The experiment was conducted to establish an accurate separation and determination method for Al
2O
3 inclusions co-existing with AlN in steels.
Three kinds of specimens were prepared so that the contents of Al and N were Al<N, Al=N, and Al>N in atomic ratio, respectively. These were tempered at 600°∼900°C after solution treatment at 1300°C.
The samples were submitted to analytical methods by I
2-CH
3OH, Br
2-CH
3CO
2CH
3, and acids, respectively, to determine AlN and Al
2O
3 contents, and furthermore to electron microscopic observation to clarify the relation between the precipitation and the chemical behavior of AlN. The oxygen contents were comfirmed to be a range of 20∼30 ppm for each sample, thus indicating the presence of definite amounts of Al
2O
3 inclusions.
The experimental results showed that the AlN values by I
2-CH
3OH method were lower than those by Br
2-CH
3CO
2CH
3 method as for the samples [Al>N] and [Al=N]; the former values were 30∼90% of the latters. These differences were proved to be based on the presence of some AlN which was decomposed by CH
3OH, and correspondence was observed between the precipitation forms and the chemical behavior of AlN.
Therefore, it is improper for correction of the Al
2O
3 value by I
2-CH
3OH method to use, as usual, the AlN value by Br
2-CH
3CO
2CH
3 method. In case of co-presence of AlN it was comfirmed that the Al
2O
3 inclusions are most effectively determined by HNO
3(1+5) dissolution method.
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