EP1340564A2 - 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 a hardenable copper alloy as a material for production of blocks for the side dams of strip caster.

The worldwide goal, especially the steel and copper industry, semi-finished products if possible casting close to the final dimensions to save hot and / or cold forming steps, has developed the so-called Hazelett belt caster before 1970 performed, in which the molten metal in the gap of two guided in parallel Ligaments solidified. In the case of the side dams consist, for example, of the US patent 3 865 176 known belt casting machine made of metal or Side dam blocks with T-slot, which are on a flexible endless belt, e.g. B. from Steel that are lined up and that are synchronized with the casting lines in the longitudinal direction move. The side dam blocks (dam blocks) delimit those by means of the casting belts a mold cavity formed.

Furthermore, EP 0 974 413 A1 is formed from blocks with tongue and groove Side dam chains for belt casting machines are known. The advantage of this further developed Form blocks with tongue and groove lies in a more precise alignment and guidance of the blocks in the casting process and leads to an improvement in the surface quality of the cast strand. To prevent premature wear on the side edges to prevent the blocks from plastic deformation and cracking a suitable material, high hardness and strength, a fine-grained structure and have good long-term softening resistance. The heat of solidification dissipating from the molten metal is also a high thermal Conductivity of the mold block material required.

Ultimately, optimal fatigue behavior is of crucial importance of the material that ensures that after leaving the casting line the thermal stresses that occur when the blocks are recooled for tearing the blocks in the corners of the built in for holding the steel band T-slot leads. Particularly high thermal stresses are necessary due to the less favorable geometry and mass distribution - with side dam blocks in the tongue and groove design is to be expected.

If such cracks caused by thermal shock occur, it already falls a short time the relevant block from the side dam chain of the belt casting machine out, leaving molten metal uncontrolled from the mold cavity can leak and damage system components. For replacing the defective Mold blocks must stop the entire strip caster and the casting process to be interrupted.

To test the tendency to crack, a test method has proven itself in which the Mold blocks subjected to a two-hour heat treatment at 500 ° C and then be quenched in water at 20 to 25 ° C. Even with multiple This thermal shock test may be repeated with a suitable material there are no cracks in the T-slot surface.

Rm bei 20°C:

635 bis 660 MPa

Rm bei 500°C:

286 bis 372 MPa

Brinellhärte:

185 bis 191 HB ( entspricht etwa 195 bis 210 HV)

Leitfähigkeit:

41,4 bis 43,4 % IACS

EP 0 346 645 B1 describes a hardenable copper-based alloy which consists 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 up to 0.2% iron, the rest copper including manufacturing-related impurities. This known copper alloy basically fulfills the prerequisites for a long service life if it is used as a material for the production of standard mold blocks for the side dams of strip casting systems. The following combination of properties is specified for this copper alloy:

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

No cracks occur in the thermal shock test. An advantage over those containing beryllium Copper based alloys have the ability to manually mold blocks to be able to grind dry, since there is no beryllium in the grinding dust. The Post-processing of side dam blocks with tongue and groove is considerable more complex and usually requires mechanical (wet) cleaning of the T-slot and the pouring surfaces (e.g. in closed chambers), which causes the release is prevented by grinding dust. Use of alloys containing beryllium would be basically possible under these conditions.

A side dam block made of the CuNiSiZr alloy described in EP 0 346 645 B1 however, tends to be disadvantageous at very high mechanical and thermal Stresses in the casting operation of a strip caster at an early stage Wear on the side edges and pouring surfaces. This wear is like test results have shown - on a material softening of the cast edges and areas attributable to a value below 160 HV. Furthermore, the Thermal shock resistance of the well-known CuNiSiZr alloy when used as Side dam block with tongue and groove not always out to prevent cracking in the T-groove effective in the casting insert.

Starting from the prior art, the invention is based on the object age-hardenable copper alloy as material for the production of side dam blocks of strip casting systems, especially those in tongue and groove design, for To provide, which even at high casting speeds changing temperature stresses is insensitive and high wear resistance resistance to softening and great resistance against cracking in the T-groove.

This object is achieved with the features specified in claim 1.

