Since we will soon have some decent ice conditions again, I started making a new set of runners. Actually the steel blanks had been cut out over a year ago on a friend’s CNC milling machine, so the current project involved heat treating them for hardness. Believe it or not, hard cold ice will soon dull the edge on ordinary mild steel.
Heat treating involves raising the temperature high enough so the crystaline structure of the steel actually changes. Part of the process is rapid cooling by quenching in water, oil or salt. The problem of warpage arises with the quenching, so I chose grade A2 tool steel which can be quenched in air, resulting in little or no deformation.
My first set of runners had been flame hardened with an oxy-acetylyne torch (MAPP gas wasn’t hot enough), but that’s a pretty uncontrolled process. I had bought a small electric kiln, & wired up a thermocouple & controller so I could accurately set the temperatures. The protocal for this steel called for preheating to 1450F/785C, raising to 1800F/982C for 10 minutes & then air quenching down to 125F.
Since hardened steel is also much more brittle, it’s necessary to temper it to improve toughness. This is done by reheating the part to 500F/260C for 2 hours. After final cooling, the layer of residue can be cleaned off & final shaping/sharpening done. The whole experience was a challenge to learn about & pull off successfully, but was fun to do. I realize this is far removed from the world of “softwater” sailboats, but I thought a few of you might be interested.