Steel Plates

The steel plate is a flat-like steel cast with molten steel and pressed after cooling.

The steel plate is flat, rectangular and can be rolled directly or cut from a wide steel strip.

According to the thickness of the steel plate, the thin steel plate <4 mm (the thinest 0.2 mm), the medium thick steel plate 4~60 mm, the extra thick steel plate 60~115 mm.

The steel plate is divided into hot rolling and cold rolling according to rolling.

The width of the sheet is 500~1500 mm; The width of the thickness is 600~3000 mm. The sheet is divided into ordinary steel, high-quality steel, alloy steel, spring steel, stainless steel, tool steel, heat-resistant steel, bearing steel, silicon steel and industrial pure iron sheet, etc. According to professional use, there are oil drum board, enamel board, bulletproof board, etc.; According to the surface coating, there are galvanized sheet, tin-plated sheet, lead-plated sheet, plastic composite steel plate and so on.

The steel grade of thick steel plate is roughly the same as that of thin steel plate. In all aspects of the product, in addition to bridge steel plate, boiler steel plate, automobile manufacturing steel plate, pressure vessel steel plate and multi-layer high-pressure vessel steel plate and other varieties are pure thick plates, some varieties of steel plates such as automobile girder steel plate (thick 2.5~10 mm), pattern steel plate (thick 2.5~8 mm), stainless steel plate, heat-resistant steel plate and other varieties are crossed with thin plates.

In addition, the steel plate and the material said that not all steel plates are the same, the material is not the same, and the place where the steel plate is used is not the same.

Properties of alloy steel plate

With the development of science and technology and industry, higher requirements have been put forward for materials, such as higher strength, resistance to high temperature, high pressure, low temperature, corrosion resistance, wear and other special physical and chemical properties, carbon steel can not fully meet the requirements.

Deficiency of carbon steel

(1) Low hardenability.Under normal circumstances, the maximum penetration diameter of carbon steel water quenching is only 10mm-20mm.

(2) The strength and yield are relatively low.For example, the σs of ordinary carbon steel Q235 steel is 235MPa, and the σs of low-alloy structural steel 16Mn is more than 360MPa. The σs /σb of steel 40 is only 0.43, which is much lower than that of alloy steel.

(3) Poor tempering stability.Due to poor tempering stability, when tempering carbon steel, in order to ensure high strength, a lower tempering temperature is needed, so that the toughness of steel is low; In order to ensure better toughness, the strength is low when the tempering temperature is high, so the comprehensive mechanical properties of carbon steel are not high.

(4) can not meet the special performance requirements.Carbon steel is often poor in oxidation resistance, corrosion resistance, heat resistance, low temperature resistance, wear resistance and special electromagnetism, and can not meet the needs of special performance.

Alloy steel plate material

According to the content of alloying elements, divided into

Low alloy steel (total alloying element less than 5%),

Medium alloy steel (total alloying elements of 5%-10%)

High alloy steel (more than 10% total alloying element).

According to the main alloying elements contained, divided into

Chromium steel (Cr-Fe-C)

Chrome-nickel steel (Cr-Ni-Fe-C)

Manganese steel (Mn-Fe-C)

Silicon manganese steel (Si-Mn-Fe-C)

According to the small sample normalizing or as-cast structure, divided into

Pearlitic steel

Martensitic steel

Ferritic steel

Austenitic steel

Letenite steel

Classification by use

Alloy structural steel

Alloy tool steel

Special performance steel

ID

The carbon content is marked numerically at the beginning of the brand. It is stipulated that the carbon content of structural steel is represented by a number of one-thousandth of the unit (two digits), tool steel and special performance steel is represented by a number of one-thousandth of the unit (one digit), and the carbon content of tool steel is not marked when the carbon content exceeds 1%.

After indicating the carbon content figure, the chemical symbol of the element indicates the main alloying element in the steel, the content is indicated by the figure behind it, and the average content is less than 1.5%, and the average content is 1.5% ~ 2.49%, 2.5% ~ 3.49%...... When the corresponding landmark 2, 3...... .

