Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C9/00—Alloys based on copper
  • C22C9/04—Alloys based on copper with zinc as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/08—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of copper or alloys based thereon

Definitions

• the present invention generally relates to a copper alloy and a method for producing the same. More specifically, the invention relates to a copper alloy having an excellent corrosion cracking resistance and an excellent dezincing resistance, in addition to characteristics of conventional brasses having an excellent machinability or cutting workability and an excellent recyclability, and a method for producing the same.
• Japanese Patent Laid-Open No. 10-183275 discloses that tin (Sn) is added to a copper-zinc alloy to be extruded to control the concentration of Sn in a gamma phase through various heat treatments to improve the dezincing resistance of the alloy.
• Japanese Patent Laid-Open No. 6-108184 proposes that Sn is added to a copper-zinc alloy to be extruded to form a single alpha phase to enhance the dezincing corrosion resistance of the alloy. That is, the above described alloys are characterized in that a larger amount of Sn than that in conventional brasses is added.
• Japanese Patent Laid-Open No. 2001-294956 proposes that very small amounts of phosphorus (P) and tin (Sn) are added to a copper-zinc alloy to be extruded and reduced to be heat-treated to form a structure wherein a beta phase is separated by an alpha phase, to improve the dezincing resistance of the alloy.
• the method for adding the very small amounts of Sn and P to carry out heat treatments can be inexpensively carried out to improve the dezincing resistance due to the small amount of additives.
• this method can not improve the stress corrosion cracking resistance of the alloy.
• a copper alloy comprises 58 to 66 wt% of copper, 0.1 to 0.8 wt% of tin, 0.01 to 0.5 wt% of silicon, and the balance being zinc and unavoidable impurities, wherein a proportion of an alpha phase is 80 vol% or more.
• the copper alloy may further contain at least one of 0.3 to 3.5 wt% of lead and 0.3 to 3.0 wt% of bismuth.
• the copper alloy may further contain at least one of 0.02 to 0.15 wt% of phosphorus, 0.02 to 3.0 wt% of nickel, and 0.02 to 0.6 wt% of iron, the total amount thereof being in the range of from 0.02 to 3.0 wt%.
• a method for producing a copper alloy comprising the steps of: preparing raw materials of a copper alloy comprising 58 to 66 wt% of copper, 0.1 to 0.8 wt% of tin, 0.01 to 0.5 wt% of silicon, and the balance being zinc and unavoidable impurities; casting the raw materials to form an ingot; hot working the ingot; cold or hot working the hot worked ingot; annealing the cold or hot worked ingot at a temperature of 300 to 600 °C for two minutes to five hours; and cooling the annealed ingot at a cooling rate of 0.2 to 10 °C/sec.
• the raw materials may further contain at least one of 0.3 to 3.5 wt% of lead and 0.3 to 3.0 wt% of bismuth.
• the raw materials may further contain at least one of 0.02 to 0.15 wt% of phosphorus, 0.02 to 3.0 wt% of nickel, and 0.02 to 0.6 wt% of iron, the total amount thereof being in the range of from 0.02 to 3.0 wt%.
• a copper alloy having an excellent corrosion cracking resistance and an excellent dezincing resistance consists of 58 to 66 wt% of copper (Cu), 0.1 to 0.8 wt% of Sn, 0.01 to 0.5 wt% of Si, an appropriate amount of at least one of Pb, Bi, P, Ni and Fe if necessary, and the balance being zinc (Zn) and unavoidable impurities, wherein the proportion of an alpha phase is 80 vol% or more.
• the amount of Cu is less than 58 wt%, a beta phase increases, so that it is not possible to improve the dezincing resistance of the alloy even if a heat treatment is subsequently carried out.
• the amount of Cu exceeds 66 wt%, a beta phase does not sufficiently deposit even in a high temperature range, so that the hot workability of the alloy deteriorates. Therefore, the amount of Cu is preferably in the range of from 58 to 66 wt%, more preferably in the range of from 60 to 62 wt%.
• Tin (Sn) has the function of improving the dezincing resistance of an alpha phase and a beta phase. If the amount of Sn is less than 0.1 wt%, it is not possible to obtain a satisfied dezincing resistance. If the amount of Sn exceeds 0.8 wt%, a hard, friable gamma phase is easy to deposit, so that the extension of mechanical characteristics deteriorates. Therefore, the amount of Sn is preferably in the range of from 0.1 to 0.8 wt%, more preferably in the range of from 0.3 to 0.5 wt%.
