RU2421538C1 - High-strength non-magnetic corrosion resistant steel - Google Patents

Abstract

FIELD: metallurgy. ^ SUBSTANCE: steel contains carbon, silicon, manganese, chromium, nickel, nitrogen, molybdenum, vanadium, niobium, boron, calcium, selenium, iron and as unavoidable impurities sulphur and phosphorus at following ratio of components, wt %: carbon 0.03 - 0.07, silicon 0.10 - 0.40, manganese 9.0 - 11.0, chromium 19.5 - 20.5, nickel 3.5 - 4.5, boron 0.001 - 0.005, molybdenum 0.7 - 1.2, vanadium 0.15 - 0.25, niobium 0.10 - 0.20, selenium 0.010 - 0.015, nitrogen 0.47 - 0.52, calcium 0.005 - 0.010, sulphur ëñ 0.02, phosphorus ëñ 0.02, iron - the rest. Ratio of expression ([Ni] + 0.1[Mn] - 0.01[Mn]2 +18[N] + 30[C]) to expression ([Cr] + 1.5[Mo] + 0.48[Si] + 2.3[V] + 1.75[Nb]) is 0.66 0.76, ratio of content of carbon to content of nitrogen is 0.06-0.14, while ratio of (Cr + 2Mo + 4V)/(C + N) is 3741. Steel has developed sub-grain structure upon hot plastic deformation at temperature 10001100C with reduction 50-80 % and successive cooling in water to room temperature. ^ EFFECT: steel possesses high strength characteristics, corrosion resistance and non-magnetic property. ^ 2 cl, 2 tbl

Description

The invention relates to the field of metallurgy of steel and can be used in mechanical engineering, instrumentation, shipbuilding and to create highly efficient drilling equipment.

Known corrosion-resistant non-magnetic steel containing 0.03% carbon, 0.4 ÷ 0.6% nitrogen; 23 ÷ 25% chromium; 5–7% manganese, 16–18% nickel and 4–5% molybdenum (grade 1.4565S steel, Materials of the conference “High Nitrogen Steels 90”, Aahen, 1990, p. 155). The main disadvantage of this steel is its low strength, poor weldability and high content of expensive and scarce nickel and molybdenum.

Closest to the proposed technical solution is steel 07X21G7AN5, adopted by us for the prototype [see AABabakov, MVPridantsev “Corrosion-resistant steels and alloys”. M .: Metallurgy, 1971. p.168, ChMTU 393-60, TsNIICHM], containing 0.05 ÷ 0.10% carbon, up to 0.7% silicon, 0.15 ÷ 0.25% nitrogen, 20 ÷ 22 % chromium, 6–8% manganese, 5–6% nickel, iron and unavoidable impurities such as sulfur and phosphorus. The disadvantages of the prototype is the insufficient level of strength properties (σ _in = 700 MPa; σ _0.2 = 400 MPa) for highly loaded parts, as well as the presence of ferromagnetic δ-ferrite in the steel structure, which is unacceptable for non-magnetic products, when the content of austenite-forming elements at the lower limit vintage composition.

The technical result of the invention is the creation of a high-strength non-magnetic corrosion-resistant steel with higher strength characteristics, corrosion resistance and non-magnetic.

The technical result is achieved in that in high-strength non-magnetic steel containing carbon, silicon, manganese, chromium, nickel, nitrogen, iron and inevitable impurities, molybdenum, vanadium, niobium, boron, calcium and selenium are additionally introduced in the following ratio of components, wt.%

carbon 0.03-0.07 niobium 0.10-0.20 silicon 0.10-0.40 selenium 0.010-0.015 manganese 9.0-11.0 nitrogen 0.47-0.52 chromium 19.5-20.5 calcium 0.005-0.010 nickel 3.5-4.5 sulfur ≤0.02 boron 0.001-0.005 phosphorus ≤0.02 molybdenum 0.7-1.2 iron rest vanadium 0.15-0.25

while for the values of the concentration of alloying elements the conditions are satisfied:

where [N], [C], [Si], [Mn], [Ni], [Cr], [Mo], [V], [Nb] is the concentration in the steel of nitrogen, carbon, silicon, manganese, nickel, chromium, molybdenum, vanadium and niobium, respectively, expressed in wt.%:

b) the ratio of carbon content to nitrogen content (wt.%) should be in the range - 0.06 ÷ 0.14;

(мас.%) должно быть в пределах 37÷41,c) content ratio

(wt.%) should be in the range of 37 ÷ 41,

at the same time, a developed subgrain structure is formed in it during hot plastic deformation at temperatures of 1000 ÷ 1100 ° C with compression of 50 ÷ 80% and subsequent cooling in water to room temperature.

The carbon content in the steel [C] = 0.03 and nitrogen [N] = 0.47 in the minimum indicated amounts is sufficient to ensure high strength of the base metal. With a carbon content of more than 0.07% and nitrogen more than 0.52%, it is therefore difficult to obtain satisfactory ductility and toughness due to the formation of large amounts of chromium carbide type Cr ₂₃ C ₆ and chromium nitrides type Cr ₂ N during thermal aging. it is difficult to obtain a pore-free metal without using increased nitrogen pressure above the melt due to the limited solubility of nitrogen in a metal of this composition. To prevent the formation of chromium carbides of type Cr ₂₃ C _{6, the} ratio of carbon to nitrogen should not exceed 0.14.

The introduction of 19.5-20.5% chromium into steel is necessary to ensure the required level of corrosion resistance and solubility of nitrogen within the specified limits. With a chromium content of more than 20.5% and nickel less than 3.5%, the steel will have reduced ductility due to the formation of ferrite and σ-phase.

обеспечивает предотвращение образования σ-фазы в структуре стали, что повышает пластичность стали.Fulfillment of the condition

prevents the formation of a σ-phase in the steel structure, which increases the ductility of steel.

