During hot forging/forming operations, the die surface and near surface region is subjected to severe wear. The failure of dies originates from the surface region. In this research work, plasma nitriding was done on two hot forming tool steels namely AISI H11 and AISI H13. The aim is to develop a hard and wear resistance surface required for hot forming operations. The mechanical and microstructural properties of the developed nitrided layer were critically examined. Thereafter the tribological characteristics of the untreated and plasma-nitrided specimens were studied on high-temperature pin-on-disc tribometer under the constant load of 25 N, sliding speed 0.5 m s −1 , sliding distance of 1500 m at different temperatures ranging from room temperature to 600°C. The results showed that the main wear mechanisms is predominantly adhesive at room temperatures and 200°C and a combination of adhesive and abrasive at elevated temperatures (400°C and 600°C).
In the current investigation, an effort was made to analyze the sliding wear and friction characteristics of the surface engineered hot forming tool steel. A surface treatment technique plasma nitriding was developed onto the surface of the hot forming tool steel namely AISI H13 with a view to reduce the friction coefficients and minimize wear. The treatment was done in various N2/H2 gas mixtures for the fixed time of 24 h and at a fixed temperature of 500 ℃. The phases formed on the plasma-nitrided surface have been identified by the X-ray diffraction technique. The surface morphology of nitrided specimens and the composition of the nitride particles have been analyzed using scanning electron microscopy/energy-dispersive spectroscopy techniques. Thereafter, the untreated and treated steel specimens were chosen to slide against high strength low alloy steel (actual workpiece material) at elevated temperatures. The tests were conducted on high-temperature tribometer under the constant load of 25 N at room temperature, 200 ℃, 400 ℃, and 600 ℃. The results have shown that the average friction coefficients and specific wear rate values decrease from room temperature to 400 ℃ and again increase at 600 ℃.
Wear, plastic deformation, and mechanical fatigue of dies are the most common failures found during hot forming operations at elevated temperatures. The change in frictional behaviour also happens. The performance of the forming operation is affected. To ensure the quality of the end products and productivity, it has become very important to control the wear and friction of die materials. Surface treatment techniques with superior wear properties and good performance can enhance the life and functionality of dies. Plasma nitriding is the most rapidly developing technique for hot forming dies. It is a cost-effective technique and improves the mechanical properties of the die surfaces. This chapter explains the tribology of hot forming dies, the plasma nitriding technique, and the procedures to develop plasma nitriding on the die steels. Thereafter, the tribological behaviour of AISI H11 and AISI H13 plasma nitrided die steels has been reported. Plasma nitriding was found to be most promising and effective in reducing wear and friction at elevated temperatures.
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