tomwalz
Materials
- May 29, 2002
- 947
I would appreciate any comments anyone cared to make on the condition of the steel in the attached picture.
This steel was part of the shoulder behind a tungsten carbide saw tip. It appears that both the steel saw plate and the tungsten carbide saw tip had been improperly prepared for brazing. Thus, when run, the braze joint was weak enough to allow the saw tip to be levered out taking a piece of steel with it. This would be the rough patch. After the tip came out the saw blade was run for a while which would explain the area labeled as “smeared steel”.
At least that is my conjecture as to what happened to the steel but I am in no way a steel man.
Following are my notes so far
This is a picture of the pocket of a carbide tipped saw blade. The center of the saw is to the right.
The saw plate or saw body with sold as being ready to braze. A pretinned tip, that is a saw tip to which the braze alloy has already been applied, was brazed into the pocket. The tip broke and most of it came out during cutting. The steel either ripped or snapped and the secondary of the steel was smeared or deformed.
The saw tip arrested in the area covered by the two red arrows labeled “Braze Alloy Stuck to Steel” and “Piece of Carbide”.
The braze alloy has a solidus of 1150 F and a liquidus of 1205F. Because the tip had been pretinned we are looking at the remelt situation so we may wish to assume that the new liquidus is about 1250 F. Current practice is to heat to about 50 F over the liquidus which would make it 1300 F.
For purposes of analyzing the grain structure of the steel we should probably wish to consider that 1400 F to 1500 F is possible with the 1400 F being much more likely.
The red arrow labeled “Vertical Lines Left From Laser Cutting” is meant to indicate all the vertical lines or vertical marks. In this case, the laser melts a series of holes which are then blown out by a gas. This leaves a surface that is been affected by the heat of melting, that has been heavily oxidized by exposure to the atmosphere while hot and in which carbon migration in the steel is suspected to be an issue in brazing. Best practice calls for grinding the surface back about 0.005 inches to 0.007 inches. In this case it appears that the brazing was done directly to the laser cut surface.
The red arrow labeled “Braze Alloy Stuck to Steel” shows that there are areas where the braze alloy preferred to stick to the steel instead of the tungsten carbide saw tip. The braze alloy is gold in color. It appears gray here because there is a layer on top of it. This layer is the layer surface treatment applied to the tungsten carbide saw tip to make it more wettable.
It appears that about half the braze alloy preferred to stick to the steel and the other half preferred to stick to the saw tip.
The green line at the top indicates the suspected location of the “chill line” or edge of the heat affected zone.
Thank you,
Tom Walz
Thomas J. Walz
Carbide Processors, Inc.
Good engineering starts with a Grainger Catalog.
This steel was part of the shoulder behind a tungsten carbide saw tip. It appears that both the steel saw plate and the tungsten carbide saw tip had been improperly prepared for brazing. Thus, when run, the braze joint was weak enough to allow the saw tip to be levered out taking a piece of steel with it. This would be the rough patch. After the tip came out the saw blade was run for a while which would explain the area labeled as “smeared steel”.
At least that is my conjecture as to what happened to the steel but I am in no way a steel man.
Following are my notes so far
This is a picture of the pocket of a carbide tipped saw blade. The center of the saw is to the right.
The saw plate or saw body with sold as being ready to braze. A pretinned tip, that is a saw tip to which the braze alloy has already been applied, was brazed into the pocket. The tip broke and most of it came out during cutting. The steel either ripped or snapped and the secondary of the steel was smeared or deformed.
The saw tip arrested in the area covered by the two red arrows labeled “Braze Alloy Stuck to Steel” and “Piece of Carbide”.
The braze alloy has a solidus of 1150 F and a liquidus of 1205F. Because the tip had been pretinned we are looking at the remelt situation so we may wish to assume that the new liquidus is about 1250 F. Current practice is to heat to about 50 F over the liquidus which would make it 1300 F.
For purposes of analyzing the grain structure of the steel we should probably wish to consider that 1400 F to 1500 F is possible with the 1400 F being much more likely.
The red arrow labeled “Vertical Lines Left From Laser Cutting” is meant to indicate all the vertical lines or vertical marks. In this case, the laser melts a series of holes which are then blown out by a gas. This leaves a surface that is been affected by the heat of melting, that has been heavily oxidized by exposure to the atmosphere while hot and in which carbon migration in the steel is suspected to be an issue in brazing. Best practice calls for grinding the surface back about 0.005 inches to 0.007 inches. In this case it appears that the brazing was done directly to the laser cut surface.
The red arrow labeled “Braze Alloy Stuck to Steel” shows that there are areas where the braze alloy preferred to stick to the steel instead of the tungsten carbide saw tip. The braze alloy is gold in color. It appears gray here because there is a layer on top of it. This layer is the layer surface treatment applied to the tungsten carbide saw tip to make it more wettable.
It appears that about half the braze alloy preferred to stick to the steel and the other half preferred to stick to the saw tip.
The green line at the top indicates the suspected location of the “chill line” or edge of the heat affected zone.
Thank you,
Tom Walz
Thomas J. Walz
Carbide Processors, Inc.
Good engineering starts with a Grainger Catalog.
