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Separate the unlock from the production line
Steel processing unlocks smelting iron plates into steel. First check the technology is completed in your actual save; a furnace connected to belts cannot bypass a missing technology. Modded research trees and alternative Space Age recipes may differ.
Iron ore and iron plates are not interchangeable at the steel stage. The ordinary route first smelts ore into iron plates, then supplies those plates to another furnace. Give burner furnaces appropriate fuel and arrange output removal; inspect each buffer rather than assuming every full-looking belt reaches the machine.
- Confirm Steel processing is complete and inspect the steel recipe shown in your game.
- Produce iron plates upstream and deliver them to a furnace with accessible fuel.
- Check the furnace input, progress and output inventory; if finished steel cannot leave, inspect the destination before increasing input.
- After changing one constraint, observe the same machine and record whether its steel output resumes.
References: Factorio Wiki: Steel processing · Factorio Wiki: Steel plate · Factorio Wiki: Stone furnace
A four-furnace planning example
Assume four ordinary-quality stone furnaces are continuously making steel with enough fuel and iron, no productivity bonus and no idle time. Each consumes five plates over 16 game-seconds and produces one steel. Four therefore require 1.25 iron plates per game-second and have a theoretical output of 0.25 steel per game-second.
Suppose the iron line actually delivers only 1 plate per game-second to this dedicated steel line. Recipe arithmetic limits sustained output to at most 0.2 steel per game-second before considering transfers, fuel and stoppages. A buffer may temporarily hide that shortage. This is a constructed calculation, not a measured factory.
| Assumption | Iron input / game-second | Steel output / game-second | Interpretation |
|---|---|---|---|
| One full-rate stone furnace | 0.3125 | 0.0625 | Theoretical machine rate |
| Four full-rate stone furnaces | 1.25 | 0.25 | All four fed continuously |
| Four furnaces; supply limited to 1 iron/s | 1 | At most 0.2 | Iron is an upper bound; other constraints can lower output |
References: Factorio Wiki: Steel plate · Factorio Wiki: Stone furnace
Find the first broken boundary
Start at the steel furnace: a lack of plates calls for tracing input upstream; a full steel output calls for checking the next inserter or container. If the furnace is inactive with fuel absent, adding an ore miner is not the first correction. A full input buffer is not proof the next stage can accept the output.
When sharing iron with other factory lines, the relevant number is what reaches the steel line over a sustained interval, not total smelter capacity elsewhere. Use a stable count over game-time and account for changing inventory; this guide does not supply a tested splitter layout or inserter rate.
| Observed boundary | First check | What would change the diagnosis |
|---|---|---|
| Steel furnace has no iron plates | Trace plate path and upstream smelter output | Plates present but furnace still idle: check fuel and research |
| Fuel slot empty | Confirm valid fuel reaches this furnace | Fuel present and output full: inspect removal |
| Steel output backed up | Inspect next inserter and destination capacity | Destination clear but no new output: inspect input and fuel |
| Buffers drain over time | Compare dedicated iron supply against five plates per steel | Short observation may reflect a temporary buffer, not steady state |
References: Factorio Wiki: Steel plate · Factorio Wiki: Stone furnace
Record a useful before-and-after test
Record the game build, installed mods, furnace type and count, observed iron input, fuel state and steel output before a single change. Repeat with the same observation interval and note whether inventories are rising or falling. An idle or blocked furnace cannot be treated as delivering its theoretical maximum.
If the recipe or machine quality in your version differs, use the values shown in-game and recalculate. Do not use the ordinary-furnace example for foundry casting or a productivity-modified recipe.
Build and mods:
Furnace type, quality and count:
Iron available to this line / game-second:
Fuel and output state:
Observation interval and inventory change:
One change and observed result:Before you play
- Confirm Steel processing is complete.
- Supply iron plates, not raw ore, to the steel stage.
- Budget five iron plates per steel under the basic recipe.
- Inspect fuel and the output path before scaling.
Frequently asked questions
Why does a steel furnace line consume iron so quickly?
The ordinary recipe uses five iron plates per steel plate. Check the actual iron available to the steel line, especially when other consumers share it.
Will four furnaces always make 0.25 steel per second?
No. That is the theoretical rate for four ordinary stone furnaces at full uptime under the stated assumptions; missing input, fuel or blocked output reduces actual production.
Does this cover the Space Age foundry?
No. Foundry casting is an alternative recipe with different inputs and bonuses; inspect it separately.
Sources & revision notes
Editorial revision: October 28, 2026; not a gameplay test date. The reference notes identify source limits and version differences.
- Factorio Wiki: Steel plate (Community)
Community-maintained reference checked October 28, 2026 for the five-iron, 16-second basic recipe and alternative foundry recipe.
- Factorio Wiki: Stone furnace (Community)
Community-maintained reference checked October 28, 2026 for ordinary furnace speed and theoretical output; not a measurement of this layout.
- Factorio Wiki: Steel processing (Community)
Community-maintained technology reference checked October 28, 2026 for the steel unlock; check modded research separately.
Added a local iron-supply calculator to the source-based recipe budget and boundary-by-boundary diagnostic; outputs are theoretical bounds, not recorded production.
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