Showing papers on "Maraging steel published in 1999"

The preferred fatigue crack propagation mode in a M250 maraging steel loaded in shear

Abstract: Macroscopic torsional fatigue cracks are shown to propagate in shear, in plain tubular specimens, in the M250 maraging steel, for stress ranges from 90% down to 40% of the yield stress. This cannot be explained in terms of microcrack coalescence for the smallest stress range, for which microcracks are scarce. The kinetics and mechanisms of mode II fatigue crack growth are thus investigated, using precracked CTS or tubular specimens. For a high ΔKII , slowly decelerating mode II propagation takes place for a distance that increases with ΔKII before branching occurs. Friction stresses along the crack flanks shield the applied load and explain this deceleration. An inverse analytical procedure is used to derive the effective stress intensity factor, allowance being made for friction effects, from displacement profiles measured from microgrids using a scanning electron microscope. The measured crack growth rates correlate much better with the effective stress intensity factor than with the nominal ΔKII value. The crack paths observed in torsion are discussed in terms of maximum crack velocity.

Spark ablation inductively coupled plasma mass spectrometry analysis of minor and trace elements in low and high alloy steels using single calibration curves

Abstract: A unidirectional high current pulse spark with a very fast rise-time, ensuring a rapid and complete transfer of energy to the sample, was used as the sampling system for the analysis of carbon steels and highly alloyed steels with the same operating conditions. The sparking operating conditions were optimised and a restrictive path was designed to decrease the quantity of eroded material reaching the plasma, in order to prevent deposition of material in the torch injector, and to minimise sampling cone blockage and drift effects. Spark ablation sampling efficiency and effectiveness of the restrictive path were evaluated. To compensate for differences in the amount of material ablated or for a variation in drift, 57 Fe and 55 Mn were used as internal standards. The calibration procedure was applied to the analysis of the elements Al, B, Co, Cu, Mn, Nb, P, Si, and V, present in the following certified reference materials: BCS (Bureau of Analysed Samples) SS-456 to SS-460 (residual series); CRMs (European Committee for Iron and Steel Standardisation) No 285-2 (Maraging steel), No 292-1 (niobium stabilised steel), No 295-1 (highly alloyed steel), and No 296-1 (jethete steel). When plotting intensity ratios (I X /I IS ) versus concentration ratios (C X /C IS ) linear calibration curves over the entire range of tested concentrations, with correlation coefficients better than 0.999, were obtained. Determination limits below 1 µg g –1 were found and the precision was better than 2.8%. It has also been shown to determine carbon contents at concentration levels greater than 0.03% with RSD values below 3%. For the elements As, Sn, Ti, W and Zr, only present in one or two of the Standard Materials, the sensitivity was also evaluated. Furthermore, the possibility of obtaining reproducible transient signals from sparking periods of only a few seconds was demonstrated.

Use of a maraging steel as an armour plate

Abstract: of EP1008659Maraging steel sheet production comprises surface hardening of the maraged sheet at below the martensite to austenite transformation temperature. Production of a sheet of a maraging steel, especially of composition <= 0.03% C, <= 0.1% Si, <= 0.1% Mn, <= 0.01% P, <= 0.01% S, 0.05-0.15% Al, 17.0-19.0% Ni, 7.0-16.0% Co, 4.0-6.5% Mo, 0.5-2% Ti, optionally one or more of <= 0.5% Cr, <= 0.5% Cu, <= 0.2% Nb, <= 0.2% V, <= 0.2% Zr and <= 0.2% W, balance Fe and impurities, comprises age hardening by heating the sheet, especially after cutting and shaping, to a temperature below the martensite to austenite transformation temperature, the sheet then being additionally surface hardened at below the martensite to austenite transformation temperature. Preferred Features: Surface hardening is carried out by plasma nitriding, hard chromium plating or coating with a hard material.

