RU2221895C1 - Corrosion-resistant steel and article made from such steel - Google Patents

Abstract

FIELD: metallurgy; making corrosion-resistant steels for soldered cellular panels which perform function of load-bearing sound-absorbing structures working at temperatures up to 500 C. SUBSTANCE: proposed corrosion- resistance steel contains the following components, mass-%: carbon, 0.005-0.03; chromium, 5.0-8.0; nickel, 14.0-18.5; molybdenum, 1.0-3.0; aluminum, 0.1-0.4; niobium, 0.1-0.3; zirconium, 0.05-0.2; boron, 0.001-0.003; copper, 0.3-0.8; at last on element from group: cerium, 0.005-0.1; lanthanum, 0.003-0.05; yttrium, 0.001-0.05; the remainder being iron. EFFECT: enhanced strength and serviceability with reduction in ductility and toughness at heating till 450 C. 4 cl, 2 tbl, 1 ex

Description

The invention relates to the field of metallurgy, and in particular to the creation of corrosion-resistant steel for soldered honeycomb panels, which are sound-absorbing supporting structures, operable up to a temperature of 450 ^o C. Steel provides the ability to obtain both sheet and tape (for sheathing honeycomb panels), and foil (for honeycomb filler).

Known corrosion-resistant steel of the martensitic class for the manufacture of power brazed-welded nodes of the following chemical composition, wt.%:
Carbon - Not more than 0.3
Chrome - 10.0-13.0
Nickel - 8.0-11.0
Molybdenum - 0.4-0.9
Titanium - 0.02-0.15
Cobalt - 0.2-0.6
Boron - 0.001-0.005
Lanthanum - 0.01-0.1
Calcium - 0.001-0.05
Iron - Else
Steel after heat treatment: quenching from a temperature of 750 ^o C + tempering at 250 ^o C has the following mechanical properties: σ _in = 95-102 kgf / mm ² , δ ₅ = 15-16% (RF patent 2175684).

Also known are corrosion-resistant steels of martensitic class for a similar purpose of the following chemical composition, wt.%:
1. Carbon - 0.03-0.08
Chrome - 12.8-14.5
Nickel - 5.2-6.5
Molybdenum - 0.7-1.2
Tungsten - 0.7-1.2
Vanadium - 0.15-0.3
Niobium - 0.08-0.3
Nitrogen - 0.01-0.03
Yttrium - 0.01-0.1
Calcium - 0.001-0.01
Zirconium - 0.01-0.1
Lanthanum - 0.01-0.1
Iron - The rest (RF patent 2176283)
2. Carbon - Not more than 0.08
Silicon - 0.5-4.0
Manganese - Not more than 4.0
Nickel - 5.0-9.0
Chrome - 10.0-17.0
Molybdenum - 0.3-2.5
Titanium - 0.15-1.0
Aluminum - Not more than 1.0
Nitrogen - Not more than 0.03
Iron - The Rest (UK Patent 2145734)
3. Carbon - 0.01
Silicon - 1.5-2.95
Manganese - Not more than 5.0
Nickel - 4.0-8.0
Chrome - 12.0-18.0
Copper - 0.5-3.5
Nitrogen - Not more than 0.15
Sulfur - Less than 0.004
Iron - Else (US Patent 4,849,166)
A disadvantage of the known corrosion-resistant steels of the martensitic class is their lack of manufacturability in the production of tape and foil, as well as a decrease in viscosity after the brazing process and operational heating at 450 ^o C.

Known corrosion-resistant steel of the austenitic class of the following chemical composition, wt.%:
Carbon - 0.02-0.08
Manganese - 1.5-2.5
Silicon - 0.5-1.0
Chrome - 12.5-14.5
Nickel - 14.5-16.5
Molybdenum - 1.5-2.5
Titanium - 0.1-0.4
Vanadium - 0.02-0.05
Tantalum - 0.005-0.2
Nitrogen - Not more than 0.01
Cobalt - 0.02-0.05
Iron - The Rest (US Patent 4,530,719)
A disadvantage of the known corrosion-resistant steel of the austenitic class is the insufficient level of strength that limits its use for the manufacture of power bearing structures.

