Hi!
As js55 stated, "I would not be surprised to find the noted answer as D. But in the real world Al is more correct than the students theoretical opinion."
Indeed, D seems to be the correct answer!
Hence 'D' would seem to be the correct answer?
'Weldablity' I don't have a copy of AWS A3.0 to hand, but according to the TWI:
"TWI Knowledge Summary
What is 'Weldability'?
by Richard Pargeter
To many people 'weldability' is simply a measure of how easy it is to make a weld in a particular material without cracks. If it is easy to avoid cracking, the material is deemed 'weldable'. For a weld to be truly successful, however, it is also necessary for it to have adequate mechanical properties, and to be able to withstand degradation in service (eg corrosion damage). Thus, weldability is a measure of how easy it is to:
Obtain crack free welds
Achieve adequate mechanical properties
Produce welds resistant to service degradation.
Weldability is not a fixed parameter for a given material, but will depend on joint details, service requirements, and welding processes and facilities available. This variability in weldability is illustrated in the following examples:
Example 1
Which of these two C-Mn steels is most weldable?
Steel 1 Steel 2
C 0.16 0.19
S 0.027 <0.002
P 0.011 0.021
Si 0.20 0.28
Mn 0.61 1.38
Ni 0.03 0.01
Cr 0.02 0.02
Mo <0.01 <0.005
V <0.01 <0.01
Cu 0.03 0.005
Nb <0.005 0.024
Ti <0.01 0.002
Al <0.001 0.047
CE IIW 0.27 0.43
Pcm 0.20 0.27
CEN 0.27 0.43
The answer clearly depends on which type of cracking is of most concern:
Low restraint fillet onto thick steel
- Hydrogen crack, steel 1 more weldable
Restrained high dilution MIG nozzle weld
- solidification crack, steel 2 more weldable
Full penetration highly restrained T butt
- lamellar tearing, steel 2 more weldable.
Example 2
Which of these materials is most weldable? (welding a fairly thin walled (~3mm) pipe)
Commercially pure titanium
316 L austenitic stainless steel
22% Cr duplex stainless steel
6% Mo high alloy austenitic stainless steel
The answer will depend on an individual's experience, and available facilities.
The titanium expert knows that it is one of the easiest materials to weld - but he is very familiar with very good back purges, and the use of a trailing shield.
The expert in austenitic stainless steel would see this level of control to be very difficult. He knows to watch out for solidification cracking, and is careful to check the penetration characteristics of each cast, and does not consider that these pose a significant risk.
An expert in duplex stainless steels will tell you that it is much easier to weld than austenitic stainless steel, because there is no real risk of solidification cracking, and less of a variable penetration problem. But now, you generally need a filler.
High alloy austenitic steel is similar to duplex, expect that with a Ni based filler there is a risk of microfissuring.
Example 3
Consider Example 2, but now add that the weld will be operating in an acid, chloride containing environment at about 30°C. Had the concern been purely about freedom from cracking, then duplex and titanium would have been on an equal footing, with the high alloy austenitic being the least weldable because of the risk of solidification cracking. Now, however, the duplex stainless steel becomes more of a problem, as it becomes necessary to work within quite a narrow heat input window. It can be difficult to pass procedure qualification tests involving corrosion tests with duplex stainless steels.
Example 4
Consider examples 2 and 3, but now add a toughness requirement. Now titanium is not so weldable, as near perfect shielding is necessary to avoid toughness degradation.
Example 5
Is AISI 4130 weldable?
The composition range for AISI 4130 is:
C 0.27-0.34
S <0.040
P <0.035
Si 0.15-0.35
Mn 0.35-0.60
Cr 0.80-1.15
Mo 0.15-0.25
It is not possible to answer this question without knowing the intended service. The answer would be different for a gear component, to operate in a warm oil bath, and a piece of wellhead equipment to carry sour gas."
C.E. values are not the be all or end all, but should be seen as another tool to be used in conjunction with other tools to assess the weldability, crack sensitivity and broadly evaluate the mech proprieties of a material!!! I don't see a problem with this.
