16HG: Polish case-hardening steel, today 16MnCr5
16HG is a Polish alloy case-hardening steel to PN-89/H-84030/02. Its modern equivalent is 16MnCr5 (1.7131) to EN 10084 and ISO 683-3; on the AISI/SAE side 5115, on the GOST side 18ХГ. It is not a structural steel: it goes into gears, shafts and pins that are carburised and hardened afterwards.
Short answer
The 16HG equivalent is 16MnCr5, 1.7131. Weldability is limited: CE (IIW) from the composition limits runs from 0.47 to 0.63, so preheat and low-hydrogen electrodes are needed. It is welded before carburising, or as a repair, but not over a carburised and hardened case.
Grade card
| Designation and standard | 16HG · PN-89/H-84030/02 |
|---|---|
| Closest equivalent | 16MnCr5 (EN 10084 / ISO 683-3) |
| Material number | 1.7131 |
| GOST | 18ХГ |
| AISI / ASTM | 5115 |
| PN | 16HG |
| ISO/TR 15608 group | 5.1 — vanadium-free Cr steel, C ≤ 0.35 %, 0.75 ≤ Cr ≤ 1.5 %, Mo ≤ 0.7 % (Table 1 criteria, 2013 edition) |
| Weldability (equivalents table) | limited, preheat usually needed |
The EN, GOST, AISI/ASTM and PN rows come from the steel grade equivalents table. An equivalent is the closest grade, not an identical one.
In the PN name, 16 is carbon in hundredths of a per cent, H chromium and G manganese. After carburising and hardening the core stays tough and the surface turns hard. Properties depend on that treatment, so for case-hardening steels the standards give mainly chemistry and hardenability rather than a single yield strength.
16HG chemical composition, % by mass
| Element | 16MnCr5 (16HG) |
|---|---|
| C | 0.14–0.19 |
| Mn | 1.00–1.30 |
| Si | ≤ 0.40 |
| S | ≤ 0.035 |
| Cr | 0.80–1.10 |
Source: steeldata (EN 10084), Global Steel Wire (ISO 683-3), Total Materia (PN-H-84030-02: C, Cr).
Phosphorus is left out: the datasheets give 0.025 % or 0.035 % (different editions of the standard). Check it on the certificate.
There is no mechanical property table here on purpose: for case-hardening steels those depend on heat treatment and section size, not on the grade alone. Take design values from the certificate or the drawing.
Carbon equivalent: CE, CET and the CEV limit
| Value | Formula | Result | Basis |
|---|---|---|---|
| CE (IIW) | C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15 | 0.63 | upper composition limits from the table |
| CE (IIW) | C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15 | 0.47 | lower composition limits from the table |
| CET | C + (Mn+Mo)/10 + (Cr+Cu)/20 + Ni/40 | 0.38 | upper composition limits from the table |
| CET | C + (Mn+Mo)/10 + (Cr+Cu)/20 + Ni/40 | 0.28 | lower composition limits from the table |
From the upper composition limits, CE falls in the calculator band: Poor — Preheat 200–350 °C, keep it warm while welding, stress relief afterwards.
The "lower limits" rows are a heat at the bottom of the composition range, "upper limits" one at the top. Even the lower result is above 0.40, so low-hydrogen electrodes are a must. The preheat table below uses the EN 1011-2 formula with CET, as the calculator does.
Enter the analysis from your mill certificate in the carbon equivalent calculator: the link opens it with the composition limits from this page, ready to overwrite.
Preheat and interpass temperature
| d, mm | CET 0.28 (lower limits) · HD 4, °C | CET 0.38 (upper limits) · HD 4, °C | CET 0.38 (upper limits) · HD 12, °C |
|---|---|---|---|
| 10 | — | 65 | 110 |
| 20 | 25 | 100 | 150 |
| 30 | 55 | 130 | 175 |
| 40 | 75 | 150 | 195 |
| 60 | 95 | 170 | 215 |
EN 1011-2, Annex C, method B, the same formula as the preheat calculator: heat input 1.5 kJ/mm, result rounded up to 5 °C, "—" means no preheat is needed. HD 4 — basic electrodes and solid wire, HD 12 — rutile electrodes.
