Ni Maraging Steel Research Articles

Soft magnetic structural alloys for elevated-temperature applications

Metallurgical efforts to develop a soft magnetic material suitable for application in the rotor of a generator or motor in advanced aerospace electric systems are reviewed. Commercial materials which have been considered include AISI 4340 steel, H-11 steel, Nivco alloy, and 15- and 18-percent Ni maraging steels. Developments described have led to several new materials with combination of good mechanical and magnetic properties at elevated temperature. Such materials include an improved maraging steel a precipitation hardenable cobalt-base alloy, a carbide strengthened Co-W alloy, dispersion-strengthened soft magnetic alloys, and unidirectionally solidified Co-Nb-Fe eutectic alloys.

The effect of trace impurities on the stress-corrosion cracking susceptibility and fracture toughness of 18Ni maraging steel

A series of 18Ni maraging steels of overall commercial purity but containing also deliberate impurity additions of S, P, C, Cr and Si + Mn has been studied. The fracture toughness and stress-corrosion resistance (determined using plane-strain fatigue-precracked specimens tested in 35x NaCl solution) of these steels have been compared to the fracture toughness and stress—corrosion resistance of a commercial-purity 18Ni maraging steel with no deliberate impurity additions, and to a similar steel prepared from special high-purity melting stock. The most important conclusions reached are that: (I) Ultra-high purity steels do not have significantly improved stress—corrosion resistance but show useful increases in fracture toughness when the C content is less than 0005 per cent; (II) Simultaneous additions of Mn + Si result in extremely low fracture toughness values; (III) High C contents (greater than 003 per cent) result in marginally improved stress—corrosion resistance; (IV) High Cr contents result in rather poor stress—corrosion properties. The fracture toughness results have been correlated with the electron transmission microstructure of the steels and the results of a fractographic analysis of the fracture surfaces.

Transmission Electron Microscopy Study of Strengthening Precipitates in 18% Ni Maraging Steel

Transmission Electron Microscopy Study of Strengthening Precipitates in 18% Ni Maraging Steel

18%Niマルエージング鋼におけるNi<SUB>3</SUB>Mo析出物の電子顕微鏡による研究

18%Niマルエージング鋼におけるNi<SUB>3</SUB>Mo析出物の電子顕微鏡による研究

The effect of surface contamination in SEM fractographic investigations

The importance of surface contamination on the interpretation of electron fractographs has been considered with respect to both the scanning and transmission electron microscopes. While surface cleanliness is essential when applying replication methods, it is of much less significance when viewing the specimen directly by the scanning electron microscope. This has been demonstrated for an environmental crack surface of an 18% Ni (250 grade) maraging steel specimen in which the surface contamination layer was sufficient to mask all essential microfractographic features in replication and yet was transparent to the image-forming electrons in the scanning electron microscope. The effect has been discussed in terms of the secondary electron image formation and the emissive characteristics of oxidised metal surfaces.

Stress-corrosion cracking behavior of an 18 Pct Ni maraging steel

Stress-corrosion cracking of an 18 pct Ni maraging steel in aqueous solutions was studied using precracked cantilever beam specimens. By appropriate heat treatments, six different structures having the same yield strength were obtained. Although significantly different plane strain fracture toughness values (KIc) resulted, it was found that the threshold plane strain stress intensity (KIscc) was the same for all structures.KIscc had the same value in 3 pct NaCl at various pH values, in 1N H2SO4, and in distilled water. Specimens tested in 3 pct NaCl under both anodic and cathodic applied potentials also exhibited this sameKIscc value. Fractographic inspection of the crack surfaces revealed no apparent differences due to changes in solution, pH, or applied potential. The crack path was intergranular in all cases. However, specimens austenitized at 1500°F exhibited crack branching, whereas in specimens austenized at much higher temperatures branching no longer occurred. Aging time and temperature seemed to change only the time to failure. The mechanism most consistent with all observations appears to be hydrogen cracking.

