Steel knowledge

I. Mechanical properties of steel

1. Yield point ( σ S)
When the steel or sample is stretched, the stress exceeds the elastic limit, and even if the pressure does not increase anymore, the steel or sample will continue to undergo obvious plastic deformation. This phenomenon is called yield, and the yield point is the minimum stress value when yield occurs. If Ps is the external force at the yield point s and Fo is the cross-section area of the sample, then the yield point σ S = Ps/Fo (MPa).

2. Yield strength ( σ 0.2)
The yield point of some metal materials is not very obvious, and it isn't easy to measure them. Therefore, to measure the yield properties of materials, it is stipulated that the stress-producing permanent residual plastic deformation is equal to a specific value (generally 0.2% of the original length), called conditional yield strength or yield strength. σ 0.2.
3. Tensile Strength ( σ B)
The maximum stress a material achieves during tension from the beginning to the time it breaks. It indicates the strength of the steel against breaking. Corresponding to the tensile strength are compressive strength, flexural strength, etc. Set Pb as the maximum tensile force before the material is pulled apart and Fo as the cross-section area of the sample, then the tensile strength σ B= Pb/Fo (MPa).
4. Elongation ( δ S)
The percentage of the plastic elongation of a material after breaking to the original sample length is called elongation or elongation.
5. Yield-strength ratio ( σ S/ σ B)
The ratio of the yield point (yield strength) of steel to the tensile strength is called the yield strength ratio. The higher the yield-strength ratio, the higher the reliability of structural parts. The yield-strength ratio of general carbon steel is 0.6-0.65, low alloy structural steel is 0.65-0.75, and alloy structural steel is 0.84-0.86.
6. Hardness
Hardness indicates the material's resistance to complex objects pressing into its surface. It is one of the critical performance indexes of metal materials. The higher the general hardness, the better the wear resistance. Commonly used hardness indicators are Brinell hardness, Rockwell hardness, and Vickers hardness.
1) Brinell Hardness (HB)
Hardened steel balls of a specific size  enerally 10mm) are pressed into the material's surface with a specific load (generally 3000kg) for some time. After unloading, the ratio of the load to the indentation area is called Brinell Hardness (HB).
2) Rockwell Hardness (HR)
When HB>450 or the sample is too small, the Rockwell hardness measurement instead of the Brinell hardness test cannot be used. It is a diamond cone with a top angle of 120 degrees or a steel ball with a diameter of 1.59 and 3.18 mm, which is pressed into the material's surface under certain loads, and the indentation's depth determines the material's hardness. There are three different scales to indicate the hardness of the tested material:
HRA: Hardness obtained with a 60 kg load and a diamond cone press-in fortoughd materials such as cemented carbides.
HRB: Hardness obtained by hardening a steel ball with a load of 100kg and a diameter of 1.58mm. It is used for materials with lower hardness (e.g., annealed steel, cast iron, etc.).
HRC: Hardness is obtained using a 150 kg load and a diamond cone press-in for materials with high hardness, such as hardened steel.
3) Vickers Hardness (HV)
A diamond square cone press presses the material surface with a load of less than 120 kg and a top angle of 136 degrees. The Vickers hardness value (HV) is defined by dividing the surface area of the material indentation recess by the load value.

II. Black Metals and Non-ferrous Metals

1. Ferrous Metals
It refeNonferrouslloy of iron and iron. Such as steel, pig iron, ferroalloy, cast iron, etc. Steel and pig iron are alloys based on iron and mainly added with carbon. They are collectively called FERROCARBON alloys.
Pig iron is made by smelting iron ore into a blast furnace, and it is mainly used for steelmaking and casting.
Cast pig iron is melted in an iron melting furnace to obtain cast iron (liquid iron with carbon content greater than 2.11%). Cast liquid cast iron into cast iron, which is called cast iron.
Ferroalloy is an alloy of iron and elements such as silicon, manganese, chromium, and titanium. Ferroalloy is one of the raw materials used in steel making and is used as a deoxidizer and additive for alloy elements.
Steel is called iron-carbon alloy with a carbon content of less than 2.11%. Steel is obtained by putting pig iron for steelmaking into the steelmaking furnace and smelting it according to a specific process. Steel products include ingots, continuous casting billets, and direct casting of various steel castings. Generally speaking, steel refers to steel rolled into multiple sheets of steel. Used for manufacturing hot forged and hot pressed mechanical parts, cold drawn and cold headed forged steel, seamless steel pipe mechanical manufacturing parts, CNC machining parts, and casting parts.

2. Non-ferrous metals
Also known as non-ferrousNonferrousfers to metals and allnonferroushan ferrous metals, such as copper, tin, lead, zinc, aluminium and brass, bronze, aluminium alloy and bearing alloys. For example, a  CNC lathe can process various materials, including 316 and 304 stainless steel plates, carbon steel, carbon steel, aluminum alloy, zinc alloy materials, aluminum alloy, copper, iron, plastic, acrylic plates, POM, UHWM, and other raw materials. It can be processed into CNC turning parts, milling parts, and complex parts with square and cylindrical structures. In addition, chromium, nickel, manganese, molybdenum, cobalt, vanadium, tungsten, and titanium are also used in industry. These metals are mainly used as alloy additives to improve the properties of metals, in which tungsten, titanium, molybdenum, and other cemented carbides are used to produce cutting tools. These nonferrous metals are referred to as industrnonferrous. In addition, there are precious metals such as platinum, gold, silver, and rare metals, including radioactive uranium and radium.

