Authors: Diana Hlushkova | V. M. Volchuk
Source: Bulletin of Kharkov National Automobile and Highway University (article, 2025-12-01)
Field: Materials Science — Materials Chemistry

Investigation of the Impact of Hydrogen Sulfide Embrittlement on the Microstructure and Prop-erties of Manganese Steel Annotation. Statement of the problem. Heat treatment significantly enhances the properties of metals and alloys, thereby extending their service life. The microstructure of many metallic materials undergoes transformation following heat treatment. The operation of oil and gas fields containing hydrogen sulfide (H₂S) necessitates the use of tubing and casing pipes resistant to sulfide stress cracking. Currently, imported pipes, such as those of grade C75-2, are employed for this purpose. Heat treatment of steels improves the operational properties of pipeline steels used in aggressive H₂S-containing environments. Consequently, testing manganese steel under the MCKP 01-85 methodology, which involves assessing resistance to sulfide stress cracking through constant strain rate testing in an H₂S-containing aggressive environment, is particularly relevant. The H₂S environment induces hydrogen embrittlement and stress corrosion cracking, leading to the formation of cracks with self-similar (fractal) morphology. To study this morphology, various approaches are employed alongside fractal theory. This study focuses on investigating the effects of an aggressive hydrogen sulfide (H₂S) environment on the microstructure and properties of manganese steel 30G2. Purpose and setting of the task. The aim of this study is to evaluate the impact of an aggressive H₂S environment on the strength and ductility characteristics of manganese steel, as well as to analyze changes in the fracture mechanisms to develop recommendations for enhancing its operational reliability. To achieve this objective, the following tasks must be accomplished: 1. Conduct heat treatment of manganese steel and perform microstructural analysis before and after exposure to the H₂S environment. 2. Perform fractographic analysis of the fracture surfaces of the steel. 3. Investigate the effect of hydrogen embrittlement induced by the H₂S environment on the microstructure and properties of manganese steel. Materials and Research Methods. Experimental tests were conducted on samples of 30G2 manganese steel in two states: the initial state (after heat treatment) and after prolonged exposure to an H₂S environment (720 hours, according to the MCKP 01-85 methodology). In the initial state, the steel exhibited high mechanical properties: ultimate tensile strength (σВ) of 842 MPa, yield strength (σT) of 736 MPa, relative elongation (δ5) of 19.6%, and relative reduction in area (ψ) of 65.6%. These values significantly exceed the standard specifications for 30G2 steel, indicating the effectiveness of the applied heat treatment. Research material and methods. Following exposure to the H₂S environment, a slight reduction in strength characteristics (by 2–3%) was observed, indicating the steel's resistance to strength degradation under aggressive conditions. However, ductility experienced a more significant decline, with relative elongation and reduction in area decreasing by 10–13%. Despite this, the ductility values remained within acceptable limits to ensure reliable operation of coupling pipes. After exposure to the H₂S environment, a transition to a more brittle fracture behavior was noted, accompanied by the formation of hydrogen-induced cracks. These changes are attributed to hydrogen penetration into the steel’s microstructure, which causes localized embrittlement and reduced ductility. The obtained results confirm the suitability of the modified 30G2 steel for use in coupling pipes for oil and gas pipelines operating in aggressive H₂S environments. However, the observed changes in ductility and fracture behavior highlight the need for further optimization of the steel’s chemical composition and heat treatment regimes. Specifically, it is recommended to consider the addition of alloying elements to enhance resistance to hydrogen embrittlement and to improve heat treatment technologies to minimize internal stresses and microstructural defects. These measures will contribute to enhancing the durability and reliability of pipes under challenging operational conditions. Conclusions. 1. The mechanical properties of coupling pipes made from 30G2 manganese steel in the initial state are characterized by high strength (σВ ≈ 842 MPa, σТ ≈ 736 MPa) and good ductility (δ₅ ≈ 19.6%, ψ ≈ 65.6%). These values exceed the standard specifications for 30G2 steel, indicating effective heat strengthening of the material. 2. After exposure of the samples to a hydrogen sulfide (H₂S)-saturated environment for 720 hours, the reduction in strength is minimal, at only 2–3%, demonstrating the resistance of 30G2 steel to strength degradation under H₂S conditions. 3. The most significant changes are observed in the ductility properties: relative elongation and reduction in area decrease by 10–13%, which is associated with hydrogen embrittlement and the formation of intergranular cracks. However, even after H₂S exposure, the ductility remains satisfactory for operational purposes (δ₅ &gt; 14%, ψ &gt; 54%). 4. Fractographic analysis revealed a transition from ductile-brittle fracture in the initial state to a more brittle fracture after H₂S exposure, confirming the accumulation of hydrogen in the steel’s microstructure and its influence on crack formation. 5. Overall, the modified 30G2 steel exhibits satisfactory resistance to H₂S-induced effects and can be considered a promising material for oil and gas pipelines operating in aggressive H₂S environments. To enhance durability, further optimization of the chemical composition and heat treatment regimes is recommended (e.g., alloying with Cr/Mo, additional tempering at 600–650 °C). Hydrogen embrittlement ; Microstructure ; Manganese ; Stress corrosion cracking ; Ductility (Earth science) ; Fracture (geology) ; Environmental stress fracture ; Corrosion ; Sulfide Material Properties and Failure Mechanisms ; Hydrogen embrittlement and corrosion behaviors in metals ; Engineering Diagnostics and Reliability