Processing and properties of sinter hardened Fe–Cr–Mo steels with admixed extra-fine nickel

Abstract

The processing and properties of chromium–molybdenum, powder metallurgy steels with admixed extra-fine nickel (XF Ni) were investigated. Prealloyed Fe–1·5Cr–0·2Mo powder was blended with different quantities of XF Ni, while a hybrid steel with lower Cr content was prepared by blending Fe–1·5Cr–0·2Mo and Fe–0·5Mo prealloyed powders, with additions of XF Ni and copper powders. These steels were compacted into different part shapes in order to evaluate the effect of part thickness on sinterhardening behaviour. These parts were also subjected to different cooling rates after sintering. This study showed that additions of XF Ni improve the compressibility, densification behaviour and mechanical properties of Cr–Mo steels. Furthermore, the properties of the hybrid steel were shown to be either equal to or greater than those of the reference material. Hardenability of all steels was sufficiently high such that part thickness was seen to have negligible impact. Higher cooling rates generally resulted in improved mechanical properties.     

Effect of plasma nitrocarburising on fatigue resistance of low alloy Cr–Mo sintered steel

Abstract

A nitrocarburising treatment was carried out on a low alloyed Cr–Mo sintered steel (1·5%Cr, 0·2%Mo) to evaluate its influence on the bending fatigue resistance of the material. Fatigue performance was compared with that obtained by a conventional through hardening and a plasma carburising. Two different green densitise (7·1 and 7·4 g cm^?3) and two different sintering temperatures (1120 and 1250°C) were adopted during preparing the as sintered steels. Fatigue strength after nitrocarburising on 1120°C sintered steels considerably increases. It is comparable with that obtained by through hardening and slightly better than that obtained by plasma carburising. On samples sintered at 1250°C the fatigue resistance of the nitrocarburissed is worse than expected, because the microstructure is softer and less homogeneous.     

Rotary cold re-pressing and heat treatment of sintered materials from Co–Cr–Mo alloy powder

Abstract

This paper presents the analysis of research results concerning the application of PM technology to produce porous implantation material from Co-Cr-Mo alloy. Rotary cold re-pressing and heat treatment has been used to increase the density and mechanical properties of sintered samples. The microstructure, hardness and compressive properties, and ultrasonic data of the obtained materials were investigated. The material had about 10% of porosity and has higher mechanical properties, i.e. UCS and plastic strain, compared with cast cobalt alloy, and had 25% lower values of Young's modulus and shear modulus.     

Industrial processing,microstructures and mechanical properties of Fe–(2–4)Mn (–0.85Mo)–(0.3–0.7)C sintered steels

Abstract

The potential of PM Mn steels has been established in laboratory experiments. This paper deals with sintering of Fe–(2–4)Mn–(0.3/0.7)C, also with 0˙85%Mo addition, in an industrial pusher furnace at 1180°C in an atmosphere of 25% hydrogen plus 75% nitrogen, obtained from a cryogenic liquid, giving an inlet dew-point of ?55 °C. Tensile, bend (including fatigue) and miniature Charpy specimens were sintered in flowing gases and in semiclosed containers with a getter of ferromanganese, carbon and alumina. The quenched and tem- pered state was investigated, as was sinter hardening (cooling rate of 55 K min ?1), simulated for comparison with slow cooling at 10 K min ?1. As there was no forma tion of oxide networks at the combination of sintering temperature and dewpoint, in accordance with the Ellingham–Richardson diagram for Mn oxidation/reduction, the use of semiclosed containers was superfluous. The quenched and tempered specimens were brittle. Sinter hardening lead to an improvement in mechanical properties. The reproducibility of tensile and TRS data was high for the sintered materials, characterised by Weibull moduli m of 12–41. All the alloy microstructures were complex and heterogeneous, consisting of, depending on the local manganese and carbon contents, the diffusive and non-diffusive transformation products (pearlite, bainite, martensite) and additionally ferrite and retained austenite. The highest mechanical properties in the entire range of compositions investigated in the furnace cooled state: yield, tensile and bend strengths of 499, 637 and 1280 MPa, respectively, with impact energy of 18 J, and tensile and bend strains of 1˙17 and 1.57%, were achieved for the Fe–2Mn–0.85Mo–0.5C alloy, marginally superior to Fe–2Mn–0.7C. For the sinter hardened Fe–4Mn–0.3C alloy yield, tensile and bend strengths were 570, 664 and 1263 MPa, respectively, at an acceptable impact energy of 14 J, with tensile and bend strains of 0.52% and 1.8%. Many of the results compare favourably with the requirements of MPIF standard 35. Mn is a more effective strengthening agent than either Ni or Cu, or their combination, though generally at reduced plasticity.     

