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THE ANALYSIS OF MONOLAYER SEGREGANTS IN STEELS

Objective



The presence of impurities at grain boundaries in steels can cause intergranular brittle failure in stress corrosion, impact or creep situations. Identification and quantification of these segregants is often carried out using Auger electron spectroscopy. However, the lack of reproducibility of AES instruments in the quantitative mode frequently makes it difficult to relate measurements made in different laboratories. A reference material with known and reproducible segregants for the major impurities encountered in practice, (P; Sn, Sb and S) has therefore been produced.

RESULTS

Difficulties in the fabrication of the low alloy steel restricted the segregant elements to P and Sn. When the heat treated at 200 C for 2 hours, water quenched and further heat treated for 48 hours at 580 C a reproducible segregation of the impurity elements was achieved. The samples were then broken under high vacuum and analyzed using AES.

After calibration of the spectrometer energy and intensity scales using the procedures developed under project RM 193, the laboratories participating in the intercomparison agreed to within +/- 15% on concentrations of the segregated P and Sn equivalent to approximately 30% of a monolayer. This represents an improvement of over an order of magnitude.

The calibration of the material is based upon the intercomparison and literature values for the Auger electron yields. Absolute certification of the material is therefore not possible but it is made available to AES users for the validation of their instrumental factors and procedures.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

National Physical Laboratory (NPL)
Address
Queen's Road
TW11 0LW Teddington
United Kingdom