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Life cycle of steel products
and recycling

Life cycle and recycling of steel products

Steel products with a wide range of properties and shapes are produced through a series of processes, including reduction of iron ore, smelting, rolling, heat treatment, and surface treatment. Steel products are then transformed into durable consumer products such as cars and home electric appliances large transportation equipment such as ships and trains, containers for beverages and food, various machines and plants, and social infrastructure such as buildings and bridges, which are the final products. After these products have completed their role in society, almost all of the steel used as materials is recovered as scrap and reused as raw materials for new steel products.

As a result, the amount of natural resources used is reduced, and energy consumption and environmental impact are greatly reduced. The steel products are then reused as raw materials for new steel products, such as cars and buildings, and one day they are collected as scrap again. Steel products have always been recycled efficiently through this kind of closed-loop recycling.

Figure 1: Life cycle of steel products

Life cycle of steel products and recycling

Figure 2: Steel Material Flow in Japan

Fig. 1. Steel Circuit of JAPAN.(Online version in color.)

The prerequisites for sustainable recycling of materials

There are five requirements for sustainable recycling of materials. As shown below, steel is a material that fulfills all of these requirements.

  1. (1)Easy separation and collection of the material

    Almost all industrial products are made up of multiple materials. Therefore, in order to recycle materials, it is extremely important to be able to easily separate them from other materials (to dispose of them separately) and sort them (to select them from a mixture). Since steel is the only industrial material that is magnetic, it can be easily separated from other materials and metals by magnetic sorting, and even small pieces of steel contained in shredder dust (trash that has been shredded by shredders) and incinerator ash can be easily recovered. Even if steel is not disposed of separately, it is always sorted magnetically at waste disposal sites, and almost all of it is collected and recycled.

  2. (2) Lower environmental impact in recycling compared to virgin material production

    If the energy consumption and environmental impact required in recycling of the materials are greater than those required in production of the material from natural resources, it would be contrary to the original purpose of recycling. Energy consumption and environmental impact in recycling of steel are significantly lower than in production from natural resources, because its product characteristics can be easily reset by melting and refining treatments in a basic oxygen furnace (BOF) or electric arc furnace (EAF) and be recycled into a new steel products by simple treatments.

  3. (3)A recycling system with economic rationality is in place

    If recycling costs are higher than production costs from natural resources, a sustainable recycling system cannot be realized. As for steel scrap, a social system for scrap recycling, such as collection system and scrap market, is established in most countries and regions, and collection of scraps and their use as raw materials are carried out according to economic rationality. There are actually not many materials for which such an economically rational recycling system has been developed internationally.

  4. (4)Flexibility of recycling into various new products

    It is important that recovered materials can be flexibly recycled into new products with various characteristics. This is because, for materials that can be recycled for a limited purposes, if the balance between the amount of collected materials to be recycled and the amount of products to be recycled does not match due to supply and demand needs, the collected materials that have been sorted with great effort may not be used effectively. Since various mechanical properties of steel products are mostly derived from its microstructure created by various thermomechanical processes (temperature control and processing (rolling etc.) control in the production process), the properties of recovered scrap is reset by melting in a BOF or EAF. After recycling, a new microstructure is created by new heating and rolling processes, which makes it possible to create a wide variety of products without being bound by the type of scrap.

  5. (5) Easy removal of impurities and less deterioration of material quality due to recycling

    Even if materials can be sorted and collected, they are often mixtures containing various added components (alloys in the case of metals), and if the quality of the materials is degraded by recycling, it will be difficult to recycle them again and again. In the case of iron and steel, many impurities can be separated and removed by oxidizing them through a simple method of oxygen blowing during the refining process. As a result, most of the impurities can be removed and the quality of the material is not degraded, which is an excellent characteristic that enables unlimited closed-loop recycling of steel materials. Among metals, steel is the only material where impurities can be removed by the simple method of oxidation removal.


Figure 3: Recycling process of steel (image)


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