Tempering characteristics of 51CrV4 steel spring material

Cr-V series spring steel has good hardenability, good resistance to decarburization and the ability to prevent austenite grain growth. After tempering, it has high elastic limit, strength limit, fatigue performance and good Shape and toughness. Therefore, it is widely used in aircraft, automobiles, railway vehicles, transportation machinery and other components. The heat treatment process has an important influence on the structure and comprehensive mechanical properties of spring steel.

The experimental 51CrV4 steel was smelted in a 25kg vacuum induction furnace. Its chemical composition (mass fraction, %) is: 0.53C, 0.93Mn, 1.04Cr, 0.10V, 0.23Si, 0.009S, 0.006P, 0.0014O, 0.0094N, The balance is Fe. After the ingot is kept at 1100°C for 2h, it is forged into a round bar of Φ42mm (refer to the spring size of CRH3 high-speed train). Wire cutting is used to cut samples with dimensions of 16mm×10mm×8mm to study the law of hardness changes under different heat treatment conditions.

After the material is oil-cooled and quenched at 850℃ for 1 hour, the following experiments are carried out:

(1) Research on the law of hardness change with tempering time: The hardness of materials under different tempering time is measured by TH320 full Rockwell hardness tester, and the test specimens are tempered at 260, 360, 460 and 560℃ for 10~240min ( A total of 9 times were designed).

(2) Research on the variation law of hardness with tempering temperature: The hardness value of materials under different tempering temperature conditions is measured by TH320 full Rockwell hardness tester, and the samples are tempered separately at 210~660℃ (a total of 16 designed temperatures) 30min.

When the tempering temperature is constant, the hardness changes with the tempering time: the hardness decreases rapidly at the beginning of tempering. When the tempering time reaches more than 30min, the change of hardness gradually stabilizes; when the tempering time is constant, the quenched steel The hardness decreases with the increase of tempering temperature, and the decrease rate of hardness is relatively gentle when tempering at 310~660℃.

The impact energy can be divided into three stages with the increase of tempering temperature: below 310℃ is the first stage, the impact energy basically does not fluctuate greatly with the increase of tempering temperature; 310~410℃ is the second stage, impact The work increases slightly with the increase of the tempering temperature; above 410℃ is the third stage, and the impact energy increases linearly with the increase of the tempering temperature.