JPH021219B2 - - Google Patents

Description

[Detailed description of the invention]

The main component of this invention is iron, nickel 35-45%,
5×10 ^-6 / containing 4% or less titanium, 1% or less niobium, unavoidable impurities due to dissolution, and cobalt.
Linear expansion coefficient of 20~300℃ smaller than ℃ and
The present invention relates to an age-hardenable iron-nickel casting alloy having a yield point of 20°C higher than 350N/mm ² . Casting alloys of this type are known (Swiss patent no.
602949), in the case of this alloy, the optimum combination of strength and coefficient of linear expansion can be obtained as long as the components nickel, titanium, cobalt and niobium satisfy the conditions of the following formula: Ni% + 0.7 × Co% - 1.25 (Ti% + 0.35 x Nb%) -2 x Ti% / (Ti% + Nb%) = 37 ~ 39 However, such age-hardened alloys have a suitably high titanium content unless their composition satisfies the above formula. Although it has a 20℃ yield point of 350N/mm ² in the content,
Expansion coefficients of less than 5x10 ^-6 /°C are not achieved in the temperature range from 20 to 300°C. Furthermore, to obtain the desired tensile strength, the minimum required content of titanium must be at least 1.7% by weight,
It is said that a good surface condition of the casting can only be achieved with a high titanium content of 2% or more. In the case of this known casting alloy, the coefficient of linear expansion is
A cobalt content of 5-16% is required to keep it low in the range of 300-600°C. The object of the present invention is to start from the iron-nickel casting alloy described in Swiss Patent No. 602,949 and to improve this alloy in such a way that the expensive cobalt content is reduced without increasing the coefficient of linear expansion. be. Experiments have surprisingly shown that with a minimum amount of titanium, the cobalt content can be reduced to 1.5 to 2.5% as indicated in the characterizing part of claim 1 of the new alloy, and properties at least equivalent to those of the known alloy can be obtained. It became. The composition of the alloy of the present invention is based on the following considerations: Nickel: An iron-nickel alloy with a nickel content of 35% is
It has a low expansion coefficient between 100℃. At higher temperatures, the curve of the expansion coefficient with respect to temperature increases rapidly (formation of a break point). As the nickel content increases to about 45%, the value of the low temperature coefficient of expansion increases slightly, but the break point moves to higher temperatures so that a relatively small coefficient of expansion exists over a wide temperature range. 45%
This must not be exceeded, since higher nickel contents undesirably increase the coefficient of expansion. Cobalt: Cobalt is added because the nickel content must be limited to a maximum of 45%. This cobalt partially supplements the effect of nickel and reduces the coefficient of expansion in the high temperature range. This means that the break point moves towards higher temperatures and therefore the linear expansion curve becomes flat as a whole. Titanium: Titanium increases the strength of the alloy by causing age hardening through the precipitation of Ni ₃ Ti. The addition of titanium binds Ni and thus reduces the Ni content.
The addition of titanium must therefore be limited to 4%. Higher titanium contents reduce the toughness of the alloy, making the material brittle. Even higher titanium content increases the coefficient of expansion. A minimum of 1% of titanium is required since otherwise age hardening will not occur. Niobium: Niobium is an extremely strong carbide former. Niobium binds carbon and improves heat resistance through carbide precipitation. The addition of niobium is considered a replacement for titanium as a carbide former. This addition is useful because titanium precipitates as Ni ₃ Ti. The niobium content is 1% because part of the nickel is combined.
shall not exceed. This new material is age hardenable due to its titanium and nickel content, and the alloy structure consists of a γ-base with carbides and a precipitated phase γ'. TiC and
NiC-type carbides appear as primary charcoals with a large surface area, as grain boundary precipitated carbides, or as spherical carbides inside grains. A particular advantage is that the alloy according to the invention is significantly cheaper due to the current high procurement costs of cobalt. Next, the present invention will be explained by two examples. The two test alloys were melted in vacuum and the diameters were measured using metal molds.
14 mm rods were cast and solidified in vacuum. To remove porosity, the rods were hot rolled to a diameter of 6 mm at 1120°C and then heat treated at 650°C for 5 hours. This rod material was machined to create strength specimens. Nickel 42.9%, Cobalt 2.14%, Titanium 1.66
%, Niobium 0.43%, Aluminum 0.13%, Carbon
A first alloy having a composition of 0.003% silicon, 0.05% silicon, balance iron and impurities based on dissolution and 37.4% nickel, 1.99% cobalt, 1.70% titanium, 0.51% niobium, 0.07% aluminum, 0.002% carbon, 0.04% silicon, A second alloy with a composition of balance iron and dissolution-based impurities exhibited the following properties:

[Table] This result is obtained when the content of nickel, cobalt, titanium and niobium is the first alloy according to the above formula.
This was achieved in spite of the fact that it was 40.5% and 34.9% for the second alloy. Silicon is an impurity. Silicon is a companion element to iron or is introduced from the melting of pig iron. Silicon has disadvantageous properties with respect to expansion coefficient, so it must be reduced to a minimum. Its complete removal is a matter of cost. Carbon is also an accompanying element of iron, or is necessarily accompanied during dissolution. Aluminum is added as a deoxidizing agent and a deoxidizing agent. This prevents oxygen and nitrogen from binding the titanium necessary for precipitation hardening. The mechanical properties of the two alloys were measured at room temperature and 600°C with the following results:

It is clear from the results that the casting alloys according to the invention are particularly suitable for machine parts with high mechanical and thermal loads, such as rotors of gas-dynamic pressure wave machines.

Claims (1)

[Scope of Claims] 1 Mainly composed of iron, containing 35 to 45% nickel, 4 to 1% titanium, 1% or less niobium, unavoidable impurities due to dissolution, and cobalt smaller than 5×10 ^-6 /°C In an age-hardenable iron-nickel casting alloy with a coefficient of linear expansion between 20 and 300 °C and a yield point of 20 °C higher than 350 N/ ^mm2 , with a cobalt content of 1.5
An age-hardenable iron-nickel casting alloy characterized by ~2.5% by weight. 2 Nickel content is 42.9%, cobalt content is 2.14
%, a titanium content of 1.66% and a niobium content of 0.43%. 3 Nickel content is 37.4%, cobalt content is 1.99
%, a titanium content of 1.70% and a niobium content of 0.51%.