Boriding kinetics of H13 steel

It is known that boriding has been employed to increase the service life of parts such as orifices; ingot molds, and dies for hot forming made of AISI H13 steel. In this study, case properties and kinetics of borided AISI H13 steel have been investigated by conducting a series of experiments in Ekabor-I powders at the process temperature of 1073, 1173 and 1273 K for periods of 1-5 h. The presence of borides FeB and Fe₂B of steel substrate was confirmed by optical microscopy and scanning electron microscopy (SEM). The results of this study indicated that the morphology of the boride layer has a smooth and compact morphology, and its hardness was found to be in the range of 1650-2000 HV. Transition zone observed between the hard boride coating and the matrix was relatively softer than the substrate. The kinetics of boriding shows a parabolic relationship between layer thickness and process time, and the calculated activation energy for the process is 186.2 kJ/mol. Moreover, boriding parameter BOP, which is only a function of boride layer thickness and activation energy, has been suggested for the prediction of layer thickness in boriding of AISI H13. There is a reasonable correlation between the progress of boride layer thickness and proposed time-temperature-compensated parameter. Similar findings have been found when it is applied to another steels including tool and low alloy steels, as well as Armco iron.     

Diffusion kinetics of borided AISI 52100 and AISI 440C steels

In this study, the case properties and diffusion kinetics of AISI 440C and AISI 52100 steels borided in Ekabor-II powder were investigated by conducting a series of experiments at temperatures of 1123, 1173 and 1223 K for 2, 4 and 8 h.The boride layer was characterized by optical microscopy, X-ray diffraction technique and micro-Vickers hardness tester. X-ray diffraction analysis of boride layers on the surface of the steels revealed the existence of FeB, Fe₂B and CrB compounds.The thickness of boride layer increases by increasing boriding time and temperature for all steels. The hardness of the boride compounds formed on the surface of steels AISI 52100 and AISI 440C ranged from 1530 to 2170 HV_0.05 and 1620 to 1989 HV_0.05, respectively whereas Vickers hardness values of untreated steels AISI 440C and AISI 52100 were 400 HV_0.05 and 311 HV_0.05, respectively. The activation energies (Q) of borided steels were 340.426 kJ/mol for AISI 440C and 269.638 kJ/mol for AISI 52100. The growth kinetics of the boride layers forming on the AISI 440C and AISI 52100 steels and thickness of boride layers were also investigated.     

Investigation of diffusion kinetics of plasma paste borided AISI 8620 steel using a mixture of B 2 O 3 paste and B 4 C/SiC

In the present study, AISI 8620 steel was plasma paste borided by using various B₂O₃ paste mixture. The plasma paste boriding process was carried out in a dc plasma system at temperatures of 973, 1023 and 1073 K for 2, 5 and 7 h in a gas mixture of 70% H₂ -30% Ar under a constant pressure of 10 mbar. The properties of the boride layer were evaluated by optical microscopy, X-ray diffraction, Vickers micro-hardness tester and the growth kinetics of the boride layers. X-ray diffraction analysis of boride layers on the surface of the steel revealed FeB and Fe₂B phases. Depending on temperature and layer thickness, the activation energies of boron in steel were found to be 124.7 kJ/mol for 100% B₂O₃.     

Electrochemical boriding and characterization of AISI D2 tool steel

D2 is an air-hardening tool steel and due to its high chromium content provides very good protection against wear and oxidation, especially at elevated temperatures. Boriding of D2 steel can further enhance its surface mechanical and tribological properties. Unfortunately, it has been very difficult to achieve a very dense and uniformly thick boride layers on D2 steel using traditional boriding processes. In an attempt to overcome such a deficiency, we explored the suitability and potential usefulness of electrochemical boriding for achieving thick and hard boride layers on this tool steel in a molten borax electrolyte at 850, 900, 950 and 1000 °C for durations ranging from 15 min to 1 h. The microstructural characterization and phase analysis of the resultant boride layers were performed using optical, scanning electron microscopy and X-ray diffraction methods. Our studies have confirmed that a single phase Fe₂B layer or a composite layer consisting of FeB + Fe₂B is feasible on the surface of D2 steel depending on the length of boriding time. The boride layers formed after shorter durations (i.e., 15 min) mainly consisted of Fe₂B phase and was about 30 μm thick. The thickness of the layer formed in 60 min was about 60 μm and composed mainly of FeB and Fe₂B. The cross sectional micro-hardness values of the boride layers varied between 14 and 22 GPa, depending on the phase composition.     

