ANALYSIS OF EFFECTS OF HEAT TREATMENT PROCEDURES ON CHARACTERISTICS OF IRON

The initial study was conducted on unalloyed ductile iron castings. The effect of austempering  time  was  examined  by  varying  austempering  time  in  the  range  of  30 minutes  to  90  minutes,  while  keeping  austenitization  temperature  and  austempering temperature constant. It was found that with the increase of austempering time, the tensile strength increased significantly. However, at 90 minutes the tensile strength decreased. The optimum temperature was found to be 60 minutes. The second variable was the effect of austenitization temperature on  ductile  iron.  Based  on  the  result  of  the  first experiment,  the  austempering was  carried  out  for  90  minutes. The austempering temperatures were kept at 270ºC and 370ºC. The austenitization temperature was varied from 850ºC to 925ºC. The study revealed that tensile strength increased at 900ºC but it decreased at 925ºC. The third major variable involving the effect of alloying additions on ductile iron, was studied by adding copper with three different values i.e. 0.5 wt. %, 1.0 wt. % and 1.5 wt. %. The fourth melt was without the addition of copper. It was found that with the increase of copper the tensile strength continued to increase up to 1.5 wt. %. The second alloying addition was nickel. One melt was made without nickel while the remaining three melts were made with the addition of 1.0 wt. %, 2.0 wt. % and 3.0% nickel. The tensile strength increased correspondingly with the increase in the addition of nickel to 3.0 wt. %. The effect of a combination of copper and nickel on ductile iron was also examined. The effect of the last alloying element which was studied was lanthanum. Four melts were made for this study.  The  first  melt  was  without  the  addition  of lanthanum  while  the  remaining  three  had  0.006  wt.%,  0.02  wt.%  and  0.03  wt.% lanthanum. The results indicated that the tensile strength increased with the increase of lanthanum content with and without austempering. Furthermore, the highest nodule count was   obtained   with   0.03   wt. % lanthanum while   the nodularity remained almost unchanged.

Thus, it  was  observed  that  the  addition  of  alloying  elements  results  in  an increase of tensile strength. The optimum austempering time was 90 minutes and the optimum austenitizing temperature was found to be 900ºC.