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Description of material
X154MU/2 is a martensitic precipitation hardening stainless steel with good mechanical properties and better resistance corrosion when compared to the typical series of martensitic grades. Metallurgical behavior during aging is basically the same as V174 grade, while its hardness in solution annealing is a little lower.
It can be used in a number of different kinds of applications, such as valves, chemical and power production components, engine parts, fittings, fasteners, shafts and pumps shafts, and parts for oil & gas plants.
Argon Oxygen Decarburization
This grade has the same general resistance corrosion as austenitic stainless steel grade 304, but better than the group of standard martensitic 400 series. For some applications, it can be used in the solution treated condition, but for maximum resistance to Chloride stress corrosion cracking, it should be aged at 600-620°C. In Sulfide aggressive environments, age at 620° C. The same choice applies in the case of situations or environments prone to cause H-embrittlement. It should be noted for this grade, as for every kind of stainless steel, surfaces should be free of contaminants and scale, and passivated for optimum resistance to corrosion.
Cold deforming capacity in the annealed condition is better than V174 and V155. Nevertheless, severe cold working requires aging at high temperatures, particularly if cold processes were characterized by operations that could prime localized high strengths. To restore or increase mechanical properties such as tensile Rm and toughness, a new solution treatment followed by a suitable aging temperature should be carried out. Nevertheless, the repetition of a single aging could be sufficient evaluating if consistent with the final use.
Machinability is good in both the solution-treated and precipitation hardening conditions, considering that this property improves when hardness decreases. A certain amount of dimensional changes, in terms of contraction, happens after the aging of parts; these dimensional variations should be evaluated.
This grade has a good weldability, doesn’t normally need preheating, and has acceptable weld properties in the as-welded condition. But welding design should be well evaluated, in order to avoid situations prone to generate stress. Small sections could be welded in the solution treatment condition followed by an aging; large or heavy sections require a suitable temperature aging, obviously followed by a new solution treatment and aging.
Ingots or large forgings require a suitable preheating in order to avoid thermal cracking. Avoid overheating and improper cooling. Cool forgings in air and then solution treats. Large forging bars and shapes should be equalized at 1030 -1040°C in the heating furnace prior to cooling. Both small or large forgings, rolled ring, flanges or bars must be cooled to under 30°C to complete the transformation of Martensite, obtaining both a good structure and mechanical properties after aging.