 

III. Classification of Steel

Besides iron and carbon, the main elements of steel include silicon, manganese, sulfur,r, and phosphorus.
There are various classification methods for steel, and the main ones are as follows:
1. Classify by Quality
(1) Common steel (P < 0.045%, S < 0.050%)
(2) High-quality steel (P, S < 0.035%)
(3) High quality steel (P < 0.035%, S < 0.030%)
2. Classification by chemical composition
(1) Carbon steel: a. Low carbon steel (C < 0.25%); B. Medium carbon steel (C < 0.25-0.60%); C. High carbon steel (C < 0.60%).
(2) Alloy steel: a. Low alloy steel (total content of alloy elements < 5%); B. Medium alloy steel (total content of alloy elements > 5-10%); C. High alloy steel (total alloy element content > 10%).
3. Classification by forming method
(1) Forged steel; (2) Cast steel; (3) Hot rolled steel; (4) Cold drawn steel.
4. Classification by Metallographic Organization
(1) Annealed state: a. Hypoeutectoid steel (ferrite + pearlite); B. Eutectic steel (pearlite); C. Hypereutectoid steel (pearlite + cementite); D. Ledeburite steel (pearlite + cementite).
(2) Normalized state: A. pearlitic steel; B. Bainitic steel; C. martensitic steel; D. Austenitic steel.
(3) No phase transition or partial phase transition
5. Classify by Use
(1) Construction and engineering steel: a. Common carbon structural steel; B. Low alloy structural steel; C. Reinforced steel.
(2) Structural steel:
A. Machinery steel: (a) tempered structural steel; (b) Surface hardening structural steels, including carburized, ammoniated, and surface hardening steels; (c) Easy-cutting structural steel; (d) Cold plastic forming steel, including cold stamping steel and cold heading steel.
B. Spring steel
C. Bearing steel
(3) Tool steel: a. Carbon tool steel; B. Alloy tool steel; C. High-speed tool steel.
(4) Special performance steel: a. Stainless acid-resistant steel; B. Heat-resistant steel: including anti-oxidation steel, heat-strength steel, and valve steel; C. Electrothermal alloy steel; D. Wear-resistant steel; E. Low-temperature steel; F. Electrical steel.
(5) Professional steel - such as bridge steel, ship steel, boiler steel, pressure vessel steel, agricultural machinery steel, etc.
6. Comprehensive Classification
(1) Common steel
A. Carbon structural steel: (a) Q195; (b) Q215 (A, B); (c) Q235 (A, B, C); (d) Q255 (A, B); (e) Q275.
B. Low alloy structural steel
C. General structural steel for specific purposes
(2)High-quality steel (including high-quality steel)
A. Structural steel: (a) High-quality carbon structural steel; (b) Alloy structural steel; (c) spring steel; (d) Easy-cutting steel; (e) Bearing steel; (f) High-quality structural steel for specific purposes.
B. Tool steel: (a) Carbon tool steel; (b) Alloy tool steel; (c) High-speed tool steel.
C. Special performance steel: (a) stainless and acid-resistant steel; (b) Heat-resistant steel; (c) Electric heat alloy steel; (d) Electrical steel; (e) High manganese wear-resistant steel.
7. Classification by Smelting Method
(1) According to furnace type
A. Converter steel: (a) acid converter steel; (b) Alkaline converter steel. Or (a) bottom-blown converter steel, (b) Side-blown converter steel, (c) Top-blown converter steel.
B. Electric furnace steel: (a) Electric arc furnace steel; (b) Electroslag furnace steel; (c) induction furnace steel; (d) Vacuum consumable furnace steel; (e) Electron beam furnace steel.
(2) According to deoxidization degree and pouring system
A. Boiling steel; B. Semi-calm steel; C. Killed steel; D. Special killed steel.

 

IV. Overview of Steel Number Representation Method in China

The product brand is generally represented by combining the Chinese alphabet, chemical element symbol, and Arabic number. That is:
(1) International chemical symbols, such as Si, Mn, Cr, etc., represent steel numbers' chemical elements. Mixed rare earth elements are represented by RE (or Xt).
(2) Product name, use, smelting and pouring methods, etc., are generally expressed by abbreviations of Chinese phonetics.
(3) Arabic numerals express the content of theleadingn chemical elements (%) in steel.
When using the Chinese alphabet to represent the product name, use, characteristics, and process method, the first letter is usually selected from the Chinese alphabet to represent the product name. When repeating the chosen letter of another product, the second or third letter can be used, or the first alphabet of two Chinese characters can be selected simultaneously.
Where there is no Chinese character or alphabet available for now, the symbols shall be English letters.