Heat treatment of austenitic steel with increased boron content
In today’s automotive industry, boron steels are popular materials. 22MnB5 grade is a typical member of this class of steels. Its boron content is between 0.0008 and 0.005%. This concentration is sufficient to change the steel’s response to rapid cooling and lead to hardening structures which normally form in materials with higher carbon levels. This paper describes the effects of boron in steels which contain more than 1% of the element. They are not ordinary carbon steels but austenitic steels derived from AISI 304 with a boron addition between 1.2% and 1.6%. These specific steels have their specific use: as receptacles (baskets) in spent nuclear fuel storage casks. This paper deals with the effects achieved by heat treatment – homogenization annealing. Heating above 1050°C changes the distribution of borides and homogenizes the concentrations of other elements. This is manifested in microstructural changes as well as mechanical properties of heat-treated castings. Results of the experimental programme are discussed and correlated with literature search data and with experience reported by an engineer who developed the steel long ago at Poldi Kladno steelmill.
ATABOR, heat treatment, spent nuclear fuel storage casks