Thermal Strengthening of Large Parts Made from High-Strength Sparingly Doped Steel in Air
- PDF / 988,250 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 73 Downloads / 147 Views
l Strengthening of Large Parts Made from High-Strength Sparingly Doped Steel in Air M. V. Maisuradzea, Yu. V. Yudina, *, and D. I. Lebedeva, b aUral
bInstitute
Federal University, Yekaterinburg, Russia of Physics of Metals, Ural Branch, Russian Academy of Sciences, Yekaterinburg, Russia *e-mail: [email protected] Received April 14, 2020
Abstract—High-strength sparingly doped steel possessing high hardenability has been studied. The degree of mechanical characteristics after continuous cooling with various intensities in the range of 0.02–20°C/s has been determined. Industrial heat treatment of large parts from the steel under study has been implemented using air as the quenching medium. Successful isothermal treatment using air media, as well as preliminary cementation aimed at the increase in the surface’s wear resistance, has been demonstrated. Keywords: steel, heat treatment, numerical simulation, microstructure, mechanical characteristics, strength, cementation, isothermal quenching DOI: 10.3103/S0967091220050083
Thermal strengthening of steel parts considers fast cooling from the austenitization temperature for the formation of nonequilibrium structural components, which include bainite and martensite. In order to realize fast cooling upon heat treatment, various quenching media are used [1–4], which either change their phase state upon quenching (water, quenching oils, solutions of salts and polymers, and other liquids) or remain in the same phase state over the entire period of detail cooling (air and gas, as well as melts of salts, alkali, and metals). Quenching media of the first group are most widely employed in the heat treatment practice regarding the details of various unit sizes made from carbon and low-alloyed steels, as well as large parts from medium and high-alloy steels, for which cooling in the air or using compressed gas does not provide necessary hardenability. In this case, internal stresses may arise in detail due to both nonuniform cooling of various detail parts and nonuniform phase and structural transformations. Combination of thermal and structural internal stresses often results in the formation of quenching cracks or strain [5–7]. Low-carbon martensite steels (LMSs) were previously developed for the solution of such problems, which provide a massive microstructure of lower bainite or martensite upon cooling in the air [8–10]. However, a low strength level (less than 1000–1200 MPa) caused by the low carbon content (up to 0.11 wt %) is the main drawback of such steels. Currently, new steels possessing high hardenability with the higher carbon content are investigated [11–14]. These steels provide
higher strength degree as compared to conventional LMSs after cooling in the air from the austenitization temperature. In this case, the following advantages are achieved as compared to the standard heat treatment of low-alloyed structural steels: (1) decreased residual stresses and the absence of quenching cracks; (2) microstructure homogeneity along the product’s entire cross-section; (3
Data Loading...
