Strengthened Alpha Brass and Method for Manufacturing the Same

Abstract

An object of the present invention is to provide a strengthened alpha brass having a good balance between high offset yield strength and formability without deteriorated stress relaxation resistance in comparison with conventional brass and a manufacturing method of the strengthened alpha brass. In order to achieve this object, a strengthened alpha brass having a composition of 63 wt % to 75 wt % copper, incidental impurities and the balance zinc; the strengthened alpha brass which is obtained by using a starting plate material subjected to a re-crystallization annealing to have a grain size from 1-micron meter to 2-micron meter followed by cold rolling in 5% to 40% reduction, then the plate material is low temperature annealed at a temperature equal to or higher than the temperature at which a 0.2% offset yield strength exhibits a maximum value to adjust the 0.2% offset yield strength ([Sigma]0.2: MPa) to be equal to or higher than 90% of its maximum value is adopted. The strengthened alpha brass has a 0.2% offset yield strength of 450 MPa to 750 MPa and [minimum bend radius (MBR)] / [plate thickness (t)] and [0.2% offset yield strength] satisfy the following formulaMBR / t≦0.0125×σ0.2−6.7 (σ0.2: 0.2% offset yield strength), and [Erichsen value (Er: mm)] and [0.2% offset yield strength] preferably satisfy the following formula.Er≧−0.011×σ0.2+13.7 (σ0.2: 0.2% offset yield strength)

Description

TECHNICAL FIELD[0001]The present invention relates to a strengthened alpha brass and a method for manufacturing the same. The strengthened alpha brass is excellent in both strength and formability, well balances within the strength and the formability, and has a certain level of stress relaxation properties.BACKGROUND ART[0002]Brass has been extensively used for forming electronic components such as terminals or connectors or electromechanical components because brass has relatively high mechanical strength, relatively good conductivity, and inexpensiveness. However, when components are subjected to severe forming, brass with lower temper grade has to be used to maintain necessary formability. Such a shift to lower temper grade results in increase of thickness of the material. As a result, the weight of the material increases and drawback in cost is caused.[0003]When conventional brass is processed with high reduction for the purpose of obtaining materials having excellent strength,...

AI Technical Summary

Benefits of technology

The present invention provides a method for manufacturing a strengthened alpha brass with excellent industrial productivity and less deviation in products quality. The strengthened alpha brass has formability and strength equal to or better than that of EH temper grade of brass or temper H of phosphor bronze, while keeping a certain level of stress relaxation resistance. The method involves using a brass plate with a grain size of 1-micron meter to 2-micron meter as a starting plate material, cold rolling the material to a certain reduction, and then subjecting it to low temperature annealing to adjust its yield strength to be in the range of 130 to 170. The strengthened alpha brass has a tensile strength of 530 MPa to 790 MPa, an 0.2% offset yield strength of 450 MPa to 750 MPa, and a stress relaxation rate of equal to or less than 52% after 100 hours at 120-deg.C. The strengthened alpha brass also has well balanced 0.2% offset yield strength and formability, and it can be suitably manufactured in industrial scale.

Problems solved by technology

However, when components are subjected to severe forming, brass with lower temper grade has to be used to maintain necessary formability.

Such a shift to lower temper grade results in increase of thickness of the material.

As a result, the weight of the material increases and drawback in cost is caused.

When conventional brass is processed with high reduction for the purpose of obtaining materials having excellent strength, resulting materials have deteriorated bend formability and poor toughness, so bending of such materials tends to be difficult.

Thus, conventional brass has such a drawback.

That is, when brass is processed to form connectors or the like, severe bending is often applied.

When a material having a higher strength than this level is required, expensive phosphor bronze is generally selected.

Furthermore, conventional brass does not exhibit excellent stress relaxation properties.

In particular, when grains are turned to be finer, the stress relaxation properties are further deteriorated, and which shows a serious problem in a practical use.

On the other hand, when relatively thick products are manufactured, difficulty may be caused to apply rolling processes with severe reduction for multiple times. Even condition of its preliminary annealing is important, Patent Document 1 discloses just a final annealing and nothing is disclosed on it.

Thus, this alloy has a decreased 0.2% offset yield strength of about 534 MPa, and poor property.

So, the evaluation result does not mean good bend formability with a bend axis along the rolling direction which is considered a Bad Way bend.

The manufacturing method disclosed in Patent Document 2 requires combination of the process with high reduction for multiple times. Therefore, it can be difficult to manufacture relatively thick products by this method.

In addition, in alpha plus beta brass, it is the fact that with fine grained micro-duplex structure of alpha phase and beta phase, the brass is much inferior to phosphor bronze in balance between 0.2% offset yield strength and bend formability.

As described above, though various suggestions are made on theoretical manufacturing methods, but managing of a manufacturing condition is difficult and manufacturing conditions that permit industrial mass production have not been found.

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