Enhancement of wear and corrosion resistance of metal-matrix composites by laser coatings

A novel technique based on laser-induced chemical reduction of metal salts has been developed to produce surface coatings on metal-matrix composites (MMCs). The substrate is predeposited with a paste, containing concentrated salts of the elements to be coated along with a thickening agent, and then subjected to high power laser radiation. The rise in surface temperature during laser irradiation led to the decomposition of salts to their native metals. The combination of metal and metalloid elements in the reaction zone forms an amorphous layer due to the specific chemical ratio and rapid cooling rate. The thickness of the coatings obtained were of the order of 50–100 m. The coatings exhibited amorphous and microcrystalline structures, possessed hardness in the range of 300–1700 H_v (substrate hardness 80–90 H_v), had superior sliding wear resistance and excellent corrosion resistance. The advantages of this process include the formation of complex coatings on MMCs by a simple, versatile technique which does not require any vacuum or inert atmosphere.     

Metallurgical and acoustical comparisons for a brass pan with a Caribbean steel pan standard

The development and fabrication of -brass pans, including the sinking of the pan head in the traditional manner using a hammer and patterning musical notes and their turning is compared with a low-carbon steel (Caribbean-type) pan as a standard. In this study these experimental pans are fabricated by welding the -brass or low-carbon steel platforms to a low-carbon steel hoop and side metal or skirt. These pans are 2.54 cm larger in diameter than pans traditionally fabricated from 55-gallon barrels. The corresponding pan head materials are examined by optical and electron microscopy and hardness profiles are measured as well. Deformation is shown to influence the acoustic response of ideal, flat, circular discs of both the -brass and low-carbon steel as well as 316L stainless steel. The frequency-amplitude-time spectra for common octave ranges are compared and chromatic tones are shown for the -brass as well as the low-carbon steel standard. These results indicate that a wide range of hard metals or alloys can be used to produce musical pan instruments.     

Annealing behaviour of amorphous Fe80B20 on continuous heating

Resistance measurements during direct heating of Fe₈₀B₂₀ amorphous alloys indicate phase changes occur at 395, 500, 720 and 840° C. Samples heated to these temperatures, and maintained for five minutes in a neutral atmosphere, show that a hardness maximum occurs at the crystallization temperature of 395° C and that annealing at 500° C produces a material with the same hardness. Above 500° C the microhardness is seen to drop below that of the amorphous alloy. Saturation magnetization measurements show a steady increase following each anneal, up to a temperature of 720° C, and the rate of increase is seen to drop in the range of 720 to 840° C. X-ray diffraction studies show that only a small fraction of the matrix is crystallized following the anneal at 395° C and the transformed phases are -Fe and Fe₃B. Following annealing at 500° C, an increased proportion of -Fe and Fe₃B are observed with complete crystallinity while samples heattreated at 720° C are seen to consist of a three-phase mixture of -Fe, Fe₂₃B₆ and Fe₂B. Annealing at 840° C is seen to produce an equilibrium phase mixture of -Fe and Fe₂B phases. Only in the sample annealed at 395° C is a fraction of the amorphous phase seen to persist, indicating that a 5 min anneal is not sufficient, at this temperature, to induce complete crystallization. These structural features are corroborated by field ion microscope analyses, made at liquid nitrogen temperature in a medium of pure neon, and scanning electron microscopy, and are also consistent with our earlier study involving the isothermal annealing, for various times, of Fe₈₀B₂₀ alloy at 780° C.     

