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Comment by lazide | Hacker News Reader

Hydrogen is well known and studied to cause many issues with steel, generally brittleness and crystal structure defects. In situations where it’s important that cracking doesn’t occur, it’s common for low/no hydrogen electrodes in welding be required, for instance.

That using a method of production that naturally exposes it hydrogen would produce higher quality steel is surprising! We should still definitely have a link to the study!

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For what it's worth to reduce surprise/skepticism, a hydrogen atmosphere is already commonly used for annealing electrical steels (eg. motor laminations or magnetic parts).

https://www.tlclam.net/annealing-process/

https://www.vac-met.com/hydrogen-annealing/

This is a process for refining iron ore, as opposed to using a blast furnace, or using the same process with decomposed natural gas instead of just hydrogen. In steel production it would be subsequently smelted.

Do you think that removes the concern? I don’t see how it would.

This process produces sponge iron, which is then fed into an electric arc furnace. There is no free hydrogen around at that point. Whatcomes out of an electric arc furnace is carbon steel.

The issue with hydrogen, which was first noted IIRC in the high-pressure Haber-Bosch ammonia production process, in which H2 and N2 at high pressure over a catalyst in a steel chamber forms NH3, is that free hydrogen reacts with the carbon in the steel under these conditions, which caused the pressure chambers to regularly explode (solution was a sacrificial lining of the chambers which was regularly replaced). For low-pressure H2 it may not be much of a problem, but that's not very efficient for transport.

Thanks for the background! So likely due to the complete remelt and re-alloying expected, it should work out?

Speaking of ammonia, any thoughts to share on an ammonia economy vs hydrogen economy? The former seems a lot more practical.

Ammonia as fertilizer is the only ammonia economy that makes sense; hydrogen economy doesn't make much sense either. Methane economy is the optional long-term solution for chemical energy sources, just CO2(atm) + H2 (water) -> CH4.

Ammonia combustion generates NOx smog, and ammonia is pretty toxic to store and transport as a gas. For fertilizer it's stored as (NH4)(NO3) or similar.

Hydrogen production has a few major use cases, but replacing natural gas is not one of them. Iron reduction, nitrogen reduction, carbon reduction, in industrial settings, is about it.

Thanks!

This process produces direct reduced iron, not steel.

What do you think Steel is, but reduced Iron (to a specific level)?

Cast Iron is also impacted by hydrogen embrittlement, albeit iron is usually already pretty brittle so folks don’t use it where that kind of failure matters as much.

It produces an intermediate product. You can't use it without further processing. In any case, the hydrogen won't be a problem.

You mean, cast iron is pretty brittle. Pure iron is not brittle.

If you're talking pure iron, then yes - it's very ductile and malleable. However, the low end of carbon allowed while still calling something steel is .3%, so with a few exceptions (wrought iron, which is arguably very soft steel), it's rare to run across it.

There are of course ways to treat cast iron so it's decently durable (ductile iron), but it's still pretty brittle compared to 99% of steel in the real world.

> low end of carbon allowed while still calling something steel is .3%

Incorrect. That is the maximum for low carbon steel (also called mild steel - the most common form of steel).

Wikipedia says “The carbon content of steel is between 0.002% and 2.14% by weight for plain carbon steel”. “Plain carbon-iron alloys with a higher than 2.1% carbon content are known as cast iron.”

https://en.m.wikipedia.org/wiki/Steel

https://en.m.wikipedia.org/wiki/Pig_iron

https://en.m.wikipedia.org/wiki/Cast_iron

https://en.m.wikipedia.org/wiki/Carbon_steel

https://en.m.wikipedia.org/wiki/Alloy_steel

https://en.m.wikipedia.org/wiki/Iron

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