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Application of PAG in heat treatment of 50CrVA leaf spring
50CrVA steel belongs to the Cr-V series spring steel. It has good resistance to decarburization and the ability to prevent austenite grain coarsening. After heat treatment, it has high elastic limit, strength limit and good plasticity. It is widely used in Automobile leaf spring manufacturing. As the load capacity of domestic heavy-duty trucks has increased from 4t in the past to more than 40t now, when 50CrVA steel is used in automobile leaf springs, the cross-section thickness requirements have also increased from 8mm to 24mm and above. However, the traditional heat treatment of 50CrVA steel During the process, the quenching medium used is ordinary quenching oil, and the critical quenching plate thickness for oil quenching is 24mm. Through analysis of a large number of fracture failures of traditional heat-treated 50CrVA material leaf springs and research on the process quality of the production site, it was found that when the cross-section thickness is close to or greater than the critical quenching plate thickness of oil quenching, normal quenching cannot occur, seriously affecting the mechanical properties of the material and the steel plate. The fatigue life of the spring. Water-soluble quenching medium - PAG, as a new type of quenching medium, has been used by more and more heat treatment researchers because of its advantages such as good cooling performance, wide application range, uniform hardenability, environmental protection, no pollution, and low fire hazards. favor. This article uses PAG water-soluble quenching medium and ordinary quenching oil to heat treat 24mm thick 50CrVA material leaf springs, and studies the metallographic structure, hardness and fatigue life of the reeds after heat treatment.
A 50CrVA material reed was selected as the heat treatment test material. Its specification is 500mm×90mm×24mm. The chemical composition of the test material is (mass fraction, %): 0.53C, 0.011S, 0.009P, 0.70Mn, 0.27Si, 0.99Cr, 0.12 V, the balance is Fe. Under the conditions of a certain heat treatment process (900℃±5℃ for 20 minutes), heating and insulation are carried out through a stepping quenching furnace, and a certain concentration of water-soluble quenching medium and ordinary quenching oil are used for quenching, and then pressed to (480±5)℃ Heat preservation for 120 minutes, water cooling and tempering, and obtain samples after heat treatment with different quenching media.
Using PAG water-soluble quenching medium instead of ordinary quenching oil, the 24mm thick 50CrVA material leaf spring sample was successfully heat treated, and no cracks were found by magnetic particle inspection. Using PAG water-soluble quenching medium to heat-treat a 24mm thick 50CrVA material leaf spring sample, the quenched and tempered metallographic structure and hardness are better than those of the sample heat-treated with ordinary quenching oil. The average fatigue life of 24mm thick 50CrVA material leaf spring specimens after heat treatment with PAG water-soluble quenching medium can reach more than 150,000 times. Compared with ordinary quenching oil heat treatment specimens, the fatigue life is nearly doubled, which greatly improves the fatigue life. Quality of leaf springs.