Fracture micromechanics of static subcritical growth and coalescence of microcracks in sintered Fe–1·5Cr–0·2Mo–0·7C steel

Abstract

Nucleation of microcracks, their growth and coalescence are analysed in powder metallurgy (PM). Fe–1·5Cr–0·2Mo–0·7C steel by fractography allied to surface replica microscopy – at several stress levels as the maximum tensile stress in three-point bend specimens was raised to 99·6% of the transverse rupture strength TRS of 1397 MPa. The fatigue limit in this material is ～240 MPa, at which stress level no microcracks were detected in static loading. Numerous microcracks, ranging in size from <5 to ～20 μm, however, were nucleated above ～800 MPa, i.e. beyond the yield strength of ～620 MPa. With increasing stress, some microcracks became dormant, whilst others grew subcritically, stress step-wise, to some 400 μm. Of particular importance are observations of the coalescence of two and three of such microcrack systems to produce a critical, propagating crack. The then estimated stress intensity factor K _a, could reach K _1C, independently estimated to be ～36 MPa m^1/2. Microcrack coalescence was associated with easy paths for crack growth, principally prior particle boundaries linking pores. Ways of making subcritical crack growth more difficult and hence improving both static and dynamic mechanical properties, are considered.     

Optimized Tribological Performance Deriving From Multiple Strengthening Effects of Fe–Ni–Mo–Cr Alloy

Metallurgical and Materials Transactions A - The tribological performance of quaternary Fe–13 pct Ni–10 pct Mo–5 pct Cr alloy was modulated by means of electromagnetic levitation...     

Solidus Surface of the Mo–Fe–B System

Powder Metallurgy and Metal Ceramics - The arc-melted Mo–Fe–B alloys with boron content up to ~41 at.% were studied after annealing at subsolidus temperatures by X-ray diffraction,...     

Tensile and fatigue behaviour of sinter hardened Fe–1·5Mo–2Cu–0·6C steels

Abstract

In the present work the tensile and axial fatigue behaviour of sintered hardened Fe–1·5Mo–2Cu–0·5C at three density levels (6·8, 7·0 and 7·2 g cm^–3) have been studied. The materials were tested under the as sintered condition, and after tempering at 180 and at 240°C. The results show that steels under the as sintered condition posses a high hardness but a brittle tensile deformation and fracture behaviour. Tempering at 180 and 250°C induces the disappearance of brittleness and tensile fracture is thus ductile although very localised at the necks. Fatigue strength is determined by the resistance of the materials to the internal damage evolution due to the nucleation of small cracks at the pores edges, and their coalescence into a long crack. Tempering induces an increase in the fatigue resistance. The greatest fatigue strength at 2 × 10⁶ cycles is displayed by the steel with a density of 7·2 g cm^–3 and tempered at 180°C.     

Characterization of Fe–C–Cr Based Hardfacing Alloys

Hardfacing is one of the adaptable methods that can build up the hard and wear resistant surface layer of different materials on the surface of substrate material. It helps them withstand wear, as well as prevent corrosion and high temperature oxidation. In the present investigation three different types of Fe–C–Cr based hardfacing electrodes with varying chemical compositions were deposited on ASTM A36 steel substrate by using manual metal arc welding (MMAW) process. ASTM A36 steel was selected as a base material after consulting with Pressure and Process Boilers, Saharanpur (India), which is a leading manufacturer of boilers. ASTM A36 steel is mostly used by this company for the production of induced draft fans. MMAW process with direct current constant current type power source was used to deposit the hardfaced layers of uniform quality. Straight polarity was used for MMAW process so that more of the arc heat should be concentrated on the electrode. The hardfaced samples were characterized using various characterization techniques and the results of the same were also outlined in the present investigation.     

Influence of the Oxygen Induced Surface Segregation Process of Solutes on the Anti-corrosion Properties of the Fe–Cr and Fe–Cr–Si Alloys

Metallurgical and Materials Transactions A - The influence of the oxygen-induced surface segregation process of Cr and Si solutes on the anti-corrosion properties of Fe–Cr and...     

Multi-Criteria Selection of Quantitative Composition of Alloying Elements of Maraging Steels of the Fe–Cr–Ni–Mo System with an Improved Set of Mechanical Properties

Metallurgist - Based on analysis of mechanical test the results a search is completed for the optimum content of the main alloying elements of maraging steels (MS) based on...     

Magnetic measurement of retained austenite in sintered steels – benefits and limitations

ABSTRACT

Measuring the magnetic saturation to quantify the retained austenite is a common method, but it is based on a relative calculation. Thus the reference, which ideally should be the same material but without retained austenite, is of extreme importance. This work focuses especially on obtaining the saturation of the reference material by using different models and applying them for determining the retained austenite content of sintered alloy steels. To verify these calculations, additional measurements of the phase fractions by X-ray diffraction were done. As a result, the contents of retained austenite vary significantly when calculating them from the saturation data using different models. Furthermore, the agreement of the results of the magnetic method and those of the X-ray measurement is not quite satisfactory. Especially when using simple approximations (reference?=?magnetic saturation of plain iron) the differences are very pronounced. However, it is shown that using the presented models results in markedly better agreement between the results of both methods (magnetic and X-ray diffraction) than using plain iron as a reference.     

Obtaining a High-Entropy Fe–Cr–Co–Ni–Ti Alloy by Mechanical Alloying and Electric Spark Plasma Sintering of a Powder Mixture

Russian Journal of Non-Ferrous Metals - A two-phase powder alloy based on substitutional solid solutions with bcc and fcc lattices has been obtained by the high-intensity mechanical treatment (HMT)...