Thermal embrittlement and purity in MAR 350 steel

Abstract

Maraging steels are recognised for their considerable combination of strength and fracture toughness. Following the work by Spaeder [1 ] 9 it has been shown that with increasing strength, fracture toughness in the aged condition is not affected by variations in the level of residual elements normally measured with these steels. Nevertheless, maraging steels may be thermally embrittled. Using Charpy impact testing, Rack and Kalish [2] reported that solution treated MAR 350 samples could be significantly sensitised by holding for 4 hours at temperatures in the range 800 0 to 950 0 C. They were unable to use age hardened samples as impact energies in this condition were too low for any sensitisation effect to be reliably monitored.

We have investigated thermal embrittlement effects in fully aged MAR 350 samples using KIC fracture toughness measurements. In particular, we have examined the effect of purity using steels having different levels of residual elements (Table 1 ) and determined the effect of time at a sensitising temperature of 900 0 C.