RU2820430C1 - Iron-based invar alloy - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to foundry production of invar alloys based on iron with minimum temperature coefficient of linear expansion. Iron-based alloy is configured to form articles with a structure without carbide phases and martensite and contains nickel, cobalt, carbon, silicon, manganese, calcium and unavoidable impurities, including oxygen, sulfur, phosphorus, nitrogen, hydrogen, with the following ratio of components, wt.%: nickel 32.0–35.0, cobalt 3.6–6.0, carbon 0.75–1.5, silicon 0.1–0.5, manganese 0.1–0.4, calcium 0.001–0.1, iron and unavoidable impurities—the rest. Following conditions are simultaneously satisfied for the alloy composition: Ni/Co=6–8 and (Ni+Co)/C=30–50, where: Ni—nickel content, wt.%, Co—cobalt content, wt.%, C—carbon content, wt.%.

EFFECT: improved fluidity properties while maintaining minimum temperature coefficient of linear expansion in the temperature range from minus 60 °C to 200 °C.

1 cl, 1 dwg, 2 tbl

Description

Field of technology

The invention relates to the field of metallurgy, namely to the foundry production of Invar alloys with a minimum temperature coefficient of linear expansion (TCLE). The scope of use of this invention may be the manufacture of small and large-sized equipment, which is used in the production of products from composite materials, in particular from carbon composites.

State of the art

From the prior art, a cast iron-based Invar alloy is known according to patent RU 2755784 C1 contains, in wt.%: nickel (Ni) 32.0 - 34.5, cobalt (Co) 2.0 - 3.5, carbon (C) 0.75 – 1.5, copper (Cu) 0.12 – 0.25, silicon (Si) 0.18 – 0.28, manganese (Mn) 0.01 - no more than 0.3, at least one a component selected from the group of rare earth elements (REM): cerium, lanthanum and yttrium in the amount of 0.05 - 0.10, the rest is iron and inevitable impurities. In this case, the following conditions are met, wt.%: Cu + Si = 0.3-0.53, Cu / Si = 0.55-1.0, Ni + Co = 35.4-37.0, Ni / Co = 9.2-17.0, (Ni + Co) / C = 24-49. The alloy has a thermal expansion coefficient in the temperature range of 20-200° at a level not exceeding 2.5×10-6K-1 with significantly improved casting properties, namely: the fluidity of the alloy is at the level of 210-230 mm according to a complex U-shaped die test.

From the prior art, a cast iron-based Invar alloy is known with the following composition, wt.%: nickel 32.0-34.5; cobalt 2.0-3.5; carbon 0.75-1.5; manganese ≤ 0.40; silicon ≤ 0.50; sulfur ≤ 0.02; phosphorus ≤ 0.02; rare earth elements (lanthanum cerium, praseodymium, neodymium) 0.05-0.30; iron - the rest. The specified casting Invar alloy is produced on an industrial scale according to TU 4112-006-32115414-07 “Castings from precision alloy grade 33NKUL”.

The disadvantage of this alloy is that the reuse of charge materials (remnants of the gating-feeding system, drains, etc.) requires additional additional charge with ferromaterials with rare earth metals (REM).

The essence of the invention

The technical problem solved by the claimed invention is to obtain an iron-based Invar alloy with the maximum approximate value of the temperature coefficient of linear expansion (TCLE) to a carbon composite in the temperature range from minus 60°C to 200°C, as well as fluidity characteristics that make it possible to obtain large-sized equipment with complex spatial geometry using shaped casting.

The technical result consists in improving the fluidity properties of the iron-based Invar alloy while maintaining the minimum temperature coefficient of linear expansion from minus 60°C to 200°C.

The technical result is achieved by the fact that the iron-based Invar alloy contains nickel, cobalt, carbon, silicon, manganese, calcium and inevitable impurities in the following ratio of components, mass. %:

Nickel 32.0-35.0 Cobalt 3.6-6.0 Carbon 0.75-1.5 Silicon 0.1-0.5 Manganese 0.1-0.4 Calcium 0.001-0.1 Iron and inevitable impurities Rest,

while the following conditions are met, wt.%:

Ni/Co=6÷8;

(Ni+Co)/C=30÷50,

where: Ni - nickel content, wt.%; Co - cobalt content, wt.%; C - carbon content, wt.%.