Hydrogen Emanation and Distribution in Metals and Alloys

Abstract Hydrogen emanation and distribution (at microstructural features) down to one micron size have been observed in 250-grade 18 Ni maraging steel weldments and in titanium-6Al-4V. A neodymium (Nd) hydrogen metal detector system was used to locate and estimate the amount of hydrogen emanation; this system operates on the basis of a chemical reaction. Neodymium, or a similar rare earth metal, is reacted with the emanating hydrogen at a temperature of 29 C or higher to form a metal hydride. A thin neodymium film is evaporated on the polished and etched metal or alloy surface to be examined. This metal film is optically transparent except at the H2 reaction sites where NdH2 is formed; therefore, the microstructural features of the metal surfaces are directly correlated to the H2 emitting sites. The NdH2 reaction nodules appear black when observed with an optical microscope. By measuring the size of the reaction sites and the thickness of the film, the amount of hydrogen reacted with the Nd to form NdH2 ...

Fatigue-crack propagation in modified 300-grade maraging steel

Fatigue-crack-propagation studies were performed on an 18Ni (300-grade) maraging steel at room temperature in dry and humid argon environments (atmospheric pressure) to examine the effect of moisture on the rate of fatigue-crack propagation and on the fracture path through the microstructure. The results showed that the rate of fatigue-crack propagation was increased by about 30 per cent by moisture in the argon. Fractographic analyses showed that the crack path in the dry-argon atmosphere was transgranular. In the humid-argon atmosphere, the crack path was predominantly transgranular with respect to prior austenitegrain boundaries, but appeared to be partly intergranular with respect to subboundaries. The fracture surfaces of the specimens were covered with fatigue striations regardless of the testing environment, an indication that the mechanism of crack growth was similar in both environments, even though the fracture surfaces of the specimens fatigued in dry argon were rougher. Therefore, although moisture in the argon environment accelerated crack growth by about 30 per cent, it apparently did not change the mechanism of crack growth. Evidently the effect of moisture in the environment is to promote striation-type crack growth along paths such as subboundaries. A comparison of fractographic results with those of previous work on hydrogen-accelerated fatigue-crack growth in 250-grade maraging steel indicates that in 300-grade maraging steel the increased rate of fatigue-crack growth in the humid environment is not hydrogen-induced.

The effects of thermal treatment on the austenitic grain size and mechanical properties of 18 Pct Ni maraging steels

A technique has been developed for controlling the austenitic grain size of 18 pct Ni maraging steels by thermal treatment alone. This treatment has been applied to two different grades, 250 and 300, of maraging steel, and a large grain size, ASTM 2, was reduced to ASTM 7 in both cases. The process of grain size refinement requires thermal cycling from a temperature belowM f to a temperature considerably above the austenitizing temperature. The minimum austenitic grain size attainable depends on the prior strain in the material as well as the thermal treatment. While significant grain size refinement can be attained by one cycle to the proper temperature, the attainment of the minimum uniform grain size requires several cycles. The effects of austenitic grain size on tensile properties have been investigated both at room temperature and at elevated temperatures. The prior austenitic grain size has a small but measurable effect on the mechanical behavior of aged material at room temperature. The austenitic grain size has a significant effect on the ultimate tensile strength at 1600°F.

Fatigue crack propagation and strain cycling properties

A mechanical model of fatigue crack propagation was studied. It is hypothesized that propagation is caused by cumulative damage due to strain cycling of the material at a crack tip. With Miner's cumulative damage law and Manson and Coffin's strain cycle fatigue: law, crack propagation rate of a material can be calculated. The calculated values are compared with data on 7075-T6 Al, 2024-T4 Al, AM 350 stainless steel, and 18 Ni maraging steel. The calculated and experimental values correlate reasonably well. The results indicate that fatigue crack propagation resistance of a material is related to its capability to sustain strain cycling, i.e. its cyclic ductility.

