Isothermal Annealing
(ITA) in India

Isothermal Annealing (ITA) is a cycle where steel is heated to austenitising temperature, cooled rapidly to an intermediate temperature (typically 620°C-680°C), and held at that temperature for a specific period to complete ferrite-pearlite transformation. Compared to full annealing (which cools very slowly in a furnace over 20-30 hours), ITA takes significantly less furnace time, yields a highly uniform ferrite-pearlite microstructure, and prevents the formation of hard spots or bainite.

Alloy steels containing chromium, nickel, and molybdenum (like EN19, EN24, 20MnCr5) tend to form hard, non-uniform microstructures if cooled uncontrolled. This causes rapid tool wear, poor surface finish, and dimensional drift on CNC lines. ITA provides a highly uniform, soft pearlitic structure with predictable, consistent hardness, ensuring optimal chip formation and fast cutting speeds.

The steel is first austenitised at 830°C to 880°C. It is then rapidly transferred or cooled to the transformation zone, typically between 630°C and 670°C. The isothermal hold lasts between 2 to 6 hours, depending on the alloy composition, to ensure complete phase transformation before final cooling to room temperature.

Microstructural banding occurs during hot rolling or forging due to segregation of alloying elements. ITA allows carbon to diffuse uniformly at the transformation temperature, recrystallizing the steel into an equiaxed ferrite-pearlite matrix and eliminating banded structures that could otherwise lead to crack propagation.

Yes, it is highly recommended for carburizing grades like 20MnCr5, 16MnCr5, and 8620. Annealing these forgings via the isothermal route gives them the exact hardness window (typically 140-180 HB) needed for clean gear cutting, shaving, and spline rolling prior to case hardening.

Absolutely. By establishing a completely uniform, stress-free microstructural base, ITA ensures that subsequent hardening, induction hardening, or carburizing treatments result in highly uniform and predictable dimensional changes, minimizing final grinding allowances.

Each batch is delivered with a digital furnace chart showing the heating, rapid cooling, isothermal hold, and final cooling times and temperatures. We also supply Brinell hardness inspection sheets, verifying that the components meet target hardness specifications.