Gas nitriding method for maraging steel

Abstract: PROBLEM TO BE SOLVED: To impart large compressive residual stress in a short time by subjecting a thin sheet in which a fluoride layer has been formed on the surface after solution heat treatment and aging treatment to nitriding treatment in gas which contains gaseous ammonia and does not contain carbon or contains it by a trace amt. and controlling the concn. of carbon in the surface to the value equal to or below the specified one. SOLUTION: The solution treatment is executed for allowing elution atoms of Ni, Al, Ti or the like to enter into solid solution in austenite. The aging treatment is executed for precipitating alloy elements entered into solid solution in supersaturated martensite and subjecting the steel to precipitation hardening. By forming a fluoride layer on the surface of the steel, the formation of an oxidized film checking the infilatration of nitrogen in the nitriding treatment is suppressed. In the fluoriding treatment, gaseous fluorine such as NF3 is used by being diluted with inert gas. In the nitriding treatment, reaction gas contg. gaseous ammonia is used, and activated nitrogen is infiltrated from the surface of the steel. The concn. of carbon in the surface of the steel is controlled to <=2 wt.%. The content of the carbon component in the nitriding reaction gas is preferably controlled to <10 vol.%.

Cobalt-free maraging steel

Abstract: PROBLEM TO BE SOLVED: To provide a cobalt-free maraging steel with >=1,900 MPa yield stress and >=6.5% fracture elongation percentage by means of aging directly after cold rolling. SOLUTION: The steel is constituted of a cobalt-free maraging steel which has a chemical composition consisting of, by weight, 18-23% Ni, 4.5-8% Mo, 1-2% Ti, 0-0.3% Al, =60%.

Maraging steel sheet excellent in fatigue characteristic, and its manufacture

Abstract: PROBLEM TO BE SOLVED: To provide a maraging steel for machine structural use, excellent in fatigue characteristic, and its manufacturing method. SOLUTION: This steel has a chemical composition consisting of, by weight, <=0.01% C, 8-19% Ni, 8-20% Co, 2-9% Mo, 0.1-2% Ti, <=0.15% Al, <=0.003% N, <=0.0015% O, and the balance essentially Fe and also has <=30 μm size of non-metallic inclusions. The above maraging steel can be easily manufactured by carrying out casting by the use of a mold in which taper Tp represented by Tp=(D1-D2)×100/H, height- to -diameter ratio Rh represented by Rh=H/D, and flatness ratio B represented by B=W1/W2 are regulated to 5.0-25.0%, 1.0-3.0, and <=1.5, respectively, and subjecting the resultant cast slab to plastic working. The fatigue strength of this maraging steel can be further improved by regulating Ti component segregation ratio and Mo component segregation ratio to <=1.3, respectively.

Manufacture of endless metal belt

Abstract: PROBLEM TO BE SOLVED: To form a uniform nitride layer on the surface of an endless metal belt by subjecting the endless metal belt to a gas soft nitriding treatment under a specified condition in a mixed atmosphere where a specified quantity of a specified RX gas is mixed to ammonia gas. SOLUTION: The maraging steel to be used is formed out of 18% Ni steel containing Ni 18-19%, Mo 47-5.2%; Al 0.05-0.15%; Ti 0.50-0.70%; and Co 8.5-9.5% which consists of a low carbon steel containing C 0.03% or less; Si 0.10% or less; Mn 0.10% or less; P 0.01% or less; and S 0.01%; or less. The ends of steel plates of such maraging steel are mutually welded to form a ring, which is then rolled to a prescribed length, and the resulting endless metal belt is subjected to a gas soft nitriding treatment. In this case, the gas soft nitriding treatment of the endless metal belt is performed in a mixed atmosphere where RX gas having a metamorphic dew point +4 deg.C is mixed in a volume ratio of 0.05-0.5 to ammonia gas at a temperature ranging from 480 deg.C to 520 deg.C within 54-60 minutes.

