Copper-base alloys having resistance to dezincification

Abstract

Copper-base alloys are provided that maintain high hot forgeability and cuttability and low-cost feature and which still are improved in resistance to dezincification. The alloys comprise 57-69% of Cu, 0.3-3% of Sn and 0.02-1.5% of Si, all percentages based on weight, with a Si/Sn value in the range of 0.05-1, and the balance being Zn and incidental impurities.

Description

BACKGROUND OF THE INVENTION

[0001] This invention relates to copper-base alloys having high resistance to dezincification corrosion which would otherwise occur during use in corrosive aqueous solutions. The alloys also have good hot working and cutting properties.

[0002] Cu—Zn alloys, commonly called brasses, have good working properties, both cold and hot, so they have found extensive use from old times. Among the best known are forging brass bars (JIS C 3771), free-cutting brass bars (JIS C 3604) and high-strength brass bars (JIS C 6782). These copper-base alloys share the common feature of including a continuous &bgr; phase for better workability.

[0003] Zinc in the &bgr; phase has high ionization tendency, so in natural environment, particularly in the presence of a corrosive aqueous solution, it is selectively leached from the above-mentioned alloys. This is why those alloys are very poor in resistance to dezincification.

[0004] Various proposals have recently been made with a view to improving the resistance to dezincification of brasses that are typically used in parts that are brought into contact with water. According to Unexamined Japanese Patent Application (JPA) No. 183275/1998, Sn is added to Cu—Zn alloys and, after hot extruding, various heat treatments are performed to control the proportion of the &ggr; phase and the Sn level in the &ggr; phase, thereby improving resistance to dezincification.

[0005] According to Unexamined Published Japanese Patent Application (JPA) No. 108184/1994, Sn is added to Cu—Zn alloys and, after hot extruding, the alloys are subjected to a heat treatment so that they are solely composed of the &agr; phase, thereby enhancing their resistance to dezincification.

[0006] The new alloys described above are characterized by having Sn added in larger amounts than the conventional brasses. However, the high inclusion of Sn in brasses has its own problems.

[0007] First, with the increase in the Sn level, the local solidification time of brasses increases and there occurs inverse segregation of Sn during casting, producing ingots with surface defects. At the same time, the adaptability to extrusion and other hot working processes is impaired, causing a significant drop in the yield of shaped products.

[0008] Secondly, in order to elicit the ability of Sn to improve resistance to dezincification, hot extruding must be followed by a heat treatment for generating a certain area of &ggr; phase at grain boundaries of the &agr; phase and causing Sn to diffuse uniformly in the &ggr; phase. However, this adds to the overall production cost.

[0009] What is specifically taught in JPA No. 183275/1998 is as follows: a heat treatment is applied at between 500° C. (inclusive) and 550° C. (inclusive) for at least 30 seconds, then cooling to 350° C. is done at a rate no faster than 0.4° C./sec; alternatively, a heat treatment is applied at between 400° C. (inclusive) and 500° C. (inclusive) for at least 30 seconds, then cooling is done; or a heat treatment is applied at between 500° C. (inclusive) and 550° C. (inclusive) for at least 30 seconds, then cooling to 350° C. is done at a rate between 0.4° C./sec (inclusive) and 4° C./sec (inclusive). The teaching of JPA No. 108184/1994 comprises hot extruding or drawing the alloy, followed by a heat treatment at 500-600° C. for a period of 30 minutes to 3 hours.

[0010] These heat treatments involve various problems. For one thing, in order to ensure the appropriate conditions, costly equipment must be used. Secondly, depending on product size, the difference in heat pattern between the interior and exterior of the product can cause variations in microstructure, which makes the process less cost-effective due to lower yield. Thirdly, products of complex shape occasionally suffer from the problems of dimensional changes, residual stress and so forth.