Flow of a Non-Newtonian Fluid past Wedges with Wall Mass Injection

2 Puzak, P. P. et al., Metallurgical Characteristics of High Strength Structural Materials (Eighth Quarterly Report), Rept. 6364, Aug. 1965, Naval Research Lab., Washington, D.C. s Kies, J. A. et al., Testing of Weldments, ASTM Symposium on Fracture Toughness Testing and its Applications, Special Technical Publication 381, 1965, American Society for Testing Materials; also CR-140, NASA. 4 Brown, W. F., Jr. and Srawley, J. E., Plane Strain Crack Toughness Testing of High Strength Metallic Special Technical Publication 410, 1967, American Society for Testing Materials. 5 Stonesifer, F. R., Toughness Formulas for Bend Specimens, Report of NRL Progress, Feb. 1968, Naval Research Lab., Washington, D.C. 6 Kies, J. A., Mechanics—Its Uses and Limitations, presented at the Failure Analysis Seminar, sponsored by American Society of Texas Chapter, NASA Manned Spacecraft Center, Houston, Texas, Nov. 9, 1965. 7 Tetelman, A. S. and McEvily, A. J.; Jr., Fracture of Structural Materials, Wiley, New York, 1967. 8 Heuschkel, J., Composition Controlled, High-Strength, Ductile, Tough Steel Weld Metals, Welding Journal, Vol. 43, p. 361. 9 Romine, H. E., Relation of Oxygen Content to Fracture Toughness in 18 Ni Maraging Steel Welds, TR 2033, May 2, 1966, U. S. Naval Weapons Lab.

The Stress-Strain Behavior of Concentric Composite Cylinders

An analytical model was developed for the elastic-ideally plastic behavior of concentric cylindrical composites under uniaxial tension. The model predicted the creation of transverse stresses in the composite during axial loading. The existence of these stresses was experimentally verified in a 4140 steel core-18% Ni maraging steel case composite system by examining the effects of the trans verse stresses on the composite axial stress-strain curve and the composite tangential surface strain ratio curve.

Stress Corrosion Behavior of High Strength Steels

Abstract The effect of stress and environment on the susceptibility to failure of HY-80, HY-130(T), 12Ni maraging, and 18Ni maraging steels has been evaluated by using both pre-notched and smooth specimens. Tests were conducted in sodium chloride solution, artificial sea water, and natural sea water, both with and without cathodic charging. Data are presented which show that the apparent susceptibility to failure is dependent on the test method used. Thus, in natural sea water, the most severe environment, notched specimens often showed failure, whereas, specimens of the same material tested in the unnotched condition did not fail. HY-80 steel was resistant to failure in all environments tested. HY-130(T) steel showed a slight reduction in load-carrying ability during cathodic charging, although the applied stress required for failure remained very high. Both 12Ni and 18Ni maraging steels failed as notched specimens in all test environments at applied stresses below the yield strength. In contrast, however, no failures were observed during the test period when these materials were tested as U-bend specimens in natural sea water.

各種超高抗張力鋼の水素脆化感受性について

The embrittlement of ultra-high strength steels due to the action of hydrogen introduced by Cd-electroplating has been studied in stress rupture (sustained load) and tensile tests for notched specimens.4340 steel, SNCM 9, 300 M steel, H-11 Mod. steel and 18%Ni maraging steel, heat-treated to the 200 kg/mm2 tensile strength level, and 5.5W-2.5Cr steel and SKS 4, heat-treated to the 170 kg/mm2 tensile strength level, were examined.The results of the present work are:(1) Susceptibility of hydrogen embrittlement estimated by redution of area and notch tensile strength were as follows:SNCM 9\fallingdotseq4340\gtrsimH-11 Mod.>SKS 4>300 M>18%Ni maraging steel>5.5W-2.5Cr.(2) Susceptibility of hydrogen embrittlement estimated by delayed failure properties were as follows:4340\fallingdotseqSNCM 9>300 M>H-11 Mod.\fallingdotseqSKS 4>18%Ni maraging steel\gtrsim5.5-2.5Cr.(3) 5.5W-2.5Cr steel and 18%Ni maraging steel were noticeably less susceptible to embrittlement by hydrogen than the others.(4) Of the hydrogen embrittled plain tensile specimens, 5.5W-2.5Cr steel showed cup and cone type fractures similar to the unplated specimen, but others showed brittled fractures whose failure was initiated just below the surface of specimens.Failure-initiated regions of SNCM 9, 4340 steel, 300 M steel and SKS 4 show the coexistence of intergrannular and transgranular crackings with respect to pre-austenite grain boundaries in away similar to the hydrogen-induced delayed failure, but the interganular cracking was predominant.

