JPS60169539A - Nickel-base alloy - Google Patents

Abstract

Nickel-based alloys containing chromium and aluminium and permitting precipitation hardening by means of a heat treatment. These alloys contain, by weight 28 to 42% of chromium, less than 25% of iron, 3 to 5% of aluminium, the remainder being nickel with the usual impurities, the iron and chromium contents being situated in the region marked I in the diagram of Figure 1 so that the said alloys have the quantity of ferrite needed to control the grain size. The alloys can be employed for applications requiring high mechanical strength with excellent corrosion resistance and additionally demanding high ductility. <IMAGE>

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Applicability] The present invention relates to an alloy containing nickel as a main component, chromium and aluminum as a main component, and which can be precipitation hardened by heat treatment.

[Conventional technology]

French Patent Publication No. 1.267.470 describes nickel-based alloys with a high content of chromium and walnut rum and precipitation hardening obtained by solution treatment and subsequent tempering. . Solution treatment of the intermetallic hardening phase can reduce the hardness level of the alloy sufficiently to allow easy forming. The solution treatment temperature should exceed 1100° C., in particular 1150° C., in order to ensure hardening, especially during tempering. If the temperature is kept higher than 1100° C., excessive coarsening of crystal grains is often induced. If the crystal grains are too coarse, the surface condition will be irregular during molding work, and
mechanical cutting operations become difficult and the metal becomes very brittle after temper hardening.

On the other hand, German Patent Publication No. 3,240,188 shows that in order to obtain a smooth polish and a decorative appearance in the aforementioned alloys it is necessary to limit the use of chromium enrichment. There is.

[Problem that the invention seeks to solve]

It is an object of the present invention to provide such alloys whose ductility is improved due to the presence of ferrite 1-.

This alloy has high oxidation resistance, corrosion resistance and mechanical strength,
It has a very high elastic limit and has excellent hardness through heat treatment.

[Failure to solve the problem]

This object, according to the invention, is a nickel-based alloy which is solution-treated and subsequently temper-hardened, with a weight ratio of 28 to 42% chromium and less than 25% iron. , 3-5% aluminum and nickel forming the balance together with the usual impurities, the iron and chromium content being included in region I in the diagram of FIG. This is achieved by alloys characterized by containing ferrite to limit the grain size.

The specific composition consists of 37-38% chromium, 7-8% iron, 3-5% aluminum and 50-5% nickel by weight.
It consists of 1%.

Other features and advantages of the invention will become more apparent from the following description with reference to the accompanying drawings.

〔Example〕

The alloy according to the invention is produced by conventional metallurgical (casting) or powder metallurgical methods. This alloy has undergone precipitation hardening by solution treatment followed by tempering. This hardening is
It is caused by discontinuous precipitation (ie cell precipitation) of r'NiJβ.

Chromium is useful for corrosion resistance and contributes to the formation of the body-centered cubic alpha phase (called ferrite).

Iron also contributes to the formation of the alpha phase.

For the alloy to undergo sufficient hardening, the chromium content must be greater than 28% and the iron content less than 25%, and to avoid excessive brittleness of the alloy, the chromium content must be greater than 28% and the iron content less than 25%. It is necessary that the content of The content of chromium is lower than 28% and the content of iron is less than 25%
%, the cell precipitation of the γ' phase becomes increasingly slow and incomplete.

The relative contents of chromium and iron should be adjusted such that the alloy according to the invention has a sufficient but not excessive amount of alpha phase at its conventional solution treatment temperature (above 1100"C). It is.

In the diagram of FIG. 1, region ABCD indicates the range of compositions according to the present invention that contain a sufficient amount of α phase to suppress grain coarsening when solutionized. The composition range included in region H below curve AB does not contain enough ferrite to suppress coarsening of crystal grains when solutionized. The composition range included in the region (2) above the curve &iDC contains too much (2) ferrite, so the ductility of the alloy is reduced.

Aluminum contributes to giving good corrosion resistance,
It functions to generate a hardened phase γ'. The content of this element should be more than 3% so that precipitation hardening is sufficient, and less than 5% to avoid manufacturing difficulties and to avoid too much brittleness.

Elements known to increase the stability of ferrite, such as molybdenum, vanadium, and titanium, can be incorporated into the alloy without changing the properties of the invention.

The alloy tiN according to the invention and the comparative alloy A, which does not contain ferrite, were particularly investigated.

Table 1 below shows the composition of each alloy expressed as a percentage by weight.

Table 1 Alloy di Ni Cr Fe Aj2 Nuance) N 50.37 37.50 7.38 4.00Δ
50.8G 33.71 10.38 4.05 Analysis of the above-mentioned alloy reveals insignificant elements that may be due to manufacturing (the content of these elements does not exceed 0.05% for each element) is revealed. Some of these elements are carbon, silicon, sulfur, phosphorus, manganese, calcium, magnesium and yttrium.

Trial case of alloys A and N which were work-hardened by rolling in advance '-1
The effect of solution treatment at 10,006 to 1,250°C followed by rapid cooling with ice on crystal grain size was investigated. Alloy N showed very fine crystals after treatment (see Figure 2); on the contrary, Alloy A showed crystals that were more λ■large-ζ not always smaller than 2 ASTM (see Figure 3). . η, Y, the solution treatment is performed at a sufficiently low hardness level (2
It should be carried out at a temperature higher than 1150°C so that the temperature is 40IIV[F].

Next, to test the tensile strength of the alloy, 1
After solution treatment at 200° C., crystal grains of 9.5 ASTM were obtained by water quenching.

Alloy A was solution-treated at 1225°C and then water-quenched to obtain -3ASTM crystal grains. The alloy was then tempered and hardened at temperatures between 650° and 800°C for several hours. According to the tempering conditions, 5001 (V ~ 700
An alloy with high hardness in the range of HV or higher was obtained.

These different treatments allow the elastic limit to be adjusted.

The alloy was then tested for tensile strength at 20°C.

The results are shown in Figure 4.5. The total elongation (Fig. 4), especially the reduction (Fig. 5), is achieved by making the crystal grains finer.
It is clear that it has improved significantly and has reached a very useful level.

The alloy according to the invention can be used in applications requiring not only very good corrosion resistance and mechanical strength but also exceptional ductility. Examples of possible applications include structural materials requiring good ductility (Pol I, piping, turbine blades)
There is.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relative weight percentages of chromium and iron for alloys according to the invention, and FIG. 2.3 is a diagram showing the relative weight percentages of chromium and iron for alloys according to the invention and for alloys without ferrite, respectively, at the solution treatment temperature θ <'c A diagram showing the value of grain size as a function of >, Figure 4 shows the elastic limit (MPa) on the horizontal axis,
Figure 5 is a diagram showing the elongation at break (%) plotted on the vertical axis, with the elastic limit (MPa) on the horizontal axis and the aperture at break (%).
%) is plotted on the vertical axis. Explanation of No. 20 ■, ■, ■... area.

Claims (3)

[Claims] (1) An alloy mainly composed of nickel, which is tempered and hardened following solution treatment, the alloy having a weight ratio of 2
Consisting of 8-42% chromium, less than 25% iron, 3-5% aluminum and nickel forming the balance together with the usual impurities, the iron and chromium content is in region I in the diagram of FIG. an alloy comprising ferrite to limit grain size at solution treatment temperatures. (2) The alloy according to claim 1, which contains, by weight, 37 to 38% chromium, 7 to 8% iron, 3 to 5% aluminum, and 50 to 51% nickel. (3) The alloy according to claim 1 or 2, which is applied to the production of structural materials that require a high degree of ductility.