Use of a hardenable copper alloy for molds

Abstract

The invention relates to use of a hardenable copper alloy containing 0.1% to 0.5% beryllium and 0.5% to 2% nickel for the production of broad side plates for thin slab continuous casting molds at casting speeds of at least 2 to 6 m/min and higher.

Description

[0001] The invention relates to the use of a hardenable copper alloy for molds, in particular, for production of broad side plates for thin slab continuous casting molds.

[0002] At the present state of the art, the mold broad plates for thin slab plants and, in particular, for CSP (Compact Strip Production) plants are produced from copper alloys such as CuCrZr (copper-chromium-zirconium) or CuAg (copper-argentum). At that, the CuAg alloy for CSP-mold plates proved to be advantageous because of its comparatively high elongation at elevated temperatures.

[0003] However, mold broad plates of CuAg or CuCrZr are not capable to withstand high thermal stresses prevailing in the region of the bath level of the molten metal, and have a tendency to form cracks in the plates in this region, with the CuCrZr having a tendency to a particularly earlier crack formation. This crack formation is a primary failure criterium for the mold broad plates and results in high repair and replacement costs incurable by an operator of a continuous casting plant.

[0004] It should be noted that CuAg, despite its reduced tensile strength, has a reduced crack formation tendency because, as a result of its increased extensibility at high temperatures in the mold plate, it is capable of absorbing stresses and because its comparatively high heat conductance permits to retain smaller mean operational temperature.

[0005] For narrow side plates of thin slab molds, at the present state of the art, usually, CuCrZr with a hardness of about 125 HB is used, with their side contact surfaces being nickel-plated for increasing hardness.

[0006] The primary failure criterium of the narrow side plates, in distinction from the broad side plates, is not the crack formation but rather wear or abrasion of contact surfaces by steel. Contrary to this, the primary failure criterium of the broad side plates is the crack formation in the molten level region.

[0007] German Patent DE 31 20 987 C2 discloses a number of precipitation-hardenable copper alloys and their use for stationary continuous casting molds, among others, different CuNiBe-alloys which contain other alloying components niobium (Nb), zirconium (Zr), magnesium (Mg), and/or titanium (Ti).

[0008] U.S. Pat. No. 2,137,281 discloses a copper alloy CuZrNiBe for a strip mold (twin-belt casting) characterized by a combination of features of a comparatively high heat conductance.

[0009] British Patent No. 954,796 discloses a copper alloy CuBeZrTi for molds which, at a comparatively good heat conductance, has comparatively high strength values.

[0010] For a disturbance-free casting operation, in particular, for thin slabs with high speeds, e.g., of 6 m/min and more, the existing mechanical characteristics of mold materials are not adequate for controlling occurring high temperatures, in particular, in the region of the bath level.

[0011] Proceeding from the above-mentioned state-of-the-art, the object of the invention is to provide suitable copper alloys for producing broad side plates for thin slab continuous casting molds at high speeds, the use of which, during a casting operation, would prevent a premature crack formation, in particular, in the region of the molten level, and the wear of contact surfaces by the fluid steel, and which would withstand, at a lasting service life, extremely high thermal and mechanical loads during a casting operation.

[0012] The object of invention is achieved by use of a hardenable copper alloy with content of beryllium from 0.1% to 0.5%, content of nickel from 0.5% to 2.0% (CuNiBe) for production of broad side plates for slab continuous casting molds.

[0013] Advantageously, this copper alloy, after being hardened, is capable of withstanding high thermal stresses in the bath level region, with reduction in crack formation, while being available over larger operational time periods.

[0014] In addition to this successful operational result, contrary to the known copper alloy such as CuCrZr or CuAg, the inventive copper alloy CuNiBe permits to achieve advantageous material characteristics, e.g., a substantially higher tensile strength of about 770 or about 650N/mm2 and, at a 0.2 proof stress, of about 500N/mm2 both at 20° C. and at 300° C. The material characteristics of three selected, by way of example, copper alloys CuCrZr, CuAg, an CuNiBe are given in the following tables:

Material Characteristics

[0015] 1 MATERIAL CHARACTERISTICS CuAg CuNiBe Approximate CuCrZr Cold- Specially Values Content Hardened Formed Hardened Chemical Composition Chemical % .70 Cr  .09 Ag 1.8 Ni Composition % .10 Zr .006 P .30 Be Physical Characteristics Heat W/mk  340 370 300 Conductance Mechanical Characteristics RT at .2 proof N/mm2 300 265 500  20° Stress Rp .2 Tensile N/mm2 415 3880 770 Strength Rm Elongation A5 % 25 18 15 RT at .2 proof N/mm2 240 195 420 300° Stress Rp. 2 Tensile N/mm2 330 200 650 Strength Rm Elongation A5 % 18 10 8 RT at Hardness HB 125 100  20° C.

[0016] Other positive characteristics, e.g., resistance to mechanical wear follow from the high harness of the inventive material of about 220 HB, because CuNiBe has approximately the same hardness as a galvanically applied nickel layer having approximately 220-230 HB. The broad side plates need not any more be nickel-plated.

[0017] The lower, in comparison with CuAg heat conductance of about 370 W/mk, heat conductance of the copper alloy CuNiBe of about 300 W/mk can be compensated by water-cooling of reduced copper wall thickness by about 25%.

[0018] The inventive copper alloy CuNiBe for production of broad side plates for thin slab continuous casting molds with high casting speeds, e.g., from 2 to 6 m/min contains as alloy components 0.1% to 0.5% beryllium, 0.5% to 2% nickel, and copper up to 99.5% by weight.

[0019] It should contain not more than 0.5% of impurities under which, e.g., traces of other metals such as Fe, Zr, Ag, Cr, Mg., etc. . . . are understood.

[0020] The invention provides for use of not obvious from the state-of-the-art, special copper alloy CuNiBe for broad side plates of continuous casting molds which enables casting of thin slabs with high speeds of at least 2 to 6 m/min and more. The noticeable improvement of operational characteristics due to the extended service life, in particular, a reduced crack formation in bath level region, economical use of material, and low-cost manufacture are results of the particular selection of the alloying components.

Claims

1. Use of a hardenable copper alloy with content of beryllium of 0.1% to 0.5% and content of nickel from 0.5% to 2% for molds, in particular for production of broad side plates for thin slab continuous casting molds.

2. Use of a hardenable copper alloy according to claim 1 for production of broad side plates for thin slab continuous casting molds with casting speeds of at least 2 to 6 m/min.

3. Use of a hardenable copper alloy according to claim 1 or 2 with alloying components of 0.1% to 0.5% beryllium and 0.5% to 2% nickel which, with a copper component amounts to at least 99.5%.

4. Use of a hardenable copper alloy according to one or more of claims 1 through 3 which, except the alloying components of beryllium, nickel and copper, contain maximum 0.5% of impurities.