Steel types in Pre-1978 GM Cars and Trucks

• Leaf spring- 5160
• Coil Spring- 5160 or 9260
• Axle Shaft- 1050
• X-mission Shaft- 1141
• Inlet Valve- 3140
• Exhaust Valve- Armco #21-YN
• Connecting Rod- 1038 or 10374

Nicholson files are 1095 (the 10 stands for plain carbon steel while the 95 is the percentage of carbon = 0.95 percent carbon). While recently manufactured 1095 files are OK, if possible get files made before 1980 for the best edge holding steel. These files will be 1.2 to 1.4 percent carbon steel, which is higher carbon than can be found anywhere else.

There are a couple of ways to identify pre-1980 files. Look for files marked Black Diamond on both sides, which dates them to 1975 or older. Later files were marked Black Diamond on one side and Nicholson on the other. Also, look at the tangs -- on old files they were hot rolled to save steel. Modern ones were sheared out.

The high carbon in these steels makes them much more difficult to work . If you overheat and coarsen the grain it won't take a good edge. Try forging at a lower temperature than you usually would. Invest in a couple of Tempilstiks (crayons that melt at a specific temperature). In this case you want to work at 1550-1600 deg. F. After working the blade, heat it to 1300-1400 for a while, then bury it in wood ashes or lime to anneal. Most steels would be annealed at a higher temperature. Use this lower heat to keep the fine grain structure.

Grind off all the scale or it will crack in heat treatment. To harden heat to 1440 or 1450 deg F for about 4-5 minutes and quench in brine. Again, invest in a Tempilstik because it's too hard to judge this temperature. Do not overheat.