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Martensitic Stainless Steel
Description of material
VAL1 is the most popular martensitic stainless steel designed to supply high mechanical properties and a good corrosion resistance in mild environments.
Table cutlery and kitchen devices, food processing equipment, bolting, fasteners, screws, steam turbine blades, pumps shafts, parts of petrochemical plants, pump parts and valve components.
Argon Oxygen Decarburization
VAL1 has its maximum corrosion resistance when in the hardened + tempered condition. As with most martensitic grades, its use in the annealed condition, or any other situation able to strongly reduce the hardness in environments containing Chloride, should be avoided. However, VAL1 offers an acceptable corrosion resistance in many industrial and domestic applications in not too aggressive environments such as fresh water, industrial and rural atmospheres, petroleum products, gasoline fuel oil and alcohol. It should be noted that this grade, as for every kind of stainless steel, surfaces should be free of contaminant and scale, heat tint, and passivated for optimum resistance to corrosion.
In the annealed condition, this grade is suitable for cold forming operations such as cold heading. In addition, a higher cold upsetting could be obtained after a long lasting annealing and very slow cooling in the furnace. It should be pointed out that VAL1 is not so prone to cause a rapid surface decarburization compared to high Carbon martensitic grades. If this were a problem, a protective atmosphere should be considered for the heat treatment of finished pieces. Blooms or large cross section billets can be cut by band and circular saw or abrasive wheel.
In the annealed condition, VAL1 with its low Sulphur content, hasn’t a good machinability while this does slightly improve in the hardened and tempered condition. On the contrary, a micro-resulphured structure strongly increases its machinability. However, it is important to know that the productivity gain depends on the type of machines, the kind of tools used and their geometry, the cutting fluids used and the kind of machine operations on the pieces produced. If small billets or bars had to be cut by cold shearing, this requires paying attention to low temperatures and clearance of tools, because this process may cause shear or stress cracks.
Preheating of small sections is necessary and must be particularly done in the case of both large cross section differences, and large welds with several interpasses. Post welding heat treatment (PWHT) is mandatory due to the transformation of martensite in the heat affected and fused zones and should be done immediately after welding. In solid state joining such as Friction Welding, VAL1 provides a quality bond line. When friction welded with different grades, a tempering or annealing of the welded piece must be done in order to soften the martensitic structure of the HAZ and bond line.
Blooms and ingots require a preheating to avoid cracks and a slow cooling in furnace after forging. Avoid overheating, which is able to cause internal bursts or promote formations of ferrite stringers. In the case of hot forging, VAL1F should be used, because has been designed to obtain a fully martensitic structure without ferrite. Improper cooling could result in stress cooling cracks. Alternatively, large forgings and large cross –section shapes should be left to cool until their core reaches room temperature and, then, immediately heat treated.
VAL1 could be air or oil hardened. The choice of quenching method depends on the thickness, shape and geometry of pieces, as well as their metallurgical-mechanical requirements. The tempering temperature has to be chosen in order to offer the best properties, avoiding those ranges of temperatures and cooling rate that are able to cause a strong reduction of toughness and corrosion resistance. It’s important to point out that high tempering temperatures, or annealing temperatures impair the corrosion resistance of all martensitic grades.