Performance characteristics of spring steel wire quenched and tempered by induction heating device

The following introduces the properties of low alloy spring steel wire 55CrSI and the results of testing items for springs made with it.

Comparison of performance of induction heating device and traditional electric furnace for instant hot quenching and tempering treatment of steel wire

The 55CRSI steel wire diameter induction heating device is oil quenched at 1000°C. The electric furnace is heated to 900°C and then insulated and quenched. Then, different tempering heating methods are used to perform tempering treatments at different temperatures. The obtained properties are compared as follows. .

(1) Comparison of temperature-appropriate strength properties. The temperature-appropriate strength performance mainly includes three properties: yield strength, tensile strength, and strength limit, which are compared in the form of yield-strength ratio and elastic-strength ratio respectively. The comparison results of the strength performance of steel wires quenched and tempered by different heating methods are given. The induction heating heating device has a higher yield strength and elastic limit than the freshly washed steel wires quenched and tempered by circuit heating. The reason is that induced adiabatic heat can obtain fine austenite grains, which is the key to obtaining high yield strength and high elastic limit steel wire, and is also the most important strength index of reaction spring steel wire.

(2) Comparison of plasticity and toughness. Comparison of plasticity and toughness indicators of steel wires quenched and tempered by different heating methods. Tests have shown that the induction heating heating device has higher plasticity and toughness than the steel wire heated and tempered by the electric furnace. The reason for this phenomenon is also related to the grain size, but at the same time it is also related to the structure of the tempered structure. Compared with electric furnace heating and tempering, induction heating tempering can significantly improve the strength of the smaller troostite and troostite in the structure and at the same time improve the toughness, giving the steel wire a good toughness ratio. This is a structural structure that cannot be obtained during traditional heating and tempering.

(3) Comparison of delayed fracture characteristics of steel wires. The delayed fracture characteristic test is to subject the spring steel wire to 20% NH4CNS under a stress of 980MPA. In 50% solution, a stress corrosion test was conducted to observe the lasting fracture events of the steel wire. The grain size of induction heated tempered steel wire is 120mm. Comparative results of a group of samples with a hardness of 50HRC show that the fracture time of the former fluctuates between 4-20H, and that of the latter fluctuates between 1-36min. This test result shows that due to the good toughness of induction heated tempered steel wire, its fracture time is significantly longer than that of electric furnace tempered steel wire. Electron microscopy fracture analysis was performed on the sample with a hardness of 53HRC. The results showed that the induction heating and tempering steel wire sample was plastic fracture, and the electric furnace heating and tempering steel wire sample was fracture along the grain boundary. When the hardness of the steel wire is less than 56HRC, the induction heating tempered steel wire also becomes brittle fracture along the grain boundary.

In summary, from the comparative results of the strength, plasticity and delayed fracture characteristics of the steel wire, the steel wire quenched and tempered by induction heating is better than the steel wire quenched and tempered by the electric furnace. The main reason is that the former uses rapid heating for oil quenching and tempering processes, which can obtain fine tempered sorbite and de-solidified round structures. This fine organizational structure is rich in comprehensive mechanical properties such as high yield strength, high elastic limit, high fatigue strength, good toughness, and good plasticity of steel wire.