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Grain‐boundary segregation of phosphorus and micro‐structural changes in the steel X 20 CrMoV 12 1 during long‐term application at elevated temperatures
Author(s) -
Mackenbrock Markus,
Grabke Hans Jürgen
Publication year - 1991
Publication title -
steel research
Language(s) - English
Resource type - Journals
eISSN - 1869-344X
pISSN - 0177-4832
DOI - 10.1002/srin.199101313
Subject(s) - grain boundary , metallurgy , phosphorus , materials science , diffusion , impurity , grain boundary diffusion coefficient , auger electron spectroscopy , carbide , analytical chemistry (journal) , chemistry , microstructure , thermodynamics , physics , organic chemistry , nuclear physics , chromatography
Phosphorus occurs as impurity in 12% CrMoV‐steels and tends to be enriched at grain boundaries. The phosphorus grain‐boundary segregation in a laboratory cast of steel X 20 CrMoV 12 1 with a relatively high phosphorus content (0.057% P) was studied by Auger electron spectroscopy and the segregation kinetics and equilibria were described. Using the results it was possible to predict and compare phosphorus segregation with measured phosphorus concentrations in long‐term annealed steels. By means of the radioactive tracer method the diffusion of phosphorus was studied in detail. The comparison with segregation kinetics showed that phosphorus is transported to the grain boundaries faster than is to be expected from bulk diffusion. Investigations by transmission‐electron‐microscopy showed recrystallisation and an agglomeration of carbides with aging time and the occurrence of new phases (Laves‐phase Fe 2 Mo). All these processes lead at first to an increase in toughness as established in notch‐impact fracture tests for the laboratory cast, after long‐term use however, a reduction in toughness is to be expected.