Cemented Carbide Grain Size Control via Recycled Scrap Pre-milling
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Solution Overview
Problem
Recycling cemented carbide scrap containing gamma phase cubic carbides poses challenges in achieving a fine-grained microstructure without sacrificing product quality, as existing methods require virgin raw materials to control grain growth and composition.
Innovation Solution
A method involving pre-milling of recycled cemented carbide scrap using the Zn recovery process to achieve a specific grain size, followed by mixing with virgin powders and sintering, which allows for the production of cemented carbide with a fine-grained gamma phase and improved properties comparable to those made from virgin materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If recycled cemented carbide scrap is used as raw material, then energy consumption and environmental impact are reduced, but the ability to control grain growth and composition is worsened
Solution Approach 1:
The recycled powder is divided into different grain size fractions (first powder fraction with finer grain size and second powder fraction with coarser grain size). This segmentation allows selective use of recycled material in the finer fraction while maintaining overall composition control, resolving the contradiction between using recycled materials and controlling grain structure.
Solution Approach 2:
The invention changes the grain size parameter of the recycled powder through classification into different fractions. By controlling the grain size distribution of recycled powder before mixing with virgin materials, the method maintains manufacturing precision while preserving the energy benefits of recycling.
2Manufacturing precision
If pre-alloyed cubic carbides with WC are used to control grain growth, then fine grained gamma phase is achieved, but only virgin raw materials can be used
Solution Approach 1:
The invention segments the raw materials into virgin cubic carbides (for precise grain size control in the gamma phase) and recycled powder fractions (for bulk material supply). This allows the use of pre-alloyed cubic carbides to control grain growth while incorporating recycled materials, thus maintaining both grain size control and raw material flexibility.
Solution Approach 2:
The invention creates a composite powder system combining virgin pre-alloyed cubic carbides with recycled powder fractions. This composite approach allows the beneficial effects of virgin materials (precise composition and grain size control) to be combined with the advantages of recycled materials (sustainability and cost-effectiveness), resolving the contradiction between grain size control and raw material flexibility.
3Productivity
If recycled cemented carbide is used without pre-milling, then processing steps are reduced, but abnormal grain growth and gamma phase clustering occur
Solution Approach 1:
The invention applies preliminary action by pre-milling the recycled powder to a controlled grain size before the main sintering process. This preliminary size reduction prevents abnormal grain growth and gamma phase clustering during sintering, ensuring fine grained microstructure while maintaining processing efficiency through the use of pre-classified powder fractions.
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
The method enables the production of cemented carbide with a fine-grained gamma phase and improved properties, matching or exceeding those of carbides made from virgin materials, while reducing energy consumption and environmental impact by utilizing recycled materials.
Implementation Method 1
subjecting the slurry to milling
Implementation Method 2
drying
Implementation Method 3
pressing and sintering
Data Source
AI summary
The present invention relates to a method of making a cemented carbide comprising mixing in a slurry a first powder fraction and a second powder fraction, subjecting the slurry to milling, drying, pressing and sintering. The first powder fraction is made from cemented carbide scrap recycled using the Zn recovery process, comprising the elements W, C, Co, and at least one or more of Ta, Ti, Nb, Cr, Zr, Hf and Mo, and the second powder fraction comprising virgin raw materials of WC and possibly carbides and/or carbonitrides of one or more of Cr, Zr, W, Ta, Ti, Hf and Nb. The first powder fraction is subjected to a pre-milling step, prior to the step of forming the slurry, to obtain an average grain size of between 0.2 to 1.5 μm.