Wear resistance: the underlying property in modern steels

Recent research predicts that the mining automation market will be worth $3.29bn by 2023 — a compound annual growth rate (CAGR) of 6.7 per cent since 2017. While automation greatly enhances productivity, it also places additional demands on steel components. Ben Smye, head of growth at materials search engine Matmatch, examines why wear resistant steels are vital to modern, enhanced production.

The research by Markets and Markets found that the recent boom in automated mining technology is going from strength-to-strength. Atlas Copco, Rio Tinto and Caterpillar are presently among the big players in automated mining, and Asia-Pacific (APAC) is set to becoming the largest market.

However, the more intense rigours of automated drilling processes also put greater demands on steels used in mining equipment. Components like rock drills are already subjected to factors that cause considerable wear — like vibration and the type of motion, temperature, load, velocity, contact area, sliding distance and atmosphere.

If the wrong steels are used for these components, then this can lead to equipment failures and downtime.

That’s why choosing the best-performing wear resistant steels is crucial to getting the best performance from automated drilling technology. Wear resistant — or abrasion resistant steels — are relied upon in applications where resistance to abrasion, impact or sliding are essential. Their popular uses include in rock drills, wear plates for rock-processing machinery, crushers and power shovels.

Wear resistant steels are typically austenitic grades, the most widely used grade of stainless steel. They are non-magnetic and contain high levels of chromium and nickel with low levels of carbon — typically of around 1.2%. Austenitic steels are usually 12% manganese, a strong austeniser, which means it helps to retain the steel’s tough properties at room temperature.

They also have work-hardening capabilities. Pure metals are rarely used in manufacturing because they are too soft. Instead, wear resistant steels contain the non-metallic elements carbon and nitrogen, the atoms of which fill the gaps between the steel’s iron atoms. This “distortion” makes it more difficult for the layers of the metal — or the lattice — to slide over each other. Wear resistant alloys are harder, less malleable and more ductile than pure metals, as a result.

This is advantageous in applications like in rock drilling, where the steel is repeatedly pounded. The more pounding the drill takes, the more the carbon and nitrogen deform the steel’s surface and the stronger it becomes.

Another layer of protection

Surface fatigue or micro-cracking are both mechanisms that affect ultra-hard materials and reduce the long-term performance of components. This is the case with Ground Engaging Tools (GETs) used in mining, construction or agriculture. GETs are often compromised because of wear caused by gouging, high-stress abrasion or impact, leading to loss of functionality or even failures.

These consequences can be avoided with an optimised steel coating — applying a tougher material onto base materials through nitriding, chromium depositing or welding. The coating can enhance a component’s hardness and toughness, protect from hard abrasives and better withstand compressive stresses. In such cases, it’s best to enlist the services of a qualified surface solutions expert, like Oerlikon Metco.

Ultimately, the properties of wear resistant steels should link directly to customers’ needs. This applies to a steel’s compatibility to heat treatment facilities and melt shops, where wear resistant grades are through-hardened in a process known as quenching and tempering (Q&T). The steel’s grain structure is changed to increase toughness and improve formability, which makes the material less brittle.

Today, it’s more possible than ever before to assess and choose the best wear resistant steels for any given application. Matmatch lists thousands of materials on its online materials platform, where design engineers can make better material choices for their end use or heat treatment requirements.

As a growing number of mining projects strive for greater levels of productivity through automation, this knowledge will be vital to ensuring that wear resistant steels remain fundamental in withstanding the rigorous demands.

Author
Ben Smye

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