1. Mechanical properties of steel
1. Yield strength (σs)
When the steel or sample is stretched, when the stress exceeds the elastic limit, even if the stress no longer increases, the steel or sample continues to experience significant plastic deformation. This phenomenon is called elasticity, and the minimum stress value when elasticity occurs is. for the elastic limit. Suppose Ps is the external force at the yield point s, Fo is the cross section of the sample, then the yield point σs =Ps/Fo(MPa).
2. Yield limit (σ0.2)
The yield strength of some metallic materials is extremely vague and difficult to measure. Therefore, in order to measure the elastic characteristics of the material, the stress when the permanent residual plastic deformation is equal to a certain value (usually 0.2% of the original length). ) is specified, which is called the yield condition or simply the yield stress σ0.2.
3. Tensile strength (σb)
The maximum stress value reached by the material from the beginning until the moment of failure during the stretching process. It indicates the steel’s ability to resist breaking. Tensile strength corresponds to compressive strength, bending strength, etc. Assuming that Pb is the maximum tensile force reached before the material fails, Fo is the cross-sectional area of the sample, then the tensile strength σb = Pb/Fo (MPa).
4. Elongation (δs)
Once the material is broken, the percentage of its plastic elongation length relative to the length of the original specimen is called elongation or elongation.
5. Yield/resistance ratio (σs/σb)
The ratio of the yield strength (yield strength) of steel to its tensile strength is called yield ratio. The higher the yield strength ratio, the higher the reliability of structural parts. Generally, the yield strength ratio of carbon steel is 0.6 to 0.65, and that of low alloy structural steel is 0.65 to 0.75. 0.86.
6.Hardness
Hardness indicates a material’s ability to resist hard objects digging 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 include Brinell hardness, Rockwell hardness and Vickers hardness.
1) Brinell hardness (HB)
Drive a hardened steel ball of a certain size (usually 10mm in diameter) into the material surface with a certain load (usually 3000kg) and keep it for a certain time. After the load is removed, the ratio of load to load is calculated. its indentation area is the Brinell hardness (HB) value.
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 or 3.18 mm to press the surface of the material to be tested under a certain load, and the hardness of the material is calculated from the depth of the indentation. Depending on the different hardnesses of the material to be tested, it is expressed according to three different scales:
HRA: This is the hardness obtained using a 60 kg load and a diamond cone intruder, and is used for extremely hard materials (like cemented carbide, etc.).
HRB: This is the hardness obtained using a load of 100 kg and a hardened steel ball with a diameter of 1.58 mm. It is used for materials of lower hardness (such as annealed steel, cast iron, etc.).
HRC: Hardness is obtained using a 150 kg load and a diamond cone intruder, and is used for very high hardness materials (such as hardened steel, etc.).
3) Vickers hardness (HV)
Use a diamond square cone intruder with a load of less than 120 kg and a vertex angle of 136° to depress the material surface by the load value, which is the Vickers hardness value (.HT).
2. Ferrous metals and non-ferrous metals
1. Black metal
Refers to iron and iron alloys. Such as steel, pig iron, ferroalloy, cast iron, etc. Steel and cast iron are iron-based alloys with carbon as the main added element. They are collectively called iron-carbon alloys.
Pig iron refers to a product obtained by smelting iron ore in a blast furnace and is mainly used to make steel and castings.
Pig iron is melted in an iron smelting furnace to obtain pig iron (liquid iron-carbon alloy with a carbon content greater than 2.11%), and the liquid iron is poured into a casting. This type of cast iron is called. a casting.
Ferroalloy is an alloy composed of iron and silicon, manganese, chromium, titanium and other elements. Ferroalloy is one of the raw materials for making steel. It is used as a deoxidizer and alloying element additive for steel during steel manufacturing.
Iron-carbon alloys with a carbon content of less than 2.11% are called steel. Steel is made by placing pig iron intended for steelmaking into a steelmaking furnace and melting it in a certain process. Steel products include steel ingots, continuous casting billets and direct casting of various steel castings. Steel generally refers to rolled steel in various steel products.
2. Non-ferrous metals
Also called non-ferrous metals, they refer to metals and alloys other than ferrous metals, such as copper, tin, lead, zinc, aluminum, brass, bronze, aluminum alloys and bearing alloys. Additionally, chromium, nickel, manganese, molybdenum, cobalt, vanadium, tungsten, titanium, etc. are also used in industry. These metals are mainly used as alloy additives to improve the properties of the metal. molybdenum, etc. are mainly used to produce cemented carbide cutting tools. The above non-ferrous metals are called industrial metals, in addition to precious metals: platinum, gold, silver, etc. and rare metals, including radioactive uranium, radium, etc.
