ON DETERMINATION OF NON-METALLIC INCLUSION IN CHROMIUM STEEL BY HOT-H₂SO₄ METHOD

Abstract

It has been recognized by Gakushin that non-metallic inclusions in high carbon steel or chromium steel was determined by the hot-H₂SO₄ method. But should quenching be not carried out on these stee1, there produced the carbide that will not be decomposed by making use of KMnO₄ oxidizing agent, and no reproducible result would be obtained.
The authors have made an investigation on the applicable limit of quenching and samples making on the alloying elements in this kind of stee1.
The results obtained were as follows.
(1) It will generally be desirable to make water quenchihg for the cutting specimens, though we trially designed the vacuum quenching apparatus for the drilling specimen.
(2) It is not necessary to quench when carbon and chromium contents in Cr-steels are less than 0.7% and 1% respegtively.
Quenching is generally required on 13% Cr-steel and 18-8 stainless steel, however, in case Ti is contained in them, TiC wil1 be produced which is not decomposed by KMnO₄ treatment.
On the other hand the authors have made an experiment on solubility of Cr₂O₃ by Hot-H₂SO₄ method, and have found that Cr₂O₃ content in chromium steel is determined by this method.
In connection with the above, as a result of quantitative analysis of Cr₂O₃ contained in bearing steel or case-hardened stee1, we reached the conclusion that its content is far 1ess than silicate or aluminate inclusons.