Harden-ability of 4130 1

[mgh70]

Currently looking at doing some HT on some rather large cross sections of 4130. What is the average through hardness depth that is usually seen out of 4130? I keep getting a wide range of values, but from what I have heard it is about 2 inches which seems low... going to be HT,Qenched and Tempered to 235 HBW max.

Looking at 3 different specimens: 20"x 17"x 44" , 20"x 17"x 24", and 21"x 18"x 65", all with a 2" through bore drilled through the entire length.

 

[israelkk]

As as far as I know 4130 maximum thickness for through hardness is only 0.5 inch if cooled from all sides. If cooled only from one side such a quenching a hollow vessel the maximum thickness for through hardness is 0.2 inch. For large sections use more alloyed steel such a 4340. I suspect that for the large billets in your case you will need to use tool steels.

 

[mgh70]

Blegh. What can I expect with forced convection?

 

[Lyrl]

235 HBW maximum is really soft - and is that correct that it is a maximum hardness?
To achieve maximum hardness with 4130, israelkk's thickness suggestions are in line with my own experience. But getting the material below 235 HBW will require basically an anneal step after the harden, and I'd guess it will be that same hardness all the way through even large sections.

 

[mgh70]

Well the maximum hardness I am wanting for this application is 235 BHW all the way through and a Minimum yield of 80ksi.

Current process will be: Normalize at 1700F for 5.5hr, then Austenitize at 1600F 5.5hr, quench below 400F, then temper at 1200 for 11 hours, finally ending with air cooling...

With this current process you're saying I should have full through hardness, even through 11" sections? Or I should expect only .5"?

-M

 

[CoryPad]

4130 will never through harden in an 11" section, you need something like 4340.

 

[mgh70]

For prototyping and concept validation we are using a worst case scenario which is production using 4130 which is common practice practice for less extreme applications of our equipment. Production will feature F22, however the customer figures if it is validated using 4130, the end user would rather spend less. So the key issue is how reliably can I achieve these properties and to what extent through the thickness for 4130. Which will allow me to inform them of their options and make a more formal recommendation.

-M

 

[Lyrl]

After the quench, the part will have a surface that is much harder than the core (or even an half inch down).
After the 11 hour temper at 1200°F (equivalent to a subcritical anneal), I believe the part will be the same (low) hardness all the way through even 11".

An 80 ksi minimum yield strength might required a minimum UTS of around 120 ksi (very approximately, yield-UTS relationships vary by alloy and part geometry). 120ksi UTS actually correlates to a little above a 235 BHN hardness. Absent previous data on tensile testing from similar parts, meeting the minimum yield strength would be more my concern than having a uniform annealed hardness level throughout the part.