3. Classification of steel
Besides iron and carbon, the main elements of steel are silicon, manganese, sulfur, phosphorus, etc.
There are many ways to classify steel, and the main methods are:
1. Ranking by quality
(1) Ordinary steel (P≤0.045%, S≤0.050%)
(2) High quality steel (P and S both ≤0.035%)
(3) High quality steel (P≤0.035%, S≤0.030%)
2. Classification according to chemical composition
(1) Carbon steel: a. Low carbon steel (C≤0.25%); b. High carbon steel (C≤0.60%);
(2) Alloy steel: a. Low alloy steel (total content of alloying elements ≤ 5%); b. Medium alloy steel (total content of alloying elements > 5 to 10%); elements > 10%).
3. Classification according to forming method
(1) Forged steel; (2) Cast steel; (3) Hot-rolled steel;
4. Classification according to metallographic structure
(1) Annealed condition: a. Hypoeutectoid steel (ferrite + pearlite); b. Hypereutectoid steel (perlite + cementite);
(2) In the normalized state: a. Pearlitic steel; c. Martensitic steel;
(3) No phase change or partial phase change
5. Classification by use
(1) Steel for construction and engineering: a. Ordinary carbon structural steel; b. Reinforced structural steel;
(2) Structural steel:
has. Steel for machine manufacturing: (a) Quenched and tempered structural steel; (b) Surface hardened structural steel: including case hardened steel, surface hardened steel; (c) Easy-to-cut structural steel; Cold plasticity Forming steel: including cold stamping steel and cold heading steel.
B. Spring steel
c. Bearing steel
(3) Tool steel: a. Alloy tool steel;
(4) Special performance steel: a. Acid-resistant stainless steel; b. Heat-resistant steel: oxidation-resistant steel and alloy steel for electric heating; ; e. Low temperature steel;
(5) Professional steel – such as bridge steel, ship steel, boiler steel, pressure vessel steel, agricultural machinery steel, etc.
6. Complete ranking
(1) Ordinary steel
has. Carbon structural steel: (a) Q195; (b) Q215 (A, B); (c) Q235 (A, B, C);
b. Low alloy structural steel
c. Ordinary structural steel for specific purposes
(2) High quality steel (including high quality steel)
has. Structural steel: (a) high quality carbon structural steel; (b) alloy structural steel; (d) easy-to-cut structural steel; (f) high quality structural steel; for specific purposes.
b. Tool steel: (a) carbon tool steel; (b) alloy tool steel;
c. Special performance steel: (a) Acid-resistant stainless steel; (b) Heat-resistant steel; (c) Electrically heated alloy steel; (e) Wear-resistant high manganese steel.
7. Classification by fusion method
(1) Depending on the type of oven
has. Conversion steel: (a) acid conversion steel (b) alkali conversion steel; Or (a) bottom blown conversion steel; (b) top blown conversion steel;
b. Electric furnace steel: (a) electric arc furnace steel; (b) electric slag furnace steel; (c) induction furnace steel; (e) electron beam furnace steel;
(2) According to the degree of deoxidation and casting system
has. Calcined steel; b. Special calcined steel;
4. Overview of my country’s steel number representation methods
Product brands are usually represented by a combination of Chinese pinyin letters, chemical element symbols, and Arabic numerals. Right away:
①The chemical elements of steel grade are represented by international chemical symbols, such as Si, Mn, Cr…etc. Mixed rare earth elements are represented by “RE” (or “Xt”).
②Product name, usage, melting and casting methods, etc. are usually represented by the abbreviated letters of Chinese pinyin.
③The content (%) of the main chemical elements in steel is expressed in Arabic numerals.
When Chinese pinyin letters are used to represent product names, uses, characteristics and processing methods, the first letter is usually selected from the Chinese pinyin representing the product name. When letters selected by another product are repeated, you can use the second letter or third letter instead, or select the first pinyin letter of two Chinese characters at the same time.
If there are currently no applicable Chinese characters or Chinese pinyin, the symbols will be English letters.
5. Subdivision explanation of steel number expression method in my country
1. Method of representing carbon structural steels and low alloy high strength structural grades
The steel mentioned above is generally divided into two categories: general purpose steel and special purpose steel. The grade representation method consists of the Chinese pinyin letters of the yield strength or yield strength of steel, the value of the yield strength or yield strength, the grade of steel and the degree of deoxidation of steel, which is actually made up of 4 parts. .
