EP1340564B1 - Use of a hardenable copper alloy - Google Patents

Abstract

Hardenable copper alloy comprises (in wt.%) 1.2-2.7 cobalt, 0.3-0.7 beryllium, 0.01-0.5 zirconium, 0.005-0.2 magnesium and/or iron, optionally up to maximum 0.15 niobium, tantalum, vanadium, hafnium, chromium, manganese, titanium and/or cerium, and a balance of copper. Preferred Features: The copper alloy contains (in wt.%) 1.8-2.4 cobalt, 0.45-0.65 beryllium, 0.15-0.3 zirconium, up to 0.05 magnesium, up to 0.1 iron and a balance of copper. Up to 80% of the cobalt content is replaced by nickel.

Description

The invention relates to the use of a curable copper alloy as a material for the production of blocks for the side dams of strip casting plants.

The worldwide goal, especially of the steel and copper industry, to cast semifinished products as close to the final dimensions as possible in order to save hot and / or cold forming steps, led to the development of the so-called Hazelett strip casters in 1970, in which the molten metal in the gap of two parallel Ligaments solidified. The side dams consist in the example of the U.S. Patent 3,865,176 known strip casting from metallic form or Seitenendammblöcken with T-groove, which on a flexible endless belt, z. As steel, are lined up and move in synchronism with the casting belts in the longitudinal direction. The side dam blocks (dam blocks) thereby limit the mold cavity formed by the casting belts.

Furthermore, from the EP 0 974 413 A1 formed from blocks with tongue and groove side dam chains for strip casting. The advantage of this weiterentwikkelten mold blocks with tongue and groove is a more accurate alignment and guidance of the blocks in the casting process and leads to an improvement in the surface quality of the cast strand. In order to prevent premature wear of the side edges of the blocks by plastic deformation and cracking, a suitable material must have a high hardness and strength, a fine-grained texture and a good long-term softening resistance. In order to dissipate the solidification heat from the liquid molten metal, a high thermal conductivity of the molding block material is also required.

Of crucial importance is, finally, an optimal fatigue behavior of the material, which ensures that after leaving the casting line, the thermal stresses occurring during the cooling of the blocks does not lead to tearing of the blocks in the corners of the incorporated for receiving the steel strip T-groove. Particularly high thermal stresses are expected - due to the less favorable geometry and mass distribution - in side dam blocks in the design with tongue and groove.

Occur such caused by thermal shock cracks, falls after a short time of the block in question from the Seitendammkette the strip casting machine out molten metal from the mold cavity leak out uncontrolled and can damage equipment parts. For the replacement of the defective mold blocks, the entire strip caster must be stopped and the casting process must be interrupted.

To test the tendency of cracking, a test method has proven in which the mold blocks are subjected to a heat treatment at 500 ° C for two hours and then quenched in water at 20 to 25 ° C. Even if this thermal shock test is repeated several times, no cracks in the T-slot surface may occur with a suitable material.

In the EP 0 346 645 B1 describes a curable copper-based alloy consisting of 1.6 to 2.4% nickel, 0.5 to 0.8% silicon, 0.01 to 0.2% zirconium, optionally up to 0.4% chromium and / or bis to 0.2% iron, balance copper including manufacturing impurities. This known copper alloy basically meets the requirements for a long service life, if it is used as a material for the production of standard shaped blocks for the side dams of strip casting plants. For this copper alloy, the following property combination is specified: Rm at 20 ° C: 635 to 660 MPa Rm at 500 ° C: 286 to 372 MPa Brinell hardness: 185 to 191 HB (corresponds to approximately 195 to 210 HV) Conductivity: 41.4 to 43.4% IACS

There are no cracks during the thermal shock test. An advantage over beryllium-containing copper-base alloys is the possibility of manually regrinding the mold blocks manually, since no beryllium is contained in the grinding dust. The post-processing of inserted side dam blocks with tongue and groove is considerably more complicated and usually requires a mechanical (wet) cleaning of the T-slot and the casting surfaces (eg in closed chambers), whereby the release of abrasive dust is prevented. A use of beryllium-containing alloys would thus be possible under these conditions.

