Equivalent Carbon value influences the tenacity of the material?

[WendelTrento]

Dears,

Good morning,

I have a technical question about heat treatment that my supplier was unable to explain.

I have forged 4140 trepanned materials.

I will perform heat treatment to meet the mechanical properties below, these are requirements from my end client.

Mechanical Properties. (All values are minimums unless otherwise noted.)
Tensile strength: 130,000 psi
Yield strength: 110,000 psi (758 MPa)
Elongation in 2" or 4D: 15%
Reduction of area: 33%
Brinell Hardness raw: 277-321 HBW

Requirements for carrying out the impact test:
Test Temperature: -30°C
Impact Energy Average of Three Specimens: 42 J
Impact Energy Single Specimen: 30 J

My heat treatment supplier said that the raw material has a carbon equivalent of 0.748, which at this value will not reach the requested impact value. To meet the requirements, the material should have at least 0.8 carbon equivalent. Material Drawing and Material Certificate are attached.

My question is, how does the carbon equivalent influence the toughness of the material? and if there are tables or mathematical equations to verify this requirement?

Example: Specify to the buyer of the material that the material must have a carbon equivalent of at least “X” to meet the impact after heat treatment.

Att,

Wendel Trento

 

[MagBen]

There is no universally accepted equation that directly relates toughness to CE for 4140. However, in general, an increase in CE can lead to a decrease in toughness, while increase in hardness and strength. any specific reason why your HT supplier says the opposite? perhaps they are concerning hardenability for suhc large diameter?

 

[EdStainless]

Or it may be that you need a material that will reach higher hardness, to allow for higher temper temperature.
To me your specs sound reasonable.


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P.E. Metallurgy, consulting work welcomed

 

[MFAMET]

The higher CE makes higher hardenability which allows a slower cooling (quenching) rate to harden (martensite transformation) a material, such as 4140. This will be more beneficial for a large section material to get a deeper martensitic layer while the cooling rate is varying between surface and core. However, the mechanical Properties of finished products including toughness is mainly dictated by the practice of HT. Particularly, the setting of tempering temperature is more critical. A property of fine grain, good ductility, and high strength is desired to enhance toughness.