ASTM A572 Gr. 50 Grain Structure 1

[After13urneR]

I have a yoke, please see attached sketch, which is bent from a 3" x 1-1/4" bar of ASTM A572 Gr. 50 Steel. If I switch from the a bent bar to a burn out, do I loose any strength due to a change in the grain structure?

 

[metengr]

For your situation no, provided the rolling direction of the plate is known. For plate as rolled with known rolling direction, the minimum reported tensile values must meet Table 3 of A 572 as with bar shapes. Look at ASTM A 6 for more information related to general requirements for tensile specimen orientation related to plate and bar shapes.

 

[TVP]

If by "burn out" you mean EDM/wire erosion, then yes, there will be some difference in strength. If you intend to use the long direction of the rectangle as the thickness of the block, then the grain will be oriented transverse to the applied loads.

 

[After13urneR]

Thank you for the replies. TVP, your on the right track, by "burn out", I'm referring to plasma cut or torch cut. The part starts as a 3" thick plate from which the "U" shape is cut. I can not be sure if the grain of the plate runs with the two "legs" of the "U" or perpendicular to them. I'm not even sure if the heat from cutting the shape changes the grain structure.

How much difference in tensile strength is there between going with the grain and going across the grain (or maybe no definite grain direction at all)?

 

[metengr]

After13urneR;
What is the application of this yolk? Is this for static load? Dynamic load conditions or both? Will this be used for lifting? These are important questions to answer because shapes made from burnouts are commonly used under limited service conditions.

 

[ornerynorsk]

Isn't it far cheaper, not to mention retaining your material props, to continue to form this part instead of thermal cutting?

 

[After13urneR]

The yoke is part of a trolley system running on an overhead rail. The trolley supports a hoist and may have as much as 7,500 lbs of load. Because it is overhead, the 7,500 lbs must be less than 20% of the ultimate strength of the ASTM A572 Gr. 50 Steel. In other words, the yoke must be capable of supporting 37,500 lbs in a tension test.

How much difference in tensile (or ultimate) strength is there between going with the grain and going across the grain (or maybe no definite grain direction at all)?

 

[After13urneR]

Much to my surprise, cutting is cheaper. Bending is about $60 per yoke (including material) in lots of 25. Cutting is $43 per yoke (including material). Bending is also causing some undesirable cracks in the bend as well.

 

[metengr]

After13urneR;
A couple of comments related to this entire project;

1. Considering the strength level of this material, cold bending to form the bracket means you obviously reached the upper limit for formability. This material can be warm or hot formed into shape but this could effect bulk properties. This would also apply to heat generated from thermal cutting.

2. Why not increase the size of the bracket necessary to reduce the applied tensile stress and go with a lower strength material, A 36 shape, where heat will not effect bulk mechanical properties upon forming? This material is easier to work with in comparison to Grade 50.

 

[CoryPad]

I'm not even sure if the heat from cutting the shape changes the grain structure.

Thermal cutting of steel certainly can change the grain structure. You could be reducing the strength of the material significantly. Considering that this is for overhead lifting of an enormous mass, you need to consult design/testing/safety standards applicable to this work. Good luck.

 

[stanweld]

Using 3" thick plate, would adversely impact the toughness and strength in the Z (through thickness direction.

 

[metengr]

Just to be clear about reference to the Z directional properties for steel plates, there is no doubt toughness will be affected. Tensile properties of normalized or Q&T plate are not as affected in the z-direction and really depend on chemical composition and heat treatment. I have seen data on actual z-directional tensile testing on 1” thick plate, and the difference in z-directional properties as a percentage of longitudinal tensile properties varies from about 75% to 95% as the sulfur content decreases from 0.010 to 0.002 mass percent, respectively.
Since tensile properties of plate are only specified at minimum values with actual values above minimum, the through thickness tensile strength should still meet minimum requirements.

 

[stanweld]

metengr,
I have had some recent experience with failed grade 50 structural shapes which barely met the 50 Ksi min Y.S and 65 Ksi min UTS per the supporting MTR. Production tensile tests didn't meet the SMYS,and as an added plus, nil ductility at 80 F.

 

[TVP]

My experience is similar to that of stanweld for grade 50 steel plate, which is not normalized or quenched and tempered. Also, ASTM A 572 allows S to be as high as 0.05% by mass, which is considerably higher than the 0.002-0.010 range that metengr mentioned. As an estimate, I would use 75% of longitudinal properties as the best case, and if the S is anything over 0.025% then expect the properties to be worse.

 

[mfgenggear]

should these parts be made from forgings, heat treated & machined?

 

[ornerynorsk]

Many tears you may weep, and heartaches reap, when the thing oughtn't to have been done on the cheap.

Not exactly industrial grade Haiku, but true nonetheless. Physicians have there "first do no harm", and we are also charged with life and death responsibility. Great products are not made by cutting corners. We're liable. My 2 cents.