Tools · Ferritic Steels

Cooling Time (t8/5) & HAZ Hardness Estimator

Calculate the weld's 800-500 °C cooling time from heat input, thickness, joint type, and preheat. The tool then predicts peak HAZ hardness for your steel's chemistry and checks the preheat against EN 1011-2.

⚠ Disclaimer: Use at Your Own Risk This tool is provided "as is," for general engineering reference and educational purposes only, with no warranty of any kind. Cooling times use the EN 1011-2 empirical equations and hardness uses published regression models (Yurioka, Düren) fitted to C-Mn and low-alloy steels. Both carry scatter of roughly ±30 HV and do not account for multipass tempering, hydrogen level, or restraint. Jeffrium and Jeffrey Sowards assume no liability for decisions, designs, procedures, or outcomes based on this tool's output. Verify against your governing code and a qualified procedure test with hardness traverse. Use of this tool is entirely at your own risk.

Joint and heat input

Cooling time is calculated at the preheat (the fastest-cooling, hardest case) and at the interpass limit (the slowest, which matters for toughness). For pipe, enter the wall thickness. Need Q? Use the heat input calculator.

Steel chemistry

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Peak HAZ hardness (Yurioka)
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Düren cross-check
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Avg. cooling rate 800-500 °C
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Min. preheat (EN 1011-2)
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CE (IIW)
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CET
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248 HV: sour-service limit (NACE MR0175). 350-380 HV: common limits for welds without PWHT.

Risk flags

Hardness, microstructure, preheat, and toughness

    Hardness vs. cooling time

    This steel's hardness curve. Filled dot: at preheat. Open dot: at the interpass limit.
    Yurioka Düren Preheat to interpass range
    How it works

    How cooling time sets HAZ hardness

    The time a weld's heat-affected zone takes to cool from 800 to 500 °C decides whether its austenite becomes soft ferrite and bainite or hard martensite. Heat input, thickness, joint shape, and preheat set that time. Chemistry sets how fast is too fast.

    The math

    Thick (3D)t8/5 = (6700 − 5T0)·Q·[1/(500−T0) − 1/(800−T0)]·F3
    Thin (2D)t8/5 = (4300 − 4.3T0)·105·(Q/d)²·[1/(500−T0)² − 1/(800−T0)²]·F2
    HardnessHV = ½(HVM + HVB) − 0.455(HVM − HVB)·arctan(t*)
    Q, d, T0kJ/mm, mm, °C
    F2, F3joint shape factors
    HVM, HVBall-martensite and no-martensite hardness

    Worked example

    GivenS355, 25 mm butt weld, Q = 1.5 kJ/mm, no preheat
    Heat flow3D (25 mm is above the 18 mm transition)
    t8/56600 × 1.5 × 0.000801 × 0.9 = 7.1 s
    Resultabout 340 HV, preheat about 80 °C

    Preheating to 100 °C stretches t8/5 to about 9 s and drops the peak to roughly 320 HV.

    More detail

    Assumptions used in this calculator
    • EN 1011-2 empirical cooling-time equations for arc welding of ferritic steels. Heat input is the true (net) value you enter.
    • The larger of the 2D and 3D results is used. Where EN 1011-2 gives a range of shape factors, the lower (shorter t8/5, more conservative) value is used.
    • Preheat is the plate temperature when the pass starts; the interpass limit gives the slowest-cooling case.
    • Peak hardness uses Yurioka (1987) for a single-pass, as-welded, coarse-grained HAZ, with no tempering from later passes. Düren is shown as a cross-check. Expect scatter of about ±30 HV.
    • The hardness models fit roughly 0.03-0.35% C and CE 0.2-0.8. They do not apply to stainless, high-alloy, or tool steels.
    • Preheat uses EN 1011-2 method B (CET), valid for CET 0.2-0.5, thickness 10-90 mm, hydrogen 1-20 ml/100 g, and heat input 0.5-4.0 kJ/mm.
    2D or 3D heat flow?

    Thick plate conducts heat away in all three directions, so cooling time doesn't depend on thickness. Thin plate can only conduct sideways, so cooling slows sharply as thickness drops. EN 1011-2 says to compute both and keep the larger; they are equal at the transition thickness, which the tool reports.

    Joint shape factors
    JointF2F3
    Bead on plate / overlay1.01.0
    Butt weld, fill passes0.90.9
    Butt weld, cap pass1.00.9-1.0
    Fillet, corner joint0.67-0.90.67
    Fillet, T-joint0.45-0.670.67

    Where EN 1011-2 gives a range, the tool uses the lower value. That gives the shorter cooling time and so the more conservative hardness.

    Carbon equivalents used

    CEIIW = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15

    CET = C + (Mn+Mo)/10 + (Cr+Cu)/20 + Ni/40

    Yurioka's model uses three more equivalents (CE1, CE2, CE3) to set the fully martensitic and martensite-free cooling times. Boron raises hardenability sharply, so it enters through a boron term when free nitrogen is low.

    Limits of the hardness models

    Both correlations were fitted to single-pass bead-on-plate tests on C-Mn and low-alloy steels, and predict the as-welded, coarse-grained HAZ. In multipass welds, later passes temper earlier HAZs, so measured hardness is often lower except in the cap. The models do not apply to stainless, high-alloy, or quenched tool steels.

    References
    • EN 1011-2, Welding: Recommendations for welding of metallic materials, Part 2: Arc welding of ferritic steels (Annexes C and D).
    • N. Yurioka, M. Okumura, T. Kasuya and H.J.U. Cotton, “Prediction of HAZ hardness of transformable steels,” Metal Construction 19(4), 1987, 217R–223R.
    • C. Düren, “Formulae for calculating the maximum hardness in the heat-affected zone of welded joints,” IIW Doc. IX-1437-86, 1986.
    • NACE MR0175 / ISO 15156-2, Materials for use in H2S-containing environments.
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