Need to improve Charpy Results

[DBCox]

Hello everyone,

We are working with 4130 for a part we are building and need to reach a Charpy impact result of at least 25 ft-lbs (avg.). We are falling way short (we are at 10, 4, 5...). From what I understand, results have been improved in the past by heat treating. Heat treating seems like it would hurt more than help in this case. What can I do to improve the results for the 4130?

Also, our tensile results are ~48,000 psi for yield, 87,000 psi ultimate; both seem low. But, our elongation at break is around 18% or so, which seems high...

I wish I had more data to give, but that is all I have at this point. Any suggestions?

Thanks

 

[metengr]

Several questions;

You need 25 ft-lbs at what minimum service temperature?

What is the original heat treatment of the 4130?

What are your minimum strength requirements for the part?

 

[EdStainless]

How has the material been heat treated? is it just normalized?

If so then you should be able to improve properties by going through a controled hardening/tempering cycle.

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Rust never sleeps
Neither should your protection

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[metengr]

If you can't provide more information, I would suspect that the 4130 was supplied where the rate of cooling created a temper embrittlement condition. This is a common problem in low alloy steel if slow cooled between 600 to 1070 deg F during fabrication.

You can improve ductility and toughness of this material by specifying a heat treatment condition. Your best bet would be a quench and temper heat treatment. The temper cycle should be outside of the 600-1070 deg F temperature range to avoid a reduction in ductility and toughness. However, you need to know your minimum strength requirements to assure selection of a proper heat treatment.

 

[redpicker]

Sounds as if your material is in the as-rolled/as-forged condition, considering the low yield and CVN.

Depending on the section size, a water quench and temper or a oil quench and temper treatment would greatly improve your impact strength. 25 Ft-Lb at room temperature is really not a problem with this material until you start getting hardnesses over 35 Rockwell 'C' or so and it sounds as if you don't need anywhere near this hardness.

The limitation with 4130 for quench and temper is the section thickness. Somewhere around 2 to 4 inches, you will not achieve through hardening, even with a water quench. Higher alloy content will be needed for the larger sections.

metengr, I believe you are describing temper embrittlement, a condition I had been led to believe did not apply to steels containing molybdenum (4130 has 0.15/0.25 Mo). Have I been misled? I have obtained very good impacts (>50 Ft-Lbs) with this material at tempering tempratures below 1000F. Am I doing something very unique? I'll admit that I was suprised at the impact levels I am achieving, but we do have a very consistent heat treating process.

rp

 

[stanweld]

From your tensile results, I would suspect the material to be in a fully annealed condition or as metengr stated. If so, normalizing or Quench and tempering will inmprove toughness of the alloy. To obtain the best heat treatment for your needs; reiterating metengr's question to you, what is the service (impact test) temperature?

 

[DBCox]

Thank you for the fast responses everyone. I am sorry, I do have a little more information for you. The test is to be performed at -20 deg. C. As for the strength requirements, I am not sure because I was not involved in the design of this component. However, I assume they expected the typical properties of 4130N (58ksi yield, 89ksi ultimate).

On a more theoretical note; I was always under the impression that quenching and other hardening processes generally caused the material to be more brittle. Am I wrong there, or is this some sort of special case?

Thanks

 

[metengr]

redpicker;
From what I have read you need to be at or above 0.75% Mo to really delay the effects of embrittlement for this material. Of course, tramp elements will be equally as important in increasing susceptibility to TE.

 

[EdStainless]

blak, The material will be brittle in the as quenched condition. When you follow this with a tempering treatment you trade strength (and hardness) for ductility and toughness. In general the higher the temper temp the softer and tougher the material becomes.

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

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

 

[unclesyd]

Your numbers are likey for a normalized material.
My number for 2" and 4" material, normalized, are in that range. The hardness is around 85 Rb with 27% El and 63% Ra. I only have Izod values, which are around 78.

The annealed material has an Izod of 45, hardness Rb 86, El 28%, Ra 56%, TS 81,000, and YS 53,000.

 

[QAFitz]

Take a look at the tensile requirements in ASTM A-540. These are accomplished by Quench and Tempering. We have had some good luck (heat treating is a smoke-and-mirrors thing) following this spec.

 

[harsuda]

Harden and temper treatment will help you to get the required results. Please ensure that after tempering you cool the material at a rate sufficient enough to avoid tempre embritlement. For this you can adapt water cooling method.