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1. Material requirements for bolts, screws and studs (GB/) Performance level Material and heat treatment Chemical composition

1) The content of boron can reach %, and its non-effective boron can be controlled by adding titanium and (or) aluminum.

2) These performance grades allow easy-cut manufacturing, and the maximum content of sulfur, phosphorus and lead is: sulfur %; phosphorus %; lead %.

3) In order to ensure good hardenability, fasteners with a thread diameter exceeding 20mm must use the steel specified by the corresponding grade.

4) The minimum manganese content of low carbon alloy steel with carbon content below % (barrel sample analysis) is: grade: %;, and grade: %.

5) The product should be marked with a horizontal line under the performance grade code. The grade should meet all the performances specified for the grade, and the lower after-fire temperature will cause different degrees of stress weakening under the condition of elevated temperature.

  6) The material used for this performance level should have good hardenability to ensure that the core of the threaded section of the fastener obtains about 90% of the martensite structure after quenching and before tempering.

  7) Alloy steel should contain at least one of the following elements, the minimum content of which is: chromium %; nickel %; molybdenum %; vanadium %

  8) Considering the tensile stress, the surface of the grade is not allowed to have a white phosphorus accumulation layer that can be detected by metallography.

  9) The chemical composition and tempering temperature are still under investigation.

2. Nut

  1. Material technical requirements for nuts (finish threads) (GB/) Performance grade chemical composition, % C max Mn min P max S max 41), 51), 61) —— 8, 9 041) 102) 051) 122 )——

  1) This performance grade can be made of free-cutting steel (unless otherwise agreed by the supplier and the buyer), and the maximum content of sulfur, phosphorus and lead is: sulfur %; phosphorus %; lead %.

2) In order to improve the mechanical properties of the nut, alloy elements can be added if necessary. Nuts of property classes 05, 8 (>M16 l-nuts), 10 and 12 shall be quenched and tempered.

  1. Material of rivet nut (GB/) Product material standard steel flat head, countersunk head, small countersunk head, 1200 small countersunk head and flat head hexagonal rivet nut 08F GB/T699 ML10 GB/T6478 aluminum alloy flat head and countersunk head rivet nut 5056 (formerly LF5-1) GB/T3190 6061 (formerly LD30)
  2. The technical requirements for the material of the effective moment steel hex lock nut should be the same as that of the nut (coarse thread). The material from which metallic or non-metallic inserts are made is to be determined by the fabricator. 3. Material technical requirements for set screws (GB/) Performance grade Material heat treatment chemical composition, % C P max S max min max 14H carbon steel 1), 2) ———— 22H carbon steel 3) Quenching and tempering—— 33H Carbon Steel 3) Quenched and Tempered – 45H Alloy Steel 3), 4) Quenched and Tempered

1) When free-cutting steel is used, the maximum content of lead, phosphorus and sulfur is: lead%; phosphorus%; sulfur%

2) Square head set screws allow case hardening.

3) Steel with a maximum lead content of % can be used.

4) It should contain one or more chromium, nickel, molybdenum, vanadium or boron alloy elements. Note: Set screws of performance grade 45H can also be made of other materials when they can meet the guaranteed torque requirements specified in Article 1 of GB/Standard.

  1. Heat-resistant threaded connection pairs are suitable for fastener material requirements that can be used under high temperature and alternating loads, but also maintain pre-tightening force and fatigue resistance to a considerable extent. 1. For materials above +300°C, see the table. 570 20CrMoVTiB 20CrMoVnBTiB 20CrMoV 21CrMoV 600 2Cr12WMoVNbB (YB/Z8) 20CrMoV 650 GH2132 GBn177 21CrMoV 1) Bolts and studs should be harder than the nut.

2) The material of the stressed casing is recommended to be the same as that of the stud.

  1. Materials should be inspected by low-magnification tissue. Among them, general porosity, central porosity and box-shaped segregation shall not exceed the second grade specified in GB1979.
  2. Material technical requirements for stainless steel fasteners Bolts, screws and stud nuts
types of nut and bolt
  1. At present, the standard parts on the market mainly include carbon steel, stainless steel and copper.

(1) Carbon steel. We distinguish low carbon steel, medium carbon steel and high carbon steel and alloy steel by the carbon content in the carbon steel material.

  1. Low carbon steel C%≤% is usually called A3 steel in China. Foreign countries are basically called 1008, 1015, 1018, 1022 and so on. It is mainly used for products without hardness requirements such as grade bolts, grade 4 nuts, and small screws. (Note: Drilling screws are mainly made of 1022 material.)
  2. Medium carbon steel%
  3. High carbon steel C%>%. Basically unused in the market
  4. Alloy steel: Add alloy elements to ordinary carbon steel to increase some special properties of steel: such as 35, 40 chromium molybdenum, SCM435, 10B38. Fangsheng screws mainly use SCM435 chrome-molybdenum alloy steel, the main components are C, Si, Mn, P, S, Cr, Mo.

