Meaning of Bolt Performance Class

       The performance grade of bolts for steel structure connection is 3.6, 4.6, 4.8, 5.6, 6.8,8.8、9.8、10.9, 12.9, etc. more than 10 grades, of which8.8Grade and above bolts are made of low-carbon alloy steel or medium carbon steel and are heat treated (quenched and tempered), commonly known as high-strength bolts, and the rest are commonly known as ordinary bolts. The bolt performance grade label consists of two parts, which respectively represent the nominal tensile strength value and yield ratio of the bolt material. For example, a bolt with performance class 4.6 means:
1. The nominal tensile strength of bolt material is 400MPa;
2. The yield ratio of bolt material is 0.6;
3. The nominal yield strength of bolt material reaches 400 × 0.6 = 240MPa performance grade10.9Grade high-strength bolts, the material after heat treatment, can achieve:
1. The nominal tensile strength of bolt material shall reach 1000MPa;
2. The yield ratio of bolt material is 0.9;
3. The nominal yield strength of bolt material is 1000 × 0.9 = 900MPa
The meaning of bolt performance level is the international standard, the same performance level of bolts, regardless of its material and origin.DifferenceIts performance is the same, only the performance level can be selected in the design.
Strength class so-called8.8Level and10.9Level
Refers to the shear stress resistance of the bolt.8.8GPa and10.9Gpa
8.8Nominal tensile strength 800N/MM2 Nominal yield strength 640N/MM2
General bolts are used "X.Y" that strength,
X * 100 = tensile strength of this bolt,
X * 100 *(Y/10)= Yield strength of this bolt
(Because according to the marking: yield strength/tensile strength = Y/10)
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such as 4.8 level
This bolt
Tensile strength: 400MPa
Yield strength: 400*8/10 = 320MPa
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Another: stainless steel bolts are usually marked as A4-70,A2-70 appearance, meaning another explanation
Metrics
There are two main units of measurement of length in the world today. One is metric, and the units of measurement are meters (m), centimeters (cm), millimeters (mm), etc., which are widely used in Southeast Asia such as Europe, China and Japan. The other is imperial, and the unit of measurement is mainly inch (inch), which is equivalent to the city inch of China's old system, in the United States, Britain and other European and American countries to use more.
1. Metric measurement:(10-base)
                1m =100 cm=1000 mm
2. Imperial measurement:(8-base)
1 inch = 8 inches 1 inch = 25.4mm 3/8 ¢ x 25.4=9.52
3. Products below 1/4 ¢ use serial numbers to indicate their address diameter, such:
        4#，  5#，  6#，  7#，  8#， 10#， 12#
Thread
A 1. thread is a shape in which a uniform helix is raised in a section of a solid outer or inner surface. According to its structural characteristics and use can be divided into three categories:
(I), ordinary thread: the teeth are triangular, used to connect or fasten parts. Ordinary threads are divided into coarse thread and fine thread according to pitch, and the connection strength of fine thread is higher.
(II), transmission thread: tooth shape is trapezoidal, rectangular, saw shape and triangle, etc.
(III), sealing thread: used for sealing connection, mainly pipe thread, taper thread and taper pipe thread.
2. thread fit grade:
The thread fit is the loose or tight size between the screw threads, and the level of fit is the specified combination of deviation and tolerance on the inner and outer threads.
(I). For unified inch threads, there are three thread grades for external threads: 1A, 2A and 3A, and three grades for internal threads:
Class 1B, 2B and 3B, all with clearance fit. The higher the grade number, the tighter the fit. In the English thread, the deviation is only specified 1A and 2A, the deviation of 3A is zero, and the grade deviation of 1A and 2A is equal.
The larger the number of grades, the smaller the tolerance.
1, 1A and 1B, very loose tolerance class, which is suitable for tolerance fit of internal and external threads.
Class 2, 2A and 2B are the most common thread tolerance classes specified for inch series mechanical fasteners.
3, 3A and 3B levels, screwing to form the tightest fit, suitable for fasteners with tight tolerances, used for safety-critical design.
