GB765305A - Method of hardening manganese steel - Google Patents

Abstract

765,305. Altering physical structure. MACLEOD, N. A. Feb. 3, 1955, No. 3194/55. Class 83 (4). A method of hardening an article of austenitic manganese steel comprises placing against the surface of the article to be hardened a sheet of explosive material, exploding said explosive material such that at least a portion of the shock-wave thereby produced will enter said surface and effect hardening of said steel in substantial depth, said hardening diminishing progressively from said surface inwardly the quantity of said explosive material being sufficient to harden said steel in substantial depth without permanently deforming the surface contour of the article. In an embodiment a layer 5 of explosive material, e.g. pentaerythritol tetranitrate, is placed on the upper surface 4 of a manganese steel workpiece 3 and exploded by a detonator 6. A hardness of about 400 Brinell is imparted to the surface 4, said hardness gradually reducing inwardly the normal heat treat hardness of 200 Brinell being encountered about one inch below the surface. The point of a digger tooth 10 (Fig. 2) is hardened by exploding a layer 12 of explosive material shaped to the contour of the point. One detonator is attached to a tongue 13 projecting from the material. After the explosion of the layer 12 another layer may be placed on the point decreasing in thickness from the edge 11 to give an additional hardening to said edge. Fig. 3 shows an explosive layer 15 moulded to the working surface of a manganese steel bowl 14 for a rock crusher and Fig. 4 an explosive sheet 18 applied to the surface of a roll shell 17 for a rolling mill. In the latter embodiment both the explosive and the roll shell are submerged in water or other liquid; sand or metal particles 19 to restrain the explosive force. An electrically ignited detonator 22 is attached to a tab 21. In a still further embodiment a manganese steel article 26 is supported on a layer of lead, rubber, plastic or fibre 27 in a jig 25 and a modifying layer 28 of softer material than the steel is placed over the surface to be hardened. A sheet 29 of explosive material is placed over the layer 28 and a cover member 30 comprising a manganese casting 31 vertically movable in guides 32 rests on the explosive material. When the layer 29 is exploded the cover member 30 yields upwardly to prevent rupture of the article: A yieldable sheet 33 may be placed between the explosive layer and the cover to protect the latter. Either or both of the explosive layer and the modifying layer are varied in thickness to control the hardening in different areas. In another embodiment the wheel treads 37 and 38 of a manganese steel railway crossing casting 35 (Fig. 7) are hardened by exploding strips 47 of explosive material which extend down over the side faces 48 of the wheel treads. The treads are hardened in turn so that the corners at the intersection of the treads receive a double treatment, thus increasing the depth of hardness in the metal adjacent the corners.