Weldabilty vs. hardness 2

[rselby7]

The quick version:
Is it possible to weld hardened 1045 to 1015 without damaging the surface hardness of the 1045 about 1-1.5 inches from the 1-inch long weld? What process?
More Details:
I am designing a cogged latching mechanism for a seat rotation mechanism to be built in Taiwan. The seat must support a 300 pound user through 30 degrees of rotation(5 deg down on seat bottom through 25 deg up). The mechanism must withstand 10,000 cycles. The teeth size and area of engagement are large enough that I am not concerned with them shearing. Teeth should wedge together to eliminate "backlash". I will assume some impact load at the teeth surfaces during engagement so I want them hard to avoid surface deformation or wear. The teeth are on 3-4 inch long 6mm thick(1045)plate, they are attaced to the side of a 6mm thick, c-channel shaped, bent-metal (1015) plate.
From reading Shigley and Mischke, best welds occur 1015-1023 although any carbon steel can be welded with degredations of properties. From another source, it says that welding case or through hardened steel tends to leave you with a poor/brittle joint. Screws and rivets are out due to alignment/slop issues across the two bends that form the c-channel.

 

[BillPSU]

The weld will probably not affect the hardness of the teeth because of the distance assuming the weld size is about 6-8mm in size. You will probably have to preheat the parts to avoid cracking in the weld. Having the parts welded overseas would be a concern because they may weld parts without preheating and have parts fail prematurely while the samples or several previous runs were fine.

 

[metengr]

rselby7;
Several more detail questions;
1. What is the hardness of the 1045 plate?
2. Is it surface hardened or thru-hardened?
3. If it is thru-hardened, why is it necessary to have it thru hardened when it is being welded to a low carbon, lower strength C channel?
2. Where exactly is the 1" weld located relative to the 1045 carbon steel plate, teeth and C-channel, and what is the weld orientation?

AISI Type 1045 carbon steel is weldable using any of the common processes (GTAW, SMAW...) but because of the carbon equivalent it will require a local preheat.

 

[rselby7]

metengr:
1 and 2. I had assumed it would be through hardened since I thought moderate carbon content steel lent themselves to through hardening. The translated Taiwan drawing says Carburized with no hardness callout.
3. The hardness is desired because we want to avoid wear at the teeth surfaces when they engage/disengage.
4. A picture is worth a thousand words, but since I do not know how to post a picture here...The bent 'C-channel' (1015) has 4 inch long legs and a 6 inch wide web. It is 12 inches long and the material is 6mm thick. The teeth are on two tabs (1045) welded to the legs and sticking up 2.5 inches from the web face. Overall tab shape is roughly a 4in x 1.25in x 6mm rectangle. This leaves an overlap of 1.5in x 1.25 in. There are 8 large teeth along one long side of each tab which go from the away from weld end to within 0.5 in from the web surface. There will be a fillet weld along the bend between the web and legs, and an additional fillet weld(s)between the tab and the legs. Welding is highly desired because with it allows us to align the teeth across the c-channel seat carrier so they mate nicely with the engaging teeth on the seat.
Thanks for your input.
Ryan

 

[metengr]

Ok. I would be concerned about depositing a weld fillet on a carburized surface layer because of underbead cracking - that is the reason for asking about the method of hardening. You might want to check the hardness of the tab to see if the entire surface of the tab has been carburized or just the teeth. If the entire tab has been carburized, you might want to locally remove (grind) the surface layer where the fillet welds will be located. This would help to improve weldability. A thru-hardened tab is weldable following the information below.

I would recommend a local preheat of 300 deg F that would be applied to the AISI 1045 material. The filler metal for welding should be an E7018 H4 (low hydrogen)electrode. The trick is to keep the interpass temperature during welding below 600 deg F, to avoid disturbing the carburized teeth.

After your done welding, slow cool and perform a Liquid Penetrant (PT) or wet fluorescent MT inspection of the welds and surrounding base metal.

 

[rselby7]

Thank you very much, metengr.
That gets me way further down the road.
Regards,
rselby7

 

[Carburize]

Be careful with the pre-heat and interpass temperature - it is likely that the part was tempered at around 300 - 325F after carburizing so any heating above this range will soften the carburized surfaces and reduce their wear resistance.