cs seamless steel pipe nitriding treatment

What is nitriding treatment

Nitriding is a chemical heat treatment process that allows nitrogen atoms to penetrate into the surface of the workpiece in a certain medium at a certain temperature. Commonly used are liquid nitriding, gas nitriding, and ion nitriding. Traditional gas nitriding is to put the workpiece into a sealed container, pass it through flowing ammonia gas and heat it. After being kept warm for a long time, the ammonia gas thermally decomposes to produce active nitrogen atoms, which are continuously adsorbed to the surface of the workpiece and diffuse into the surface layer of the workpiece. , thereby changing the chemical composition and structure of the surface layer and obtaining excellent surface properties. If carbon is simultaneously infiltrated during the nitriding process to promote the diffusion of nitrogen, it is called nitrocarburizing. Commonly used are gas nitriding and ion nitriding.

cs seamless pipe nitriding treatment process

In the entire manufacturing process of nitrided parts, nitriding is often the last process, followed by fine grinding or grinding at most. The process flow of nitrided parts is generally: forging → normalizing (annealing) → rough machining → quenching and tempering → finishing → stress relief → rough grinding → nitriding → fine grinding → assembly.

The preheating treatment before nitriding includes normalizing (annealing), quenching and tempering treatment, and stress relief.

a. The purpose of normalizing (annealing) is to refine the grains, reduce the hardness, and eliminate forging stress.

b. Quenching and tempering treatment can improve the processing performance of steel and obtain a uniform tempered sorbite structure to ensure sufficient strength and toughness in the center of the part, and at the same time, the nitrided layer and the base can be firmly bonded.

c. Stress relief treatment: For precision parts with complex shapes, stress relief should be performed 1 to 2 times before nitriding to reduce deformation during the nitriding process.

cs seamless pipe nitriding treatment production preparation

a. Decontamination treatment. Before the parts are installed in the furnace, they must be degreased and decontaminated with gasoline or alcohol. No rust or dirt is allowed on the surface of the parts.

b. Anti-seepage treatment. For non-nitrided parts of parts, electroplating or coating methods can be used to prevent nitriding.

c. The surface quality of nitrided parts should be good and no decarburized layer is allowed. Therefore, sufficient machining allowance should be left before pre-heat treatment of the parts so that all decarburized layers can be removed by machining before nitriding. Ensure the quality of the nitrided layer.

d. Before installing the furnace, check the equipment and nitriding fixtures, electrical systems, pipelines, ammonia decomposition analyzers, etc. to ensure normal use; the nitriding fixtures are not allowed to have dirt or scale, and if so, they should be removed.

e. Furnace samples. The samples shipped with the furnace should be made of the same material as the nitrided parts and undergo the same pre-treatment.

Precautions for nitriding treatment

a. Preliminary heat treatment and quenching and tempering before nitriding - the nitriding workpiece should be quenched and tempered before nitriding to obtain the tempered sorbite structure. The tempering temperature in the quenching and tempering treatment is generally higher than the nitriding temperature.

b. Preliminary heat treatment and stress relief treatment before nitriding - before nitriding, the internal stress generated during the machining process should be eliminated as much as possible to stabilize the size of the parts. The stress relief temperature should be lower than the tempering temperature, and the holding time should be longer than the tempering time. It should be longer, and then slowly cool to room temperature. Parts with larger cross-sections should not be normalized. Tool and die steel must be quenched and tempered, and annealing is not allowed.

c. The surface roughness Ra of nitrided parts should be less than 1.6um, and there should be no defects such as burrs, bruises, or rust on the surface. Parts that cannot be processed in time must be protected with oil to avoid rust. Use clean gasoline when hoisting into the furnace. Wipe clean to ensure cleanliness.

d. Workpieces containing sharp corners and edges are not suitable for nitriding treatment.

e. To protect the parts that are not nitrided, it is not advisable to leave a machining allowance.

f. Workpieces whose surfaces have not been ground must not be nitrided.

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