Alloy structural steel 40Cr, the average carbon content is 0.40%, the main alloying element Cr content is less than 1.5%.

Alloy tool steel 5CrMnMo, the average carbon content is 0.5%, the main alloying elements Cr, Mn, Mo content are below 1.5%.

Special steel is indicated by the Chinese pinyin prefix for its purpose.

For example, ball bearing steel is marked with "G" before the steel number. GCr15 represents ball bearing steel with a carbon content of about 1.0% and chromium content of about 1.5%(this is a special case where chromium content is expressed in numbers in thousandths of a percent).

Y40Mn, which means free-cutting steel with carbon content of 0.4% and manganese content of less than 1.5%, etc.

For high-grade high-quality steel, the word "A" is added to the end of the steel to indicate, such as 20Cr2Ni4A

§7-1 Alloying of steel

When alloying elements are added to steel, the basic components of steel, iron and carbon, interact with the added alloying elements. The purpose of steel alloying is to improve the structure and properties of steel by using the interaction of alloying elements with iron and carbon and the influence on the iron-carbon phase diagram and the heat treatment of steel.

1. Use

Alloy tempered steel is widely used in the manufacture of automobiles, tractors, machine tools and other important parts on the machine, such as gears, shafts, connecting rods, bolts and so on.

2. Performance requirements

Most of the tempering parts bear a variety of working loads, the stress situation is more complex, requiring high comprehensive mechanical properties, that is, with high strength and good plasticity, toughness. Alloy tempered steel also requires good hardenability. However, different parts have different forces, and the requirements for hardenability are not the same.

3. Ingredient characteristics

(1) Medium carbon: carbon content is generally between 0.25% and 0.50%, mostly 0.4%;

(2) Add elements to improve hardenability Cr, Mn, Ni, Si, etc. : In addition to improving hardenability, these alloy elements can also form alloy ferrite and improve the strength of steel. For example, the performance of 40Cr steel after tempering treatment is much higher than that of 45 steel;

(3) Add elements to prevent the second type of tempering brittleness: alloy tempered steel containing Ni, Cr and Mn, which is easy to produce the second type of tempering brittleness when tempered at high temperature and cooled slowly. The addition of Mo and W to steel can prevent the second type of tempering brittleness, and the appropriate content is about 0.15% ~ 0.30%Mo or 0.8% ~ 1.2% W.

Comparison of properties of 45 steel and 40Cr steel after tempering

Steel number and heat treatment state Section size/mm sb/ MPa ss/MPa d5/ % y/% ak/kJ/m2

45 Steel 850℃ water quenching, 550℃ tempering f50 700 500 15 45 700

40Cr steel oil quenched at 850℃, tempered at 570℃ f50 (core) 850 670 16 58 1000

4. Steel grades and grades

(1)40Cr low hardenability tempered steel: The critical diameter of oil quenching of this type of steel is 30mm ~ 40mm, which is used to manufacture important parts of general size.

(2) hardenability alloy tempered steel in 35CrMo: the critical diameter of oil quenching of this type of steel is 40mm ~ 60mm, and the addition of molybdenum can not only improve the hardenability, but also prevent the second type of temper brittleness.

(3)40CrNiMo high hardenability alloy tempered steel: The oil quenching critical diameter of this type of steel is 60mm-100mm, mostly chrome-nickel steel. Adding appropriate molybdenum to chrome-nickel steel not only has good hardenability, but also can eliminate the second type of temper brittleness.

5. Heat treatment and organizational properties

The final heat treatment of alloy tempered steel is quenching and tempering at high temperature (tempered treatment). Alloy tempered steel hardenability is high, generally oil, hardenability is particularly large and can even be air cooled, which can reduce heat treatment defects.