Relationships Between Electrochemical Measurements and Stress Corrosion Cracking of Maraging Steel

Abstract Stress corrosion cracking of 18Ni maraging steel foil has been studied in deionized water solutions with the pH adjusted by NaOH additions over a range from 8 to 13. The full range of NaCl contents from saturated solutions to no addition was tested with specimens stressed to 75 percent of yield strength. For each variation in NaCl content, the specimen failure times go through a minimum with respect to pH. With increasing NaCl content, the minimum becomes more pronounced and its position shifts towards higher pH values. The position of each minimum is indicated by electrode potential measurements. Potentiostatic measurements as a function of pH confirm that maximum susceptibility to stress corrosion cracking occurs just prior to the onset of passivation.

Effect of Structure on Magnetic Properties of High-Temperature Alloys

Direct-current magnetic behavior of several high-temperature alloys was studied at various temperatures up to 600° or 760°C and after cooling to room temperature. Overaging of intermetallic precipitates and partial reversion of the martensitic matrix to austenite, both reactions commencing at temperatures near 500°C, appear to be responsible for the increase in coercive force and flattening of the magnetization curve in 15% Ni and 18% Ni maraging steels. The continuous decrease in magnetic hardness of H-11 tool steel is dependent on the structural changes primarily associated with agglomeration of the carbide particles. A similar behavior is shown in a precipitation-hardened 23%-Ni-Co-base alloy.

Destructive tests of full-size rocket motor cases and their application to lightweight design

This paper describes experimental stress investigations of burst-tests under internal pressure of three full-size rocket motor cases made of Ladish D6AC steel. Two full-size cases made of 18% Ni maraging steel were also burst-tested for strength evaluation. Fifteen subscale vessels were also tested to destruction. Electric strain gages (SR-4) were used in all tests. Strain data in the plastic region were reduced by a digital computer. The results indicated that 1) a biaxial ultimate strength equal to 343 ksi has been achieved in 18% Ni maraging steel rocket motor cases; 2) within the range of radius-to-thickness ratios between 40 and 300, the subscale vessels behave essentially in the same way as the full-size cases with respect to the biaxial gains and the total elongation of the vessel at failure; 3) in a 2:1 stress field, the experimental biaxial gains in the elastic range vary from 15.5 to 16.5%, which are in close agreement with values predicted by Huber-Hencky-Von Mises theory of constant energy of distortion; 4) the experimental biaxial gains in the cylinder at fracture are in the range of 13 to 16%; and 5) the total elongadons in the cylindrical vessels at failure are approximately one-fifth of those obtained from the uniaxial specimens.

Stress Corrosion Behavior Of Maraging Nickel Steels In Natural Environments

Abstract Stress corrosion cracking behaviors of several laboratory and commercially produced heats of 18, 20 and 25 percent Ni maraging steels have been observed in marine and industrial atmospheres and in sea water. Resistance of 18 percent Ni maraging steels was strongly affected by their structure and thermal histories. In properly processed materials rate of growth of stress corrosion cracks was low in most environments tested, and many stressed specimens lasted more than 500 days. Lower-yield-strength 18 percent Ni maraging steels were more resistant to stress corrosion cracking than higher strength alloys, also more resistant to hydrogen cracking when cathodically protected in sea water. Composition affected behavior of maraging steels, 20 percent Ni materials having relatively poor resistance and 25 percent Ni maraging steels good resistance, particularly in anoveraged condition. Control specimens of AISI 4340 steel hardened to 240-ksi yield strength failed rapidly in all test environments and conditions.

A concentrator for generation of high intensity ultrasound at 1 Mc/s: Rosenberg, L.D., and Sirotjuk, M.G. Akust. Zh., 9, no. 1, p. 61 (1963)

The fracture toughness of quenched and tempered steels, such as AISI 4340, AISI 4130 and 300M, can be increased by 50–100% by minor changes in heat treating procedures. Certain microstructural features, particularly blocky ferrite, upper bahnte and twinned martensite plates, are deleterious to fracture toughness. Similarly, the presence of undissolved carbides and sulfide inclusions, which act as crack nuclei, can lower fracture toughness by 25–50%. Other microstructural constituents, such as lower bainte, autotempered martensite, and retained austenite can enhance fracture toughness. By controlling the amounts and distributions of the microstructural constituents, the fracture toughness values of AISI 4340, AISI 4130 and 300M can be raised to the fracture toughness level of 18Ni maraging steel at equivalent values of yield strength.