Decarburization of Low Ni and Cr Cast Irons

Abstract

In the growth test or the resistance to oxidation test of cast irons in air, there are always phenomena such as oxidation and decarburization. In this paper, using low Ni and Cr cast irons after the abovementioned test, the decarburization coefficient K was obtained. The equation employed is
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When n=3, the expansion of eq. (1) divided by 2C₀ leads to
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Here, the above equation may be taken as C⁄2C₀=f(K).
For a variety of radius r, C⁄2C₀=f(K) is plotted on a graph where by the values of K are readily read.
If the radius r changes, the decarburization coefficient K must always remain constant. But, the values of K are more or less variable. Then, the K of the specimen is the mean value of the K which is obtained from eq. (2) at two points on the radius r. The values of K for other specimens are similarly calculated. The results obtained are as follows:
(1) On heating at 950°C for 60 hr, the decarburization coefficient K of specimens containing Cr is 2.5×10⁻⁷∼6.25×10⁻⁷(cm²·sec⁻¹). These values of K vary inversely with the Cr content.
The values of K for specimens containing Ni are 3.18×10⁻⁷∼6.25×10⁻⁷(cm²·sec⁻¹), varying proportionally with the Ni content.
(2) On heating at 800°C for 90 hr and 40 hr, the values of K(0.61×10⁻⁷∼1.42×10⁻⁷(cm²·sec⁻¹) for 90 hr, 0.99×10⁻⁷∼1.31×10⁻⁷ (cm²·sec⁻¹) for 40 hr) of specimens containing Cr, vary inversely with the Cr content. The effect of Ni additions or K is not so clear, but the value is 1.09×10⁻⁷∼1.34×10⁻⁷(cm²·sec⁻¹) for in case of the 90 hr heating and 1.06×10⁻⁷∼1.34×10⁻⁷(cm²·sec⁻¹) in case of the 40 hr heating.