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 and specific Cr/Co mass ratio, combined with 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 chromium is added to improve corrosion resistance, then wear resistance improves, but brittleness increases and impact toughness deteriorates
Solution Approach 1:
The patent creates a non-uniform chromium distribution within the cemented carbide structure. The chromium content varies from the surface to the bulk, with higher concentration at the surface for corrosion protection and lower concentration in the bulk to maintain toughness. This local variation in composition resolves the contradiction between surface corrosion resistance and bulk impact toughness.
Solution Approach 2:
The patent changes the chromium concentration parameter spatially within the material. By controlling the chromium content to range from 0.04-0.19 mass ratio relative to cobalt at the surface versus lower amounts in the bulk, the material achieves different properties in different regions, simultaneously obtaining corrosion resistance at the surface and impact toughness in the bulk.
2Reliability
If surface hardness is increased to reduce wear, then wear resistance improves, but brittleness increases and early damage occurs
Solution Approach 1:
The patent implements a hardness gradient where the surface layer has higher hardness for wear resistance while the bulk material maintains lower hardness for ductility. This is achieved through localized chromium enrichment at the surface that creates a harder surface layer without compromising the toughness of the underlying material.
Solution Approach 2:
The chromium addition and resulting hardness gradient are built into the material structure during manufacturing, before the insert is put into service. This preliminary creation of a hard surface layer with a softer, tougher substrate prevents early damage by ensuring the surface can withstand wear while the bulk can absorb impact energy.
3Strength
If cobalt content is increased to improve ductility, then impact toughness improves, but hardness decreases and wear resistance deteriorates
Solution Approach 1:
The patent creates a spatial variation in cobalt content that complements the chromium distribution. The surface region has lower cobalt content (higher chromium/Co ratio) for hardness and wear resistance, while the bulk has higher cobalt content for ductility and impact toughness. This local differentiation resolves the contradiction between surface wear resistance and bulk ductility.
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 solution significantly reduces wear and breakage, improves corrosion resistance, and increases impact toughness, resulting in a rock drill insert with enhanced durability and resistance to early 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
the addition of Cr results in an improvement of the corrosion resistance of the Co-binder phase, which reduces the wear in wet drilling conditions.
Implementation Method 3
the combined effects of compressive stress induction and binder hardening have surprisingly been discovered being particularly strong for chromium-containing inserts both during the pre-application treatment in the high-energy oscillation collision process and also during the drilling application itself.
Data Source
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AI summary
A rock drill insert made of cemented carbide that comprises hard constituents of tungsten carbide (WC) in a binder phase comprising Co, wherein the cemented 5 carbide comprises 4-18 mass % Co and balance WC and unavoidable impurities, characterized in that said cemented carbide also comprises 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 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. 10