①General structural steel uses the pinyin letter “Q” which represents the yield strength. The yield strength value (unit: MPa) and symbols such as quality level (A, B, C, D, E) and deoxidation method (F, b, Z, TZ) specified in the table 1 are used to form a level. in order. For example: carbon structural steel grades are expressed as follows: Q235AF, Q235BZ; high strength low alloy structural steel grades are expressed as: Q345C, Q345D.
Q235BZ represents killed carbon structural steel with yield strength value ≥235MPa and B grade quality.
The two grades Q235 and Q345 are the most typical engineering steel grades, with the largest production and usage, and the most widely used grades. These two brands are available in almost every country in the world.
In the composition of carbon structural steel grades, the killed steel symbol “Z” and the special killed steel symbol “TZ” may be omitted. For example: Q235 steel with quality grades C and D respectively, its grades should be Q235CZ and Q235DTZ. But it can be omitted as Q235C and Q235D.
High strength low alloy structural steel includes killed steel and special killed steel, but the symbol indicating the deoxidation method is not added at the end of the grade.
②Special structural steel is generally represented by the symbol “Q” representing the yield strength of the steel, the yield strength value and the symbol representing the use of the product specified in Table 1. By example: the steel grade for pressure vessels is expressed as “Q345R”. “; the weathering steel grade represented by Q340NH; the Q295HP steel grade for welding gas cylinders; the Q390g steel grade for boilers; the Q420q steel grade for bridges.
③ Depending on requirements, grades of high-strength low-alloy general structural steel can also use two Arabic numerals (indicating the average carbon content, in ten thousandths) and chemical element symbols, expressed in the order of low special purpose shades; -high strength structural steel alloy. The brand name may also be expressed in sequence using two Arabic numerals (indicating the average carbon content in parts per ten thousand) and chemical element symbols, as well as certain prescribed symbols representing the uses of the product.
2. How to indicate the grades of high quality carbon structural steel and high quality carbon spring steel
High-quality carbon structural steel uses two Arabic numerals (indicating the average carbon content in ten thousandths) or a combination of Arabic numerals and element symbols to form a mark.
①For boiling steel and semi-killed steel, add the symbols “F” and “b” respectively at the end of the grade. 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%, its grade is expressed as “10b”.
② Killed steel (S and P ≤ 0.035% respectively) is generally not marked with a symbol. For example: the grade of killed steel with an average carbon content of 0.45% is expressed as “45”.
③ For high-quality carbon structural steel with higher manganese content, the manganese element symbol is added after the Arabic numeral indicating the average carbon content. For example: the grade of steel having an average carbon content of 0.50% and a manganese content of 0.70% to 1.00% is expressed as “50Mn”.
④ For high quality carbon structural steel (S and P ≤ 0.030% respectively), add the symbol “A” after the grade. For example: the high-quality carbon structural steel grade with an average carbon content of 0.45% is expressed as “45A”.
⑤High quality special grade carbon structural steel (S≤0.020%, P≤0.025%), add symbol “E” after the grade. For example: the grade of high quality special grade carbon structural steel with an average carbon content of 0.45% is expressed as “45E”.
The method of expressing grades of high-quality carbon spring steel is the same as the method of expressing grades of high-quality carbon structural steel (65, 70, 85 and 65Mn steels exist in both standards GB/T1222 and GB/T699 at the same time).
3. Representation of alloy structural steel and alloy spring steel grades
①Alloy structural steel grades are represented by standard Arabic numerals and chemical element symbols.
Use two Arabic numerals to indicate the average carbon content (in parts per 10,000) and place it at the top of the category.
The method of expressing the alloy element content is as follows: when the average content is less than 1.50%, only the element is indicated in the grade, and the content is generally not indicated; the average alloy content is 1.50% ~ 2.49%, 2.50% ~; 3.49%, 3.50% ~ 4.49%, 4.50% ~ When 5.49%,…, it is written 2, 3, 4, 5… after the alloying elements .
For example: alloy structural steel with average carbon, chromium, manganese and silicon contents of 0.30%, 0.95%, 0.85% and 1.05% respectively. When the S and P contents are respectively ≤ 0.035%, the grade is expressed as follows: “. 30CrMnSi”.
High quality advanced alloy structural steel (S and P content ≤ 0.025% respectively) is represented by the addition of the symbol “A” at the end of the grade. For example: “30CrMnSiA”.
For high quality special grade alloy structural steels (S≤0.015%, P≤0.025%), add the symbol “E” at the end of the grade, for example: “30CrM nSiE”.
For special alloy structural steel grades, the symbol representing the product use specified in Table 1 shall be added to the head (or tail) of the grade. For example, the steel number of 30CrMnSi steel specially used for rivet screws is ML30CrMnSi.
②The grade expression method of alloy spring steel is the same as that of alloy structural steel.
