Materials, units and hardness conversion
Property cards for about 32 common engineering materials with thickness and diameter dependence of the strength values, an exact unit converter for engineering quantities and hardness conversion HV ↔ HB ↔ HRC ↔ Rm per EN ISO 18265.
S355J2 (1.0577)
Structural steel · EN 10025-2 · +AR/+N
Higher-loaded welded parts, crane construction, toughness down to −20 °C
Strength (size range ≤ 16 mm)
Physical properties
Strength ranges by dimension
| Size range | Re min. | Rm [N/mm²] |
|---|---|---|
| ≤ 16 mm | 355 | 470 – 630 |
| > 16 – 40 mm | 345 | 470 – 630 |
| > 40 – 63 mm | 335 | 470 – 630 |
| > 63 – 80 mm | 325 | 470 – 630 |
Strength values are guaranteed minimum values of the standard (real heats lie above); physical values are typical datasheet values. Sources: Q1, Q3 (see knowledge documentation for the source list).
Formulas and fundamentals
Material cards: The strength values are guaranteed minimum values from the respective material standards and apply per size range. The engine picks the first range whose limit covers the entered thickness or diameter; above the largest range it deliberately warns instead of extrapolating. If the shear modulus is not stored, it is derived from G = E / (2 · (1 + ν)).
Units: All linear quantities pass through the SI base value, i.e. value_SI = value · factor of the source unit and value_out = value_SI / factor of the target unit. The factors are exact definition values per NIST SP 811 and DIN 1301, for example 1 kp = 9.80665 N, 1 lbf = 4.4482216152605 N, 1 PS = 735.49875 W. Temperature is converted affinely (K = °C + 273.15; °F = 1.8 · °C + 32), never via a linear factor.
Hardness conversion: The tool interpolates linearly between the published support points of EN ISO 18265 (table A.1 for unalloyed and low-alloy steels). Outside the validity range of a scale, e.g. HRC below 22 or Rm above 2180 N/mm², the tool deliberately returns no value. The conversion is an approximation and does not replace a measurement in the target method.
Worked example
Strength lookup: For an S355J2 plate with t = 25 mm the range above 16 up to 40 mm applies, so Re min = 345 N/mm² and not the headline value of 355 N/mm². A quenched and tempered 42CrMo4 shaft with d = 50 mm falls into the range above 40 up to 100 mm: Rp0.2 min = 650 N/mm², Rm = 900 to 1100 N/mm².
Units: A hydraulic system at 3000 psi corresponds to 3000 · 6894.757 Pa = 206.84 bar or 20.68 MPa. A US tightening torque of 250 lbf·ft equals 250 · 1.3558179 = 338.95 N·m, and a legacy-drawing force of 2500 kp is 2500 · 9.80665 N = 24.52 kN.
Hardness: 32 HRC is measured on a quenched and tempered 42CrMo4 shaft. Interpolating between the support points HRC 29.8 (HV 300, Rm 965) and HRC 35.5 (HV 350, Rm 1125) yields about 319 HV and Rm ≈ 1027 N/mm².
Frequently asked questions
Where do the material properties come from?
The values are curated from publicly available manufacturer datasheets and material portals and cross-checked against a second source where possible; the source IDs are shown on each property card. The standard and the supplier's inspection certificate remain decisive for the individual case. Individual guide values are marked accordingly.
Why does the yield strength decrease with thickness or diameter?
Thicker sections cool more slowly during rolling and heat treatment and end up with a coarser microstructure, so the standards guarantee lower minimum values there. S355J2, for example, drops from 355 to 345 and 335 N/mm², 42CrMo4 +QT from 900 via 750 to 650 N/mm². Entering the governing dimension in the tool selects the correct range automatically.
Are the displayed strength values typical values or minimum values?
They are guaranteed minimum values of the standards; real heats usually lie above them. Strength verifications are calculated with the minimum values. For condition-dependent materials such as copper alloys and for plastics the tool shows typical ranges with a note instead.
What is the difference between N/mm², MPa and bar?
1 N/mm² is exactly 1 MPa; both denote the same stress unit. 1 bar, in contrast, is only 0.1 MPa and is used for pressures. The legacy unit kp/mm² corresponds to 9.80665 N/mm², and 1 MPa is roughly 145 psi.
How accurate is the hardness conversion per EN ISO 18265?
The conversion is valid only for unalloyed and low-alloy steels within the tabulated range and is an approximation with a technical uncertainty of roughly 10 percent. It is invalid for austenitic steels, aluminium or carbides. If a hardness value is contractually agreed, it must be measured in the agreed method.
Why does the tool distinguish PS and hp?
The metric horsepower PS is defined as 75 kp·m/s = 735.49875 W, the mechanical horsepower hp as 550 lbf·ft/s ≈ 745.70 W. The difference is about 1.4 percent, which is why both are kept as separate units and never treated as synonyms.