A method has been discovered to enhance the strength of steel structures.

In various industrial sectors, particularly in the production of critical components such as aerospace parts and nuclear reactor components, martensitic aging steels are widely utilized. These steels derive their name from the presence of martensite—a unique structure that forms when the atoms within the metal rearrange during heating and subsequent cooling. This structure imparts exceptional strength, ductility, and impact toughness to the alloys. Despite these advantageous properties, it is crucial to monitor the crack resistance of such materials to prevent the failure of structures made from them. Researchers at Perm Polytechnic University have investigated how the quenching temperature of the metal affects its final characteristics and have developed recommendations to enhance crack resistance.

2025-02-25 10:00:42https://naked-science.ru/article/column/stalnye-konstruktsii-bole

The article was published in the journal "Physics of Metals and Metallography." The heat treatment of martensitic aging steels involves several key stages. Various elements, such as nickel, cobalt, titanium, aluminum, and others, are added to strengthen the steel. The resulting alloys are heated to a temperature above the critical point (800-950 °C) and held there to ensure the uniform distribution of these elements and to achieve a special structure known as martensite, after which they are cooled. This process is referred to as quenching.

Next, the steel is reheated to 450-550 °C and maintained for several hours. This treatment is known as aging. During this phase, martensite decomposes, forming internal crystal precipitates, such as nickel-titanium, nickel-aluminum, and so on, with sizes measuring just a few nanometers.

All of this leads to the strengthening of the alloy; however, the size of these compounds plays a crucial role in enhancing crack resistance, which varies based on aging temperature. Expanding the knowledge base on such phenomena requires studying the changes in material structure under different factors. Similar tests are conducted periodically, but the polytechnics utilized their own equipment, specific steel, and certain conditions under which experiments had not been previously performed.

Scientists from Perm Polytechnic studied the crack formation resistance during periodic loading using one of the most commonly used domestic martensitic aging steels – 03Х11Н10М2Т (EP-678). This steel is employed in the production of power-welded and machined components, highly loaded disks for turbomachines, gears, and parts for aircraft construction, operating at temperatures ranging from -200 to +400 °C, and also in corrosive environments such as seawater, among others.

Industrial ingots were subjected to hot forging, and samples were prepared for research. The blanks were quenched in water from 920 °C and held at temperatures of 300-560 °C for three hours. Tests for crack resistance were conducted on a specialized machine for rigid loading. The samples were then compared before and after the experiments using both optical and electron microscopes.

“It is commonly believed that the finer the structure, the higher the crack resistance. However, the study of this steel showed that the coarsening of its elements increases resistance to failure under periodic loading conditions. Notably, the maximum positive effect was observed at low loads – no more than 1-2 tons: for instance, after quenching from 1200 °C (coarse-grained steel), the crack growth rate was three times slower than after quenching from 920 °C (fine-grained). This indicates that the higher the quenching temperature and the larger the grain, the slower the material degrades,” comments Yuri Simonov, head of the "Metallurgy, Thermal and Laser Treatment of Metals" department at PNIPU, professor, and Doctor of Technical Sciences.

The characteristics of the changes in crack resistance of martensitic aging steels display a range of features that must be considered when determining specific thermal treatment regimes. In the case of this steel, the scientists discovered a pattern: the larger the dispersed particles, the higher the resistance to failure, although typically it is the opposite.

The research conducted by the scientists at Perm Polytechnic can be applied in the machine engineering, oil and gas, aerospace, and other industrial sectors to select the optimal quenching temperature and enhance the crack resistance of materials. The results of the experiments allow for more substantiated quenching regimes that will provide materials with greater resistance to failure.