4. For external threads, there is a fit tolerance for grades 1A and 2A, but not for grade 3A. Class 1A tolerance is 50% larger than Class 2A tolerance and 75% larger than Class 3A tolerance. For internal threads, Class 2B tolerance is 30% larger than Class 2A tolerance. Class 1B is 50% larger than Class 2B and 75% larger than Class 3B.
(II), metric thread, external thread has three thread grades: 4h, 6 h and 6g, internal thread has three thread grades: 5H, 6 H, 7H. (Japanese standard thread accuracy grade is divided into I, II and III levels, usually II level) In metric thread, the basic deviation of H and H is zero. The basic deviation of G is positive, and the basic deviations of e, f and g are negative. As shown in the figure:
1. H is the common tolerance zone position of internal thread, which is generally not used as surface coating or extremely thin phosphating layer. The basic deviation of G position is used for special occasions, such as thicker coating, which is generally rarely used.
2.G is often used to plate 6-9um thin coating. For example, if the product drawing requires 6h bolts, the thread before plating shall adopt a tolerance zone of 6g.
3. Thread matching is best combined into H/g, H/h or G/h. For refined fastener threads such as bolts and nuts, 6H/6g matching is recommended in the standard.
(III) Thread mark
Four, self-tapping, self-drilling thread of the main geometric parameters:
(I), major diameter/tooth outer diameter (d1), which is the imaginary cylinder diameter of the thread top. The large diameter of the thread basically represents the male of the thread size.
weigh the diameter.
(II), minor diameter/tooth base diameter (d2): the imaginary cylinder diameter of the thread tooth base.
(III) and pitch (p): the axial distance between two corresponding points on the median line of adjacent teeth. In the imperial system, every inch (25.4
Mm) to indicate the tooth spacing.

The following table lists the common specifications of tooth pitch (metric) number of teeth (imperial)
1. Metric self-tapping:
Specification S T 1.5 S T
1.9        S T
2.2        S T
2.6        S T
2.9        S T
3.3        S T
3.5        S T
3.9        S T
4.2        S T
4.8        S T
5.5        S T
6.3        S T
8.0        S T
9.5
Tooth 0.5 0.6 0.8 0.9 1.1 1.3 1.3 1.3 1.4 1.6 1.8 1.8 2.1 2.1
2. Imperial self-tapping:
Specifications 4# 5# 6# 7# 8# 10# 12# 14#
Tooth
Number AB teeth 24 20 20 19 18 16 14 14
A tooth 24 20 18 16 15 12 11 10
Materials
1. currently on the market.Standard partsMainly carbon steel, stainless steel, copper three kinds of materials.
(I) carbon steel. We distinguish low carbon steel, medium carbon steel and high carbon steel and alloy steel by the content of carbon in carbon steel materials.
Low carbon steel C%≤ 0.25% is commonly referred to as A3 steel in China. Foreign basic known as 1008,1015,1018,1022 and so on. Mainly used for 4.8 grade bolts and 4 grade nuts, small screws and other products without hardness requirements. (Note: Drill nails are mainly made of 1022 materials.)
2. medium carbon steel 0.25%8.8Grade bolts and8.8Grade Hexagon products.
3. High carbon steel C%>0.45%. At present, the market is basically not used
4. Alloy poetry: alloy elements are added to ordinary carbon poetry to increase some special properties of poetry materials: such as 35, 40 jump molybdenum, SCM435,10B38. Aromatic screws mainly use SCM435 Jump alloy poetry, the main components are C, Si, Mn, P, S, Cr, Mo.
(II) stainless steel. Performance class: 45,50,60,70,80
Mainly divided into austenite (18% Cr, 8% Ni) good heat resistance, good corrosion resistance, good weldability. A1,A2,A4
Martensite and 13% Cr have poor corrosion resistance, high strength and good wear resistance. C1,C2,C4 ferritic stainless steel. 18% Cr has good upsetting and corrosion resistance is stronger than martensite. At present, the imported materials on the market are mainly Japanese products. According to the level of the main points SUS302, SUS304, SUS316.