By using a copper base alloy made from 1.2 to 2.7% by weight cobalt, 0.3 to 0.7% by weight beryllium, 0.01 to 0.5% by weight zirconium, optionally 0.005 to 0.2% by weight of magnesium and / or iron and the balance including copper manufacturing-related impurities and customary processing additives on the one hand, sufficient hardenability of the material to achieve a high strength, hardness and conductivity can be ensured. On the other hand, is only a relatively low cold deformation of up to a maximum of 40% is required to achieve a fine-grained structure with sufficient plasticity. Through the specifically graded Zirconium content will be both the fatigue strength and the Improved heat resistance properties.

Another improvement in the mechanical properties of the side dam blocks, in particular an increase in tensile strength can be advantageous according to claim 2 can be achieved in that the copper alloy 1.8 to 2.4 wt .-% cobalt, 0.45 to 0.65% by weight beryllium, 0.15 to 0.3% by weight zirconium, up to 0.05% by weight Contains magnesium and / or up to 0.1% iron.

The invention allows that according to the features of claim 3 in the Copper alloy up to 80% of the cobalt content can be replaced by nickel.

Further improvements in the mechanical properties of a side dam block can be achieved if the copper alloy up to a maximum of 0.15 % By weight of at least one element from the niobium, tantalum, vanadium, hafnium, Contains chromium, manganese, titanium and cerium group. Usual deoxidizers such as boron, lithium, calcium, aluminum and phosphorus can also up to 0.03% by weight maximum are added without the mechanical properties to adversely affect the copper alloy according to the invention.

According to a further embodiment (claim 4), part of the zirconium content by up to 0.15% by weight of at least one element from the cerium, hafnium, Group comprising niobium, tantalum, vanadium chromium, manganese and titanium his.

The blocks for the side dams are advantageous from double belt casting machines the copper alloy according to the invention according to claim 5 by the process steps Casting, hot forming, cold forming up to 40%, solution annealing at one in the temperature range from 850 to 970 ° C and a 0.5 up to 16-hour curing treatment at 400 to 550 ° C.

With particular advantage, the copper alloy according to claim 6 Hot forming can be cold worked by 5 to 30%. One within this area horizontal degree of cold deformation of 10 to 15% is particularly preferred.

It is particularly advantageous if the side dam blocks in the hardened state a tensile strength of at least 650 MPa, in particular 700 to 900 MPa, a Vickers hardness of at least 210 HV, in particular 230 to 280 HV, an electrical conductivity of at least 40% IACS, in particular 45 to 60% IACS a hot tensile strength at 500 ° C of at least 400 MPa, in particular of at least 450 MPa, a minimum hardness of 160 HV 500 hours of aging at 500 ° C and a maximum grain size according to ASTM E. 112 of 0.5 mm.

Side dam blocks made from the copper alloy according to the invention are particularly preferred according to claim 10, when in the cured state an ASTM E 112 determined grain size between 30 and 90 microns.

With the sequence of the process stages specified in claim 5 above it succeeds in a surprisingly simple way, that of the well-known CuCoBe alloys observed poor recrystallization behavior during hot forming and eliminate solution heat treatment. The poor recrystallization behavior leads in the production of mold blocks from CuCoBe alloys in hot-formed, solution-annealed and hardened state to one for the Intended use unacceptable coarse-grained structure with grain sizes up to over 1 mm. However, if the material is between the hot forming and the Solution heat treatment of cold working up to a maximum of 40%, preferably subject to a maximum of 15%, this additional processing step leads to a significantly more fine-grained structure. Corresponding series of investigations have confirmed that materials for mold blocks for the side dams of strip casting machines, which are cold worked below the recrystallization temperature and then solution annealing results in a significantly finer structure with grain sizes have below 0.5 mm, while higher degrees of cold forming above about 40% in the subsequent solution annealing to a grain coarsening secondary recrystallization with grain sizes over 1 mm.

The invention is explained in more detail below on the basis of exemplary embodiments. The advantages of the copper alloys according to the invention are shown on three alloys according to the invention (A, B and C) and three comparison alloys (D, E and F). The composition of the copper alloys in percentages by weight is given in Table 1 below: 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 00:34 rest e 2.1 - 0.55 - - - rest F 1.0 1.1 0.62 - - - rest

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

All copper alloys were melted in an induction crucible furnace in the continuous casting process to round blocks with a diameter of 280 mm shed. The round blocks of the sample alloys A, B and C were on one Extrusion press at a temperature above 900 ° C to form flat bars Dimension 79 x 59 mm extruded and then with one Cross-sectional decrease of 12% drawn to the dimension 75 x 55 mm. The Blocks of the comparative alloys D, E and F became direct at the same temperature extruded to the dimension 75 x 55 mm and no additional Subjected to cold forming. The CuCoBe and CuCoNiBe materials were then solution annealed at 900 to 950 ° C and in the temperature range cured between 450 and 550 ° C for 0.5 to 16 hours.