The closest in chemical composition and purpose to the proposed one is steel VNS-55 (03X14H4N3G3M2SBYU), adopted as a prototype. Steel has the following chemical composition, wt.%:
Carbon - 0.005-0.03
Chrome - 12.6-14.1
Nickel - 2.5-4.8
Molybdenum - 1.2-2.0
Manganese - 2.1-5.0
Aluminum - 0.25-0.6
Silicon - 0.75-1.2
Zirconium - 0.01-0.08
Niobium - 0.1-0.4
One or more elements from the group:
Cerium - 0.005-0.1
Lanthanum - 0.003-0.05
Yttrium - 0.001-0.05
Iron - Else
provided that the sum of cerium, lanthanum, yttrium is not more than 0.1 (USSR copyright certificate 1340213, BI 14, 1991).

The disadvantage of the steel adopted for the prototype is the lack of technological ductility in the production of foil and a significant decrease in viscosity after operational heating at 450 ^o C. A decrease in the viscosity of steel during operation reduces the efficiency and reliability of cellular power load-bearing structures.

The technical task of the present invention is the creation of corrosion-resistant steel with the high values of strength, ductility and toughness, which remain after the brazing process and operational heating at temperatures up to 450 ^o С, which ensures high reliability of cellular power bearing structures, which is technologically advanced in the production of tape, sheet and foil.

To achieve this goal, high-strength corrosion-resistant steel containing iron, carbon, chromium, nickel, molybdenum, aluminum, niobium, zirconium, at least one element from the group: cerium, lanthanum, yttrium, characterized in that it additionally contains copper, boron, is proposed the following ratio of components, wt.%:
Carbon - 0.005-0.03
Chrome - 5.0-8.0
Nickel - 14.0-18.5
Molybdenum - 1.0-3.0
Aluminum - 0.1-0.4
Niobium - 0.1-0.3
Zirconium - 0.05-0.2
Boron - 0.001-0.003
Copper - 0.3-00.8
At least one item from the group:
Cerium - 0.005-0.1
Lanthanum - 0.003-0.05
Yttrium - 0.001-0.05
Iron - Else
and a product made of this steel.

The ratio of components that determine the content of austenite (A, vol.%) In steel should satisfy the ratios:
K _m = Cr + Mo + 1.2Ni + 56С + 0.2Сu = 23 ÷ -30 (1) - for sheet and tape;
K _m = Cr + Mo + 1.5Ni + 56C + 0.2Cu ≥ 34 (2) - for foil, where K _{m is the} equivalent of martensite formation.

The selected ratio of components allows us to obtain for the metal going to the production of tape and sheet, a martensitic structure with a regulated content of residual austenite (10-30 vol.%) And a point of the beginning of the reverse transition α → γ in the temperature region of 450 ^o C, which provides a high level of mechanical properties of steel and products made from it, both in the initial state and after heating to a temperature of 450 ^o C.

 The selected ratio of the components for the foil provides a highly plastic austenitic structure that allows rolling the foil up to 0.05 mm thick with a sufficient level of strength.

 The specified low carbon concentration in the inventive steel provides high technological ductility in the hardened state and the absence of grain boundary emissions during delayed cooling after the brazing process.

The introduction of the indicated concentrations of chromium (5-8%) into steel provides satisfactory corrosion resistance and does not lead to a decrease in viscosity when heated to 450 ^o C, associated with the separation of the solid solution in chromium. At a lower chromium content (below 5%), the corrosion resistance is unsatisfactory, and at a higher (more than 8%), embrittlement is observed after heating at 450 ^o C.

The indicated nickel content in steel provides (when ratios 1 and 2 are fulfilled) the required austenite content in steel: 8-30 vol.% - for sheet and 100 vol. % - for foil, and also reduces the point of the reverse α → γ transition to 450-500 ^o C.

 Doping with molybdenum within the specified limits inhibits the formation of carbonitrides along the grain boundaries during slow cooling after soldering.