The final properties of alloy tempered steel are determined by the tempering temperature. Generally used 500℃-650℃ tempering. By selecting the tempering temperature, the desired performance can be obtained. In order to prevent the second type of tempering brittleness, fast cooling after tempering (water cooling or oil cooling) is conducive to the improvement of toughness.

The microstructure of alloy tempered steel after conventional heat treatment is tempered sorbite. For parts requiring wear resistance on the surface (such as gears, mainshafts), induction heating surface quenching and low temperature tempering are carried out, and the surface structure is tempered martensite. The surface hardness can reach 55HRC ~ 58HRC.

After quenching and quenching, the yield strength of alloy tempered steel is about 800MPa, and the impact toughness of 800kJ/m2 core hardness can reach 22HRC ~ 25HRC. If the cross-section size is large and not quenched thoroughly, the performance is significantly reduced.

Steel plate classification

Steel plate (includingClassification of strip steel:

1, according to the thickness of the classification: (1) sheet, the thickness is not more than 3mm(except electrical steel plate) (2) plate, the thickness of 4-20mm (3) thick plate, the thickness of 20-60mm (4) extra thick plate, the thickness is greater than 60mm

2, according to the production method classification: (1) hot rolled steel plate (2) cold rolled steel plate

3, according to the surface characteristics of the classification: (1) galvanized sheet (hot galvanized sheet, galvanized sheet) (2) tinplate (3) composite steel plate (4) color coated steel plate

4, classified by use: (1) bridge steel plate (2) boiler steel plate (3) shipbuilding steel plate (4) armor steel plate (5) automobile steel plate (6) Roof steel plate (7) Structural steel plate (8) electrical steel plate (silicon steel sheet) (9) spring steel plate (10) heat-resistant steel plate (11) alloy steel plate (12) other

1, high-quality carbon structural steel hot rollingSheet steel and steel strip

High quality carbon structural steel hot rolled sheet steel and steel strips are used in the automotive, aviation and other sectors. The grade of its steel is boiling steel: 08F, 10F, 15F; Killed steel: 08, 08AL, 10, 15, 20, 25, 30, 35, 40, 45, 50. 25 and below are low carbon steel plates, 30 and above are medium carbon steel plates.

2, high-quality carbon structural steel hot rollingThick steel plate and wide steel strip

High quality carbon structural steel hot rolled thick steel plates and wide steel strips are used for various mechanical structural parts. Its steel grade is low carbon steel including: 05F, 08F, 08, 10F, 10, 15F, 15, 20F, 20, 25, 20Mn, 25Mn, etc.; Medium carbon steel includes: 30, 35, 40, 45, 50, 55, 60, 30Mn, 40Mn, 50Mn, 60Mn, etc.; High carbon steel includes: 65, 70, 65Mn, etc.

Special structural steel plate

1, pressure vessel steel plate:It is indicated by capital R at the end of the grade, and its grade can be indicated by the yield point or the carbon content or alloying element. For example, Q345R and Q345 are yield points. Another example: 20R, 16MnR, 15MnVR, 15MnVNR, 8MnMoNbR, MnNiMoNbR, 15CrMoR, etc., are expressed by carbon content or alloying elements.

2. Steel plate for welding gas cylinder:Use capitalized HP at the end of the brand, its brand can be represented by the yield point, such as: Q295HP, Q345HP; It can also be represented by alloying elements such as 16MnREHP.

3, boiler steel plate:Use a lowercase g at the end of the label. Its grade can be indicated by the yield point, such as: Q390g; It can also be expressed by carbon content or alloying elements, such as 20g, 22Mng, 15CrMog, 16Mng, 19Mng, 13MnNiCrMoNbg, 12Cr1MoVg, etc.

4, bridge steel plate:Use lowercase q at the end of the brand, such as Q420q, 16Mnq, 14MnNbq, etc.

5. Steel plate for automobile girder:Use a capital L at the end of the brand, such as 09MnREL, 06TiL, 08TiL, 10TiL, 09SiVL, 16MnL, 16MnREL, etc.