RU2576773C1 - High-corrosion-resistant steels of the transition class - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to a high strength corrosion resistant steels of the transition class used for the manufacture of highly loaded parts and structures in mechanical engineering and shipbuilding, working in conditions of corrosive environment. Steel contains wt.%: 0.12-0.35 carbon, nitrogen 0.11-0.21, 14.0-15.0 chromium, nickel 2.5-3.5, manganese 0.5-1.5, molybdenum 1.2-1.7, Si 0.2-0.6, 1.5-2.0 copper, vanadium 0.05-0.10, calcium 0.005-0.050, 0.005-0.030 cerium, yttrium 0.005-0.030, lanthanum 0.005-0.030, 0.005-0.020 barium, iron - the rest.

EFFECT: it ensures a high level of mechanical and corrosion properties.

4 cl, 2 tbl

Description

 The invention relates to steel metallurgy, in particular to the field of alloyed corrosion-resistant high-strength steels used for highly loaded parts and structures in mechanical engineering and shipbuilding.

Known corrosion-resistant steel martensitic class (RF Patent No. 2291912) of the following chemical composition (wt.%):

carbon 0.08-0.12 chromium 12.5-14.0 nickel 4.0-5.0 molybdenum 2.3-2.8 manganese 0.3-0.7 nitrogen 0.05-0.10 silicon 1.7-2.5 niobium 0.2-0.4 cobalt 4.0-5.0 lanthanum 0.001-0.05 yttrium 0.001-0.05 iron rest

The main disadvantages of this steel are insufficiently high strength (σ _B = 1650 MPa) and a high content of expensive nickel and cobalt.

Known corrosion-resistant steel martensitic class (RF Patent No. 2077602) of the following chemical composition (wt.%):

carbon 0.04-0.09 chromium 12.5-15.0 nickel 4.0-6.5 molybdenum 2.5-3.5 manganese 0.1-1.0 nitrogen 0.02-0.1 silicon 0.3-1.6 niobium 0.02-0.42 cobalt 3,5-6,0 cerium 0.001-0.050 calcium 0.001-0.050 iron rest

The main disadvantages of this steel are insufficiently high strength (σ _B = 1600 MPa; σ _0.2 = 1300 MPa) and a high content of expensive nickel, cobalt and molybdenum.

Closest to the invention, taken as a prototype, is a high-strength corrosion-resistant steel of the martensitic class (RF Patent No. 2318068) of the following chemical composition (wt.%):

carbon 0.04-0.07 silicon no more than 0.6 chromium 15,5-16,5 nickel 4.8-5.8 nitrogen 0.11-0.18 niobium 0.03-0.08 vanadium 0.03-0.08 manganese 0.5-1.0 calcium 0.02-0.03 iron and inevitable impurities rest

The main disadvantages of this steel are the relatively low strength (σ _0.2 = 1450 MPa) and the high content of expensive nickel.

The problem to which the present invention is directed, is to create an economically alloyed corrosion-resistant high-strength steel.

The technical result is to increase the strength (σ _B = 1800-1850 MPa; σ _0.2 = 1600-1650 MPa) of steel while maintaining ductility that is satisfactory for practical use (δ = 10-12%; Ψ = 40-50%), which provides increased reliability and increased durability of structures made of this steel during their operation.

The technical result is achieved in that, in comparison with the prototype steel, the proposed steel containing carbon, nitrogen, chromium, nickel, manganese, silicon, vanadium, calcium and iron, according to the invention additionally contains molybdenum, copper, cerium, yttrium, lanthanum and barium in the following ratio of components (in wt.%):

carbon 0.12-0.35 nitrogen 0.11-0.21 chromium 14.0-15.0 nickel 2.5-3.5 manganese 0.5-1.5 molybdenum 1.2-1.7 silicon 0.2-0.6 copper 1.5-2.0 vanadium 0.05-0.10 calcium 0.005-0.050 cerium 0.005-0.030 yttrium 0.005-0.030 lanthanum 0.005-0.030 barium 0.005-0.020 iron rest

The ratio of the elements determining the phase composition in steel should be determined by the following equalities:

C + N = 0.25 ÷ 0.45;

C / N = 1.1 ÷ 2.3;

K _m = Cr + Mo + 1.5Ni + 30 (C + N) +0.7 (Mn + Si) = 30 ÷ 33,

K _f = Cr + Mo + 2Si- {1.5Ni + 30 (C + N) + 0.7Mn} = 2.5 ÷ 6.2;

where K _m is the equivalent of martensite formation, and K _f is the equivalent of ferrite formation;

The presence in the steel of the indicated concentrations of carbon and nitrogen is necessary to ensure high strength. With a carbon and nitrogen content of more than 0.35 and 0.21%, respectively, it is difficult to obtain satisfactory ductility and toughness, as well as to obtain a high-quality metal without porosity due to the limited solubility of nitrogen in steel.

