Fe Bal Research Articles

Laser-Directed Energy Deposition of Dissimilar Maraging Steels with a Defect-Free Interface: Design for Improved Surface Hardness and Fracture Toughness

Maraging steels are a class of low-carbon ultra-high-strength martensitic steels. Due to their excellent weldability, these steels have been widely applied for laser-based additive manufacturing (AM). MAR-60HRC is a newly developed maraging grade for AM with a nominal chemical composition of 13.0Ni-15.0Co-10.0Mo-0.2Ti, Fe bal. (wt%), capable of achieving hardness levels of ~ 740 HV. Alternatively, 18Ni300 is a commercialized maraging steel with an excellent combination of strength and toughness at the peak aged hardness (i.e., ~ 590 HV). This work aims to investigate the properties and microstructure of MAR-60HRC fabricated by Laser Directed Energy Deposition (L-DED). Further, the manufacturability of bimetallic parts comprising a tough 18Ni300 core and a hard MAR-60HRC on the surface was evaluated. After proper aging, the multi-layered material showed a surface hardness of ~ 720 HV1 and apparent fracture toughness of 71 MPa m1/2, higher than that of MAR-60HRC (i.e., 60 MPa m1/2), and lower than 18Ni300 (i.e., 90 MPa m1/2). The excellent combination of surface hardness and fracture toughness was discussed, considering the crack arrest at the interface and the flawless interface between the two steels.Graphical

Stress Distributions in P91 Martensitic Steel and in AISI 316LN Steel Welds for Gen IV Nuclear Applications

Neutron diffraction has been used to investigate the stress field in two different welds developed for nuclear applications, namely those obtained by tungsten inert gas welding of P91 martensitic steel (Cr 9, Mn 6, Mo 1, C 0.1, and Fe bal wt %) and hybrid (laser beam and gas metal arc) welding of AISI316LN austenitic steel (17.8 Cr, 12.3 Ni, 1.7 Mn, 2.4 Mo, 0.3 Si, and Fe bal wt %). The sizes of the investigated samples were 100 × 50 × 12 mm for the P91 weld and 220 × 160 × 15 mm for the 316LN weld; unstrained references were prepared for both welds. The neutron diffraction measurements have been carried out utilizing the E3 diffractometer at the BER II reactor in Berlin, with a gauge volume of 2 × 2 × 2 mm3. Lines perpendicular to the weld direction were scanned at different depths inside the material and at different distances from the weld centerline, including the heat affected zone and the weld centerline. Strain and stress values were determined in the three principal directions. In the TIG P91 weld, the stresses are almost completely relieved after a post weld heat treatment for 2 h at 760°C. In the laser beam and gas metal arc 316LN weld not submitted to post weld heat treatment, nearly balancing longitudinal and transverse stress components as high as 300–350 MPa are found within a range of approximately 3 mm around the centerline of weld.

Effect of Applied Stress on Pitting Corrosion Behavior of Type 304 Stainless Steel in Chloride Environment

