Heat Treating Steel

[orezok]

Since we have a real metallurgist on here, perhaps Orezok has some thoughts on what they are doing (if in fact they are not reheating after quenching, and not just failing to show us that step).

It’s been over 50 years since graduation, and since I didn’t work in the field since that time, I have forgotten 99% of what I learned. Yes, your post has brought back memories and you are spot on, but any comments I might make would be just guessing at this point.

 

[Gary Fowler]

Very interesting John. Thanks for taking to time to explain. I have a question on mild steel if that is OK. If you crudely heat a piece to dull red or maybe even orangey/yellow with your torch so that it bends/deforms easily is there any difference in the end product properties if it is left to air cool or is quenched in water?

gg

I am not a metallurgist, but having worked with steel for 45 years (welding and fabricating ) I can tell you that with mild steel plate and pipe the kind we mostly see in commercial applications and around the home, heating up to bend doesn't affect it in any way. Heating to red/orange hot then quenching in water will soften it a bit. I used to do that to my welding test straps that were being subjected to an ASME bend test. It made them bend easier without any stress cracking.

 

[chriswheeler]

Lucky to have worked with some skilled blacksmiths in the past. Best success comes from using the proper grade of steel to make the parts from. I worked with a grade of tool steel, W1 tool steel which is water hardening, or 01 which is oil hardening. Others like 4140 and leaded 4130 lend them to the heat treating process. Heating the part first to a point where a common magnet would not stick anymore marked the first quench point. After that, polishing the part and drawing back the hardness with heating to a straw brown and a no quench cooling usually did the job. In other cases, looking up a temp and time in a heat treating chart. Not having access to that heat treating oven make most of us use the color method. If you have a complicated part to make, think about sending out to a pro to heat treat, lots of jobs don't require this expense. Guess it can come down to the application.
Chris

 

[jaxs]

When I was a youngster,I didn't know how much skill and knowledge blacksmiths had. Heat treating and other processes were an every day practice and they could repair most anything brought to them. At the time (late 40s-early 50s) Texas was planted in cotton as far as the eye could see and blacksmiths were an important part of the industry. Someone figured out plows could be used until worn out without routinely heating and beating to sharpen. With that mainstay of blacksmith shops gone,they disappeared overnight and smitty tools went to scrap yards. A few years ago while men from three generations visited around a campfire,the question of how metal was joined before welding machines became available came up. As an aside for those who believe recreational hunting is barbaric and shameful, fellowship is a huge part of hunting. Theories ranged from it being cast to alien assistance. After injoying the discussion for a while,I told them about hammer welding which lead to more debate and a few whispers the old man has finally lost it. The following year, my grandsons recieved hammer welded fire pokers to stir the council fire.

 

[WranglerX]

Something everyone who is attempting heat treating should have...

Heat Treater's Guide Companion - Apps on Google Play

Dale

 

[ruffdog]

With the multitudes of different materials out there, we are barely scratching the surface. Case hardening, through hardening, heat soak times, annealing, hardness testing, hard coatings/treatments, flame hardening vs heat treat oven, on and on and on.....

Even when a person works in a shop, it is necessary to consult literature because there are so many variables including how the finished product will be used. Sometimes you can't even depend on the steel supplier to get the correct material.

 

[stuckmotor]

Years ago when I was even more foolish than I am now, I welded on some heavily galvanized flat bar that I had been used by a nearby electrical crew. The bar appeared to be mild steel. I welded on this material on several occasions and sometimes cooled it with water. I was amazed that it became brittle. Is there anything in a zinc coating that would impart brittleness to mild steel?

For everyone who expected this to be another story about zinc fume poisoning. That's a story for another day.

 

[ruffdog]

The bar appeared to be mild steel.

When we would order steel, the bars were marked on the end with colored paint that signified what type of steel it was. Cold rolled 1018 looks just like cold rolled 1060 as does cold rolled 4140. You can't judge steel by its looks. Without color coding, it's called mystery steel.

 

[Reb954]

In general if you need to know if a material is high carbon or low carbon you can do a quick spark test. The finer the spark the higher the carbon content. The coarser the spark the lower the carbon content. That won't tell you what the material is but it will give you an idea of carbon content. If you need to know more about the material you can then heat treat a piece to narrow it down as to what the material is.

Someone mentioned the color coding. For that to be reliable you have to know which supplier it came from due to the industry not having a standard color code for materials.

 

[Reb954]

Also, in regards to mild steel, there are differences in what is termed "mild steel". Most steel suppliers I have dealt with will have 1018 mild steel but some will have 1011 mild steel and there is a lot of difference in the strength of the two materials. The 1011 is commonly used by companies that do laser or plasma cutting due to it cutting faster and leaving a cleaner cut. 1011 is commonly cold rolled where 1018 is hot rolled so if you are buying mild steel and it is cold rolled you should be suspect of it as it may not have the strength you need.

I bought a new trailer last year. When I was looking it over I thought they used heavier material than I would have but then realized they were using plasma or laser to cut out the parts so it was 1011. To make up for the loss of strength from 1011 to 1018 they used thicker material. And don't get me wrong, I like the trailer, it is a little heavier than it needs to be but by using laser or plasma to cut out the parts they also saved a lot of costs. I am adding a winch mount on the front of the trailer now but it will be all 1018 material for strength. I use materials and design to make up for my lack of welding skills. :laughing: