Abstract: A joint body of the present disclosure includes a substrate including a base member having insulating properties and a metal layer positioned on a first main surface of the base member, a metal joint layer, and a metal member. The metal joint layer is positioned between the metal layer and the metal member of the substrate. The metal joint layer includes a nickel layer, a solder layer, and a composite layer containing a mix of nickel and solder. The nickel layer, the composite layer, and the solder layer are positioned in this order from the metal layer side to the metal member side. The nickel in the composite layer extends from the nickel layer in the thickness direction and forms protrusions and recesses.

Abstract: A method for the production of an electric seam welded steel pipe for oil-well use which has good resistance to collapse pressure and souring, by providing a steel containing 0.08-0.26% C by weight, 0.8-1.9% Mn by weight, 0.5% or less Si by weight, the remainder being Fe and unavoidable impurities, subjecting the steel to hot rolling, and hardening, and coiling the treated steel at a temperature not exceeding 250.degree. C., after which the steel is then formed into tubular form and welded by electric resistance welding to produce an electric seam welded pipe, and the weld heat affected zones of the pipe are subjected to heating to a temperature of 900.degree. C. or more to effect hardening, and then the whole pipe is tempered.