High carbon steel wires are produced by drawing red hot billets to a desired diameter. Post drawing, these wires undergo two heat treatment cycles to impart desired properties to the wire product. In the first heat treatment cycle the wire is heated to ~1000oC, followed by water quenching, which results in the formation of a martensite phase in the microstructure. During the 2nd heat treatment cycle, the wire is reheated to ~ 450oC followed by water quenching to achieve the desired tempered martensite phase in the microstructure.
During quality checks, it is found that the steel wires exhibit cracking at some locations and the wire may completely fracture from these cracks. The microstructural analysis of the steel surface near the crack shows the presence of untempered martensite (inadequate tempering) (Refer to Figure 1).
A solution is being sought that can point to a range of heat treatment parameters (e.g. temperature, flow rate of water, line speed, etc.) that affect the properties of the wire rod, especially the untampered martensitic structure. The range of parameters can then be adjusted if it goes out of range. It is expected to use the data (temperate, flow rate, line speed, etc.) to correlate to the microstructure of the wire.