Improvement of Crane Rail Hardness while Using Plasma Discrete Surface Treatment
Crane wheels and rails are subjected to intensive wear in the process of operation. For this reason improvement of operating capability for these components is considered as a problem of great importance. A promising direction in this regard is surface treatment by highly concentrated energy flows such as laser beams or plasma jets. The paper proposes to use gradient plasma surface treatment with the purpose to improve operating capability of crane rails. While carrying out investigations hardened zones have been deposited on crane rails under different treatment modes. Microhardness has been measured both on the surface and in depth while using custom-made microsections. The paper presents results of the investigations for plasma surface hardening influence on wear resistance of crane rails. Change of plasma surface treatment parameters (current, plasma torch movement speed, argon gas flow rate) allows to obtain the required steel hardness and structure and selection of optimal location for the hardened zones makes it possible significantly to improve wear- and crack resistance. Plasma surface hardening contributes to obtain a fine-grained martensite structure mainly with lamellar morphology and higher hardness rate in comparison with induction hardening or overlaying. Wear tests of carbon steels have revealed that plasma surface treatment reduces abrasive wear rate by 2-3 times in comparison with the initial state. Rather sharp boundary between hardened and non-hardened portions has a positive effect on the performance of parts under dynamic loads, contributing to crack stopping during the transition from solid to soft metal. According to the obtained properties plasma surface hardening can efficiently substitute induction hardening or overlaying for carbon and low alloy rail steels. The mode range for plasma surface treatment that allows to obtain a surface layer with specific complex of operational properties has been determined in the paper.