The Effect of Heat Treatment on the Fracture Toughness and Subcritical Crack Growth Characteristics of a 350-Grade Maraging
The heat treatment response of a 350-grade maraginf steel, with the nominal composition 18.5 Ni, 12 Co. 4.6 Mo, 1.4 Ti, balance le. has been determined in billet and bar form. When ■ged at temperatures below 90(rF, the material was very susceptible to subcritica! crack growth, and premature brittle Iracture occurred in unnotched tension specimens loaded at a slow strain rate in laboratory air. Fracture mechanics was used to interpret this behavior. The introduction of reverted austenite signiticantly decreased the strength level but had little effect on Iracture toughness. The resistance to brittle Iracture of this material is contrasted with that ot high-strength steels currently used by the airplane industry. INTRODUCTION F'he continuing demand lor ultra-high-strength steels prompted the recent development ol two 3S0-grade maraging steels. The development and properties of one alloy nominal composition P.5 Ni. i:.5Co. .VK Mo. 1.7 Ti. 0.15 Al. balance le were recently described ( I ). Vasco Metals, a subsidiary of I eledyne. Inc.. introduced a second alloy that is lower in titanium than the first to avoid segregation problems and has slightly higher nickel and molybdenum contents. Fn this paper, the effect of heat treatment on the fracture toughness and subcritical crack growth resistance of this second alloy is described.
The physical metallurgy of maraging steels
AbstractMaraging steels are a class of high-strength steels characterised by very low carbon contents and the use of substitutional elements to produce age-hardening in iron–nickel martensites. The term 'maraging' was coined from a combination of martensite and age-hardening.
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.