Molten lead is used for tempering of valve-spring wire. Lead has drawbacks due to slow temperature changes. In 1991 the Swedish Parliament passed a Government Bill, in which proposals were made to phase out the use of lead in the long term, primarily through voluntary measures. Tempering of SIS 2090 (SAE 9254, DIN 55SiCr7) wire with different dimensions using induction heating was tested in a pilot process line. An induction coil for six wires and two coils with different lengths designed for single wires were tested. The results showed that an induction coil for six wires gave excessive temperature and property variations between the wires. The shorter of the single wire coils gave fluctuations in temperature and properties using a 3.00-mm wire. No such fluctuations were observed with the longer coil. One of the experiments showed that the process might need time to reach stable conditions. The results so far indicate that it is possible to produce valve-spring wire with induction tempering. The process needs more control and monitoring compared to tempering in molten lead. © Blackwell Munksgaard, 2003.

The alternatives to lead bath for patenting of high carbon steel wire are discussed. It is found that it is possible to achieve properties of high-speed gas patented music wire without using a soaking furnace. Laboratory experiments with patenting in a fluidized bed, showed that the process could give the required mechanical properties for the valve spring wire. It is also found that small alterations in process parameters in the industrial trials has a large impact on the mechanical properties and microstructures.

Most of today's hardened valve spring wires are tempered in a lead bath. The lead bath provides a stable and accurate degree of tempering of the wire, but it has environmental disadvantages and limitations in flexibility. This paper describes how induction heating can replace lead bath and how this may affect the material properties. The study includes FEM-simulations, calculation of the tempering parameter and experiments with induction tempering of three different SiCr valve spring steels carried out under pilot production. The mechanical properties of the test samples were measured. Fatigue testing of one of the steels was performed on finished springs. The results were evaluated by comparing induction-tempered wire with the conventional lead tempered reference wire. The induction tempered wire fulfilled the product requirements and corresponded in performance with the lead tempered wire.