Machining aspects of alloy steel
There is no scientific definition, but in practice, alloy steels are carbon steels with additional alloying elements (on top of the carbon and Manganese) of up to 5%. These elements are added to improve the strength, toughness, corrosion resistance, wear resistance, hardenability, and the steel’s hot hardness.
Table of Contents
Introduction
The simplest and cheapest form of steel used in mechanical components is carbon steel. For various general-purpose components, it is good enough; however, in many cases, for a mechanical part to function, it needs specific properties such as wear resistance, strength, hardness, hot hardness, etc.
Thankfully, adding certain alloying elements to carbon steel yields alloys with better mechanical and metallurgical characteristics.
Don’t forget the Carbon!
Don’t forget the Carbon!
As important as all these alloying elements are, Carbon content is still the primary factor determining steel mechanical properties and machinability. Therefore, before you dive into this article, we recommend you be familiar with our article about carbon steel.
Classification System
The most common classification system for alloy steel is the ASTM/SAE system based on a 4 digits format.
For example: 4340, 5132, and 8630.
- Digit 1 – Series number and Main classification. For example, 3xxx is a series of
Alloy steel serieses
| Series (SAE/ASTM) | Description | Molybdenum | Chromium | Nickel | Tungsten | Silicon | Vanadium | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1xxx | Plain Carbon Steel - More details in a Separate Article | |||||||||||||
| 2xxx | Nickel Steel | 3.5-5.0% | ||||||||||||
| 3xxx | Nickel-Chromium Steel | 0.6-1.6% | 1.2-3.0% | |||||||||||
| 4xxx | For 4xxx series see details in the Below Table | |||||||||||||
| 5xxx | Chromium Steel | 0.5-1.5% | ||||||||||||
| 6xxx | Chromium-Vanadium Steel | 0.6-0.9% | 0.1-0.15% | |||||||||||
| 7xxx | Tungsten-Chromium Steel | 0.7-0.8% | 1.7-1.8% | |||||||||||
| 8xxx | Nickel-Chromium-Molybdenum Steel | 0.1-0.4% | 0.4-0.5% | 0.3-0.6 | ||||||||||
| 92xx | Silicon-Chromium Steel | 0.6-0.7% | 1.4-2.0% | |||||||||||
| 93xx-98XX | Nickel-Chromium-Molybdenum Steel | 0.1-0.25 | 0.2-1.2% | 0.5-3.3% | ||||||||||
4xxx Series
The 4xxx is the most common alloy steel in machine shops and it has seven sub-serieses
| Series (SAE/ASTM) | Description | Molybdenum | Chromium | Nickel | ||||
|---|---|---|---|---|---|---|---|---|
| 40xx | Molybdenum steel | 0.2-0.5% | ||||||
| 41xx | Chromium-molybdenum Steel | 0.1-0.3% | 0.4-0.6% | |||||
| 43xx | Nickel-chromium-molybdenum steel | 0.2-0.3% | 0.5-0.8% | 1.7-1.9% | ||||
| 44xx | Molybdenum steel | 0.4-0.5% | ||||||
| 46xx | Nickel-molybdenum steel | 0.2-0.3% | 0.9-1.8% | |||||
| 47xx | Nickel-chromium-molybdenum steel | 0.2-0.3% | 0.4-0.5% | 1.0-1.1% | ||||
| 48xx | Nickel-molybdenum steel | 0.2-0.3% | 3.4-3.6% | |||||
Alloying elements
- Important note: The information below refers to the addition of alloying elements in small quantities relevant to alloy steel only! The same alloying elements can have a completely different effect when added in higher doses. For example, when adding chromium and nickel in higher quantities, the steel becomes austenitic stainless steel. Check out our separate article to learn about the broader effects of Alloying Elements
Alloying elemnts effects on machining and material properties
| Alloying Element | Effect on Properties | Effect on Machining | ||
|---|---|---|---|---|
| Molybdenium [Mo] |
Improves:
Damages:
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| Chromium [Cr] |
Improves:
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| Nickel [Ni] |
Improves:
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| Tungsten [W] |
Improves:
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| Silicon [Si] |
Improves:
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| Vanadium [V] |
Improves:
Damages: |
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