A side dam block from in the EP 0 346 645 B1 However, CuNiSiZr alloy described disadvantageously tends at very high mechanical and thermal stresses in the casting operation of a strip casting plant for premature wear of the side edges and casting surfaces. This wear is - as research results have shown - due to a material softening of the casting edges and surfaces to a value below 160 HV. Furthermore, the thermal shock resistance of the known CuNiSiZr alloy when used as a side dam block with tongue and groove is not always sufficient to effectively prevent cracking in the T-slot in the casting insert.

EP 0 548 636 A and US 4 179 314 A disclose other Cu alloys and their use for molds

By the use according to the claims on the one hand sufficient hardenability of the material to achieve high strength, hardness and conductivity can be ensured. On the other hand, only a relatively small cold deformation of 5% to a maximum of 30% is required to set a fine-grained structure with sufficient plasticity. The targeted graded zirconium content improves both the fatigue strength and the heat resistance properties.

With the sequence of the process steps specified in claim 1, it is also possible in a surprisingly simple manner to eliminate the poor recrystallization behavior observed in the hot forming and solution annealing treatment observed by the known CuCoBe alloys. The poor recrystallization behavior results in the production of blocks of CuCoBe alloys in the hot-formed, solution-annealed and cured state to a non-acceptable for the intended use coarse-grained microstructure with grain sizes up to 1 mm. However, if the material is subjected to cold working of 5% to a maximum of 30%, preferably up to a maximum of 15%, between the hot working and the solution annealing treatment, this additional processing step leads to a considerably finer grain structure. Corresponding series of tests have confirmed that materials for mold blocks for the side ram of strip casters, cold worked below the recrystallization and then solution annealed have a much finer microstructure with grain sizes below 0.5 mm, while higher degrees of cold work above about 40% in the subsequent solution annealing to a Grain coarsening by secondary recrystallization with grain sizes above 1 mm lead.

Reference to exemplary embodiments, the invention will be explained in more detail below. The advantages of the invention are shown in three examples of the invention (alloys A, B and C) and three comparative examples (alloys Comparative Example - D, E and F.) The composition of the copper alloys in percent by weight is given in Table 1 below: Table 1 alloy Co (%) Ni (%) Be (%) Zr (%) Si (%) Cr (%) Cu (%) A 2.1 - 0.54 0.18 - - rest B 2.2 - 0.56 0.24 - - rest C 1.3 1.0 0.48 0.15 - - rest D - 2.0 - 0.16 0.62 12:34 rest e 2.1 - 0.55 - - - rest F 1.0 1.1 0.62 - - - rest

The composition of alloy D is a known CuNiSi base alloy, while E and F are standardized CuCo2Be and CuCoNiBe materials, respectively.

All copper alloys were melted in an induction crucible furnace and cast in a continuous casting process into round blocks with a diameter of 280 mm. The round blocks of the example alloys A, B and C were extruded on an extruder at a temperature above 900 ° C to flat bars of dimension 79 x 59 mm and then drawn with a cross-sectional decrease of 12% to the dimension 75 x 55 mm. The blocks of the comparative alloys D, E and F were extruded directly at the same temperature to the dimension 75 x 55 mm and subjected to no additional cold working. The CuCoBe or CuCoNiBe materials were then solution-annealed at 900 to 950 ° C and cured in the temperature range between 450 and 550 ° C for 0.5 to 16 hours.

The CuNiSi-based alloy was solution-annealed at 800 to 850 ° C and cured under the same conditions. When cured, tensile strength Rm, Vickers hardness HV10, electrical conductivity (as a substitute for thermal conductivity), ASTM E112 grain size, Rm heat resistance at 500 ° C and softening resistance via Vickers hardness measurement (HV10) after aging at 500 ° C determined after a period of 500 hours.

