Surface crack analysis and quality enhancement of 30Х13 (AISI 420) martensitic stainless steel gate valve shutters via electrolytic plasma hardening

• Surface cracks of 1.25 mm depth observed in gate valves during operation. • The hardness gradient from 531 HV to 395 HV may contribute to crack propagation. • Silicon-rich inclusions (up to 98.7 % Si) identified as crack initiation sites. • Electrolyte-plasma hardening improves surface quality and reduces fatigue cracks. • Optimised material purity and treatments enhance gate valve durability. This study examines the mechanisms of crack formation in gate valve shutters, identifies the underlying causes, and proposes an effective prevention method through electrolytic plasma surface treatment technology. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) with a JSM-6390LV SEM were used to evaluate the chemical composition, morphology, structure, and surface defects of the shutters at nano- and microscale levels. To assess mechanical properties, Vickers microhardness testing (ISO 6507–1) was conducted using a DuraScan 20 microhardness tester, while the phase composition of 30Х13 steel (AISI 420) was examined through X-ray diffraction (XRD) analysis. The results demonstrate a significant increase in surface microhardness in samples subjected to electrolytic plasma hardening, with values reaching up to 650 HV. Furthermore, the phase composition of the treated surface exhibited notable changes, including the dissolution of carbides in austenite and the formation of martensite as the predominant phase. Based on these findings, electrolytic plasma hardening is proposed as an effective alternative to traditional volumetric quenching methods. An optimal treatment mode has been developed for 30 × 13 steel, ensuring enhanced surface properties and improved durability. The experimental results validate the effectiveness of this approach in enhancing the mechanical performance and operational reliability of gate valves.