DE1608401C - Use of a cold-formable cobalt alloy as a material for the tubular jacket of core electrodes - Google Patents

Description

Cobalt alloys are widely used as construction materials, heat and corrosion resistant Materials used in magnets, as weld-on alloys and wear-resistant materials. Because of their poor processability, cobalt and cobalt alloys are generally only used in Cast form applied. The difficulty of making articles from cobalt and cobalt alloys by cold forming manufacture places a severe limitation on the use of this otherwise so versatile detail represent.

The fact that cobalt and most high cobalt alloys cannot be cold worked is due to work hardening of the metal, which reduces ductility and makes further cold working impossible until the metal parts have been stress relieved by heat treatment. At room temperature cobalt normally has a hexagonal crystal lattice with a so-called closest packing, and it is known that the cold forming of a metal with such a crystal structure leads to cold hardening or internal stresses. In contrast, cobalt has ^{a face-centered cubic crystal lattice at temperatures above 415 °} C., which would allow cold forming if it were also present at normal temperatures. However, at around 415 ° C there is an allotropic transformation of the crystal structure from the cubic to the hexagonal form.

The stresses caused by cold forming cobalt can only be removed by annealing. The production of cold-formed cobalt sheets or wires is therefore cumbersome and expensive. The reduction in rolling must be done in many small steps, after each step must be relaxed by annealing in order to eliminate the work hardening and the alloy for the to soften the next molding process.

An important use for cold formable cobalt and cold formable cobalt alloys is the manufacture of tubular core electrodes, i. H. a tubular shell that is inside Contains alloy components. By keeping cobalt and cobalt alloys from being cold formed Such tubular sheaths can be processed, the use of cobalt in this Shape, although cobalt is known to be an excellent material for these welding methods.

It has now been found that alloys consisting predominantly of cobalt with cobalt Easily process carbon, iron and / or nickel by cold working and as a material for the Let use tubular sheaths of core electrodes.

The invention relates to the use of a cold-formable cobalt alloy, which consists of at least 70 percent by weight cobalt and 0.5 to 0.75 percent by weight carbon, 6 to 11 percent by weight Iron and / or 24 to 30 percent by weight nickel is used as the material for the tubular Sheath of soul electrodes.

According to the invention, the use of cold-deformable cobalt alloys is also provided, which contain at least 70 percent by weight cobalt and iron and nickel side by side and in which the minimum amount of iron and nickel by the equation

% Fe + j / o / o Ni = 4.7

is determined, at least one of the elements iron and nickel being present in amounts of at least 1% is.

In the alloys used according to the invention, the point of allotropic conversion of the Cobalts from the face-centered cubic crystal lattice to the tightly packed hexagonal crystal lattice Shifted to a point below room temperature.

It has been found that an addition of 0.5 weight percent carbon may cause this change in the transition temperature, which usually is located at 415 ⁰ C, for cobalt. Furthermore, with an iron addition of 6% it is possible to retain the cubic crystal lattice of cobalt. The amount of nickel required to achieve the same effect is at least 24 percent by weight when nickel is added as the only element to cobalt. If nickel and iron are added, the required amounts of nickel are lower because the effects of the elements nickel and iron increase synergistically. If iron and nickel are added together to the cobalt, the required minimum amount is given by the equation

% Fe +] /% Ni = 4.7

determined, wherein at least one of the additional metals is present in amounts of at least 1 ⁰ Zo.

The maximum amounts of these elements that can be added to the cobalt are 0.75% Carbon, 11% iron and 30% nickel.

The cobalt alloys used according to the invention resist due to their cubic crystal lattice moderate to severe cold forming without severe impairment of ductility or detrimental increase of hardness. Although these alloys also have a cubic crystal lattice, which in pure Cobalt is absent at room temperature, they have similar physical and mechanical properties Properties like pure cobalt, so that in many cases they are used instead of pure cobalt be able.

Table A.

alloy Mon SoIl-Zu
Cr get together
Fe g in weight
Ni »Percent
C. Co crystal
grid * Cold
malleability A. 100 H bad B. 0.3 99.7 H bad C. 0.6 99.4 K Well D. 2.5 0.6 96.9 K Well E. 4.0 96 H bad F. 1 4th . 95 H bad G 4th 4th 92 K Well FI 4th 4th 0.1 91.9 K Well I. 6th 94 K Well J 24 76 K Well

♦ H = hexagonal crystal lattice of closest packing.

K =

In Table A above, the crystal structure at room temperature and cold formability are a number of cobalt alloys. From the values in this table it can be seen that through Addition of iron, carbon and nickel to cobalt results in the allotropic conversion of cobalt in one Point below room temperature is pressed. The presence of the face-centered cubic The crystal lattice at room temperature is due to the addition of these elements.

Commercial cobalt can contain a small amount of nickel, iron, carbon or other impurities that cannot be avoided during refining of the metal, however these elements are neither present in sufficient quantities nor in the correct proportions to achieve the

face-centered cubic crystal lattices at room temperature hold back.

The ductility of some of these alloys after cold working was determined using hardness and Bending tests determined. These tests were carried out with ordinary cobalt alloys and the predominantly made of cobalt alloys according to the invention. In the bending tests sheets of the alloys mentioned were bent and the angles at which the convex Side broke at the bending point. Materials that can be bent 180 ° without breaking, have high ductility. The results of these tests are given in Table B, where the Alloy compositions C, D etc. correspond to the alloys given in Table A.