Work out your own CET, thickness and hydrogen in the preheat calculator (the link opens it with the CET from the upper composition limits).
Interpass: from the preheat up to 250 °C, as in the calculator. After welding, cool the part slowly so the heat-affected zone does not harden to brittle martensite; on heavy sections the tempering step is set by the heat-treatment engineer.
Filler metal
| Process | Filler | Gas |
|---|---|---|
| 111 — stick (MMA) | E 42 4 B 42 H5 — Lincoln Basic 7018, ESAB OK 48.00 | — |
| 135 — MAG, solid wire | G3Si1 / ER70S-6 | Ar + 15–20 % CO₂ |
An ordinary basic electrode deposit has no chromium, so after carburising and hardening it will not reach the hardness of the parent metal. If the weld is to go through heat treatment with the part, agree the filler with the heat-treatment engineer; for repairs and joints to structural steel the low-hydrogen filler in the table is enough.
How to weld it
- Weld in the soft condition, before carburising.
- Grind off the carburised case in the weld area if the part has already been treated — otherwise a hard, brittle band forms under the weld.
- Preheat from the table or the preheat calculator with the CET from the certificate, held until welding is finished.
- Redried basic electrodes, hydrogen at HD 5 ml/100 g or lower.
- Slow cooling after welding.
Substituting the equivalent: what changes in the paperwork
16MnCr5 is a direct chemistry equivalent of 16HG. Swapping to a structural steel (S235, S355) to make welding easier changes the part: such a steel will not carburise and harden to the same result. That decision is the designer's.
In the WPS, write 16MnCr5 and ISO/TR 15608 group 5.1, and check that the qualified procedure covers that group: a procedure qualified on group 1 structural steel does not.
Where the figures come from
- steeldata, 16MnCr5 (1.7131)
- Global Steel Wire, 16MnCr5 (ISO 683-3)
- Total Materia, PN 16HG
- ISO/TR 15608:2013, tab. 1 (later ISO/TR 15608:2017; replaced by ISO 15608:2025)
Figures from distributor and manufacturer datasheets are for information; for a given delivery, the EN 10204 3.1 certificate decides. CE, CET and preheat are calculated when the page is shown, with the same formulas as the calculators.
Frequently asked questions
What is the equivalent of 16HG?
16MnCr5, material number 1.7131 (EN 10084, ISO 683-3); AISI/SAE 5115, GOST 18ХГ. They are case-hardening steels with about 1 % chromium and manganese.
Is 16HG weldable?
Yes, with limits. CE (IIW) from the composition limits is 0.47–0.63: preheat and low-hydrogen electrodes are needed. It is welded before carburising; if the part has been carburised and hardened, the case is ground off the weld area first.
What is the composition of 16HG (16MnCr5)?
C 0.14–0.19 %, Mn 1.00–1.30 %, Si up to 0.40 %, Cr 0.80–1.10 %, S up to 0.035 % (steeldata, ISO 683-3 datasheet). The phosphorus limit differs between datasheets (0.025 or 0.035 %), so check it on the certificate.
What preheat for 16HG?
From the EN 1011-2 formula with CET 0.38 (upper composition limits), basic electrodes HD 4 and 1.5 kJ/mm: 100 °C at 20 mm and 150 °C at 40 mm. At the lower limits (CET 0.28) it comes to 25 °C and 75 °C.
Which ISO/TR 15608 group is 16MnCr5?
By the Table 1 criteria of the 2013 edition, 5.1: vanadium-free Cr-Mo steels with C up to 0.35 %, Cr 0.75–1.5 % and Mo up to 0.7 %. 16MnCr5 has no molybdenum, which the "Mo up to 0.7 %" criterion allows.
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