GGG140B is the highest-strength grade in this ductile iron series and, at a roughly 1400 N/mm² minimum tensile strength, sits firmly in austempered ductile iron (ADI) territory rather than the conventional as-cast or simply quenched-and-tempered range. It lines up closely with EN-GJS-1400-1 under EN 1564, the European standard covering ADI grades. Reaching this strength means austenitizing the casting and then quenching it isothermally into the lower end of the bainite-forming range — commonly cited around 250°C for this strength level — rather than continuing to room temperature. The result is a very fine ausferritic matrix (bainitic ferrite plus a smaller, more stable fraction of retained austenite than in the softer ADI grades) wrapped around the graphite nodules, trading away elongation for the highest strength and hardness the ductile iron family can practically reach.

As with the other "B"-suffixed grades in this series, we're inferring the letter's meaning from context rather than citing one specific, independently verifiable standard clause — treat it as a marker of a specially heat-treated, strengthened delivery condition and confirm the exact processing route with your foundry. With only a 1% minimum elongation, GGG140B gives up nearly all the forgiving ductility that makes ordinary ductile iron attractive, in exchange for wear resistance and fatigue strength that can approach hardened alloy steel — appropriate for severe-wear components like ground-engaging tools, gear teeth, and other parts where surface durability outweighs the need for shock absorption.

GGG140B is the most difficult grade in this entire ductile iron family to machine, and by a meaningful margin. The lower-temperature austempering cycle that gets it to 1400 N/mm² produces the hardest, most refined bainitic ferrite matrix in the series along with a smaller but still work-hardening-prone retained austenite fraction. Bulk hardness commonly runs above 400 HB, putting this material closer to a hardened tool steel than to any conventional cast iron in terms of cutting difficulty.

Cutting forces, tool-tip temperatures, and abrasive wear are all at their highest point in this family here, and the graphite nodules that make softer ductile iron grades relatively easy to cut are a minor factor at this hardness — the matrix dominates cutting behavior almost entirely. As with GGG120B, the work-hardening tendency of any remaining retained austenite means a dull edge or excessive dwell time compounds the problem on subsequent passes rather than just wearing gradually.

This grade calls for the most conservative approach in the series: rigid, vibration-free setups, sharp positive geometries to promote clean shearing over rubbing, reduced feed and speed relative to the softer grades, and premium coated carbide with strong hot hardness and abrasion resistance. Where possible, roughing to remove most of the stock before a light finishing pass helps limit the total tool-edge exposure to this demanding matrix.