## Mechanical Properties Of Steel

### 1.Yield Point (σs)

When the steel or sample is stretched, when the stress exceeds the elastic limit, even though the stress does not increase, the steel or sample still continues to undergo obvious plastic deformation, which is called yield. The minimum stress value at which the yield phenomenon occurs is the yield point. Suppose Ps is the external force at the yield point s and Fo is the fault area of the sample, then the yield point σs =Ps/Fo(MPa).

### 2.Yield Strength (σ0.2)

The yield point of some metal materials is not obvious and it is difficult to measure. Therefore, in order to measure the yield characteristics of materials, the stress at which the permanent residual plastic deformation is equal to a certain value (usually 0.2% of the original length) is defined as the conditional yield strength or yield strength σ0.2 for short.

### 3.Tensile Strength (σb)

Tensile strength is the maximum stress reached by a material during tensile process from the beginning to fracture. It expresses the ability of steel to resist breaking. Corresponding to the tensile strength, there are compressive strength, flexural strength, etc. If Pb is the maximum tensile force of the material before it is broken and Fo is the cross-section area of the sample, then the tensile strength σb= Pb/Fo (MPa).

### 4.Elongation (δs)

After the material is broken, the plastic elongation of the length and the percentage of the original specimen length is called elongation or elongation.

### 5. Yield Strength Ratio (σs/σb)

The ratio of the yield point (yield strength) of steel to the tensile strength is called the yield strength ratio. The larger the yield ratio, the higher the reliability of the structural parts. Generally, the yield ratio of carbon steel is 0.6-0.65, low-alloy structural steel is 0.65-0.7, and alloy structural steel is 0.84-0.86.

### 6.Hardness

Hardness is the ability of a material to resist hard objects pressing into its surface. It is one of the important performance indicators of metal materials. Generally, the higher the hardness, the better the wear resistance. Commonly used hardness indicators are Brinell hardness, Rockwell hardness and Vickers hardness.

1) Brinell Hardness(HB)

A hardened steel ball of a certain size (generally 10mm in diameter) is pressed into the surface of the material with a certain load (generally 3000kg). After a period of time, the ratio of the load to the indentation area is brinell hardness value (HB).

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2) Rockwell Hardness(HR)

When HB>450 or the sample is too small, the Brinell hardness test cannot be used and the Rockwell hardness measurement is used instead. It uses a diamond cone with an apex angle of 120° or a steel ball with a diameter of 1.59 and 3.18mm, which is pressed into the surface of the tested material under a certain load, and the hardness of the material is obtained from the depth of the indentation. According to the different hardness of the test material, it is expressed in three different scales:

HRA: is the hardness obtained with a 60kg load and a diamond cone indenter, used for extremely hard materials (such as cemented carbide, etc.).

HRB: It is the hardness obtained by using a 100kg load and a hardened steel ball with a diameter of 1.58mm. It is used for materials with lower hardness (such as annealed steel, cast iron, etc.).

HRC: It is the hardness obtained by using a 150kg load and a diamond cone indenter, and is used for materials with high hardness (such as quenched steel, etc.).

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3) Vickers Hardness (HV)

Use a load within 120kg and a diamond square cone indenter with an apex angle of 136° to press into the surface of the material, and divide the surface area of the material indentation pit by the load value, which is the Vickers hardness value (HV).

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## Ferrous And Non-Ferrous Metals

### 1.Ferrous Metal

Ferrous metals refer to iron and iron alloys. Such as steel, pig iron, ferroalloy, cast iron, etc. Steel and pig iron are based on iron, with carbon as the main element of the alloy, collectively known as iron carbon alloy.

Pig iron refers to a product made by smelting iron ore in a blast furnace, which is mainly used for steelmaking and casting.

The cast iron is smelted in an iron melting furnace to obtain cast iron (a liquid iron-carbon alloy with a carbon content greater than 2.11%), and the liquid cast iron is cast into a casting, which is called a cast iron.