The CuNiSi base alloy was solution annealed at 800 to 850 ° C and under the same Conditions hardened. In the cured state, the tensile strength Rm, the Vickers hardness HV10, the electrical conductivity (as a replacement for the Thermal conductivity), the grain size according to ASTM E112, the heat resistance Rm at 500 ° C and the softening resistance via Vickers hardness measurement (HV10) after aging determined at 500 ° C after a period of 500 hours.

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

All test results are summarized in Table 2 below. alloy Rm MPa HV 10 % IACS Grain size µm Rm (500 ° C) MPa Hardness HV 10 after aging at 500 ° C for 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 the cracks found in the T-slot was in those classified as "cracked" Form blocks at 2 to 5 mm, in individual cases the crack length was up to 10 mm. The comparison shows that compared to the materials E and F only those produced according to the invention with additional low cold forming Surprisingly, copper alloys A, B and C with optimal properties uniform and fine-grained structure and the necessary resistance to Show cracks when used as a form block with tongue and groove. Also at The copper alloys according to the invention have use as a conventional mold block a significantly better softening resistance than the known CuNiSi alloy D and a slightly better softening resistance compared to alloys E and F.

The copper alloy according to the invention is therefore extremely suitable as a material for the production of all of them changing during the casting process Mold blocks subject to temperature stress for the side dams of Strip casters. These are both the previously used form blocks as well as the Mold blocks in the tongue and groove design according to EP 0 974 413 A1.

Claims (10)

Hardenable copper alloy from 1.2 to 2.7% cobalt, 0.3 to 0.7% Beryllium, 0.01 to 0.5% zirconium, optionally 0.005 to 0.2% magnesium and / or 0.005 to 0.2% iron and possibly up to a maximum of 0.15% at least one element from niobium, tantalum, vanadium, hafnium, Group comprising chromium, manganese, titanium and cerium, the rest copper including manufacturing-related impurities and usual processing additives as a material for the production of blocks for the side dams of strip caster. Copper alloy according to claim 1, which is 1.8 to 2.4% cobalt, 0.45 to 0.65% Beryllium, 0.15 to 0.3% zirconium, up to 0.05% magnesium, up to 0.1% Iron, balance copper including manufacturing-related impurities and contains common processing additives. Copper alloy according to claim 1 or 2, in which up to 80% of the cobalt content is replaced by nickel. Copper alloy according to one of claims 1 to 3, in which a part of the zirconium content by up to 0.15% of at least one element from the Including cerium, hafnium, niobium, tantalum, chromium, manganese, titanium and vanadium Group is replaced. Copper alloy according to one of claims 1 to 4, which according to the Hot forming of the cast blank up to 40% cold worked, then at a temperature in the range of 850 to 970 ° C solution annealed and then a 0.5 to 16 hour curing treatment is subjected to at 400 to 550 ° C. Copper alloy according to claim 5, which is the hot forming after the method step is cold worked by 5 to 30%. Copper alloy according to claim 5 or 6, which after the hot forging 10 to 15% is cold worked Copper alloy according to one of claims 1 to 7, which in the hardened Condition a tensile strength of at least 650 MPa, a Vickers hardness of at least 210 HV, an electrical conductivity of at least 40% IACS, a hot tensile strength at 500 ° C of at least 400 MPa, a Minimum hardness of 160 HV after aging for 500 hours at 500 ° C and has a maximum grain size according to ASTM E112 of 0.5 mm. Copper alloy according to one of claims 1 to 8, which in the hardened Condition a tensile strength of 700 to 900 MPa, a Vickers hardness of 230 up to 280 HV, an electrical conductivity of 45 to 60% IACS, a Warm tensile strength at 500 ° C of at least 450 MPa and a minimum hardness of 160 HV after aging for 500 hours at 500 ° C. Copper alloy according to any one of claims 1 to 9, which is an ASTM E112 determined grain size between 30 and 90 microns.