Casting shapes stainless steel parts basically. Heat treatment boosts their strength, corrosion resistance, and stability. QD performs professional, standard heat treatment processes.
Why Must Castings Undergo Heat Treatment?
During the casting of stainless steel parts, factors like uneven cooling rates and uneven phase transformation cause problems inside the castings, such as residual stress, uneven structure, and segregation. You need to solve these problems with proper heat treatment. Without it, the castings will have a shorter service life, and there will be potential safety hazards.
The main purposes of heat treatment are as follows:
- Relieve casting stress: This prevents the castings from deforming or cracking during processing or use.
- Homogenize the structure: This refines the grain size, makes the composition uniform, and improves overall performance.
- Optimize corrosion resistance: You can restore or enhance the castings’ corrosion resistance through methods like solution treatment.
Detailed Explanation of Core Heat Treatment Processes
At QD, we precisely control three core process parameters—temperature, time, and cooling rate. This allows us to adjust the material’s microstructure and get the desired performance.
Below is an in-depth breakdown of several core processes:
Solution Treatment
Principle:
During casting, carbon and chromium combine at the grain boundaries. This forms chromium carbide precipitates. It directly causes the chromium content near the grain boundaries to drop. This creates a “chromium-depleted zone”. The chromium-depleted zone has weak corrosion resistance. In corrosive environments, intergranular corrosion occurs here first. This can make the casting fail from the inside, even while the surface looks intact.
Solution treatment heats the casting to a high temperature between 1050°C and 1150°C. The exact temperature depends on the specific steel grade. It is held at this temperature for a sufficient time.
During this process:
- The chromium carbide at the grain boundaries dissolves back into the austenite matrix.
- Carbon and chromium become evenly distributed throughout the material.
We create precise process cards for each material grade. These cards strictly control the maximum temperature and holding time. If the temperature is too low or the time is too short, the carbides will not fully dissolve. If the temperature is too high or the time is too long, the grains may grow coarse. This harms the mechanical properties.
Quenching
Principle:
The choice of quenching medium and the control of cooling speed directly determine the result of the solution treatment. For austenitic stainless steel, the heat treatment process requires it to quickly pass through the sensitization temperature range (450-850°C) within seconds. This prevents chromium carbide from precipitating.
For thin-walled castings with complex structures, QD uses high-speed air quenching. This method ensures the required cooling speed. It also effectively reduces quenching stress and controls deformation. For most standard castings, water quenching is used. This provides the strongest resistance to intergranular corrosion.
Our cooling system has temperature and flow monitoring. This ensures each batch of castings experiences the same cooling conditions. It guarantees consistent and repeatable product performance.
Annealing
The main goals of annealing are to reduce hardness, improve machinability, or eliminate work hardening
Principle:
We heat the casting to a suitable temperature, which can be below or above its transformation point. After holding at this temperature, it is cooled slowly. This process changes unstable, high-hardness structures into more stable ones with lower hardness. It also fully removes internal stresses.
QD does not use a “one-size-fits-all” annealing process. We offer customized solutions. We use different annealing methods for different castings. This saves you machining time and cost.
- For castings that require heavy machining, we use full annealing to achieve the lowest hardness.
- For castings that only need stress relief while maintaining strength, we use stress relief annealing.
Stabilization Treatment
This is a strengthening measure for specific steel grades.
Principle:
For stabilized austenitic stainless steels containing titanium or niobium, we sometimes use stabilization treatment. The process heats the casting to 850°C – 930°C and holds it at this temperature. At this stage, carbon first bonds with titanium or niobium. These elements are more reactive. This forms stable titanium or niobium carbides. Therefore, the carbon does not deplete the chromium at the grain boundaries. This provides extra protection against intergranular corrosion. It ensures the material can safely serve in the sensitization temperature range for medium to long terms.
If your product will be welded or will operate in moderately high temperatures long-term, our engineers can assess it. They will recommend whether to use stabilization treatment. This provides double protection for your critical components.
Special Case Handling
| Stainless Steel Type | Recommended Heat Treatment Process | Description |
| Low-carbon stainless steel (e.g., 304L, 316L) | Solution treatment | Low carbon content prevents carbide precipitation. Stabilization treatment is not required. |
| Martensitic stainless steel (e.g., 420) | Quenching+tempering | High hardness and strength are obtained through quenching and tempering. |
| Precipitation-hardening stainless steel (e.g., 17-4PH) | Solution+aging treatment | Strengthening phases are precipitated through aging to improve strength and hardness. |
Note: Stainless steel castings of different materials and service environments need custom heat treatment paths. We can provide tailored solutions based on your specific requirements.
Contact Us
At QD, we are equipped with:
- Fully automated heat treatment furnaces. Temperature uniformity is controlled within ±5°C.
- Precision temperature control systems. They monitor and record temperature curves in real-time. This ensures consistent processing for every batch.
- Complete process documentation. Each batch of castings has its own heat treatment report. This supports full traceability.
We not only follow standard procedures but also focus on process control and data management. This ensures the performance of every batch of castings you receive is stable and predictable.
Do you have special requirements for mechanical properties, corrosion resistance, or dimensional stability?
QD can create custom heat treatment processes for you. Just provide your specific performance needs. We will design the most suitable heat treatment solution for you.
FAQ
1. Is machining needed after heat treatment?
Usually, yes. Heat treatment may cause slight distortion. We recommend finishing machining after heat treatment to ensure dimensional accuracy.
2. Does heat treatment affect the surface quality of castings?
If not properly controlled, issues like oxidation or decarburization may occur. QD uses controlled atmosphere furnaces to effectively protect surface quality.
3. Do heat treatment processes vary greatly for different stainless steels?
Yes, significantly. For example, austenitic stainless steels often use solution treatment, while martensitic stainless steels require quenching and tempering. The material determines the process.
4. How long does a typical heat treatment cycle take?
The time varies. It depends on the material, part size, and specific process. Cycles typically range from several hours to tens of hours. We evaluate the exact time based on your parts.
5. How do you verify the heat treatment results?
You can verify the results through different methods. These include metallographic analysis, hardness testing, corrosion tests, and mechanical property tests.
6. Can QD provide a heat treatment process report?
Yes. We provide a complete process record and test report for every batch. This ensures the process is traceable and the results are verifiable.