induction hardening

[petedie]

Hello,

I had done hardeness analysis of a HF induction harden cutting blade (1045 steel) which shows a heat effected zone (HAF) about 0.7mm from cutting tip at ~ 32HRc to about 1.0mm, while tip hardness is ~ 52 HRc and body hardness is 44 HRc.

I was under the impression that HAF is not generated by HF induction hardening? Am I correct???

Thanks Pete

 

[Yallapragada1022]

Try to provide us with a picture of the zone you have been talking about.

Rao Yallapragada

 

[petedie]

Unfortunately there are no pictures, only written report (no soft copy either). Pete

 

[dbooker630]

What is the microstructure of the heat affected area? Does it appear to have been austenitized but perhaps slack quenched?

 

[EdStainless]

That is the right question, why is there a HAF. With proper heating and quenching the transition or HAF should be small.
You need to find out if the problem is with heating, did this area not get hot enough, or is it quench, too much delay.

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[petedie]

Unfortunately, the report does not mention the microstructure...

 

[Yallapragada1022]

Can you perform a complete metallurgical analysis in-house? You need to send the sample outside to have complete metallurgical analysis done, if you don't have a metallurgical lab in-house.

It sounds like you only have some hardness data and you need to have a complete metallurgical analysis done to understand the issue at hand.

Rao Yallapragada

 

[swall]

You need to find out how the hardness traverse was performed. If done with microhardness with low load (say 100g), the indenter could have hit a ferrite patch, giving a low hardness reading in the transition zone.

 

[swall]

OK. I thought about this some more and figured it out. At your stated body hardness of 44 Rc for 1045 material, you had to start out with pre-hardened stock.Hot rolled or cold rolled 1045 will run around Rc 30, not Rc 44. With induction hardening, you always get a hardness transition zone from case to core. This is usually a continuous transition with decreasing hardness values until core hardness is reached. But, if you induction harden a component that was already hardened,the hardness results you have reported are consistent with what would be expected. Yes, you have created a HAZ with this sort of processing.

 

[Yallapragada1022]

It makes sense to me know after I have read your 2nd post. Thanks Swall.

Rao Yallapragada

 

[EdStainless]

But to continue Swall's thought, if the induction hardening was done properly with rapid heating, focused field, and rapid quench, then the HAZ should be narrow.
If you look at a cross section the HAZ should also follow the contour of the hardened edge.
If the HAZ is wide mess, then I would suspect that the inductor was not well focused and you got a lot of stary field heating, and/or there was a delay before quench.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[Yallapragada1022]

EdStainless: Thanks for keeping the discussion going.

I don't normally get a transition zone on a 4150H (quenched & tempered to 42 to 45.0 HRC) shaft that we induction harden because of very good quench. Case depth on this shaft is 0.250" to 0.350" to 50HRC.

I do see a transition zone on a 15B41 (normalized) shaft and the case depth is 0.350 to 0.450" to 40HRC. It is very difficult to quench this part effectively because so much heat is put in to the part to obtain the case depth. The transition zone widens if the quench severity worsens.

In my opinion also, the transition zone would be narrow or absent if part was quenched very well.

Rao Yallapragada

 

[dbooker630]

To continue EdStainless' thought on focused field, another possibility is that the high frequency was not as high as it should be. A blade tip can be IH'd with 10kHz, perhaps the machine frequency was running lower creating increased depth of heating which did not fully quench out.

 

[petedie]

Thanks for all the interesting feedback... Pete

 

[EdDanzer]

If the knife edge is sharp, air turbulence could be cooling the edge before quench. We have made a circular tooth with a sharp edge. To get uniform hardness at the last .010” of the sharp we had to make a fixture to hold the heat when transferring from furnace to quench.