Effect of isothermal quenching temperature on strain hardening of ADI

Abstract

The effect of isothermal quenching temperature on the mechanical properties of ADI materials was investigated. The heat treatment of the test samples consisted of heating above the temperature of conversion of the ferrite component into austenite and isothermal quenching at temperatures from 280 to 380 °C. Liquid tin was used as the quenching medium. In the specified temperature ranges, the plastic characteristics and strength parameters of the samples were studied depending on heat treatment. Particular attention is paid to the parameters of strain hardening. It is established that at isothermal tempering temperatures in the range of 330-350 °C, plastic deformation produces a TRIP effect, which is accompanied by a high rate of hardening due to the conversion of residual austenite into martensite. Strengthening of specimens at plastic deformation has 2 stages. In the first stage, the hardening is by the traditional mechanism due to the plastic deformation of residual austenite. As the load increases, the TRIP effect plays the basis of strengthening. Plastic characteristics change with increasing tempering temperature. At 280 °C, the strength and hardness of the metal is maximum and the plastic characteristics are minimal. The optimum mechanical properties, including fatigue resistance, are observed in the temperature range 330-350 °C. For parts of the tillage agricultural machinery operating at low loads (cultivator paws), quenching to lower bainite should be used. In this case, hardness plays a more significant role. Isothermal hardening at 330-350 °C should be used for heavy loads of parts (brazing saws, saw blades, chisels). When using such parts, the TRIP effect is important, which ensures high durability and a lifetime of operation.

Keywords

• аustempering ductile iron (adi)
• isothermal quenching temperature mechanical properties
• strain hardening transformation induce plasticity (trip effect).