VALVE MAGAZINE Spring 2025

In valve applications, industry standards such as ASME, API and ASTM define material requirements, pressure ratings and temperature limits to ensure safety and reliability. Metallurgy directly influences these ratings through alloy composition, heat treatment and microstructural control. Role of heat treatment and crystal structures Heat treatment processes refine material microstructures to enhance strength, hardness, toughness and corrosion resistance, ensuring optimal performance in industrial applications. The table on p. 31 summarizes key heat treatment processes. Each process is crucial in modifying the material’s phase and structure to achieve specific characteristics. Solution annealing and precipitation hardening, for instance, are used to optimize corrosion resistance and strength in specific alloys like austenitic stainless steels and nickel-based alloys. By controlling the heat treatment parameters, engineers can tailor materials to meet the demands of high-stress and corro sive environments . Heat treatments and crystal structures define material performance. Martensitic steels, formed through rapid cooling, develop a body-centered tetragonal (BCT) struc ture and offer high hardness and wear resistance, ideal for valve trim and seats. Austenitic steels, with a face-cen tered cubic (FCC) structure, provide superior ductility, toughness and corrosion resistance, making them suitable for valve bodies and chemical processing. Ferritic steels, featuring a body-centered cubic (BCC) structure, deliver moderate strength and oxidation resistance for cost-ef fective industrial valves (Figure 2). Duplex stainless steels combine dual FCC and BCC phases (Figure 3) for high strength and corrosion resistance, requiring careful heat treatment to prevent sigma phase formation. Figure 1B: Microstructural analysis of a fractured cast iron yoke stem bushing made of D-2C materials revealed a mix of nodular graphite and filamentary structures due to insufficient magnesium content, resulting in poor nodularity during manufacturing. This deviation from ASTM standards compromised the mechanical properties, ultimately leading to bushing failure.

Understanding Metallurgy for Valve Applications

BY: FADILA KHELFAOUI, Corporate Engineer COMPANY: VELAN

Material selection for valves is a complex process that must consider temperature, pressure, corro sion and wear. A comprehensive understanding of metal lurgical principles enables engineers and manufacturers to make informed decisions, ensuring valves perform reliably in demanding environments while reducing operational costs and improving safety. What is metallurgy? Metallurgy is the science and engineering of metals, focusing on their extraction, processing and transformation into functional components. It examines how composition, structure and processing methods affect mechanical and chemical properties such as strength, toughness, corrosion resistance and thermal stability (see an example in Figure 1).

Figure 1A : Fractured cast iron yoke stem bushing made of D-2C material. All Photos: Velan Inc. (unless otherwise noted)

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WINTER 2024 SPRING 2025