Low-Cost Treatment of Rolled Products Used to Make Long High-Strength Bolts

Abstract

The set of structural-mechanical properties of steel 40X has been optimized in preparation for the cold upsetting of long high-strength bolts. The properties were optimized by analyzing different factors that determine the quality of the sized rolled products used for the production of hardware items by cold upsetting. An effi cient method was developed to prepare steel 40X rolled products with diameters of 9.65 and 11.7 mm and a 9.8 strength rating for the production of long high-strength short-head bolts without having to quench and temper the products. The low-waste technology that is proposed for preparation of the rolled products replaces spheroidizing annealing with the isothermal process of patenting. Such a substitution reduces energy and labor costs while improving the environmental characteristics of the production process and the reliability of bolted products. It also eliminates the formation of quench cracks, obviates the need for knurling the products, reduces the danger of the formation of defects on the threads, and lowers the cost of making long bolts. These changes in turn make it possible to shorten the production process and reduce the cost of producing high-strength bolts.Among the most important goals in modern mechanical engineering are improving the quality of metal products and parts made from them, elevating their performance and reliability to world standards, ensuring that Russian-made products are competitive in the domestic and international markets, and satisfying environmental regulations while also developing new production processes [1-3]. Fasteners made from wire composed of medium-carbon, high-carbon, and alloy steels constitute one of the most widely used class of parts in machine construction here and abroad. In connection with this, the most widely used and most progressive method of making hardware items is the cold upsetting of bright-drawn rolled products.Steel 40X is now used quite frequently in hardware production. Roughly 60% of the fasteners of strength class 10.9 or higher are made of this steel, with upset bolts of steel 40X subsequently undergoing quenching and tempering. Highstrength fasteners account for only 15-18% of all of the fasteners made in Russia, but abroad this percentage is 90-95% (for fasteners of strength class 8.8 or higher). Thus, expanding the production and use of high-strength fasteners is an important concern for Russian industry.In the existing process production, the entire rolled product is rid of scale by pickling it in a concentrated solution of sulfuric acid. The technology used to make long high-strength bolts should ensure the production of bolts with a strength rating of 8.8 or higher under the government standard GOST 1759.4-87. In other words, hardware items need to be made with the use of quenching and tempering in order to obtain the necessary mechanical properties.The main method of producing high-strength fasteners composed of steel 40X is upsetting of the rolled product after drawing, when it has a microstructure of granular pea...

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