VALVE MAGAZINE Spring 2025

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Microstructure Phase/Formed

Effect on Material Properties Prepare for hardening, enhances ductility

Heat Treatment Process

Material Type

Austenitization

Carbon and alloy steels

Austenitic phase (FCC)

High hardness, but increased brittleness due to trapped carbon Reduces brittleness while maintaining hardness Improves strength and ductility, refines grain structure

Quenching

Austenitized steel

Martensite (BCT)

Tempering

Martensite

Refined martensite (BCT)

Normalizing

Carbon and low-alloy steels

Fine-grained (BBC)

Dissolves carbides and precipitates, enhances corrosion resistance

Austenitic stainless steel and nickel-based alloys

Stabilized austenitic phase (FCC)

Solution annealing

Strengthens by obstructing dislocation movement, improving mechanical properties Prevents chromium carbide precipitation, preserves corrosion resistance

Nickel-based alloys and certain stainless steels (e.g.,17-4PH)

Fine precipitates in FCC/BCT matrix

Precipitation hardening

Austenitic stainless steels (e.g., 321, 347)

Stabilization heat treatment

Austenitic phase (FCC)

Table 1: Examples of heat treatment and the effects on materials Nickel-based alloys, such as Inconel and Hastelloy, leverage their FCC structure to maintain oxidation and corrosion resistance under extreme conditions, making them essential for high-temperature, high-pressure valves. Cobalt-based alloys like Stellite provide outstanding wear and galling resistance, commonly used for hardfacing valve components. Titanium alloys, with a hexagonal close packed (HCP) structure, offer an excellent strength-to weight ratio and corrosion resistance, valuable in seawater and aerospace applications.

Understanding heat treatments and crystal structures allows engineers to optimize valve performance and ensure reliability in demanding applications. Metallurgy matters Selecting the appropriate materials for valves is a complex process requiring careful consideration, not only of the material group, but also specific grades, heat treatment conditions and compliance with industry standards like NACE (National Association of Corrosion Engineers) for sour service applications. In this application, compliance

Figure 2: Molecular structure of common valve steels. Source: Metallurgical Engineering.

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