Rebar Steel Grades — B500A vs B500B vs B500C

Rebar steel grades tell you everything about how a reinforcing bar will perform in concrete: its strength, how much it can stretch before it breaks, and how it behaves under overload or an earthquake. Across Europe the dominant family is B500 — covering B500A, B500B and B500C — all defined under EN 10080 (European reinforcing steel) and the German standard DIN 488, and used in design to EN 1992-1-1 / Eurocode 2. The three grades share the same nominal strength but differ sharply in ductility, which is what separates a slab mesh from seismic reinforcement.

This page is built to settle the question once and for all. Below you will find a master comparison table, a plain-English explanation of the “500” and of ductility class, the chemistry and weldability that underpin the grades, and a short FAQ. If you already know your requirement, you can request a quotation with full export documentation.

What does the “500” mean?

In every B500 grade, the 500 is the characteristic yield strength in megapascals (MPa) — the stress at which the steel begins to deform permanently. A 500 MPa minimum yield (Re or R_e) means a 16 mm bar with a cross-section of about 201 mm² will start to yield at roughly 100 kN of tension. The leading letter “B” denotes reinforcing steel for concrete (German: Betonstahl). So B500A, B500B and B500C all share the same 500 MPa strength floor — the trailing letter is what changes everything else.

What ductility class means — and why it matters

Ductility is the steel’s ability to stretch and absorb energy before it fractures. Two numbers define it:

• k = R_m/R_e — the ratio of ultimate tensile strength to yield strength. A higher k means the bar keeps gaining strength well past yield, giving warning and reserve capacity instead of a sudden snap.
• A_gt — total elongation at maximum force, i.e. how far the bar stretches uniformly before necking. Higher Agt = more deformation capacity.

The trailing letter encodes the ductility class: A = normal, B = high, C = seismic. This matters for two practical reasons. First, moment redistribution: ductile reinforcement lets a continuous beam or slab shed load from an overstressed section to a stronger one, so the whole structure carries more before failure. Eurocode 2 permits greater redistribution — and tighter detailing — when higher-ductility steel is used. Second, seismic resistance: in an earthquake, structural members must flex through repeated large cycles without brittle fracture. That demands the high k and high Agt of B500C, which is why seismic codes (and Eurocode 8) call it up where ground motion governs.

German legacy grade: BSt 500 S

Before the harmonised B500 designations, German practice used BSt 500 S (S = Stabstahl, hot-rolled bar) and BSt 500 M for mesh. BSt 500 S broadly corresponds to today’s high-ductility hot-rolled bar and is essentially the predecessor of B500B. You may still see BSt 500 S on older drawings, stockholder labels and re-rolled material; for new work under DIN 488 / EN 10080 it is specified as B500B (or B500C where seismic ductility is required).

When to specify each grade

• Specify B500A when reinforcement is delivered as welded mesh or small-diameter coil for slabs, screeds and lightly-stressed elements where normal ductility is acceptable and the cold-rolled/coil product form is the efficient choice.
• Specify B500B for the vast majority of cast-in-place reinforced concrete — foundations, columns, beams, walls and slabs. As the high-ductility hot-rolled B500B bar, it is the workhorse grade that most Eurocode-2 designs assume by default.
• Specify B500C for seismic zones, ductile frames, plastic-hinge regions and any structure where high deformation capacity and energy dissipation are required. Its tighter k window (1.15–1.35) and 7.5% Agt are the seismic differentiators.

Chemistry & weldability (C_eq)

All B500 grades are low-carbon, low-alloy steels whose weldability is governed by the carbon equivalent, C_eq, calculated from carbon, manganese, chromium, molybdenum, vanadium, nickel and copper content. EN 10080 / DIN 488 cap the maximum carbon and C_eq precisely so that the steel can be welded reliably on site. In practice this keeps Ceq around the order of 0.50% maximum, allowing tack, lap and butt welding when carried out to DIN EN ISO 17660 (welding of reinforcing steel). Weld procedures, preheat and consumables should always follow that standard and the project specification. Because B500C achieves its ductility partly through controlled chemistry and rolling, its weldability is comparable to B500B when the same procedures are observed.

Identification & markings

Reinforcing bars carry a rolled-in rib pattern that identifies the producing mill and the country/grade according to the EN 10080 marking system: a start mark followed by a coded count of normal ribs between thicker ribs encodes the mill identity and origin. The rib geometry itself (relative rib area, f_R) also governs bond with the concrete. On delivery, the authoritative grade record is the Mill Test Certificate to EN 10204 3.1, which states the actual measured Re, Rm, k, Agt and chemistry for the heat — this, not the visual marking alone, is what you check against your specification. See standards & certification for the full documentation set.