RU2751064C1 - High strength corrosion resistant powder steel - Google Patents

Abstract

FIELD: iron and steel industry.

SUBSTANCE: invention relates to the field of ferrous metallurgy, namely to the production of powder corrosion-resistant martensitic-aging steel used in technologies for the additive production of power elements of gas turbine engines operated at temperatures from -70 to +550°C. Steel contains components in the following ratio, weight percentage: chromium 12.50-13.50, nickel 4.50-5.50, molybdenum 3.50-4.50, cobalt 8.50-9.50, manganese no more than 0.30, silicon no more than 0.10, niobium 0.08-0.15, yttrium no more than 0.02, lanthanum no more than 0.02, carbon no more than 0.02, sulfur no more than 0.01, oxygen no more than 0.06, iron the rest. Steel has a tensile strength of no less than 1400 MPa, a yield strength of no less than 1170 MPa, a relative elongation of no less than 14%, a transverse narrowing of no less than 50%.

EFFECT: new high strength steel is obtained.

1 cl

Description

The invention relates to the field of ferrous metallurgy, namely to the production of powder corrosion-resistant maraging steel with high strength and plastic characteristics for use in technologies for the additive production of gas turbine engine (GTE) elements, including blades and collectors, operating at temperatures from - 70 ° C to + 550 ° C.

Known corrosion-resistant casting austenitic steel (SU 981440 A1, C22C 38/50, publ. 12/15/1982), containing, mass. %:

carbon 0.25-0.35 silicon 0.10- 0.80 manganese 0.80-1.50 chromium 18.00-20.00

nickel 8.00-10.00

tungsten 1.00-1.50 niobium 0.20-0.50 molybdenum 1.00-1.50 titanium 0.20-0.50 copper 0.10-0.30 aluminum 0.01-0.05 calcium 0.005-0.05 REM 0.005-0.08 Iron rest

The steel has good casting properties and high ductility, toughness and corrosion resistance. The disadvantage of steel is its low strength characteristics.

Known corrosion-resistant steel of the martensitic class (RU 2307876 C2, C22C 38/44, publ. 10.10.2007), containing, in mass. %:

carbon 0.005-0.04 silicon no more than 0.50 manganese 0.10-3.00 chromium 10.00-15.00

nickel 4.00-8.00

molybdenum 2.80-5.00 aluminum 0.001-0.10 nitrogen no more than 0.07 phosphorus no more than 0.04 sulfur no more than 0.01 iron and inevitable impurities rest

The steel has high corrosion resistance to carbon dioxide gas and resistance to stress corrosion cracking. The disadvantage of steel is the reduced values of the yield stress (σ _0.2 = 910-1027 MPa).

Known casting steel (EP 1001044 A2, C22C 37/08, publ. 05/17/2000), efficient at an operating temperature of 600 ° C. Steel contains the following ratio of alloying elements, wt%:

carbon 0.07-0.15 silicon 0.05-0.30 manganese 0.10-1.00 chromium 8.00-10.00

nickel 0.01-0.20

vanadium 0.10-0.30 tungsten 1.00-2.50 niobium and tantalum 0.01-0.20 molybdenum 0.10-0.70 cobalt 0.10-5.00 nitrogen 0.001-0.03 boron 0.002-0.01 iron and accidental impurities rest

With the specified ratios of carbon and chromium, the steel has insufficient corrosion resistance. In addition, this material has low values of the yield point (620-670 MPa).

Known ultra-strong corrosion-resistant steel (US 2010258217 A1, B01J 39/20, publ. 14.0.2010), strengthened by nanocarbide precipitates, containing, wt%:

carbon 0.10-0.30 silicon no more than 0.10 manganese no more than 0.50 chromium 6.00-12.00 nickel 0.00-10.00 niobium no more than 0.30 cobalt 8.00-17.00 molybdenum no more than 3.00 vanadium no more than 0.80 copper no more than 0.15 tungsten no more than 3.00 tantalum no more than 0.20 boron no more than 0.005

iron rest

The disadvantage of steel is the reduced values of ductility. In addition, the presence of nanocarbide inclusions in the steel structure reduces the resistance to stress corrosion cracking.

