---
title: "Plain carbon steel versus alloy steel"
subject: "Civil Engineering Materials"
chapter: 8
key: "semester_3/civil_engineering_materials:plain-carbon-vs-alloy-steel"
source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/plain-carbon-vs-alloy-steel
site: BCT Engineering
---

# Plain carbon steel versus alloy steel

Civil Engineering Materials · Chapter 8: Metals and Alloys

- Asked in: 2075 Asoj, 3 marks
- Video: [Types of steel, Steel types, Carbon steel, Alloy steel, Tool steel #ss #steel #alloy #engineering](https://www.youtube.com/watch?v=xaP0jaYoFvw) — Mechanical Engineering Management
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/plain-carbon-vs-alloy-steel
- Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-8

## Question

Distinguish between plain carbon steel and alloy steel.

## Short answer

Plain carbon steel contains iron and carbon up to 1.5% with moderate strength and poor corrosion resistance. Alloy steel has added Cr, Ni, etc., providing higher strength, deeper hardenability, and good corrosion resistance, but higher cost.

## Answer

| Point | Plain carbon steel | Alloy steel |
|---|---|---|
| Composition | Iron + carbon (up to 1.5%), small Mn, Si | Iron + carbon + added Cr, Ni, Mo, V, Mn, etc. |
| Strength | Moderate | Higher |
| Hardness / hardenability | Lower, shallow | Higher, deeper |
| Corrosion resistance | Poor | Good (stainless steel) |
| Heat/wear resistance | Low | High |
| Cost | Cheap | Costly |
| Weldability | Good at low carbon | Needs care |
| Uses | Rebars, general structures | Tools, high-rise frames, stainless items, machines |

## Check yourself

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

1. Plain carbon steel consists of:
   A. Iron + carbon (up to 1.5%) with small Mn, Si
   B. Iron + large amounts of Cr and Ni
   C. Only iron
   D. Iron + copper
   Answer: A. Alloy steel additionally has added Cr, Ni, Mo, V, Mn etc. (Key point: Composition)

2. Compared with plain carbon steel, alloy steel has:
   A. Shallower hardening and poor corrosion resistance
   B. Deeper hardening, higher strength and better corrosion and heat resistance
   C. Lower cost
   D. Better corrosion resistance but lower strength
   Answer: B. Alloying raises strength, hardenability, and corrosion, heat and wear resistance. (Key point: Hardenability and corrosion)

3. Which is correct?
   A. Plain carbon: tools, stainless items; alloy: rebars
   B. Plain carbon: rebars and general structures, cheap; alloy: tools, stainless items, machines, costly
   C. Both cost the same
   D. Alloy steel is always easier to weld
   Answer: B. Plain carbon steel is cheap and used for general work; alloy steel is costly and needs weld care. (Key point: Uses and cost)

## Related in Civil Engineering Materials

- [Function of carbon in steel](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Acarbon-function-in-steel) — Civil Engineering Materials, chapter 8, asked 2×
- [Modulus of toughness of medium carbon steel](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Anumerical-modulus-toughness-415) — Civil Engineering Materials, chapter 1
- [Phases in 0.80% carbon steel](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Acarbon-percent-0-80-phases) — Civil Engineering Materials, chapter 8
- [Phases in 0.33% carbon steel](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Acarbon-percent-0-33-phases) — Civil Engineering Materials, chapter 8
- [Phases in 0.35% carbon steel](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Acarbon-percent-0-35-phases) — Civil Engineering Materials, chapter 8
- [Cast iron versus steel](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Acast-iron-vs-steel) — Civil Engineering Materials, chapter 8, asked 2×

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