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Effects of impurities in steels on mechanical properties and corrosion behaviour
Author(s) -
Grabke Hans Jürgen
Publication year - 1987
Publication title -
steel research
Language(s) - English
Resource type - Journals
eISSN - 1869-344X
pISSN - 0177-4832
DOI - 10.1002/srin.198700250
Subject(s) - materials science , grain boundary , metallurgy , embrittlement , intergranular corrosion , ductility (earth science) , impurity , creep , stress corrosion cracking , corrosion , nucleation , austenite , carbon fibers , auger electron spectroscopy , stress (linguistics) , composite material , chemistry , microstructure , physics , organic chemistry , composite number , nuclear physics , linguistics , philosophy
In steels produced and utilized in the Fed. Rep. of Germany the elements P and Sn may occur as impurities. Both these elements tend to enrich (segregate) at grain boundaries. The equilibria of grain boundary segregation in iron and the effects of alloying elements have been studied for P and Sn by Auger‐electron‐spectroscopy and were thermodynamically described. For a 3.5% NiCrMoV‐turbine steel the grain boundary segregation of P and its effect on ductility have been studied in detail, with the results that the long‐term embrittlement of this steel during application at temperatures around 400°C can be predicted and the maximum bulk concentration of P can be given. The effect of Sn on the creep of a 1% CrMoNiV steel at 550°C has been investigated, Sn favours cavity nucleation and growth, therefore tertiary creep starts earlier and premature failure occurs with increasing Sn content. Therefore, the Sn content should be kept as low as possible in heat resistant steels. Since carbon also segregates to grain boundaries and can displace P and Sn if there is enough free C in a steel, plain carbon steels are not subjected to embrittlement by P and Sn. The susceptibility to intergranular stress corrosion cracking in nitrates and other electrolytes is somewhat enhanced by P, however, only in a restricted range of potentials. In the range of maximum susceptibility the impurities have no effect, all carbon steels are susceptible to IGSCC, independently of their purity. So stress corrosion cracking cannot be suppressed by diminishing the content of phosphorus – only by avoiding the critical corrosion conditions concerning electrolyte and potential.