• Silicon (Si) remarkably has the functions of improving the dezincing resistance of a beta phase and of improving the stress corrosion cracking resistance of the whole alloy if a predetermined proportion of Si is solid-dissolved in beta and alpha phases. If the amount of Si is less than 0.01 wt%, these functions can not be obtained. Since the zinc equivalent of Si is a high value of 10, if the amount of Si to be added exceeds 0.5 wt%, the proportion of a beta phase increases, and the extension of mechanical characteristics deteriorates. Therefore, the amount of Si is preferably in the range of 0.01 to 0.5 wt%, more preferably in the range of 0.1 to 0.2 wt%.
• a third element such as Sn, Si or Ni
• a third element such as Sn, Si or Ni
• it is often solid-dissolved in alpha and beta phases without forming a specific phase.
• the amount of Zn increases or decreases is produced in the copper-zinc alloy, so that the alloy has properties corresponding thereto.
• Guillet has proposed amethod for expressing this relationship by using the zinc equivalent of an additional element.
• the proportion of an alpha phase is 80 vol% or more, advantageous effects will be described below.
• the beta phase is inferior to the alpha phase with respect to both of stress corrosion cracking resistance and dezincing resistance.
• the zinc equivalents of Sn and Si are 2 and 10, respectively, and the solid solutions of Sn and Si are preferentially formed in a beta phase. If the amount of these elements to be added increases, the proportion of the beta phase increases, and the hardness of the whole material increases to decrease the elongation thereof.
• the proportion of the alpha phase is set to be 80 vol% or more, the residual beta phase can be reinforcedby adding a very small amount of elements without damaging the elongation of the whole material, and the stress corrosion cracking resistance of the alpha phase can be improved by the solid solution of Si. Therefore, the proportion of the alpha phase is preferably 80 vol% or more, and more preferably 90 vol% or more.
• a copper alloy having an excellent stress corrosion cracking resistance and dezincing resistance preferably contains at least one of 0.3 to 3.5 wt% of Pb and 0.3 to 3.0 wt% of Bi.
• Pb and Bi serve to improve the machinability or cutting workability of brasses, respectively. If the amount of Pb is 0.3 wt% or more, it is possible to obtain a good free-cutting workability. However, if the amount of Pb exceeds 3.5 wt%, the mechanical properties of brasses deteriorate to tend to cause embrittlement. Therefore, the amount of Pb is preferably in the range of from 0.3 to 3.5 wt%. In addition, since the material cost of Pb is low, the amount of Pb is more preferably in the range of 2.5 to 3.5 wt%.
• the amount of Bi is in the range of from 0.3 to 3.0 wt%, preferably in the range of from 1.4 to 2.5 wt%, it is possible to obtain a good free-cutting workability. Since Pb is harmful to the human body although Bi is more expensive than Pb, Bi can be substituted for Pb.
• a copper alloy having an excellent stress corrosion cracking resistance and dezincing resistance preferably contains at least one of 0.02 to 0.15 wt% of P, 0.02 to 3.0 wt% of Ni, and 0.02 to 0.6 wt% of Fe, the total amount of these elements being in the range of from 0.02 to 3.0 wt%.
• Nickel (Ni) has the function of decreasing the size of crystal grains, and also has the function of increasing the proportion of the alpha phase since the zinc equivalent of Ni is negative. If the amount of Ni is less than 0.02 wt%, it is not sufficiently obtain these functions. On the other hand, if the amount of Ni exceeds 3.0 wt%, there are problems on mechanical characteristics and adding costs. Therefore, the amount of Ni is preferably in the range of 0.02 to 3.0 wt%, and more preferably in the range of 0.1 to 0.4 wt%.
• Phosphorus (P) has the function of improving the dezincing resistance of the alpha phase without damaging mechanical characteristics. However, if the amount of P is less than 0 .02 wt%, it is not possible to obtain such a function, and if the amount of P exceeds 0.15 wt%, intergranular segregation is caused to deteriorate the ductility and stress corrosion cracking resistance of the alloy. Therefore, the amount of P to be added is preferably in the range of from 0.02 to 0.15 wt%.
• Iron has the functions of inhibiting the size of the alpha phase from being increased and of stabilizing mechanical characteristics. Since most of scrap materials include Fe, costs increase if the amount of Fe is less than 0.02 wt%, and the elongation of the alloy deteriorates if the amount of Fe exceeds 0.6 wt%. Therefore, the amount of Fe to be added is preferably in the range of from 0.02 to 0.6 wt%.
