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铸造竖炉炉栅通常采用铸造生铁浇注,由于长期在高温下工作,炉栅表面发生氧化坑蚀、剥落和产生不可逆的体积膨胀(通常称为铸铁热生长)。这是因为炉中氧化性气体沿石墨边界和裂纹渗入到铸件内部,发生氧化。以及部分渗碳体在高温下产生石墨化,生成比重较小而体积较大的石墨,使炉栅体积长大、性能下降、发脆,直至严重开裂,最后导致炉栅烧毁。普通铸造生铁炉栅使用后的金相组织如图1所示。可以看出表面氧化层非常严重,氧化沿石墨边界渗入到内部。
Casting shaft furnace grates are usually cast cast iron castings that, due to long-term service at elevated temperatures, oxidize pitting, flaking and irreversible volumetric expansion (commonly referred to as cast iron thermal growth) at the grate surface. This is because the oxidizing gas in the furnace permeates the inside of the casting along the graphite boundaries and cracks and oxidation occurs. And part of the cementite is graphitized at a high temperature, resulting in a smaller specific gravity and larger volume of graphite, which causes the volume of the grate to grow up, deteriorates in performance, becomes brittle until it is severely cracked and finally burns down. Ordinary cast iron grate after use of the microstructure shown in Figure 1. It can be seen that the surface oxide layer is very serious and the oxidation penetrates into the interior along the graphite boundary.