Hot rolled steel failure analysis.

[LASERNINJA]

I am a independent laser mechanic. I have a client that cuts commercial saw blades. In the past they have machined the teeth out of the stock material. Recently they have been cutting the saws on the laser. The problem is, sometimes, they have a 90% failure rate. The teeth of the saw blade break off right at the shoulder of the tooth.

Is there someone who can recommend a consulting company to look at this problem. It is my feeling that the blade is becoming tempered by the laser and causing a brittle zone where the cracks form and propagate.

Or any thoughts in general would be great.

 

[MikeMet]

Laser; There are numerous companies that can do an excellent job of failure analysis. Try to find one in your area so you can more easily interact. In the Gulf Coast I recommend Capstone Engineer (Lloyds Register Capstone) in Houston.

 

[unclesyd]

AsS you refer to big saws I assume you are in the North West. I would give these folks a call.

http://www.nwlabs1896.com/

 

[Robertmet]

Cutting steel with a laser leaves a thin layer of hardened but UNtempered steel .This is brittle and may be the cause of failure and a simple tempering operation may fix it. I remember in the 60s with the then new EDM we had to spend a lot of time educating people to temper after EDM for the same reasons.

 

[LASERNINJA]

Wow. Thanks for the help.

To give a bit more information, they are 10" saw blades, but they are for cutting plywood in a commercial setting. The RPM are something like 10 times that of normal table saw.

Let be bounce this Idea around. The laser, as you may imagine, cuts at a pretty high temperature. The shield gas they are using is nitrogen at about 150 psi and 15-20 cfm. The nitrogen comes from a liquid cylinder, turned into vapor/gas and the output through the same orifice as the beam. My question is, could the gas quench the molten steel fast enough to change the material properties in the heat effected zone? Or, is the effect of the cold gas going through an "expansion orifice" negligible?

Also, in response to the tempering comment in my first post, my terminology is a little rusty, its been a while.

Robert you mention the idea of a tempering operation. To me, that means cooking the saws at about 1100 degrees for about an hour. That is an option. Before I recommend it let me ask this, Because the steel comes from a coil, flattened, and then shipped to my client, in your opinion, or anyone's, would a tempering operation warp the saws? Would the saws want to return to the shape they were in when they were on the coil?

 

[swall]

The quench effect from the gas is negligible. The quench effect which hardens the steel is due to the very shallow layer of heated metal being backed up by a large mass of cold (room temperature) steel.

 

[LASERNINJA]

I suppose if I would have thought about it, conduction is a more effective mode of heat transfer than convection. Thanks.

 

[unclesyd]

I presummed that you were talking about very large saws with inserts, I have several 10" and 12" saw blades that were laser cut and on two it looks like the cast layer is still on the blades in the slots where they tuned and balanced the blade.

Just out of curosity as you state your starting material is hot rolled and my question is how do you process the material prior to machining?

As for annealing, we used to make some disk out of AISI 1060-1065 with a large number of holes that was about 0.125" thick and we annealed the disk at 1000F with no problems. The disk we in a rach and the disks were on edge. The only thing we did extra was we brought the oven up slowly.

 

[Robertmet]

The temper doesn't necessarily have to be as high as 1100 F.All you have to do is temper the martensite.The higher temperatures offer stress relief /temper/subcritical anneal !Run some experiments and determine exactly what you need.

 

[arunmrao]

Sorry to hijack this thread,but the topic is common. Large saws for a paper mill. I have been asked if I could cast 8 mm thick saw blades with the teeth profile in Hadfield Steel. I was not sure and declined,but made a suggestion to procure 6/8 mm thick rolled Manganese steel material and cut the teeth profile . Maching the profile from the blank is not possible as it would work harden. Any experience ot ideas that can be shared welcome. Sorry once again about going off topic from the original.

Learn the rules,so you know how to break them properly.
Dalai Lama

_____________________________________

 

[LASERNINJA]

No problem with the hijack.

Yup, they are 10" blades with about 100 to 120 teeth on them. What is interesting, is these are the only saws with broken teeth. These saws do have inserts on them but that part is common to both laser cut and machined saws. The "Cast" you see is from Oxygen cut, instead of nitrogen.

As far as processing before machining, I would have to check with my client to see what they are doing.

As far a laser cutting steel with Manganese, my wife says there may be some concern about the fumes, but I'll try anything once.

 

[dik]

Any chance the nitrogen can be forming nitrites or nitrogen type of compounds?

Dik

 

[Maui]

What material are the saw blades made from? What is the material thickness? Are you performing any post-cutting thermal treatment to treat these blades? These are questions that need to be answered in order to provide you with a worthwhile response. There are several potential causes for the problem that you describe, and I would recommend that a metallurgical analysis be performed by a competent lab to determine the cause of the failure. Based on your description, it sounds like the teeth are failing because cracks are forming in the gullets during use of these saw blades. The gullets are where the tensile stresses are typically the highest during use. Laser cutting may result in a remnant re-austenitized white layer on the surfaces of the teeth. These white layers are usually very thin, on the order of 0.0001" to 0.0005" in thickness. If this layer is not removed by a subsequent grinding operation or softened by a tempering or stress relieving process, then cracks can easily grow through them into the base material. These cracks often cause premature failure. Another possibility is that there is a heat affected zone generated by the laser cutting process that hardens the material and produces untempered martensite in the vicinity if the tooth. This will lead to a brittle condition that could cause crack growth as well.

Maui

 

[MOB1]

Is the steel being used for the blades one which should be preheated before laser cutting? Preheating reduces the quench rate after cutting and serves to temper the hardened zone in the heat affected zone.

 

[skibum2b]

Can you post pictures of the failed teeth/blade?

 

[LASERNINJA]

Good idea with the preheat. It has been my experience that the laser cuts some metals poorly if the work is too hot. We'll have to try it and see.

I'll have to check with the client to see what type of pictures they have. I'll post asap.