Showing papers on "Maraging steel published in 2005"

Effects of austenite reversion during overageing on the mechanical properties of 18 Ni (350) maraging steel

Abstract: The sequence of austenite reversion during overageing in 18 Ni (350) maraging steel was examined and its effects on the mechanical properties were evaluated. Austenite with different morphological features were identified at different stages of overageing. The reverted austenite caused decrease in the yield strength (YS) and ultimate tensile strength (UTS) and increase in the tensile ductility. Though the presence of austenite appeared to be beneficial to impact toughness in the initial stages of overageing, severe embrittlement was noticed in samples subjected to prolonged ageing. The observed deterioration in toughness with continued overageing was associated with the coarsening of intermetallic precipitates formed during the early stages of ageing. Electron probe micro analysis (EPMA) carried out on fracture surface identified the embrittling species as precipitates rich in titanium and nickel.

Microstructure and mechanical properties of a 2000 MPa grade co-free maraging steel

Abstract: The precipitation kinetics in the aging temperature range of 713 to 813 K in a 2000 MPa grade Co-free maraging steel (Fe-18.9 pct Ni-4.1 pct Mo-1.9 pct Ti, mass pct) has been studied. Study on microstructure and mechanical properties showed that a great deal of Ni3Ti and a type of unknown spheroidal precipitates both with average diameter of 2 to 3 nm are formed in the early aging stage at 713 K, which results in a high strength and a relatively low fracture toughness. Ni3Ti precipitates grow into needle or rod shape and become the main precipitation as the aging time is prolonged. Strength increases and fracture toughness (K IC ) decreases with growth of the precipitates. The ultra-high strength of the maraging steel subjected to long-time aging at 713 K is attributed to the high resistance to coarsening of the precipitates. The strengthening in the underaged condition at 713 K is a combination of dislocations cutting through precipitates and the Orowan mechanisms. Aged at 813 K, the size of Ni3Ti precipitates is seriously nonuniform at the early stage and a small amount of interlath reverted austenite is formed. Thereafter, Ni3Ti precipitates coarsen sharply accompanied with the embrittlement. Intralath reverted austenite appears subsequently. In the later stage of aging, the coarsened Ni3Ti precipitates dissolve into the striplike intralath reverted austenite that is disorderly embedded in the matrix. All of these result in a low strength and low fracture toughness under overaging condition. Analysis shows that the formation of reverted austenite contains the diffusion and Kudjumov-Sachs (K-S) and Nishiyama-Wassermann (N-W) shear mechanisms.

Effect of Humidity on Fatigue Strength of Maraging Steel

Abstract: Rotating bending fatigue tests were carried out for an 18%Ni maraging steel in order to investigate the effect of humidity on a crack initiation and its propagation of the steel. Moreover, the effect of reverted austenite on the sensitivity of fatigue strength for humidity was also investigated. Many cracks were initiated at the specimen surface and intergranular cracks were observed on the fracture surface when humidity was high. Both of the crack initiation and the early stage of the crack propagation were accelerated by humidity, especially the effect on the crack initiation was large. However, the effect of humidity on the crack initiation and its propagation was decreased and the intergranular cracking was suppressed by the formation of reverted austenite.

Semisolid metal injection molding machine components

Abstract: The present invention provides an alloy for components of semi-solid injection molding machinery. In particular, the alloy is a intermetallic-hardened steel, known as a Maraging steel alloy. The Maraging steel alloy includes Cr, Co, Mo, and about 0.15% or less by weight C.

Structure and Mechanical Properties of Maraging and Low-Carbon Martensitic Steels

Abstract: The structure, mechanical properties, and crack resistance after tempering of maraging steel 03Kh11N10M2T (EP-678) and low-carbon martensitic steel 12Kh2G2NMFT are studied. The range of tempering temperatures ensuring the combination of properties required for massive parts (σr #x2265; 1300 MPa, σ0.2 ≥ 1100 MPa, KCT ≥ 0.2 MJ/m2) is determined. It is shown that steel 12Kh2G2NMFT is better adaptable to manufacture because it is hardened by air-cooling.