Ferroalloy is an alloy composed of iron and silicon, manganese, chromium, titanium and other elements. Ferroalloy is one of the raw materials for steel making. Ferroalloy is used as deoxidizer and alloy element additive in steelmaking.

The iron carbon alloy with carbon content less than 2.11% is called steel, and the pig iron used for steelmaking is melted in the steelmaking furnace according to a certain process to obtain steel. Steel products include ingots, continuous casting billets and direct casting into various steel castings. Generally speaking, steel generally refers to steel that is rolled into various types of steel.

### 2.Non-Ferrous Metals

Non-ferrous metals refer to metals and alloys other than ferrous metals, such as copper, tin, lead, zinc, aluminum, and brass, bronze, aluminum alloys, and bearing alloys. In addition, chromium, nickel, manganese, molybdenum, cobalt, vanadium, tungsten, titanium, etc. are also used in the industry. These metals are mainly used as alloy additions to improve the performance of metals. Among them, tungsten, titanium, molybdenum, etc. are mostly used to produce cemented carbide cutting tool. The above non-ferrous metals are all called industrial metals, in addition to precious metals: platinum, gold, silver, etc. and rare metals, including radioactive uranium, radium, etc.

## Steel Classification

In addition to iron and carbon, the main elements of steel are silicon, manganese, sulfur and phosphorus.

There are various classification methods of steel, and the main methods are as follows:

### 1.Classification By Quality

①Ordinary Steel (P≤0.045%，S≤0.050%)

②Quality Steel (Both P and S≤0.035%)

③High Quality Steel (P≤0.035%，S≤0.030%)

### 2.Classification By Chemical Composition

①Carbon Steel: a. low carbon steel(C≤0.25%); b. Medium-Carbon Steels (C≤0.25～0.60%); c. High Carbon Steel(C≤0.60%).

②Alloy Steel: a. Low Alloy Steel(Total alloying element content≤5%); b. Medium Alloy Steel(Total alloying element content﹥5～10%); C. High Alloy Steel(Total alloying element content﹥10%).

### 3.Classification By Forming Methods

①Forged Steel; ②Cast Steel; ③Hot Rolled Steel; ④Cold Drawn Steel.

### 4.Classification By Micro Structure

①Annealed: a. Hypoeutectoid steel(ferrite +pearlite); b. Eutectoid steel(pearlite); c. Hyper-eutectoid steel (pearlite+cementite); d. Ledeburitic steel(pearlite+cementite).

②Normalizing: a. Pearlitic steel; b. Bainitic steel; c. Martensitic steel ; d. Austenite steel.

③No micro structure change or partial  micro structure change.

### 5.Classification By Use

Construction and Engineering Steel: a. Carbon Structural Steel; b. Structural low alloy steel; c. Concrete Steel.

Constructional Steel:

a. Steel for machinery: (a)quenched and tempered steel; (b) Surface hardened structural steel: Including carburized carbon steel, ammoniated steel, surface hardening steel; (c) Free-cutting structural steel; (d) Steel for cold plastic forming: Including cold stamping steel, cold heading steel.

b. Spring steels

c. Bearing steel

Tool steel: a. Carbon tool steel; b. Alloy tool steel c. High-speed tool steel.

Special steel: a. Stainless acid resistant steel; b. Heat resistant steel: Including oxidation resistant steel, thermal strength steel, valve steel; c. Electrothermal alloy steel; d.Wear-resistant steel; e. Cryogenic Steel; f. Electrical steel.

Speciality Steel: Such as bridge steel, ship steel, boiler steel, pressure vessel steel, agricultural machinery steel and so on.

### 6.Comprehensive Classification

①Common 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. Ordinary structural steel for a particular purpose

② Quality steel(Including high quality steel)

a. Structural steel: (a) Quality carbon structure steel; (b) Structural alloy steel (c) Spring steel; (d) Free 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 steel: (a) Stainless acid resistant steel; (b) Heat resistant steel; (c) Electrothermal alloy steel; (d) Electric steel; (e) High manganese wear-resistant Steel.