Carrying out the invention

The claimed invention is illustrated in graphic materials, where in Fig. Figure 1 shows a photo of the microstructure of the proposed alloy, which is based on an austenitic matrix and graphite precipitation.

The inventive casting Invar alloy has improved fluidity characteristics compared to its analogue while maintaining a minimum temperature coefficient of linear expansion from minus 60°C to 200°C. The study of fluidity using a complex U-shaped chill test depending on the carbon content showed values in the intervals: 208-227 mm.

It is known that carbon has a negative effect on the TCLE value. The presence of carbon is due to the need to increase the fluidity and crack resistance of the alloy, in order to produce complex castings without restrictions on shape and size. Concentration limits are determined by the following conditions: the lower limit (0.75 wt.%) - ensuring sufficient fluidity to fill the mold and the absence of hot cracks, the upper limit (1.5 wt.%) is regulated by the factor of increasing the permissible value of the alloy's thermal expansion coefficient (2.5× 10 ^-6 K ^-1 ).

To reduce oxidation of the melt and the formation of non-metallic inclusions, melting is carried out with the supply of argon into the furnace space. Deoxidation of the melt with aluminum reduces the oxygen content in the metal and refines the grain in the castings. The presence of calcium in the alloy promotes the release of carbon in the form of spherical graphite.

The alloy can be contaminated with impurities of the elements oxygen, sulfur, phosphorus, nitrogen, manganese, hydrogen, i.e. include inevitable harmful technological impurities. To reduce the negative impact on the properties of the alloy, the amount of impurities is controlled in order to achieve their minimum quantitative value.

The presence of oxygen in the alloy reduces the casting properties due to the possible formation of cracks during crystallization, subsequent cooling or operation due to oxide non-metallic inclusions. In addition, oxygen can cause gas porosity.

The causes of cracks in the Invar alloy can be sulfides formed during the interaction of sulfur with melt components, which in turn act as stress concentrators, reducing mechanical properties. The use of pure charge materials ensures a low sulfur content and eliminates its negative impact. The sulfur content in the alloy is no more than 0.02 wt. %.

When phosphorus is present in an alloy, it accumulates along the grain boundaries, thereby having a significant impact on the mechanical properties of the alloy. This determines the maximum quantitative value of phosphorus in the alloy – ≤0.02 wt.%.

Nitrogen is an inevitable impurity; at elevated levels, nitrides are formed inside dendrites, which can block their channels during crystallization, contributing to the appearance of microporosity. In this regard, the nitrogen content is strictly regulated and is ≤0.01 wt.%

A manganese content of more than 0.4 wt.% in the alloy leads to an increase in TCLE. Based on this, the manganese content in the final alloy is controlled in the range of 0.1-0.3 wt.%.

The harmful effects of sulfur, phosphorus, oxides and nitrides are due to the fact that they liquidate at grain boundaries, softening the matrix and increasing the thermal expansion coefficient.

When comparing the claimed cast Invar alloy with a similar alloy, distinctive features were identified, namely the absence of rare earth metals (REM), which allows us to conclude that the claimed invention complies with the “novelty” condition.

Casting invar alloy NS-33NK5UL was smelted in high-frequency open type induction furnaces with a capacity of 160 kg, 1 and 2 tons using a neutral lining.

Before smelting, rolled electrical steel was cleaned of traces of corrosion and other contaminants in a shot blast chamber. The remaining charge materials (cobalt, nickel, graphite) were used at a high degree of purity.

For smelting the alloy the following was used:

– Rolled steel of electrical grade 10895 (mass content of C not more than 0.035%, Mn, Si, Cu not more than 0.3%, S not more than 0.030%, P not more than 0.20%);

– Cobalt grade K1Au (mass content of Co is not less than 99.90%, C is not more than 0.01, the rest is impurities);

– Nickel H1 (mass content of Ni is not less than 99.83%, C is not more than 0.01, the rest is impurities);

– Crushed graphite.

