Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Reexamination Certificate
2000-04-17
2002-10-15
Wyszomierski, George (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
C148S685000, C148S412000, C148S413000, C420S476000, C420S477000
Reexamination Certificate
active
06464810
ABSTRACT:
This application is a U.S. national phase application of International application PCT/JP98/04786 filed Oct. 22, 1998.
TECHNICAL FIELD
This invention relates to a brass material and a method of manufacturing the same, mainly relates to a brass pipe material and a method of manufacturing brass.
BACKGROUND ART
Previously, a brass pipe material generally comprises a single &agr; phase material. This is a result of reducing a &bgr; phase ratio which inhibits cold ductility , providing for cold draw out (drawing) or cold bending fabrication.
However, a brass pipe material of a single &agr; phase does not utilize a &bgr; phase excellent in machinability and polishability so that it has problems of inferior in machinability and polishability.
Also, the conventional brass pipe materials were made crystal grain diameter relatively large similarly to ensure cold ductility so that they have problems of inferior in corrosion resistance and strength.
An object of the present invention is to improve machinability and polishability in a brass material prepared through a cold working, particularly in a brass pipe material.
DISCLOSURE OF THE INVENTION
In the process of a brass material according to the present invention, a brass material excellent in machinability and polishability can be provided by increasing an area ratio of a crystal phase other than an &agr;-phase after extrusion or rolling.
As a suitable embodiment, when a composition comprises an apparent Zn content of 33.5 to 43% by wt., by heating to 550 to 800° C., and when an apparent Zn content is 38.5 to 43% by wt., by heating to a temperature region of 550 to 800° C., or 400 to 500° C., the area ratio of a &bgr; phase can be increased, preferably the area ratio of a &bgr; phase can be made 5% or more.
Here, the term “an apparent Zn content” is used in the meaning of “{(B+t·Q)/(A+B+t·Q)}×100” wherein A is a Cu content [% by wt.], B is a Zn content [% by wt.], t is a Zn equivalent of the third element (e.g., Sn), and Q is a content of the third element [% by wt.].
For preventing decrease of the P phase once increased during cooling, when the temperature region to be heated is 550 to 800° C., it is rapidly cooled at a cooling rate of 5° C./sec or higher until 400° C., and when the temperature region to be heated is 400 to 500° C., it is rapidly cooled at a cooling rate of 1° C./sec or higher until 400° C.
As the other suitable embodiment, when an apparent Zn content is 33.5 to 43% by wt. and Sn content is 0.5 to 2.0% by wt., by heating to a temperature region of 400 to 500° C., an area ratio of a &ggr; phase can be increased, preferably the area ratio of the &ggr; phase can be made 1% or more.
Here, when the temperature region of 400 to 500° C. is maintained for one hour or more, the &ggr; phase becomes spherical so that strength or machinability and polishability are more improved. Also, for preventing decrease of the &ggr; phase once increased during cooling, it is preferably rapidly cooled at a cooling rate of 1° C./sec or higher until 400° C.
Incidentally, when an apparent Zn content is 33.5 to 43% by wt. and Sn content is 0.5 to 1.3% by wt., a cold working is easy since the Sn amount is relatively low, and in the case of the composition where an apparent Zn content is 33.5 to 43% by wt. and Sn content is 1.3 to 2.0% by wt., a &ggr; phase can be easily precipitated since the Sn amount is relatively large.
As the suitable embodiment in the present invention as mentioned above, a cold working such as bending processing or drawing processing of a pipe material can be carried out before a heat treatment step.
In this case, it is preferred that before the cold working, a heat treatment step for making an &agr; phase to increase the area ratio of the &agr; phase whereby cold ductility is previously secured. This heat treatment step for making an &agr; phase is to maintain, for example, at 450 to 550° C. for 10 minutes or longer when an apparent Zn content is 33.5 to 43% by wt. If a crystal grain size is coarsened during the heat treatment step for making an a phase, it can contribute to improve ductility at the time of the cold working.
And according to such a heat treatment step for making an &agr; phase, before the cold working, the area ratio of the &agr; phase can be made 90% or higher, preferably 95% or higher, or elongation in cold can be made 20% or higher, preferably 35% or higher.
Incidentally, after the cold working, an annealing step for controlling an internal stress is usually carried out. The timing of effecting the annealing step may be before or after the heat treatment step.
Also, in the method of production the brass material according to the present invention, by having a crystal grain size fining treatment during the heat treatment or in a step before the heat treatment, surface roughening at a bending processing can be reduced while further improving polishability by making the average crystal grain size of 50 &mgr;m or smaller, preferably 25 &mgr;m or smaller.
Such a crystal grain size fining treatment is desirably carried out after the cold working. That is, before the cold working, the crystal grain size is made relatively larger to ensure cold ductility, but when the crystal grain size is remained in a larger size after the cold working, polishability, corrosion resistance and strength become poor. Thus, by going through the crystal grain size fining treatment after the cold working, the crystal grain size can be certainly made small whereby the polishability, etc. are improved.
As a suitable embodiment, the crystal grain size fining treatment can be carried out by recrystallizing transformation introduced by the cold working under heating. In this case, it is desired to make a transformation density as high as possible at the cold working and a sectional area reduction ratio of 20% or more is preferred.
Also, in order to prevent the crystal grain size coarsen again, it is desired to set an upper limit in a heating time or to rapidly cooled after heating. For example, in a heat treatment heating to 550 to 800° C., coarsening again of the crystal particle size can be prevented by making an upper limit of a heatingmaintaining time within 30 minutes.
As a suitable embodiment of the cold working in the present invention as mentioned above, when the cold working and annealing are carried out repeatedly, it is desired that an area reducing ratio at the final cold working is made large, and a temperature at the final annealing is made lower than the annealing during the procedure. For example, when the annealing temperature during the procedure is 500 to 600° C., the annealing temperature at the final is desirably 500° C. or lower.
Also, as a use of a process for producing a brass material according to the present invention, it is desirably applied to a method for producing a brass pipe material. This is because a pipe material is subjected to cold drawing and bending processing in many cases.
Subsequently, the brass material according to the present invention comprises satisfying at least one of (1) a machining resistance index based on, as the reference, the free-cutting brass bar conforming to JIS (Japanese Industrial Standard) C 3604 is 50 or higher,preferably 80 or higher, (2) through dezinking test conducted in accordance with the technical standard T-303 of JBMA (Japan Brass Makers Association ),corrosion resistance was confirmed as fellows: If the direction of maximum dezinking penetration depth is parallel with the working direction, the maximum dezinking penetration depth is not deeper than 100 &mgr;m, and if the direction of the maximum dezinking penetration depth is rectangular to the working direction, the maximum dezinking penetration depth is not deeper than 70 &mgr;m.
As a suitable embodiment of such a brass material, there is a pipe material, and it can be applied not only to the pipe material prepared by casting and extrusion after casting, but also to the pipe material (seam welded pipe, etc.) prepared by a plate material being subjected
Nakamura Katsuaki
Uchida Toru
Frishauf Holtz Goodman & Chick P.C.
Toto Ltd.
Wyszomierski George
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