Detailed Performance of RTSi5 Heat-Resistant Cast Iron Grate Bars under High-Temperature Conditions

I. Basic Material Parameters
Grade: RTSi5, heat-resistant cast iron conforming to Chinese national standards, with a silicon content of 4.5%–5.5% and a predominantly ferritic matrix;
Design long-term safe operating temperature: 750°C–850°C; capable of withstanding short-term peak temperatures of up to 880°C.
II. Comprehensive Performance (under optimal conditions) within the Suitable Temperature Range (750–850 °C, typical boiler operating conditions)

1. High-Temperature Oxidation Resistance (Key Advantage)
A dense, intact protective layer of SiO₂ (silicon dioxide) spontaneously forms on the heated surface, adhering firmly to the outer layer of the casting:
This isolates the surface from atmospheric oxygen, preventing continued oxidation and erosion of the matrix, and avoids extensive flaking, spalling or thinning;
In conventional coal- and biomass-fired furnaces, the rate of grate wear and thermal damage during year-round operation is very low;
Compared to ordinary grey cast iron: at equivalent temperatures, its oxidation resistance lifespan is 2.5 to 4 times that of grey cast iron.
2. Thermal Shock Resistance (Alternating Hot and Cold)
Boiler start-up and shutdown, fire damping, and intermittent heating cause sudden rises and falls in temperature:
Superior to grey cast iron and high-chromium cast iron;
Drawback: Not as tough as ductile iron or cast steel;
During routine start-up and shutdown of intermittent heating boilers, cracking or fragmentation is virtually non-existent; however, frequent and abrupt thermal shocks (such as cold water being poured into the furnace or large volumes of cold air suddenly entering the furnace) may still cause cracking.
3. High-Temperature Strength and Deformation
At 750–850 °C:
Low high-temperature creep; resistant to warping and bending deformation; grate gaps do not widen, nor does coal leakage increase;
Stable load-bearing capacity; fully adequate for withstanding the pressure of coal distribution in chain grate systems.
4. Resistance to Flue Gas Corrosion
Ordinary low- to medium-sulphur coal: Sulphur dioxide corrosion is minimal, and service life is stable;
Biomass fuels such as straw and wood chips: Resistance to corrosion by potassium- and sodium-rich alkaline ash is acceptable, and the material is not prone to spalling due to alkali metal corrosion;
Weakness: Resistance to high-sulphur corrosion is far inferior to that of chromium-containing heat-resistant cast iron.
5. Wear Resistance
At high temperatures, the material’s inherent coefficient of friction is moderate; wear caused by the reciprocating friction of the chain grate’s drive pin shafts and by ash and slag erosion is moderate, meeting the 12–24-month service life requirement for conventional coal-fired boilers.
III. Performance gradually deteriorates under overheating conditions (＞880°C, sustained high temperatures)
880°C–950°C
The surface silica protective film begins to soften, crack and flake off, losing its protective function:
The grate undergoes rapid oxidation, becoming thinned, with peeling and flaking at the edges;
High-temperature creep intensifies, causing the grate plates to bend and warp as a whole, resulting in misalignment of clearance gaps, which leads to chain jamming and coal leakage;
Brittleness increases significantly, leading to fracture even under slight vibration or thermal shock;
Service life is directly reduced by more than half.
Prolonged operation at >950°C
Silicon 5 is completely unsuitable: the rate of oxidation is extremely rapid, and the grate will be ablated and rendered unusable within a matter of months.
IV. Disadvantages and Weaknesses (Inherent Defects in High-Temperature Environments)
Poor resistance to sulphidation corrosion
When burning high-sulphur or low-grade coal, SO₂ penetrates the silicon oxide film and corrodes the base material, resulting in pitting and rust pits, with a marked reduction in service life; under such operating conditions, it is inferior to low-chromium cast irons such as RTCr1 and RTCr2.
Low toughness; poor resistance to impact and repetitive compression
Under the stress conditions of the reciprocating grate’s back-and-forth movement and impact, brittleness increases further when exposed to high temperatures, making it prone to edge fractures and cracking; cast steel or ductile iron is the preferred choice for reciprocating grates.
Moderate resistance to strong alkaline slag erosion
The extensive combustion of pure straw and rice husks results in alkaline ash that continuously melts and adheres to the grate; prolonged exposure to high temperatures will gradually erode the surface layer.
V. Reference Service Life under Different Operating Conditions (Silicon 5 grate bars)
24-hour continuous combustion of standard raw coal, furnace temperature around 800°C: 18–26 months
Intermittent heating boilers, started and stopped daily: 12–18 months
Co-firing with small amounts of biomass pellets: 12–20 months
Continuous operation at a high furnace temperature of 900°C: 4–8 months before scrapping
Long-term combustion of high-sulphur low-grade coal: 8–12 months
VI. Summary in a Nutshell
Silicon 5 is the material offering the best value for money for conventional coal-fired or biomass chain-grate boilers operating at 750–850°C; provided temperatures do not exceed the specified limits and the fuel’s sulphur content is not too high, it is durable and trouble-free. However, should the furnace temperature consistently exceed 880°C or high-sulphur fuel be used, its overall performance will deteriorate significantly.

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