How to optimize the microstructure of heat-resistant steel frame castings through heat treatment process?

Optimizing the microstructure of heat-resistant steel frame castings to improve their creep resistance and oxidation resistance is one of the core goals of heat treatment process. The following are the specific methods and principles to achieve this goal through heat treatment process:

Heat Resistant Steel Casting Tray Castings

1. Solution Treatment
Solution treatment is a process in which the alloy is heated to a high temperature and maintained for a period of time to fully dissolve the alloy elements in the matrix, and then rapidly cooled to obtain a supersaturated solid solution.
Function:
Refine the grains and improve the strength and toughness of the material.
Eliminate residual stress in the casting and reduce the risk of thermal cracks.
Provide a uniform organizational basis for subsequent aging treatment.
Process parameters:
The heating temperature is usually between 1000℃ and 1150℃, and the specific temperature depends on the composition of the heat-resistant steel.
The holding time is determined according to the size and shape of the casting, generally 1 to 4 hours.
The cooling method usually uses water cooling or air cooling, and water cooling can obtain finer grains.

2. Precipitation Hardening
Aging treatment is to heat the alloy that has undergone solid solution treatment to a lower temperature and keep it for a period of time, so that the alloy elements precipitate to form a dispersed phase, thereby improving the strength and hardness of the material.
Function:
By precipitating dispersed phases (such as carbides, nitrides or intermetallic compounds), dislocation movement is hindered and creep resistance is improved.
Stabilize grain boundaries and reduce high-temperature oxidation rate.
Process parameters:
The aging temperature is usually 550℃~750℃, and the specific temperature depends on the alloy composition and the type of precipitated phase.
The holding time is generally 2~10 hours, and the specific time needs to be determined by experiment.
The cooling method is usually air cooling or furnace cooling.

3. High-Temperature Tempering
High-Temperature Tempering is to heat the casting to a higher temperature and keep it for a period of time to improve the toughness and crack resistance of the material while maintaining a certain strength.
Function:
Reduce quenching stress and improve the toughness of the material.
By precipitating a stable second phase, the high-temperature strength and oxidation resistance of the material are improved.
Process parameters:
The tempering temperature is usually between 600℃ and 700℃.
The holding time is determined according to the size and shape of the casting, generally 2 to 6 hours.
The cooling method is air cooling or furnace cooling.

4. Surface treatment and coating technology
In addition to the optimization of the internal microstructure, surface treatment and coating technology can also significantly improve the oxidation resistance of heat-resistant steel frame castings.
Oxide film treatment:
By controlling the oxidation conditions (such as temperature and atmosphere), a dense oxide film (such as Al₂O₃ or Cr₂O₃) is formed on the surface of the casting to prevent further oxidation.
Coating technology:
Apply a high-temperature oxidation-resistant coating (such as MCrAlY coating, where M is Ni, Co or Fe).
The coating can be prepared by processes such as physical vapor deposition (PVD) or chemical vapor deposition (CVD), which significantly improves the oxidation resistance of the casting.

5. Simulation and optimization
In practical applications, the heat treatment process parameters can be optimized to ensure the uniformity of the microstructure and the stability of the performance by combining simulation software (such as finite element analysis) and experimental verification.
Simulation analysis:
Use heat treatment simulation software to predict the microstructure changes under different process parameters.
Optimize the heating and cooling curves to obtain the ideal organization and performance.
Experimental verification:
Verify the simulation results through metallographic analysis, mechanical properties test and anti-oxidation performance test.
Adjust the heat treatment process parameters according to experimental feedback.

6. Precautions in practical applications
Composition control: The composition of heat-resistant steel is crucial to the heat treatment effect, and the content of alloying elements needs to be strictly controlled.
Process stability: The heat treatment process needs to be stable to avoid temperature fluctuations and insufficient holding time.
Quality inspection: Regularly conduct microstructure inspection (such as metallographic analysis) and performance tests (such as tensile test, creep test) to ensure the heat treatment effect.