Table B.
Remaining ductility after cold forming

Together
settlement Condition after cold forming Hardness,
Default- Bend angle the alloy Rockwell B test VUl DiULIl C. Relaxed by glow 80 180 ° * C. Cold formed, 10% reduction, no stress relief annealing 91 160 ° D. Relaxed by glow 74 180 ° * D. Cold formed, 10% reduction, no stress relief annealing 91 180 ° * E. Relaxed by glow 83 180 ° E. Cold formed, 10% reduction, no stress relief annealing Rc = 24 ** 90 ° H Relaxed by glow 50 180 ° * H Cold formed, 10% reduction, no stress relief annealing 75 180 ° * H Cold formed, reduction 30%, no stress relief annealing 79 180 ° *

The samples were folded flat without breaking.

Corresponds to a Rockwell B value of 101.

Since it is already relatively small in quantities, it can be considered as pure cobalt. In Table C some carbon, iron or nickel are the face-centered physical and mechanical properties of cubic crystal lattice in cobalt at room temperature several of the alloys mentioned here can cause the same, the resulting alloy consists of 40 properties of pure cobalt predominantly made of cobalt and has many properties ,
of pure cobalt, but a better workable table C
Properties of some typical alloys

A. C. alloy
D. E. H Hardness, Rockwell B 79 * 79 76 92 83 Curie temperature, ⁰ C 1116
60.46 **
H
8.9 1110
73.82
6.0
K
8.9 1093
80.85
6.45
K
8.7 3.5
H
8.7 1019
61.16
6.5
K Tensile strength, kp / mm ² 8.5 Erichsen value, mm *** Predominantly crystal structure Density, g / cm ³

* Cast cobalt according to "Cobalt" by R. S. Young, Reinhold Publishing Corp. 1948, p. 66.

** Kneaded and annealed according to "Metals Reference Book" by C. J. Smithells, Interscience Publisher, Inc. 1955, Vol. 2, p. 803. ♦♦ * Erichsen value is the deepening in mm that can be formed in sheet metal with a standard arbor press without cracks.

The alloys can be melted using the usual methods. Melting is preferred in a vacuum, when as few oxides and gas inclusions as possible are desired. To have good thermoformability To ensure the alloy, the sulfur and phosphorus content must be kept as low as possible as these elements severely impair formability.

The essential similarity of the properties of these alloys, which predominantly consist of cobalt and the properties of pure cobalt enables the manufacture of tubular core electrodes. These welding wires consist of a tubular jacket with alloy components inside contains. When processing these welding wires according to the usual welding technology

In the niche process, the weld bead is made from an alloy of the metal of the tubular jacket with the elements it contains. Typical elements contained in such pipes are Carbon, nickel, cobalt, tungsten, molybdenum and other alloy components.

The use of such tubular core electrodes to form weld beads from Made of iron or nickel alloys, it is widely used in technology because these materials are themselves cold form both easily thin-walled, small-diameter tubes. The difficulty, To process alloys with a high cobalt content into thin-walled tubes with a small diameter, precluded the practical and economical manufacture of cobalt welding wires of this type. At present, welding wires made of cast and wrought cobalt alloys are made in solid rod form manufactured. They are used to produce wear-resistant and / or corrosion-resistant surfaces used by build-up welding. With the help of the use of cold-formable cobalt alloys according to the invention, it is now economically possible to consist of these alloys jackets for tubular Manufacture soul electrodes. This tubular, which was previously only produced in short cast lengths Soul electrodes can now be used as uninterrupted snakes from the harder and more wear-resistant Varieties of cobalt weld-on alloys are produced.

A tubular core electrode with a jacket made of the ductile cobalt alloy according to the invention could for example contain a filler material of the following composition: 72% chromium, 14% tungsten, 1% iron, 3.5% carbon and 3.5% cobalt. With a tubular welding wire A welding bead could be laid in this way, as it was previously only possible with cast welding wires was achievable.

A cold-formable cobalt alloy could also be processed into jackets for tubular core electrodes which contain tungsten carbide as a filler material. An existing from 8 ^o / o chromium, and 92% tungsten carbide filler material was placed in a überwiegehd consisting of cobalt tubular shell. Such a material is suitable for producing wear-resistant surfaces by surfacing. During the welding process, the molten cobalt alloy of the shell dissolved part of the tungsten carbide and, after cooling, precipitated tungsten carbide in solid form. In this way an overlay was obtained which had large particles of unmolten tungsten carbide retained in a cobalt-rich mass. This pad had excellent ■ wear resistance. "

The filler material can be in the form of a pre-alloyed powder or in the form of particles of the pure elements are used.

Claims (3)

20. Patent claims: 1. Use of a cold-formable cobalt alloy, consisting of at least 70 percent by weight Cobalt and 0.5 to 0.75 percent by weight carbon, 6 to 11 percent by weight iron and / or 24 to 30 percent by weight nickel as a material for the tubular jacket of core electrodes. 2. Use of a cobalt alloy composed of at least 70 percent by weight cobalt and iron and nickel, where the minimum amounts of iron and nickel by the equation % Fe is determined and at least one of the elements iron and nickel in amounts of at least 1% is present for the purpose of claim 1. 3. Use of a cobalt alloy composed of 91.9% cobalt, 0.1% by weight carbon, 4 percent by weight iron and 4 percent by weight nickel for the purpose of claim 1.