Understanding the Difference Between Carbon Steel and Alloy Steel
Definition of Carbon Steel and Alloy Steel
Steel, as we all know, is a general term for iron-carbon alloys. Carbon steel (abbreviated as carbon steel) is an iron-carbon alloy with a carbon content of less than 2.11%. In its chemical composition, in addition to iron and carbon, there are also limited impurities such as silicon, manganese, phosphorus, and sulfur, and there will be no other alloying elements.
The output of carbon steel accounts for about 80% of the total steel output, and is widely used in construction, bridges, vehicles, ships, machinery manufacturing, industry, petrochemicals, marine development and other fields.
Alloy steel is a steel with one or more other alloying elements added to carbon steel, such as chromium, nickel, tungsten, titanium, vanadium, manganese, copper, aluminum, molybdenum, etc., in order to increase certain specific properties of steel. These chemical elements are added in different proportions/combinations to give the material different effects, such as increasing hardness, improving corrosion resistance, enhancing strength, improving formability, changing weldability, etc.
The output of alloy steel accounts for about 20% of the total steel output and is widely used in various fields such as machinery manufacturing, petrochemicals, construction, daily chemicals, medical equipment, synthetic fibers, transportation, etc.
Classification of Carbon Steel and Alloy Steel
- Classification of carbon steel
According to the carbon content, it can be divided into: low carbon steel, medium carbon steel, high carbon steel; the higher the carbon content, the higher the hardness and the lower the toughness.
Low carbon steel: carbon content C%≤0.25%. Common low carbon steels used to make fasteners include A3 steel, Q215A steel, Q235 steel, 20# steel, 22# steel, etc.
Medium carbon steel: carbon content 0.25%＜C%≤0.45%. Common medium carbon steels used to make fasteners include 35# steel, 45# steel, etc.
High carbon steel: carbon content C%＞0.45%, high carbon steel is basically not used to manufacture fasteners on the market, because of its high carbon content, hard and brittle material, easy to break.
- Classification of alloy steel
According to the total content of alloy elements, it is divided into: low alloy steel, medium alloy steel, high alloy steel, with different alloy content and composition, and different performance.
Low alloy steel: total alloy content ≤5%;
Medium alloy steel: 5%＜total alloy content ≤10%
High alloy steel: alloy content＞10%.
Common alloy steels used to make fasteners include: 30CrMo, 40Cr, 35CrMo, 42CrMo, etc.
Characteristics of Carbon Steel and Alloy Steel
- Characteristics of carbon steel
The performance of carbon steel depends on its carbon content. The higher the carbon content, the higher the strength and hardness, and the lower the plasticity, toughness and weldability.
Advantages: good plasticity and weldability; cheap price, easy to smelt; good processing technology; performance can be improved by adjusting the carbon content or changing the processing method;
Disadvantages: slightly poor strength; poor hardenability; insufficient low temperature resistance; low corrosion resistance; low magnetic conductivity; easy to be magnetized in a magnetic field.
- Characteristics of alloy steel
Different alloy elements added have different properties.
Advantages: good comprehensive performance; available for special purposes; high strength and high toughness; good hardenability, not easy to deform and crack; wear resistance, corrosion resistance, low temperature resistance, high temperature resistance, non-magnetic, etc.;
Disadvantages: expensive; more complicated molding and heat treatment processes.
Uses of Carbon Steel and Alloy Steel
- Uses of carbon steel
Carbon steel is often used to manufacture various building components, containers, boxes, furnace bodies and agricultural machinery, small load-bearing parts, washers, cotter pins, tie rods, stampings and welded parts, etc.
Carbon steel used to manufacture fasteners
Q215A steel is suitable for manufacturing washers;
Q235 steel is suitable for manufacturing bolts, nuts, screw sleeves, cotter pins, rivets, etc., and is mostly used for products without hardness requirements such as 4.8-grade bolts, 4-grade nuts, and small screws;
35# steel and 45# steel belong to high-quality carbon steel structures, and are mostly used to manufacture 8.8-grade bolts, 8-grade nuts and 8.8-grade hexagon fasteners.
- Uses of alloy steel
Alloy steel can be used to manufacture parts for transportation vehicles such as automobiles, ships, and airplanes; parts for machine tools, rockets, missiles, etc.; and to manufacture various rolling bearings, cutting tools, measuring tools, springs, hot and cold molds, rolling molds, springs, instruments, etc.
Used in special occasions, heat-resistant and corrosion-resistant environments, such as steam turbines, boilers, chemical equipment, etc.
Alloy steel used to manufacture fasteners
Mainly used to produce high-strength bolts and nuts, such as 10.9 grade materials include 30CrMo and 40Cr; 12.9 grade materials include: 35CrMo, 42CrMo, etc.
30CrMo is often used to manufacture bolts and studs under high loads; various fasteners used in high temperature (below 450℃) environments such as steam turbines and boilers; flanges and nuts used in high temperature (below 500℃) pressure environments;
40Cr is suitable for manufacturing screw sleeves, pins, connecting rod screws, nuts, etc.;
35CrMo is often used to manufacture various fasteners under high loads, such as fasteners for steam turbine generators; various fasteners used in high temperature (below 480℃) environments such as boilers;
42CrMo is suitable for manufacturing fasteners that require higher strength than 35CrMo.
Considering the characteristics of carbon steel and alloy steel, when choosing fastener materials, carbon steel can be given priority on the premise of meeting the use requirements; if the specifications are large, the shape is more complex, and the strength and precision requirements are high, or there are requirements for hot hardness and other special performances, then alloy steel should be used.
After reading this, can you distinguish between carbon steel and alloy steel?
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