JPH06148170A - Analyzing method for trace oxygen of iron and steel - Google Patents

Abstract

PURPOSE:To provide a method capable of perfectly removing the oxide adhered to a sample surface even in the state where the surface oxidation at sample preparation by a grinder or file is present, precisely measuring the extremely trace oxygen quantity in iron and steel and also analyzing it in a short time. CONSTITUTION:In an analyzing method of trace oxygen in iron and steel which comprises heating, extracting and measuring the trace oxygen in an iron steel sample after grinding its surface by a grinder or file, the sample after grinding treatment is put in a carbon crucible and preliminarily heated at a temperature of 900 deg.C or more and less than 1400 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a trace amount of oxygen in steel with high precision and in a short time by removing oxygen adhering to the surface of an analytical sample.

[0002]

2. Description of the Related Art With the improvement in quality of steel, the amount of oxygen in the trace amount of steel has come to be considered important, and the accuracy of analysis in the trace amount region has become an important issue. For example, in Al deoxidized steel, the amount of oxygen in the steel is also a measure of inclusions in the steel,
In high-grade high-carbon steel used as a bearing material, the amount of inclusions is severely limited, and the oxygen content in the steel is required to be 10 ppm or less.

A method often used for analyzing such a trace amount of oxygen is that a rod-shaped sample of about 1 g is heated to about 2000 ° C. in a graphite crucible under a helium gas atmosphere to melt the sample. A method in which oxygen in the sample is extracted as CO gas and infrared absorption is measured to obtain (hereinafter,
Inert gas melting-infrared absorption method).

Normally, the surface of an analytical sample is oxidized at the time of sampling, and a thick oxide layer is formed. Therefore,
A method of grinding this oxide layer with a grinder or a file is used. However, it is known that even after polishing, surface oxidation has already started from the time of polishing, and about 2 to 4 ppm of oxygen adheres and remains (iron and steel, vol.71 (1885),
S412).

In addition, a method of quantifying true oxygen in steel by chemically polishing or electrolytically polishing the sample surface is also known (iron and steel, vol.78 (1992), 774-781).

[0006]

From the above, in the method of polishing the surface of the analytical sample with a grinder or a file, the true oxygen in the steel and the surface oxide on the surface of the sample exist in the CO gas extracted. However, there is a problem in that true oxygen in steel cannot be quantified because it is mixed with oxygen.

On the other hand, the amount of oxygen existing as a sample surface oxide is not constant and varies depending on, for example, the polishing material, polishing time, polishing pressure, etc., so that there is a problem in that there are large variations in analysis values.

Further, the method of chemically polishing or electrolytically polishing the surface of the sample has a problem that the pretreatment of the sample becomes complicated and it takes time.

The present invention has been made in order to solve the above problems, and completely removes the oxide adhering to the sample surface even when there is surface oxidation during sample preparation with a grinder or a file. However, it is an object of the present invention to provide a method capable of accurately measuring an extremely small amount of oxygen in steel and performing analysis in a short time.

[0010]

The present invention provides an analytical method for accurately measuring an extremely small amount of oxygen in steel which achieves such an object, and the surface of the steel sample is grinded, sanded or the like. In the method of heating and extracting a trace amount of oxygen in the sample after grinding, the sample after the grinding treatment is put in a carbon crucible and preheated at a temperature of 900 ° C. or more and 1400 ° C. or less.

An appropriate amount of steel sample is taken, and the sample surface is ground by a physical means such as a grinder or a file. The amount of sample may be about 0.8 to 1.2 g. Place an accurately weighed sample in a carbon crucible such as graphite or other container.

A carbon container containing a sample is placed in a reaction tube and preheated in an inert gas atmosphere such as helium. This preheating will be described with reference to FIG. In FIG. 1, the temperature of the sample is raised in two steps (1000 ° C. → 2500 ° C.) and the amount of extracted oxygen is measured with time. The vertical axis represents the oxygen extraction signal intensity obtained by measurement with an infrared spectrophotometer, and the horizontal axis represents time. In the case of pretreatment with a grinder and a file, an extraction curve is obtained after heating for several tens of seconds at 1000 ° C. At this time, the obtained oxygen extraction signal indicates that the sample was not dissolved, so that the oxygen adhering to the sample surface layer reacted with carbon and was extracted. Next, the sample is melted by heating to 2500 ° C., and an extraction signal of oxygen in steel is obtained.

From the above, it is necessary that the preheating temperature is a temperature at which the oxide on the surface of the sample is sufficiently decomposed and the oxygen in the steel is not extracted.

Preheating is 900 ° C or higher 140 from other experimental results.
A temperature of 0 ° C or lower is suitable, and a temperature of 1000 ° C or higher and 1200 ° C or lower is particularly preferable. The preheating time depends on the temperature, for example 10
At 00 ° C, it is preferably about 60 to 70 seconds. After completion of the preheating, the temperature of the reaction tube is raised, the temperature is set to a temperature at which the steel sample is melted, and the analysis may be performed by a conventional method.

The detector is preferably one capable of detecting an extremely small amount of oxygen with high sensitivity, and for example, an infrared absorption detector may be used.

[0016]

[Examples] Samples A and B having different oxygen concentrations prepared by drawing up from molten steel were grinders (SiC system, 80
No.), and after weighing, put it in a graphite crucible. This crucible was put in a heating furnace, and helium gas was sent from a cylinder to a reaction tube through a gas regulator to replace the whole system with helium gas. Then turn on the heater of the heating furnace and turn it on.
Heated at 00 ° C for 60 seconds. After completion of this preliminary heating, the temperature was raised to 2500 ° C. and heating was performed for 30 seconds. The carbon monoxide concentration in the helium gas continuously discharged from the reaction tube was measured by an infrared absorption detector to determine the oxygen content rate.

Table 1 shows the ultratrace oxygen concentration of each steel sample thus obtained. In addition, grinder (SiC system, 80
No.) The results of measuring the oxygen concentration of the above-mentioned steel samples polished or electrolytically polished by the conventional method are also shown in the same table.

[0018]

[Table 1]

The number of repeated analyzes was 10 in each method.

The conventional belt polishing method has a shorter total analysis time from the pretreatment to the analysis than the method of the present invention, but the analysis value is high and the variation σ is large.

The analysis result of the method of the present invention shows a good agreement with the conventional electrolytic polishing method, and the variation σ is improved compared to the conventional belt polishing method as well as the electrolytic polishing method. Further, the total analysis time was reduced to 1/3 or less as compared with the electrolytic polishing method.

[0022]

According to the present invention, oxygen adhering to the surface during sample preparation can be easily removed, and accurate determination of oxygen in steel can be measured in a short time.

[Brief description of drawings]

FIG. 1 is a graph in which the temperature of a sample is raised in two steps and the amount of oxygen extracted is measured with time in the method of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroyasu Yoshikawa 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Yoshihiro Funabiki 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Date Main Steel Pipe Co., Ltd.

Claims (1)

[Claims] 1. A method of grinding a surface of a steel sample with a grinder, a file, etc., and then extracting and measuring a trace amount of oxygen in the sample by heating, and putting the sample after the grinding treatment into a carbon crucible.
Method for analysis of trace oxygen in steel characterized by preheating at a temperature of 900 ° C or more and 1400 ° C or less