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### 7.Classification By Smelting Method

① According To Furnace Type

a. Converter Steel: (a)bessemer steel; (b)Basic converter steel.

Or (a)Bottom blown converter steel;(b)Side blown converter steel;(c)Top-blown converter steel.

b. Electric furnace steel: (a)arc furnace; (b)Electroslag furnace steel; (c)Induction furnace steel; (d)Vacuum consumable furnace steel; (e)Electron beam furnace steel.

② According to the degree of deoxidation and pouring system

(a)Rimming steel; (b)balanced steel; (c)killed steel ; (d)Special killed steel

## Outline of Chinese Steel Number Representation Method

The representation of product grades is generally represented by a combination of Chinese pinyin letters, chemical element symbols and Arabic numerals. That is:

①The chemical elements in the steel grade are represented by international chemical symbols, such as Si, Mn, Cr, etc. Mixed rare earth elements are represented by “RE” (or “Xt”).

②The product name, application, smelting and pouring method, etc. are generally represented by the abbreviations of Chinese Pinyin.

③The content of main chemical elements in steel (%) is expressed in Arabic numerals.

When the Chinese phonetic alphabet is used to indicate the product name, use, characteristics and process methods, the first letter is generally selected from the Chinese phonetic alphabet representing the product name. When it is repeated with the letter chosen by another product, the second letter or the third letter can be used, or the first pinyin letter in two Chinese characters can be selected at the same time.

If there are no Chinese characters or Chinese pinyin available for use, the symbols shall be English letters.

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## Subdivision Description of The Representation Method of Steel Grades in China

### 1.Representation Method of Carbon Structural Steel and Low Alloy High Strength Structural Grade

The above steel is usually divided into general steel and special steel two categories. The designation method of the grade is composed of the Chinese pinyin letters of the yield point or yield strength of the steel, the yield point or yield strength value, the quality grade of the steel, and the degree of deoxidation of the steel, which is actually composed of 4 parts.

①General structural steels use the pinyin letter “Q” representing the yield point. Yield point value (unit: MPa) and quality grade (A, B, C, D, E), deoxidation method (F, B, Z, TZ) and other symbols, in order to form the label. For example: carbon structural steel grades are expressed as: Q235AF, Q235BZ; low alloy high strength structural steel grades are expressed as: Q345C, Q345D.

Q235BZ represents a killed carbon structural steel with yield point value ≥235MPa and quality grade B.

Q235 and Q345 are the most typical grade of engineering steel, the largest in production and use, and the most widely used grade. These two brands are available in almost every country in the world.

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In the grade composition of carbon structural steel, the kill steel symbol “Z” and the special kill steel symbol “TZ” can be omitted. For example: Q235 steel with quality grades C and D respectively, its grades should be Q235CZ and Q235DTZ, but can be omitted as Q235C and Q235D.

Low alloy high strength structural steel has killed steel and special killed steel, but the tail does not write to indicate the deoxidation method symbol.

②Special structural steel is generally represented by the symbol “Q” representing the yield point of the steel, the yield point value and the symbol representing the use of the product. For example: the steel grade for pressure vessels is expressed as “Q345R”;The grade of weathering steel is Q340NH; Q295HP steel grade for welding gas cylinder; Q390g is boiler steel grade; Q420q steel grades for bridges.

③According to needs, the grades of general-purpose low-alloy high-strength structural steels can also be expressed in order by two Arabic numerals (representing the average carbon content, in ten thousandths) and chemical element symbols; The grade of special low alloy high strength structural steel may also be indicated by two Arabic numerals (indicating the average carbon content in parts ten thousand) and the symbol of the chemical element, as well as some prescribed symbols representing the use of the product, in order.

### 2.Representation Metold of High Quality Carbon Structural Steel and High Quality Carbon Spring Steel

High quality carbon structural steel uses two Arabic numerals (in a few tens of thousands to indicate the average carbon content) or Arabic numerals and element symbols, etc.