[0011] A recent proposal worth particular mention is free-cutting copper alloys having Si added to Cu—Zn alloys (JPA Nos. 119774/2000 and 119775/2000). These alloys contain at least 1.8 wt % of Si with a large portion of Cu/Si &ggr; phase at grain boundaries of the &agr; phase. Under environment of actual use, the Cu/Si &ggr; phase has better resistance to dezincification than the &bgr; phase but is not as resistant as a Cu/Sn &ggr; phase. If the Si content is 1.8% or more, the thermal conductivity of the material drops considerably and the blade of a cutting tool becomes unduly hot during cutting to cause many problems such as a shorter life of the cutting tool, lower precision in cutting and limit on the cutting speed.

SUMMARY OF THE INVENTION

[0012] The present invention has been accomplished under these circumstances and has as an object providing copper-base alloys that have outstanding resistance to dezincification, hot forgeability and cuttability and which still can be fabricated at reasonably low cost.

[0013] The present inventors conducted intensive studies in order to ensure that the addition of Sn would prove effective in preventing dezincification of copper-base alloys to the fullest extent and found the following: when Si as well as Sn were added and the ratio of Si to Sn was adjusted to lie in an appropriate range, secondary dendrite arms grew sufficiently thinner and longer during solidification to suppress segregation of Sn; upon hot working, the &ggr; phase was dispersed uniformly between regions of &agr; phase. This phenomenon made a great contribution to improvements in resistance to dezincification and hot working properties.

DETAILED DESCRIPTION OF THE INVENTION

[0014] The stated object can be attained by any one of the following copper-base alloys having improved resistance to dezincification.

[0015] (1) A dezincification resistant copper-base alloy comprising 57-69% of Cu, 0.3-3% of Sn and 0.02-1.5% of Si, all percentages based on weight, with a Si/Sn value in the range of 0.05-1, and the balance being Zn and incidental impurities.

[0016] (2) A dezincification resistant copper-base alloy comprising 57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of Pb, all percentages based on weight, with a Si/Sn value in the range of 0.05-1, and the balance being Zn and incidental impurities.

[0017] (3) A dezincification resistant copper-base alloy comprising 57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of Pb, with a Si/Sn value in the range of 0.05-1, further containing in a total amount of 0.02-0.2% at least one element selected from the group consisting of 0.02-0.2% of P, 0.02-0.2% of Sb and 0.02-0.2% of As, all percentages based on weight, and the balance being Zn and incidental impurities.

[0018] (4) A dezincification resistant copper-base alloy comprising 57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of Pb, with a Si/Sn value in the range of 0.05-1, further containing in a total amount of 0.01-3% of at least one element selected from the group consisting of 0.01-2% of Fe, 0.01-2% of Ni, 0.01-2% of Mn, 0.01-2% of Al, 0.01-2% of Cr, 0.01-3% of Bi, 0.01-2% of Be, 0.01-2% of Zr, 0.01-3% of Ce, 0.01-2% of Ag, 0.01-2% of Ti, 0.01-2% of Mg, 0.01-2% of Co, 0.01-1% of Te, 0.01-2% of Au, 0.01-2% of Y, 0.01-2% of La, 0.01-2% of Cd and 0.01-1% of Ca, all percentages based on weight, and the balance being Zn and incidental impurities.

[0019] (5) A dezincification resistant copper-base alloy comprising 57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of Pb, with a Si/Sn value in the range of 0.05-1, further containing in a total amount of 0.02-0.2% at least one element selected from the group consisting of 0.02-0.2% of P, 0.02-0.2% of Sb and 0.02-0.2% of As, still further containing in a total amount of 0.01-3% of at least one element selected from the group consisting of 0.01-2% of Fe, 0.01-2% of Ni, 0.01-2% of Mn, 0.01-2% of Al, 0.01-2% of Cr, 0.01-3% of Bi, 0.01-2% of Be, 0.01-2% of Zr, 0.01-3% of Ce, 0.01-2% of Ag, 0.01-2% of Ti, 0.01-2% of Mg, 0.01-2% of Co, 0.01-1% of Te, 0.01-2% of Au, 0.01-2% of Y, 0.01-2% of La, 0.01-2% of Cd and 0.01-1% of Ca, all percentages based on weight, and the balance being Zn and incidental impurities.

