When manufacturing pressure turned sheet metal products one usually starts from metallic work pieces, preferable of soft steel with good forming properties. During the forming operation one achieves a certain degree of deformation hardening, which however is insufficient for obtaining an ultra-high-tensile final product. In the case one should start from a material that initially is ultra-high-tensile with a yield point preferably more than 700 MPa, this material would not have sufficient ductility to be formed to any greater extent during the pressure turning operation. This is so because the material would brake during the forming operation.

The object of the present invention is to provide a method for manufacturing an ultra-high-tensile pressure turned sheet metal product of steel, that has initially been alloyed with chromium, nickel and carbon in predetermined proportions. The characteriz- ing features of the invention are stated in the subsequent claims.

Thanks to the invention one has now provided a method for manufacturing an ultra-high-tensile pressure turned sheet metal product of steel, which in an excellent manner fulfils its object at the same time as the manufacture can take place very rationally with already existing machines to a low cost. During the pressure turning a final product is obtained according to the invention, in which parts of or the whole product has an yield point more than 700 MPa and also values far away over that, for example 1.500 MPa. This result with a strong and

controlled deformation hardening of the whole or parts of the product is achieved during the pressure turning by that the product is plastically cold worked in combination with that the alloy maintains a good ductility during the pressure turning with a temperature adapted to the yield point of the final product wanted and at the same time to a deformation degree adapted to the yield point of the final product also wanted. If one has a low or not so high deformation degree and would like a high tensile this can be compensated using a lower temperature, i. e. by cooling before, during or after or in combination of these criteria during the working operation. If one has a high deformation degree, a deformation hardening can be obstructed in that the work piece is allowed to keep a higher temperature.

The invention is described in more detail below with the aid of an embodiment example described below.

In a preferred embodiment example of the invention the pressure turned sheet metal product manufactured according to the invention is constituted of a work piece of iron, which has been alloyed with chromium, nickel and carbon in predetermined proportions. In the example chosen the iron has been alloyed with 17% Cr, 7% Ni and 0, 1% C or alloys closely related to these and the temperature of the work piece before and/or during the manufacturing operation has been kept or is kept at a controlled level, wherby a strong but controlled deformation hardening is achieved during the pressure turning when a plastic cold working of the work piece in combination with maintaining a good ductility of the alloy. Furthermore the temperature of the finally formed pressure turned product can be controlled directly after the working operation itself. The alloyed metal work piece, that forms the initially work piece according to the invention, can be formed or plastically cold worked in traditional machines for pressure turning in order to increase its yield point from an original, low yield point of about 300 MPa to a final product that completely or partially obtains a yield point of more than 700 MPa.