I am not sure of the grade of the spring steel that I have been using for flat and V springs on some of my vintage revolvers and long guns. A few years back I purchased one of those cheap Sino instant-spring-up screen gazebos to keep the mossies at bay while enjoying a pint in the back garden. The gazebo was one that came folded up in somewhat of a circular fashion with a sewn-in flat steel spring frame. When you untied it and threw it on the ground it self-erected. I attempted several times to fold it up without success (might have been a pint or two over my personal muscular coordination limit). I made one final futile attempt to do so before the snow came; again without success. In frustration I went to the shed and retrieved my three foot bolt cutters. The screening went into the trash but the flat spring steel framework was cut into two-foot sections and retained. I have used it several times for various jobs. For flat spring applications I use the steel as is being careful not to overheat the material by quenching it in water as I grind it. For V springs, I heat it to cherry red and shape it, taking care to ensure that the V bend has a radius both inside and out to duplicate the original. I temper V springs in oil using a technique that I found in Brownell's (US) book "Gunsmith Kinks". This step should be completed outdoors. I place the spring in a shallow metal pan that closely fits the dimension of the spring and barely cover it with SAE 30 motor oil. I then use a propane torch to burn off the oil, moving the torch around the spring, until no oil is left in the pan. After cooling, I scribe its outline on a piece of paper followed by a squeeze in the vice to approximate its dimension under load. It is then removed and checked against original outline on paper to ensure it returns to its original dimension. So far this has worked well for me.