Wear Resistance of 18%Cr-9%Ni Steel Used for Cast Parts of Pumps Operating in Corrosive – Erosive Environments

Abstract

This paper presents the results of experimental studies, the main aim of which has been to demonstrate that changes in the microstructure of austenitic 18%Cr-9%Ni cast steel provoked by the addition of 1.4% boron, and boron with titanium, give increased wear resistance. After melting the high-alloyed 18%Cr-9%Ni cast steel with an addition of boron, and boron with titanium, metallographic examinations were conducted using light microscopy and SEM. These examinations revealed in the austenitic structure of the 18%Cr-9%Ni cast steel, the presence of a eutectic rich in boron and chromium, and characterised by a microhardness of 1838-1890 µ HV 20 . Additionally, in the cast steel inoculated with boron and titanium, the presence of titanium nitride precipitates was observed. Changes that have occurred in the microstructure as a result of introducing the additions of boron, and boron with titanium, also caused an increase of the cast steel hardness from 212 HV 30 to 290-320 HV 30 and 320-350 HV 30 , respectively. To determine the abrasive wear resistance, 16-hour Miller test was performed (ASTM G 75-07), wherein the abrasive medium was a mixture of SiC and water. Obtaining the hard, rich in boron and chromium, eutectic and titanium nitride precipitates in the structure of 18%Cr-9%Ni cast steel increased the abrasive wear resistance by approximately 21%, according to the data recorded in the sixteenth hour of the test cycle. As an additional benchmark point for the results obtained served the wear resistant, structural, L35GSM steel used for castings working in difficult conditions. Comparing the values of abrasive wear resistance obtained for the 18%Cr-9%Ni cast steel and cast L35GSM steel, an increase in the wear resistance of the 18%Cr-9%Ni cast steel by about 35% has been proved.Keywords: austenitic, cast steel, miller test, slury abrasiv resistance, microstructure W artykule przedstawiono wyniki badań eksperymentalnych, których celem było wykazanie, że zmiany w mikrostrukturze austenitycznego staliwa 18%Cr-9%Ni na skutek wprowadzenie dodatku 1,4% boru oraz boru i tytanu skutkują zwiększeniem odporności na zużycie. Po wytopieniu wysokostopowego staliwa 18%Cr-9%Ni z borem oraz z dodatkiem boru i tytanu przeprowadzono badania metalograficzne z wykorzystaniem mikroskopu świetlnego i skaningowego. Badania te wykazały obecność w austenitycznej strukturze staliwa 18%Cr-9%Ni eutektyki bogatej w bor i chrom, o mikrotwardości 1838-1890 µHV 20. W staliwie modyfikowanym borem i tytanem dodatkowo stwierdzono obecność wydzieleń azotków tytanu. Zmiany jakie zaszły w mikrostrukturze po wprowadzeniu dodatków boru oraz boru i tytanu spowodowały również wzrost twardości staliwa z 212 HV 30 odpowiednio do 290-320 HV 30 oraz do 320-350 HV 30 . Do określenia odporności na zużycie ścierne wykonano 16-godzinny test Millera (ASTM G 75-07), w którym medium ścierającym była mieszanina SiC i wody. Uzyskanie twardej eutektyki bogatej w bor i chrom oraz wydzieleń azotków tytanu w strukturze staliwa 18%Cr-9%Ni doprowadziło do zwiększenia odporno...

Changes in Abrasion Resistance of Cast Cr-Ni Steel as a Result of the Formation of Niobium Carbides in Alloy Matrix

“…The applied method of wear testing allows the author to compare the currently obtained results with the results of their own experiments conducted previously, and with the results obtained by other research teams [ 18 , 21 , 22 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 ]; however, the latter is possible only when the tests are conducted under identical conditions of abrasion. In these studies, in most cases, the conditions of the conducted experiments were not precisely specified, and therefore, the author could compare the obtained results only with their previous research.…”

“…In [ 18 ], the results of experimental studies are discussed, showing that changes in the microstructure of cast austenitic 18%Cr-9%Ni steel as a result of the addition of about 1.4% boron and 1.4% boron with titanium increase the wear resistance of this steel grade. It was demonstrated that the matrix of cast austenitic steel contained titanium nitride precipitates and a eutectic rich in boron and chromium with a microhardness close to 1900 HV0.02.…”