Rybalko I. Experimental, theoretical and technological basics of hardening products with the use of modifying agents

The dissertation presented for defence is based on theoretical, experimental and technological research involving new, effective and less expensive approaches to increase the durability of products intended for different purposes. With this in view, secondary raw materials were used – a nonmagnetic detonation charge obtained by ammunition recycling and bentonite clay extracted from natural deposits. The thesis considers a tubing assembled of steel Р-110 with a diameter of 73 mm and a wall thickness of 5.5 mm, and cultivator shares with a thickness of 6-6.5 mm. The incorporation of different products in one thesis stems from the fact of using the same detonation agent to improve different properties of products during their manufacture, though along different lines during their maintenance and operation. To increase the operational durability of threaded joints whose damage leads to 55% of all failures and emergencies, a method for introducing a modifying agent to the lubricating grease of such joints is proposed and the agent’s composition is defined. It was found that a detonation charge obtained by recycling ammunition of a special grading, composition and preparation method ensures the formation of secondary protective structures (oxide films) and reduces the friction coefficient. A method is proposed to introduce a modifying agent into the molten weld pool while building up cultivator shares. For this purpose, an additive in the form of a coating was applied onto electrode Т-620. Investigations have found that, introducing the modifying agent of the nonmagnetic part of the detonation charge as 5-7% of the electrode’s part, eliminates the formation of defects related to a molten weld pool temperature drop. Such a drop is caused by the insoluble diamond fraction that plays the role of local micro coolers. In this case, the metal structure becomes finer. The carbide phase precipitates in the form of granular inclusions distributed more evenly in the matrix. For in-depth research, a natural component was also used – bentonite clay. The additive was applied onto the electrode as optimal 6-8% of its part. Comparative metallographic studies have shown that the introduction of such an additive facilitates the formation of a more homogeneous structure practically in all coating zones due to the reduction of needle-like carbide precipitates that makes them granular. In both coating variants (with the introduction of the modifying clay and without it), the matrix tempering martensite structure crystallises. Additional modification reduces the transition zone section by a factor of three. Applying a coating onto a thin-wall cultivator share fully penetrates it, whereas introducing bentonite clay keeps the base metal up to 50%. The research result was the development and proposal of a new method of hardening cultivator shares. The method consists in applying hardening strips onto the tip of the share face and onto its wings on the backside. According to analysis of wear processes, an optimal scheme is the building up of 20 mm hardening strips on the tip and 12-15 mm strips on the wings with a minimum 10 mm distance between them to prevent the overlap of thermal action zones.