What is the difference between carbon steel and alloy steel?

What is carbon steel and alloy steel?

What is carbon steel?

Steel, as we all know, is a general term for iron-carbon alloys. The carbon steel (referred to as carbon steel) is the carbon content of less than 2.11% iron carbon alloy, its chemical composition, in addition to iron and carbon, there are limited amounts of silicon, manganese, phosphorus, sulfur and other impurities, there will be no other alloying elements.

The output of carbon steel accounts for about 80% of the total output of steel, and is widely used in construction, Bridges, mentioning, vehicles, ships, machinery manufacturing, industry, petrochemical, Marine development and other fields.

What is alloy steel?

Alloy steel is a steel that adds one or more other alloying elements, such as chromium, nickel, tungsten, titanium, vanadium, manganese, copper, aluminum, molybdenum, etc., on the basis of carbon steel in order to increase the specific properties of steel. These chemical elements are added in different proportions/combinations to make the material have different effects, such as increasing hardness, improving corrosion resistance, increasing strength, improving formability, changing weldability, etc.

The output of alloy steel accounts for about 20% of the total output of steel, widely used in machinery manufacturing, petrochemical, construction, daily chemical, medical equipment, synthetic fibers, transportation and other fields.

Classification of carbon steel and alloy steel

Classification of carbon steel

According to the carbon content 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%, commonly used in the manufacture of fasteners are A3 steel, Q215A steel, Q235 steel, 20# steel, 22# steel, etc.

Medium carbon steel: carbon content 0.25% < C%≤0.45%, commonly used in the manufacture of fasteners are 35# steel, 45# steel and so on;

High carbon steel: carbon content C% > 0.45%, the market basically will not use high carbon steel manufacturing fasteners, because of its high carbon content, the material is hard and brittle, easy to break.

Classification of alloy steels

According to the total content of alloying elements is divided into: low alloy steel, medium alloy steel, high alloy steel, alloy content and composition are different, the performance is different.

Low alloy steel: total alloy content ≤5%;

Medium alloy steel: 5% < total alloy content ≤10%

High alloy steel: alloy content > 10%.

Commonly used to manufacture fasteners are: 30CrMo, 40Cr, 35CrMo, 42CrMo and so on.

3. 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 strength and hardness will increase, and the plasticity, toughness and weldability will decrease.

Advantages: good plasticity, weldability; Cheap, easy to smelt; Good processing technology; The performance can be improved by adjusting the carbon content or changing the processing method;

Insufficient: slightly poor strength; Poor hardenability; Low temperature resistance is insufficient; Low corrosion resistance; Low magnetic permeability; Easily magnetized in a magnetic field.

Characteristics of alloy steel

The properties are different with the addition of different alloying elements.

Advantages: good comprehensive performance; Available for special purposes; High strength, high toughness; Good hardenability, not easy to deform and crack; Wear resistance, corrosion resistance, low temperature resistance, high temperature resistance, non-magnetic, etc.

Disadvantages: the price is more expensive; The molding process and heat treatment process are more complicated.

The use of carbon steel and alloy steel

The use of carbon steel

Carbon steel is often used in the manufacture of various building components, containers, boxes, furnace bodies and agricultural machinery, bearing smaller parts, pad iron, cotter pin, tie rod, stamping parts and welding parts.

Carbon steel used to make fasteners

Q215A steel is suitable for making gaskets;

Q235 steel is suitable for the manufacture of bolts, nuts, screw sleeves, cotter pins, rivets, etc., mostly used in 4.8 bolts, 4 nuts, small screws and other products without hardness requirements;

35# steel and 45# steel are high-quality carbon steel structures, which are mostly used to manufacture 8.8 bolts, 8 nuts and 8.8 hex fasteners.

The use of alloy steel

Alloy steel can be used in the manufacture of automobiles, ships, aircraft and other transportation parts; Parts of machine tools, rockets, missiles, etc.; Manufacture all kinds of rolling bearings, tools, measuring tools, springs, hot and cold molds, rolling molds, springs, instruments and so on.

For special occasions, heat resistant, corrosion resistant environment, such as steam turbines, boilers, chemical equipment and so on.

Alloy steel used to make fasteners

Mainly used for the production of high-strength bolts and nuts, such as 10.9 grade materials 30CrMo, 40Cr; Grade 12.9 materials: 35CrMo, 42CrMo, etc.

30CrMo is often used in the manufacture of high-load bolts, stud bolts, etc. Various fasteners used in high temperature (below 450℃) environment such as steam turbines and boilers; Flanges and nuts for use in high temperature (below 500℃) pressure environments;

40Cr is suitable for the manufacture of screw sleeves, pins, connecting rod screws, nuts, etc.

35CrMo is often used to manufacture various fasteners under high loads, such as fasteners for turbogenerators; Various fasteners for boilers and other high temperature (below 480℃) environment;

42CrMo is suitable for manufacturing fasteners with higher strength requirements than 35CrMo.