①The symbols “F” and “B” shall be added to the tail of the grade of boiling and semi-killed steels. For example: boiling steel with an average carbon content of 0.08%, its grade is expressed as “08F”; Semi-killed steel with an average carbon content of 0.10% is designated as “10b”.

②killed steel(both S、P≤0.035%), it’s usually not signed. For example: Killed steel with an average carbon content of 0.45% is designated as “45”.

③For high-quality carbon structural steel with higher manganese content, the manganese element symbol is added after the Arabic numerals representing the average carbon content. For example: steel with an average carbon content of 0.50% and a manganese content of 0.70% to 1.00%, its grade is expressed as “50Mn”.

④High quality carbon structural steel (S, P ≤0.030%), add the symbol “A” after the grade. For example: high-quality carbon structural steel with an average carbon content of 0.45%, its grade is expressed as “45A”.

⑤Premium quality carbon structural steel(S≤0.020%、P≤0.025%)，add the symbol “E” after the grade. For example, the special grade high-quality carbon structural steel with an average carbon content of 0.45% is designated as “45E”.

The representation method of high-quality carbon spring steel grades is the same as that of high-quality carbon structural steel grades (65, 70, 85, 65Mn steels exist in both GB/T1222 and GB/T699 standards respectively).

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### 3.Alloy Structural Steel and Alloy Spring Steel Grades Representation Method

①Alloy structural steel grades are represented by Arabic numerals and standard chemical element symbols.

Use two Arabic numerals to indicate the average carbon content (in ten thousandths) and put it on the head of the brand.

Alloy element content is expressed as: When the average content is less than 1.50%, only the element is indicated in the grade, and the content is generally not indicated; When the average alloy content is 1.50% to 2.49%, 2.50% to 3.49%, 3.50% to 4.49%, 4.50% to 5.49%,… and write 2, 3, 4, 5… after the alloying elements accordingly.

For example: the average content of carbon, chromium, manganese, silicon is 0.30%, 0.95%, 0.85%, 1.05% of the alloy structural steel. When the content of S and P is less than or equal to 0.035%, its grade is expressed as “30CrMnSi”.

High quality alloy structural steel(S, P content ≤0.025% respectively), add the symbol “A” to the end of the grade. Such as: “30CrMnSiA”.

Super high quality alloy structural steel(S≤0.015%、P≤0.025%)，add the symbol “E” to the end of the grade. Such as:“30CrM nSiE”.

Special alloy structural steel grades should be added to the head (or tail) of the grade with a symbol representing the use of the product. For example, 30CrMnSi steel for riveting screw, the steel number is indicated as ML30CrMnSi.

②The expression method of alloy spring steel grades is the same as that of alloy structural steel.

Spring steel with average content of carbon, silicon and manganese of 0.60%, 1.75% and 0.75% respectively, and its grade is expressed as “60Si2Mn”.

### 4.Free Cutting Steel Grade Representation Method

Free-cutting steels are represented by standard chemical element symbols, prescribed symbols and Arabic numerals. Arabic numerals indicate the average carbon content (measured in parts per 10,000).

①For vulcanized free-cutting steel and sulfur-added and phosphorus free-cutting steel, no free-cutting element symbol is added after the symbol “Y” and Arabic numerals. For example: free-cutting steel with an average carbon content of 0.15%, its grade is expressed as “Y15”.

②Sulfur-added and phosphorus free-cutting steels with higher manganese content add manganese element symbols after the symbol “Y” and Arabic numerals. For example, the free-cutting steel with an average carbon content of 0.40% and a manganese content of 1.20% to 1.55% is designated as “Y40Mn”.

③For free cutting steels containing free cutting elements such as calcium and lead, the symbol “Y” and Arabic numerals are followed by the symbol of the free cutting element. Such as: “Y15Pb”, ”Y45Ca”.