"An expert in duplex stainless steels will tell you that it is much easier to weld than austenitic stainless steel, because there is no real risk of solidification cracking, and less of a variable penetration problem. But now, you generally need a filler."
Unless you have to pass a G48 or restrictive phase balance specification.
So weldability now finds its basis in customer specification requirements. Weldability becomes a moving target in that you can weld two samples of a material, duplex for example, the EXACT same way, and in one case it is definitionally and metallurgically weldable and in another it is not, even utilizing the erroneous TWI definition.
By 803056 
Date 06-27-2011 20:52
Edited 06-27-2011 21:04
Life can be so complicated.
I can agree that carbon equivalency is but one useful tool in the welding engineer's tool belt. It is not going to provide useful information about the mechanical properties other than to say the steel with a higher carbon equivalency has the potential to have higher hardness, higher tensile strength, lower ductility than a steel with a lower carbon equivalency given the same heat treatment. Until the specific heat treatment is known, what mechanical processing has been used, etc., we are at a loss to say what the mechanical properties could be.
Careful 46.00, it would appear you are coming over to the dark side in by in, word by word.
Best regards - Al
Hey Henry! Good to hear from you.
We've had these discussions before with Bhadeshia. He will certainly set your head to spinning.
I still, to this day, have a stack of Bhadeshia articles I have yet to get to (there are literally hundreds available on line), including his humungous tome on Bainite.
You read a prolific author like Bhadeshia to learn something and then somewhere in the process realize you know nothing.
"quote"You read a prolific author like Bhadeshia to learn something and then somewhere in the process realize you know nothing."end quote"
Jeff,
That happens to me on this forum alot.
I would take it, that welding without a filler wire would fail G48 test? but would possibly pass x-ray?and your point is?
I thought it was clear. My bad.
CE as a criteria for weldability in and of itself is meaningless (you can have high CE with a very weldable material and low CE with an unweldable material), though it certainly has somewhat greater emphasis in AISC/AWS structural land. It is an exceedingly small tool in the toolbox. This I believe is consistent with Al's point, and muddies the water considerably for Answer D. There IS logic to Answer D, but it is not squeeky clean, and I believe, though I certainly do not need to speak for him, this was Al's main point to arguing for Answer B.
As for the duplex, by AWS and TWI definition the duplex weld of your example would be a weld of low, or nonexistent weldability since by failing G48 it is not suitable for the service intended, even though RT may have been water clear, the welder performed the weld with his eyes closed and one hand on a peanut butter and jelly sandwich, and the only cracking in the immediate vicinity was the crack of his ass.
And perhaps this thread has been interminable for some, though for myself it has certainly clarified some thinking that previously I had not given due consideration.
Hi!
js55, I have the utmost respect for you and others on this site!
I find myself in a quandary, I see where you are coming from, but my education prohibits me from agreeing with you! You state that you understand the reason for answer 'D' being correct, but also deny it?
'Weldablity is not a fixed parameter for a given material, but will depend on joint details, service requirements, and welding processes.' and also client requirements!
Interesting thread!
Ah. Disagreement.
I've disagreed with some of the best minds in this forum. Al, jon, john, Gerald, henry, marty, and many others. And in every single case except one I was right.
Of course, I ain't sayin which case.
Thing is, an issue with respect doesn't even enter into the thinking.
Its what drives the discussion.
We've had these threads before. These questions, many of em student generated AWS
CWI study questions, are poorly written. And thats when the fun begins.
Besides, I didn't say correct. I said I can see the logic. If there wasn't any logic to it at all there would have been no thread. The discussion was based (IMO) upon best answer, not possibly acceptable answer. Or, this answer is decent as long as we consider all of these mitigating and troublesome circumstances, and if we hold our tongue right during the waxing phases of the moon.
Its like the comedien Chris Rock in his routine about the OJ case. "I'm not sayin he should have done it, but I understand."
THANK YOU JEFF!!!
