Testing of Post‐fire Brittleness for Certain Standard Duplex and Lean Duplex Stainless Steel Grades

The results of post‐fire brittle cracking susceptibility tests conducted on samples made of selected duplex type stainless steel grades exhibiting austenitic‐ferritic structure, in particular on standard duplex X2CrNiMoN22‐5‐3 steel and on lean duplex X2CrMnNiN21‐5‐1 steel, are presented and widely discussed. General conclusions are based on the force‐displacement graphs obtained by the instrumented Charpy impact test. Prior to the test all samples have been subjected to simulated fire action following the steady‐state heating regime and then cooled down to room temperature. Two heating levels have been considered, namely 600°C and 800°C. The first of these levels has been considered as to low, while the second as sufficiently high, to induce in the considered steel structural changes of permanent character. For comparison, two groups of samples have been tested. Samples belonging to the first group have been heated for one hour (simulation of a short fire), while the ones belonging to the second group have been heated for ten hours (simulation of a long fire). In addition, two alternative cooling modes have been considered, i.e. slow cooling in the muffle furnace and rapid cooling in water mist. The toughness tests on samples made of both steel grades have been conducted at two different temperature values, that is at +20°C to simulate the continued service in summer conditions and at ‐20°C to simulate this future service in winter conditions.