are you sure you don't mean ASTM572? that's "below" 588. most grades are weldable with 70ksi electrode. grades 60 and 65 should probably be welded with 8018-C3.

Mild steel electrodes are commonly used for ASTM A 572 Grade 50 (Standard Specification for High-Strength Low-Alloy Columbium-Vanadium Structural Steel).  For Manual shielded metal-arc welding consider E7018, a low-hydrogen, usually DC, all-position electrode. It has the capability of producing more uniform weld metal, which has better impact properties at temperatures below zero.

Core Ten (A242 & A588) steels welds are specified for similar corrosion resistance and color match.  On single pass welds, mild steel electrodes are commonly used.
(1) AWS A5.1 Low Hydrogen Only
(2) AWS A5.5 Low Hydrogen Only usually use E8016
There is usually enough pickup from the base metal to obtain a good color match.  On multiple pass welds, low-alloy electrodes are commonly used to obtain a good color match and similar corrosion resistance. The electrodes commonly specified include those with the suffixes -B1, -B2, -C1, -C2, and -C3.

For the welding spec, weld in accordance with the American Welding Society Code for Building Construction D1.1.

Agree, boo1---except I never had much success with 'core ten' with E7018. I preferred E80xx or similar. Never welded the stuff with wire so - ???

Rod

Evelrod for
Core Ten we have used E8016 for large projects
ASTM A 572 Grade 50 I have used E7018 home jobs

I think of matching fillers to the parent materials strength.
See:
http://www.jflf.org/pdfs/papers/keyconcepts6.pdf