ASTM A387 Grade 9 Class 2 Plates What is ASTM A387 Grade 9 Class 2 Steel Plate? ASTM A387 Grade 9 is a chromium-molybdenum alloy steel plate, specially designed for use in pressure vessels and boilers operating at high temperatures. The addition of chromium enhances corrosion and oxidation resistance, while molybdenum improves strength an