Nitrogen MetallurgyIn order to achieve the high nitrogen content aimed for it is possible to influence two factors which are described using Sievert's square root law (Fig. 2) Sievert's law and parameter for the calcu]ation of the nitrogen solubility at 1 600'C.

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The paper presents a new process for nitrogen alloying austenitic steels beyond solubility limit in a pressurized electroslag remelting furnace using Si3N4 as nitrogen source. With the aid of this process it is possible to attain nitrogen percentages far beyond the solubility limit at atmospheric pressure. These high nitrogen contents impart a distinct improvement to the properties of the material. Yield strengths Rp0.2>600 N/mm2 at ambient temperature are achieved. The high tensile values are attributable to the lattice expanding effect of force‐dissolved nitrogen. A reduction in forming characteristics A5 and Z normally associated with a distinct increase in tensile strength is not noticeable. The tests at ambient temperature have further shown that nitrogen alloyed steels display high fatigue strength values. If results of the fatigue tests are evaluated on the basis of the empirical relation 0.30 < σzdw/Rm<0.45 it is found that the values of the steels tested are generally at the upper limit of this value or even above it. The very good creep test results of nitrogen alloyed steels deserve emphasis. Up to 800°C they are comparable to the creep values of high temperature alloys. This is attributable to the precipitation behaviour of the steels caused by the presence of nitrogen. Embrittlement occurs only to a very small extent and precipitates, in particular Cr2N, enhance creep resistance owing to their favourable arrangement. The new technique of nitrogen alloying beyond the solubility limit opens up favourable opportunities for nitrogen alloyed austenitic steels in new applications. This development offers further advantages in that considerable savings in nickel as an alloying element can be made and that material can be much better utilized in the design of components.