AISI 4320-modified, Higher Tensile properties:1260mpa and Impact @-40DegC

[Qual7Eng]

thread330-174717
Hi, my first post, hope em at the ryt place to solve dis..
we have an RFQ for gear casting, in AISI 4320-Modified chemistry(C:.23-.28, Mn:.75-1.25, Cr:.6-1.0, Ni:1.5-2.0,Mo:.4-.5, Ti:.015-.045)requires UTS(min): 1260mpa, Y.S(min):1000mpa, Elong:9min, Charpy V impact@ -40DegC: 15J min. Hardness : 395(min)

HT:WQ+ Temp 1 +Temp2, and we are only jus crossing the 1000 for UTS,

comments please on the feasibility of this grade, and heat treatment..

 

[CoryPad]

How large is the part? How thick are the sections? The low carbon concentration will limit the strength attainable especially in large, thick parts.

 

[EdStainless]

Do these get forged or are they machined from the casting?
You may need an extended homogenization HT before the hardening. The Ni and Mo will partition on solidification and you would not get uniform properties.
That said, section thickness is the biggest issue.
You are going to have to quench this very aggressively in order to get good hardening.
I am not sure if retained austenite will be an issue or not, you may need to quench, temper, cryo, temper in order to get strength and toughness.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[Qual7Eng]

we had made trials on a 60mm thick 250mm long blocks which are castings,also.n some cases after grinding some minor cracks are observed...
while quenching we kept the samples on motion in water
and loaded directly fr tempering

 

[Qual7Eng]

also can anybdy advise whether dis values are achievable???

 

[CoryPad]

Those properties would be achievable in wrought material, but I would be skeptical that a thick as-cast version of this material could achieve either the strength or the toughness.

 

[weldstan]

I must agree with CoryPad. Are you obtaining tensile samples at 1/4 T location or 1/2 T location or somewhere else?
Were the cast keel blocks somewhat representative of the rough gear casting? Will there be major changes of dimensions within the casting?

 

[Qual7Eng]

casting only we tried for.. WELDSTAN :sample extracted from 1/2T of 60mm thick block,
Usually what standard properties are meant for this Gr.AISI 4320, any suggestion for an alternate cast material??

 

[weldstan]

You will need to increase the carbon content.

 

[Qual7Eng]

I just dont wanna bury this...
Or can anybody suggest me an alternate choice of material with strength and toughness/ Heat treatment

thanks

 

[redpicker]

you could always try 4330V. Depending on casting practices and heat treatment, you might be able to do it.

 

[TVP]

I agree with redpicker, 4330V seems like a good next step-- somewhat increased C level, still has considerable hardenability with Ni, Cr. What heat treating parameters have you used so far? Austenitizing temperature, quench temperature, tempering temperature?

 

[Qual7Eng]

Thanks for the suppport..

Hardening at 880 Deg C:during heating soaked at 700 Deg C for 2hours, then rose to 880 Deg C, soak for 6 hours, after completion of soaking raise 15 Deg C higher (895 Deg C) and keep it for 15minutes, then quenched in the water.Intermediate Tempering @ 550Deg C and final Tempering @ 550DegC.

 

[tbuelna]

What casting process are you using? The metallurgical quality of the casting will be significantly affected by the casting process used. For example, you will get a much better quality result using a vacuum investment casting process than you will using a sand casting process. And with a fatigue sensitive application like a gear, the metallurgical quality of the material can have a big impact on service life.

Also, in the related thread there was some discussion of the gear being carburized. Is that still the case?

 

[TVP]

I don't have references in front of me, but 550 C seems too high of a tempering temperature to reach your desired strength. Have you tried 450-500 C?

 

[Qual7Eng]

Thru Sand casting, no carburising here..whats makes me firm s I have reference f acheiving strength wid even low carbon levels...
TVP. 450-500 also trialed BT low impact performance..