 d compressive strengths of 27.8 MPa,37.5 MPa and 48.4 MPa,the 6 h electric flux of 950 C and the diffusion coefficient of 1.65×10−12 m2/s.

Strength and Toughness of Steel Fibre Reinforced Reactive Powder Concrete Under Blast Loading

The blast resistance of structures used in buildings needs to be investigated due to the increased threat of a terrorist attack. The damage done by Composition B or Powergel to steel fibre reinforced reactive powder concrete （SFRPC） panels and ordinary reinforced concrete （RC） panels of equivalent static flexural strength is compared. A 0. 5 kg charge was detonated at a distance of 0. 1 m from the 1. 3 m × 1. 0 m × 0. 1 m （thick） panels, which were simply supported and spaning 1.3 m. Dynamic displacement measurements, high-speed video recording and visual examination of the panels for spall and breach were undertaken. The SFRPC panels withstood the bare charge blast better than the reinforced ordinary concrete panels. Neither type of panel was breached using a O. 5 kg charge, The RC panel exhibited more spalling when Composition B was used. Under successive Composition B loading conditions, the RC panel was breached. In comparison the SFRPC panel was not breached. Exposure to fragmenting charge loading conditions confirmed these performance differences between the SFRPC panel and the reinforced ordinary concrete panel.

Preparation of high nitrogen and nickel-free austenitic stainless steel by powder injection molding

High nitrogen and nickel-free austenitic stainless steel has received much recognition worldwide because it can solve the problem of ＂nickel-allergy＂ and has outstanding mechanical and physical properties. In this article, 0Cr17Mn11Mo3N was prepared by powder injection molding （PIM） technique accompanied with solid-nitriding. The results show that the critical solid loading can achieve up to 64vol% by use of gas-atomized powders with the average size of 17.4 μm. The optimized sintefing conditions are determined to be 1300℃,2 h in flowing nitrogen atmosphere, at which the relative density reaches to 99% and the N content is as high as 0.78wt%. After solution annealing at 1150℃for 90 rain and water quench, the 0.2% yield strength, ultimate tensile strength （UTS）, elongation, reduction in area, and hardness can reach as high as 580 MPa, 885 MPa, 26.0%, 29.1%, and Hv 222, respectively.

Effect of inclusion on high cycle fatigue response of a powder metallurgy tool steel

The high cycle fatigue response of a high V-alloyed powder metallurgy tool steel （AISI 11） with different inclusion sizes was studied. Two materials of this grade at a similar hardness of about HRC 60 were subjected to axial loading fatigue tests, tensile tests and fracture toughness measurements to investigate their mechanical properties. Large inclusion above 70 ~rn is indicated to be responsible for the tensile fracture which happens before yielding. The fatigue strength obtained up to 107 cycles is found to decrease from approximately 1 538 MPa to 1000 MPa with the inclusion size increasing above 30 Izm. The internally induced crack initiation is mainly attributed to the surface compressive residual stress of 300-450 MPa. Fractographic evaluation demonstrates that the crack initiation and propagation controlling factors of the two materials are almost the same, indicating that the two factors would be insignificantly affected by the inclusion size level. Paris sizes of the two materials both show a tendency to decrease as the ratio of stress intensity factor of crack origin to factor of fish-eye increases. The investigation into the relationship between stress intensity factors and fatigue life of the two materials further indicates that the high cycle fatigue behavior of AISI 11 is controlled by crack propagation.

Effects of Steel Slag Powder on Workability and Durability of Concrete

The workability and durability of a type of sustainable concrete made with steel slag powder were investigated. The hydrated products of cement paste with ground granulated blast furnace slag（GGBFS） alone or with a combined admixture of GGBFS-steel slag powder were investigated by X-ray diffraction（XRD）. Furthermore, the mechanism of chemically activated steel slag powder was also studied. The experimental results showed that when steel slag powder was added to concrete, the slumps through the same time were lower. The initial and fi nal setting times were slightly retarded. The dry shrinkages were lower, and the abrasion resistance was better. The chemically activated steel slag powder could improve compressive strengths, resistance to chloride permeation and water permeation, as well as carbonization resistance. XRD patterns indicated that the activators enhanced the formation of calcium silicate hydrate（C-S-H） gel and ettringite（AFt）. This research contributes to sustainable disposal of wastes and has the potential to provide several important environmental benefi ts.

Effect of inclusion size on the high cycle fatigue strength and failure mode of a high V alloyed powder metallurgy tool steel

The fatigue strength of a high V alloyed powder metallurgy tool steel with two different inclusion size levels, tempered at different temperatures, was investigated by a series of high cycle fatigue tests. It was shown that brittle inclusions with large sizes above 30μm prompted the occurrence of subsurface crack initiation and the reduction in fatigue strength. The fracture toughness and the stress amplitude both exerted a significant influence on the fish-eye size. A larger fish-eye area would form in the sample with a higher fracture toughness subjected to a lower stress amplitude. The stress intensity factor of the inclusion was found to lie above a typical value of the threshold stress intensity factor of 4 MPa.m^1/2. The fracture toughness of the sample with a hardness above HRC 56 could be estimated by the mean value of the stress intensity factor of the fish-eye. According to fractographic evaluation, the critical inclusion size can be calculated by linear fracture mechanics.

