Abstract
Among the various grades of commercially available 18 wt. % nickel maraging steels, the one with nominal 0.2% proof strength in the range 1700-1750 MPa is the most commonly used and is distinguished by an excellent combination of high strength and high fracture toughness. The main alloying elements are nickel, cobalt, molybdenum and titanium. The first three of these are present at relatively high concentrations in the chemical composition. The high cost of these metals leads to a high cost of production and this becomes a deterrent to extensive use of the steel. In the present study, an attempt was made to produce the steel by pegging the levels of these alloying elements in the lower half of the specified range. The objective was to save on the raw material cost, while still conforming to the specification. The steel so produced could not, however, attain the specified tensile properties after final heat treatment. The observed behavior is explained based on the role played by the different alloying elements in driving the precipitation hardening reaction.
Highlights
18 wt% Ni maraging steels based on iron-nickel martensite constitute a very important family of high strength steels
The higher strength variants are used where high strength is of paramount importance for design and one can manage with moderate levels of fracture toughness
The 1988 symposium [1] deliberated on important developments and applications of maraging steels and more recently the metallurgy of 18% Ni maraging steels has been reviewed by Rao [2]
Summary
18 wt% Ni maraging steels based on iron-nickel martensite constitute a very important family of high strength steels. They distinguish themselves by demonstrating an unparalleled combination of high strength and high fracture toughness in heat treated condition and excellent hot and cold workability and weldability. Because of their high strength to weight ratio, they find extensive application in aerospace sector. Titanium is used as the primary strengthening element in these steels; precipitation of titanium bearing intermetallic particles in martensitic matrix in a uniform and finely dispersed manner during aging leads to development of very high strength levels. The 1988 symposium [1] deliberated on important developments and applications of maraging steels and more recently the metallurgy of 18% Ni maraging steels has been reviewed by Rao [2]
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