Chromium WC-Co Rock Drill Insert With Surface Hardness Gradient
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Solution Overview
Problem
Rock drill inserts made of traditional WC-Co based cemented carbide face challenges with corrosion resistance, wear, and impact toughness, particularly in wet drilling conditions and under severe impact loads, leading to early damage and brittleness.
Innovation Solution
A rock drill insert with a chromium-containing WC-Co based cemented carbide, featuring a hardness gradient between the surface and bulk, achieved through milling, compacting, sintering, and a high-energy oscillating collision process to induce compressive stresses, enhancing surface hardening and corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional WC-Co based cemented carbide is used for rock drill inserts, then the insert can withstand impact loads, but the corrosion resistance is insufficient leading to increased wear in wet drilling conditions
Solution Approach 1:
The invention changes the chemical composition parameters by adding chromium (0.05-5 mass%) to the WC-Co cemented carbide, creating a new material grade that simultaneously improves corrosion resistance and maintains impact toughness. This compositional modification transforms the binder phase properties without compromising the overall structural integrity
Solution Approach 2:
The invention creates a composite material system by combining WC hard phase, Co binder phase, and Cr additive that forms chromium carbides and modifies the binder phase. This multi-component composite structure provides both corrosion resistance from Cr and impact resistance from the WC-Co matrix
2Reliability
If the cemented carbide is made harder to increase wear resistance, then wear resistance improves, but the ductility decreases making the insert too brittle to withstand impact loads
Solution Approach 1:
The invention optimizes the Cr content parameter (0.05-5 mass%) to achieve a balance where sufficient chromium carbides form to harden the surface and improve wear resistance, while the Cr/Co ratio remains controlled (0.005-0.5) to prevent excessive binder phase hardening that would cause brittleness. This precise parameter control resolves the hardness-ductility trade-off
Solution Approach 2:
The invention creates local quality differences through the formation of chromium carbides primarily at grain boundaries and in the binder phase, while the bulk WC grains maintain their toughness. The surface layer develops different properties than the bulk material, with the surface being harder due to chromium carbide formation while the interior retains ductility
3Reliability
If chromium is added to improve corrosion resistance, then corrosion resistance increases, but the manufacturing process complexity increases
Solution Approach 1:
The invention merges the chromium addition step with the existing powder metallurgy manufacturing process. Chromium powder or Cr3C2 is mixed with WC and Co powders in the same milling process, and all components are sintered together in a single sintering cycle. This integration avoids adding separate manufacturing steps while achieving the desired material properties
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 chromium-containing cemented carbide insert exhibits improved wear resistance, reduced risk of breakage, and increased impact toughness, maintaining performance in harsh drilling conditions while preventing premature failure.
Implementation Method 1
The drill insert is then subjected to post-treatment which introduces high levels of compressive stresses in the insert, such as a special high-energy oscillating collision process
Implementation Method 2
a powder comprising the elements of the cemented carbide is milled and compacted into a compact which is then sintered
Data Source
AI summary
A rock drill insert made of cemented carbide having hard constituents of tungsten carbide (WC) in a binder phase including Co, wherein the cemented carbide includes 4-18 mass % Co and a balance of WC and unavoidable impurities. The cemented carbide also includes Cr in such an amount that the mass ratio Cr/Co is within the range of 0.04-0.19, and the difference between the hardness at a 0.3 mm depth at any point of the surface of the rock drill insert and the hardness of the bulk of the rock drill insert is at least 40 HV3.