Effects of Non-metallic Inclusions on Machinability of Free-Cutting Steels Investigated by Nano-Indentation Measurements

Abstract

In the present paper, the nano-indentation technique is used to investigate the effects of inclusions on machinability of free-cutting steel. Firstly, the hardness, elastic moduli, and loaddisplacement curves of inclusions are analyzed and compared with matrix. Secondly, the effects of inclusions on machinability are investigated using nano-indentation measurements and thermodynamic calculations. Lastly, errors of nano-indentation measurements and macrohardness tests are analyzed. The hardness of BN is lower than that of MnS. Both of them have lower hardness than those of matrices. Since the hardness of Al 2 O 3 and TiN is higher than that of matrices, they exist as hard spots in steels. The elasticities of BN and MnS are much better than those of Al 2 O 3 , TiN, and matrices. BN and MnS which have lower hardness values and better elasticities than matrices can improve the machinability of steel effectively. Special attention should be paid to the effects of inclusions in steel on the results of nano-indentation measurement and macrohardness test.

Modification of Non-Metallic Inclusions in Stainless Steel by Addition of CaSi

“…However, it is also reported that some inclusions (such as MnS and Ca-modified oxides, among others) can help to improve the steel machinability (for instance by decreasing the wear on the cutting tool, thus extending the tool's life) [2]. Previous studies [3][4][5] show that inclusions improve machinability primarily by two ways: (1) as a source of stress concentration effects, favoring machinability by reducing the cutting force and increasing the chip breakability during machining, (2) as a lubricant (tool protection layer) in the contact zone of the cutting tool and material (reducing the abrasive and chemical wear of the tool), which is beneficial for the tool life. Thus, modification of NMIs and control of their characteristics in steels during steel manufacturing are very important to balance favorable machinability properties with the desired mechanical property for diverse types of steels.…”

Influence of Non-metallic Inclusions in 316L Stainless Steels on Machining Using Different Cutting Speeds

“…However, even when using the same tools to machine steels with similar mechanical properties, steels having different non-metallic inclusions (NMIs) also can show different machinabilities. [2][3][4][5][6][7][8][9][10][11][12][13][14] The different hardnesses and thermal expansions of NMIs in steels will play different roles (negative or positive) during the machining of these steels. Rigid inclusions (such as Al 2 O 3 , TiCN) will scratch the tool surface and decrease the tool life dramatically.…”

“…This, in turn, will lead to an increased tool life and cutting surface quality. [1][2][3][4][5][6][7][8][9] Thus, a modification of NMIs is beneficial to balance the preferred machinability and required mechanical properties.…”

“…The behavior and role of non-metallic inclusions have been discussed in several previous studies, [2][3][4][5][6][7][8][9][10][11][12][13][14] as mentioned above. However, the benefit of the modification of NMIs was not the same for different cutting conditions or different reference materials, according to previous studies.…”

Influence Of Large Non-Metallic Inclusions On Bending Fatigue Strength Hardened And Tempered Steels

“…The allowable impurity content of steel, the morphology of impurities and their influence on steel strength (mainly under variable loads) have been analyzed by numerous authors. Despite years of research and analyses, our knowledge of the impact of non-metallic inclusions on the properties of steel elements is still ambiguous and limited [5,[10][11][12]. The aim of this study was to determine the influences of large non-metallic inclusions on bending fatigue strength hardened and tempered performed on industrially manufactured high-grade, carbon structural steel of high purity.…”