4330 Modified (3.40 Ni) Charpy Results Failing - Need Heat Treat Advice 2

[Macdost]

Greetings,

We are using a 4330 modified;
C - 0.32
Mn - .60
Si - .26
Ni - 3.40
Cr - 1.20
Mo - .48
V - .118

We need transverse -40f impacts @ 34J average no lower than 27J
We cannot meet these requirements after many different heat treatments.

Does any one have experience with this grade mod and heat treating?
All I could find was an investigation by US Army that concluded;
Austenize @ 1500f, i hour, oil quench and double temper at 400f (2 hr. AC + 2 HR AC)! However their Ni was half ours (1.80)

Thank you, pulling our hair out!

 

[Macdost]

thread330-156227

 

[CoryPad]

There are some other important factors for impact performance, like grain size and sulfur concentration. Can you share more about your product and application?

 

[Macdost]

They are Quenched and Tempered Alloy Steel (4330 Modified), Fluid Cylinder Forgings.

Sulfur - .002
Cu - .16

58" x 103" - 4330MOD Ingot(s) Note the high Ni

Anything else that could help?

 

[metengr]

The sulfur content is well within range to achieve the required impact values. You need to look at the forging temperature, grain size and heat treatment after forging to determine why you can't achieve the impact values. What is the specified strength level for the forgings?

 

[Macdost]

Tensile Min;
Longitudinal - 160 ksi (1103 mpa)
Transverse - 160 ksi (1103 mpa)

Yield 0.2% Offset Min;
Long. - 145 ksi (1000 mpa)
Trans. - 145 ksi (1000 mpa)

Elongation in 2" Min;
Long. - 14%
Trans. - 10%

Reduction in Area, Min;
Long. - 38%
Trans. - 25%

 

[metengr]

Take a look at this alloy
AISI 4330V mod/1.6562, Firmodur 6562. Assuming forging and heat treatment are within stated parameters, your chemical ranges are slightly out of range with what is stated for the alloy mentioned. Your elevated V content would concern me along with the current carbon content regarding achieving target impact values.

 

[Macdost]

Thank you very much for your time on this! Merry Christmas and Happy New Year

 

[CoryPad]

metengr,

Can you explain your concern regarding V? It should help prevent grain growth during hot forging, which should have a positive effect. I know that there are complex effects with regards to temperatures used during thermomechanical processing and other elements like N, Al, Nb, and Ti.

 

[metengr]

Secondary hardening with V(CN) precipitates is common in these types of alloys. I have seen this during tempering or with power plant turbine steels; Cr-Mo-V alloys. As you know, carbon content plays a significant role with impact values and understanding the beneficial affects of V with resistance to tempering and grain growth during forging. I believe there is a balance between these two elements.

 

[CoryPad]

Thanks!

 

[weldstan]

Agree with metengr re V content. What were the actual tensile properties achieved versus the required values stated? Additions of .02 to .04% Al will help mitigate some of the issues with your high V content.

 

[TVP]

Very good advice so far. Just wanted to reiterate that grain size, meaning prior austenite grain size, is extremely important for meeting these low temperature impact properties. Have you been evaluating this? The forging temperatures need to be low enough that the PAGS is ASTM 6 or finer, preferably 8-10. The final hardening temperature prior to quenching should be in the range of 1500-1550 F.

 

[redpicker]

What is your situation? Do you have one or two particular lots that are difficult, or a process stream that is giving you fits?

For one or two lots, normalize at 1775F, then Q&T as normal.

If it is a process stream, I would look at the cooling from forging. With that high V and Cr contents, and the Ni, you will get a lot of M23C6 carbides at the forging grain boundaries with slow cooling. It takes a very high austenitizing to break these carbides up, so either cool quickly from forging temp to below 1200F or so, or include a high temperature normalize. The object is to not let these complex carbides form at the grain boundaries on cooling from forging, or if they do, dissolve them (>1750F) again prior to hardening.

If you can control the austenitizing, you may find austenitizing at 1775F, cooling to 1500F then oil quench will work, if you can keep the time at the time >1750F well controlled (<30 minutes) and can soak at 1500F prior to quenching.

You may also investigate secondary hardening to maintain strength. I would think a tempering temperature of around 1100F could still maintain the 145K yield and the higher temper would help the impacts. With < 0.005 Sulfur, the impacts in the longitudinal and transverse directions should be similar, particular with Calcium treatment, and 34J (25 Ft-Lb) shouldn't be that difficult with this alloy at this strength level.

rp

 

[Macdost]

Thank you for all the information, I will bring it to the quality people and let them chew on it for awhile. I do not have the answers to all of your questions right now. I will post updates and answers if and when I get them.

Thank you again for your time it is much appreciated.

 

[MagBen]

58x103'', that's a huge ingot! If your parts had a comparable size, I could not imagine how to obtain a uniform cooling from the center to outside. You could see a big variation of properties across the section.

Higher Ni is added obviously for toughness. As pointed out, if the cooling from forging was too slow (especially at center portion), and forging finish temperature was too high, you would get coarse grains and coarse, or even networked carbides, both of which are bad for impact property.

considerably increasing temeprature to break up the carbides sounds a valuable suggestion. Slight increasing temperature, say 1550-1600F, maybe another method worth trying to maintain a cerain percetage of austenitic phase to increase the tougness without much sacrifice in strength.

 

[metengr]

Also, watch your nitrogen content in this type of steel because vanadium has great affinity for nitrogen and this could easily influence impact properties.

 

[mrfailure]

In the linked thread you posted after your initial question, TVP wondered about the impact of nitrogen. Do you have a high N content here and if so, do you think it could be affecting your impact energies?

 

[Macdost]

We tested a broken Charpy specimen to determine average austenitic grain size = ASTM 2.0

We then had a "McQuaid-Ehn" Test performed = ASTM 6.0 !

More questions than answers now..........

 

[weldstan]

You will never meet the toughness requirements with grain size of 2.
Fine grain melting with .02% to .04%. Then Normalize & Quench and temper.
Assuming that you are stuck with existing wrought material, see redpicker.
The coarse grain is no doubt due to the forging conditions (time and temperature in furnace and final forging temp and degree of hot work) and while the grain can be refined by normalizing prior to Q&T, it will never be refined to finer than 6 with heat treatment. If you have more reforging billets of this material, control the forging conditions and heat treat as above. Tempering at 900F to 1000F should meet you tensile properties.