(III) copper. Commonly used materials for brass... Zinc copper alloy. The market is mainly made of copper H62, H65 and H68Standard parts.
Carbon steel products used by the plate element:
Material available for serial number type
1 Grade 4.8 Hexagon bolt 1008K 1010 1015K
2 6.8 grade hexagon bolt 1032 1035 1040 CH38F 1039
3        8.8Grade hexagon bolt 1035ACR (below M10) 1040ACR (above M12) CH38F 1045ACR 1039 10B21 10B33 10B38
4        8.8Grade Hex socket bolt CH38F 1039 10B21(M10-M12)10B33(M14)10B38(M12-M24)10B21
5        10.9Grade Hex Bolt 1045ACR 10B38
6 │ 8 │ Grade Nut 1008K 1010
Nut 1015 Grade 8 (M<16) CH38F (M≥ 16)
8 Nut, Grade 10 CH38F 1039 10B21 10B33
9 Grade 12 Nut 1039 10B21 10B33 10B38
10 Carriage Screw 1008 1010 1015
11 Hexagon stud CH38F 1039 10B21 10B33 10B38
12 Hexagon Wood Screw 1008K 1010
13 Self-tapping nails and wall panel nails
Drill tail nail, splint nail 1018 1022 CH22A
14 Machine screw Furniture screw 1008 1010
The influence of various elements in 3. materials on the properties of steel:
1. Carbon (C): Improve the strength of steel parts, especially its heat treatment performance, but with the increase of carbon content, plasticity and toughness decrease, and will affect the cold heading performance and welding performance of steel parts.
Manganese (Mn): Improve the strength of steel parts and improve the hardenability to a certain extent. Manganese also improves the surface quality, but too much manganese is detrimental to ductility and weldability. And will affect the plating control.
Nickel (Ni): Improve the strength of steel parts, improve the toughness at low temperatures, improve the resistance to atmospheric corrosion, and ensure a stable heat treatment effect, reduce the effect of hydrogen embrittlement.
4, chromium (Cr): can improve the hardenability, improve wear resistance, improve corrosion resistance, and is conducive to maintaining strength at high temperatures.
Molybdenum (Mo): It can help control the hardenability, reduce the sensitivity of steel to temper brittleness, and have a great influence on improving the tensile strength at high temperatures.
6, boron (B): can improve the hardenability, and help to make low carbon steel to heat treatment to produce the expected reaction.
7. Alum (V): Refine austenite grains and improve toughness.
Silicon (Si): to ensure the strength of steel parts, the appropriate content can improve the plasticity and toughness of steel parts.
Brief introduction of the characteristics of stainless steel materials in 4. (304, 316)
(I) the three materials are 300 series of austenitic stainless steel, its chemical composition is as follows:
名称        C        Si        Mn        P        S        Ni        Cr        Mo        Cu
304M ≤0.06 ≤1.0 ≤2.0 ≤0.045 ≤0.03 8.91-10.0 18.0-20.0 0 0
316 ≤0.03-0. 06 ≤1. ≤2.0 ≤0.045 ≤0.03 10.0-14. 16.0-18. 2.0-3. 0
304HC ≤0.08 ≤1. 0≤2.0 ≤0.045 ≤0.03 8.0-10. 17.0-19. 0 1.0-3. 0
The relationship between the main chemical composition of the (II) and the properties of stainless steel.
1, carbon C can increase the hardness and strength, the content is too high will reduce its ductility and corrosion resistance
2, chromium Cr can increase corrosion resistance, oxidation resistance, so that the grain refinement, increase the strength, hardness and wear resistance
3, nickel Ni can increase the high temperature strength, corrosion resistance, reduce the rate of cold work hardening
4. Molybdenum Mo increases strength and has excellent corrosion resistance to oxides and seawater
5, copper Cu is conducive to cold processing molding, reduce magnetic
Other properties of (III) material
1. The above materials are non-magnetic in normal state. 304M is slightly magnetic after cold working (about 1.6 u-2.0u); The magnetic properties of 304HC are (about 1.01 u-1); The magnetic properties of 316 materials after cold working are less than 1.01u.
