The number refers to the carbon content of the steel used in the iron. Its listed as a percentage of the total material content. 1030 would be approximately 0.30 percent carbon. 1025 would be approximately 0.25 percent carbon and 1020 would be about 0.20 percent carbon. What your asking about though is the softness of these materials in a golf club. All things being equal, the 1020 would be the softess. However, feeling soft when you hit a golf shot is a different story and is relative to how the club was processed. In other words if nike has a different forging process and different quenching and tempering methods than mizuno which I think they do, it will come out different and feel different. I think mizuno has something called grain flow forging which is to say they make sure the grain structure is consistent on the molecular level. They do this through tempering after the initial quench. Bridgestone has something called endo forging which I really have no idea what is involved. I've heard the miura forging process is like 4 different forging steps to get a very uniform structure. Really though, all of the big companies that make forged irons have a different forging process that gives a different feel. The process is the key though, not the material. They use these particular materials because they are the easiest to work with on a large scale. They are all good materials though.
One thing to think about though, feel is largly based on sound.
Edited by bennycoop9882, 01 April 2008 - 09:30 AM.