With an increase in nickel content of more than 4.5% - due to a decrease in the solubility of nitrogen in the metal, it is impossible to obtain steel with a given amount of nitrogen. Obtaining a manganese content at the level of 9-11% ensures the stability of austenite with respect to the γ → α (M) conversion, increases the solubility of nitrogen and promotes metal deoxidation. The introduction of vanadium and niobium into steel in an amount of 0.15-0.25% and 0.1-0.2%, respectively, provides a fine-grained structure due to niobium nitrides and an increase in strength (due to the formation of finely dispersed vanadium nitrides). At lower concentrations of vanadium and niobium, the positive effect of its administration is negligible. An increase in the content of vanadium and niobium by more than 0.25% and 0.20% leads to a decrease in the strength of the metal due to depletion of the solid solution with nitrogen as a result of the formation of thermally stable niobium nitrides dissociating in austenite at temperatures above 1150 ° C and a decrease in impact strength due to increase in the amount of vanadium nitrides. An additional introduction of molybdenum from 0.7% to 1.2% in steel prevents the formation of a ferromagnetic phase (δ-ferrite) in the metal. Additives of calcium and selenium in amounts of 0.005-0.010 and 0.010-0.015%, respectively, improving the morphology of non-metallic inclusions, increase the ductility of the metal and its manufacturability, especially machinability. If the calcium and selenium in the metal are less than 0.005 and 0.010%, respectively, a significant effect from their introduction is not provided, with an increase in their content more than 0.010 and 0.015%, respectively, further improvement of properties is not achieved. The introduction of boron steel of 0.001-0.005% improves the ductility of the metal during hot heating by reducing coarse grains in slabs. With a boron content of more than 0.005%, steel is destroyed along grain boundaries at temperatures above 1100 ° C due to the formation of a fusible boron eutectic.

Fulfillment of the condition:

provides non-ferromagnetic steel (µ <1.01 G / E). With a decrease in the ratio values of less than 0.66, it is not possible to obtain an austenitic structure without ferromagnetic phases (martensite and ferrite). When the ratio is more than 0.76 in steel, the required level of nitrogen solubility is not achieved.

Austenite with a developed subgrain structure in the proposed steel, providing high strength properties, can be obtained as a result of hot plastic deformation (forging or rolling) at temperatures of 1000-1100 ° С with compression of 50 ÷ 80% and subsequent cooling in water to room temperature. Plastic deformation at temperatures below 1000 ° C reduces the ductility and toughness of steel and complicates the process of obtaining high-quality products due to the high resistance of the metal to plastic deformation. The best combination of strength and plastic properties of steel is achieved with a reduction of 50 ÷ 80%. Compressions of less than 50% do not provide the required level of strength properties, and compressions of more than 80% lead to a significant reduction in ductility. The high cooling rate in water from the temperature of hot deformation prevents the formation of nitride phases in the metal volume, which reduce the ductility of steel, and the ferromagnetic phase - martensite.

Steel was smelted in an open induction furnace with a capacity of 50 kg. At a temperature of 1100 ° С, the metal was forged onto bars 13 × 13 mm. The metal structure was determined on an x-ray diffractometer. Mechanical tests were carried out on an Instron-1185 machine.

In steel, after hot deformation (during forging), high hardening is achieved (σ _in = 1080–1130 MPa; σ _0.2 = 915–980 MPa) while maintaining increased ductility (δ = 30.2–34.9%; ψ = 51-53.8%) and impact strength (KCU = 1.10-1.31 MJ / m ² ). The results of the chemical analysis of the proposed steel and prototype, as well as the test results are shown in tables 1 and 2.

table 2 Mechanical properties and magnetic permeability of steel. Steel No. of swimming trunks Treatment σ _in MPa σ _0.2 MPa δ,% ψ,% KCU, MJ / m ² µ, G / E Prototype Quenching from 1100 ° С in water 692 395 31 63 2.9 1.009 Proposed one Forging at 1100 ° С, cooling in water 1080 915 31.9 53.8 1.31 1.009 2 Forging at 1070 ° C, cooling in water 1100 941 31.8 52,4 1.20 1.008 3 Forging at 1000 ° C, cooling in water 1130 980 30,2 51.0 1.10 1.007

Claims (2)

1. High-strength non-magnetic corrosion-resistant steel containing carbon, silicon, manganese, chromium, nickel, nitrogen, iron and sulfur and phosphorus as inevitable impurities, characterized in that it additionally contains molybdenum, vanadium, niobium, boron, calcium and selenium in the following ratio of components, wt.%:
carbon 0.03-0.07 silicon 0.10-0.40 manganese 9.0-11.0 chromium 19.5-20.5 nickel 3.5-4.5 boron 0.001-0.005 molybdenum 0.7-1.2 vanadium 0.15-0.25 niobium 0.10-0.20 selenium 0.010-0.015 nitrogen 0.47-0.52 calcium 0.005-0.010 sulfur ≤0.02 phosphorus ≤0.02 iron rest,
while for the values of the concentration of alloying elements, the condition

,
where [N], [C], [Si], [Mn], [Ni], [Cr], [Mo], [V], [Nb] is the concentration in the steel of nitrogen, carbon, silicon, manganese, nickel, chromium, molybdenum, vanadium and niobium, respectively, expressed in wt.%,
the ratio of carbon concentration to nitrogen content is 0.06 ÷ 0.14, and the ratio of content

in wt.% is 37 ÷ 41. 2. Steel according to claim 1, characterized in that it has a developed subgrain structure after hot plastic deformation at temperatures of 1000 ÷ 1100 ° C with compression of 50 ÷ 80% and subsequent cooling in water to room temperature.