2, each material has good ductility, easy cold forming, tensile strength, yield strength, can meet the requirements. (Ts tensile strength min700N/mm, Ys yield strength min 450N/mm)
(IV) Conclusion
1.304M, 304HC and 316 are one of the most widely used materials in 300 series austenitic stainless steel. The obvious difference of each material is that the magnetic properties of the material after cold working are 316<304HC<304M. The 316 material has excellent chemical corrosion resistance, pitting corrosion resistance and seawater corrosion resistance relative to 304M and 304HC.
2. In short, stainless steelStandard partsThe characteristics are corrosion resistance, beauty and hygiene, but its strength and hardness are equivalent to carbon steel (grade 6.8) under normal circumstances. Therefore, stainless steel products should not be impacted, knocked, and attention should be paid to maintaining their surface smoothness and precision. Moreover, stainless steel products should not be applied with the same force as carbon steel products, nor should they be applied with too much force. At the same time, due to the good ductility of stainless steel, steel chips generated during use are easy to stick to the nut tooth level, increasing friction, easy to lead to lock, and the use of carbon steel even if the iron will fall, relative to stainless steel is not easy to lock.
Product category
(I) Hexagon bolt (HEXAGON HEAD BOLTS)
1. The reference standard for inch bolts is ANSI/ASME B18.2.1, and the Japanese standard is JIS B1180 (Wechsler tooth). Inch reference BSW916 (Wechsler Tooth).
(1) HEX MACHINE BOLT: no Chinese, with bundle tail and half tooth hexagon bolt,
(2), HEX TAP BOLT: no Chinese, no tail, full tooth hexagon bolt,
(3) HEX CAP SCREWS: Hexagon bolts with Chinese division, beam tail and half tooth,
2. The reference standards for metric bolts are as followsDifferenceAs shown in the table:
Old national standard new national standard ISO standard DIN (German standard)
GB30
GB5780 (half tooth)
GB5781 (full teeth)
GB5782 (half tooth)
GB5783 (full tooth) ISO4016
ISO4018
ISO4014
ISO4017          DIN601
DIN558
DIN931
DIN933
(II), carriage screws/square head bolts (Carriage Bolts):
ANSI/ASME B18.5;DIN603;ISO 8677;GB12;GB14
(III) and hexagon socket bolts (Hexagon socket-head cap screws):
DIN912;GB70; ISO4762; ANSI /ASME B18.3
(IV), Hex Wood Screws (Hexagon Head Lag Screws):
ANSI/ASME B18.2.1 DIN 571
(V), furniture screws (Furniture screws): according to customer standards
(VI) Hexagon flange bolt (Hexagon Flange Bolt):
          IFI 111    GB 5787  DIN 92
3. mark and performance grade
(1) Signs. Hexagon head bolts and screws (thread diameter ≥ 5mm). The top surface of the head shall be marked with embossed or concave characters, or the side surface of the head shall be marked with concave characters. Including performance level and factory standard. Carbon steel: The strength grade mark code consists of two parts of numbers separated. The meaning of the digital part before "•" in the mark code indicates the nominal tensile strength, for example, "4" of grade 4.8 indicates 1/100 of the nominal tensile strength of 400N/MM2. The meaning of "•" and the digital part after the point in the mark code indicates the yield ratio, that is, the ratio of nominal yield point or nominal yield strength to nominal tensile strength. For example, the yield point of 4.8 grade products is 320 N/mm2. The strength grade mark of stainless steel products consists of two parts separated. The symbol before "-" in the symbol code indicates the material. Such as: A2,A4 and other signs "-" after the strength, such as: A2-70
(2), grade. Carbon steel: metric bolt mechanical properties can be divided into: 3.6, 4.6, 4.8, 5.6, 5.8, 6.8,8.8、9.8、
          10.9, 12.9 a total of 10 performance levels. StainlessSteel is divided into 60,70,80 (austenite);50,70,80,110 (martensite);45,60 (iron) three categories.