Effect of N and B on Properties of 18Cr-12Ni Stainless Steel

Abstract

In previous reports (Tetsu-to-Hagane 45, 11, 1276; 46, 5, 566; 46, 14, 1758), the authors reported the effect of Nb, Ti, W and Mo on properties of 18Cr-i2Ni austenitic stainless steels.
This report concerned the effect of N and B on aging behavior, microstructure, precipitates, tensile properties at various temperatures and creep-rupture strength of the same steel.
The following results were obtained:
1) The specimen with N was scarecely hardened during aging. The specimen with B was hardened when the C content was higher.
2) In the specimen with N, precipitates of Cr₂₃C₆ and Cr₂N were observed. In the specimen with B, CrB₂, Fe₂B and B₄C remained after solution treatment for one hour at 1100°and Cr₂₃C₆ precipitated during aging.
3) Tensile strength was increased linearly with the increase of N content at all testing temperatures, but that of the specimen coutaining B was raised with the increase of B content below 600°.
4) Creep rupture strength of the specimen with N reached maximum when the N content was about 0.16%. Creep-rupture strength of the specimen with B was increased greatly with the B content, but increased slightly when the B content exceeded 0.1%.
5) Oxidation resistance was almost invariable with different N contents when the Ncontent was less than 0.16% but grew slightly worse when the N content exceeded that content.
Oxidation resistance of the specimen containing B grew remarkably worse with increase that the B content.