What is difference between carburizing and nitriding?

What is the difference between carburizing and nitriding? Is it similar to coating or coating?

Carburizing and nitriding are chemical methods to infiltrate carbon or nitrogen elements into the surface of certain materials (generally steel) at a certain temperature, so as to increase its content and improve its surface hardness. Carburizing is generally low-carbon steel.

Carburizing:

Carburizing is a kind of surface treatment of metal. Most of the carburized parts are low carbon steel or low alloy steel. The specific method is to put the workpiece into the single-phase austenite area with active carburizing medium and heat it to 900-950 ℃. After holding for enough time, the active carbon atoms decomposed from the carburizing medium will penetrate into the surface of the steel piece, so as to obtain high carbon on the surface and keep the original composition in the core, After quenching and low temperature tempering, the surface layer of the workpiece has high hardness and wear resistance, while the central part of the workpiece still maintains the toughness and plasticity of low carbon steel.

Carburizing can be divided into gas carburizing, solid carburizing, liquid carburizing and carbonitriding (cyaniding). Widely used gas carburizing, heating temperature 900-950 ℃. The carburizing depth mainly depends on the holding time, which is generally estimated as 0.2-0.25 mm per hour. The surface carbon content can reach 0.85-1.05%. After carburizing, it must be heat treated. It is often tempered at low temperature after quenching. The wear-resistant and impact resistant parts with high hardness on the surface and high toughness in the center are obtained.

Carburizing process is widely used in mechanical parts of aircraft, automobiles and tractors. Such as gear, shaft, camshaft, etc.

Nitriding:

The principle of nitriding is similar to that of carburizing. It is a chemical heat treatment process that makes nitrogen atoms penetrate into the surface of workpiece in a certain medium at a certain temperature. Liquid nitriding, gas nitriding and ion nitriding are common.

Nitriding is the most widely used gas nitriding with heating temperature of 500-600 ℃. Nitrogen atom forms nitride with aluminum, chromium and molybdenum in the surface of steel, with a general depth of 0.1-0.6 mm. The nitride layer can obtain high hardness without quenching. This property can be maintained to 600-650 ℃. The deformation of workpiece is small, which can prevent the corrosion of water vapor and alkaline solution. But the production cycle is long, the cost is high, the nitriding layer is thin and brittle, and it is not suitable to bear the concentrated heavy load.

Nitriding temperature is low, workpiece distortion is small, it can be used for parts with high precision and wear-resistant requirements, such as boring bar and spindle of boring machine, spindle of grinding machine, cylinder sleeve, etc. However, due to the thin nitriding layer, it is not suitable for wear-resistant parts with heavy load.

Is "carburizing" and "nitriding" similar to coating and coating?

Coating, coating, is a physical method. "Carburizing" and "nitriding" are chemical changes. It's fundamentally different.

Coating: a physical means of attaching a substance (usually a liquid) to the surface of another.

Coating: chemical method is used to adsorb one substance on the surface of another.