American Welding Society Forum
I would really like to open this topic for expanded discussion. For example, how can it be explained more simply or made more practical for all metal working trades . Why is the number 6 used in the denominator?
There are several different carbon equivalent equations. I assume you are referring to the International Institute of Welding (IIW) equation for non-alloyed steels with >0.18% carbon that looks like:
CE(IIW) = C + (Mn + Si)/6 + (Ni + Cu)/15 + (Cr + Mo + V)/5
These equations are empirical, meaning they are based on experience of what works and not on scientific principles. The number 6 used as the denominator for Mn + Si was chosen simply because it made the answer fit with known good experience.
Mountains and mountains of data.
These crack, these don't.
This is the approximate threshold, with some factor of error and margin of safety.
But there are a lot of carbon equivelence equations out there. Marty hit one of the most common.
You are right Marty, that equation has been gotten by empirically. Just look again the equation. They found that if the Carbon affects 1, Mn or Si will affect 1/6.
The number 6 in the denominator simply means that the additions of those elements only have 1/6th the influence of carbon on the hardenability of the alloy steel.
To put it a different way, it would take 6% manganese added to pure iron to have the same hardness as iron with only 1% carbon added to it.
The effects of 3% Manganese and 3% Silicon added to pure iron would still produce the same hardenability as iron with 1% carbon added to it.
Best regards - Al
Of course One needs to remember that 1% carbon in a carbon steel is pretty much, and You can get pretty good hardenability with 1/2 of that. A spring is roughly 1/2% carbon, and a file about 1% carbon. The most carbon I can recall in any tool steel is 2%, go much above that and You have cast iron.
Anything above 0.3% carbon is considered to be "difficult" to weld due to the need for "high" preheat temperature and the potenital of increased hardness in the HAZ.
Dave, you're close on the carbon content of cast iron vs. steel. My references list steels as having a carbon content of 1.7% or less and cast iron has more than 1.7% carbon.
Anyone that has welded cast iron knows the problems that it can create. My best results has always been to torch weld cast iron. I have to admit that I've had very poor results with the arc welding methods of repair.
Speaking of carbon equivalency equations, I use the CE listed in the appendix of D1.1 with good results when I encounter a repair on cast steel press frames or unknown steels. I send a sample to a lab for analysis and punch the numbers into the equation and it hasn't let me down yet. I usually assume the H2 condition for hydrogen control and typically assume the highly restrained condition when I do repairs on large equipment.
Best regards - Al
Al The only tool steel I know of with 2% carbon is AISI D3. This is a high carbon high chrome extremely wear resistant tool steel with 12% chrome. I think a lot of that carbon is tied up with chrome forming chrome carbide. Altho that would be a bad thing in a stainless steel, that chrome carbide is what gives the wear resistance [if My guess at the internal structure is right]. We used this material for motor lamnation dies where I served My apprenticeship. If We needed more wear resistance than the D3 offers We used tungsten carbide.
I checked with a website to look at the carbon content of a couple of tool steels and you are on the mark regarding the high carbon and chrome content. They must be air hardenable with that much carbon and chrome. I'm sure the chrome carbides do promote the wear resistance to mentioned.
Interesting to note that my references list the break point between cast iron and steel as 1.7% carbon. I run into similar disparities with the amount of chrome necessary to be classified as a stainless steel. The value for the chrome content varies between 10 and 12% depending on the author.
Best regards - Al
D2 is air hardening HCHC tool steel, that has12% chrome and *only* 1.5% carbon. The D3 is an oil hardening steel, verry deep hardening for an oil hardening steel. These are both slightly rust resistant when heat treated. Abrasion resistance is these steels claim to fame. D3 [62-63 RC when tempered] is a litle harder than D2 [60-62 RC when tempered]. D2 being air hardening is safer in heat treatment than D3 as the oil quench is more likely to cause warpage or cracking.
I don't work with tool steels, but it is good information to know.
Do you ever get involve with repairing dies and tooling employing the tool steels?
Best regards - Al
Al, I am a tool & die maker by trade, and worked in that field full time for 14 years. I built and repaired a lot of different types of tooling, but mostly stamping dies for various industries. In all that time I never welded tool steels. The auto frame plant I worked in did weld tool steel, but that was a union shop, and electric welding was done by "electric arc welders" PERIOD. I could heat, braze or cut with a hand torch or a track torch, but electric welding, air arc, and the plate cutting line tracer were off limits.
There is a company about twenty miles from where I live that specializes in repairing tooling and dies. It is a lot more involved than what most of us are doing.
Best regards -Al
The auto frame plant was Dana Corp. Parrish Pressed Steel Div. We had some better tool welders but We had some welders that welded tools too. The guy assigned to night shift in the Tool & Die building, the main toolroom where I worked, was a repair welder from the strip mines, and would not TIG weld. We had a SMAW rod for tool steel which He would use to refurbish working surfaces. One of His sayings was "I don't put it on with a paint brush" He was NOT an artist. One of the tool repair shops in one of the production buildings had a guy called "8 ball" He was good with TIG welding. This guy WAS an artist.
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