Quality of Steel Wires and Parts for Hyundai Kia MS124-24 Bolts and Nuts

The standard “Hyundai Kia MS124-24 Quality of steel wires and parts for bolts and nuts” developed by Hyundai Motor Company describes the requirements for the quality of steel wires and parts for bolts and nuts. Steels for bolts and nuts must comply with the tables titled “Steel bolts” and “Steel nuts” given in the standard.

The general requirements in this standard are described as follows:

• Bolts and nuts should be free from defects such as quench cracks, forging cracks, laps and tool marks on visual inspection.
• The definition and tolerance limits of surface discontinuities for bolts are given in the standard “ISO 6157-1 Fasteners - Surface discontinuities - Part 1: General requirements for bolts, screws and studs”. Also, the definition and tolerance limits of surface discontinuities for nuts are given in the standard “ISO 6157-2 Fasteners - Surface discontinuities - Part 2: Nuts”.

This standard describes the detailed requirements as follows:

• Chemical composition: The chemical composition determined by ladle analysis should be in accordance with the tables titled “Chemical composition of carbon steel” and “Chemical composition of alloy steel”. The allowable tolerance of the product analysis should be in accordance with the standard “MS125-14 Analysis methods and tolerances for structural steels”.
• Mechanical properties: The mechanical properties of bolts and nuts shall conform to the tables entitled “Mechanical properties of bolts” and “Mechanical properties of nuts”. Tensile testing may be performed unless the drawing requires a tensile test if the bolt is:
  • Bolts with a head or cylindrical shape that has less strength than the threaded part
  • Bolts with a nominal length less than 2,5 times the nominal diameter
• Hardenability: Hardenability properties must conform to the table titled “Hardenability”.
• Macro-line-defect: The macro-line-defect of steel wires must comply with the table titled “Macro-line-defect”.
• Non-metallic inclusions: Non-metallic inclusions of steel wires must comply with the table titled “Non-metallic inclusions (general)”.
• Microstructure: Unheat treated products should have a uniform ferrite and pearlite structure, and quenching and sweating heat treated products should have a uniform sweating martensite structure, and hardening heat treated products should have a martensite, bainite complex structure.
• Decarburization depth: Decarburization depth must comply with the “MS100-04 Decarburization and surface discontinuities criteria for bolts and studs” standard.
• Hydrogen embrittlement removal heat treatment: Bolts with appropriate grade 10T or more hardness shall be subjected to hydrogen embrittlement removal heat treatment after electroplating. The heat treatment condition shall conform to the standard “MS100-50 Hydrogen embrittlement removal heat treatment for steel parts”.
• Prohibition of hazardous substances: Must meet the requirement of the standard “MS201-02 Prohibition and notification of the use of hazardous substances - Parts and materials”.

Test methods described in this standard include:

• Chemical composition analysis: This test must comply with the standard “KS D 1801 General rules for chemical analysis of iron and steel”. The allowable tolerance of the chemical composition analysis must comply with the standard “MS 125-14 Analysis methods and tolerances for structural steels”.
• Tensile test: This test must comply with the standard “KS B 0233 Mechanical properties of steel bolts and screws” or the standard “ISO 898-1 Mechanical properties of fasteners made of carbon steel and alloy steel - Part 1: Bolts, screws and studs with specified property classes - Coarse thread and fine thread”.
• Wedge tensile test: The wedge tensile test must comply with the standard “KS B 0233 Mechanical properties of steel bolts and screws” or the ISO 898-1 standard.
• Proof load test: The proof load test of nuts shall be in accordance with the standard “KS B 0234 Mechanical properties of steel nuts” or “ISO 898-2 Mechanical properties of fasteners made of carbon steel and alloy steel - Part 2: Nuts of specified property classes - Coarse thread and fine thread”. The proof load values ​​for the test are calculated using the proof load stress and the nominal stress area. The nominal stress area is calculated using the formula given in the standard.
• Head strength test: This test must be in accordance with the “KS B 0233 Mechanical properties of steel bolts and screws” or ISO 898-1 standard.
• Hardness test: The hardness test of bolts must comply with the “KS B 0233 Mechanical properties of steel bolts and screws” standard or ISO 898-1. In addition, the hardness test of nuts must comply with the “KS B 0234 Mechanical properties of steel nuts” standard or ISO 898-2 standard.
• Hardenability test: This test must comply with the standard “KS D 0206 Steel - Hardenability test by final quenching (Jominy test)” or “ISO 642 Steel - Hardenability test by final quenching (Jominy test)”.
• Macro-line-flaw test: This test shall comply with the standard “KS D 0208 Macro-line-flaw test method for steel” or the standard “ISO 3763 Macroscopic methods for assessing the content of coarse grains of steel”.
• Non-metallic inclusion test: This test shall comply with the standard “KS D 0204 Steel - Determination of the content of non-metallic inclusions - Micrographic method using standard diagrams” or the standard “ISO 4967 Steel - Determination of the content of non-metallic inclusions - Micrographic method using standard diagrams”.
• Microstructure analysis: The microstructure should be observed after polishing and grinding.
• Decarburization depth: This test must comply with the standard “KS D 0216 Method for the decarburization depth of steels” or “ISO 3887 Steels - Determination of decarburization depth”.

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