53 KB1068 KB51 KB200020242004Grabke, Hans Jürgen12 straniletnik:38številka:5str. 211-222ISSN:1580-2949COBISSID:361386URN:URN:NBN:SI:doc-JW2D87QLenInštitut za kovinske materiale in tehnologijeMateriali in tehnologijejeklopliniporoznostprenasičenježelezoSupersaturation of iron with nitrogen, hydrogen or carbon and the consequences|Reactions leading to supersaturation of iron with nitrogen, hydrogen or carbon are described and some of the consequences of the supersaturation. The formation of the thermodynamically stable state of the elements. N2(gas), H2(gas) and graphite from the supersaturated solid solutions may cause defects or even destruction of iron and steels. High nitrogen concentrations and instable nitrides are attained in flowing NH3-H2 mixtures, in a steady state where nitrogenation is fast but N2-desorption slow, the supersaturation leads to porosity by N2-formation in the metal or in the nitride layer. High hydrogen concentrations are established by the electrochemical reactions in pickling or by annealing at elevated temperatures, and may cause porosity in steels or blistering of coatings by H2-formation. Supersaturation with carbon occurs in nonequilibrium gas atmospheres, e.g. syngas CO-H2 and leads to disintegration of iron and steels by graphite formation, after cementite has formed as an intermediate. Parallels and similarities in these processes are pointed outOpisane so reakcije, ki vodijo do prenasičenja železa z dušikom, vodikom, ogljikom, in nekatere posledice. Formiranje termodinamično stabilnega stanja elementov: N2(plin), H2(plin) in grafit, iz prenasičene trdne raztopine lahko povzroči poškodbe ali celo propad železa in jekla. Visoka koncentracija dušika in nestabilni nitridi, izpostavljeni plinski mešanici NH3-H2, v stabilnem stanju, kjer je nadušičenje hitro, toda desorpcija dušika počasna, prenasičanje vodi do poroznosti zaradi formiranja N2 v kovinah ali v nitridni plasti. Visoka koncentracija vodika nastaja v elektrokemijskih reakcijah pri luženju ali pri žarjenju pri povišanih temperaturah, povzroča poroznost v jeklih oziroma tvorbo mehurčkov H2 v prevlekah. Prenasičanje z ogljikom nastaja v neravnovesnih plinskih atmosferah, kot npr. v plinu Co-H2, in vodi do tvorbe grafita, potem ko se je najprej oblikoval cementit, in tako do razkroja železa in jekel. Prikazane so vzporednosti in podobnosti med opisanimi procesiTEXTznanstveno časopisjejournalsSlovenian National E-content AggregatorNational and University Library of SloveniaInštitut za kovinske materiale in tehnologije