Steel
Overview
Steel (스틸, 강철) is an alloy composed primarily of iron (Fe) and containing roughly 0.02%–2.1% carbon (C). It has higher strength and hardness than pure iron, and a wide range of physical properties can be obtained through heat treatment and the addition of alloying elements, making it the foundational material of modern industry, used throughout construction, automobiles, shipbuilding, home appliances, and the energy industry. Roughly 1.8 billion tons or more are produced worldwide each year, and its production volume is also used as an indicator of a country's level of industrialization.
Main content
Definition and classification
Steel is broadly divided into carbon steel and alloy steel. By carbon content, it is classified as low-carbon steel (0.02–0.25%), medium-carbon steel (0.25–0.6%), and high-carbon steel (0.6–2.1%); the higher the carbon content, the greater the strength and hardness, but the lower the ductility and weldability. Adding chromium (Cr), nickel (Ni), manganese (Mn), molybdenum (Mo), vanadium (V), and the like yields alloy steels with improved corrosion resistance, heat resistance, and toughness.
Representative types
- Stainless steel: Contains 10.5% or more chromium, making it resistant to corrosion; used for kitchen appliances, medical devices, and architectural exterior materials.
- Tool steel: With tungsten, vanadium, and other elements added, it is used for cutting tools, dies, and molds.
- Electrical steel: Contains silicon, giving it excellent magnetic properties; used for transformer and motor cores.
- High-strength low-alloy steel (HSLA): Achieves higher strength through micro-alloying elements; used in automobile bodies, bridges, and pipelines.
Manufacturing process
Modern steelmaking is broadly divided into the blast furnace–converter (BOF) route and the electric arc furnace (EAF) route. In a blast furnace, iron ore is reduced with coke to produce pig iron, and in a converter, oxygen is blown in to remove carbon and produce steel. The EAF uses scrap steel as its raw material, which is advantageous in terms of energy efficiency and recycling. The steel then undergoes continuous casting, rolling, heat treatment, and surface treatment to be processed into a variety of products such as plates, bars, sections, and steel pipes.
Properties and characteristics
Steel balances strength, toughness, workability, weldability, corrosion resistance, and magnetic properties, and its greatest strength is that the desired properties can be realized by controlling the microstructure (ferrite, pearlite, martensite, bainite, etc.) through alloy design and heat treatment. It is also 100% recyclable, making it important from a circular economy perspective as well.
Industrial significance
In construction, rebar, H-beams, and steel plates form the framework of structures, while in the automotive industry, ultra-high-strength steel and hot-stamped steel are used to secure both weight reduction and crash safety at the same time. Its range of applications—shipbuilding, wind power, oil pipelines, home appliances, packaging materials—is virtually limitless.
Latest trends
Decarbonization and green steel
The steel industry accounts for about 7–8% of global carbon dioxide emissions, so decarbonization pressure is intense. In 2024–2025, hydrogen-based direct reduced iron (H2-DRI) technology entered the commercialization stage, with Sweden's SSAB, Germany's ThyssenKrupp, and Korea's POSCO among those launching demonstrations of hydrogen-based processes. EAF-based electric-arc-furnace green steel is also an expanding trend.
High-value-added and lightweight materials
With the spread of electric vehicles (EVs), demand for electrical steel for motors and battery housings and for lightweight ultra-high-strength steel is surging. As of 2025, competition continues over hot-stamped steel of the 1.5 GPa class or higher and the development of new 2 GPa-class materials.
Digital transformation and smart steel mills
AI-based process optimization, digital twins, and predictive maintenance technologies are being introduced throughout steel mills, improving energy efficiency and quality stability.
Supply chain restructuring and trade issues
With the imposition of U.S. steel tariffs (Section 232) and the EU's Carbon Border Adjustment Mechanism (CBAM), the structure of global steel trade is being reshaped, and countries are working to protect their domestic steel industries and achieve technological self-reliance.
Related topics
- [[Steel industry]]
- [[Alloy]]
- [[Hydrogen direct reduced iron]]
- [[Electrical steel]]
- [[Stainless steel]]
- [[Carbon neutrality]]