Where Each Grade Comes From
St37-2 is a general structural steel from the German standard DIN 17100, the specification that shaped steel procurement in Germany and neighbouring countries for decades. The designation reads as a minimum tensile strength of 37 kgf/mm², roughly 370 MPa, with the suffix distinguishing the weldable, tested quality class from the basic grades. DIN 17100 has since been withdrawn and superseded by the European standard EN 10025.
S235JR is the modern designation under EN 10025-2, the European standard for non-alloy structural steels. In this system S means structural steel, 235 is the minimum yield strength in MPa for the thinnest section range, and JR denotes the impact quality, namely a minimum Charpy V-notch energy of 27 J at +20 °C. For most practical purposes S235JR is the direct successor of St37-2 and it is the grade that appears on current European drawings and CE-marked products.
Chemical Composition Comparison
| Element | St37-2 (DIN 17100) | S235JR (EN 10025-2) |
|---|---|---|
| Carbon (C) | ≤0.17%, with slightly higher allowances in thick plate | ≤0.17% up to 40 mm |
| Manganese (Mn) | Around 0.40% maximum; the old grade was a leaner manganese steel | ≤1.40% |
| Phosphorus (P) | ≤0.050% | ≤0.035% |
| Sulfur (S) | ≤0.050% | ≤0.035% |
| Nitrogen (N) | Not specified | ≤0.012% |
| Silicon (Si) | Only specified for the fully killed grades | Specified when required for the deoxidation route |
The most important difference is the manganese allowance. DIN 17100 kept St37-2 lean in manganese, so strength and toughness depended largely on the rolling practice of the mill. EN 10025-2 permits up to 1.40% manganese in S235JR, which strengthens the steel and allows the carbon content to stay low; the result is a more uniform product with better and more predictable weldability. The modern standard also tightens phosphorus and sulfur to 0.035% each and caps nitrogen, three changes that reduce the risk of hot cracking and brittle behaviour in service. A manganese figure of only 0.35–0.40% quoted for St37-2 in some comparisons should be read as an upper limit of the withdrawn German grade, not as a typical range for the modern material.
Mechanical Properties Comparison
| Property | St37-2 (DIN 17100) | S235JR (EN 10025-2) |
|---|---|---|
| Minimum yield strength | 235 MPa for thickness up to 16 mm | 235 MPa up to 16 mm, then graded with thickness |
| Tensile strength | 360–510 MPa | 360–510 MPa |
| Charpy V-notch impact | Not required as standard, tested by agreement | 27 J minimum at +20 °C |
| Weldability | Good, with limited control of carbon equivalent | Good, with carbon equivalent restricted in the standard |
| Typical delivery condition | As-rolled, in rimmed, semi-killed or fully killed quality | As-rolled, normalized or controlled rolled on request |
At 235 MPa minimum yield and 360–510 MPa tensile, the two grades sit in the same strength class, which is why they are treated as equivalents. The real difference lies in consistency: because EN 10025-2 fixes impact energy, chemistry limits and carbon equivalent values, a designer can rely on S235JR behaving the same way from batch to batch, whereas St37-2 quality varied more with the steelmaker and the deoxidation route.
Weldability and Substitution Notes
Both grades weld easily with rutile, basic or metal-cored consumables matched to the parent strength, and neither normally needs preheating below about 30 mm thickness. S235JR has the advantage that low carbon, low sulfur and a controlled carbon equivalent reduce the risk of solidification cracking and hydrogen induced cold cracking in restrained joints. For thick sections, low-temperature service or dynamically loaded structures, welding procedure qualification should be based on the modern standard even when the drawings still show the old German designation.
Substitution is straightforward in most cases: an S235JR plate can replace an St37-2 plate of equal thickness in general structural work, because the yield, tensile and elongation properties are matched or better and the impact requirement is at least as strict. The reverse substitution is not advisable, because a withdrawn DIN 17100 grade may not carry a guaranteed impact value or the traceability that a modern project specification demands. When replacing material in an existing structure, always confirm the design assumptions, the corrosion allowance and the required impact class before ordering plate.
Frequently Asked Questions
Q: Is St37-2 exactly equivalent to S235JR?
They are treated as equivalent in strength class, and S235JR is the recognised successor of St37-2. Strict equivalence cannot be claimed, because the two grades belong to different standards with different chemistry, impact and testing requirements.
Q: Which of the two grades is stronger?
They share the same specified values: minimum yield strength of 235 MPa up to 16 mm and a tensile range of 360–510 MPa. S235JR is usually the more consistent product in practice because its chemistry and impact properties are more tightly controlled.
Q: Why does S235JR allow more manganese than St37-2?
EN 10025-2 permits up to 1.40% manganese so that strength can be achieved with a very low carbon content, which improves weldability. DIN 17100 kept the manganese level of St37-2 low, so the older grade depended more on mill rolling practice.
Q: Is St37-2 still available today?
Plate is still produced and stocked by some suppliers, but DIN 17100 has been withdrawn. New designs should specify S235JR under EN 10025-2, and St37-2 is generally requested only for replacement or repair of older German equipment.
Q: What does the JR suffix in S235JR mean?
JR denotes the impact quality class: a minimum absorbed Charpy V-notch energy of 27 J tested at +20 °C. Other suffixes in the same family indicate lower test temperatures, for example J0 at 0 °C and J2 at −20 °C.
Q: Can S235JR replace St37-2 in an existing structure?
Yes in most structural applications, provided the thickness, impact class and welding procedures are checked against the original design. The substitution should be recorded in the project documentation and approved by the responsible engineer.