To deoxidize the alloy, silicocalcium SK25 (mass content of Ca is not less than 25%, C is not more than 0.5%, the rest is silicon, iron and impurities) and aluminum rod A5E-PT (mass content of Al is not less than 99.5%, the rest is impurities) were used.

The thermal expansion coefficient of the cast Invar alloy was determined using a Netzsch DIL 402 EXPEDIS Supreme dilatometer. The measurements were carried out on five samples from each heat, made from both separately cast samples and the finished casting.

To determine the chemical composition of the alloy, samples were poured from the ladle into a separate mold. The chemical composition was determined using a Q4 Tasman 170 desktop optical emission analyzer, an MSA II V5 emission spectrometer, and a G4 ICARUS HF carbon and sulfur analyzer.

Table 1 shows the chemical composition of the proposed alloy for four experimental melts and an analogue alloy.

Table 1. Characteristics of the chemical composition of the alloy type 33NKUL

Alloy Ni, % Co,% C, % Rare earth metal alloy (REM), % Mn, % Si, % S, % P, % Cu,% Cr, % Al,% Fe,% 33NKUL 32.0-34.5 2.0-3.5 0.75-1.5 0.05-0.30 ≤0.40 ≤0.50 ≤0.02 ≤0.02 - - - rest The claimed alloy The claimed alloy 34.1 4.5 1.0 - 0.14 0.39 0.006 0.013 0.06 0.10 0.038 rest The claimed alloy 33.5 4.5 0.95 - 0.14 0.43 0.003 0.010 0.06 0.09 0.068 rest The claimed alloy 34.0 4.5 0.98 - 0.14 0.40 0.006 0.011 0.05 0.09 0.053 rest The claimed alloy 33.9 4.5 0.96 - 0.14 0.41 0.004 0.012 0.06 0.09 0.042 rest

Table 2 presents the temperature coefficients of linear expansion and fluidity of the proposed alloy for four experimental melts and an analogue alloy.

Table 2. Characteristics of the temperature coefficient of linear expansion and fluidity

No.
p/p Alloy Temperature coefficient of linear expansion, ×10 ^-6 K ^-1 Fluidity according to complex chill U test 20-100°С 20-200°С 1 33NKUL according to TU 4112-006-32115414-07 - 2.2 226 2 The claimed alloy 1.19 2.07 220 3 The claimed alloy 1.57 2.37 227 4 The claimed alloy 1.07 1.96 212 5 The claimed alloy 1.38 1.92 208

The fluidity of the proposed casting Invar alloys is similar to the fluidity of the alloy of the control example 33NKUL (prototype) and is sufficient for the production of castings with complex spatial geometry, practically unlimited in weight and size by shaped and special casting methods.

Studies of the alloy have shown that the structure of the castings is stable and is a combination of grains of γ - a solid solution of nickel in iron and graphite inclusions of predominantly spherical shape, without carbide phases and martensite.

The claimed qualitative composition and quantitative ratio of nickel, cobalt, carbon, silicon, manganese and iron allows obtaining the minimum required LTEC values (0≥2.5×10 ^-6 K ^-1 ) in the temperature range from minus 60°C to plus 200°C and optimal fluidity indicators.

The above-mentioned casting properties and characteristics of the chemical composition indicate the presence of a new technical result in achieving minimum TCLE with optimal casting properties for producing large-sized cast pieces.

Claims (6)

Iron-based Invar alloy, designed to form products with a structure without carbide phases and martensite and containing nickel, cobalt, carbon, silicon, manganese, calcium and inevitable impurities, including oxygen, sulfur, phosphorus, nitrogen, hydrogen, in the following ratio of components , wt.%: nickel 32.0-35.0 cobalt 3.6-6.0 carbon 0.75-1.5 silicon 0.1-0.5 manganese 0.1-0.4 calcium 0.001-0.1 iron and inevitable impurities rest, while the following conditions are met, wt.%: Ni/Co=6-8; (Ni+Co)/C=30-50, where: Ni - nickel content, wt.%, Co - cobalt content, wt.%, C - carbon content, wt.%.