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The resistance of and low-carbon stainless steel, containing nitrogen and silicon, to hydrogen embrittlement and slow failure is investigated, in a corrosive medium with hydrogen saturation. The resistance is relatively high.

The research topic selected is the influence of nitrogen and silicon (separately and together) on the stability of the austenitic structure in chromonickel stainless steel, as well as its mechanical properties, durability in a corrosive medium with hydrogen, crack formation, and corrosion in highly oxidative media. The solid-solution hardening of the steel is mainly due to nitrogen; silicon is largely responsible for the increased corrosional life in highly oxidative media. The positive influence of nitrogen on the durability of such stainless steel in aggressive media is due to the increased stability of austenite and reduced local microstress concentration.

The limiting solubility of nitrogen at atmospheric pressure in low-carbon stainless steels containing not more than 0.03% carbon, 13–25% chromium, 5–13% nickel, 0–5% silicon is calculated. Using Scheffler diagrams and the calculated limiting nitrogen content within steels of the system Fe–Cr–Ni–N–Si limits are determined for phase areas in relation to values of nickel and chromium equivalents. Temperatures are calculated for the start of martensitic transformation during cooling and plastic deformation of steels containing a different amount of chromium, nickel, nitrogen, and silicon.

The effect of nitrogen is considered on the mechanical and corrosion properties of austenitic stainless steels of the alloying systems Fe–Cr–N*, Fe–Cr–Ni–N, Fe–Cr–Ni–Mo–N, Fe–Cr–Ni–Mn–N, Fe–Cr–Ni–N–Si, and Fe–Cr–Mn–N; methods for introducing nitrogen into steels are analyzed. General dependences are obtained for the dependence of mechanical properties on nitrogen content. The effect of nitrogen on resistance to local corrosion is considered. Examples are provided for use of nitrogen-containing stainless steels.

Results of a study of austenitic corrosion-resistant steels of the Fe – Cr – Ni–N–Si alloying system are studied. The steels possess higher parameters of strength (by 25 – 30%) and corrosion resistance (by a factor of 5 – 28) as compared to chromium-nickel steels of type 18–11 serving today in strongly oxidizing media. Comparative analysis of the properties of the new steels and of steel 03Kh18N11 (GOST 5632) widely used in the chemical industry is performed.

The history of the creation and further development of corrosion-resistant steels in Russia is considered. The most important corrosion and mechanical properties of steels of different structural classes and alloys based on iron and nickel are provided. The effect on them of alloying and heat treatment is analyzed. Fields of application for commercial steels and alloys are presented.

Results of a study of the set of properties of corrosion-resistant steels based on the Fe−Cr−Mn system alloyed additionally with nitrogen and nickel are analyzed from the standpoint of their use as materials for high-duty structures in weakly and moderately aggressive media.

The concentration of elements in existing austenite-ferrite steels varies in a rather narrow range. This is associated with the necessity of ensuring an optimum austenite/ferrite proportion in the structure (∼ 40–60%), which is attained by adding ferrite- and austenite-forming elements in specified amounts. The article concerns the structure, mechanical properties, and corrosion resistance of low-carbon austenite-ferrite steels with 18–25% Cr, 2–6% Mo at −7% Ni and 0.15% N and the choice of the most suitable limiting concentrations of chromium and molybdenum.

1. Alloying of Cr-Ni steels with molybdenum (up to 4–5%) leads to additional hardening in the original quenched condition but has almost no effect on hardening during aging of steels not containing cobalt and does not change the character of the redistribution of atoms of alloying elements in the solid solution during aging. 2. The structure of Cr-Ni steel alloyed with molybdenum and cobalt in the quenched condition can be regarded as a heterogeneous solid solution in which the separation of molybdenum atoms occurs to a considerable extent. During subsequent aging the differentiation of atoms of Cr, Mo and atoms of Fe, Co, and Ni continues, and also ordering in sections rich in iron and cobalt.

1. Martensitic stainless steels of the 9Cr−14Co−Ni and 9Cr−14Co−6Ni−Mo types are promising materials for the development of high-strength steels for cryogenic technology. The presence of nickel and molybdenum (the latter up to 3%) simultaneously increases the strength and lowers the sensitivity to stress concentrations at 20 and −196°. 2. An ultimate strength of 150 kgf/mm2 is the level at which one observes an increase in the sensitivity to stress concentrations at −196° for steels of the 9Cr−14Co−6Ni−Mo type, manifest in lower values of σbCr, KIc, andanIV. 3. Stainless steel of the Cr−14Co−6Ni−Mo system has high sensitivity to cracks with σb>150 kgf/mm2. 4. Qualitative agreements between the variations of σbCr, KIc, andanIV with the strength level and chemical composition of the steel were found.

1. The addition of 2–10% Mo to martensitic steels 13Cr−14Co−6Ni and 9Cr−14Co−6Ni increases the amount of retained austenite. Steels with 13 and 9% Cr become almost completely austenitic with 2 and 10% Mo respectively. Intermetallic phase of the Fe2Mo type is formed, the temperature-time range in which it exists being considerably broader in steels with 13% Cr (at the same molybdenum concentration). 2. Raising the molybdenum content of the steels investigated increases the strength slightly and lowers the toughness after quenching due to formation of Fe2Mo in grain boundaries. 3. Tempering of martensitic steels with 9% Cr at 500° leads to a substantial increase in strength, the effect increasing with the molybdenum content from 2 to 6% Mo. The increase in the strength of the steel with 9% Cr to 210 kg/mm2 after tempering is evidently due to the formation of finely dispersed intermetallic R phase. Tempering at 500° does not induce any increase in the strength of steels with 13% Cr and 2–10% Mo, which have an austenitic structure. 4. Steels of the 9Cr−14Co−6Ni system alloyed with 2–6% Mo can be used as the basis for the development of high-strength corrosion resistant steels retaining their toughness at low temperatures.

1. The addition of cobalt to Fe−Cr alloys lowers Ms and Mf without noticeably reducing the amount of martensite at the end of the transformation. 2. Nickel lowers the temperature range of the martensitic transformation, its effect increasing in the presence of cobalt, which is characterized by a change in the linear variation of Ms=f(% Ni) to quadratic. 3. Molyblenum lowers Ms and Mf greatly, substantially increasing the amount of retained austenite. 4. In the steels investigated, nickel and cobalt lower and molybdenum slightly increases the initial temperature of the reverse α→γ transformation. 5. Reducing the amount of chromium from 13 to 9% stimulates the martensitic transformation, as the result of which the concentrations of nickel, cobalt, and molybdenum can be increased in alloys with 9% Cr, with retention of a martensitic structure. Only limited amounts of these elements can be added to the steel with 13% Cr due to suppression of the martensitic transformation.