其实是同一个东西。520是厂商起的名字,4130是AISI标准名称
520 is the proprietary designation for a range of butted frame tubes made by Reynolds using a chromium molybdenum steel alloy similar to the AISI 4130 standard.
Other manufacturers also make butted frame tubes of AISI 4130 chromium molybdenum alloy.
The raw material used for Reynolds 520 is essentially 4130, so the difference between 520 and 4130 is that 520 refers to the finished tube sets from Reynolds, while 4130 is simply a steel alloy that other manufacturers use to make their own tube sets competing with Reynolds 520.
Not just similar, but actually 4130.