1. Yield strength of spring material. Generally speaking, the higher the yield strength of spring material, the higher the fatigue strength. Therefore, in order to improve the fatigue strength of spring, try to improve the yield strength of spring material itself or use the material with higher yield strength to tensile strength ratio. Compared with the same material, the yield strength of fine grain structure is higher than that of coarse grain structure, and the corresponding fatigue strength is also higher.

2.弹簧材料的表面质量。表面状态的应力通常发生在弹簧材料的表层，所以弹簧的表面质量对其疲劳强度有很大的影响。例如，弹簧材料在轧制、拉拔和卷制(电脑弹簧机)过程中造成的裂纹、疵点和伤痕等缺陷往往是造成弹簧疲劳断裂的主要原因。

2. Surface quality of spring material. The maximum stress of surface state usually occurs on the surface of spring material, so the surface quality of spring has a great influence on its fatigue strength. For example, the spring material in the rolling, drawing and rolling (computer spring machine) process caused by cracks, defects and scars are often the main cause of spring fatigue fracture.

材料表面的粗糙度越低，其应力集中越小，疲劳强度也就越高。材料表面粗糙度对疲劳极限的影响是随着粗糙度的增加，其疲劳极限下降。在同一粗糙度的情况下，不同的材料和不同的弹簧机卷制方法，其疲劳极限降低程度也有所不同，如冷卷弹簧降低程度比热卷弹簧小。因为钢制热卷弹簧和热处理加热时，由于氧化使弹簧材料表面变粗糙和产生脱碳现象，这样就会降低弹簧的疲劳强度。这也就是为什么我们有时会材料表面进行磨削、强压、抛丸和滚压等处理，主要就是为了提高弹簧的疲劳强度。

The lower the surface roughness is, the smaller the stress concentration is and the higher the fatigue strength is. The effect of surface roughness on fatigue limit is that the fatigue limit decreases with the increase of roughness. In the case of the same roughness, the reduction degree of fatigue limit of cold coil spring is smaller than that of hot coil spring. Because the steel hot coil spring and heat treatment heating, the surface of the spring material becomes rough and decarburized due to oxidation, which will reduce the fatigue strength of the spring. This is why we sometimes grind, press, blast and roll the surface of the material, mainly to improve the fatigue strength of the spring.

3.尺寸效应。材料的尺寸愈大，由于各种冷加工和热加工工艺所造成的缺陷可能性越高，其表面缺陷产生的可能性也就越大，这些原因都会导致弹簧疲劳强度下降。因此在应用中我们计算弹簧的疲劳强度时要考虑尺寸效应的影响。

3. Size effect. The larger the size of the material, the higher the possibility of defects caused by various cold working and hot working processes, the greater the possibility of surface defects, which will lead to the decline of spring fatigue strength. Therefore, the size effect should be considered when calculating the fatigue strength of spring.

4.冶金缺陷。冶金缺陷是指材料中的非金属杂质、气泡和元素的偏析等。存在于材质表面的夹杂物是应力的集中源，将会导致夹杂物和基体界面之间过早地产生疲劳裂纹。因些，采用真空冶炼和真空浇注等措施，可以大大提高钢材的质量。

4. Metallurgical defects. Metallurgical defects refer to nonmetallic impurities, bubbles and segregation of elements in materials. The inclusions on the surface of the material are the concentrated source of stress, which will lead to premature fatigue crack between the inclusion and the matrix interface. Therefore, the quality of steel can be greatly improved by means of vacuum smelting and vacuum casting.

5.腐蚀介质。弹簧在腐蚀介质中工作时，由于表面层产生点蚀或表面晶界被腐蚀而成为疲劳源，在变应力作用下就会逐步扩展而导致断裂现象。例如在淡水环境中工作的弹簧钢，其疲劳极限仅为空气中的10%~25%。腐蚀介质对弹簧疲劳强度的影响，不仅与弹簧受变载荷的作用次数有关，还与工作寿命有关。所以设计和计算受腐蚀影响的弹簧时，应将工作寿命考虑进去。

5. Corrosive medium. When the spring works in the corrosive medium, the fatigue source is caused by pitting corrosion of the surface layer or corrosion of the surface grain boundary, which will gradually expand under the action of variable stress and cause fracture. For example, the fatigue limit of spring steel in fresh water environment is only 10% ~ 25% of that in air. The influence of corrosive medium on the fatigue strength of spring is not only related to the number of times of spring subjected to variable load, but also related to the working life. Therefore, the working life should be taken into account when designing and calculating the spring affected by corrosion.

实际应用中，考虑到在腐蚀条件下工作的靖江弹簧厂生产的弹簧，为了保证其疲劳强度，可采用抗腐蚀性能高的材料，如不锈钢、非铁金属，或对弹簧进行表面处理来加保护层，如镀层、氧化、喷塑、涂漆等。实践应用表明镀镉可以大大提高弹簧的疲劳极限。

In practical application, in order to ensure the fatigue strength of the spring produced by Jingjiang Spring Factory under corrosive conditions, materials with high corrosion resistance, such as stainless steel, non-ferrous metal, or surface treatment of spring to add protective layer, such as coating, oxidation, plastic spraying and painting, can be used. Practical application shows that cadmium plating can greatly improve the fatigue limit of spring.

6.温度系数。温度碳钢的疲劳强度，从室温到120℃之间下降，从120℃到350℃之间上升，温度高于350℃时又下降，在高温时没有疲劳极限。在高温条件下工作的弹簧，要考虑采用耐热钢;在低于室温的条件下，钢的疲劳极限有所增加。

6. Temperature coefficient. The fatigue strength of temperature carbon steel decreases from room temperature to 120 ℃, increases from 120 ℃ to 350 ℃, and then decreases when the temperature is higher than 350 ℃. There is no fatigue limit at high temperature. Heat resistant steel should be considered for springs working at high temperature, and the fatigue limit of steel will be increased when the temperature is lower than room temperature.