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High Alloy Steels
Published in P. C. Angelo, B. Ravisankar, Introduction to Steels, 2019
Carbon is the element that increases both hardness and hardenability and thus increases abrasion (wear) resistance. Carbon is the cheapest alloying element in tool steels. Chromium increases hardenability, wear resistance by forming carbides and corrosion resistance by forming chromium oxide layer. Chromium also increases resistance to molten metal and oxidation useful in making die steels for melting low temperature metals such as aluminium. It also increases scaling resistance. Five percent chromium can resist scaling up to 650°C, 8% chromium is required for scaling resistance up to 750°C. About 10–12% chromium is required to resist temperature of 850°C. Addition of Si (0.8–1%) increases strength of chromium oxide layer and can further increase the resistance to oxidation and scaling. Chromium also protects from chemical attack and liquid metal attack. Vanadium and molybdenum form primary carbides and act as grain refiners apart from increasing hardenability. Silicon increases hardenability and high temperature strength. Nickel increases hardenability and toughness and imparts shock resistance to tool steels and reduces cracking while quenching by decreasing austenitizing temperature. Cobalt improves red hardness (or) hot hardness (resistance to thermal softening) but it decreases hardenability. Normally, reduction in hardenability due to cobalt is compensated by adding other alloying elements that increase hardenability. Tungsten apart from forming primary carbides improves hot hardness.
A Review on Internally Cooled Smart Cutting Tools
Published in P. C. Thomas, Vishal John Mathai, Geevarghese Titus, Emerging Technologies for Sustainability, 2020
The materials chosen for cutting tool regardless for conventional machining or ECMP must possess a number of important properties to avoid excessive wear, fracture failure and high temperatures in cutting. Hardness (or also called hot hardness) at elevated temperature is the most important factor in choosing cutting materials, so that the hardness and strength of the cutting edge can be preserved at high temperature. Toughness, wear resistance, surface finish, chemical inertness and thermal conductivity are other major characteristics of the tool materials.
Integrated Nanomechanical Characterisation of Hard Coatings
Published in Sam Zhang, Jyh-Ming Ting, Wan-Yu Wu, Protective Thin Coatings Technology, 2021
Ben D. Beake, Vladimir M. Vishnyakov, Tomasz W. Liskiewicz
The higher Al-fraction coatings display multifunctional and adaptive behaviour in high-speed metal cutting. Reasons for their improved tool life include [121]:age-hardening by spinodal decomposition more effectively than more Ti- or Cr-rich compositionsforming more protective alumina-based tribo-films than the less protective rutile and chromia tribo-filmslower thermal conductivity at elevated temperature than TiAlN which (together with the tribo-film) protects the tool from thermal softening, i.e. acting as a thermal shieldlow brittleness at elevated temperatureAlTiN has generally performed well when cutting conditions require relatively high coating plasticity to minimise intensive adhesive-fatigue interaction with workpiece materials (e.g Ti6Al4V, Ni-based superalloys or austenitic stainless steel). Its lower brittleness helps provide more favourable, low wear conditions for effective tribo-film formation protecting the cutting tool surface against chipping. The high temperature micro-scratch data and the analytical modelling described in this section fully support this. Although it has relatively poor high temperature stability at >250 °C, it retains sufficient load support below this temperature, for example as in interrupted cutting of Ti alloys. However, in applications requiring high hot hardness at the cutting temperature, such as continuous turning or end milling of hardened steel, AlTiN is outperformed by other Al-rich coatings that have higher hot hardness (e.g. AlCrN, annealed AlTiN, TiAlCrN, TiAlCrSiYN and TiAlCrSYN/TiAlCrN multilayers).
Influence of substrate bias on machining performance of TiAlN-coated drill bits
Published in Materials and Manufacturing Processes, 2023
Nitin Tandekar, Pooja Miryalkar, L. Rama Krishna, Krishna Valleti
Inconel 718 (Nickel-based superalloy) has wide-ranging applications in aerospace, nuclear power, petrochemical sectors, and others.[1–3] The materials employed for such applications must exhibit high hot hardness, corrosion resistance, and oxidation resistance at all operating temperatures.[4] Though Inconel 718 provides excellent high-temperature properties, its machining is immensely challenging – reflected in its poor machinability (short tool life, low productivity, poor machining efficiency, etc.).[5,6] Several techniques, such as applying cryogenic cooling, lubrication, wear-resistant coating, tool material, and textured cutting tools, are employed to improve the machinability of such difficult-to-cut alloys.[7–10] However, such techniques have their limitations. For instance, utilizing lubricant or coolant may increase the machining cost (coolant cost and cost incurred for its disposal) while compromising with operator’s health. Advanced tool materials are relatively costly. Therefore, their use in machining superalloys is also not economically viable. Coated tools, although makes the machining process expensive, result in tangible cost savings in terms of cost incurred per component machined. Hence, coated tools remain the most popular among all techniques for machining difficult-to-cut materials, especially at higher cutting speeds.[11]
Comparative study on machining performance of TiAlSiN, AlTiN/TiAlSiN-coated cutting tools
Published in Transactions of the IMF, 2023
C. G. Sriram, N. Ariharan, N. Radhika
In recent years, there has been an increasing demand for machining of industry-relevant hard materials like Titanium alloys, Inconel 718, etc., in dry environments contrary to the traditional coolant-based machining due to the various environmental impacts produced in the latter.1–5 High-speed dry machining of such materials generally involves elevated cutting temperatures and extreme cutting conditions and hence the cutting tool must have a sufficiently high hot-hardness to avoid high wear rates and quick failure.6–8 Thin film coatings deposited through vapour deposition techniques are widely used to improve wear properties of the cutting tool.9,10 Hard ceramic coatings like TiAlN, AlTiN, TiAlSiN provide properties such as good oxidation resistance, thermal and chemical stability even at temperatures of 800–1000°C and hence prove to be a viable solution to the aforementioned issues.11–15
How cryogenic techniques help in machining of nickel alloys? A review
Published in Machining Science and Technology, 2018
Yogesh Vasantrao Deshpande, Atul B. Andhare, Pramod M. Padole
Reddy et al. (2009) and SreeramaReddy et al. (2009) reported that in all the cutting conditions used for turning, the cryogenically treated inserts performed better than untreated inserts and observed better wear resistance for treated inserts. They also reported increase in tool-life by a factor of 1.27. This was said to be because of increase in thermal conductivity and reduction in tool tip temperature. They also found enhancement in hot hardness. The enhancement of machinability in terms of tool-life, cutting forces and surface roughness was observed while using cryogenically treated inserts between the speed of 200 m/min and 350 m/min. Speedy wear was observed at last, probably due to a total wear out of the coating material. In such a case, the substrate material of tool directly touches the workpiece in machining. Table 4 shows the comparison and percentage improvement in tool-life using P-30 and P-40 WC untreated and cryogenically treated inserts (Reddy et al., 2009; SreeramaReddy et al., 2009). The improvement of tool-life in P-40 inserts was more in all cutting conditions compared to P-30 cryogenically treated inserts as shown in Figure 15.