Kudos to SOA...new goodies
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The polished areas of the crank are still treated, just polished.
Would be nice if they plated the bearing surfaces with TiN or TCiN. From the looks of the naked crank, that coating is just for corosion resistance. The crank doesn't see temperatures high enough to take advantage of the benefits of nitriding, and I can't see a benefit to increasing just the surface hardness NOT on the bearing surfaces. As some one already mentioned, the crank is already plenty strong.
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Joined: Jun 2006
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From: Waynesboro, VA
Car Info: '05 STi
nitriding is only a surface treatment. If you grind, you remove it, most if not all of it. The coating is very likely NOT going to have any effect on the strength of the crank, especially since it's not everywhere. A chain is only as strong as its weakes link, so please don't be mystified by the coating.
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No one's mystified...just excited that the OE is making a stronger/better part that costs about the same as the older version.
"Surface" hardening is a little misleading, as the nitrogen penetrates ~.75mm into the part; the polished areas are still treated.
It sounds like you have some expertise in this area...can you share?
"Surface" hardening is a little misleading, as the nitrogen penetrates ~.75mm into the part; the polished areas are still treated.
It sounds like you have some expertise in this area...can you share?
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No one's mystified...just excited that the OE is making a stronger/better part that costs about the same as the older version.
"Surface" hardening is a little misleading, as the nitrogen penetrates ~.75mm into the part; the polished areas are still treated.
It sounds like you have some expertise in this area...can you share?
"Surface" hardening is a little misleading, as the nitrogen penetrates ~.75mm into the part; the polished areas are still treated.
It sounds like you have some expertise in this area...can you share?
-Noah
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Joined: Jun 2006
Posts: 25
From: Waynesboro, VA
Car Info: '05 STi
I think the coating is more a corrosion inhibitor than anything else.
Do you know specifically how the nitriding was performed? There are several methods with different depths of penetration. .75mm is on the deep side, but just for argument sake, lets say it is that deep.
From the pictures it's fairly obvious that the surface treatment was before final finishing (grinding the bearing surfaces). If you've seen a crank prior to finishing you know that the forging process leaves the bearing surfaces of the crank in a rough condition, not to mention the bearing surfaces are likely not precisely concentric to each other. Same hold true for the connectin rod surfaces, likely not precisely parallel to the crank centerline. My point here is this is the time when the crank gets surface treated, before all grinding takes place.
Because of the tolerance variations coming right from the forging presses quite a bit of material is removed (ground) from these bearing surface. Regardless of how deep the surface treatment the more you grind off the more hardness you loose. It's not like it it's super hard down to .75mm then soft (according to the base material specs). It's super hard at the surface and gets gradually softer as you go down into the material.
IMO since the surface treatment is BEFORE grinding, most if not all, of the treatments properties are lost in the ground areas. This leads me to believe the nitriding is not deep in the first place and only for corrosion prevention.
Do you know specifically how the nitriding was performed? There are several methods with different depths of penetration. .75mm is on the deep side, but just for argument sake, lets say it is that deep.
From the pictures it's fairly obvious that the surface treatment was before final finishing (grinding the bearing surfaces). If you've seen a crank prior to finishing you know that the forging process leaves the bearing surfaces of the crank in a rough condition, not to mention the bearing surfaces are likely not precisely concentric to each other. Same hold true for the connectin rod surfaces, likely not precisely parallel to the crank centerline. My point here is this is the time when the crank gets surface treated, before all grinding takes place.
Because of the tolerance variations coming right from the forging presses quite a bit of material is removed (ground) from these bearing surface. Regardless of how deep the surface treatment the more you grind off the more hardness you loose. It's not like it it's super hard down to .75mm then soft (according to the base material specs). It's super hard at the surface and gets gradually softer as you go down into the material.
IMO since the surface treatment is BEFORE grinding, most if not all, of the treatments properties are lost in the ground areas. This leads me to believe the nitriding is not deep in the first place and only for corrosion prevention.
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