Stainless steels are widely used in structural applications due to their superior corrosion resistance. However, stainless steels sometimes suffer from pitting corrosion and stress corrosion cracking in chloride environments. It was reported that applied stress promoted pitting corrosion and changed the morphology of pitting corrosion 1. Moreover, it is known that stress corrosion cracking is often initiated at pits in stress environment 2. Elucidating the effect of applied stress on pitting corrosion behavior is important to make clear the initiation mechanisms of the stress corrosion cracking of stainless steels. As yet, however, the effect of applied stress on pitting corrosion behavior remains unclear. A commercial AISI 304 (18Cr-8Ni) austenitic stainless steel sheet was used in this study. The chemical composition is shown in mass percentages: 0.06% C, 0.39% Si, 1.11% Mn, 0.029% P, 0.0026% S, 8.02% Ni, 18.0% Cr, 0.13% Mo, 0.22% Cu, 0.002% Ti, 0.002% Al, 0.038% M, 0.003% O, Fe bal. The 0.2% proof stress of the steel was 222 MPa. This steel was heat-treated at 1373 K for 30 min and then quenched in water as solution treatment. Sensitization was conducted by annealing the steel at 923 K for 2 h and then quenching in water after the solution treatment. After these heat-treatments, the surfaces of specimens were successively polished with a diamond paste down to 1 μm. Potentiodynamic anodic polarization measurements were carried out in 0.01 M, 0.1 M, 1M, 4 M MgCl2 solution to clarify the effect of chloride concentration on pitting corrosion. All the potentials reported in this study refer to an Ag/AgCl (3.33 M KCl) electrode. The electrode areas were ca. 10 mm ×10 mm. The potential scan rate as was set at 23 mV / min. Figure 1 shows the polarization curves of the solution-treated steel under no applied stress, and the morphology of pitting corrosion after polarization. As shown in Fig. 1a, the pitting potential decreased with chloride concentration. In 0.01 and 0.1 M MgCl2 solutions, a small pit with a lacy metal cover was initiated. On the other hand, a large shallow pit was generated in 4 M MgCl2. To analyze the effect of applied stress on the pitting corrosion behavior and the morphology of pitting corrosion, micro-electrochemical measurements were utilized. As a result of preliminary experiments of solution-treated steels, pitting corrosion always occurred in 4 M MgCl2 solution when the electrode area was 1 mm × 1 mm. Therefore, experiments were conducted at the condition that the electrode area was 1 mm × 1 mm. The effect of applied stress on the pitting corrosion behavior was analyzed in 4 M MgCl2 at 298 K. During potentiodynamic anodic polarization, the potential scan was stopped after pit initiation. After that, the specimen was left at open circuit potential for 2 days under applied stress. The applied stress was 80% of 0.2% proof stress. Figure 2 shows the change of the corrosion potential with time. It was observed that the corrosion potential increased with time. From the surface observation, no crack occurred in this study. It was suggested that the effect of temperature is also the important factor affecting the initiation of the pit-induced stress corrosion cracking of austenitic stainless steels. References N. Shimahashi, I. Muto, Y. Sugawara, N. Hara, J. Electrochem. Soc., 161 (2014), C494-C500H. Masuda, Corros. Sci., 49 (2007), 120-129 Figure 1

Sintering of AISI M<sub>2</sub> High Speed Steel with the Addition of NbC

The influence of adding 6 wt% (NbC) niobium carbide on the sintering temperature and microstructure of high speed steel - AISI M2(0.87% C, 5.00% Mo, 6.00% W, 4,00% Cr, 2.00% V and Fe bal.) powder was studied. The starting material was obtained by vacuum melting followed by atomization in water. The samples were axially cold compacted in a cylindrical matrix and then vacuum sintered at 1250 and 1350 °C. Dilatometry and differential scanning calorimetry measurements indicated an increase in sintering temperature with addition of niobium to the AISI M2steel. Optical and scanning electron microscope observations revealed a microstructure with uniformly distributed niobium carbides.

The mechanism of enhanced magnetic properties of sintered permanent magnets by substitution of Pr for Nd

In this study, the influence of substitution of Nd with Pr on the magnetic of sintered permanent magnets was investigated. The samples were prepared by traditional powder metallurgical technique. The nominal composition of the alloys is (Nd 1− x Pr x ) 29Dy 1.3R 3.1Fe bal (R = Al 0.3Cu 0.2 Co 1.5 B 1Zr 0.1, wt%) with x varying from 0 to 1 in steps of 0.2. Experimental results show that the overall magnetic properties, especially the intrinsic coercivity and thermal stability of the magnets, could be improved by substituting Nd with Pr in the magnets. When the Pr replaces all Nd in the magnets, excellent performance magnets with Br = 13.65 KGs, Hcj = 22.13 KOe, (BH) max = 46.1 MGsOe are obtained with a low Dy content (1.3 wt%).

