Is blueish color bad after temper?

B

BallewBlade

Joined
Oct 10, 2011
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713
So I heat treated some O-1 in my propane forge, then tempered it in my oven for 2, 2 hour cycles @ 400 degrees, and the blade was straw yellow, but all along the edge about 1/4 into the blade was a bluish color. It seems to hold an edge pretty well but was wondering if that blue coloring means the edge got too soft. I may have ground my edge to thin prior to HT, what do you think?:confused:
 
If your oven was up to temp before you put the blade in it's likely OK. This assuming the temp is correct and your oven is really at 400. You can over heat a thin edge if the blade is put into an oven while it's coming up to temp.

I usually have to go higher temp to get any blue on a blade.
 
The colors on a blade after temper mean nothing ... most of the time. If you have any oil or other things on the blade ( even soap from washing it off) that will turn all sorts of rainbow colors when tempered. If you think the oven or the blade went to 600°F during the temper, and the whole blade is a beautiful and even blued color, then you may have a problem....otherwise, just sand it clean and finish it.

A quick edge check will show if the edge rolls easily, as would an edge that was tempered in the blue range.
After temper, just sharpen a quick edge at about 15° per side. Place on a brass rod and flex the edge sideways a bit.
If it rolls and stays bent, the temper was too high or the HT was bad. You will need to re-do the HT.
If it chips badly, the Ht is fine, but the temper may need to be done one more time at a slightly higher temp. Add about 20-25°F.
If it flexes, and returns to near straight, the HT and temper are good.
After this test, dull the edge back and finish the blade. DO NOT MAKE THE MISTAKE OF LEAVING IT SHARP.
 
Yeah I left the blade in the oven as it came up to temp.
Don Hanson III said:
If your oven was up to temp before you put the blade in it's likely OK. This assuming the temp is correct and your oven is really at 400. You can over heat a thin edge if the blade is put into an oven while it's coming up to temp.

I usually have to go higher temp to get any blue on a blade.
Click to expand...
 
Thanks I will try checking my edge this way, it seems to be holding up pretty well so far. I have a separate temp gauge in the oven and it was reading 400 on the money. I think I'm ok, I was just worried about the blue being just on the edge! Thanks!
bladsmth said:
The colors on a blade after temper mean nothing ... most of the time. If you have any oil or other things on the blade ( even soap from washing it off) that will turn all sorts of rainbow colors when tempered. If you think the oven or the blade went to 600°F during the temper, and the whole blade is a beautiful and even blued color, then you may have a problem....otherwise, just sand it clean and finish it.

A quick edge check will show if the edge rolls easily, as would an edge that was tempered in the blue range.
After temper, just sharpen a quick edge at about 15° per side. Place on a brass rod and flex the edge sideways a bit.
If it rolls and stays bent, the temper was too high or the HT was bad. You will need to re-do the HT.
If it chips badly, the Ht is fine, but the temper may need to be done one more time at a slightly higher temp. Add about 20-25°F.
If it flexes, and returns to near straight, the HT and temper are good.
After this test, dull the edge back and finish the blade. DO NOT MAKE THE MISTAKE OF LEAVING IT SHARP.
Click to expand...
 
As Stacy mentioned, I often get a couple of blue and purple spots from where my quenchant burned off. The rest of the blade (at 400F anyway) should be a bronze/straw color.
 
This is from another thread currently on this forum:


The first rule for oven tempering is the same whether you have a Paragon or a Tappan.

The first rule is - PRE HEAT the oven to the target temp until it is stable. That is usually 20 to 30 minutes.

For a kitchen oven:
Placing a thermal mass in a kitchen oven will aid in evening out gradations of heat. A 16X6" plate of 1/2" mild steel placed on the center rack makes a great thermal mass. Place a 2X2" piece of the same steel on the plate.
Once the oven and steel plate have been at the desired temperature for ten minutes, place the blade on the steel plate .... and place the probe of a digital oven thermometer under the 2X2 block ..... with the probe tip sitting on the blade. Do this and close the door as quickly as possible.
This will allow your blade to be very evenly heated, and allow you to know the real temperature of the blade, not the oven air. When the blade is at the temper target point, start the timer.
Temper for two hours. Check the temperature form time to time to assure the oven does not drift. Adjust the oven setting if needed.
Remove the blade ( leave the oven on and the probe in place) and cool off with running tap water for about 60 seconds.
Dry off and put back in the oven as before for two more hours.
Some people use a third temper, but for any steel but complex stainless steels or high alloy steels, that isn't really needed. It won't hurt anything, but in normal steels, virtually all retained austenite is converted in the first temper, and all martensite has been tempered by the second. 1084, 1095, 5160, O-1 are all fine with two tempers.
Cool after tempering in running water. Slow cooling can cause some less desirable metallurgical situations. These probably won't make much difference, but the best procedure is rapid cooling from temper to room temp. Rapid cooling from temper will not warp or crack the blade, as there is no change in structure occuring.

A basic digital oven thermometer with probe costs about $20-30 at any kitchen store or big box. Kmart probably has them, too. If you get one with a temperature alarm feature ( fairly standard), set it for 10° above the target. If the oven fluctuates or drifts 10° too high, the alarm will sound. This is a real plus for guaranteeing the temper does not drift off too much. Many of these thermometers have a timer, too....a double plus!
 
Wow thanks for that Stacy some good info there! I like the steel plate idea also to sandwich the blade and keep it straight during temper.


bladsmth said:
This is from another thread currently on this forum:


The first rule for oven tempering is the same whether you have a Paragon or a Tappan.

The first rule is - PRE HEAT the oven to the target temp until it is stable. That is usually 20 to 30 minutes.

For a kitchen oven:
Placing a thermal mass in a kitchen oven will aid in evening out gradations of heat. A 16X6" plate of 1/2" mild steel placed on the center rack makes a great thermal mass. Place a 2X2" piece of the same steel on the plate.
Once the oven and steel plate have been at the desired temperature for ten minutes, place the blade on the steel plate .... and place the probe of a digital oven thermometer under the 2X2 block ..... with the probe tip sitting on the blade. Do this and close the door as quickly as possible.
This will allow your blade to be very evenly heated, and allow you to know the real temperature of the blade, not the oven air. When the blade is at the temper target point, start the timer.
Temper for two hours. Check the temperature form time to time to assure the oven does not drift. Adjust the oven setting if needed.
Remove the blade ( leave the oven on and the probe in place) and cool off with running tap water for about 60 seconds.
Dry off and put back in the oven as before for two more hours.
Some people use a third temper, but for any steel but complex stainless steels or high alloy steels, that isn't really needed. It won't hurt anything, but in normal steels, virtually all retained austenite is converted in the first temper, and all martensite has been tempered by the second. 1084, 1095, 5160, O-1 are all fine with two tempers.
Cool after tempering in running water. Slow cooling can cause some less desirable metallurgical situations. These probably won't make much difference, but the best procedure is rapid cooling from temper to room temp. Rapid cooling from temper will not warp or crack the blade, as there is no change in structure occuring.

A basic digital oven thermometer with probe costs about $20-30 at any kitchen store or big box. Kmart probably has them, too. If you get one with a temperature alarm feature ( fairly standard), set it for 10° above the target. If the oven fluctuates or drifts 10° too high, the alarm will sound. This is a real plus for guaranteeing the temper does not drift off too much. Many of these thermometers have a timer, too....a double plus!
Click to expand...
 
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