[0020] On the following pages, the criticality of the compositional ranges for the ingredients in the copper-base alloy of the invention is described in detail.

[0021] Cu:

[0022] An increase in the Cu content adds to the &agr; phase and improves corrosion resistance but if its content exceeds 69%, there occurs a marked drop in hot forgeability. Since Cu is more expensive than Zn, the Cu content is desirably minimized from an economical viewpoint. If the Cu content is smaller than 57%, the proportion of the &bgr; phase increases to improve forgeability at elevated temperature; on the other hand, resistance to dezincification decreases and so do the strength and elongation of the material. Considering these merits and demerits, the compositional range of Cu is specified to lie between 57 and 69%, preferably between 59 and 63%, on a weight basis.

[0023] Sn:

[0024] Adding at least 0.3% of Sn is effective in improving resistance to dezincification. What is more, the improvement in resistance to dezincification is marked if the addition of Sn is increased. However, adding Sn in excess of 3% not only induces deep defects in the surface of ingots being cast but also fails to bring out a corresponding improvement in the resistance to dezincification. In addition, Sn is more expensive than Zn and Cu, so it is a factor in increasing the production cost. For these reasons, the content of Sn in the copper-base alloy of the invention is specified to lie between 0.3 and 3%, preferably between 0.5 and 2%.

[0025] Si:

[0026] Silicon is added for the particular purpose of improving castability and eliciting the ability of Sn to improve resistance to dezincification. Adding a suitable amount of Si is effective in improving the fluidity of a melt during casting and suppressing the segregation of Sn. As a result, in the absence of any heat treatment after hot extruding and forging, the ability of Sn to improve resistance to dezincification is elicited to the fullest extent, thereby providing consistent and outstanding dezincification resistance and mechanical characteristics.

[0027] If the Si content exceeds 1.5%, an increased amount of Si/Cu &ggr;, &kgr; or &bgr; phase appears at grain boundaries of the &agr; phase to deteriorate the resistance to dezincification. In addition, the increased amount of Si oxide is detrimental to castability and hot workability. If the Si content further increases to 1.8% or more, the thermal conductivity of the material drops considerably and the blade of a cutting tool becomes unduly hot during cutting to cause many problems such as a shorter life of the cutting tool, lower precision in cutting and limit on the cutting speed.

[0028] If the Si content is less than 0.02%, there is obtained no effect of improving castability or suppressing the segregation of Sn. For these reasons, the compositional range of Si is specified to lie between 0.02 and 1.5%, preferably between 0.06 and 0.6%.

[0029] Si/Sn:

[0030] The Si/Sn value is specified in the present invention since in order to maximize the ability of Sn to improve resistance to dezincification, Si must be added in an optimum amount that depends on the amount of Sn addition. If the Si/Sn value is controlled at an appropriate level, secondary dendrite arms grow in a sufficiently finer and longer form during solidification to suppress the segregation of Sn and, after hot working, the &ggr; phase is dispersed uniformly between regions of &agr; phase to improve resistance to dezincification while assuring hot deformability. If the Si/Sn value is greater than 1, the Si content is excessive. Due to the high zinc equivalent of Si, there occurs increased precipitation of the &bgr; phase and the &bgr; phase surrounding the &agr; phase cannot be fragmented by the &ggr; phase, which results in impaired resistance to dezincification. If the Si/Sn value is smaller than 0.05, the intended effect of suppressing the segregation of Sn is not attained and in order to elicit the effect of improving resistance to dezincification, a heat treatment must be performed after hot working. Therefore, the Si/Sn value is preferably in the range of 0.05-1, more preferably in the range of 0.1-0.5.

[0031] P, Sb, As:

[0032] These elements are effective in suppressing dezincification without impairing cuttability and forgeability. If their addition is less than 0.02%, the intended effect of suppressing dezincification is not obtained. If their addition exceeds 0.2%, boundary segregation occurs to reduce ductility while increasing stress corrosion cracking sensitivity. Hence, the contents of P, Sb and As are each specified to lie between 0.02 and 0.2%.

