IS 432:1982 Part 1 is the Indian Standard (BIS) for mild steel and medium tensile steel bars and hard-drawn steel wire for concrete reinforcement - part 1: mild steel and medium tensile steel bars. This code specifies the manufacturing, chemical, and mechanical requirements for mild steel (Grade I and II) and medium tensile steel bars used as concrete reinforcement. While largely superseded in everyday practice by deformed TMT bars (IS 1786), it remains the active specification for plain Fe 250 reinforcement bars.
Specifies requirements for mild steel and medium tensile steel bars used as reinforcement in concrete, commonly superseded by IS 1786 for new designs.
Grade I (Fe250) and Grade II (Fe350) plain mild-steel and medium-tensile bars — yield, UTS, elongation, bend, mass tolerance and chemistry.
| Reference | Value | Clause |
|---|---|---|
| Grade I (mild steel) — yield stress (min) | 250 MPa (≤20 mm) / 240 MPa (>20–50 mm) | Cl. 5 (Table 1) |
| Grade II (medium tensile) — yield stress (min) | 350 MPa (≤20 mm) / 340 MPa (>20–50 mm) | Cl. 5 (Table 1) |
| Grade I — ultimate tensile strength (min) | 410 MPa | Cl. 5 (Table 1) |
| Grade II — ultimate tensile strength (min) | 540 MPa | Cl. 5 (Table 1) |
| Grade I — elongation (min, gauge 5.65√A) | 23 % | Cl. 5 (Table 1) |
| Grade II — elongation (min) | 20 % | Cl. 5 (Table 1) |
| Bend test — Grade I bars ≤25 mm | 180° around 2 φ mandrel | Cl. 6 (Table 2) |
| Bend test — Grade I bars >25 mm | 180° around 3 φ mandrel | Cl. 6 (Table 2) |
| Bend test — Grade II bars ≤25 mm | 180° around 3 φ mandrel | Cl. 6 (Table 2) |
| Bend test — Grade II bars >25 mm | 180° around 4 φ mandrel | Cl. 6 (Table 2) |
| Standard nominal sizes — plain round bars | 6, 8, 10, 12, 16, 20, 22, 25, 28, 32, 36, 40, 45, 50 mm | Cl. 4 (Table 3) |
| Mass tolerance — bars 6–10 mm | ± 7 % per length | Cl. 7 |
| Mass tolerance — bars 12–16 mm | ± 5 % | Cl. 7 |
| Mass tolerance — bars ≥20 mm | ± 3.5 % | Cl. 7 |
| Carbon (max) — Grade I | 0.23 % | Cl. 4 (Table 1) |
| Sulphur + Phosphorus (max) — Grade I | 0.055 % each (S ≤ 0.055, P ≤ 0.055) | Cl. 4 (Table 1) |
| Carbon (max) — Grade II | 0.25 % | Cl. 4 (Table 1) |
| Length tolerance — exact-length bars | ± 25 mm (typical) / +75, −25 over 12 m | Cl. 8 |
| Standard length — bars supplied | 5–13 m (typically 12 m) | Cl. 8 |
| Application — RCC use status | Largely superseded by IS 1786 HYSD/TMT for RCC | see IS 456 Cl. 5.6 |
IS 432 Part 1:1982 specifies mild steel and medium tensile steel bars for concrete reinforcement (Part 2 of the series covers hard-drawn steel wire). It is the legacy plain-round / medium-tensile reinforcement standard — the steel of older RCC structures, and still referenced for plain mild-steel bars used as stirrups in some details, dowels, lateral ties and fabrication, even though high-strength deformed IS 1786 TMT bars dominate new main reinforcement.
It is read with the RCC stack:
IS 432 Part 1 covers Grade I (mild steel) and Grade II (medium tensile steel) plain bars, defined by:
In IS 456 design these map to a characteristic strength fy = 250 N/mm² for mild steel — used with the appropriate partial safety factor and the longer plain-bar development length.
Scenario: 8 mm mild-steel (Fe 250) two-legged stirrups in a beam; check spacing and anchorage.
Step 1 — material: plain round bar to IS 432 Part 1 Grade I, fy = 250 N/mm².
Step 2 — shear design to IS 456: stirrup spacing s = 0.87·fy·Asv·d / Vus — note fy = 250 (not 500), so for the same steel area a mild-steel stirrup carries less shear than a TMT one; spacing comes out closer.
Step 3 — code limits: s ≤ 0.75 d and ≤ 300 mm (and tighter near supports / for ductile detailing).
Step 4 — anchorage: because the bar is plain, the stirrup must be closed with 135° hooks and adequate hook extension — plain bars rely on hooks/bends, not surface bond, to anchor.
Step 5 — BBS: cut/bend lengths per IS 2502, allowing the bend deductions. Mild steel's ductility makes it well-suited to tight stirrup bends.
1. Using fy = 415/500 for mild-steel bars. IS 432 mild steel is fy = 250; carrying over a TMT design value over-estimates capacity badly.
2. Plain-bar bond treated like deformed bond. Plain round bars have low bond — development/anchorage lengths are much longer and hooks/bends are mandatory; designing plain bars as if ribbed is unsafe.
3. Specifying IS 432 for modern main reinforcement. New structural main steel should be high-strength deformed to IS 1786; IS 432 is for stirrups/ties/dowels/legacy work, not economical main bars.
4. Skipping the bend/re-bend test. Brittle bars crack on bending — the IS 1599 bend test is the field guard, especially for stirrup fabrication.
5. Mixing grades on site without identification. Plain mild steel and ribbed TMT must be distinguishable and used per the drawing — substitution changes capacity and bond.
IS 432 Part 1 is largely superseded in practice by IS 1786 for main reinforcement — TMT Fe 500/Fe 500D is more economical and is what mills produce — but the code remains reaffirmed and relevant for plain mild-steel bars (stirrups in some practices, lateral ties, dowels, hold-fasts, fabrication and the assessment/retrofit of older RCC built with Fe 250).
The practitioner discipline is twofold: when assessing or extending an existing structure, identify the original steel — if it is IS 432 plain mild steel, design with fy = 250 and long plain-bar anchorage with hooks, not modern TMT values; and for new work, don't specify plain mild bars for main steel on cost/availability grounds. Mild steel's high ductility is genuinely useful for tight stirrup bends and energy-dissipating secondary detailing — that is where it still earns its place.
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Minimum Yield Strength (Mild Steel Grade) | 250 MPa (for Grade I / Fe 250) | 250 MPa (for Grade R250N) | AS/NZS 4671:2019 |
| Minimum Ultimate Tensile Strength (UTS) | 410 MPa (for Grade I / Fe 250) | 420 MPa (for Grade 40 [280]) | ASTM A615/A615M-22 |
| Minimum Elongation (on 5.65√A gauge length) | 23% (for Grade I / Fe 250) | 22% (for Grade RB300) | ISO 6935-1:2019 |
| Maximum Carbon (C) Content (Ladle Analysis) | 0.25% (for Grade I) | 0.24% (for Grade RB300) | ISO 6935-1:2019 |
| Maximum Sulphur (S) Content | 0.055% | 0.050% | ISO 6935-1:2019 |
| Maximum Phosphorus (P) Content | 0.055% | 0.050% | ISO 6935-1:2019 |
| Bend Test Mandrel Diameter (for bar Ø ≤ 20mm) | 2d (where d = nominal diameter) | 3d (for Grade 40 [280], bar Ø ≤ 16mm) | ASTM A615/A615M-22 |