Fe-Si-B amorphous alloys with high silicon concentration

Amorphous phase formation with good ductility has been found in Fe-Si-B ternary alloys with high silicon concentration using a melt-spinning technique. The formation range of these amorphous alloys is in the range 0 to 29 at % silicon and 5 to 26 at % boron, being much wider than the previously reported range (0 to 19 at % silicon and 10 to 26 at % boron). The crystallization temperature (T _x) and Vickers hardness (H _v) of the Fe-Si-B amorphous alloys containing more than 19 at % silicon increase significantly with increasing boron content, while the increase in silicon content causes a decrease inT _x andH _v. TheT _x andH _v of Fe₆₆Si₂₈B₆ alloy with the highest silicon concentration are 740 K and 500 DPN, respectively. The decreases inT _x andH _v with silicon content are interpreted owing to the increase in the contribution of the repulsive interaction between silicon and silicon against the attractive interactions between iron and silicon or boron. Furthermore, the silicon-rich amorphous phase has been found to crystallize by the almost simultaneous precipitation of the two equilibrium compounds of Fe₃Si and Fe₂B, Fe₂Si_0.4B_0.6 or Fe_4.9Si₂B.     

The growth kinetics of borides formed on boronized AISI 4140 steel

The growth kinetics of boride layer on boronized AISI 4140 steel is reported. Steel samples were boronized in molten borax, boric acid and ferro-silicon bath at 1123, 1173 and 1223 K for 2, 4, 6 and 8 h, respectively. The morphology and types of borides formed on the surface of AISI 4140 steel substrate were analyzed by means of optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction analysis (XRD). The boride layer thickness ranged from 38.4 to 225 μm. Iso-thickness diagrams for pre-determined thickness according to treatment time and temperature, were graphed by MATLAB 6.0 software. The hardness of borides formed on the samples changed between 1446 and 1739 HV_0.1, according to treatment time and temperature. Layer growth kinetics way analyzed by measuring the extent of penetration of FeB and Fe₂B sublayers as a function of treatment time and temperature in the range of 1123-1223 K. For practical use, an iso hardness diagram was established as a function of treatment time, temperature and boride layer thickness. The depth of the tips of the most deeply penetrated FeB and Fe₂B needles were taken as measures for diffusion in the growth directions. The kinetics of the reaction, were also determined by varying the treatment temperature and time. The results show that K increased with boronizing temperature. The activation energy (Q) was formed to be 215 kJ mol⁻¹. The growth rate constant (K) ranged from 3×10⁻⁹ to 2×10⁻⁸ cm²s⁻¹.     

A Comparison of the performance and wear characteristics of high-speed steel circular saw blades machining Nimonic PK31, AISI O1 Tool Steel, Inconel 600L, and AISI 1018 Carbon Steel

High-speed steel circular saw blades are widely used in industry for a variety of cut-off operations that require a combination of high-dimensional accuracy and a good-quality surface finish. The authors have been involved in an extensive programme of work to evaluate the effectiveness of applying advanced surface engineering treatments to enhance the performance and life characteristics of this form of tool. The work included optimizing cutting conditions with respect to tool performance when machining different workpiece materials, characterizing the wear mechanisms developed throughout tool life, and evaluating of the effect of different substrate surface preparations and advanced surface engineering treatments on the performance and wear characteristics of the tool.One interesting feature to arise from the work that has not been reported elsewhere has been the notable variation in performance and wear characteristics of nominally identical tools machining materials with similar hardness. The current paper compares the performance and wear characteristics of high-speed steel circular saw blades machining a tool steel and a nimonic nickel-based alloy (340–390 H_v. These are termed difficult to cut materials because of their poor machinability. A comparison is also made of the performance and wear characteristics of an Inconel nickel-based alloy and a low-carbon steel (120–150 H_v), both of which exhibit good machining characteristics. Differences identified between the resulting wear mechanisms emphasize the difficulties inherent in developing a universal tooth geometry and advanced surface engineering coating system that would be effective for all machining applications.     

Phase investigation in laser surface alloyed steels with TiC

Laser technology enables melting and alloying specimen surfaces without the substrate itself being heated, whereby surfaces with special attributes are obtained with the properties of the substrate remaining unaffected. The surfaces of Armco iron and AISI 1045 steel were laser-alloyed with TiC powder, a CO₂ laser of 2.5 kW maximum power being used. Optimal laser and powder-feed parameters were established. Particles of TiC were injected into the molten surface layer, forming a composite material, steel + TiC. The microstructures were investigated metallographically. Some of the particles had partially melted during their passage through the laser beam and had re-solidified, forming small and fine dendrites. Phase identification by X-ray diffraction revealed the presence of -Fe, martensite, and Fe₃C phases, as well as amounts of stochiometric TiC and unknown phases. Identification of phases by TEM and diffraction of electrons revealed the presence of unknown phases, such as tetragonal TiC and (FeTi)C. Mössbauer results show ternary Fe-Ti-C phases, which can be related to the TEM and X-ray diffraction results. A correlation was found between the substrate's composition, microstructures, and the different phases present.     

