Carefully attaching Pt-wire to mild/carbon steel surface

Question

Problem:

I have a near 100% Pt wire (25 AWG / D ≈ 0.45mm) that I would like to attatch to a cold rolled steel (E235 / EN 1.0308) surface. Assume this surface is flat.

Goal:

• Keep wire attached to the surface for ~3 minutes while temperature sinks from 800C to 500C. The wire is not carrying any load except its own (max 20 cm).

While:

• Minimizing added heat capacity / mass
• Avoiding gases up to 1000C (so no tape)
• Thermal conductivity
• Minimizing steel tempering (solidus ~1420C)

Thoughts:

I have considered soldering/brazing with a silver alloy (mechanically weak, but strong enough?). I soldered an iron wire onto the same surface with 60/40 Sn-Pb soldering wire in 20 seconds and achieved a solder strong enough to lift the entire test object (over one kilo) and bounce it around. Looking briefly at the metallic and atomic properties of Pb/Sn and Ag, I'm hoping silver will bond even stronger with the steel surface. I assume I should also be trying to dissolve/reduce the oxidation layer on my steel before and during the soldering.

I've also been thinking an Al-Mn alloy can be easily made with a perfect melting temperature, achieve a BCC crystal structure (like my steel), and hopefully create a stronger bond to the steel. Is this a realistic approach? I have no experience with obtaining this, its price and the overall doability. I'm also unsure of whether corrosion makes an aluminum alloy unsuitable for this brazing technique.

I have previously considered welding the platinum straight onto the steel, but I assumed this would have a major impact on the mechanical strength of my steel.

Question:

Does anyone have a good way to solve this that is preferably swift, simple, repeatable and does not require expensive machinery (2000 USD+). I already have soldering, brazing and TIG/MIG/stick welding capabilities.

Answer 1

I think you are asking how to attach a Pt wire to carbon steel for a short time at 800 C /1472 F. I expect a plain carbon steel weld, like MIG, would do it. It may not melt the Pt during the few seconds of welding ; the Pt would be mechanically attached by the weld deposit . Keeping in mind that Pt thermocouples are routinely used to measure molten steel temperatures above 3200 F. Because your steel is "cold rolled" , not heat-treated , strength properties of the weld HAZ will not change significantly; trading cold rolled ( strength ?) for a fast normalize. PS - "solidus" has nothing to do with tempering steel.