Investigation of microstructural evolution under neutron irradiation in Eurofer97 steel by means of small-angle neutron scattering

Small-angle neutron scattering (SANS) has been utilized to investigate in Eurofer97 steel (9Cr, 0.01C, 1W, 0.2V Fe bal wt%) the microstructural effect of neutron irradiation at 300 °C up to a dose level of 8.4 dpa. For each irradiated sample an unirradiated reference was measured to distinguish as accurately as possible the actual effect of the neutron irradiation. The SANS measurements were carried out at the D22 diffractometer at the High-Flux Reactor of the Institut Max von Laue–Paul Langevin, Grenoble, France. Analysing separately the nuclear and magnetic SANS components obtained after subtraction of the reference from the irradiated sample it appears that the microstructural inhomogeneities produced under such irradiation conditions are non-magnetic ones, such as microvoids. Their size distributions are presented and compared with those previously obtained for the same steel irradiated at 2.5 dpa: with increasing the dose, the volume fraction is increased by a factor of 2 roughly, while the average size of these inhomogeneities remains nearly unchanged.

LIGAS AÇO MATRIZ + NbC - CARACTERIZAÇÃO

This work is part of a research line in which the “matrix steel concept + NbC” is used to develop alloys with the AISI M2 high speed steel matrix (Fe bal. - 0.5 wt%C – 2 wt%W – 3 wt%Mo – 4.6 wt%Cr – 1 wt%V) and different volume fractions of niobium carbides. Five alloys were cast to obtain one with the matrix of the AISI M2 HSS composition and the others with Niobium (2.5% and 5%) and stoichiometric carbon to produce NbC carbides. Titanium was added in 0.1wt% to modify de NbC carbides morphology. The alloys were characterized by optical microscopy and scanning electron microscopy. The alloys microstructures are correlated to phase equilibrium diagrams and Scheil solidification diagrams, calculated with the CALPHAD methodology, allowing to define the alloys solidification path. It is verified a good correlation between the equilibrium and Scheil solidification diagrams and the as cast microstructure

Development of brazing foils to join monocrystalline tungsten alloys with ODS-EUROFER steel

Results on rapidly solidified filler metals for brazing W with W and monocrystalline W with EUROFER steel (FS) are presented. Rapidly quenched powder-type filler metals based on Ti bal–V–Cr–Be were developed to braze polycrystalline W with monocrystalline W. In addition, Fe bal–Ta–Ge–Si–B–Pd alloys were developed to braze monocrystalline W with FS for helium gas cooled divertors and plasma-facing components. The W to FS brazed joints were fabricated under vacuum at 1150 °C, using a Ta spacer of 0.1 mm in thickness to account for the different thermal expansions. The monocrystalline tungsten as well as the related brazed joints withstood 30 cycles between 750 °C/20 min and air cooling/3–5 min.

Microstructural investigation, using small-angle neutron scattering (SANS), of Optifer steel after low dose neutron irradiation and subsequent high temperature tempering

The microstructural effect of low dose neutron irradiation and subsequent high temperature tempering in the reduced activation ferritic/martensitic steel Optifer (9.3 Cr, 0.1 C, 0.50 Mn, 0.26 V, 0.96 W, 0.66 Ta, Fe bal wt%) has been studied using small-angle neutron scattering (SANS). The investigated Optifer samples had been neutron irradiated, at 250 °C, to dose levels of 0.8 dpa and 2.4 dpa. Some of them underwent 2 h tempering at 770 °C after the irradiation. The SANS measurements were carried out at the D22 instrument of the High Flux Reactor at the Institut Max von Laue – Paul Langevin, Grenoble, France. The differences observed in nuclear and magnetic SANS cross-sections after subtraction of the reference sample from the irradiated one suggest that the irradiation and the subsequent post-irradiation tempering produce the growth of non-magnetic defects, tentatively identified as microvoids.

