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铸铁的热疲劳是由于在热循环条件下,热膨胀及收缩受到限制而产生的循环应力所造成的。铸件在加热时外表层受到的是压应力,在冷却时受到拉应力。冷却到最低温度时产生的拉应力最大,往往使铸件产生裂纹。灰铁及蠕铁的热疲劳就是属于这类。球铁不容易产生裂纹,但往往由于变形而使铸件不能继续使用。对于抗热疲劳能力好的材质来说,应该具有以下几方面的性能: ①高的导热性能;②低的弹性模数;③室温及高温强度要好;④抗氧化性能好;⑤组织稳定性高。同一材质要求具备这几方面的性能是不可能的,因此在使用时应综合地分析。灰铁的导热系数高、弹性模数低,但是它的强度、
The thermal fatigue of cast iron is due to the cyclic stress caused by the thermal expansion and shrinkage under thermal cycling conditions. Castings in the heating surface is subjected to compressive stress, when subjected to tensile stress. The maximum tensile stress produced when cooled to the lowest temperature tends to crack the castings. Thermal fatigue of gray iron and vermicular iron belongs to this category. Ductile iron is not easy to crack, but often due to deformation of the casting can not continue to use. Good thermal fatigue resistance for the material, it should have the following properties: ① high thermal conductivity; ② low modulus of elasticity; ③ room temperature and high temperature strength is better; ④ good oxidation resistance; ⑤ high tissue stability . The same material requirements with these aspects of the performance is impossible, so the use should be comprehensive analysis. Gray iron has a high thermal conductivity, low elastic modulus, but its strength,