Known corrosion-resistant steel of the austenitic-martensitic (transitional) class for cast shaped parts operating up to 400 ° C (Reference book "Aviation materials", vol. 2), containing, wt%:

carbon 0.10-0.16 chromium 10.50-12.50

nickel 4.50 - 6.50

molybdenum 4.00-5.00 manganese no more than 0.60 silicon no more than 0.60 sulfur no more than 0.02 phosphorus no more than 0.02

iron rest

The disadvantages of steel are reduced values of steel ductility (transverse narrowing ψ ~ 30%) and insufficient corrosion resistance.

Known corrosion-resistant maraging casting steel, adopted by the authors as a prototype (RU 2169789 C2, C22C 38/52, publ. 27.06.2001), for the manufacture of power cast parts of power plants, containing the following ratio of components, masses. %:

carbon 0.01-0.05 nitrogen 0.01-0.08 chromium 10.00-13.50

nickel 4.50-6.00

molybdenum 4.00-5.00 manganese 0.20-0.90 silicon 0.20-0.75 cobalt 8.00-10.00 calcium 0.001-0.05 cerium 0.001-0.05 vanadium 0.03-0.30

iron rest

Nitrogen and vanadium were introduced into the steel to accelerate bulk crystallization due to the formation of additional crystallization centers - vanadium nitrides - and to reduce the segregation of alloying elements in order to ensure uniform mechanical properties over the section of shaped castings.

The melting of the metal workpiece to obtain a powder occurs in a vacuum, which reduces the assimilation of nitrogen in the metal, and thus the effect of increasing the bulk crystallization rate is not achieved.

Also, steel is used at a temperature of 300 ° C and has a large variation in mechanical properties (tensile strength σ _in = 1325-1570 MPa, a yield strength σ _0,2 = 1030-1275 MPa, elongation δ = 10-20%, cross narrowing ψ = 35-70%).

The technical problem and technical result of the invention is the creation of a corrosion-resistant powder steel for use in additive manufacturing technologies, having a tensile strength of at least 1400 MPa, a yield point of at least 1170 MPa, a relative elongation of at least 14%, a transverse contraction of at least 50%, and workable up to temperature 550 ° C.

To achieve the technical result, a high-strength corrosion-resistant maraging steel containing chromium, nickel, molybdenum, silicon, cobalt, manganese, iron is proposed, characterized in that the steel additionally contains niobium, yttrium and lanthanum and inevitable impurities of carbon, sulfur and oxygen at the following ratio of components, wt. %:

chromium 12.50-13.50

nickel 4.50-5.50

molybdenum 3.50-4.50 cobalt 8.50-9.50 manganese no more than 0.30 silicon no more than 0.10 niobium 0.08-0.15

yttrium no more than 0.02

lanthanum no more than 0.02 carbon no more than 0.02 sulfur no more than 0.01 oxygen no more than 0.06

iron rest

The steel contains a small amount of silicon to increase the ductile properties.

Additional alloying of steel with niobium makes it possible to increase the strength characteristics of the steel due to aging during hardening heat treatment, as well as to increase the resistance to stress corrosion cracking due to the binding of carbon into niobium carbides, which makes it possible to use the steel at temperatures up to 550 ° C.

The introduction of chromium of at least 12.5% ensures high corrosion resistance of steel, the chromium content above 13.5% can lead to the appearance of delta-ferrite, which reduces the ductility and toughness of steel.

When nickel is added less than 4.5%, the required ductility of the steel is not achieved, the nickel content above 5.5% increases the amount of retained austenite, which reduces the strength properties.

The content of manganese in steel up to 0.3% is sufficient to reduce the harmful effect of sulfur, the amount of manganese over 0.3% increases the content of retained austenite, providing a yield point of at least 1170 MPa.

Cobalt reduces the solubility of molybdenum in martensite and promotes, during aging, the precipitation of strengthening phases such as Fe ₂ Mo or (Fe, Ni, Co) ₂ Mo, Ni ₃ Mo. The indicated amount of cobalt and molybdenum helps to achieve the required steel strength of 1400 MPa.

Microalloying with rare earth elements (REM) Υ and La in the indicated ratio allows to reduce the content of non-metallic inclusions and refines the grain.

