Título

ALLOYING EFFECTS ON MICROSTRUCTURE, MECHANICAL PROPERTIES AND HARDENABILITY OF A MODIFIED SAE 5120 STEEL

ALLOYING EFFECTS ON MICROSTRUCTURE, MECHANICAL PROPERTIES AND HARDENABILITY OF A MODIFIED SAE 5120 STEEL

Autoria

Coletti, Argos Yoneda; Sandim, Hugo Ricardo Zschommler

DOI

10.5151/2594-5297-34270

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Resumo

SAE 5120 STEEL IS LARGELY USED TO MANUFACTURE TRANSMISSION GEARS AND SHAFTS FOR AUTOMOTIVE INDUSTRY. ALLOYING WITH NIOBIUM AND BORON IS INTENTIONALLY MADE TO MODIFY THE MICROSTRUCTURE AND, CONSEQUENTLY, PROMOTING CHANGES IN METALLURGICAL AND MECHANICAL PROPRIETIES. ALLOYING WITH NIOBIUM INHIBITS AUSTENITE GRAIN GROWTH (ZENER PINNING EFFECT), LEADING TO AN INCREASE OF PRODUCTIVITY SINCE HIGHER ROLLING MILL AND HEAT TREATMENT TEMPERATURES CAN BE EMPLOYED. BORON CAN BE FOUND EITHER IN THE SOLUBLE FORM OR INSOLUBLE IN STEELS. ON ONE HAND, SOLUBLE BORON INCREASES HARDNESS BECAUSE IT SEGREGATES TO GRAIN BOUNDARIES RETARDING THE NUCLEATION OF FERRITE. INSOLUBLE BORON, ON THE OTHER HAND, ALSO PREVENTS AUSTENITE GRAIN GROWTH DUE TO ITS CHEMICAL REACTION WITH N FORMING BN WHOSE DISSOLUTION TEMPERATURE IS AROUND 1360ºC. THE MAIN TARGET OF THIS WORK WAS TO EVALUATE THE KINETICS OF PHASE TRANSFORMATIONS BY CONTINUOUS COOLING TRANSFORMATION (CCT) FROM THE AUSTENITIC FIELD (930OC). THE MICROSTRUCTURE WAS ANALYZED BY LIGHT OPTICAL MICROSCOPY AND VICKERS HARDNESS TESTING, ALLOWING BUILDING THE CCT DIAGRAMS WITH DIFFERENT COOLING RATES. THERMO-CALC SOFTWARE ALLOWED TO PREDICT THE THERMODYNAMICALLY STABLE PHASES, PROVING THAT BORON AND NIOBIUM FORM STABLE PRECIPITATES AT HIGH TEMPERATURES (ABOVE 1150ºC). THE HARDENABILITY AND MECHANICAL PROPERTIES WERE INVESTIGATED BY JOMINY AND BRUGGER IMPACT TESTS, RESPECTIVELY. ALLOYING EFFECTS WERE ANALYZED BY LINEAR REGRESSION USING MINITAB SOFTWARE.

 

SAE 5120 STEEL IS LARGELY USED TO MANUFACTURE TRANSMISSION GEARS AND SHAFTS FOR AUTOMOTIVE INDUSTRY. ALLOYING WITH NIOBIUM AND BORON IS INTENTIONALLY MADE TO MODIFY THE MICROSTRUCTURE AND, CONSEQUENTLY, PROMOTING CHANGES IN METALLURGICAL AND MECHANICAL PROPRIETIES. ALLOYING WITH NIOBIUM INHIBITS AUSTENITE GRAIN GROWTH (ZENER PINNING EFFECT), LEADING TO AN INCREASE OF PRODUCTIVITY SINCE HIGHER ROLLING MILL AND HEAT TREATMENT TEMPERATURES CAN BE EMPLOYED. BORON CAN BE FOUND EITHER IN THE SOLUBLE FORM OR INSOLUBLE IN STEELS. ON ONE HAND, SOLUBLE BORON INCREASES HARDNESS BECAUSE IT SEGREGATES TO GRAIN BOUNDARIES RETARDING THE NUCLEATION OF FERRITE. INSOLUBLE BORON, ON THE OTHER HAND, ALSO PREVENTS AUSTENITE GRAIN GROWTH DUE TO ITS CHEMICAL REACTION WITH N FORMING BN WHOSE DISSOLUTION TEMPERATURE IS AROUND 1360ºC. THE MAIN TARGET OF THIS WORK WAS TO EVALUATE THE KINETICS OF PHASE TRANSFORMATIONS BY CONTINUOUS COOLING TRANSFORMATION (CCT) FROM THE AUSTENITIC FIELD (930OC). THE MICROSTRUCTURE WAS ANALYZED BY LIGHT OPTICAL MICROSCOPY AND VICKERS HARDNESS TESTING, ALLOWING BUILDING THE CCT DIAGRAMS WITH DIFFERENT COOLING RATES. THERMO-CALC SOFTWARE ALLOWED TO PREDICT THE THERMODYNAMICALLY STABLE PHASES, PROVING THAT BORON AND NIOBIUM FORM STABLE PRECIPITATES AT HIGH TEMPERATURES (ABOVE 1150ºC). THE HARDENABILITY AND MECHANICAL PROPERTIES WERE INVESTIGATED BY JOMINY AND BRUGGER IMPACT TESTS, RESPECTIVELY. ALLOYING EFFECTS WERE ANALYZED BY LINEAR REGRESSION USING MINITAB SOFTWARE.

Palavras-chave

SAE 5120; Hardenability; Microstructure; Impact test

SAE 5120; Hardenability; Microstructure; Impact test