A new nitrogen alloying technique - a way to distinctly improve the properties of austenitic steel

Abstract

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.

Corrosion resistance of three austenitic stainless steels for biomedical applications

“…Only a slight superficial attack was found on the last type of SS supporting the hypothesis that the increase in current at potentials around 1,100 mV was due to the oxygen evolution reaction rather than pitting. These findings support the electrochemical results obtained from EIS and polarization data that indicated the more protective character of the oxide film on the surface of the DIN 1.4460 high N. Finally, it must be pointed out that the high nitrogen and fully austenitic 1.4460 steel shows very high mechanical strength and toughness [13].…”

On Cr2N precipitation mechanisms in high-nitrogen austenite

“…by pressurized electroslag remelting [13]. The resulting steel was received in the form of a On the other hand, the stability domain of ferrite starts at temperatures as low as 1300 ºC, and annealing at higher temperatures results in duplex microstructures [11].…”

“…Nevertheless, at later precipitation stages long-range volume diffusion of nitrogen induces retardation of new nucleation events and inhibition of active reaction fronts that eventually cease to migrate. This results in incomplete decomposition even though the matrix may still be supersaturated in nitrogen and the reaction driving force is not equal to zero [10,13,15,16].…”

Deoxidation and desulfurization of pressurized liquid high nitrogen stainless steels with calcium.

“…3) Recently pressurized electroslag remelting process (PESR)has been developed as a manufacturing process for high nitrogen steels. 4,5) This process needs a closed pressure vessel.…”

“…I Substituting Eqs. (4) and (5) The following equation can be derived frorn Eqs. (6), (9) and (10) .…”