In the context of the cut-off system model (for more information, please refer to the ecoinvent website) the secondary use cycle of a material starts at the point of waste collection (e.g. steel scrap collected from households), while the point of cut off is the recycling activity. Hence, the supply chain for secondary materials (produced through recycling activities) includes their collection and recovery (sorting and dismantling), which is why secondary products are often not wholly burden free. For steel, this means that the collection and recovery of steel scrap would be included but that the recycling of recovered steel scrap in an electric arc furnace is “cut-off”.
The products “waste reinforcement steel” and “steel scrap”, that you mention in your email, are both wastes. Waste reinforcement steel is treated through one of three activities: “treatment of waste reinforcement steel, recycling”, “treatment of waste reinforcement steel, collection for final disposal” or “treatment of waste reinforcement steel, sorting plant”. The system boundaries of the inventories includes on-site energy use for dismantling and sorting, plus transport and disposal. No bonuses or burdens are given for recycled material and no secondary products are available; i.e. the system boundary cuts off the recycling process entirely. Similarly, “scrap steel” can only be treated by either landfill or incineration; it never goes to recycling.
So how can secondary steel products be included in an inventory? The collection and recovery of ferrous scrap is included in the ecoinvent database through the “iron scrap” recycling chain, not “steel scrap”. This is, obviously, not ideal and can easily lead to confusion: despite being ostensibly the same, “scrap steel” is a waste that is sent for disposal; “iron scrap” is a recyclable that is collected and recovered for recycling.
The collection of “iron scrap, unsorted” is represented by the activity “iron scrap, unsorted, Recycled Content cut-off”. This is then sorted and pressed in the activity “sorting and pressing of iron scrap”, which produces “iron scrap, sorted, pressed”. The sorted iron scrap is then made available, burden-free, for its secondary use cycle by “iron scrap, sorted, pressed, Recycled Content cut-off”. “Iron scrap, sorted, pressed” is consumed, burden free, by the activities “steel production, electric, chromium steel 18/8” and “steel production, electric, low-alloyed”, which represent the production of steel products in an electric arc furnace from ferrous scrap.
How one might include an input of 95% recycled steel: 95% of the steel used in your inventory should be “steel, low-alloyed” or “steel, chromium steel 18/8”, supplied directly from the activity “steel production, electric, low-alloyed” or “steel production, electric, chromium steel 18/8”, respectively. The remaining 5% can come from “steel, low-alloyed” or “steel, chromium steel 18/8” that is supplied directly from “steel production, converter, low-alloyed” or “steel production, converter, chromium steel 18/8”, respectively.