X-ray microanalysis and properties of multicomponent plasma-borided layers on steels

The structure and chemical composition of composite and multicomponent borided layers obtained by a new method that combines the chemical electroless and plasma boriding techniques are described. Quantitative X-ray microanalysis examinations show that on the surface of nickel–phosphorus coated steel borided at 923 K three boride phases of the type (Ni _x Fe_{1 – x} )₄B₃, (Ni _x Fe_{1 – x} )₂B and (Fe _x Ni_{1 – x} )B formed, whereas in the samples borided at 1123 K only two borides (Fe_{1 – x} Ni _x )B and (Fe_{1 – x} Ni _x )₂B are present. The shape and the distribution of the phases depends on the thickness of the Ni–P layer deposited on the steel substrate before boriding. The thicknesses of boride zones obtained on nickel coated steels are much greater than those obtained on the same steel without nickel coating. Also the diffusion zone between the Ni–P layer and the steel increases during boriding, which improves the adhesion of the layer to the substrate. The composite layers obtained show a high wear resistance, with their resistance to corrosion being markedly greater than that of uncoated and only borided steel.     

Surface structure of boride layers grown on Fe-C-Ni alloys

Three Fe-C-Ni synthetic alloys differing in Ni content have been produced, powder borided for 15 h at 850° C with a B₄C-base mixture and then characterized by using surface Mössbauer spectroscopy, X-ray diffraction, metallography and microhardness measurements. The nature and disposition of the interaction products, boriding depths and hardness values of the predominant boride Fe₂B have been determined. The role of the Ni content in the alloy on the boriding process has been outlined.     

Erosion–Corrosion of Low Carbon (AISI 1008 Steel) Ring Gasket Under Dynamic High Pressure CO2 Environment

R39 AISI 1008 steel ring gasket, used as sealing element in choke valve of a gas well, suffered erosion–corrosion after being used for a relatively short time, which resulted in the leakage of gas. Scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and hardness testing were used to determine the most probable causes of the failure. The results showed that the composition and hardness of ring gasket were in accordance with the required parameters of API 6A Style R39, Class D ring gasket, and AISI 1008 steel. The composition of corrosion products were mainly Fe₂O₃, Fe₃O₄ and scaling layer were composed of FeCO₃. The investigations indicated that failure of the ring gasket was caused by erosion–corrosion.     

Macroscopic characteristics of plasma-nitrided AISI 4340 steel

Plasma-nitrided AISI 4340 steel, in a low-pressure abnormal glow discharge was studied. The layer formation and their characteristics, were studied as a function of the main macroscopic parameters of the gas discharge: gas flow, N₂/H₂ mixture, treatment time and sample temperature. The nitrided layers were characterized using a metallographic microscope coupled to a microhardness tester and X-ray techniques. Typical results obtained for samples which were nitrided for 2 h in a gas mixture of 0.9N₂+0.1 H₂ at 793 K, showed a white layer composed of and phases, 20 m thick, and a 1100 HV20 microhardness.     

Effect of boronising on mechanical properties,wear and corrosion of N80 steel

Abstract

The effect of boronising on N80 steel tube was investigated by pack boriding. During the present investigation, microstructures of boride layer and substrate, hardness, mechanical properties, wear and corrosion were examined. In order to improve the tensile properties of the steel substrate after boronising, four different cooling methods were employed including annealing, air cooling, fan cooling and fan cooling with a graphite bar in the centre of boriding agent. Among these methods, the fan cooling with a graphite bar in the centre of the boriding agent makes the microstructure of ferrite and pearlite finest and the mechanical properties highest, in accordance with the mechanical properties required by API SPEC 5L. The borided N80 steel showed a better wear resistance at an applied load of 50 N with a sliding velocity of 0˙785 m s^–1, it also displayed a better corrosion resistance in both H₂SO₄ and HCl acid environments.     

