Heat Treat 4130

[TonyBuser]

We have a customer that is requesting that we heat treat and quench .250 thick flat parts we make for them in water. The request is being made because they feel that the water quench give them better core toughness. We are concerned about this process. Does anyone have any experience in using water as quench media for 4140?

 

[HIMES]

Tony - What are you customer's final strength requirements? I recently performed through hardenability testing on a 4"L x 4" dia bar of 4340 (different material I realize) which was 10bar nitrogen gas quenched. The quench rate was slower than a comparable water quench rate. It was greater than RC40 throughout (which was our minimum requirement). You don't need a water quench for 1/4" 4130 unless they have unusually tight/high requirements.

 

[TonyBuser]

They are looking for 43-47 on the c scale. The customer is requesting water quench and we only have experience using oil. They say that oil won't work because the part will not be tough enough at the core.

 

[HIMES]

....and to answer your customer's concern, in our case we demonstrated adequate material response to the quench and temper process, which resulted in typical (or at least minimum) strength and toughness (although not tested) properties. Also, you can sell them away from a water quench with the increased risk of cracking and/or distortion (if that's what you're trying to do.)

 

[HIMES]

Granted water has a greater cooling capability than oil, I think the 0.25 thickness will erase that difference. Dig up some end quench data and you'll see a fairly flat hardness for at least the first quarter inch for most alloys (like 4130) designed to have high hardenability. And that represents a 0.5" thickness.

What is your concern using water other than inexperience? Can you test the process out on a section of 0.25" stock first? Can you use 4340 instead?

 

[HIMES]

This should have been my first post: A water quench will result in a higher hardness than oil. You must also consider your temper temperature when considering toughness. You may get a greater toughness at a given temper temp after water quench due to slightly higher strength. So in that regard your customer is right. But you can meet their stated harndess requirements with an oil quench. If your contract says maximize toughness, then water quench.

 

[arunmrao]

I have water quenched thick section castings and ended up with cracking problems though the hardness was found to be above RC 55.
For your section thickness of 0.25in oil quench should be more than adequate and achieving a hardness of RC 45-47 should not be difficult.

In case customer insists on faster rate of quenching you can try polymer quenching where a polymer is added to water. The quenching is faster than oil without any fear of cracks. Hope thhis helps

 

[stanweld]

An oil quench and proper temper will provide full section hardness in 1/4-inch thick material that meets the Customer's requirements.

 

[GRoberts]

We water quench a lot of heavy section 8630 and 4130 (a lot more 8630 though) and occasionally do get quench cracking. It is probably 1 in 50 or less as far as major cracking goes. There may be small repariable cracks that I am not aware of. I think that the thin sections you are using would be less susceptable though.

 

[Madjekal57]

You could try 2 stage quenching where you would use water to quench the steel for a short amount of time, then using a second medium, such as oil, to finish the cooling. Using this method will reduce the risk of cracking or distortion. Also, agitating the water will help cool the metal faster.

 

[mdighe]

Hi

I have considerable experience with 4330H material. We have quenched it in oil (upto 1.5 inch thick) and tempered it at 500F to get Rc 46 or higher. It has worked well for us and did not have any problems with cracking.

You should be able to oil quench 4330 and still get Rc 47 through out.

You may have to adjust the tempering temperatures depending on your as quenched hardness.

My person opinion : whenever possible stick with oil quench.

 

[diamondjim]

Why not give the customer what he wants?
You can quench this material in water and
even brine might be better. If they crack,
pass the cost on to the customer. How many
parts are you talking about? If you will not
do it, someone else will.

 

[arunmrao]

Diamondjim
I like this attitude of yours,if I do not a job,someone else will utilise this opportunity and this customer may never come back again,thinking you are unreasonable. But as long as the customer is willing to support let us also assist him by letting him know the pitfalls.

Right today I have had a customer who wanted me to polish as cast surface of a CF8M casting and provide a smmoth defect free surface without machining. My trying to convince failed. Please let me know what I can do. For if I ignore him someone else will take away the customer with a false assurance.

 

[Maui]

I think there is some confusion on your customer's part regarding core toughness. Water is a more aggressive type of quenchant than oil. For this reason, parts that are made in large cross sections may experience better through hardening if they are given the water quench. But a higher core hardness typically goes hand in hand with a lower toughness. So your customer's statement that water quenching will provide them will better core toughness is incorrect. The opposite is true.

And since your parts are only 1/4" thick, they will likely through harden given either quench. But the water quench will have a greater probability of producing more distortion or quench cracking. If your customer is made aware of this, they may decide that oil quenching is the better choice.


Maui

 

[metman]

Probably I am beating on a dead horse but am surprized that nobody has commented on the following:

Yield strength is closely related to the percent of as-quenched Martensite. Also toughness is in part a function of microstructure. And yes you can easily achieve the required hardness level with oil quench in this relatively thin section but if what HIMES stated "A water quench will result in a higher hardness than oil" is true does this not equate to higher percentage Martensite? So...when you temper this higher percentage Martensite to come up with the required hardness, you probably will have a tougher product like the customer wants.

Also if the geometry of the part is not complex or does not have geometric stress risers, then water quenching such a thin section should not hazard quench cracks. This phenomenon occurs from relatively thick sections because the core transforms later than the surface. Since Martensite takes up more volume than Ferite or Austenite, the later expansion at the core puts the surface in tension.
If the part has sharp changes in section or other potential quenching stress risers then prewarn your customer and then if cracks occur, so be it.

Jesus is THE life,
Leonard

 

[Linstrum]

In my copy of the 23rd Edition Machinery's Handbook it specifically mentions that the 4130 test samples used for generating the data for that alloy in the properties section were quenched in water. The 1/4 inch thick parts in question after quenching and stress relieved at 300 degrees F should have a hardness of 49 Rockwell C all the way through with an ultimte yield strength of about 212,000 psi. The chrome-moly alloy 4130 was very specially designed to eliminate hardness and cracking problems caused by very rapid quenching, its original purpose was as a weldable high strength alloy for use where post-weld heat treatment for stress relieving and to eliminate brittleness was not possible. As mentioned previously, it seems that the customer does not have a good grasp of how fast heat transfers through very thin sections. Here, the 1/4 inch thick sections will quench virtually as fast with oil as with water, but it is a moot point in this specific case. Richard Linstrum