Showing papers on "Maraging steel published in 1973"

Fatigue crack propagation in martensitic and austenitic steels

Abstract: Fatigue crack growth rates were measured in an annealed and in an aged maraging steel and in three different austenitic steels Microhardness measurements were used to determine the plane strain plastic zone sizes as a function of ΔK and to evaluate the cyclic flow stress of the material near the crack tip The presence of a reversed cyclic plastic zone within the monotonic plastic zone was confirmed The two maraging steels work soften near the tip of the crack while the three austenitic steels work harden The fatigue crack growth rates of the maraging steels are independent of the monotonic yield stress and are typical of the growth rates of steels with a bcc crystal structure The crack growth rates in the stainless steels are an order of magnitude lower than for maraging steels for ΔK< 30 ksi √in The excellent fatigue crack growth resistance of austenitic stainless steels is related to the de-formation induced phase transformations taking place in the plastic zone and to the low stacking fault energy of the alloys

The stress intensities for slow crack growth in steels containing hydrogen

Abstract: A test technique has been developed to determine the stress intensity for slow crack growth in hydrogen precharged steels. Measurements on several grades of maraging steel and a 300M steel show that hydrogen contents on the order of 2 ppm reduce the stress intensity for slow crack growth by 50 pct or more of theK Ic values. At equivalent hydrogen contents the 300M steel was more severely embrittled than the mar aging steels. Comparison of the present results with aqueousK Iscc data indicates that the amount of hydrogen “picked up by the steels in stress corrosion increases with increasing yield strength.

Fluoride Salt Corrosion and Mass Transfer in High Temperature Dynamic Systems

Abstract: Corrosion tests ranging from 3000 to 20,000 hours were conducted on nickel and iron based alloys in fused fluoride salt at temperatures ranging from 450 to 704 C (842 to 1299 F). The objective of the experiment was to find suitable fused salt container material for application in the nuclear molten salt reactor. The materials tested were Hastelloy N, titanium modified Hastelloy N, Type 304L stainless steel, and a maraging steel. The two types of salts were (1) LiF-BeF2 with varying amounts of UF4, ThF4, and ZrF4, (fuel salt), and (2) a mixture of NaBF4 and NaF (coolant salt). The compatibilities of these materials with the salts were determined from weight change data and chemical, metallographic, and electron microprobe analyses of the test specimens along with chemical analyses of the salts. The corrosion was manifested as temperature gradient mass transfer. The rate of corrosion of Hastelloy N in LiF-BeF2 base salts was controlled by diffusion of chromium in the alloy and was very small (<0.1 ...

Influence of Preloading on the Sustained Load Cracking Behavior of Maraging Steels in Hydrogen

Abstract: Precracked center notch specimens of 18% Ni maraging steel (250) and (300) were preloaded in dry argon and air, respectively, to various percentages of KIc, unloaded, and then threshold st...

Evaluation of shuttle solid rocket booster case materials. Corrosion and stress corrosion susceptibility of several high temperature materials

Abstract: Candidate alloys for the Shuttle Solid Rocket Booster (SRB) case were tested under simulated service conditions to define subcritical flaw growth behavior under both sustained and cyclic loading conditions. The materials evaluated were D6AC and 18 Ni maraging steel, both heat treated to a nominal yield strength of 1380 MN/sq m (200 ksi). The sustained load tests were conducted by exposing precracked, stressed specimens of both alloys to alternate immersion in synthetic sea water. It was found that the corrosion and stress corrosion resistance of the 18 Ni maraging steel were superior to that of the D6AC steel under these test conditions. It was also found that austenitizing temperature had little influence on the threshold stress intensity of the D6AC. The cyclic tests were conducted by subjecting precracked surface-flawed specimens of both alloys to repeated load/thermal/environmental profiles which were selected to simulate the SRB missions. It was found that linear removal operations that involve heating to 589 K (600 F) cause a decrease in cyclic life of D6AC steel relative to those tests conducted with no thermal cycling.

Processing and Properties of 18Ni Maraging Steel by Powder Metallurgy

Abstract: : Using 18Ni Mar 300 powder processed by the rotating electrode process, rods were extruded under varying temperatures and ram speeds. It is observed that control of both variables allows structure control and increases the Charpy V-notch toughness from 7 to 23 ft-lb at room temperature.

Structure and phase composition of weld seams in maraging steel

Abstract: 1. The structure and phase composition of welds made by electroslag welding were investigated after different heat treatments. 2. The possibility of grain refining of the heat-affected zone and the weld seam was shown. 3. The chemical microheterogeneity and phase heterogeneity of the weld seam and heat-affected zone were investigated. The existence of segregation heterogeneity is responsible for the difference in tendency to precipitation hardening in different sections of the seam, and the phase heterogeneity reduces the effect of aging. 4. The phase heterogeneity is eliminated by heating in the austenitic range, and homogenization also eliminates segregation heterogeneity to a considerable extent.

Effect of the thermal cycle in welding on the structure and phase composition of the heat-affected zone in maraging steel

Abstract: 1. The increase of grain size during welding depends on the cooling rate and on the time the metal remains at temperatures above the α→γ transformation temperature. 2. Cooling from α→γ transformation temperatures at a low rate leads to an increase in the amount of retained austenite and some reduction of hardness in the heat-affected zone.

The Effect of Hydrostatic Pressure Environment on the Low Cycle Fatigue Properties of a Maraging Steel

Abstract: To investigate the low cycle fatigue properties of an 18 percent nickel maraging steel, a high pressure fatigue testing machine including the high pressure chamber and associated hydraulic controls was designed and developed to apply simultaneously to the specimen (1) constant fluid pressure up to 100,000 psi, (2) mean uniaxial tensile or compressive stress, and (3) alternating push-pull load at a selected rate. Using this machine, notched and unnotched specimens were tested. Results indicated a definite increase in fatigue life of the material in the high pressure environment.