Forging San Mia Question

[Dennis Paish]

Greetings,
Given 2 materials (15N20 / 1080 / 15N20) are surface ground to 0.25" thick. All material are 6" long and 1.5" wide. Pressed firmly together and welded lines on all sides placed in a forge at 2400 F till critical temperature is reached. Borax is applied and back for another heat.

Question: Is there a formula or thoughts once welded, what the ratio of compression each material moves?

Any thoughts or advice from the San Mia masters are much appreciated on this topic.

Regards,

Dennis Paish

 

[Boogaloo]

Not at all a San Mai master (never done it) but everything should move the same amount assuming uniform heat and all alloys have same modulus of elasticity.

 

[Stacy E. Apelt - Bladesmith]

2400F is about 1000F above critical.....but it is what you want for welding.

If the seams are welded all around, there is no need for borax or flux.

The 15N20 will move more than the 1084.

Unless you have a press or power hammer, 1/4" each layer is way too thick. For most billets, I would use 1/8" 1084, and .080/.090" 15N20. If the knife will be a big honker, use 3/16" 1084 and 1/8" 15N20.

Weld from end to end and on both sides several times to assure the core is fully bonded to the san-mai. Start the welds at the white temp and quit when it gets to the orange-yellow. DO NOT try to weld at red-orange. Weld between 2400 and 1900F.

Once the billet is fully welded (you will hear the difference), forge it out at upper forging temps until it is reduced to the needed thickness and length. That would be between 2200F and 1800F. The final forging to shape can be done between 2000F and 1600F, but don't go lower or you can split a weld apart.

Sticking a coat hanger in the forge with a little borax on it and poking the hot billet will tell you if it is ready to weld. The coat hanger will stick to the billet when it is ready.