On thermoforming blocks (1) measuring 70 x 50 x 40mm and shaped blocks (2) with tongue and groove measuring 70 x 50 x 47mm, the thermal shock behavior was finally tested. For this purpose, the mold blocks were first annealed for two hours at 500 ° C and then quenched in water at 20 to 25 ° C. The T-slot of the blocks was then examined for cracks with the naked eye and a microscope at 10x magnification.

All test results are summarized in Table 2 below. Table 2: alloy Rm MPa HV 10 Guide% IACS Grain size μm Rm (500 ° C) MPa Hardness HV 10 after aging at 500 ° C over 500h Behavior after thermal shock test Block (1) Block (2) A 801 254 50 30-90 523 173 crack-free crack-free B 804 245 51.5 45-90 464 175 crack-free crack-free C 812 255 49.5 45 -90 485 167 crack-free crack-free D 652 205 43 45 -90 387 118 crack-free cracked e 786 260 50.5 up to 5000 423 150 cracked cracked F 807 248 48.5 up to 3000 434 152 cracked cracked

The extent of observed cracks in the T-slot was 2 to 5 mm in the blocks classified as "cracked", in some cases the crack length was up to 10 mm. The comparison can be seen that compared to the materials E and F, only the examples of the invention with optimum properties have a surprisingly uniform and fine-grained structure and the necessary resistance to cracking when used as a mold block with tongue and groove. Even when used as a conventional molding block, the inventive examples have a significantly better resistance to softening compared to the known CuNiSi alloy D and a slightly better resistance to softening compared to the alloys E and F.

The copper alloy disclosed in claim 1 is therefore eminently suitable as a material for the production of all mold blocks for the side dams of strip casting plants subject to the casting process of a typical alternating temperature stress. These are both the previously used mold blocks and the mold blocks in the design with tongue and groove according to EP 0 974 413 A1 ,

Claims (2)

1. Use of a hardenable copper alloy for casting moulds - in particular for side dams for strip-casting installations, in that a hardenable copper alloy in accordance with the following composition:

   • 1.2 to 2.7% cobalt, wherein up to 80% of the cobalt content can be replaced by nickel

   • 0.01% to 0.5% zirconium

   • 0.3 to 0.7% beryllium

   • optionally 0.005 to 0.2% magnesium and/or iron

   • optionally up to a maximum of 0.15% of at least one element from the group comprising niobium, tantalum, vanadium, hafnium, chromium, manganese, titanium and cerium

   • remainder copper including impurities caused by production

   is subjected to the method steps

   • cold forming of the hot-formed cast blank by between 5 and a maximum of 30%

   • solution annealing of the blank which has been cold formed by 5 to 30% in the temperature range of 850 to 970°C

   • 0.5 to 16 hours of hardening of the solution annealed blank at 400 to 550°C and in the hardened state has

   • a tensile strength of at least 650 MPa

   • Vickers hardness of at least 210 HV

   • electrical conductivity of at least 40% IACS

   • hot tensile strength at 500°C of at least 400 MPa

   • minimum hardness of 160 HV after 500 hours of ageing at 500°C

   • and a maximum grain size determined according to ASTM E112 of 0.5 mm.
2. Use of a copper alloy according to claim 1, which contains 1.8 to 2.4% cobalt, 0.45 to 0.65% beryllium, 0.15 to 0.3% zirconium, up to 0.5% Mg, up to 0.1% iron, remainder copper including impurities caused by production, is subjected to the method steps according to claim 1 with a cold forming of 10 to 15% after the hot forming and has, in the hardened state, a

   • tensile strength of 700 to 900 MPa

   • Vickers hardness of 230 to 280 HV

   • electrical conductivity of 45 to 60% IACS

   • hot tensile strength at 500°C of at least 450 MPa

   • minimum hardness of 160 HV after 500 hours of ageing at 500°C

   • a grain size determined according to ASTM E112 of between 30 and 90 µm.