The steel is phase-balanced. The ratio of austenite and ferrite forming elements in cast steel should be determined by the following equality:

K _m = Cr + 1.5 Ni + 50 (C + Ν) +0.2 Co + 0.7 (Mn + Si) = 23-26;

K _f = Cr + Mo + 2 Si- (1.5 Ni + 50 (C + Ν) +0.6 Co + 0.7 Μn) = 2-4.

K _m is the equivalent of martensite formation, while the content of retained austenite in cast steel ranges from 5 to 10%.

K _f - the equivalent of ferrite formation, can contain from 0 to 3% delta-ferrite in cast steel.

The selected ratio of alloying elements (Km and Kf) makes it possible to obtain, after layer-by-layer laser alloying and hardening heat treatment, 4-6% retained austenite and the absence of delta-ferrite, as a result of which the material has high plastic characteristics and toughness.

In contrast to the prototype, with the selected ratio of alloying elements, cold treatment of steel is not required.

Steel contains no more than 0.01% sulfur and no more than 0.06% oxygen; an increased amount of these impurities reduces the strength and toughness of the steel.

Examples of implementation

In production conditions FSUE "VIAM" carried out testing of the proposed steel.

The workpiece for spraying (atomization) was melted in a vacuum induction plant (VIA) with control of the phase composition by a magnetic sample during the melting process.

In the crucible, in accordance with the stated content, the main alloying elements were loaded: iron, nickel, chromium, molybdenum, niobium, cobalt and melted in vacuum at a temperature of 1550 ° C. After holding for 10 min, ferrosilicon was introduced into the molten metal. Then, manganese and REM ligatures (NiY, NiLa) were added in small granules, with an exposure time between each addition for 2 min. The steel smelting process was monitored by measuring the magnetism of the cast sample on an IFSS device (an indicator of the phase composition of steel), which makes it possible to determine the phase composition of steel (the percentage of austenite and martensite). The metal was poured into a pipe with a diameter of 90 mm.

The preparation of the powder of the proposed steel was carried out on a HERMIGA10 / 100VI installation (atomizer), which has a main working range of particles of 10-100 microns. The cast billet was loaded into a melting chamber and a vacuum was applied. The power was turned on after reaching a residual pressure of not more than 5 × 10 ^-2 mbar, but not earlier than 1 hour after the start of the evacuation.

After melting the metal, the melting chamber and the atomization chamber were filled with argon to an overpressure of 0.05 bar. After reaching the operating temperature, the melt was kept for 10 minutes, 3 minutes before draining, the atomization test was switched on and the operating pressure was set at the nozzle; 30 s before draining, argon was fed into the melting chamber up to the operating pressure, and draining was started. After controlling the formation of the metal jet, atomization was started.

The powder was removed not earlier than 4 hours after the end of the atomization process. Then the powder was subjected to aerodynamic classification to remove the 10 μm fraction. The size of the main fraction was chosen -63 + 10 μm.

Table 1 shows the composition of the proposed steel.

Printing of blanks for samples was carried out on a ConceptLaserM2 Cusing installation with a working space of the construction zone of 250 × 250 × 280 mm. The blanks were made of a simple square-sectional shape with parallel orientation of the layers relative to the symmetry axis of the blank.

The synthesized workpieces were subjected to hot isostatic pressing followed by annealing.

After hardening heat treatment (quenching and aging), samples were made for mechanical tests.

The mechanical properties of the proposed steel are presented in table 2.

Claims (3)

1. Powder corrosion-resistant maraging steel containing chromium, nickel, molybdenum, cobalt, carbon, manganese, silicon, iron, characterized in that it additionally contains niobium, yttrium, lanthanum, sulfur and oxygen in the following ratio of components, wt .%: chromium 12.50-13.50 nickel 4.50-5.50 molybdenum 3.50-4.50 cobalt 8.50-9.50 manganese no more than 0.30 silicon no more than 0.10 niobium 0.08-0.15 yttrium no more than 0.02 lanthanum no more than 0.02 carbon no more than 0.02 sulfur no more than 0.01 oxygen no more than 0.06 iron rest 2. Powder corrosion-resistant maraging steel according to claim 1, characterized in that the martensite formation coefficient is 23-26, and the ferrite formation coefficient is 2-4.