Production of Fe-P-C amorphous wires by in-rotating-water spinning method and mechanical properties of the wires

Continuous amorphous wires with high strength and good ductility have been produced in the Fe-P-C alloy system by the in-rotating-water spinning technique; however, no amorphous wires are formed, using the same technique, in the Fe-P-B, Fe-P-Si and Fe-B-C systems. The Fe-P-C amorphous wires have a circular cross-section, smooth peripheral surface, and diameters in the range of about 80 to 230m. Their tensile strength, _f, and Vickers hardness,H _v, increase with increasing phosphorus and/or carbon content and reach 3000 MPa and 895 DPN for Fe₇₅P₁₀C₁₅. Fracture elongation, _f, including elastic elongation is about 2.8%. Cold-drawing to an appropriate reduction in area causes an increase in _f and _f of about 3.7 and 79%, respectively. This increase is interpreted to result from an interaction between crossing deformation bands introduced by cold-drawing and the increase in the uniformity of shape for the drawn wires. Further, the undrawn and drawn amorphous wires are so ductile that no cracks are observed even after a sharp bending test. Thus, the Fe-P-C amorphous wires are attractive for fine-gauge high-strength materials both because of the uniform shape of the wires and because of their superior mechanical qualities.     

Relationship between work-hardening exponent and load dependence of Vickers hardness in copper

Micro-Vickers hardness measurements were conducted on pure copper under cold-worked and annealed conditions at loads ranging 0.147 to 9.8 N as well as tensile tests. Characteristics of the load dependence of the Vickers hardness (H _v) of these specimens were compared with the work-hardening exponents,n, obtained through tensile tests. There was a trend that the slope of the load dependence of the hardness was larger in copper with a smallern. The slope,S, was a good measure for correlating withn, andn could be expressed asn=–0.293/S. The 0.2% offset stress _0.2 and ultimate tensile stress _UTS were estimated by usingn determined from theS-n relation and the relations of Cahoonet al. and Tabor. The estimated _0.2 and _UTS showed good coincidence with those obtained from tensile tests.     

Effect of spin polarization on the structural properties and bond hardness of Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>B (<Emphasis Type="Italic">x</Emphasis> = 1, 2, 3) compounds first-principles study

In this paper, spin and non-spin polarization (SP, NSP) are performed to study structural properties and bond hardness of Fe _x B (x = 1, 2, 3) compounds using density functional theory (DFT) within generalized gradient approximation (GGA) to evaluate the effect of spin polarization on these properties. The non-spin-polarization results show that the non-magnetic state (NM) is less stable thermodynamically for Fe _x B compounds than spin-polarization by the calculated cohesive energy and formation enthalpy. Spin-polarization calculations show that ferromagnetic state (FM) is stable for Fe _x B structures and carry magnetic moment of 1.12, 1.83 and 2.03 μB in FeB, Fe₂B and Fe₃B, respectively. The calculated lattice parameters, bulk modulus and magnetic moments agree well with experimental and other theoretical results. Significant differences in volume and in bulk modulus were found between the ferromagnetic and non-magnetic cases, i.e., 6.8, 32.8%, respectively. We predict the critical pressure between ferromagnetic and non-magnetic phases. The model for hardness calculation using Mulliken population coupled to semi-empirical hardness theory proved effective in hardness prediction for the metal borides which agree well with the experimental values. These results would help to gain insight into the spin-polarized effect on the structural and bond hardness.     

Superconductivity and spin correlation study by Fe3+ - ESR in (La1−xSrx)2Cu1−yFeyO4−z

Fe³⁺-ESR measurements are carried out for the samples of (La_1–xSr_x)₂Cu_1–yFe_yO_4–z. Peak-peak width H_pp of the signals decreases with falling temperature until minimum value and rises sharply with further decreasing temperature, which is approximated by H_pp = C₀ +C₁/T + BT. The H_pp behavior at high temperature and at low temperature can be analyzed by Korringa mechanism and slowing down of Fe₃₊ spin fluctuation, respectively. From the analysis of coefficient B's of Korringa terms, C₀ and g-shift, it is revealed that the magnetic interaction of Fe³⁺ with hole carriers and Ce²⁺ spins depends strongly on hole density.