aisi 4820 vs en36c 2

[rmetzger]

We are looking for an easier to obtain (overseas) alternate for AISI 4820 and I'm looking at EN36C. Any comments or recommendations? It's for a splined shaft.

 

[Carburize]

What are you going to do with the material? Is it for carburizing?

En36C has slightly lower carbon than 4820 but an addition of chromium which will make it more hardeneable than 4820.

 

[rmetzger]

Its primary use is for gearing and carburizing is part of the processing.

 

[Carburize]

It will carburize slightly differently in terms of case formation rate and you will get a higher core hardness in the En36C compared to 4820. En36C ( BS970 Grade832M13) is a widely used carburized gear material.

 

[rmetzger]

We are currently specing the following (excuse the case, it was taken directly from a print):

CARBURIZE AND HARDEN PER AMS 2759/7 CLASS 3 TO RC58-RC62 SURFACE HARDNESS. EFFECTIVE CASE DEPTH TO BE .020-.030 (RC50) WITH A CORE HARDNESS OF RC32-RC46.

Will En36C be able to be conditioned to this spec or is an increase in core hardness neessary?

thanks for the assist.
Ron

 

[Carburize]

En36C will work fine - my guess would be a core hardness around 40 - 42Rc. I assume you will provide test material to your carburize heat treater to fine tune his process parameters but based on the chemical analysis of En36C a carburizing boost diffuse cycle of 3 hrs at 1725F at a carbon potential of 1.1% followed by a 1 hr diffuse with a 0.85% carbon potential should put you at the top end of the case depth specification.

 

[rmetzger]

thanks, you've been a ton of help.

 

[CoryPad]

A 14 point spread on core hardness on the HRC scale is huge. You could get just about any material to meet that. Do you know why that range is so large?

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Carburize]

32 Rc is the minimum core hardness for bending strength calculations in some rating systems - I suspect the top end nummber was imposed to give some measure of core ductility - if you are getting a 0.1 or 0.2% carbon steel above 46 Rc it is probably marginal on ductility.

 

[rmetzger]

The spec we're using is pretty old and I'm in process of reverse engineering it to find the rational behind it. The specs I gave are generally called out on gears and pinions and cross a number of differnet material boundaries (4820, 9310, 9317, PD970-832M13...).

 

[mewhg]

Carburize,
Could you explain the reason for 2 different carbon potentials?
thanks

 

[Carburize]

The two different carbon potentials are an integral part of the "boost-diffuse" cycle. This is a way of shortening the total cycle time for the part and producing a flatter carbon gradient and subsequently a flatter hardness profile for the case. This case profile is important in parts which are finish ground following carburizing - the manufacturer needs grind stock so that the final surface still meets the minimum hardness - the case of gears for example 58HRC is specified in a number of standards as th eminimum surface hardness. If there is a steep gradient it is very easy to grind through the top layer of the case down to material which is below specified surface hardness.