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Martensitic Stainless Steel
Description of material
VAL1SB is a free machining martensitic stainless steel with a Carbon content able to provide a suitable value of hardness after heat treatment, together with a good machinability. This grade is substantially similar to VAL1Z but its special chemical balance, with its exact steel processing and final NDT bar inspection, have been particularly designed to offer the best results in the fabricating of high –quality precision rifle and pistol barrels. VAL1SB is usually supplied in precision straightened and stress relieved bars.
High quality precision rifle barrels and all other products where a deep hole length of drilling and reaming processes are very important and indispensable properties. In addition, VAL1SB is widely used in the same applications as VAL1Z and in automatic machining industries.
VAL1SB offers substantially the same resistance corrosion of type 416 grades such as VAL1Z. In any case, it should be well considered that, as with all free machining grades, Sulphur is added to improve machinability and the formation of MnS inclusions could prime points of pitting if exposed to some corrosive environments. In any case, its resistance corrosion will depend on the corrosive capacity of the environment. This means that this condition may not be so detrimental in atmospheric corrosion or only slightly reduced, in mild aqueous environments, if the rifle is properly maintained. 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, VAL1SB is not suitable for cold heading and up-setting due to the embrittlement effect of the Sulphur content and has not been specifically designed for cold forming and is usually supplied as cold finished bars for machining processes. The hammer forging rifle barrel process is not recommended for this grade because this process may cause stress cracks due to the Sulphur embrittled structure.
VAL1SB has the good machinability typical of martensitic free machined grades. Productivity gain depends on the types of machines used, the kind of tools used and their geometry, cutting fluids and the kind of machine operations on the pieces produced. As a general rule, machinability depends on either Sulphur content and hardness in addition with a suitable structure of bars or shapes. It is useful to know that the Sulphur content is not so as high as VAL1Z or VAL1HS but sufficient to minimize built-up edge warranting either short chips and low roughness, even if this last characteristic is obviously influenced by structure hardness. In any case, special drilling machines such as Gun Drills or Deep Hole Drills must be used to drill deep accurate holes in order for the drill come out to within the expected position in the centre.
VAL1SB is not recommended for both fusion and friction welding.
The same as type 416 grades such as VAL1Z.
VAL1SB is normally supplied in the hardened + tempered and stress relieved condition, with different cold finish executions and mechanical properties according to Customer requirements. Nevertheless, it is well known that the fabricating processes of rifle barrels could cause or leave residual stresses resulting in the barrel bending after the processes have been completed. In this case, a further stress relieving after a new straightening operation may be unavoidable. The stress relieving temperature has to be chosen in order to maintain the properties of the supplied bars, avoiding those ranges of temperatures and cooling rates able to cause a strong reduction of toughness and corrosion resistance.