### 5.Representation Method of Non-Quenched and Tempered Mechanical Structural Steel Grades

Non-quenched and tempered mechanical structural steels, the symbols “YF” and “F” are added to the head of the brand respectively to represent free cutting non-quenched and tempered mechanical structural steels and hot forging non-quenched and tempered mechanical structural steels. The other contents of the designation method are the same as those of alloy structural steel. For example, “YF35V”, “F45V”.

### 6.Tool Steel Grade Representation Method

Tool steel is divided into three categories: carbon tool steel, alloy tool steel and high-speed tool steel.

①Carbon tool steels are represented by standard chemical element symbols, prescribed symbols and Arabic numerals. Arabic numerals indicate the average carbon content (measured in parts per thousand).

a. Ordinary manganese containing carbon tool steel, tool steel symbol “T” after Arabic numerals. For example, carbon tool steel with an average carbon content of 0.80% is labeled “T8”.

b. For carbon tool steels with high manganese content, add the manganese element symbol after the tool steel symbol “T” and Arabic numerals. Such as: “T8Mn”.

c. High-quality carbon tool steel, add “A” at the end of the grade. For example: “T8MnA”.

②Alloy tool steel and high speed tool steel.

Alloy tool steel and high-speed tool steel grades are represented in the same way as alloy structural steel grades. It is represented by the alloying element symbols and Arabic numerals specified in the standard, but generally does not indicate the average carbon content figure. For example: alloy tool steel with an average carbon content of 1.60%, chromium, molybdenum, and vanadium content of 11.75%, 0.50%, and 0.22%, respectively, its steel grade is expressed as “Cr12MoV”;High speed tool steel with average carbon content of 0.85%, tungsten, molybdenum, chromium and vanadium content of 6.00%, 5.00%, 4.00% and 2.00% respectively, its steel grade is expressed as”W6Mo5Cr4V2″.

If the average carbon content is less than 1.00%, an Arabic numeral can be used to represent the carbon content (in thousands). For example, an alloy tool steel with an average carbon content of 0.80%, a manganese content of 0.95% and a silicon content of 0.45% is designated as “8MnSi”.

For low-chromium (average chromium content <1.00%) alloy tool steel, add a number “0” before the chromium content  (measured in parts per thousand). For example, alloyed tool steels with an average chromium content of 0.60%, its grade is expressed as “Cr06”.

### 7.Representation Method of Plastic Mold Steel Grade

Plastic mold steel grades are expressed in the same way as high-quality carbon structural steel and alloy tool steel grades, except that the symbol “SM” is added to the head. For example: carbon plastic mold steel with an average carbon content of 0.45%, its grade is expressed as “SM45”;The average carbon content is 0.34%, the chromium content is 1.70%, and the molybdenum content is 0.42% of the alloy plastic mold steel, and its grade is expressed as “SM3Cr2Mo”.

### 8.Representation Method of Bearing Steel Grades

Bearing steel is divided into four categories: high carbon chromium bearing steel, carburized bearing steel, high carbon chromium stainless bearing steel and high temperature bearing steel.

①For high carbon chromium bearing steel, the symbol “G” is added to the head of the grade, but the carbon content is not indicated. Chromium content is measured in thousandths, and other alloying elements are expressed by the alloy content of alloy structural steel. For example, bearing steel with an average chromium content of 1.50% is labeled “GCr15”.

②For carburized bearing steel, the grade of alloy structure steel is used, and the symbol “G” is added to the head of the steel grade. For example, “G20CrNiMo”.

③For high carbon chromium stainless bearing steel and high temperature bearing steel, the designation method of stainless steel and heat-resistant steel is adopted, and the symbol “G” is not added to the head of the designation. For example: high carbon chromium stainless bearing steel “9Cr18” and high temperature bearing steel “10Cr14Mo”.

### 9.Designation Method of Stainless Steel and Heat-Resistant Steel

The grades of stainless steel and heat-resistant steel are represented by the alloying element symbols and Arabic numerals specified in the standard, and “Y” is added to the head of the grade for cutting stainless steel and free-cutting heat-resistant steel.

