20CrMnTi vs AISI 4320/8620

[SZ9]

Thanks in advance for any help.

So, the company I work for uses big gears PD ~20" Face 8" Thick. Material we current use is AISI 4320 / 8620. I started searching for vendors in China and the usual response I get is they want to replace the material with 20CrMnTi. What is the difference? I am having difficulty finding a direct comparision. I have read the thread thread367-143938 but did not know if their application used gears similar to size as ours.

Thanks.

Steve

 

[Goahead]

As you are dealing with large and thick gears, in order to obtain suitable core properties your material has to provide sufficient hardenability. This quality will assure adequate strength and impact resistance in the volume with the least cooling rate.
At a minimum you could ask for Jominy test profiles for the proposed material and compare it with those of the steels you know and trust.

http://www.welding-advisers.com/

 

[arunmrao]

C 0.21, S 0.017, P 0.02,
Mn 1.0 , Si 0.26, Cr 1.19, 'Ti 0.03, Cu 0.95,balance Fe . A google search provided the chemistry of 20CrMnTi.

This chemistry indicates no Mo and the presence of Ti may be more as tramp. Normally there have bben attempts to replace Ni by Cu,hence the nearly 1% Cu presence.

It is advisable to specify 4320 or 8620 alloy.Most of the Chinese companies seem to be popularising 20CrMnTi.

Why did you not explore the possibility of sourcing from India? Cost/availability??

 

[CoryPad]

The Chinese grade does not use Ni or Mo, which are common to USA alloys due to higher availability of ore. Rather, the Chinese alloy uses Cr, which is common for Asian alloys.

These are obviously carburizing grades, so the core properties are not likely to be as important as the surface.

What are your requirements for properties?

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[dbooker630]

I am also seeing more use of 20MnCr5 (similar to SAE 5120) from our forge source in India. Again the push is to get away from the NiCrMo grades whenever possible due to the cost of nickel and moly. There is a lot of activity in trying out 41xx and 51xx grades these days.

Depending upon core properties desired, and since this is a large gear, you may need to restrict the chemistry/hardenability to the high side somewhat so there is not too much dropoff in performance from the NiCrMo grade.

 

[arunmrao]

20MNCr5 is a popular forging grade steel in India in the earth moving equipment industry.

But as is suggested Ni and Mo are absent. But since it is a large gear forging suggest Ni and Mo additions in the alloy selected.

 

[SZ9]

First, thanks everyone for thier input.

Now:

Arunmrao: We have looked into companies from India and in fact have some parts from them. However, we are interested in exploring China because they may be able to outsource other parts as well. However, if you have a reliable source in India and are open to sharing that with me, it would be appreciated.

CoryPad: the gears need to be able to be hardened to 56-62 Rc. They are used for a low speed, high torque application. Torque ~ 280,000 ft-lb.

dbooker630: so, there is indeed a drop off in performance? What about wearability? The important part is the gear tooth life as changing a broken gear is time consuming and costly. I doubt the gear would fail from the core, but rather from the tooth. Am I correct in this assumption?

Again, thanks for all your help everyone.

Steve

 

[arunmrao]

SZ9
If you give me some more details perhaps I can suggest a few more Indian companies. My business line is steel castings .

 

[CoryPad]

Your only requirement is that the hardness must lie within the range 56 HRC to 62 HRC? Measured where? After what hardening process?


Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[dbooker630]

When I tested 20MnCr5 vs 4320/8620/8627 I used a chemistry that would fall into standard bands for those 43 & 86xx grades. That's what was available, and it tested fine.

The 20MnCr5 hardenability band extends well below the mins for 4320 and its max is typically 4 points below 8620.

I cannot say for sure that there will be a dropoff but I did not want to take the chance of allowing the use of the full band of material without testing a low side chemistry.

 

[SZ9]

CoryPad: Our drawing specifies carburized and hardened to 56-62 Rc and that it is AMGA level 6. I assume the material specification will take care of the rest. Am I wrong? The gear is used in conjunction with 2 others...one of which is the driving pinion gear. Our biggest fear is breakage of a tooth or failure, which often breaks the other gears in the gearbox.

dbooker: thanks for the info. I will ask the company if they have this material. Any other suggestions for material substution?

Steve

 

[Yallapragada1022]

What is the core hardness specification?

Standard hardenability bands may or may not work for you. You need to pay attention to the core hardness that you have been getting using the current material. Based on the hardenability of the current steel, you can figure out the equivalent J position for the core hardness and make sure that 20CrMnTi has enough hardenability to meet your core hardness requirements. You may have to specify the hardenability band and D.I. that you can live with to obtain the core hardness.

Hope this helps.

Rao Yallapragada