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Secondary ion and sputtered neutral mass spectrometry

Secondary ion mass spectrometry (SIMS) and sputtered neutral mass spectrometry (SNMS) are used in the study of various metallurgical problems, specifically in areas which utilize the sensitivity, surface specificity or imaging capabilities of these techniques. Research was carried out into the quantification of nitrogen pick up during the bright annealing of stainless steel, the determination of the spatial distribution of light elements in titanium carbonitride and iron boride, precipitates and the application of SIMS for the identification of nonmetallic inclusions using a chemical tracer technique.

Nitrogen pick up in stainless steel:
The presence of nitrides has effects on such properties as corrosion resistance and hardness. Clearly, it is desirable to have techniques capable of measuring the degree of nitrogen pick up within the surface layers of steel (ie less than 1 micron). SNMS has potential within this area.
Type 420 grade stainless steels were annealed in both nitrogen and hydrogen atmospheres and compared with data obtained from abraded material. The SNMS data were obtained from the first few microns of the steel surface over an area of approximately 1 mm{2}. The chromium and nitrogen determinations were compared to bulk chemical analysis. Nitrogen pick up was at its maximum for the material processed in nitrogen, and at its minimum for the abraded material. The material annealed in hydrogen also displayed a significant surface nitrogen content. It is suggested that this is due to the small amounts of nitrogen in the hydrogen gas, coupled with a reduced moisture contents promoting nitrogen pick up.

Light element imaging SIMS:
The chemistry of titanium carbonitride particles has been investigated in Type 409 stainless steel. Extensive negative ion mass spectrometry of the particles, using oxygen dosing, revealed that carbide, carbonitride and nitride fraction could be imaged. Qualitatively, the particle consisted of a titanium nitride core surro unded by a titanium carbide skin, with some titanium carbonitride contained within each fraction.
Secondly, a phase in steel suspected to be iron boride was examined to assess its boron distribution. The SIMS boron image obtained showed clear correlation between the suspect iron boride phase and the SIMSimage.

Chemical tracer studies:
In order to improve the cleanness of steel products, it is necessary to ascertain which if the many sources of oxide inclusions are the most important. Armed with this knowledge, it is possible to direct effectively the resources required for their minimization. A method has been developed which utilizes the sensitivity of SIMS to detect the presence of chemical tracers within the nonmetallic inclusions and hence give some indication of origin.

Reported by

British Steel plc
S60 3AR Rotherham
United Kingdom
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