An Arabic number is generally used to indicate the average carbon content (in parts per thousand); When the average carbon content is ≥1.00%, it is represented by two Arabic numerals; When the upper limit of carbon content＜0.10%, “0” represents the carbon content; When the upper limit of carbon content ≤0.03%, > 0.01% (ultra-low carbon), “03” represents the carbon content; When the carbon content upper limit (≤0.01% extremely low carbon), “01” represents the carbon content. When there is no lower limit for carbon content, Arabic numerals are used to represent the upper limit of carbon content.

The expression method of alloy element content is the same as that of alloy structural steel. For example: stainless steel with an average carbon content of 0.20% and a chromium content of 13% is designated as “2Cr13”; The upper limit of carbon content is 0.08%, the average chromium content is 18%, and the chromium-nickel stainless steel with nickel content of 9%, its grade is expressed as “0Cr18Ni9”; Free cutting chromium stainless steel with sulphur and an upper carbon content of 0.12% and an average chromium content of 17%, and its grade is “Y1Cr17”; High carbon chromium stainless steel with an average carbon content of 1.10% and a chromium content of 17% is designated as “11Cr7”; The upper limit of carbon content is 0.03%, the average chromium content is 19%, and the ultra-low carbon stainless steel with nickel content is 10%, and its grade is expressed as “03Cr19Ni10”; The upper limit of carbon content is 0.01%, the average chromium content is 19%, and the ultra-low carbon stainless steel with nickel content of 11% is designated as “01Cr19Ni11”.

The current Chinese stainless steel standards are revised according to JIS standards, but the marking method of stainless steel is different from the standards of Japan and other countries.China is represented by alloying elements and average C content, while Japan is represented by letters and Arabic numerals to indicate usage.For example, stainless steel grades SUS202, SUS316, SUS430, S-steel (steel), U-use (purpose), S-stainless (stainless steel). For example, heat-resistant steel grades SUH309, SUH330, SUH660, H-Heatresistins. Different numbers in the grades represent various types of stainless and heat-resistant steel. Japan represents various products of stainless and heat-resistant steel, and the corresponding letters are added after the grade, such as stainless steel bar SUS-B, hot-rolled stainless steel plate SUS-HP; heat-resistant steel bar SUHB, heat-resistant steel plate SUHP. In Western countries such as the United Kingdom and the United States, the representation method of stainless heat-resistant steel grades is basically the same as that in Japan, mainly represented by Arabic numerals, and the numbers represented are the same, that is, the grades are the same.

### 10.Representation Method of Steel Grades for Welding

The welding steel includes carbon steel for welding, alloy steel for welding and stainless steel for welding, etc., and the marking method is to add the symbol “H” on the head of the welding steel. For example: “H08”, “H08Mn2Si”, “H1Cr18Ni9”.

High quality welding steel with the symbol “A” at the end of the grade.

### 11.Representation Method of Silicon Steel Grades for Electrical Use

Steel grades consist of numbers, letters and numbers.

The letter symbols of non-oriented and oriented silicon steels are “W” and “Q” respectively.

The thickness is placed in front, the letter symbol in the middle, and the iron loss number in the back, such as 30Q113. In oriented silicon steel, the letter symbols “G” and “Q” with high magnetic induction are placed together, such as 30QG113.

The numbers after the letters indicate 100 times the iron loss value (W/kg).

The letter “G”, indicating the test at high frequency; Without the letter “G”, it means that the test is carried out at a frequency of 50 cycles.

30Q113 indicates that the maximum iron loss per unit weight of cold-rolled grain-oriented silicon steel products for electrical use is 1.13W/kg at a frequency of 50 Hz.

The representation method of cold-rolled silicon steel is consistent with the Japanese standard (JISC2552-86), but the letter symbols are different. For example, the grade of oriented silicon steel is 27Q140, the corresponding JIS grade is 27G140, and the corresponding JIS grade of 30QG110 is 30P110 (G: Stands for ordinary material  P: Indicates high orientation).  The grade of non-oriented silicon steel is 35W250, and the corresponding JIS grade is 35A250.

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