Some features of CrNi70Al alloy production

The quality of the alloy produced depends greatly on the technological metal plasticity. The present research aims at studying the low technological plasticity reasons of the CrNi70Al alloy and developming measures focused on its improvement. It is known that high-temperature brittleness of the CrNi70Al alloy is related to the influence of intermetallides and carbonitrides on metal grain boundaries. We proposed to put chrome in a liquid metal bath which significantly reduces melting time and therefore reduces the time of metal saturation by nitrogen. It is known that positive impact on long-term strength of the alloy can be obtained with small additions of zirconium. It is shown that the maximum long-term durability is achieved when the zirconium content is about 0.1 wt. %. Zirconium binds nitrogen, however, it was proposed for more complete removal of nitrogen in the metal to change the order of zirconium input in the alloy dividing its feeding into two stages. One part of zirconium (0.05 wt. %) is put in the alloy at the end of melting, and the second (0.05 wt. %) is put during refining together with alumobarium ligature and cerium close to the metal tapping from the furnace. It was shown that the introduction of measures proposed during the production of the CrNi70Al alloy allowed to reduce the nitrogen content in forgings on average from 0.025 to 0.018 wt. %. Tensile sheet strain increased from 59 to 65 %, and as a result the number of the first class sheets increased from 40 to 70 % of the total number.