FV520B materials and heat treatment

A. +P1070 means that the steel has been solution annealed (1030-1050 C) then oil quenched or air cooled to approximately ambient temperature, then subsequently re-heated (called precipitation hardened or age hardened) to 550 °C for 4 hours, followed by air cooling. +P1000 just means that the precipitation hardening temperature is 580 C, while +P930 is 620 C. +AT means that the steel is only solution annealed. Depending on the exact manufacturing sequence, some companies may want the steel already heat treated to the final end use condition, which is +P930, +P1000, or +P1070. Alternatively, some companies may want to perform some type of forming or machining while the part is in the +AT solution annealed condition, and then subsequently harden the semi-finished or finished part. Which heat treatment is used depends on the nature of the end use requirements for strength, corrosion resistance, etc.

A. FYI - I do work for a stringently controlled industry (although I will decline to state which one). The BS standards that achieve the material condition are commonly believed to be incorrect and are currently being contested. (Being contested by a heat treatment specialist that used to work at Firth Vickers (FV520B) and I agree with him).

It is believed that if you heat treat as per the BS spec you will overage and as a result have poor mechanical properties. A decent heat treatment company should be able to look through the bumf and inform you of the true required heat treatment which for P1070 would normally be 460 degrees.