Introduction
Nitriding is a process used to enhance corrosion and wear resistance of a material. It is a form of heat treating performed by introducing nitrogen into a material at a temperature between 500 and 565 °C, also known as the nitriding temperature. Generally, nitriding is applied to metals, such as steel, in which a thin layer of nitride is formed on the surface. There are many types of steel which can be nitrided, including low-alloy steel, high-alloy steel, stainless steel and tool steel. Each type of steel requires different process parameters and conditions in the nitriding process.
Low-alloy Steel
Nitriding low-alloy steel is a widespread method for improving the surface properties of steel and is often used for machinable parts, such as bolts and connectors. The process parameters for nitriding low-alloy steel includes a nitriding temperature of 530–540 °C and a nitriding time of 3–5 hours. The process parameters must be strictly controlled to ensure uniform nitriding and to prevent cracking or distortion of the material. It is important that the material is preheated to a temperature matching the nitriding temperature to reduce process time and to achieve uniform nitriding. If the nitriding temperature is higher than 540 °C, the nitrided surface can become brittle, leading to cracking and distortion.
High-alloy Steel
Nitriding high-alloy steel is also frequently used to improve the surface properties of steel but is often more expensive compared to nitriding low-alloy steel. The process parameters for nitriding high-alloy steel includes a nitriding temperature of 490–510 °C and a nitriding time of 7–12 hours. Due to the high alloy content of the steel, the process parameters must be closely monitored to ensure uniform nitriding and to avoid cracking. Similar to nitriding low-alloy steel, the material must be preheated to the nitriding temperature before nitriding to reduce process time and to achieve uniform nitriding.
Stainless Steel
Nitriding stainless steel is not as common as for low-alloy or high-alloy steel, due to its high alloy content and increased cost. However, it is still used to achieve the desired surface properties. The process parameters for nitriding stainless steel includes a nitriding temperature of 480–500 °C and a nitriding time of 10–12 hours. To ensure uniform nitriding and avoid cracking, the process parameters must be closely monitored and the material must be preheated to the nitriding temperature before nitriding.
Tool Steel
Nitriding tool steel is also used to improve the surface properties of steel. The process parameters include a nitriding temperature of 460–480 °C and a nitriding time of 7–12 hours. It is important to ensure uniform nitriding by preheating the material to the nitriding temperature before nitriding. If the temperature is too high, the nitrided surface will become brittle, leading to cracking and distortion.
Conclusion
The process parameters for nitriding steel depend on the type of steel being nitrided. It is important to closely monitor the process parameters and preheat the material to the nitriding temperature to ensure uniform nitriding and avoid cracking. Low-alloy steel is typically nitrided at 530–540 °C for a time of 3–5 hours, while high-alloy steel is nitrided at 490–510 °C for 7–12 hours. Stainless steel is nitrided at 480–500 °C for 10–12 hours, while tool steel is nitrided at 460–480 °C for 7–12 hours.
