| Abstrakt: |
Machinability of metals can be defined as the removal of material due to the transformation of a semi-finished product. There are different machining techniques. A common machining technique is turning and milling. Machinability is related to factors such as workpiece material properties, cutting tool properties and processing parameters. The machinability property is influenced by the chemical such as microstructure, grain size, chemical composition, hardness, heat treatment, yield strength and tensile strength composition, microstructure, and non-metallic inclusions in the metallic material. Material properties of a material affect its machinability. The research focused on low-alloy ferritic-pearlite steels for forging and machining with basic compositions, on the determination of the diferent level of Ti and S content on the formation of non-metalic inclusion, mechanical properties and machinability of steel . In the first series charges, the content of titanium in the steel varied from 0.0184 to 0.0591%, while in the second series charges, with the higher % addition of aluminum and calcium, and the content of sulfur in the steel varied from 0.026 to 0.084%. Non-metallic inclusions as oxide inclusions, elongated manganese sulfides, MnS and modified oxide inclusions, which also act as nucleation sites for sulfide inclusions, are present in all charges. Titanium nitrides, TiN are also present in Ti-alloyed charges. Measurement of mechanical properties at room temperature, including tensile strength and elongation, and Rockweell hardness was performed. Toughness was measured by the Charpy fracture toughness. Machinability investigations under the conditions of rough and fine turning were done on a CNC lathe equipped with force meters and using standard ISCAR cutting, cutting with diferent a cutting speed, a feed rate and a depth of cut. The machinability of steels were tested by cutting process with measurement of cutting forces, which included cutting force (Fc), push force (Fp) and feed force (Ff). The workability indicator is also the quality of the treated surface. The better machinability of the steels is also manifested in lower forces for turning and in lower roughness or finer surface qualities the workpiece. The obtained research results showed the following dependencies. The hardness and tensile strength of the investigated low-carbon steel increase with increasing Ti content, while impact toughness and elongation decrease. In contrast, with an increase in S content and the formation of softer sulfide inclusions, the hardness and yield strength decrease, and impact toughness and elongation increase. In accordance with the increase in hardness and tensile strength, the cutting forces also increase with increased Ti content. And this is true for both, rough and fine turning. In contrast, with an increased content of S and corresponding decrease in hardness, the cutting forces decrease while steel machinability is improved. However, the influence S is smaller as compared to Ti. Although the addition of Ti increases the hardness and makes machining more difficult, it results in a finer surface. The addition of S, on the other hand, increases the toughness, which causes the formation of long spiral chips and a rougher surface. [ABSTRACT FROM AUTHOR] |
