Manganese steel wear liners
Manganese steel has been used in crushing applications for over 100 years, so it’s easy to take it for granted. It continues to be used because of the remarkable property that makes it ideal for wear liners: the harder you hit it, the harder it gets.
Austenitic manganese steel – steel alloyed with more than 10% manganese – is work-hardening. That means that high impacts – like those in a crushing chamber for example – cause the formation of a extremely hard surface layer that is two to three times harder than the rest of the alloy If impacted enough, this results in a hard exterior layer backed by a softer core. In the right conditions, this can give manganese steel the dual qualities of wear resistance (deriving from its hard exterior) and impact strength (deriving from its ductile core). It’s clear why manganese has remained such an important element in the crushing industry.
How much manganese?
So the more manganese the better, right? There’s a little more to it than that. It’s true that, within a certain range, the higher the manganese content in an alloy, the harder it will be. This simple relation probably explains the popularity of alloys with a high manganese content over the last few decades.
However, by increasing the hardness of a wear liner you also increase its brittleness. A more brittle alloy is more vulnerable to cracking under high impact. An alloy with a slightly lower manganese content (around 13-14%) will be more ductile and durable, and can therefore absorb more hits without cracking. Depending on the application, harder isn’t always better. Alloys with a high manganese content are especially good for crushing abrasive rocks, but for crushing harder rocks you may be better with a lower manganese content that offers greater impact resistance.
Then there is the presence of other elements in the alloy – carbon increases the hardness and wear resistance of the alloy, and chromium helps prevent ‘metal growth’ (where the liner expands and becomes too large for the crusher). Getting the right ratio of these elements relative to manganese is a delicate balance. Too much carbon or chromium affects the atomic structure of an alloy, stopping it from solidifying into an austenitic microstructure – this would make the alloy far weaker and it wouldn’t have the desired work-hardening qualities.
The manganese balance
So, for wear liners, the key is finding the right balance for every application. Sandvik have a range of liners comprised of different manganese alloys – depending on the material you are crushing, either impact resistance or wear resistance might be a more important consideration for you. Each Sandvik alloy has its own characteristics and benefits to consider.
Different compositions of Sandvik alloys give them individual qualities and strengths.
You’ll notice that the M9 alloy provides particularly high resistance against wear – that’s Sandvik’s new premium alloy mix, available for CS and CH crushing chamber solutions. It offers up to 20% longer lifetime than conventional alloy mixes, resulting in more uptime and lower operating costs.
As well as having the right composition, wear liners need to be expertly manufactured. Small variations in the production process can cause major weaknesses – for example, if not heat treated properly, carbides can form along the grain boundaries which are affecting both strength and durability. If the liners are not quenched at the right moment and at the correct temperature, the austenitic microstructure can change, meaning that the all-important work-hardening will not occur.
Sandvik brings a deep manufacturing process knowledge and decades of industry experience to create the highest quality wear liners. It begins with high-quality raw materials, in order to minimize impurities. Careful temperature control during the melting and pouring stage ensures the right grain structure for the castings, then heat-treating and quenching dissolves carbides and maintains the austenitic microstructure.