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Vacuum Heat Treatment Process of 38CrMoAl Steel

38CrMoAI is one of the bonded steels, and it is a special nitrided steel. After vacuum heat treatment and finishing, the 38CrMoAI round steel has high surface hardness, wear resistance and fatigue strength, and has good heat resistance. and corrosive. After treatment, the dimensional accuracy is high. Usually, the surface hardness of 38CrMoAI after nitriding is above 920HV. 38CrMoAI has a fast nitriding speed and can obtain a deeper nitrided layer depth, but the nitrided layer is relatively brittle and has low hardenability, so it is not suitable for making parts that bear a lot of impact.

38CrMoAl use

38CrMoAl bonded steel is a special steel that is resistant to seawater corrosion. Mainly used to make pipes and equipment. It has the advantages of strong corrosion resistance and convenient installation.

Reasons for corrosion resistance:

(1) 38CrMoAl combined with Al (aluminum) in the steel material can chemically react with 0 (oxygen) in the air to form A12O3 (aluminum oxide) to form a protective film, which is both anti-corrosion and corrosion-resistant.

(2) Cr (chromium), Mo (molybdenum) and ions in 38CrMoAl combined steel can automatically supplement the gaps formed by Cl (chloride) ions in seawater for pitting corrosion of steel, forming a dense protective layer and preventing pitting corrosion from developing in depth . In turn, it is resistant to corrosion and prolongs its service life.

38CrMoA1 seamless steel pipe material has good welding performance and is equipped with special corrosion-resistant welding rods, without special welding requirements.

Application examples

38CrMoAl seamless steel pipe material is the most ideal material for pipelines and processing parts for coastal power plants, coastal oil fields, coastal natural gas and petrochemical plants to transport water, oil and gas and seawater-containing media. 38CrMoAl is a special nitriding steel. It is generally only used for parts that require high wear resistance and nitriding. Usually, the surface hardness after nitriding is above 920HV, and the pretreatment is quenched and tempered (usually quenched and tempered hardness requires ≥ 260HB, such as 262 HV). ~302HB). 38CrMoAl has a fast nitriding speed and can obtain a deeper nitride layer depth, but the nitride layer is relatively brittle, so it is not suitable for making parts that bear a lot of impact.

Vacuum heat treatment process

The purpose of vacuum heat treatment is to change the internal structure of steel to improve the properties of steel.

To significantly improve the mechanical properties of steel and prolong the service life of machine parts. The vacuum heat treatment process can not only strengthen metal materials, fully tap the performance potential of materials, reduce structural weight, save energy, but also improve the quality of mechanical products and greatly extend the service life of machine parts.

Three stages of vacuum heat treatment: heating, holding and cooling.

Five elements: heating medium, heating rate, heating temperature, holding time and cooling rate (as shown in the figure below).

Normalizing of 38CrMoA1

Normalizing temperature: 930~970℃ fine pearlite + massive ferrite + a small amount of sorbite. The appearance of abnormal tissue is related to the cooling rate.

38CrMoAl normalizing photo

Pearlite + Ferrite.

Process condition: normalizing after forging

Etching method: 4% nitric acid alcohol solution etching

Microstructure description: granular bainite, pearlite in black lumpy areas and white lumpy ferrite. The grain size is about 5~6 grades. 38CrMoA1A is a kind of nitriding steel. The comprehensive properties of the nitrided layer, especially the brittleness, are closely related to the grain size of the original structure. Therefore, before nitriding, the normalizing process is generally used to refine the grains and then quenched and tempered. Due to the obvious segregation of the forging structure of the sample, the compositional deviation of each region leads to different critical points in each region, and different microstructure transformations must occur during the heating and cooling process.

38CrMoAl vacuum quenching and tempering

Process condition: vacuum quenching and tempering after carburizing

Etching method: 4% nitric acid alcohol solution etching

Microstructure description: microstructure and morphology of carburized layer at tooth top, coarse acicular martensite (grade 6), retained austenite (grade 5), and a small amount of small lump carbide (grade 1).

Surface hardness: 713~754HV1, (equivalent to 61.0HRC)

Heart hardness: 490~511HV1

Effective hardened layer depth DC9.802/600=0.46mm.0d

Recommended vacuum heat treatment equipment: The vacuum heat treatment furnace produced by SIMUWU is a high-quality product for the vacuum heat treatment of tooling and molds. Good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum heat treatment process. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.