The Damascus Project

                                                                             Lunar Steel Making

Many possibilities are raised herein. Errors are sure to exist. Irregardless of those errors, and no matter how iron is obtained on the Moon, it has to be combined with some carbon to strengthen it and then converted to steel. Is it possible to take pure iron, melt it in a solar furnace, "sprinkle" carbon dust over it and agitate somehow to form steel? Easy as cooking a peppered slab of beef in a microwave oven... Or are the ferocious temperatures of the blast furnace the only way to make liquid iron take up carbon uniformly, combine chemically with the carbon, and form cast iron, white or grey? Or is a blast of hot oxygen on top of red hot molten cast iron thru a lance the only way to make steel? There is blister steel made simply by heating iron and carbon, but this is a slow  process.

Steel making is thus an impressive process, and soft pure iron is turned into the hard metal that cars, excavators, tools, bridges, railways and machines of all sorts are made of ? We cannot mine the Moon with aluminum or magnesium mining shovels and bulldozers. Those fly weight metals are too soft. They are fine for airplanes and rockets, but they are not the stuff of ships or skyscrapers. Ninety five percent of the metal produced on Earth is steel. Aluminum is in second place followed by magnesium. We make millions of tons of steel every year but only about 30,000 tons of magnesium. That's how important it is. On the Moon it will not rust in the vacuum and even mild steels will be strong in the low gravity. But to drill or chip through rock or make good tools we will need good steel, as good as anything on Earth, but first we just have to get steel. Without it, there will be no industrialization of the Moon, no mining, and no space future. We will never colonize Mars without the Moon and we not reach the stars centuries from today either. The shining Moon, the shining stars, depend upon shining steel.

Unless you can beat a blast furnace, here are some ideas.

What is steel?

Steel is an alloy of iron and carbon, often mixed with other elements. Steels contain 0.04% to 2.25% carbon. Cast iron, malleable iron, and pig iron contain 2% to 4% carbon. The properties of steels at different temperatures depend on the amount of carbon present and how it is distributed.

Before heat treatment most steels consist of a mixture of ferrite, pearlite and cementite.

Ferrite contains small amounts of carbon and other elements in a metallic solution (yes, the carbon is dissolved in solid metal) and is soft and ductile. Cementite contains about 7% carbon. It is very brittle and hard. [Most of the iron exists combined chemically with carbon as Fe3C. Atomic mass iron = 56 56x3=168 carbon = 12 Fe3C = 180 12/80 = 0.07]

Pearlite is a mixture of ferrite and cementite. Depending on the proportions of ferrite and cementite, pearlite has a structure and physical characteristics somewhere between the structure and characteristics of its two constituents.

The toughness and hardness of steel that is not heat treated depend on the proportions of these three ingredients.
White cast iron is mostly cementite. It is made by sudden cooling of liquid iron from a blast furnace. Grey cast iron is mostly ferrite. It's made by slow cooling.

As the carbon content of a steel increase, the amount of ferrite decreases and the amount of pearlite increases until, when the carbon content is 0.8% the steel is entirely composed of pearlite. Steel with more carbon becomes a mixture of pearlite and cementite.

Heating the steel changes the ferrite and pearlite to a form of iron-carbon called austentite. All the free carbon in the steel gets dissolved. If this metal is cooled slowly the austentite reverts to ferrite and pearlite. If cooling is sudden the austentite is "frozen" or changes to martensite, an extremely hard steel. Martensite resembles ferrite but contains more carbon is solid solution.

When hardened steel is tempered by mild reheating the martensite transforms to more stable phases. These changes are complex, but the result is the formation of grains of ferrite and cementite.

When steel with 0.8% to 0.9% carbon is tempered it changes into pearlite. Tempering steel with less the this much carbon changes into a mixture of ferrite and pearlite grains on the microcrystalline level. With more the 0.9% carbon tempering yields a mix of cementite and pearlite.

Case-hardening gives steel a hard surface. Medium carbon steel is heated in contact with carbon or sodium cyanide until a thin surface layer is converted to high-carbon steel that can be hardened with heat treatment. Some alloy steels are heated in an atmosphere of ammonia to form a surface layer of metal nitrides.

These microcrystalline structures in steel can be seen with a microscope at 100x to 1000x. Good optical microscopes can magnify up to 900x and 1000x with an oil drop lens. With UV optical microscopes can reach 2000x. Electron microscopes can even see large molecules and large atoms.

IDEAS

Could store liquid oxygen in buried vaults  with thick iron liners cast in molds of sintered basalt. Regolith is a good insulator. There isn't enough chromium or nickel on the Moon for stainless steel cryogenic liquid storage tanks. Thus, we may have to do things in more pimitive ways on the Moon. 

Naturally we will start out with small furnace systems and build bigger ones later. We aren't going to build anything huge right away. 

Why the CaO flux? To react with the SiO2 in the minerals to form slag (CaSiO3) to get the silicon away from the iron. A little SiO2 (1-2%) is added to the charge to prevent SiC formation. Also, the slag floating above the molten iron prevents oxidation of the iron.

Where do we get the CaO? Acid leaching of anorthosite?  Or is there another way?  Reoxidation of calcium from fluxed electrolysis.  This would require upporting LiF and CaF.  Fluxed electrolysis operates at lower temps than molten silicate electrolysis but there will be corrosion problems.  Silicon, oxygen, aluminum and calcium can be obtained by fluxed electrolysis of purified anorthosite (CaAl2Si2O8).  Apollo samples showed that highland regolith consisted of 75% to 95% anorthosite.  Si for solar panels. Al for wires, cables, light weight structures.  Ca for electrical cables with less resistance than copper and by reoxidation-CaO. 

Wild eyed idea-carbothermal reduction of pure anorthosite.  Could it yield CaO as well as Al/Si alloy or just slag?

It's gonna take cubic money. The bottom line.
Proceeding from faulty assumptions leads to sophistry.  Mistakes not to repeat...
David A. Dietzler, 2007