[0033] Pb:

[0034] Lead is added to improve the cuttability of the material. If its addition is less than 0.5%, the desired cuttability is not attained. If the Pb addition exceeds 3%, hot working such as extruding or forging is difficult to perform. If Pb is to be added, its compositional range is between 0.5 and 3%, preferably between 1.5 and 2.3%.

[0035] If desired, the copper-base alloy of the invention may further contain at least one element selected from the group consisting of 0.01-2% of Fe, 0.01-2% of Ni, 0.01-2% of Mn, 0.01-2% of Al, 0.01-2% of Cr, 0.01-3% of Bi, 0.01-2% of Be, 0.01-2% of Zr, 0.01-3% of Ce, 0.01-2% of Ag, 0.01-2% of Ti, 0.01-2% of Mg, 0.01-2% of Co, 0.01-1% of Te, 0.01-2% of Au, 0.01-2% of Y, 0.01-2% of La, 0.01-2% of Cd and 0.01-1% of Ca; these elements may be contained in a total amount of 0.01-3%. If added in amounts within the specified ranges, these elements are effective in improving mechanical characteristics and cuttability without damaging resistance to dezincification and hot workability.

[0036] The copper-base alloy of the invention with its composition adjusted to the ranges set forth above has outstanding resistance to dezincification, hot forgeability and cuttability and still can be fabricated at reasonably low cost.

[0037] The mode for carrying out the present invention is described below with reference to examples.

EXAMPLES

[0038] Samples of the dezincification resistant copper-base alloy of the invention were prepared as described below. Comparative samples were also prepared. The chemical ingredients listed in Table 1 were melted in an induction furnace and cast semicontinuously into billets (80 mm&phgr;) at temperatures of the liquidus plus about 100° C. The castability of each composition was evaluated by checking the depth of surface defects such as inclusions in the cast billets. The results are shown in Table 1 as evaluated by the following criteria: ⊚ (depth of surface defect<1 mm); ∘ (1-3 mm); × (>3 mm). 1 TABLE 1 Sample Chemical ingredients (wt %) No. Cu Zn Sn Si Si/Sn Pb P Fe Ni Invention 1 61.3 bal. 1.50 0.71 0.473 1.7 — — — 2 59.5 bal. 1.38 0.65 0.471 1.8 — — — 3 60.2 bal. 1.40 0.63 0.450 1.9 0.07 — — 4 58.5 bal. 2.50 0.24 0.096 2.0 — — — 5 60.7 bal. 1.08 0.20 0.185 2.0 0.04 0.11 — 6 61.2 bal. 0.87 0.21 0.241 1.9 0.05 0.13 0.17 7 61.8 bal. 1.00 0.12 0.120 1.7 0.05 0.10 0.30 8 61.2 bal. 1.50 0.18 0.120 1.6 0.07 0.17 — 9 59.0 bal. 1.50 0.36 0.240 1.4 0.08 0.23 0.60 10 62.2 bal. 1.24 0.70 0.565 1.8 0.06 0.12 0.06 11 62.0 bal. 1.24 0.60 0.484 0.8 — — — 12 61.8 bal. 1.16 0.30 0.259 1.5 — — — 13 60.8 bal. 0.80 0.20 0.250 1.8 0.05 0.10 0.06 14 63.0 bal. 1.80 0.80 0.444 1.5 0.05 — — Comparison 15 62.0 bal. 1.50 — — 1.9 — — — 16 60.6 bal. 0.46 1.00 2.174 2.0 0.05 — — 17 59.0 bal. 0.20 0.01 0.050 — 0.04 — — 18 58.0 bal. — 2.5 — 1.9 — — — 19 61.0 bal. — 3 — — — — — 20 59.0 bal. 1.5 1.9 1.267 — — — —

[0039] The 80-mm&phgr; billets were held at 800° C. for 30 minutes and later hot extruded into bars having a diameter of 30 mm.

