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.彈簧材料的表面質量。表面狀態的應力通常發生在彈簧材料的表層，所以彈簧的表面質量對其疲勞強度有很大的影響。例如，彈簧材料在軋制、拉拔和卷制(電腦彈簧機)過程中造成的裂紋、疵點和傷痕等缺陷往往是造成彈簧疲勞斷裂的主要原因。

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，其應力集中越小，疲勞強度也就越高。材料表面粗糙度對疲勞極限的影響是隨著粗糙度的增加，其疲勞極限下降。在同一粗糙度的情況下，不同的材料和不同的彈簧機卷制方法，其疲勞極限降低程度也有所不同，如冷卷彈簧降低程度比熱卷彈簧小。因為鋼制熱卷彈簧和熱處理加熱時，由于氧化使彈簧材料表面變粗糙和產生脫碳現象，這樣就會降低彈簧的疲勞強度。這也就是為什么我們有時會材料表面進行磨削、強壓、拋丸和滾壓等處理，主要就是為了提高彈簧的疲勞強度。

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.尺寸效應。材料的尺寸愈大，由于各種冷加工和熱加工工藝所造成的缺陷可能性越高，其表面缺陷產生的可能性也就越大，這些原因都會導致彈簧疲勞強度下降。因此在應用中我們計算彈簧的疲勞強度時要考慮尺寸效應的影響。

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屬雜質、氣泡和元素的偏析等。存在于材質表面的夾雜物是應力的集中源，將會導致夾雜物和基體界面之間過早地產生疲勞裂紋。因些，采用真空冶煉和真空澆注等措施，可以大大提高鋼材的質量。

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.腐蝕介質。彈簧在腐蝕介質中工作時，由于表面層產生點蝕或表面晶界被腐蝕而成為疲勞源，在變應力作用下就會逐步擴展而導致斷裂現象。例如在淡水環境中工作的彈簧鋼，其疲勞極限僅為空氣中的10%~25%。腐蝕介質對彈簧疲勞強度的影響，不僅與彈簧受變載荷的作用次數有關，還與工作壽命有關。所以設計和計算受腐蝕影響的彈簧時，應將工作壽命考慮進去。

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.

實際應用中，考慮到在腐蝕條件下工作的靖江彈簧廠生產的彈簧，為了保證其疲勞強度，可采用抗腐蝕性能高的材料，如不銹鋼、非鐵金屬，或對彈簧進行表面處理來加保護層，如鍍層、氧化、噴塑、涂漆等。實踐應用表明鍍鎘可以大大提高彈簧的疲勞極限。

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.溫度系數。溫度碳鋼的疲勞強度，從室溫到120℃之間下降，從120℃到350℃之間上升，溫度高于350℃時又下降，在高溫時沒有疲勞極限。在高溫條件下工作的彈簧，要考慮采用耐熱鋼;在低于室溫的條件下，鋼的疲勞極限有所增加。

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.