ON THE METHOD OF TAKING SAMPLE FOR THE DETERMINATION OF OXYGEN IN IRON AND STEEL BY THE LEDEBUR METHOD (III).

Abstract

Nickel-thoria catalyst, used for the determination of oxygen in iron and steel by the hydrogen reduction process, is generally kept in containers of horizontal type. In this kind of container, hydrogen is liable to be not in uniform contact with nickel oxide, from which metallic nickel is produced as catalyst by reduction. Consequently, it is difficuit to obtain a satisfactory blank value of the catalyst The authors replaced the container of horizontal type by a vertical type in order to let hydrogen reduce nickel oxide as completely as possible by bringing them in uniform contact, and achieved to keep the blank value of the catalyst very low, such as 0.037mg. per hr. when the catalyst is at about 250°C. The blank value of the reduction tube with a boat was 0·065mg. per hr. when the tube was heated at 1, 200°C. With the improved apparatus, experiments were carried out to investigate whether the sample in the form of fine powder can be adopted for accurate analysis or not. Armco iron, a commercial carbon steel and two special steels were used as the materials for the test. It was confirmed that the oxygen contained in Armco iron can be analized with satisfactory accuracy under the following conditions:-
(1) The thickness of individual grain of the sample should be less than about 0·1mm.; (2) The surface oxygen of the sample should be extracted by reduction in hydrogen at 500°C during more than 1·5hrs. before the analysis is begun; (3) at the reduction temperature of 1, 200°C, time to be kept at this temperature should be at least 2hrs.
The accurate analysis of other kin ls of steel was unsuccessful under the same conditions as stated above. It was found that a very careful investigation should be carried out befor a satisfactory result is obtained about these materials.