(2) Stainless steel. Performance grade: 45, 50, 60, 70, 80 Mainly divided into austenite (18%Cr, 8%Ni), good heat resistance, good corrosion resistance, good weldability. A1, precision hardware, A2, A4 martensite, 13%Cr has poor corrosion resistance, high strength, and good wear resistance. C1, C2, C4 ferritic stainless steel. 18%Cr has better upsetting forgeability and stronger corrosion resistance than martensite. At present, imported materials on the market are mainly Japanese products. According to the level, it is mainly divided into SUS302, SUS304 and SUS316.

No. Type Available material

Grade 1 hex bolt 1008K 1010 1015K

Grade 2 hex bolt 1032 1035 1040 CH38F 1039

Grade 3 hex bolt 1035ACR (below M10) 1040ACR (above M12) CH38F 1045ACR 1039 10B21 10B33 10B38

Grade 4 hexagon socket head bolt CH38F 1039 10B21 (M10-M12) 10B33 (M14) 10B38 (M12-M24) 10B21

Grade 5 hex bolt 1045ACR 10B38

6│8│grade nut 1008K 1010

7 Grade 8 nut 1015(M<16) CH38F (M≥16)

8 Grade 0 nut CH38F 1039 10B21 10B33

9 Grade 12 Nut 1039 10B21 10B33 10B38

10 Carriage screw 1008 1010 1015

11 Hex flange bolt CH38F 1039 10B21 10B33 10B38

12 Hex wood screw 1008K 1010

13 Self-tapping screws, wallboard screws, drilling screws, plywood screws 1018 1022 CH22A

14 Machine screws Furniture screws 1008 1010

  • Commonly used materials are brass…zinc-copper alloy. H62, H65 and H68 copper are mainly used as standard parts in the market.
bolt nut screw

3. The influence of various elements in the material on the properties of steel:

  1. Carbon (C): Improves 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.
  2. Manganese (Mn): Improve the strength of steel parts, and improve the hardenability to a certain extent. That is, the strength of hardening penetration is increased during quenching, and manganese can also improve the surface quality, but too much manganese is not good for ductility and weldability. And it will affect the control of the coating during electroplating.
  3. Nickel (Ni): Improve the strength of steel parts, improve the toughness at low temperature, improve the resistance to atmospheric corrosion, and ensure a stable heat treatment effect, reducing the effect of hydrogen embrittlement.
  4. Chromium (Cr): It can improve hardenability, improve wear resistance, improve corrosion resistance, and help maintain strength at high temperatures.
  5. 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 temperature.
  6. Boron (B): It can improve hardenability and help low-carbon steel produce the expected response to heat treatment. 8k1Dj1@0z
  7. Alum (V): Refining austenite grains, improving toughness, Suzhou Precision Hardware.
  8. Silicon (Si): To ensure the strength of steel parts, proper content can improve the plasticity and toughness of steel parts.
  9. Introduction to the characteristics of stainless steel materials (304, 316)

(1) The three materials are all 300 series austenitic stainless steel, and their chemical composition is as follows:

Name C Si Mn P S Ni Cr Mo Cu

304M ≤ ≤ ≤ ≤ ≤ 0 0

316 ≤ ≤ ≤ ≤ ≤ 0

304HC ≤ ≤ ≤ ≤ ≤ 0

(2) The relationship between the main chemical composition and the performance of stainless steel.

  1. Carbon C can increase the hardness and strength, if the content is too high, it will reduce its ductility and corrosion resistance
  2. Chromium Cr can increase corrosion resistance and oxidation resistance, refine grain, increase strength, hardness and wear resistance
  3. Nickel Ni can increase high temperature strength, corrosion resistance, and 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 forming and reduces magnetic properties

(3) Other properties of the material

  1. The above materials are non-magnetic in normal state. 304M is slightly magnetic (left and right) after cold working; 304HC is slightly magnetic (left and right); 316 material is less magnetic after cold working.
  2. All materials have good ductility, easy to be formed by cold processing, and the tensile strength and yield strength can meet the requirements. (Ts tensile strength min 700N/mm, Ys yield strength min 450N/mm)

Conclusion

  1. The three materials of 304M, 304HC and 316 are currently one of the most widely used materials of 300 series austenitic stainless steel. The obvious difference of each material is: the magnetic properties of the material after cold working are 316<304HC<304M. The 316 material is resistant to chemical corrosion, pitting corrosion resistance and seawater corrosion resistance compared to 304M and 304HC.
  2. In short, the characteristics of stainless steel standard parts are corrosion-resistant, beautiful and hygienic, but their strength and hardness are normally equivalent to carbon steel (grade), so stainless steel products should not be hit, knocked, and attention should be paid to maintaining their surface finish and precision, and Do not apply force casually like carbon steel products, and do not apply 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 teeth of the nut, which increases friction and easily leads to locking. However, even if carbon steel is used, iron filings will fall off, which is not easy to lock up compared to stainless steel.

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