Dear Engineering Hive Mind of the Internets,
I currently work for a facility that through-hardens 440c small Bearing Races via Induction Hardening.
Recently, a part that was "only soft on one side" was brought to me for analysis. After polishing/microhardness/etch, there is a visibly "shiny" area about .030" in from the "softest" surface. Under a microscope, this area does not show any of the "carbon etch pits" that are exhibited throughout the rest of the sample, and in fact shows very little microstructural details at all. We have been finding one or two parts that exhibit this behavior every few days.
I saw the exact same sort of structure from a part that was heat treated with some of the rusty scale (from when the forgings were shipped over here) still on it. Softness and a lack of carbon near the rusty edge, etc.
Disclosure: We buy forgings and tubings in the spherodized, annealed condition. We have seen wild variation in the material before.
HT Procedure: 2030 F for ~2 mimuntes, submerge on a roundness holding die in room temperature quenchant until cooled.
My questions are many:
1) What are the chances of this being a bit of surface de-carb? IIRC this would be caused by a localized over-heating, but the ol' brain fluid is pretty viscous this morning, corrections are invited and encouraged.
2) These tend to be roto-rocked/cold-rocked/indie-rocked forgings. Would there be something in the processes there that would encourage this behavior?
3) How do I keep my sanity while using material that makes these parts that undergo the same process yet turn out wildly different?
4) Could this be a "centered in the coil" IH problem? (I don't believe this to be the case myself having observed a few, but you never know.)
I currently work for a facility that through-hardens 440c small Bearing Races via Induction Hardening.
Recently, a part that was "only soft on one side" was brought to me for analysis. After polishing/microhardness/etch, there is a visibly "shiny" area about .030" in from the "softest" surface. Under a microscope, this area does not show any of the "carbon etch pits" that are exhibited throughout the rest of the sample, and in fact shows very little microstructural details at all. We have been finding one or two parts that exhibit this behavior every few days.
I saw the exact same sort of structure from a part that was heat treated with some of the rusty scale (from when the forgings were shipped over here) still on it. Softness and a lack of carbon near the rusty edge, etc.
Disclosure: We buy forgings and tubings in the spherodized, annealed condition. We have seen wild variation in the material before.
HT Procedure: 2030 F for ~2 mimuntes, submerge on a roundness holding die in room temperature quenchant until cooled.
My questions are many:
1) What are the chances of this being a bit of surface de-carb? IIRC this would be caused by a localized over-heating, but the ol' brain fluid is pretty viscous this morning, corrections are invited and encouraged.
2) These tend to be roto-rocked/cold-rocked/indie-rocked forgings. Would there be something in the processes there that would encourage this behavior?
3) How do I keep my sanity while using material that makes these parts that undergo the same process yet turn out wildly different?
4) Could this be a "centered in the coil" IH problem? (I don't believe this to be the case myself having observed a few, but you never know.)
