4140 - Impacts 1

[MetalsInc]

This is a follow up to this thread....

http://www.eng-tips.com/viewthread.cfm?qid=79829

I'm looking to achieve:
UTS - 180 ksi
YS - 150 ksi
HRC - 36 Minimum
Charpy - 60 J

Looking at the thread above I'm thinking of a Quench and double temper around 950F. But there was no mention of the impact values. This is a one-off part so the usual development is not practical.

Tubular part with WT ~0.75" and about 6" OD.

 

[metengr]

Regarding your stated conditions;
At what temperature do you need 60J CVN impact energy?

You might want to consider AISI Type 4340 alloy steel - quenched and tempered.

 

[MetalsInc]

The 60J CVN is for room temperature.

The trick here is that this part has to be welded on and can't be heat treated (beyond a PWHT) after welding.

 

[metengr]

From the data I have seen you will have less than 40J CVN impact energy @ 23 deg C for 4140 quenched and tempered (actually the impact data of 40J was for a lower strength UTS of 120 Ksi Q&T). At your stated strength levels and impact requirement, you need an alloy steel with Ni added to assure strength and adequate toughness, and good weldability, like AISI Type 4340.

Welding in this high strength condition will present a serious challenges. Off-hand, if you were to upgrade to an AISI Type 4340 alloy steel tube, the top end filler metal that you could use without any form of PWHT is probably an SFA 5.28 ER120S-1 weld wire. The tensile strength will be 120 Ksi minimum, as welded, which will be less than 160 Ksi UTS. You will have to decide if you can accept this material in your design, or modify the component design to reduce service stresses. Other options include fastening versus welding.

If you decide to weld, the welding should be performed using the GTAW process with a 450 deg F local preheat. The GTAW process will provide a better chance of maintaining base metal HAZ impact properties. The ER120S-1 weld metal toughness will be well above 60J at RT. Use stringer beads with about a 50% bead overlap to sequentially deposit the weld. The reason for this technique is to attempt to soften the base metal heat affected zone using heat from well placed stringer beads. Keep the interpass temperature below 600 deg F. After the completion of welding, slow cool and perform a wet fluorescent MT.

 

[MetalsInc]

Thanks for the input. I have been questioning the material choice. I'm not satisfied that the customer really needs properties that are that high. It has been suggested that they are "starting high" so that the reduced properties after welding will be good enough. Enough said.

I'll make some suggestions and let you know what happens.

 

[stanweld]

Have you considered Electron Beam welding this part? High strength 4140 and 4340 tubular and bar fabricated shafts have been EB welded followed by PWHT at an appropriate temperature.