• the total amount of Ni, Fe and P is preferably in the range of from 0.02 to 3.0 wt%, and more preferably in the range of from 0.05 to 0.5 wt%.
• the mixture is cast to form an ingot, it is extruded in a temperature range of from 600 to 850 °C.
• a temperature range of from 600 to 850 °C By the mixing, it is possible to obtain an alpha-plus-beta phase structure having a good hot workability in a high temperature region.
• the bar After the hot forging or cold reduction of a bar thus obtained is carried out, the bar is heat-treated at a temperature of 300 to 600 °C for two minutes to five hours, and then cooled at a cooling rate of 0.2 to 10 °C/sec to control the structure.
• the beta phase portion after extruding is changed to an alpha or gamma phase except for a part of the beta phase portion.
• the concentration of additives in the residual beta phase increases, and the solid solution of Si is formed in the alpha phase, so that the stress corrosion cracking resistance and dezincing resistance of the bar are improved.
• the heat treatment temperature is lower than 300 °C , phase transformation is not sufficiently carried out.
• the heat treatment temperature is higher than 600 °C, the beta phase is stable, so that no alpha-plus-gamma phase is deposited. Therefore, the heat treatment temperature is preferably in the range of from 300 to 600 °C.
• the cooling rate is higher than 10 °C/sec, there is the possibility that distortion may be caused by cooling.
• the cooling rate is lower than 0.2 °C /sec, there are some cases where the size of crystal grains increases to have an influence on dezincing resistance. Therefore, the cooling temperature is preferably in the range of from 0.2 to 10 °C/sec.
• Raw materials of components in each of Examples 1 through 20 shown in Table 1 were mixed to be melted in an induction furnace to be semi-continuously cast to form a bar having a diameter of 80 mm. Then, the bar was hot-extruded so as to have a diameter of 30 mm, and cold-drawn so as to have a diameter of 29.5 mm. Thereafter, in each example, the bar was heat-treated on heat treatment conditions shown in Table 2, and the cooling rate was in the range of from 0.2 to 10 °C/sec.
• the proportion of the alpha phase was obtained by the point calculating method on a microphotograph of a cross section (see "Handbook of Metals” (edited by Japan Society for Metals, the revised fifth edition, Maruzen), p 289). Furthermore, 23 x 30 points were measured at intervals of 10 ⁇ m in a lattice.
• the dezincing resistance was evaluated on the basis of ISO 6509 by observing the depth of dezincing resistance after the sample was dipped in a solution containing 12.7 g/L of CuCl 2 ⁇ 2H 2 O at a temperature of 75 ⁇ 3 °C for 24 hours. The sample was tested so that the direction of extruding was coincident with the direction of dezincing corrosion. After the region of 10 mm x 10 mm was measured, the dezincing resistance was evaluated as "good” when the maximum dezincing depth was 100 ⁇ m or less, and the dezincing resistance was evaluated as "not bad” when the maximum dezincing depth exceeds 100 ⁇ m.
• each of the samples before cold drawing was cut into pieces having a thickness of 1.5 mm to be hot-rolled so as to have a thickness of about 0.5 mm, and the surface thereof was cold-rolled by about 0.03 mm. Thereafter, a heat treatment was carried out, so that a sample having a thickness of 0. 5 mm, a width of 10 mm and a length of 140 mm was prepared. Then, a stress being 50 % of the proof stress was applied to each of the samples by the two-point load method based on JIS H8711, and each of the samples was held in a desiccator including 14 % NH 3 . In this state, the time required to cause corrosion cracking was measured. The stress corrosion cracking resistance was evaluated by "bad" when cracks were produced within 5 hours, "not bad” when cracks are produced in 5 to 15 hours, and "good” when no cracks are produced after 15 hours or more.
• Table 2 shows the proportions of the alpha phase and the results of dezincing tests and stress corrosion cracking tests in Examples 1 through 20. As can be seen from this table, in all examples, the proportions of the alpha phase were 80 vol% or more, and the stress corrosion cracking resistance and dezincing resistance were good.

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• 2003
  • 2003-08-18 AT AT03018581T patent/ATE353981T1/de not_active IP Right Cessation
  • 2003-08-18 DE DE60311803T patent/DE60311803T2/de not_active Expired - Lifetime
  • 2003-08-18 EP EP03018581A patent/EP1508625B1/fr not_active Expired - Lifetime

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