Exhaust-gas turbocharger having a turbine housing with a receiving region, arranged centrally with respect to a turbine housing axis, for a turbine impeller of the exhaust-gas turbocharger and with at least one turbine spiral duct which tapers in a helical shape towards the receiving region for the turbine impeller, wherein, in the turbine housing, there is arranged a wastegate valve with a spindle arm and a flap plate arranged thereon or a variable exhaust-gas guiding device with bearing discs and guide vanes, characterized in that at least one of the components: turbine housing, spindle arm and flap plate, or bearing discs and guide vanes, has a steel material for high-temperature applications, the material composition of which, in addition to iron, Fe, consists of the following alloy constituents in amounts within the stated limits in percent by weight: carbon, C: 0.4-0.5%; silicon, Si: 1.25-1.75%; manganese, Mn: 3.0-12.0%; chromium, Cr: 19.5-20.5%; nickel, Ni: 5.0-6.0%; niobium, Nb: 1.00-1.5%, and optionally additionally comprises at least one of the further alloy constituents in proportions up to at most the stated amounts in percent by weight: tungsten, W: up to 0.6%; vanadium, V: up to 0.12%; copper, Cu: up to 0.25%; cobalt, Co: up to 1.0%; sulfur, S: up to 0.03% and phosphorus, P: up to 0.04%, and has unavoidable impurities in proportions which are negligible with regard to the material properties. wherein, in the turbine housing, there is arranged a wastegate valve with a spindle arm and a flap plate arranged thereon or a variable exhaust-gas guiding device with bearing discs and guide vanes, characterized in that at least one of the components: turbine housing, spindle arm and flap plate, or bearing discs and guide vanes, has a steel material for high-temperature applications, the material composition of which, in addition to iron, Fe, consists of the following alloy constituents in amounts within the stated limits in percent by weight: carbon, C: 0.4-0.5%; silicon, Si: 1.25-1.75%; manganese, Mn: 3.0-12.0%; chromium, Cr: 19.5-20.5%; nickel, Ni: 5.0-6.0%; niobium, Nb: 1.00-1.5%, and optionally additionally comprises at least one of the further alloy constituents in proportions up to at most the stated amounts in percent by weight: tungsten, W: up to 0.6%; vanadium, V: up to 0.12%; copper, Cu: up to 0.25%; cobalt, Co: up to 1.0%; sulfur, S: up to 0.03% and phosphorus, P: up to 0.04%, and has unavoidable impurities in proportions which are negligible with regard to the material properties. carbon, C: 0.4-0.5%; silicon, Si: 1.25-1.75%; manganese, Mn: 3.0-12.0%; chromium, Cr: 19.5-20.5%; nickel, Ni: 5.0-6.0%; niobium, Nb: 1.00-1.5%, and optionally additionally comprises at least one of the further alloy constituents in proportions up to at most the stated amounts in percent by weight: tungsten, W: up to 0.6%; vanadium, V: up to 0.12%; copper, Cu: up to 0.25%; cobalt, Co: up to 1.0%; sulfur, S: up to 0.03% and phosphorus, P: up to 0.04%, and has unavoidable impurities in proportions which are negligible with regard to the material properties. tungsten, W: up to 0.6%; vanadium, V: up to 0.12%; copper, Cu: up to 0.25%; cobalt, Co: up to 1.0%; sulfur, S: up to 0.03% and phosphorus, P: up to 0.04%, and has unavoidable impurities in proportions which are negligible with regard to the material properties.