Carburization surface hardening of maraging steel

Abstract: PROBLEM TO BE SOLVED: To improve the strength such as fatigue strength of a maraging steel, at the time of executing an age precipitating treatment, by executing a carburizing treatment at a temp. in the age precipitating treatment. SOLUTION: After a maraging steel is processed by a solution treatment at about 800 deg.C, it is executed by an age precipitating treatment at 450 to 500 deg.C for about 1 to 4 hr to toughen the material thereof. In this case, the maraging steel is executed by a carburizing treatment at the temp. in the age precipitating treatment. The carburizing treatment may be executed by a gas method, a liq. method, a plasma method, an electrolytic carburizing method or the like. By thermodynamically unstable elements such as Ni, Co or the like contained in the maraging steel, the activity of iron is reduced and the carburization is sufficiently progressed at the treating temp. without forming a cementite layer on the surface of the steel. In this way, the maraging steel is processed by the age precipitating treatment to toughen it and simultaneously, to increase its strength.

High-strength crack-resistant concentration-inhomogeneous powder nickel steels

Abstract: The transformation of metastable austenite into strain martensite in concentration-inhomogeneous powder nickel steels under a load promotes an increase in their strength and crack resistance.

Effect of radiation on the properties of high-strenght martensitic steels

Abstract: A comparative study of the radiation resistance of high-strength low-carbonh martensitic steels 03Kh11N10M2, 03Kh12N3D, and 05Kh14N5DM is presented from the standpoint of their possible use in reactors.

Hot ductility behaviour of 18%Ni maraging steel

Abstract: The hot ductility behaviour of a material exhibits a good correlation with its heat affected zone (HAZ) hot cracking sensitivity. This study was aimed at evaluating the HAZ hot cracking susceptibility of 18%Ni maraging steel and exploring the relationship between hot ductility and microstructure of the HAZ in an 18%Ni maraging steel. Optical metallography and scanning electron microscopy (SEM) investigations revealed that the ductility loss was accompanied by fracture transition from ductile transgranular mode to brittle intergranular mode. Fracture specimens were examined using SEM with an attached energy dispersive X-ray spectrometer. The SEM fractographs indicate that the ductile transgranular dimple fracture (i.e. coarse) surface was the titanium rich inclusion precipitated at the grain boundary, which promotes microvoid nucleation, growth, and coalescence and leads to localisation deformation until final fracture. Results of hot ductility tests also indicate that the titanium rich inclusion ...

Cobalt-free and titanium-free maraging steel

Abstract: A maraging steel is free from cobalt and titanium and has specified nickel, molybdenum and aluminum contents. A cobalt-free maraging steel has the composition (by wt.) 14-23% Ni, 4-13% Mo, 1-3.5% Al, ≤ 0.01% C, balance Fe and impurities, the sum of Ni + Mo being 23-27% and the sum of Ni + 2.5 x Mo + 2.3 x Al being ≥ 38%.

Maraging steel free from cobalt and titanium

Abstract: PROBLEM TO BE SOLVED: To produce a maraging steel contg. no cobalt and titanium and suitable for producing watch parts and bands. SOLUTION: This steel contains, by weight, 14 to 23% Ni, 4 to 13% Mo, 1 to 3.5% Al, =38%. It is preferable that the yield stress Re in an aging state after hot baking to >=800 deg.C or after cold working is regulated to >=1900 MPa, the elongation percentage is regulated to >=4%, and the cold working ratio is regulated to 0%-30%.

Method of heat treatment of structures

Abstract: FIELD: heat treatment of structures made of age-hardenable alloys and operating under conditions of high and low temperatures, vibration and corrosive media, particular, treatment of soldered-welded structures having parts of maraging steel and age-hardenable nickel alloy. SUBSTANCE: the claimed method includes heating of structure for soldering or welding up to temperature of 1200 10 C, holding at this temperature for 6-9 min, and cooling at cooling rate of 50-70 C/min. Further on, structure is subjected to double heating up to temperature of 860 10 C, holding at this temperature for 4-5 h and cooling in the air. Then, it is treated with cold at temperature of minus 50 minus 70 C for 2-3 h and tempering at temperature of 200-250 C for 2-3 h. EFFECT: high enough mechanical characteristics of soldered-welded structure serviceable under extreme operating conditions without failure. 1 tbl