Abstract
M.Tech.
Owing to the difficulties in the procurement of internationally certified reference materials
for iron and steel, local firms are using their own standards manufactured by casting
techniques. It is necessary to assess the integrity of these materials using international
standards as control to these in-house reference materials. Macro and micro-examination
were carried out to reveal the nature of reference materials and hence evaluate their
quality. The consistency of chemical composition of standard materials and the accuracy of
the analyses based on the in-house standards were evaluated.
The results showed that local standards were characterised by gross casting defects. In
comparison the imported standards had micro-structural uniformity and free from casting
defects. This shows the essential difference in production method. Casting has severe
limitations when it comes to the production of components of low segregation and internal
soundness. First, the partitioning of solutes between solid and liquid phases invariably
leads to segregation and loss of homogeneity. Second, the volumetric change
accompanying solidification results in shrinkage cavities.
If stringent production controls are not observed, the proprietary standards are bound to
have a widely varying chemical composition. In this regard, the calibration and
standardisation would essentially be flawed. Hence the subsequent chemical analyses of
standards cannot be reliable. It is necessary to establish an analytical methodology that
yields reliable results. Standards used for calibration should have a high degree of chemical
purity and homogeneity. The study covers other possible production options for standards
that can be used for accurate calibration and standardisation of spectrometers for chemical
analysis of iron and steel. The use of vacuum melting followed by rapid casting in special
chill mould is recommended.