---
title: "Short note: properties of steel"
subject: "Civil Engineering Materials"
chapter: 8
key: "semester_3/civil_engineering_materials:properties-of-steel-note"
source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/properties-of-steel-note
site: BCT Engineering
---

# Short note: properties of steel

Civil Engineering Materials · Chapter 8: Metals and Alloys

- Asked in: 2070 Chaitra (old course), 4 marks
- Video: [Properties of Construction Materials - Station 1 Week 1](https://www.youtube.com/watch?v=HlMJQ8wi9GM) — Ahmed WA Hammad
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/properties-of-steel-note
- Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-8

## Question

Write a short note on properties of steel.

## Short answer

Steel is an iron–carbon alloy (≤1.5% C) with high tensile and compressive strength. Mild steel yields ~250 N/mm²; HYSD bars 415–500 N/mm². It is ductile, weldable at low carbon, elastic modulus ~2×10⁵ N/mm², density ~7850 kg/m³, and rusts unless protected.

## Answer

Steel is an alloy of iron and carbon (up to about 1.5% C) that is the most important structural material in construction. Its properties depend on the carbon content and heat treatment.

- **Strength:** High strength in both tension and compression. Mild steel has yield strength about 250 N/mm²; HYSD (Fe 415/500) bars have 415–500 N/mm².
- **Ductility:** Mild steel stretches a lot before failure, giving warning. Ductility falls as carbon increases.
- **Malleability and toughness:** It can be rolled, forged and bent into shapes, and absorbs energy well.
- **Hardness:** Increases with carbon content and by quenching.
- **Elasticity:** Modulus of elasticity about $2 \times 10^5$ N/mm², nearly constant for all grades.
- **Weldability:** Good in low-carbon steel; poor when carbon exceeds about 0.3%.
- **Density:** About 7850 kg/m³.
- **Fatigue resistance and homogeneity:** Uniform material with predictable behaviour.
- **Thermal and electrical conductivity:** Good conductor; loses strength above about 400–500 °C.
- **Corrosion:** Rusts in moist air unless protected by paint, galvanising or alloying.
- **Magnetic:** Ordinary steel is magnetic (stainless austenitic grades are not).
- **Recyclable.**

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which strength statement is correct?
   A. Steel is strong only in compression
   B. Steel is strong in tension and compression; mild steel yields at about 250 N/mm2, HYSD bars 415-500 N/mm2
   C. Mild steel yields at 5 N/mm2
   D. HYSD bars are weaker than mild steel
   Answer: B. HYSD (Fe 415/500) bars have higher yield strength than mild steel. (Key point: Strength)

2. As carbon content rises:
   A. Ductility and weldability increase
   B. Hardness increases, ductility falls and weldability becomes poor above about 0.3% C
   C. Hardness decreases
   D. Nothing changes
   Answer: B. Higher carbon makes steel harder but less ductile and harder to weld. (Key point: Effect of carbon)

3. Steel's modulus of elasticity and density are about:
   A. 2 x 10^5 N/mm2 and 7850 kg/m3
   B. 2 x 10^3 N/mm2 and 2700 kg/m3
   C. 10^5 N/mm2 and 7200 kg/m3
   D. 2 x 10^5 N/mm2 and 2700 kg/m3
   Answer: A. E is nearly constant for all grades. (Key point: Elastic modulus and density)

4. Which is true?
   A. Steel never rusts
   B. Steel rusts in moist air unless protected, and loses strength above about 400-500 C
   C. Steel is non-magnetic always
   D. Steel is a poor conductor
   Answer: B. Protection by paint, galvanising or alloying is needed; steel is magnetic except austenitic stainless. (Key point: Corrosion and heat)

## Related in Civil Engineering Materials

- [Importance and types of steel](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Aimportance-of-steel-types) — Civil Engineering Materials, chapter 8, asked 2×
- [Compare cast iron, steel, aluminium](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Acompare-cast-iron-steel-aluminium) — Civil Engineering Materials, chapter 8

## Related in other subjects

- [Cutting tool materials and their properties](https://www.bctengineer.com/question.md?key=semester_4%2Fmanufacturing_and_production_processes%3Acutting-tool-materials-characteristics-economics) — Manufacturing and Production Processes, chapter 7