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This article has not been revised for the current version (U40-494396). It was last updated for LU-356355. It may contain inaccuracies.
This article has not been revised for the current version (U40-494396). It was last updated for LU-356355. It may contain inaccuracies.

Liquid Steel is the Liquid state of Steel. It has the highest thermal conductivity and largest thermal range of any liquid, making it ideal for complex high-temperature processing.


Liquid Steel is produced by heating Steel to 2429.85 °C. The easiest way to do this is to run a Kiln in a vacuum, though care must be taken that its contents do not exchange heat with the steel upon melting.

Cooling a full Pipe of Water with a Steel Thermo Aquatuner in a vacuum will displace enough heat to melt the Aquatuner before the overheat damage breaks it, as long as it remains powered.

Buildings constructed from both Steel and Plastic will convert completely to liquid steel when melted. The Germ Sensor, Liquid Pipe Germ Sensor, and Gas Pipe Germ Sensor are the most effective way of doing this, all converting 50 kg of plastic to metal per tile, and melting quickly due to their low mass.


Diamond is the only buildable material capable of holding maximum-temperature liquid steel indefinitely. Airflow Tiles containing a Vacuum can also function as a tank, but will melt almost instantly on exposure to gas (or if placed in the cell directly above the liquid). Natural tiles made of Refined Carbon can also be produced by heating Coal.

In practice, Insulation serves as an upper bound on the temperature of liquid steel as a working fluid, as it will melt at 3624.85 °C, though this can be partially offset by alternating packets of high- and low-temperature fluid. Tungsten further restricts the use of Radiant Liquid Pipes to below 3421.85 °C, or 2679.85 °C for Thermium - while the alternating fluid bypass can also be used here, it still serves as a limit on the average temperature, which is what's relevant to heat exchange.

No Liquid Pump can be submerged in even low-temperature liquid steel without overheating, so a tricked pump is necessary to load it into pipes without heavy resource use (repairs) or manual labour (repeated rebuilds).


Nothing directly consumes liquid steel, but its thermal properties make it an ideal means of conducting heat at high temperatures. The primary uses for this are melting solids, gaining advantage over machine processing:

  • Melting any natural tile will produce 100% of its mass as liquid, compared to 50% mass as debris from mining. Note that this is not always reversible - Metal Ore will produce Refined Metal when cooled, and any Raw Mineral will become Igneous Rock.
  • Melting Sand will produce 100% of its mass in Liquid Glass, 4x the 25% mass output of the Glass Furnace (8x if used on unmined natural sand tiles) without any duplicant labour.
  • Cooking natural Clay tiles will convert 100% of tile mass to Ceramic, which then drops to 50% when mined. Mining the clay (50% loss) and then firing it to ceramic in a Kiln ends in the same ratio of clay to ceramic, but also requires Coal.
  • Abyssalite and Insulation can be melted into Liquid Tungsten, though radiant pipes cannot be used.
  • Melting Thermium separates it back into Liquid Tungsten and Liquid Niobium in the same ratio used to produce it.

Melting various materials and taking advantage of changes in specific heat capacity allows the conversion of minerals directly to heat, and thus to energy. As the generated heat is in the form of thermal mass, not an increase in temperature, this still requires an external heat source - it can't be directly used to heat the main liquid steel loop.

  • Melting Regolith into Magma at 1414.85 °C multiplies its heat content by 5, producing
  • Obsidian is generally harder to source than regolith, but has a similar reaction at the much higher temperature of 2726.85 °C, resulting in 2181.48 kDTU/kg.
  • Salt Gas condenses to Molten Salt at 1461.85 °C. Re-boiling that molten salt by raising it to 1467.85 °C requires less heat than was moved in condensing it, due to a change in SHC. Unlike regolith or obsidian this method does not require input materials, and acts as a flat 1.26x heat multiplier. This also makes molten salt useful as a "transformer", transferring heat from high-temperature pipelines through gas into lower-temperature pipelines or thermal storage before being fed to turbines.

Heat Sources[]

The simplest heat source for any liquid steel setup is the Metal Refinery, the only machine capable of working on a fluid which is in pipes and increasing its temperature arbitrarily. Rocket engines also transfer a fixed amount of heat to the tiles below them; using diamond Window Tiles and tungsten radiant pipes can capture and transfer this heat to the liquid steel system.

In Spaced Out!, a Research Reactor with limited coolant can produce extremely high-temperature waste, allowing for a steady heat source which does not require manual intervention or duplicants.