Lead-Free Brass Hot Forging for Uniform Dezincification Resistance
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Solution Overview
Problem
Existing methods for producing hot forged products using lead-free brass alloys face challenges in achieving consistent dezincification resistance across varying thicknesses and shapes, particularly at sites with low degrees of working, where α transition is incomplete, leading to inadequate corrosion resistance.
Innovation Solution
A method involving controlled heating and cooling rates during hot forging, with a heating rate of 5.2 °C/s or more from 350°C to the forging temperature and a cooling rate of 2 °C/s or more after forging, to suppress crystal grain coarsening and enhance dezincification resistance, while ensuring the alloy composition includes 59.2-63.0% Cu, 1.00-2.00% Sn, and 0.05-0.25% Pb, to produce a uniform brass alloy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thermal treatment at 350°C to 650°C is applied after hot forging to promote α transition, then dezincification resistance is improved, but crystal grain size becomes large at sites with low degree of working, resulting in insufficient corrosion resistance
Solution Approach 1:
The patent applies dynamic recrystallization during hot forging by controlling temperature and deformation parameters, rather than relying solely on post-forging thermal treatment. This changes the fundamental mechanism from static thermal treatment to dynamic process control, achieving fine crystal grains even at sites with low degree of working.
Solution Approach 2:
The patent performs crystal grain refinement during the hot forging process itself through dynamic recrystallization, before final cooling and service. This preliminary action ensures fine grains are established throughout the product, including thick sections, preventing later corrosion resistance issues.
2Reliability
If Sn content is increased to 1.0% or more to improve stress corrosion cracking resistance in lead-free brass, then stress corrosion cracking resistance is improved, but cold mechanical properties such as elongation and impact value are lowered
Solution Approach 1:
The patent optimizes the Sn content to a specific range (0.5-1.0%) rather than simply increasing it, and combines this with controlled hot forging parameters to achieve the desired balance between corrosion resistance and mechanical properties through process-material interaction.
Solution Approach 2:
The patent creates a composite microstructure through dynamic recrystallization during hot forging, combining refined α phase with controlled β phase distribution, which provides both corrosion resistance and acceptable mechanical properties even with moderate Sn content.
3Reliability
If heating rate is increased to suppress crystal grain coarsening, then dezincification resistance is improved, but energy consumption and heating time are increased
Solution Approach 1:
The patent applies a relatively high heating rate to quickly pass through the temperature range where harmful grain coarsening occurs, then maintains temperature for the necessary duration to achieve dynamic recrystallization and fine grain structure, reducing total energy consumption compared to slow heating followed by prolonged holding.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively improves dezincification resistance and stress corrosion cracking resistance, ensuring consistent performance across different regions of a forged product, including areas with low degrees of working, and allows for the production of products like valves and water faucets with enhanced corrosion properties.
Implementation Method 1
a copper alloy containing 60 to 63% by mass of Cu is subjected to a thermal treatment at 350°C to 650°C after hot forging, thereby causing α transition of the structure
Implementation Method 2
when gradual cooling at a rate of 10 °C/sec or less is conducted after hot forging, a β phase is fragmented and surrounded by an α phase, resulting in an improvement in a dezincification resistance
Data Source
Figure 1
Figure 2
Figure 3(a)~3(b)
AI summary
To contribute to an improvement in a dezincification resistance of a copper alloy, focusing attention on a relation between a dezincification resistance of a copper alloy and the crystal grain size of an α phase, and the specific object is to provide a method of producing a hot forged product using a lead-free brass capable of ensuring corrosion resistances such as a prescribed dezincification resistance and the like even at sites of different thickness and shape, a hot forged product, and a wetted product such as a valve and a water faucet, molded using the same. A method of producing a hot forged product using a brass, comprising heat-treating a raw material to be subjected to forging work using a brass having a composition containing at least 59.2 to 63.0% by mass of Cu, 1.00 to 2.00% by mass of Sn and 0.05 to 0.25% by mass of Pb and containing the residue composed of Zn and inevitable impurities at a heating rate of 5.2 °C/s or more from 350°C until reaching the forging temperature.