The introduction of 14.0-15.0% chromium into steel is due to the provision of the required corrosion resistance and increased solubility of nitrogen. When the concentration of chromium is more than 15.0% and nickel less than 2.5%, the steel will have a lower viscosity, especially at low temperatures, due to the appearance of δ ferrite in the structure, and also due to an increase in the temperature of the viscous-brittle transition. With an increase in nickel content of more than 3.5%, the solubility of nitrogen in steel decreases.

Manganese in an amount of 0.5-1.5% is introduced into steel to increase the solubility of nitrogen and deoxidation of steel. An increase in manganese content of more than 1.5% leads to an increase in the amount of residual austenite and thereby to a decrease in strength characteristics.

Additives of vanadium in an amount of up to 0.1% provide a fine-grained structure. An increase in the content of vanadium of more than 0.1% leads to a decrease in strength due to depletion of the solid solution with nitrogen as a result of the formation of vanadium nitrides VN.

Alloying with molybdenum in an amount of 1.2-1.7% increases the corrosion resistance, solubility of nitrogen and inhibits the formation of carbonitrides along grain boundaries and thereby increases the toughness of steel.

Additional doping with barium allows you to change the shape of sulfides to globular and thereby improves the deformability of the ingots.

Alloying with copper 1.5-2.0% eliminates delta ferrite in the microstructure of steel, and also increases the corrosion resistance and strength during aging due to the release of dispersed particles of a phase rich in copper.

The presence of cerium 0.005-0.030% and calcium 0.005-0.030% reduces the content of impurities at the grain boundaries, thereby changing the kinetics of aging along the grain boundaries and reducing the degree of embrittlement.

Alloying with lanthanum and yttrium contributes to the deoxidation of steel and grinding of grain.

The selected ratio of components allows to obtain a stable steel structure with a given ratio of martensite and austenite.

Steel was smelted in an open induction furnace. The compositions of the steel experimental swimming trunks are shown in table 1.

The proposed steel after hot plastic deformation (the temperature at the end of deformation should be lower than the temperature of the onset of collective recrystallization), followed by cooling in water, combined with cold treatment and subsequent tempering at 400 ° C, has a martensitic-austenitic fine-grained (15-20 μm) structure, with a given amount of martensite (75-85%) and austenite (25-15%) that does not contain δ-ferrite and σ-phase, which allows to ensure a high level of mechanical and corrosion properties of steel and the product made from it. The technical result is an increase in strength (σ _B = 1800-1850 MPa; σ _0.2 = 1650-1700 MPa) while maintaining ductility that is satisfactory for practical use (δ = 10-12%; Ψ = 40-50%), which provides increased operational reliability and increased service life of structures made of this steel during their operation. The results of mechanical testing of the metal are shown in table 2.

Claims (4)

1. High-strength corrosion-resistant steel of the transition class, containing carbon, nitrogen, chromium, nickel, manganese, silicon, vanadium, calcium and iron, characterized in that it additionally contains molybdenum, copper, cerium, yttrium, lanthanum and barium in the following ratio of components, in wt.%:
carbon 0.12-0.35 nitrogen 0.11-0.21 chromium 14.0-15.0 nickel 2.5-3.5 manganese 0.5-1.5 molybdenum 1.2-1.7 silicon 0.2-0.6 copper 1.5-2.0 vanadium 0.05-0.10 calcium 0.005-0.050 cerium 0.005-0.030 yttrium 0.005-0.030 lanthanum 0.005-0.030 barium 0.005-0.020 iron rest 2. High-strength corrosion-resistant steel of the transition class according to claim 1, characterized in that the following conditions are fulfilled for the carbon and nitrogen content: C + N = 0.25 ÷ 0.45, C / N = 1.1 ÷ 2.3. 3. High-strength corrosion-resistant steel of the transition class according to claim 1, characterized in that the ratio of austenitic and ferrite-forming elements that determine the phase composition in steel is determined by the following equalities:
K _m = Cr + Mo + 1.5Ni + 30 (C + N) +0.7 (Mn + Si) = 30 ÷ 33,
K _f = Cr + Mo + 2Si- {1.5Ni + 30 (C + N) + 0.7Mn} = 2.5 ÷ 6.2,
where K _m is the equivalent of martensite formation, and K _f is the equivalent of ferrite formation. 4. High-strength corrosion-resistant steel of the transition class according to claim 1, characterized in that after hot plastic deformation, the end temperature of which is lower than the temperature of the onset of collective recrystallization, followed by cooling in water, cold working and subsequent tempering at 400 ° C, it exhibits martensitic fine-grained austenitic structure with a grain of 15-20 microns, with the amount of martensite 75-85% and austenite 25-15% without δ-ferrite and σ-phase.