Dimensional Structure of Non-Metallic Inclusions in High-Grade Medium Carbon Steel Melted in an Electric Furnace and Subjected to Desulfurization

Abstract

Non-metallic inclusions may be introduced to liquid steel from the outside, usually with charge material, or they may be produced in the metallurgical process. According to literature, if evenly distributed, non-metallic inclusions may affect the functional properties of steel, mainly its fatigue strength. The aim of this study was to determine the quantity and dimensional structure of non-metallic inclusions in high-grade medium carbon steel melted in an electric furnace and subjected to desulfurization. The experimental material consisted of semi-finished products of high-grade, medium-carbon constructional steel containing manganese, chromium, nickel, molybdenum, and boron. The levels of phosphorus and sulphur impurities did not exceed 0.02%. Billet samples were collected to determine the chemical composition, microstructure, the relative volume of non-metallic inclusions, and the size of impurities. The results were processed and presented in graphic form.

The Effect of Fine Non-Metallic Inclusions on the Fatigue Strength of Structural Steel

“…Despite vast progress in manufacturing technologies, non-metallic inclusions have not been completely eliminated from steel [12][13][14]. Their negative impact on fatigue strength has been widely discussed in the literature [2,15,16], mostly in studies of hard-fatigue steels with low plasticity and inclusions larger than 5 µm.…”

Effect Of The Spacing Between Submicroscopic Oxide Impurities On The Fatigue Strength Of Structural Steel

“…7. Fatigue resistance coefficient k of steel hardened and tempered at all tempered temperatures subject to arithmetic average distance between submicroscopic oxide impurities (impurities spacing) λ k = -0.0181 l + 1.249 and r = 0.8098 (14) Statistical parameters representing the results of the experiment are presented in Table 2. Parameters representing mathematical models and correlation coefficients are presented in Table 3.…”

“…An analysis of regression coefficients and dissipation fatigue resistance coefficients k indicates that changes in coefficients k as a function of impurities spacing λ can be described with satisfactory accuracy by a single equation (14) at all tempering temperatures.…”

“…The level of fatigue-inducing load was adapted to the strength properties of steel. Maximum load was set for steel tempered at a temperature of: 200°C -650 MPa, from 300°C to 500°C -600 MPa, 600°C -540 MPa [13][14][15][16]27,28]. During the test, the applied load was gradually reduced in steps of 40 MPa (to support the determinations within the endurance limit).…”

“…The mechanical properties and fatigue strength of structural materials should also be evaluated in view of crystallization conditions [5][6][7][8][9][10][11], the manufacturing process [12][13][14][15], microstructure [16,17], microsegregation [18][19][20][21][22] and the existing defects [23][24][25].…”