Microstructure Identification - Heat Treated E110 Steel

[aviator09]

Hi everyone, first time poster here so please be gentle

Working on a project that investigates the effects of heat treatment methods on a low-carbon (0.18% C) alloy steel, E110 (17CrNiMo6).

Heat treatment for this material typically involves case-hardening and carburizing, but I wanted to see how processes like annealing, normalizing and quenching would affect its microstructure. I made a number of samples, all of which were austenitized at around 950C, then water-quenched, air-cooled or furnace cooled. Selected samples were then tempered at varying temperatures.

Link to Microstructures Album

It seems to me that despite the low carbon content, I obtained a martensitic microstructure for the water quenched samples, and coarse/fine pearlite with a pretty dominant primary ferrite phase for the annealed and normalized specimens respectively (though identification of the typical lamellar structures is difficult)- would you agree?

I am limited to 1000x optical magnification, and do realize that one or two of the specimens are slightly over-etched, but I don't think it's too bad.

As for the tempering, it seems that the tempered martensite structure consists of dispersed carbides, but I'm not certain. Any ideas on the normalized/annealed & tempered microstructures?

Any assistance/opinions are greatly appreciated!

 

[cloa]

Carbon is low determiner of hardenability- much stronger is alloy content- its a through hardening alloy steel- no surprises water quench gives you martensite.

 

[aviator09]

thanks for your response. I should have clarified...I'm not surprised about getting martensite, since I've had a look at the TTT-curves for the alloy and the critical quenching rates are easily obtainable using water. I'm more concerned with the effects of tempering on the annealed and normalized specimens.

 

[cloa]

How long did you temper (same time for each hopefully)- and is the sample from the air-cooled or furnace? I wouldn't say that I know micro-structures but this answers will help more knowledgeable people than me.

 

[aviator09]

Tempering was performed for 45 min and was consistent across all tempered specimens. The only tempering variable that I modified was temperature. The link I posted above is an album that contains three images (above each image you can click a link to get to the next/previous)-- each image shows an untempered microstructure (quenched, annealed or normalized) and three additional microstructures resulting from tempering at different temperatures. Hope this helps.

 

[TVP]

aviator,

I just looked through the images, but need more details. What was the exact process for the annealed specimens?

 

[aviator09]

hi TVP, the annealed samples were left inside the (switched off) furnace overnight. I daresay the cooling time to room temperature was around the 18 hour mark.

 

[aviator09]

maybe I should provide more detail:

All annealed samples were heated to 950C and left inside the furnace for 45 minutes to austenitize. after 45 minutes, the furnace was switched off, and the samples were left inside to cool to room temperature over an ~18 hour period. Sample (a) in the annealed images should be reflective of this. Then, selected samples were tempered for 45 minutes, but at different temperatures for each sample, as labelled in figures (b), (c) and (d). following tempering, they were then air cooled to room temperature.

hope this helps!