There's two issues here that are difficult to deal with independently, much less at the same time. The degree to which these factors interact with one another will determine the most suitable wear material to provide.

First, alloy steels lose their toughness ability as temperatures fall. The -40 degree F figure is a plenty hostile environment! Alloy steels become less resistant to breakage in temperatures this low.

Second, the compressive strength value of the material being reduced is also a consideration, as well as the noted abrasiveness. If the compressive strength of the crushed material is low -- less than 20k p.s.i. -- a medium hardness (400 bh) high nickel carbon steel may possibly be in order. If the impact resistance is higher than the noted 20k p.s.i., then manganese steel may be more suitable.

Manganese has a better ability to maintain its toughness in cold temperatures than do carbon steels. However, manganese would be less resistant to abrasion wear. You could use a silica content factor of + .4 to determine degree of abrasive wear resistance as a lower limit wear ability factor.

The long and short of it -- if you're crushing a highly friable and highly abrasive material, use the carbon steel. If the material is both high in compressive strength and possesses a moderate to high silica content, use the higher carbon value premium manganese steel. The governing issue at hand is the compressive strength value of the material being reduced. If it's hard, abrasive and located somewhere that cold, it had better be of high value, as it's going to be difficult to produce. Sizing considerations and type of crushing equipment add to the considerations in selecting the least detrimental wear material choice.

The manganese liners require a solid base to fully bear against, due to the immense forces put upon them -- both from the crushing work, and from the movement that the work hardening process creates.

Without a substantial base for the part to bear against, the manganese itself would soon fail due to fatigue. There have been a very few crusher manufacturers that have tried to provide metal-to-metal fit cone parts. To provide fitted tapers that bear line on line in a machined state requires very good quality machine tools... too good to be viable in the machining of manganese steel. Not only does manganese work harden with crushing action, but machining the parts hardens them as well.

Manganese steel is a difficult material to machine; it's very hard on both the tools and the machines. As a result, maintaining equipment well enough to provide the kind of accuracy required for fitted machined surfaces hasn’t proven to be cost effective.

The additional time required to machine a part to this degree of accuracy raises the cost of the parts considerably, as well. Most crusher makers have found that shorter, more accurately obtainable machined surfaces on cone crushers is the most viable solution. Filling the remaining casting voids with backing material has proven most effective.

I haven't seen the fitting method that's to be used in this new Metso model. For a related subject, please see my response to a previous question regarding non-backed liners with metal-to-metal fits.

Some attempt at metal-to-metal fitting is likely being used with this new Metso model. The old Symons/Nordberg Gyra-Disc crushers were the most successful run of crushers with metal fit mounting. However, they were relatively short and had flatter 25-degree seated parts. The longer the parts become, the more difficult it is to maintain tapered fits. Maintaining the quality of seat condition in the crusher itself becomes something to consider as well.

The term “mantle” is likely an arbitrary choice of nomenclature that just stuck.

Funk and Wagnalls defines a mantle as “something that covers, enfolds or envelopes”. Perhaps years ago someone in our industry assigned a rather formal title to the "frustro-conical" shaped piece that cloaks a crusher head.

Take with a grain of salt the accepted verbiage used to define crusher parts or equipment behavior. In such an obscure industry, there’s a tendency for folks to apply overly scientific-sounding terms to their business. (I personally find the term “interparticulate communation” to be a particularly stuffed shirt description of “rock on rock” crushing!)

The seemingly insignificant detail of the appearance of the side edge profile of a jaw crusher die has as much bearing on the performance of a jaw crusher as the tooth form or wear face design of the jaw die.

There are varying degrees of fully curved, straight, or straight with curved end profiles commonly available, as well as some specialty side profiles. Various side profiles can be used to “size” the jaw crusher to the feed material available. These are vertically symmetrical jaw dies that can be reversed top to bottom to optimize wear and more fully expend the part.

Fully curved jaws would be used when the crusher is larger than needed for the size of feed being introduced. With full curve jaws, the largest feed size wouldn’t exceed the dimension between the jaw dies just above the horizontal centerline of the crushing cavity. Rock larger than that horizontal dimension will then have its first “bite” taken at a point with a greater included angle, than what exists below that horizontal centerline. Slippage can occur with the larger feed and output reduced.

Straight jaw dies are best used when the feed blend is generally coarse with pre-scalping of fines and maximum feed opening of the crusher is required for the largest sizes of the feed material. Straight dies with a curved end are applied when the feed material includes a blend of enough volume of fines, that the end or toe of a completely straight jaw would wear off rapidly.

There are many variations of all these profiles, plus some specialty side profiles. Examples are asymmetrical cullet, tapered (thin to thick), tapered with curved ends, concave, convex, and more. Variations and cross combinations of any of these side profiles can be used to optimize crusher size to feed material. We have many examples of job designed jaw dies that were made and used specifically for particular sizing situations.