The present invention relates to a method for manufacturing an ultra-high-tensile expanded metal of steel.

When manufacturing an expanded metal one usually starts from metallic work pieces, preferably 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 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 expanded metal. This is so because the material would break during the forming operation.

US 2,018,085 disclose a method of making expanded metal of stainless steel. The work piece is plastically treated, by conventional methods, in order to form the expanded metal, whereupon the material becomes deformation hardened. In the method according to US 2,018,085, there are attempts to avoid deformation hardening.

The object of the present invention is to provide a method for manufacturing an ultra-high-tensile expanded metal, which is constituted of iron that has been alloyed to give a strong deformation hardening when being subjected to plastic cold machining in combination with maintaining good ductility of the alloy at the same time as the final product achieves a yield point more than 700 MPa. These objects can be achieved by a method according to claim 1.

Thanks to the invention one has now provided a method for manufacturing an ultra-high-tensile expanded metal 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 low cost.

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

In a preferred embodiment of the invention, the expanded metal 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 is alloyed with 17% Cr, 7% Ni and 0,1% C or alloys closely related to these and that the temperature of the work piece before and/or during the manufacturing operation has achieved or is kept at a controlled level, wherein a strong but controlled deformation hardening is achieved when plastic cold working the work piece in combination with maintaining a good ductility of the alloy. Furthermore, the temperature of the finally formed expanded metal is controlled after the working operation. The alloyed metal work piece that forms the initial work piece is formed in traditional machines for expanded metal fabrication 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.