Hi arftist. You asked about spark testing. Spark testing for checking the red hardness of steels absolutely requires standards. These are available over the Internet or from kind fellow blacksmiths. The main alloying ingredients which contribute to hot work capabilities are molybdenum, chromium, or tungsten. See my gallery photos for ways to distinguish the molybdenum spear point. For chromium, most commonly known in automobile spring steel, look for "flowers" along the main shaft. They look like little hairs before the burst end. For tungsten, get some HSS drills, or known M-2. It affects the color and length of the sparks. Drill bits spark with few bursts, and look like low carbon, but they are very hard and hardenable. The color of the sparks is a dull red. Of course, you could always grind TIG electrodes, but these look nothing like steel.
A smith once told me that you could judge hot work potential simply by forging the steel. He said that 5160 and S-7 are similar under the hammer as they are cooling. I am not sure about this, but he has punched a lot more hammer heads with OCS than I have with S-7, so I defer to his experience.
As for cost of tool steels, your observation of high prices from retailers is correct. I have found that Ebay sellers such as Pacific, NES, or Speedy Metals sell tool steel drops for approximately $1 per pound plus shipping. I bought a block of S-7 and D-2 about 3x2x1 for a very reasonable price. You can just cut slices off the end, since they are sold dead soft annealed.
Here is an excerpt of a post I made some time ago:
"The H-13 pieces listed on ebay at rem's (cut offs) from our production cutting o
perations. Here's a sample of sizes (in inches):
2 x 3 x 27, .75 x 3 x 36, .75 x 2.5 x 33, 1.5 x 4.5 x 13, 1 x 2 x 12... Let us k
now if these sizes will work."
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