Laws of Influence of Structural Characteristics on the Strength and Crack Resistance of Aging Metallic Materials

Abstract: The structural characteristics (the volume fraction, size, and shape of and the distance among hardening-phase particles) of aging alloys and steels, which define the behavior of the critical stress intensity factor during thermal hardening, are determined using the structural-mechanical approach we have developed. It is experimentally demonstrated for maraging steels that our approach is capable of proving the correlations of strength, plasticity, and crack- resistance with the structural characteristics, which were varied by changing the chemical composition of steel and thermokinetic aging conditions

Contribution to the understanding of Austenite stability in a 12Cr-9Ni-4Mo maraging steel

Abstract: Maraging steels show an excellent combination of high strength and ductility, which makes them very attractive in a large variety of potential applications. The present work is concerned with the main factors influencing the stability of metastable austenite in such a steel. At subzero temperatures a large variation in the isothermal transformation behaviour of austenite to martensite has been observed. Factors such as the austenite grain size and the interstitial content in solid solution are known to influence austenite stability and, therefore, the martensitic transformation. In this steel, the addition of titanium results in carbonitride precipitation. These precipitates play an indirect but important role in the stability of austenite by means of removing interstitials from the solid solution and by inhibiting an austenite grain growth. The combination of techniques such as X-ray diffraction, magnetisation measurements, three-dimensional neutron depolarisation, and internal friction measurements enables a complete characterisation of the transformation. A step towards understanding the factors responsible for the variation in the behaviour observed is the main contribution of this work.

Sintering of maraging steel with phosphorous additions

Abstract: The aim Of this study was to develop a steel powder system for rapid tooling applications. The properties required are rapid densification, dimensional precision. high mechanical strength and corrosion resistance. To this end. the densification and microstructural development of a loose packed 200 grade maraging steel powder sintered with ferrophosphorous additions was examined. Liquid initially formed from a reaction of the Fe3P and carbon, which was a residue of the polymeric binder used to shape the powder compact. This liquid caused a burst of sintering which ceased as the liquid dissipated. On further heating, a phosphorous rich supersolidus liquid appeared at triple points and grain boundaries leading to rapid densification and a sintered density of 98%.

Thin steel strip superior in strength, fatigue strength, corrosion resistance and abrasion resistance, and manufacturing method therefor

Abstract: PROBLEM TO BE SOLVED: To provide a thin steel strip which has higher fatigue resistance than 18Ni maraging steel, superior mechanical properties, a low cost, adequate nitrided characteristics, and superior strength, fatigue strength, corrosion resistance and abrasion resistance. SOLUTION: The thin steel strip has a composition comprising, by wt.%, 0.05-0.15% C, less than 1.0% Si, 0.2-1.5% Mn, 4.0-5.0% Ni, 15.0-17.0% Cr, 2.5-3.5% Mo+1/2W, 0.5% or less Cu, 0.05-0.15% N, 0.0100% or less O, 0.01% or less Al, 0.05% or less Ti, 0.025% or less P, 0.010% or less S and the balance substantially Fe. COPYRIGHT: (C)2006,JPO&NCIPI

Steel for thin strip, and thin strip

Abstract: PROBLEM TO BE SOLVED: To provide a steel for a thin strip, which keeps such a feature of a maraging steel as high strength and high toughness, and simultaneously shows more excellent fatigue strength properties than known steel. SOLUTION: The steel for the thin strip has an alloy composition comprising, by wt.%, 0.05-0.15% C, 10.0-18.0% Ni, 5.0-30.0% Co, 1.0-5.0% Mo, 0.5-1.3% Al, 1.0-3.0% Cr, 0.10% or less Ti, 0.003% or less S, 0.03% or less P, 0.03% or less N, 0.03% or less O, and the balance Fe with unavoidable impurities. The alloy composition may further comprise one or more elements selected from among some optionally adding elements. COPYRIGHT: (C)2007,JPO&INPIT

Phase Transformation in Fe-Based Alloys in High Magnetic Fields

Abstract: The effects of a high magnetic field on phase transformation behaviors and microstructures in Fe-based alloys have been extensively studied. It was found that a magnetic field accelerates ferritic and martensitic transformation, changes the morphology of the transformed microstructures and increases the A3 and A1 temperature. In a magnetic field of 10 Tesla, the A1 temperature increases by about 15°C for Fe-0.8C, the A3 temperature for pure Fe increases by about 8°C and the martensitic transformation temperature Ms in 18Ni maraging steel increases by 20°C. Ferrite grains are elongated and aligned along the direction of magnetic field in Fe-0.4C and Fe-0.6C alloys by ferritic transformation, but elongation was not found in pure Fe, Fe-0.05C alloy and Fe-1.5Mn-0.11C-0.1V alloy. Aligned structure was not found either by pearlitic transformation in Fe-0.8C alloy or by cementite precipitation from martensite.

