How hardness and impact resistance affect wear part service life in earthmoving

Two key elements that determine the suitability of a wear part for an earthmoving application are its ‘hardness’ and ‘impact resistance’, and ratings for both should be analysed to determine fit-for-purpose.

Broadly, harder products tend to offer better wear protection, but may be more brittle and therefore offer less impact resistance and be more susceptible to breaking.

Conversely, products with more impact resistance tend not to be as hard, and therefore may be more susceptible to wear.

Consider glass. It is very hard and resistant to wear, however also very brittle and so not resistant to impact. Now consider tyres. They are not very hard and designed to wear, however are extremely resistant to impact.

Do you want hardness or wear protection?

At Cutting Edges, customers often ask us to make their wear parts harder so they last longer. However, usually, what they are asking for is better wear protection, according to General Manager of Engineering, Manufacturing and Procurement, Gary Kidd.

“Wear part service life improvements are achieved through a combination of both hardness and impact resistance, as determined by the part’s chemistry [metallurgical makeup] and the manufacturing process. For example, the same material put through different heat treatment will give you different hardness and wear characteristics,” Gary said.

“Hardness is related to wear, but hardness alone will not deliver wear resistance. You can have two parts with the same hardness but different impact resistance. It is the about how the product is manufactured to meet your unique operating conditions.”

For example, if you are working in cold conditions, consider that quench and tempered steel becomes very brittle when it is cold. In fact, this is what caused the Titanic to sink. If your wear part is to perform in cold conditions, the chemical composition of the steel must be altered during the manufacturing process to account for it.

“A wear part’s chemistry makeup, as created in the manufacturing process, is what gives it wear characteristics, including hardness and impact resistance,” Gary said, adding that hardness is critical to consider, but only when other factors are also accounted for.

Measuring Hardness:

Wear part hardness is commonly measured using the Brinell or Rockwell scales. While Brinell is more common in Australia, both measurement units are comparable and can be converted to each other.

Measuring Impact Resistance:

Impact resistance is measured in joules at a range of temperatures, often down to as low as minus 20 degrees Celsius.

Through-hardness:

When steel wear parts are hardened in the manufacturing process, one challenge is to deliver the hardening properties throughout the part, and not only on the surface.

“This is important as it will help the wear part wear evenly rather than it being softer internally,” Gary said.

“Through-hardening is more achievable with an experienced metallurgist and high-quality manufacturing facilities with strict quenching temperature and material controls,” he added.

“Cutting Edges has a focus on through-hardened wear parts in our Australian manufacturing facilities, however even with the best processes you will still see some softening inside.

“That is simply the science and you should question anyone who tells you otherwise,” Gary said.