Alloying with aluminum makes it possible to increase the strength of martensite as a result of aging and thereby the required level of strength σ _of ≥1100 MPa for the sheet). When the aluminum content is less than 0.1%, the required level of strength is not achieved, and when the aluminum content is more than 0.4%, significant embrittlement is observed when heated at 450 ^o C.

 Doping with niobium and zirconium provides an increase in the temperature of recrystallization and the possibility of heating to elevated temperatures (when soldering) without significant grain growth.

 Boron, being a surface-active element, prevents the formation of grain-boundary segregation during prolonged operational heating and thereby increases the viscosity of steel.

 Copper (0.3-0.8 wt.%) Is introduced to balance the phase composition (obtaining a regulated content of residual austenite), reduce hardness in the hardened state and increase the corrosion resistance of steel. A lower copper content does not provide a solution to these problems, and a larger one leads to embrittlement during operational heating.

Thus, as a result of complex alloying with the specified ratio of alloying elements within the proposed composition, the necessary characteristics of steel for cladding and honeycomb filler are achieved (high initial strength and toughness, the absence of embrittlement during the thermal soldering cycle and after operational heating at 450 ^o C), which allows you to create soldered honeycomb panels, which are supporting sound-absorbing structures.

Implementation example
In the experimental laboratory conditions, the proposed composition of the steel smelted in a vacuum induction furnace was tested in comparison with the well-known steel VNS-55 (03X14N4G3M2SBYU) for optimal, limit and transcendental values of the content of alloying elements.

 The chemical and phase compositions and mechanical properties of steels are given in table. 12; they were determined on standard equipment.

The mechanical properties were determined after the following heat treatment modes:
1. Quenching from 860 ^o C, air + tempering 500 ^o C, 2 h (mode 1) - the initial state.

2. Heating at 1030 ^o C, delayed cooling to 500 ^o C for 2.5 hours + tempering at 500 ^o C, 2 hours (mode 2) - imitation of the thermal soldering cycle.

3. Mode 2 + heating at 450 ^o C, 100 h (mode 3) - simulation of operational heating after soldering.

As can be seen from the table. 2, the proposed steel (an option for the manufacture of casing of honeycomb panels - compositions 1, 2 and 3) is increased in comparison with the prototype: the level of strength and fluidity in the initial state and after the thermal soldering cycle is 100-150 MPa; the values of impact strength (CST) in the initial state - 1.5 times, and after the thermal cycle of soldering and operational heating at 450 ^o C - 4-5 times.

Thus, the use of the proposed steel will reduce the weight of the supporting sound-absorbing structures and raise the operating temperature to 450 ^o With high characteristics of reliability and stability of the material.

Claims (4)

1. Corrosion-resistant steel containing carbon, chromium, nickel, molybdenum, aluminum, niobium, zirconium, iron, at least one component from the group of cerium, lanthanum, yttrium, characterized in that it additionally contains copper and boron in the following ratio of components, wt .%: Carbon 0.005 - 0.03 Chrome 5.0 - 8.0 Nickel 14.0 - 18.5 Molybdenum 1.0 - 3.0 Aluminum 0.1 - 0.4 Niobium 0.1 - 0.3 Zirconium 0.05 - 0.2 Boron 0.001 - 0.003 Copper 0.3 - 0.8 At least one component from the group Cerium 0.005 - 0.1 Lanthanum 0.003 - 0.05 Yttrium 0.001 - 0.05 Iron Else 2. Corrosion-resistant steel according to claim 1, characterized in that the ratio of the components is characterized by the following formula: K _m = Cr + Mo + 1.2 Ni + 56C + 0.2 Cu = 23-30, where K _m is the equivalent of martensite formation. 3. Corrosion-resistant steel according to claim 1, characterized in that the ratio of the components is characterized by the following formula: K _m = Cr + Mo + 1.5 Ni + 56C + 0.2 Cu ≥ 34, where K _m is the equivalent of martensite formation. 4. The product is made of corrosion-resistant steel, characterized in that it is made of steel according to any one of claims 1 to 3.

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