engleski

Influence of Austenitizing Temperature on Quenching Cracks in Hardening of High Carbon Steels

Quenching is the rapid cooling of a work piece to obtain certain material properties. In heat treatment, quenching is most commonly used to harden steel by introducing martensite, in which case the steel must be rapidly cooled through its eutectoid point, the temperature at which austenite becomes unstable. In heat treatment there are two critical temperature ranges. One is the temperature range for the pearlitic transformation, typically about 600 to 500°C, and the other is the martensitic start temperature range, which is about 300 to 200°C for carbon steels. Typically, it is recommended that the cooling rate in the 600 to 500°C range be maximized to ensure optimal hardness and the cooling rate in the 300 to 200°C range be minimized to prevent cracking. The formation of cracks when quenching heated steels is a major problem. As the carbon content of a steel increases the tendency to crack increases. The tendency toward quench cracking is also increased with higher austenitizing temperatures. Steels with coarser grain size are more susceptible to cracks than fine grained steels because the latter have more grain boundary area to block the movement of cracks, and grain boundaries help to absorb and redistribute residual stresses. This paper presents the results of a case study on the influence of the different austenitizing temperature of high carbon steel for hand tools on the quenching cracks occurrence and propagation.

heat treatment; high carbon steel; quenching cracks; austenitizing temperature

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