Overview Of The Iron And Steel Materials Industry Knowledge

Overview of the Iron and Steel Materials Industry Knowledge

I. Definition and Core Status of Iron and Steel

Iron and steel are general terms for alloys composed primarily of iron (Fe) and carbon (C), along with other elements such as manganese (Mn), silicon (Si), phosphorus (P), and sulfur (S). They are the most widely used and crucial metallic materials in modern industry, often called the "backbone of industry." Their properties can be varied over an extremely wide range by adjusting chemical composition and heat treatment processes to meet different requirements.

II. Core Classification: Pig Iron, Steel, and Steel Products

Pig Iron: High carbon content (>2.11%), hard and brittle, primarily produced via blast furnace smelting. Most is used as raw material for steelmaking, with a small portion used for casting (foundry pig iron).

Steel: Generally contains 0.02% to 2.11% carbon, characterized by a good combination of strength, toughness, and plasticity. Steel is produced from pig iron by oxidizing to remove carbon and impurities in a steelmaking furnace; it is the base material for steel products.

Steel Products: Finished or semi-finished products made by plastically processing steel through rolling, forging, drawing, etc., such as plates, pipes, sections, and wire rods.

III. Core Classification Systems for Steel

The classification of steel is complex; common systems include:

By Chemical Composition:

Carbon Steel: Primarily composed of iron and carbon. Subdivided by carbon content into low-carbon steel (C<0.25%), medium-carbon steel (0.25%≤C≤0.60%), and high-carbon steel (C>0.60%). Lower cost, most widely used.

Alloy Steel: Based on carbon steel, one or more alloying elements (e.g., chromium Cr, nickel Ni, molybdenum Mo, vanadium V) are intentionally added to obtain specific properties. Can be divided into low-alloy steel, medium-alloy steel, and high-alloy steel.

By Quality​ (mainly based on harmful impurity content, phosphorus and sulfur):

Ordinary Steel​ (P≤0.045%, S≤0.050%)

Quality Steel​ (P, S both ≤0.035%)

High-Quality Steel​ (P≤0.035%, S≤0.030%)

By Smelting Method and Deoxidation Degree:

Open-Hearth Steel​ (largely obsolete)

Basic Oxygen Furnace (BOF) Steel​ (mainstream production process)

Electric Arc Furnace (EAF) Steel​ (often used for producing high-quality alloy steel)

By deoxidation degree: Rimmed Steel (F), Killed Steel (Z), Semi-Killed Steel (b), and Special Killed Steel (TZ).

By Metallographic Structure​ (related to heat treatment state):

Annealed state: Hypoeutectoid steel, eutectoid steel, hypereutectoid steel.

Normalized state: Pearlitic steel, bainitic steel, martensitic steel, austenitic steel.

By Application​ (most common classification method):

Structural Steel: Used for construction, bridges, ships, vehicles, pressure vessels, etc. Emphasizes strength and toughness.

Tool Steel: Used for making cutting tools, molds, measuring tools. Emphasizes high hardness, wear resistance, and hot hardness.

Special Purpose Steel: Possesses special physical/chemical properties, e.g., Stainless Steel​ (corrosion-resistant), Heat-Resistant Steel, Abrasion-Resistant Steel.

IV. Main Production Process Flow

Modern integrated iron and steel complexes primarily follow two models: "Long Process" and "Short Process":

Long Process: Sintering/Pelletizing → Blast Furnace Ironmaking → Basic Oxygen Furnace Steelmaking → Secondary Refining → Continuous Casting → Rolling. Uses iron ore and coal as main raw materials. Large capacity, mainstream process.

Short Process: Electric Arc Furnace Steelmaking → Secondary Refining → Continuous Casting → Rolling. Uses recycled scrap steel as the main raw material. Relatively lower energy consumption and emissions, more environmentally friendly. A key direction for green transformation.

V. Key Performance Indicators

Mechanical Properties: Strength (yield strength, tensile strength), plasticity (elongation, reduction of area), toughness (impact energy), hardness.

Physical & Chemical Properties: Corrosion resistance, heat resistance, wear resistance, weldability, hot/cold workability.

VI. Main Application Areas

Construction: Reinforcing bars (rebar), wire rods, H-beams for reinforced concrete structures.

Manufacturing: Automotive steel sheets (body panels, steel for gears), steel for machinery manufacturing, bearing steel, spring steel.

Energy & Transportation: Pipeline steel for oil/gas transmission, steel for wind turbine towers, steel for ships and offshore platforms, rails and wheels for railways.

Household Appliances & Consumer Goods: Casings for various appliances, cutlery (stainless steel).

VII. Current Industry Development Trends

Green and Low-Carbon Transition: Developing hydrogen-based metallurgy, carbon capture, utilization, and storage (CCUS), and increasing the proportion of EAF steel to address climate change.

Product Upgrading to High-End: Focusing on R&D and production of special steels with high strength, high toughness, corrosion resistance, and resistance to extreme environments (high/low temperature) to achieve import substitution.

Intelligent Manufacturing: Utilizing industrial internet, big data, and artificial intelligence to optimize production, achieving cost reduction, efficiency improvement, and quality stability.

Service-Oriented Material Supply: Evolving from simply selling steel to providing material solutions and full lifecycle services.