[0040] The as-extruded bars were evaluated for resistance to dezincification, resistance to hot deformation, hardness, tensile strength and elongation. The dezincification test was conducted by two methods under different conditions, one specified in JBMA T303-1988 and the other in ISO 6509-1981. Test samples as cut from the extruded bars were set so that the direction of corrosion coincided with the extruding direction. In order to investigate the extent of the change in resistance to dezincification that was caused by heat treatment, evaluation was also made for the resistance to dezincification of samples that were subjected to a heat treatment at 400° C. for 3 hours.

[0041] To measure the resistance to hot deformation, cylindrical samples 15 mm in both diameter and height were cut on a lathe from the extruded bars and subjected to a drop-hammer test. The test temperature and the distortion rate were 750° C. and 180 S−1, respectively.

[0042] The cutting test was performed by cutting on a lathe and chip fragmentation was evaluated by the following criteria: ∘ (all chips were completely fragmented); × (chips were not fragmented). For sticking property, 10 cutting tests were conducted with a continuous feed of 100 mm and the results were evaluated by the following criteria: × (copper stuck to the tip of the blade); ∘ (no copper stuck). The cutting conditions were as follows: rotating speed, 950 rpm; depth of cut, 0.5 mm; feed speed, 0.06 mm/rev.; feed, 100 mm; cutting oil, none; cutting tool material, superhard steel. The hardness of the copper-base alloy was Vickers hardness and measured according to JIS Z 2244 under a testing force of 49 N on a section perpendicular to the extruding direction. The tensile test was conducted in accordance with JIS Z 2241 on No. 4 specimens which were stretched in a direction parallel to the extruding direction. The results of the tests are shown in Table 2. 2 Maximum depth of Maximum depth of Resistance Cuttability Tensile dezincification by JBMA dezincification Sample to hot sticking to Chip Hardness strength Elongation after heat by ISO (&mgr;m) No. Castability deformation the blade tip fragmentation Hv MPa % as-extruded treatment as-extruded Invention 1 ⊚ 78 ∘ ∘ 130 451 27 59 59 115 2 ⊚ 67 ∘ ∘ 132 445 28 65 64 130 3 ⊚ 67 ∘ ∘ 129 433 34 60 60 125 4 ∘ 72 ∘ ∘ 141 452 25 41 39 80 5 ⊚ 75 ∘ ∘ 107 407 45 57 55 115 6 ⊚ 76 ∘ ∘ 105 399 46 59 58 115 7 ⊚ 74 ∘ ∘ 110 445 45 57 56 110 8 ⊚ 73 ∘ ∘ 118 418 44 53 51 95 9 ⊚ 68 ∘ ∘ 133 467 44 52 52 95 10 ⊚ 68 ∘ ∘ 137 475 25 45 42 75 11 ⊚ 69 ∘ ∘ 135 437 28 52 50 85 12 ⊚ 71 ∘ ∘ 124 415 33 55 53 95 13 ⊚ 77 ∘ ∘ 102 398 40 58 58 105 14 ⊚ 73 ∘ ∘ 121 416 32 21 19 65 Comparison 15 X 79 ∘ ∘ 119 412 36 92 71 135 16 ⊚ 67 ∘ ∘ 132 423 25 115 116 450 17 ⊚ 85 ∘ X  98 387 48 173 167 835 18 X 75 X ∘ 140 440 21 134 135 745 19 X 73 X X 146 453 19 165 171 585 20 X 65 X X 165 527 26 155 157 95

[0043] Sample Nos. 1-14 prepared in accordance with the alloy composition of the invention showed outstanding castability, mechanical characteristics and cuttability, as well as low resistance to hot deformation comparable to that of hot forging alloy C 3771 (deformation resistance, 70 MPa). They all had high resistance to dezincification since the maximum depth of dezincification was no more than 65 &mgr;m in JBMA T303-1988 and no more than 130 &mgr;m in ISO 6509-1981.

[0044] What was particularly interesting about the samples of the invention was that the maximum depth of dezincification as measured by JBMA was little different between the as-extruded state and the heat-treated state. It was therefore clear that by adding suitable amounts of Si, the copper-base alloys were given consistent and outstanding resistance to dezincification even when they were just subjected to hot working without any subsequent special heat treatments.

