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铸铁的热疫劳是在热循环过程中,由于热膨胀和收缩受阻而产生的周期应力所引起的。在500℃以上,铸铁的内部和外部氧化以及珠光体分解使抗热疲劳能力下降;在720℃以上,奥氏体转变也促使寿命缩短。灰铸铁损坏的通常原因是开裂、而球墨铸铁则是变形。温度差、最高温度和加热冷却速度决定热循环条件的苛刻程度。为了获得良好的抗热疲劳能力,铸铁必须具有高的导热系数,低的弹性模数,高的室温和高温强度,在500～550℃条件下使用时还要具有抗氧化和抗组织变化能力。铸铁的相对分级随服役条件而异。实验数据和生产经验表明:当冷却速度高时,高导热系数和低弹性模数是至关重要的。因此,含碳量高的(3.6-4％)灰铸铁性能最佳。如含碳量不变,加入钼和铬可以改善性能。在中等冷却速度条件下,铁素体球墨铸铁和蠕虫状石墨铸铁的抗裂能力最好,但容易变形。在冷却速度缓慢时,高强度珠光体铸铁或硅、钼合金球墨铸铁的抗裂能力和抗变形能力最佳。
The hot blast of cast iron is caused by the cyclic stresses that occur during thermal cycling due to thermal expansion and contraction. Above 500 ° C, the internal and external oxidation of cast iron and the decomposition of pearlite decrease the thermal fatigue resistance; above 720 ° C, the austenitic transformation also contributes to a reduction in life expectancy. The common cause of gray cast iron damage is cracking, while ductile iron is deformed. Temperature difference, maximum temperature and heating and cooling rate determine the severity of thermal cycling conditions. In order to obtain good thermal fatigue resistance, cast iron must have high thermal conductivity, low modulus of elasticity, high room temperature and high temperature strength. It also has the ability to resist oxidation and to resist tissue deformation when used at 500-550 ℃. The relative grading of cast iron varies with service conditions. Experimental data and production experience show that: when the cooling rate is high, the high thermal conductivity and low elastic modulus is crucial. Therefore, high carbon content (3.6-4%) gray cast iron performance best. If the carbon content of the same, adding molybdenum and chromium can improve performance. Ferrite nodular cast iron and worm-like graphite cast iron have the best crack resistance at moderate cooling rates, but are easily deformable. When the cooling rate is slow, the high strength pearlite cast iron or silicon, molybdenum alloy ductile iron best crack resistance and deformation resistance.