Welding Hardened SUS 440 to SUS 304?

By ravi theCobra (**)

Date 01-25-2010 16:57

How hard do you need the 440 C to be ?

By Gerard Kennedy Date 01-26-2010 08:11

The 440 is already hardened to 54-56 HRC (Rockwell Scale)

By labib

Date 01-26-2010 16:46

Is it dissimiler steel? If yes..... you can weld hard steel of about 55RC to unhard steel(mild steel) by MAGNA 303G - This one electrode welds virtually every type of steel in existence successfylly.

By ravi theCobra (**)

Date 01-26-2010 19:52

What is the geometry of the two parts ? Where do you need the hardness ?

By jarcher (**)

Date 01-27-2010 03:07

Like most things in welding, depends. What do you want to do with this joint? It seems like an odd combination, 440 A, B, or C in the hardened condition is a martenistic stainless used primarily for its wear resistant properties and moderate corrosion resistance, whereas 304 (18-8) is an austenetic stainless used chiefly for its corrosion resistance. The yield for 440C fully hardened is around 200K yield, while 304 would normally come in around 30K. Welding should be possible, but not easy, the 440 has a carbon content of ~ 1.0%, making a high preheat mandatory. Further, welding would very probably interfere with the hardened condition of the 440 in the area of the weld. Brazing might be a better way of joining. With proper filler selection, a braze should be able to develop 40-45K ultimate tensile, which would be close to the UTS of the 304.

By Superflux (****)

Date 01-27-2010 06:04

In the "For What it's Worth department".

When I was making knives, I would weld 304 "guards" to my blades with 308L on 440C and ATS34, then PWHT and differentional harden with no complaints from customers. I also made personal throwing knives (this is SEVERE SERVICE!) with no catastrophic failures.

I am fraught with anticipation to hear of the results of this inquiry.

By Gerard Kennedy Date 01-27-2010 11:27

OK, details.
The parts are to be used in a machine assembling a medical device.
The Hardened 440 piece is a wedge shaped piece for opening a plastic clamp by sliding it down the wedge.
As this is a pharmaceutical application particle generation is not good so hence the hardened steel.

The 304 is the mounting arm for the wedge as it's not product contact it does not need to be hardened.

The arm slots into the wedge in a tenon joint effect. The arm end is 4mm x 23mm (Width X Height) and sits
5mm into the wedge which has a matching slot cut into it. The minimum wall thickness of the wedge around
this slot is 2.5mm. I would post some pictures but the man upstairs says "NO".

We had the two pieces made before some one realised the weldability hadn't been checked. If there's going
to be problems welding them that any of you know of at least I can tell the boss why.
The alternatives as I see it are:

Brazing as suggested above (Would the braze be suitable for a pharma environment?)

Use a hardened steel for both parts (but is welding hardened steel a problem regardless of the mating part? I
have seen some comments elsewhere on it causing cracking. Also there's the effect on the materials hardness.
The immediate area around the weld is not "product contact" but the overall piece thickness (max 20mm) means
I can only imagine that the effect would spread through most of the piece)

Use hardenable steels, weld them 1st and harden after? (Is that even possible?)

These two pieces of tooling are more complex than they sound above and costing a small fortune to make
so if there's remakes needed after a screw up I may not be getting paid for a while.

Thanks for the help so far, keep it coming please

By jarcher (**)

Date 01-28-2010 08:54

Thanks for the detailing.

Here's my thoughts for FWIW:

1. Brazing with a well designed joint fit up should be fine for your application, as long as the filler contains no toxic materials, e.g., lead, cadium. Bronze or most silver solders should not be a problem. Use a filler with a melting point <760 C and use 304L for the 304 side of the joint.

2. Welding two hardenable steels is possible. There are formula's to determine the preheat needed according to the CE and the rate of cooling needed, unfortunately a HD crash has cost me the links I could point you to online, maybe somebody else will have them.

3. Welding with your current material is possible, though you will want to be sure to use 304L, since sensitization could occur otherwise. I would say GTAW with 308L filler would produce the desired results. Yes there will be some annealing in the HAZ on the 440, but you indicate that hardening in that area is not critical, so if I understand the joint correctly, it shouldn't be an issue.