I wouldn't want any any knife edge of mine to get over 450 for any length of time. 1/100 of a second or less. Tempering does have more effect over time, but stuff starts to happen right away and the edge is a very thin section. The reason a hatchet, ax, of hawk is usually tempered to a higher temp is the nature of its cutting with a high striking force means that it would be much more prone to chipping than a knife. The edge of an ax is also at a much wider angle than a knife and therefore it will not roll over at a softer temp. But, ax, knife or anything else will benefit much more from a long soak at the desired temp in a controlled oven than any torch type temper. You are reforming or refining the martensite formed during hardening when you temper and the process is far more complete with time. A second temper is also done because during the first temper the retained austentite from hardening is converted to martensite and it needs to be tempered, which occurs during the second temper. After those steps you can soften the body of the ax or a knife to a softer state with a torch while keeping the edge cool and hard. The smiths of old did not have even kitchen ovens with temp controls and they did not, have the means to achieve a better temper. You do. USE it.
There are lots of people here with far more knowledge than me. Some of them are highly educated in metallurgy. They are very willing to share their knowledge and it behooves you to listen to them. I have and still do. I thank them for the knowledge they have given me. I highly suggest you read the stickys and do some seaching if you want to understand what is going on. Your questions make it obvious that you do not.
There are several types of bluing processes and the temps necessary to achieve bluing with them vary from ambient air temps to over 600f. IF you Want to keep a carbon steel blade at an acceptable hardness you need to use one that works below 450f.
The colors that you achieve heating in an oven vary according to the steel, what contaminants are on the steel and the atmosphere in the oven. Heat coloration is not very durable at all.