[0045] Sample Nos. 15-20 were comparisons and had various defects. Sample No. 15 did not contain Si, so it was not only low in castability and resistance to dezincification but also characterized by considerable difference in the maximum depth of dezincification between the as-extruded state and the heat-treated state. Sample No. 16 had a Si/Sn value beyond the range specified by the invention, so an excessive &bgr; phase surrounded the &agr; phase, deteriorating the resistance to dezincification.

[0046] Sample No. 17 contained less Sn and Si than the lower limits specified by the invention, so the proportions of the &ggr; and &kgr; phases were insufficient to prevent marked drop in resistance to dezincification; what is more, the resistance to hot deformation was great and chips could not be fragmented. Sample Nos. 18 and 19 did not contain Sn, so they were poor in resistance to dezincification; in addition, they contained more Si than specified by the invention, so copper stuck to the tip of the cutting blade showing how poor the cuttability of the material was.

[0047] Sample No. 20 contained both Sn and Si but the Si/Sn value exceeded the range specified by the invention; what is more, the Si content was greater than 1.8%. Hence, the sample was poor in resistance to dezincification and castability and copper stuck to the tip of the cutting blade.

[0048] As described above, the present invention offers copper-base alloys that have outstanding resistance to dezincification, hot forgeability and cuttability and which still can be fabricated at reasonably low cost.

Claims

1. A dezincification resistant copper-base alloy comprising 57-69% of Cu, 0.3-3% of Sn and 0.02-1.5% of Si, all percentages based on weight, with a Si/Sn value in the range of 0.05-1, and the balance being Zn and incidental impurities.

2. A dezincification resistant copper-base alloy comprising 57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of Pb, all percentages based on weight, with a Si/Sn value in the range of 0.05-1, and the balance being Zn and incidental impurities.

3. A dezincification resistant copper-base alloy comprising 57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of Pb, with a Si/Sn value in the range of 0.05-1, further containing in a total amount of 0.02-0.2% at least one element selected from the group consisting of 0.02-0.2% of P, 0.02-0.2% of Sb and 0.02-0.2% of As, all percentages based on weight, and the balance being Zn and incidental impurities.

4. A dezincification resistant copper-base alloy comprising 57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of Pb, with a Si/Sn value in the range of 0.05-1, further containing in a total amount of 0.01-3% of at least one element selected from the group consisting of 0.01-2% of Fe, 0.01-2% of Ni, 0.01-2% of Mn, 0.01-2% of Al, 0.01-2% of Cr, 0.01-3% of Bi, 0.01-2% of Be, 0.01-2% of Zr, 0.01-3% of Ce, 0.01-2% of Ag, 0.01-2% of Ti, 0.01-2% of Mg, 0.01-2% of Co, 0.01-1% of Te, 0.01-2% of Au, 0.01-2% of Y, 0.01-2% of La, 0.01-2% of Cd and 0.01-1% of Ca, all percentages based on weight, and the balance being Zn and incidental impurities.

5. A dezincification resistant copper-base alloy comprising 57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of Pb, with a Si/Sn value in the range of 0.05-1, further containing in a total amount of 0.02-0.2% at least one element selected from the group consisting of 0.02-0.2% of P, 0.02-0.2% of Sb and 0.02-0.2% of As, still further containing in a total amount of 0.01-3% of at least one element selected from the group consisting of 0.01-2% of Fe, 0.01-2% of Ni, 0.01-2% of Mn, 0.01-2% of Al, 0.01-2% of Cr, 0.01-3% of Bi, 0.01-2% of Be, 0.01-2% of Zr, 0.01-3% of Ce, 0.01-2% of Ag, 0.01-2% of Ti, 0.01-2% of Mg, 0.01-2% of Co, 0.01-1% of Te, 0.01-2% of Au, 0.01-2% of Y, 0.01-2% of La, 0.01-2% of Cd and 0.01-1% of Ca, all percentages based on weight, and the balance being Zn and incidental impurities.