For example: spring steel with average content of carbon, silicon and manganese is 0.60%, 1.75% and 0.75%, respectively, and its grade is expressed as “60Si2Mn”. For high quality spring steel, add the symbol “A” at the end of the grade, and its grade is expressed as “60Si2MnA”.
4. How to express the grades of free-cutting steel
Free-cut steels are represented by standard chemical element symbols, prescribed symbols and Arabic numerals. Arabic numerals indicate the average carbon content (in parts per 10,000).
① For free-cutting steel added with sulfur and free-cutting steel added with sulfur and phosphorus, the symbol of the free-cutting element is not added after the symbol “Y” and the Arabic numeral. For example: the free-cutting steel grade with an average carbon content of 0.15% is expressed as “Y15”.
② For free-cutting steels added with sulfur or sulfur and phosphorus with a higher manganese content, the manganese element symbol is added after the symbol “Y” and the Arabic numeral. For example: the grade of free-cutting steel having an average carbon content of 0.40% and a manganese content of 1.20% to 1.55% is expressed as “Y40Mn”.
③ For free-cutting steels containing free-cutting elements such as calcium and lead, add the symbol of the free-cutting element after the “Y” symbol and the Arabic numeral. For example: “Y15Pb”, “Y45Ca”.
5. Method of expressing the grades of unquenched and tempered engineering steel
For unquenched and tempered structural steel, the symbols “YF” and “F” are added to the grade header to indicate easy-to-cut unquenched and tempered structural steel and the unquenched and tempered engineering steel for hot forging. Other contents of the shade representation method are consistent with the structure of the alloy. For example: “YF35V”, “F45V”.
6. How to Express Tool Steel Grades
Tool steel is divided into three categories: carbon tool steel, alloy tool steel and high-speed tool steel.
①Carbon tool steel is represented by standard chemical element symbols, prescribed symbols and Arabic numerals. Arabic numerals indicate the average carbon content (in parts per thousand).
has. For ordinary carbon tool steel containing manganese, the tool steel symbol “T” is followed by an Arabic numeral. For example: carbon tool steel with an average carbon content of 0.80%, its grade is expressed as “T8”.
b. For carbon tool steel with a higher manganese content, add the manganese element symbol after the tool steel symbol “T” and the Arabic numeral. For example: “T8Mn”.
c. For high quality carbon tool steel, add “A” to 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 expressed in the same manner as alloy structural steel grades. It is represented by the alloy element symbols and Arabic numerals specified by the standard, but the average carbon content is generally not stated. For example, the average carbon content is 1.60% and the chromium, molybdenum and vanadium contents are 11.75%. 0.50% and 0.22% respectively. Alloy tool steel, its grade is expressed as “Cr12MoV”; the high-speed tool steel grade with an average carbon content of 0.85% and tungsten, molybdenum, chromium and vanadium contents of 6.00%, 5.00%, 4.00% and 2.00% respectively is “W6Mo5Cr4V2”. “.
If the average carbon content is less than 1.00%, an Arabic numeral may be used to express the carbon content (in thousandths). For example: the alloy tool steel grade with an average carbon content of 0.80%, manganese content of 0.95% and silicon content of 0.45% is expressed as “8MnSi”.
For low chromium alloy tool steels (average chromium content <1.00%), add the number “0” before the chromium content (in parts per thousand). For example: the grade of alloy tool steel with an average chromium content of 0.60% is expressed as “Cr06”.
7. How to express steel grades for plastic molds
Except for the addition of the “SM” symbol on the head, plastic mold steel grades are expressed the same as high quality carbon structural steel and carbon steel grades. Allied tools. For example: carbon plastic mold steel with an average carbon content of 0.45%, its grade is expressed as “SM45”; alloy plastic mold steel with average carbon content of 0.34%, chromium content of 1.70% and molybdenum content of 0.42%, its brand is “SM3Cr2Mo”.
8. How to express bearing steel grades
Bearing steel is divided into four categories: high carbon chrome bearing steel, case hardened bearing steel, high carbon chrome stainless bearing steel and bearing steel at high temperature.
①For high carbon chrome bearing steel, add the symbol “G” to the head of the grade, but do not indicate the carbon content. Chromium content is expressed in parts per thousand and other alloying elements are expressed in terms of the alloy content of the alloyed structural steel. For example: the bearing steel grade with an average chromium content of 1.50% is expressed as “GCr15”.
②Carburized bearing steel is represented by the alloy structural steel grade, and the symbol “G” is added to the head of the grade. For example: “G20CrNiMo”. High quality carbide bearing steel, add “A” to the end of the grade. For example: “G20CrNiMoA”.
