Bearing retaining nut analysis
As a key part of mechanical connection to prevent loosening, the choice of material directly affects the performance, life and application scenarios. The following is a detailed analysis of commonly used materials, performance characteristics, surface treatment and application scenarios:
First, commonly used materials and their characteristics
( one) medium carbon structural steel: 45 # steel
1. Composition and organization of
carbon content: 45 # steel is a medium-carbon steel, comprehensive mechanical properties are good, tempered or normalized treatment can be obtained after a certain degree of strength and toughness.
Organizational characteristics: ferrite + pearlite in the annealed state, after heat treatment to adjust the mechanical properties. 2.
2. Mechanical properties
Strength: tensile strength of about 600MPa, yield strength of about 355MPa, good overall mechanical properties.
Toughness: after tempering treatment (quenching + high temperature tempering), impact toughness is good, not easy to brittle break.
Hardness: the hardness can reach HB217~255 after tempering, and the hardness can be upgraded to HRC40~45 after surface quenching.
3. Processing and cost
Cutting processability: excellent cutting performance, easy for turning, milling and threading.
Cost advantage: low price, is one of the most commonly used materials in general mechanical connections.
4. Application Scenario
General machinery: common machine tools, agricultural machinery, light industrial equipment and other occasions that do not require high strength.
Civilian products: furniture, construction hardware, daily tools, etc., to meet the basic fastening needs.
( two) alloy structural steel: 42CrMo
1. Composition and organization of
carbon content: 42CrMo is a medium-carbon alloy structural steel, with high strength and good toughness, hardenability is also good.
Organizational characteristics: alloying elements to improve hardenability, easy to obtain uniform martensite organization after quenching, good tempering stability.
2. Mechanical properties
High strength: tensile strength ≥ 1080MPa, yield strength ≥ 930MPa, far more than 45# steel.
High toughness: tempered impact toughness (αk) ≥ 60J/cm², excellent fatigue resistance.
High temperature resistance: can still maintain high strength below 500℃, suitable for high temperature working conditions.
3. Processing and cost
Cutting machinability: alloying elements increase the difficulty of cutting, need to cooperate with special tools or cutting fluid.
Higher cost: material price and heat treatment cost is higher than 45# steel, belongs to the middle and high end application materials.
4. Application Scenarios
Precision machinery: CNC machine tools, aerospace equipment, mold tooling and other high-precision occasions.
Heavy-duty working conditions: engineering machinery, metallurgical equipment, high-pressure pipeline connections and other scenes subject to alternating loads.
Surface treatment: blackening (oxidation) process
1. Principle of the process
Through chemical oxidation to generate a dense layer of iron tetraoxide (Fe₃O₄) thin film on the surface of the nut, the thickness of about 0.5 ~ 1.5 μm. 2.
2. Impact on material performance
Corrosion prevention: oxidized film isolates air and moisture, improves the nut's ability to resist rust and corrosion, suitable for wet or slightly corrosive environments.
Anti-friction: The film layer increases the surface roughness, slightly improves the friction of the thread contact surface, and assists in anti-loosening.
No effect on precision: the film layer is very thin and has no significant effect on the fitting precision of Class 6H threads.
3. Blackening effect of different materials
45# steel: the oxide film is blackish gray, with good bonding force, suitable for general anti-corrosion needs.
42CrMo: the oxide film color is deeper (nearly black), the film uniformity is better, can be used for occasions with higher appearance requirements.
Fourth, the material selection comparison and application recommendations
| project | 45# steel lock nut | 42CrMo lock nut |
| strength | Low to medium strength, suitable for static loads | High strength, resistant to alternating loads and impacts |
| Accuracy adaptability | General accuracy (6H class for general needs) | Machining up to higher precision (e.g. with 7g6h) |
| cost | Low and cost-effective | High, suitable for high-end applications |
| Typical scenario | Furniture, general machinery, construction | Machine tools, aviation, heavy equipment |
Selection principle:
If the load is small and the precision requirement is general, give priority to 45# steel blackened nut, which is low cost and easy to be processed;
If high strength, fatigue resistance or high temperature working condition is required, select 42CrMo material, and enhance the comprehensive performance with blackening treatment.
Extension, Optimization direction of material and process
Surface strengthening: Nitriding (hardness of nitriding layer HRC60+) can be further adopted for 42CrMo nuts to improve wear resistance and anti-loosening ability.
Anti-loosening structure: Combining with the material characteristics, design the structure of groove, nylon inserts, etc. to realize double anti-loosening with 6H grade threads.
Environmental adaptability: In marine or highly corrosive environments, consider 42CrMo + zinc plating (be aware of the risk of hydrogen embrittlement) or Dacromet treatment as an alternative to the blackening process.
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