Heat treatment processes for difference maters of valve body castings

Heat treatment is essential for enhancing the mechanical properties, stability, and machinability of valve body castings. Different materials require specific heat treatment processes to achieve optimal performance. Below are the heat treatment processes based on different valve body materials:

1.Heat Treatment of Gray Cast Iron

Gray cast iron undergoes various heat treatments after casting to achieve different purposes. In valve production, two commonly used heat treatment processes for gray cast iron valve bodies are:

Stress Relief Aging (Heat Aging): This is a mandatory process to eliminate residual casting stresses.

High-Temperature Annealing: Used only when primary cementite is present in the casting due to improper chemical composition or cooling control. In such cases, annealing replaces heat aging to eliminate free cementite.

Valves

2.Heat Treatment of Carbon Cast Steel

Cast steel retains significant residual casting stress and may develop coarse or overheated structures, which negatively affect dimensional stability, mechanical properties, and machinability. To address these issues, carbon steel valve bodies undergo:

Annealing or Normalizing + Tempering

Annealing: Reduces hardness, refines grains, and improves machinability.

Normalizing + Tempering: Refines the microstructure, enhances mechanical properties, and improves cutting performance.

3.Heat Treatment of Austenitic Stainless Acid-Resistant Steel

Austenitic stainless acid-resistant steel is prone to intergranular corrosion, which can be prevented through heat treatment. Common processes include:

Solution Treatment (Quenching): Dissolves carbides and homogenizes the microstructure.

Stabilization Treatment: Enhances resistance to intergranular corrosion.

Cryogenic Treatment: Improves toughness and corrosion resistance.

4.Heat Treatment of Martensitic Heat-Resistant Steel

Martensitic heat-resistant steel requires immediate annealing after casting to prevent cracking. Key considerations include:

Annealing:

Held at a sufficient temperature for 4 to 8 hours to eliminate stress, refine grains, and reduce hardness for better machinability.

Prepares the structure for final heat treatment.

Final Heat Treatment:

Normalizing + Tempering improves toughness and wear resistance.

5.Heat Treatment of Carbon Steel

Taking 35# forged steel valve bodies as an example:

Normalizing is performed after forging to refine the structure.

Final heat treatment follows the valve manufacturing specifications, typically involving quenching and tempering to enhance strength and toughness.

Proper heat treatment enhances mechanical properties, reduces stress, and improves machinability, ensuring high-performance valve bodies. Selecting the appropriate heat treatment process based on material properties is crucial for reliable and durable valve components. Email:sales@haihaogroup.com