Thin steel strip for metallic strip ring of belt in continuously variable transmission, and manufacturing method therefor

Abstract: PROBLEM TO BE SOLVED: To provide a high-strength thin steel strip for a metallic strip ring of a belt in a continuously variable transmission, which has higher fatigue resistance than 18Ni maraging steel, superior mechanical properties, adequate corrosion resistance, a low cost, and adequate nitrided characteristics SOLUTION: The thin steel strip for the metallic strip ring of the belt in the continuously variable transmission has a composition comprising, by wt%, 005-015% C, less than 10% Si, 02-15% Mn, 40-50% Ni, 150-170% Cr, 25-35% Mo+1/2W, 05% or less Cu, 005-015% N, 00100% or less O, 001% or less Al, 005% or less Ti, 0025% or less P, 0010% or less S and the balance substantially Fe COPYRIGHT: (C)2006,JPO&NCIPI

The influence of multiple solution annealing on kinetics of structural transformation of maraging steels

Abstract: The paper presents effects of multiple solution-annealing on kinetics of structural transformation of maraging steels 18 9 5. Multiple solution-annealing testing was carried out in dilatometer by simultaneous registration of transformation temperatures austenite start As at heating and martensite start Ms at cooling and registration of linearly dilatatic changes. Analysis of dilatometric curves has quantified coefficients of dilatation during heating and coefficient of contraction during cooling, and has established mathematical model for determination of quantity of retained austenite in microstructure of maraging steels.

Influence of post-weld solution treatment on mechanical properties and microstructure of fusion zone of cobalt free maraging steel weldment

Abstract: Post-weld solution treatment (PWST) was carried out on gas tungsten arc weldments of a cobalt free maraging steel. A substantial increase in fusion zone toughness was observed after PWST. It was established that the increase in fusion zone toughness was due to a reduction in austenite content of the fusion zone. The volume fraction of austenite decreased with increasing solution treatment temperature. The PWST led to a decrease in severity of microsegregation, which in turn caused a reduction in austenite content of the fusion zone. The activation energy for the process of homogenisation of austenite was found to be 265 kJ mol−1. The present work has clearly demonstrated that PWST before aging improves the fusion zone toughness in cobalt free maraging steel weldments.

Magnetic micro-probe determination of the condition of maraging steel

Abstract: Microstructural and mechanical properties of precipitation-hardened maraging steel could be stated on a basis of magnetic properties of such a material. A correlation between mechanical and magnetic properties of the maraging steel is treated from the view of non-destructive testing during and after heat treatment as well as during use under unfavourable conditions at elevated operating temperatures. A group of maraging steels shows numerous technical and technological properties, which substantially differ from those of classical steels, i.e. excellent weldability, high ductility in soft state, high hardening ability and favourable suitability for EDM machining. All of those properties are extremely important in machining of technologically exacting products such as die casting dies. The selected maraging steel contains 12 % of nickel and is primarily intended for the production of hot-working dies and various machine elements exposed to heavy mechanical and thermo-mechanical loads. Non-destructive testing of maraging steels enables cheaper and more reliable production. Selected characteristic properties for testing of maraging steel after precipitation hardening are impact toughness, hardness, and residual magnetism. Supervision should be performed not only during precipitation hardening but also during the use of such a material at elevated temperatures at which additional precipitation may occur, which could lead to overaging of the micro-structure. A fast and reliable method of non-destructive testing of mechanical properties could significantly affect the time, price and quality of production as well as maintenance of products made of maraging steel.

Non-Homogenous Precipitation Annealing of Maraging Steels

Abstract: Nickel maraging steels in the as-delivered state show a microstructure consisting primarily of oversaturated lath martensite. The final mechanical properties are achieved with precipitation annealing, during which the dissolved alloying elements start to precipitate. The newly-formed precipitated phases efficiently hinder shifts of dislocations, which results in considerable changes of the mechanical properties. Strength and hardness thus essentially increase whereas the material shows a relatively high fracture toughness. The precipitated phases formed during precipitation annealing also cause some distortion of a workpiece and transformational residual stresses on the micro and macro scales. Linear strains after precipitation annealing range from -0.05% to -0.1% and depend primarily on temperature/time conditions during the precipitation process. The non-homogenous annealing such as laser annealing produces temperature-induced residual stresses which are combined with transformational stresses. These stresses are expected to be lower and much more different than the stresses occuring in comparable classical heat-treated steels, however they cannot be neglected due to the exceptional performance of maraging steels and also their employment with high-demanding products. The results of the residual stress measurements after laser-induced and classical heat treatments of Ni-Co-Mo maraging steel with 12% nickel are presented.