③High carbon chrome stainless bearing steel and high temperature bearing steel are represented by grades of stainless steel and heat resistant steel, without the symbol “G” at the head of the grade. shade. For example: high carbon chrome stainless bearing steel “9Cr18” and high temperature bearing steel “10Cr14Mo”.
9. How to indicate grades of stainless steel and heat resistant steel
Grades of stainless steel and heat-resistant steel are represented by alloy element symbols and Arabic numerals specified in the standard. To cut stainless steel and easy-to-cut heat-resistant steel, a “Y” is added to the head of the grade.
Generally, an Arabic numeral is used to express the average carbon content (in thousandths); when the average carbon content is ≥ 1.00%, it is expressed with two Arabic numerals, when the upper limit of the carbon content is < 0,10 %, elle est exprimée ; comme "0" "exprimer Teneur en carbone ; lorsque la limite supérieure de la teneur en carbone est ≤0,03 % et >0.01% (very low carbon), the carbon content is expressed as “03” when the upper limit of the carbon content (≤0.01% is extremely low carbon; ), it is expressed as ” 01 » » which represents the carbon content. When there is no lower limit for carbon content, Arabic numerals are used to indicate the upper limit for carbon content.
The method of expressing the 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 chromium content of 13% has a grade of “2Cr13”; the upper limit of carbon content is 0.08%, the average chromium content is 18%, and the nickel content is 9%. Chrome nickel is not. Stainless steel, its grade is expressed as “0Cr18Ni9”; the upper limit of carbon content is 0.12% and the average chromium content is 17%, free-cutting chromium stainless steel added to sulfur, its grade is expressed as “Y1Cr17”; the average carbon content is 1.10%, high carbon chromium stainless steel with 17% chromium content, its brand name is “11Cr7”; ultra-low carbon stainless steel with an upper carbon content limit of 0.03%, an average chromium content of 19%; a nickel content of 10%, i.e. The grade is expressed as “03Cr19Ni10”; the upper limit of carbon content is 0.01%, the average chromium content is 19% and the nickel content is 11% of ultra-low carbon stainless steel, its grade is expressed as “01Cr19Ni11”.
The current national standards for stainless steel and heat-resistant steel are revised with reference to JIS standards, but the method of expressing the grades of stainless steel and heat-resistant steel is different from the standards of the Japan and other countries. We express it by alloying elements and average C content, while Japan expresses it by Arabic letters and numbers indicating the purpose. 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 grade indicate different types of stainless and heat resistant steel. Japan represents different types of stainless steel and heat resistant products, adding corresponding letters after the brand name, such as SUS-B stainless steel rod, SUS-HP hot rolled stainless steel sheet , SUHB heat-resistant steel rod, heat-resistant; SUHP steel plate. In Western countries like the United Kingdom and the United States, the method of expressing heat-resistant stainless steel grades is basically the same as in Japan. It is mainly expressed by Arabic numerals, and the numerals expressed are the same, i.e. that is, the notes are the same. Because stainless and heat-resistant steel from Japan comes from the United States.
10. Representation of steel grades for welding
Welding steel includes carbon steel welding, alloy steel welding and stainless steel welding, etc. The grade is expressed by adding the symbol “H” to the head of each type of steel grade to be welded. For example: “H08”, “H08Mn2Si”, “H1Cr18Ni9”.
For high quality welding steel, add the symbol “A” to the end of the grade. For example: “H08A”, “08Mn2SiA”.
11. How to Express Silicon Steel Grades for Electricians
The steel number is made up of numbers, letters and numbers.
The symbol letters for unoriented and oriented silicon steel are “W” and “Q” respectively.
The thickness is placed in the front, the letter symbol is placed in the middle and the iron loss value is placed in the back, for example 30Q113. In oriented silicon steel, the symbol letters “G” and “Q” for high magnetic sensitivity are placed together, such as 30QG113.
The number after the letter represents 100 times the iron loss value (W/kg).
Those with the letter “G” represent high frequency tests; those without “G” represent tests at a frequency of 50 cycles.
30Q113 states that the maximum unit weight iron loss value of cold-rolled oriented silicon steel products for electrical applications at a frequency of 50 Hz is 1.13 W/kg.
The expression method of cold rolled silicon steel conforms to the Japanese standard (JISC2552-86), but the letter symbols are different. For example, the oriented silicon steel grade is 27Q140, the corresponding JIS grade is 27G140 and the corresponding grade. The JIS grade of 30QG110 is 30P110 (G: means ordinary material, P: indicates high orientation). The non-oriented silicon steel grade is 35W250 and the corresponding JIS grade is 35A250.
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