Grain in plate (A36) 1

[jmen68]

When cutting A36 plate on a plasma table, is there a preferred way to cut a long slender piece. Lets say the starting plate is a standard 8' x 40' x 1/2" thk and I need 10 ea. 7'-0" x 4" strong backs cut. Ignoring plate utilization, what would be my best way to nest these pieces... will the "grain" of the plate affect my slender pieces cutting longitudinal vs transverse? Would the orientation affect welding? Can someone clear up what orientation the grain would be in the first place? My previous education seems to be failing me at the moment. Keep in mind this just an example I am purely looking for a learning experience here.

Thanks

 

[metengr]

First, rolling direction would need to be established by chemical etching samples removed from two edge surfaces of the plate. Plates today can be cross rolled as part of manufacture.

Second, regarding your application, and considering the plate is supplied as A36, you can cut the strong backs based on maximizing the use of the plate to avoid waste. For this plate thickness, some ferrite banding will probably be present. Regarding welding, there should not be any significant concerns. Follow good practice regarding placement of fillet welds to avoid possible lamellar tearing from banding.

http://www.aws.org/wj/supplement/WJ_1976_11_s341.pdf

 

[weldstan]

Even with initial cross rolling, the grain direction will be in the 40' length (primary rolling) direction. For making strong backs, it won't matter which direction you cut the matetrial. Cut to minimize wastage.

 

[tbuelna]

It is interesting to learn that rolled A36 steel plate can have a predominate grain orientation either longitudinal or transverse.

However, I think that if the strong backs are plasma cut from the steel plate stock, then there is the issue of uncontrolled metallurgy in the remelt/HAZ around the plasma cut line. This can have an effect on the properties of the finished weld joint in this area, which may be of more concern than the plate grain orientation.

 

[jmen68]

I have no idea how to use the quote function in this forum, but in reply to tbuelna comment... "I think that if the strong backs are plasma cut from the steel plate stock, then there is the issue of uncontrolled metallurgy in the remelt/HAZ around the plasma cut line. This can have an effect on the properties of the finished weld joint in this area, which may be of more concern than the plate grain orientation."

I work in the bridge/bridge component fabrication business, and I cant accurately put a number on it but for our company about 75% of parts cut are cut via cnc plasma table, the rest oxygen-fuel gas or shear. Also we abide by AWS D1.5 Bridge code and AWS D1.1 structural code, and I don't ever remember reading or hearing that addressed plasma cuts affecting properties near the weld joint being not acceptable or alter strength to any significant degree. I don't mean that it doesn't at all, just that in my area of business these reductions are insignificant.

Again, to tbuelna. I am generously curious, in the aerospace business, how do you control HAZ when cutting material? Is everything punched or sheared? What about welding?

 

[tomwalz]

It can be a big deal in brazing. The HAZ will make for very weak braze joints and is best removed before brazing.

Grain direction also indicates direction of residual stress. If it has not been removed before brazing the parts the parts can warp.

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[tbuelna]

jmen68,

Aerospace is a much different world than the civil engineering/construction business for sure.

As to your specific question regarding how the remelt/recast layer resulting from processes like flame cutting, plasma cutting, laser cutting, EDM, etc. is addressed when that area of the part will later be welded, the recast/remelt layer must always be completely removed. As far as the HAZ around a trimmed edge or a weld joint, this is always taken into consideration when the part or weldment is analyzed by applying the appropriate knock-down factors. Normally, weldments or parts made using a process that involves temperatures sufficient to produce a phase change (melting) in the metal, are stress relieved and/or re-heat-treated after the welding or cutting process.

Obviously, A36 steel is only used for GSE or test fixtures in aerospace applications. And A36 would only require a stress relief after welding or thermal cutting since it is not a heat-treatable steel. But in the aerospace business, even GSE and test fixture designs are given a thorough analysis.