STAINLESS AND ELECTRICAL STEELS UDC 669.14.018.8 HIGH-STRENGTH AUSTENITIC STAINLESS STEEL V. G. Gavrilyuk 1 and H. Berns 2 Translated from Metallovedenie i Termicheskaya Obrabotka Metallov , No. 12, pp. 17 – 19, December, 2007. Based on the studies of carbon and nitrogen effects on the electron structure, short-range atomic order, and thermodynamic stability of iron solid solutions, a physical concept for alloying steels with carbon and nitro- gen is proposed. The concept is used for the design of a cost-effective austenitic corrosion-resistant steel of super-high strength and fracture toughness. INTRODUCTION Preliminary calculations of electron structure give evi- dence that the replacement of carbon by nitrogen in g iron in- creases the density of electron states at the Fermi level, i.e., enhances the metallic character of interatomic bonds (see e.g. [1]). This conclusion is consistent with data on the con- centration of conduction electrons obtained by measure- ments of electron spin resonance [1 – 3]. A correlation be- tween electron structure and short-range atomic order was shown in [1] where the thermodynamic stability of iron- based solid solutions is discussed in terms of ordering result- ing from prevailing metallic interatomic bonds or from clus- tering caused by covalent bonds. Subsequent measurements on austenitic steels, where a part of nitrogen was replaced by carbon, revealed a further enhancement of the metallic interatomic bonds [4, 5]. These results made it possible to propose a physical con- cept for alloying steels with carbon together with nitrogen [4]. The aim of the present study is to show how this concept can be used for the development of a new austenitic high- strength corrosion-resistant steel. RESULTS AND DISCUSSION Atomic Interactions and Thermodynamics The concentration of conduction electrons r c in austenitic steels as a function of the C, N or C + N contents is presented in Fig. 1. Carbon does not cause any significant change in r c , which suggests that it contributes its electrons to states below the Fermi level, i.e., assists strengthening of covalent interatomic bonds. With nitrogen content increasing up to some optimal value of about 0.6 wt.%, r c increases and then decreases at higher nitrogen contents. A remarkable in- crease of r c occurs if some part of nitrogen is replaced by carbon and, moreover, the maximum of r c is shifted to higher contents of interstitial atoms. Two conclusions follow from these results: (1 ) the en- hancement of the metallic character of interatomic bonds due to alloying with C + N should improve the toughness of austenitic steels; (2 ) the shift of the r c maximum in C + N Metal Science and Heat Treatment Vol. 49, Nos. 11 – 12, 2007 566 0026-0673/07/1112-0566 © 2007 Springer Science + Business Media, Inc. 1 G. V. Kurdyumov Institute for Metal Physics, Kiev, Ukraine. 2 Ruhr University Bochum, Bochum, Germany. 4.0 3.0 2.0 1.0 0 1.0 2.0 3.0 4.0 0 0.2 0.4 0.6 0.8 1.0 1.2 C(N), wt.% (Ñ + N), at.% r s – 22 –3 10 , ñm ´ 0.5 0.7N 0.88N 0.8 0.95 1.07 Ñ+N Ñ+N Fig. 1. Concentration of conduction electrons r c in austenitic steels as a function of C, N or C + N contents: :) Cr13Mn18C0.4N0.4; =) Cr13Mn18C0.25N0.25; O) Cr19Mn19C0.49N0.58; N) Cr18Mn19C0.34N0.61; &) Cr18Mn20N0.88; q) Cr13Mn18N0.7; p) Cr15Mn17N0.45; )) Cr18Ni16Mn10N; ^) Cr18Ni16Mn10C.