Study on rapid stabilization of steel slag powder

Dry ball milling and wet ball milling were used to treat converter slag with particle size < 10 mm and the converter slag powder was stabilized by H_2O only and H_2O coupled with CO_2.respectively.Results showed that when CO_2 &H_2O was used,the free-calcium oxide(f-CaO) content in converter slag decreased significantly and after an-hour treatment the f-CaO content was reduced to 3%;however,when only treated by H_2O without CO_2, f-CaO needed 3-hour stabilization to decrease its content to 3%.When f-CaO in converter slag powder was treated by CO_2 &H_2O,its main reaction products were CaCO_3 and then Ca(OH)_2;however,when only H_2O was used, the f-CaO content decreased gently and the main products were Ca(OH)_2.

Wear and mechanical properties of carburized AISI 8620 steel produced by powder metallurgy

The effect of carburization on the tensile strength and wear resistance of AISI 8620 steel produced via powder metallurgy was investigated.Alloys 1 and 2(with 0.2wt%C and 0.25wt%C,respectively)were first pressed at 700 MPa and then sintered at 1300,1400,or 1500℃for 1 h.The ideal sintering temperature of 1400℃was determined.Afterward,Alloys 1 and 2 sintered at 1400℃were carburized at 925℃for 4 h.The microstructure characterization of alloys was performed via optical microscopy and scanning electron microscopy.The mechanical and wear behavior of carburized and noncarburized alloys were investigated via hardness,tensile,and wear tests.After carburization,the ultimate tensile strength of Alloys 1 and 2 increased to 134.4%and 138.1%,respectively.However,the elongation rate of Alloys 1 and 2 decreased to 62.6%and 64.7%,respectively.The wear depth values of Alloy 2 under noncarburized and carburized conditions and a load of 30 N were 231.2 and 100.1μm,respectively.Oxidative wear changed to abrasive wear when the load transitioned from 15 to 30 N.

Effects of copper content on the shell characteristics of hollow steel spheres manufactured using an advanced powder metallurgy technique

Metallic hollow spheres are used as base materials in the manufacture of hollow sphere structures and metallic foams. In this study, steel hollow spheres were successfully manufactured using an advanced powder metallurgy technique. The spheres＇ shells were characterized by optical microscopy in conjunction with microstructural image analysis software, scanning electron microscopy（SEM）, energy-dispersive X-ray spectroscopy（EDX）, and X-ray diffraction（XRD）. The microscopic evaluations revealed that the shells consist of sintered iron powder, sintered copper powder, sodium silicate, and porosity regions. In addition, the effects of copper content on various parameters such as shell defects, microcracks, thickness, and porosities were investigated. The results indicated that increasing the copper content results in decreases in the surface fraction of shell porosities and the number of microcracks and an increase in shell thickness.

Mechanical Properties of Powder Based Steel used as Backing Plate in Heavy Duty Brake Pad Manufacturing

The aims of the present study is to develop a powder based steel used as backing plate for heavy duty brake pad applications. Three powder based back plate steel compositions namely B1 (C- 0.3, Cu – 1.5, P -0.3, Fe – 97.9), B2 (C- 0.1, Cu – 2.5, SiC-1, Fe – 96.4) and B3(C- 0.5, Cu – 2.5, SiC-1, Fe – 96.0) were prepared using a hot powder preform forging technique. The forged samples are of (25× 50×10 mm3) dimensions. These samples were hot rolled and annealed to relieve the residual stresses. These samples were characterized in terms of microstructure, porosity content/densification, hardness and tensile properties. Densification as high near to theoretical density has been realized. Hot powder preform forging using closed die showed better densification. Rolled and annealed microstructure showed lesser porosity content than the forged one. Phosphorous causes hardening of ferrite in solid solution with iron. Compositions B1, showed reasonable elongation and it improved further on annealing. It was observed in this present investigation that, the addition, such as SiC and Cu caused increase in strength. Steel developed in the investigation are used as powder based backing plate in Manufacturing of iron based brake pads used in heavy duty applications.

Development and application of fluorine-free mold powder for low carbon steel

Fluorine in mold powder is known as harmful to human health and the environment. Being the advocate of green production, Baosteel developed an environmentally friendly mold powder without fluorine. The main problem of fluorine-free flux film is small heat resistance and thus the heat transfer intensity of the mold is too large, which to some extent hinders the increase of the casting speed. With the heat flow simulation equipment, controlling precipitation of crystal in flux and solidification temperature properly, fluorine-free mold powder for low carbon steel,which substitutes F with B203 ,was successfully developed and applied in industrial production. The production results show that, by using boronic fluorine-free mold powder,the boron increment in molten steel is less than 1.3ppm for conventional aluminium killed low carbon steel.

Sintering Mechanism of Stainless Steel in Powder Injection Molding

Stainless steel samples were made by Powder injection Molding (PIM) process with-400 mesh powder in order to investigate the sintering mechanism in this system and develop the PIM of stainless steels. The process included mixing, injection molding, debin- ding and sintering. Neck growth model was used to analyze the sintering mechanism. The results show that lattice (volume) diffusion is the main mechanism in the sintering process, the products with higher density (>95%) and properties are obtained. At lower temperatures, grain boundary diffusion may play a role in the sintering densification.