Abstract: A tube-formed rock bolt is expandable into contact with the wall in a bore hole without stretching the periphery of the rock bolt. The rock bolt has an elongated tube (12) with a closed cross section. The tube is provided with a longitudinal depressed part (13). End pieces (14, 24) are secured to the ends of the tube, and the end pieces are provided with axial channels (15, 35) having peripheries which provide a seal resulting from deformation of material when the rock bolt is assembled by joining together different sections. By connecting one end (30) of the assembled rock bolt to a high pressure pump (39), the entire assembled rock bolt can be expanded at the same time.

Abstract: A steel alloy contains in weight-% 0.5-1.0 C, 1-2 Si, max 0.2 Mn, preferably max 0.001 S, 0.1-0.5 Cr, balance essentially only iron. In the form of a cold rolled, hardened and tempered strip it can be used as a backing material for band saw blades, frame saw blades and circular saw blades, where the teeth are tipped with a different material than the backing material. This steel strip has a structure consisting of tempered martensite, and possibly remaining carbides, obtainable by hardening from a temperature between 780.degree. and 1000.degree. C. and tempering at a temperature between 200.degree. and 550.degree. C.