Homogeneity of Hcj in Sintered Bulk Nd-Fe-B Magnets

High performance magnets not only have high magnetic properties, but also have good homogeneity. The homogeneous of Nd 14.2Dy xAl 0.8Cu 0.1B 6.2Fe bal. bulk magnets was studied. The sizes of the samples produced by conventional sintering process were 53 × 50.5 × 25.3/40.2/50.4/61.0 mm. The magnetic character and microstructure of the samples were determined by NIM-10000H hysteresigraph, optical metaloscope, and SEM respectively. The results show that the H cj reduces with increasing C content at the same process parameters. And the H cj shows dependence not only on the ageing processing but also on the size of the bulk and loading capacity etc. The H cj increases with prolonging ageing time and the ageing time should be different with different size of the bulk. With the increase of the loading capacity, the H cj reduces promptly and is very inhomogeneous. The microstructure of the samples shows that the grain of the hard magnetic phase is finer and the neodymium-rich boundary is distributed homogeneously with prolonging ageing time. And so is the sample in a small amount of the bulks.

塩化鉄（ＩＩＩ）系溶液でエッチング中のアンバー合金の腐食電位と表面粗さの関係

A relationship between corrosion potential and surface finish of Invar (Ni36%-Fe bal. alloy) etched in ferric chloride solutions was studied.The Invar was attached to a rotating disk electrode equipment. The rotation rate was set at 1600rpm in order to approximate the actual etching process. A principal ingredient of etchants was FeCl3. The concentration of FeCl3, FeCl2, free HCl and Ni2+ were 40 to 48mass%, 1.87±0.08mass%, 0.20±0.04m (molality) and 0.43±0.02m, respectively. The temperature was maintained at 60 to 80°C.We found a strong correlation between the surface finish and corrosion potential of Invar. When it was more noble than 200mV (SHE), the surface finish was smooth, while a rough finish was observed at less noble than 150mV. The difference of surface finish was shown distinctly in SEM photographs.

Hot deformed HDDR NdFeB permanent magnets

Abstract Isotropic fine-grained Nd 1.65 Fe bal. Ga 0.6 B 6 was prepared by the HDDR process. Permanent magnets obtained by die upsetting of the HDDR material show a remanence of 1.1 T and a coercivity μ 0 J H c of 0.9 T. The hot deformation is dominated by a diffusion supported resolution process. The activation energy of this process is about 200 kJ/mol and the stress exponent is n ≈ 1.

Relation between magnetic properties and crystallographic texture of columnar Alnico 8 permanent magnets

The purpose of this work is to correlate solidification rate during a controlled cooling and magnetic properties of columnar Alnico 8 or Ticonal 1500 (Al 7.5%, Ni 14%, Co 35%, Cu 3%, Ti 4.3%, Nb 1.2%, Fe bal). Our investigations involved a controlled solidification with vertical zone melting furnace, micrographic examinations of the specimens, and magnetic measurements of the specific energy product, (BH)_{\max} . In order to study the texture of the different samples we have carried out X-ray diffraction experiments using SCHULZE's method, with an automatic pole figure recorder developped by RUER. At freezing rate of 0.7 cm/hr and a temperature gradient of about 150 K/cm we obtain single crystal structure. For medium freezing rate the samples show dendritic structures with disappear utterly after heat treatments. The dendritic grains may have various orientations. For high freezing rates (> 9 cm/hr) the crystals are well oriented : the directions are parallel to the sample longitudinal axis. After heat treatment the specific energy product (B.H)_{\max} reaches 10 MG.Oe ; ( B.\mu_{o}H = 79.5 kJ/m3.

MT磁石の製造における熱処理の研究

The results of fundamental researches on MT magnet (C 2.0%, Al 8.15% and Fe bal.) were already reported. In this report, the most appropriate condition for heat treatment was investigated in the course of industrialization for commercial production. The optimum temperature of quenching for magnetic properties and yielding rate of heat treatment is between 1210 and 1250°. Coating with charcoal and cementing materials is effective in preventing decarburization at requenching. The soundness of casting as well as their size and alloying elements constitute an important factor in relation with hardening cracks. With interrupted quenching, hardening cracks are smaller than in the case of the usual quenching process, but derogation of magnetic properties is more remarkable. MT magnet steel reduces its hardness so much as to become machinable by means of annealing at 800°C.