Stainless non-magnetic steel with high manganese and chromium content, resistant to stress corrosion and useful for drilling equipment, also the process for manufacturing rods from this steel

摘要

Steel with austenitic structure, characterised by the corresponding mass proportions of the following elements: Carbon /= 0.025 %, preferably /= 0.020 %, Manganese 15 to 25 %, Chromium 10 to 15 %, Nickel 0.25 %, Molybdenum 1.0 to 1.3 %, Nitrogen 0.30 to 0.50 %, Silicon 1.0 %. The process of manufacture comprises the following stages: production of a starting ingot made of a steel as above; first homogeneous heating, to a temperature above the recrystallisation temperature of the steel; blanking the bar by hot drawing of the ingot; first cooling to ambient temperature; second homogeneous heating; forming the bar by forging and dressing in the press; second cooling to ambient temperature; and lastly final machining. In this way it is possible to produce a cold-worked nonmagnetic steel bar of length greater than 2.5 m exhibiting, over its whole length and homogeneously, a yield point, in lengthwise direction, of at least 760 MPa in the case of finished products of diameters of between 79 and 175 mm and of 690 MPa in the case of finished products of diameters of between 178 and 254 mm, and an insensitivity to intergranular corrosion and to stress corrosion.