Manufacturing forged steel screws with excellent tensile strength and high ultimate extension, employs specified sequence of heat treatments and deformation

摘要

The forging (4) is formed from steel rod (3). It is heated to 830-900[deg] C. First tempering follows, at 100-300[deg] C. A second tempering then takes place, at 300-400[deg] C. During first tempering, the forging is quenched in a salt bath, at a temperature in the range 100-300[deg] C; it is tempered for 60-130 minutes. During the second tempering, the forgings are quenched in a salt bath at a temperature in the range 300-400[deg] C; this which continues for 30-150 minutes. The forgings are heated to 830-900[deg] C for 30-120 minutes. The forging is preheated to 550-650[deg] C for 30-90 minutes, before heating to 830-900[deg] C. The steel rod is hardened wire, selected from nickel-chromium-molybdenum steel and chromium-molybdenum steel. The forging is deformed during a first stage (a) as follows. It is subjected to a first annealing. The rod is then removed and coated. An intermediate stage of drawing follows. Then it is subjected to a second annealing. Removal and coating is repeated. It is further drawn by after-rolling. It is forged using a stamp and roller cut, to complete the forging.