Application Of Cast Steel Machined Parts in The Steam Turbine Industry

1. Cylinder castings (high-pressure cylinder, intermediate pressure cylinder, low-pressure cylinder, exhaust cylinder)
-Structure: Large thin-walled+thick walled composite structure, with complex split surfaces, bolt holes, extraction ports, steam flow channels, and cat claw support platform; One of the most valuable cast steel components for steam turbines.
-Process: Casting and forming → Stress relief annealing → Rough machining → Quenching and tempering/normalizing → UT/MT/PT non-destructive testing → Semi precision → Precision machining of split surfaces, locating pin holes, flange sealing surfaces, cat claws, and grooves (bearing seat installation reference).
-Function: A sealed pressure chamber that accommodates rotors and partitions, and can withstand steam pressure, thermal shock, self weight, and pipeline thrust.

2. Valve cast steel parts (main steam valve, regulating steam valve, reheat main steam valve, globe valve, drain valve housing/body)
-Structure: Irregular thick walled cavity with built-in valve seat, valve chamber, flow channel, flange, bolt holes, and complex flow channel surface.
-Processing focus: precision machining of valve seat sealing surface after welding with Stellite alloy, boring of valve cavity holes, flange sealing surface, bolt holes; The flatness and roughness of the sealing surface directly determine the steam leakage rate.

3. Nozzle chamber, nozzle group shell
-Location: Inside the high-pressure cylinder, the first stage steam intake component is in direct contact with the high-temperature main steam
-Features: There are multiple curved surfaces in the inner cavity flow channel, and the flow channel surface requires CNC milling; The material is mostly Cr-Mo-V heat-resistant cast steel
-Function: evenly guide steam to the first stage moving blades and distribute steam flow; The machining accuracy of the flow channel directly affects the efficiency of the unit.

4. Bearing seat, bearing box, support seat, cat claw support
-Material: Carbon cast steel or low-alloy cast steel. Some low-pressure bearing seats may also use cast iron, but cast steel is preferred for high-power and high-temperature sides
-Processing focus: bearing groove (boring), positioning surface, anchor bolt hole, oil chamber, oil return groove; The roundness and coaxiality of the concave groove are the benchmarks for the alignment of the rotor core
-Function: Support rotor bearings, bear rotor weight, isolate vibration, and store lubricating oil.

5. Connecting pipes, tees, reducers, and header castings
-Irregular pressure bearing castings for main steam/reheat steam pipelines, pipeline corners, branch positions, and forgings that are difficult to form complex branches
-Processing: Two end flange, groove processing, sealing groove; Internal wall polishing+flaw detection, controlling the amount of wall thickness reduction
-Operating conditions: high temperature and high pressure, coupled creep and fatigue loads.

6. Partition sleeve, retaining ring, guide ring, low-pressure cylinder reinforcement
-Partition sleeve: used to fix the static blade partition, inner and outer ring cast steel parts, and machined grooves for clamping the partition;
-Low pressure exhaust cylinder guide ring: improves exhaust flow field, reduces eddy current loss, large thin-walled cast steel parts are prone to deformation, and processing time control is key.

7. Other auxiliary cast steel parts
The oil pump housing, steam filter housing, various brackets, lifting ears, connecting blocks, balance pipe joints, etc. are mostly made of carbon cast steel.