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...
A widely spread and most productive way to obtain finished metal articles with high structural and mechanical properties are methods of cold heading out of rolled metal, which must have a certain quality - the required plasticity, uniform structure and process parameters along the full length, as well as soundness. In conditions of fierce competition in order to improve the quality of the upset metal articles, the enterprises are forced to find reserves at all the points of the process chain for transformation of the original rolled metal. The greatest effect is achieved by the excluding of energy-consuming and labor-intensive annealing in protective gas furnaces and control of surface defects by etching or mechanical operations. This paper is presenting an economical and environment-friendly technology for structural and mechanical maintenance of high quality of rolled stock for upsetting of metal articles. The rolled steel prepared by this technology has a highly dispersed equally spaced structure without a decarburized layer with increased plasticity, which enables to reduce the number of transitions in the process of upsetting of metal articles and to increase the tools service life.
Abstract. Hardware items are one of the products for mass consumption. Rolled metal for cold forging shall have the required ductility, uniform mechanical characteristics along the mill length, corresponding chemical composition and shall be free from internal or superficial defects. Standard mechanical characteristics have been reviewed in this document and fracture criteria of calibrated rolled steel 40Х have been calculated after its isothermal treatment at different temperatures in nitre bath and subsequent drawing with different deformation degrees. Comparison of synergy fracture criteria showed that rolled stock, treated as per the proposed conditions: bath patenting at the temperature of 400ºС and drawing with reduction rate of 5% and 10%, are more preferable, comparing to processing conditions, existing in the industry.
Doctor of Technical Sciences* D. G o n c h a r o v a ** A. F i l i p p o v PhD*
Initial blank for the production of calibrated rolled stock is hot-rolled steel, ductility of which is largely determined by the structure and quality of the rolled stock surface. Hot-rolled steel should have a high degree of surface cleanliness and defect-free cross-section. In this paper, using the example of hot-rolled steel 40X, it is shown that the structural condition and quality of the rolled stock surface largely determine the further quality of calibrated rolled stock for automobile long length bolt products made from it. In this case, the mechanical characteristics, which are the most widely used indicators of the steel quality, are largely determined by plastic and heat treatment, which change the structure at the macro- and microscopic level.
We have studied the influence of corrosive environment on the mechanism of changes in fatigue resistance of automotive structural steels. Analysis of the experimental data has shown that the fatigue resistance of metal materials in corrosive environments is reduced significantly with the increased time of testing. This, in turn, causes a continuous decrease in fatigue curves in the multi-cycle area without reaching the endurance limit. We have identified the factors affecting the resistance to fatigue failure: the medium and its aggressiveness; stress cycle frequency, shape and asymmetry. The presence of a corrosive environment makes it problematic to determine the moment of origin of a macro crack, necessary for the analytical assessment of the time before its appearance. The proposed use of the current sag curves under the sample cyclic loading will allow to fix the moment of the crack origin and to determine the speed of its subsequent propagation. This allows to optimize the choice of structural materials for machines taking into account the operating conditions and to justify the technological manufacturing process in order to reduce material consumption, increase durability and maintainability.
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