Steel 38KhMYuA Research Articles

The structure of alpha phase in the nitride case on steels 38KhMYuA and 1Kh13

The structure of alpha phase in the nitride case on steels 38KhMYuA and 1Kh13

Hardness of the nitride case at elevated temperatures

1. The hardness of the nitride case and the core decreases considerably when steel 38KhMYuA is heated to 400–500°C. 2. The most reliable data on the red hardness are obtained when the temperatures of the sample and the indentor are identical.

The nitrided case on steel 38KhMYuA after heat treatment

1. The brittleness of the nitrided case on steel 38KhMYuA is a direct function of the grain size resulting from heat treatment. With the standard heat treatment for steel 38KhMYuA used in diesel plants the case is brittle to a depth of 0.10 mm. 2. Steel 38KhMYuA is susceptible to grain growth with slight overheating, and therefore the heating temperature must be strictly controlled. 3. The brittleness of the case can be reduced by grain refining (by induction heating) in the heat treatment and by reducing the activity of the nitriding medium (diluting ammonia with nitrogen).

The modulus of elasticity of nitrided steel 38KhMYuA

The modulus of elasticity of nitrided steel 38KhMYuA

Effect of original structure on the depth and hardness of the nitrided case

1. With increasing tempering temperatures the case depth and hardness decrease on steels 38KhMYuA and 40Kh. 2. The use of preliminary decarburizing before nitriding in a mixed atmosphere (70% N2+30% NH3) results in high hardness and case depth without an increase of brittleness in steel 38KhMYuA. 3. Nitriding with over 60% dissociation lowers the hardness and case depth.

Resistance of structural steels to microplastic deformation after high-temperature thermomechanical treatment (HTTMT)

1. HTTMT of alloy structural steels leads not only to higher tensile and yield strengths but, particularly, to an increase of the elastic limit, which characterizes the resistance to low plastic deformation. The elastic limit of structural steels 38KhMYuA and 40KhN2SVA is highest after tempering at 300–350°C following quenching or HTTMT. 2. After HTTMT the relaxation resistance of structural alloy steels increases substantially in the first testing period (300–400 h at 150°C).

Local protection of steel 38KhMYuA from nitriding by chemical nickel plating

Local protection of steel 38KhMYuA from nitriding by chemical nickel plating

Wear resistance of the pair: Spinning ring-traveler

1. It is uneconomical to use carbonitrided steels 45G2, 30KhGSA, 40Kh, ShKh15 and 38KhMYuA as replacements for carbonitrided steel 40 for spinning rings because their resistance is low. 2. Rings made of carbonitrided steel 4Kh13, quenched and low tempered last 1.5–2 times longer on wool and 4.8 times longer on silk spinning machines compared with similar rings of steel 40. 3. Steels 4Kh13, 2Kh13 and 1Kh13 were included in the proposed State Standard Specification “Ring-Spinning and Splicing Machines”. 4. Carbonitrided steels 4Kh13, 2Kh13 and 1Kh13 are recommended for heavily loaded parts operating under high specific pressures.

Embrittlement of the nitrided case on steel 38KhMYuA [ASTM A355-57T

1. The brittleness of a nitrided case indented with a diamond pyramid (mean value of 10 imprints) can serve as a criterion to determine the layer's tendency to form “grit” during grinding. 2. The brittleness of the nitrided layer determined from the appearance of the diamond pyramid impression depends not only on the inherent brittle strength of the layer but also on the compressive stresses in it. Other conditions being equal, the higher these compressive stresses, the more brittle it is and grit formation during grinding is more likely. 3. The formation of grit on the nitrided layer is associated with compressive stresses caused by sudden surface heating. 4. With increasing core hardness of a nitrided steel part, the nitrogen content and compressive stresses in the case increase, thereby increasing its brittleness. 5. The more thorough the quench-hardening operation (the higher the as-quenched hardness), the less brittle is the nitrided case. Quenching from 900 instead of 950°C results not only in an increased brittle strength of the case in bending tests but also in a reduced brittleness in a diamond indentation test. 6. The decrease of brittleness with increasing nitriding temperature, as determined from a diamond pyramid test is connected with the reduced compressive stresses.