Effect of cooling rate of steel ( 25 Cr Mo4 ) on its hardness and microstructure

Khadir, Jassim Mohammed.

doi:10.30684/etj.27.11.15

	Effect of cooling rate of steel ( 25 Cr Mo4 ) on its hardness and microstructure
Engineering and Technology Journal
Article 1, Volume 27, Issue 11, 2009, Pages 348-363 PDF (507.41 K)
DOI: 10.30684/etj.27.11.15
Author
Jassim Mohammed. Khadir
Abstract
In this work , structural low – alloyed steel (25 Cr Mo4 ) was melted in medium frequency coreless induction furnace of (60) kgs . capacity , lined with high alumina lining powder . Samples of disc shaped (Ø25- Ø30) mm and about (10) mm thick ,for spectro – analyzing and cylindrical parts (Ø10×100) mm, were poured to manufacture dilatometric specimens by machining to the required standard dimensions of (Ø5.5×50) mm. Testing of (12) specimens by electronic dilatometer type ( 402) , using different cooling rates , enable getting results of hardness and microstructures Tests showed that ferritic structure with slow cooling i.e.( 0.1 , 0.2 and 0.5) ˚C /min .was obtained –(hipoeutectoid). While pearlite started with (1.0) ˚C /min .Cooling rate , and full pearlitic appeared by (10.0) ˚c /min . Bainitic structure , started with ( 20.0) ˚C /min .cooling rate together with pearlite , reaching full bainitic by cooling with (100) ˚C /min. By oil guenching (i.e about 120 ˚C / sec .) and by water guenching ( i.e about 400 ˚C/ sec.) [ 8] martensitic structure was achieved. Those transformations in the structure was accomplished with increasment of Vickers hardness values from (175 ) HV with ( 0.1˚C /min ) cooling rate to ( 579 ) HV with water guenching . Those results enable the choosing of suitable cooling rate ( cooling medium) to obtain the required hardness and microstructure of this steel

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