Alloy Steel Vs Stainless Steel: A Comprehensive Guide

The debate on alloy steel vs stainless steel has been ongoing for years. Some people consider alloy steel to be a supertype of steel. On the flip side, many manufacturers convince their customers to use stainless steel. Both of these steel types have their unique perks. 

 

Those perks make their selection process very confusing and tedious. That’s where this article will help you. I know that both alloy and stainless steel are excellent in their way. However, this article will go into the nitty gritty of these alloys. I will aim to help you know their actual value. So, let’s get started!

 

Overview of Alloy Steel & Stainless Steel

Alloy steel is a mixture of alloy elements, such as chromium, nickel, and vanadium. The stainless steel is a subtype of alloy steel with at least 10.5% chromium. Alloy steel is generally very robust and challenging. The stainless steel stands out due to its rust resistance.

 

Remember, steel consists of two primary elements: iron and carbon. Both of these alloys use these elements. Along with iron and carbon, they consist of other elements. These additional elements are added to enhance the properties of these alloys. Alloy steel consists of chromium, nickel, vanadium, and manganese.

 

The portion of chromium is what differentiates alloy steel from stainless steel. All the stainless steels will have at least 10.5% of chromium. On the flip side, alloy steels don’t have this high level of chromium. Remember, high chromium is responsible for better corrosion resistance in stainless steel. 

 

Remember, these alloys are made artificially by adding alloy elements. Both of them came into existence in the 19th century. They both are used in various industries, including aerospace and construction. However, stainless steel, being more rust-resistant, is considered premium and very expensive.

 

Differences Between Alloy Steel and Stainless Steel

 

In the section above, I discussed the basics of these steel alloys. As said above, these alloys vary from each other in many ways. Let’s dive deeper and discuss each of the factors that differentiate them.

 

1- Composition

 

First, alloy steel and stainless steel contain iron and carbon. Along with these two, they also consist of many other alloy elements. The ratio of those alloy elements is what makes a difference. The stainless steel contains more than 10.5% of chromium. Conversely, the alloy steel contains a very low proportion of chromium. 

 

Here is a table showing the composition of both of these alloys:

 

Element	Alloy Steel (%)	Stainless Steel (%)
Iron (Fe)	90–98%	65–80%
Carbon (C)	0.1–2%	0.03–1.2%
Chromium (Cr)	0.3–12%	10.5–30%
Nickel (Ni)	1–5%	8–20%
Manganese (Mn)	0.5–2%	1–2%
Molybdenum (Mo)	0.2–1%	0.2–3%
Silicon (Si)	0.2–1%	0.5–2%

 

Looking at the table, you will notice that these alloys have the same alloy elements. However, the ratio and percentage of those alloy elements vary. Due to higher chromium, stainless steel is considered superior to alloy steel. 

 

2- Corrosion Resistance

Corrosion is a big problem that manufacturers face. It kills the durability and look of the different products. Therefore, manufacturers prefer using stainless steel when rustproofing is essential. The reason is that stainless steel contains a higher proportion of chromium.

 

Chromium makes a thin oxide layer when it comes in contact with oxygen. This layer is a chromium oxide layer and plays a key role in rust protection. On the flipside, the alloy steel has a lower proportion of chromium. So, it does not make a strong chromium oxide layer that could promote rust protection.

 

You’ll never see stainless steel products getting rusty quickly. The chromium oxide layer remains in good shape for many years. So, it keeps protecting itself. The alloy steel is also decent as small chromium is also present in that alloy. However, stainless steel wins as it has more than 10.5% of chromium quantity.

 

Quick Highlight: The stainless steel looks shiny, matte, and polished. On the contrary, alloy steel looks dim and dull. The reason behind this difference is also the chromium oxide layer. This layer makes stainless steel look more shiny and aesthetically pleasing. The lack of potent chromium oxide makes alloy steel look dull.

 

3- Tensile Strength 

 

Tensile strength indicates the force that material can bear before breaking. Materials that have higher tensile strength are generally more robust. The alloy steel has a tensile strength of around 800 to 1800 MPa. This means this material can bear a maximum of 1800 MPa of stress before breaking.

 

On the other hand, stainless steel can only bear a force of around 512 to 800 MPa. It indicates that stainless steel is compromised in terms of tensile strength. The alloy steel is suitable for applications where the material bears stress. Stainless steel cannot perform well in such a scenario.

 

4- Types & Versatility

Both of these steel alloys are very versatile and have different types. For example, alloy steel has four basic types, which are as follows:

 

• Low alloy steel
• High alloy steel

 

The low alloy steel has an alloy element below 5%. This type is very popular due to its excellent weight-to-strength ratio. Conversely, the high alloy steel uses a greater (above 5%) concentration of alloy elements. The standard alloy elements include vanadium, chromium, nickel, manganese, and molybdenum.

 

Similar to alloy steel, stainless steel also has four main types. These types vary from each other in terms of chromium content. Types with a higher chromium percentage are more corrosion-resistant and vice versa. The names of those types and their composition are as follows:

 

Type Name	Composition Ratio
Austenitic	Chromium: 16–30%, Nickel: 6–20%
Ferritic	Chromium: 11–27%, Nickel: 0–1%
Martensitic	Chromium: 14–18%, Nickel: Low to None, Carbon: 0.2–1.2%
Duplex	Chromium: 18–28%, Nickel: 3.5–5.5%

 

Austenitic stainless steel has the highest proportion of chromium. Therefore, it offers excellent rust protection. Generally, this type is used to make products used in harsh outdoor conditions. Duplex is considered the most challenging and least brittle. It does not break easily, even if you hit it with anything. 

 

5- Fatigue Strength & Impact Resistance

 

Both fatigue strength and impact resistance are essential parameters. Let’s understand each of these parameters before going into details. The fatigue strength of the material indicates its ability to bear repeated stress or load. This load is usually applied cyclically. On the flip side, impact resistance means the ability of a material to bear the sudden load.

 

I consider both alloy steel and stainless steel equally good in these aspects. If we look critically, alloy steel is better in terms of fatigue resistance. Austenitic stainless steel is significantly compromised in this regard. However, martensitic and duplexes offer optimal performance. 

 

The impact resistance is always better in a more ductile material. All the alloy steel shows excellent ductility. It means they have top-notch impact resistance. The austenitic stainless is also ductile and has higher impact resistance. Duplex stainless steel is more brittle and less ductile. Its impact resistance is very compromised.

 

6- Heat Treatment and Fabrication

 

Manufacturers pass these alloys under heat treatment and different fabrication processes. Interestingly, both of these alloys can easily undergo those processes. Manufacturers put them under those processes to enhance their properties. The famous process is as follows:

 

• Weldability
• Formability
• Machinability

 

Both of these two types support all these processes. However, how easily an alloy goes through the process can vary. For example, austenitic stainless steel’s machinability is easier than duplex. Why? Because austenitic stainless steel is ductile, and machine tools can work on it. On the flip side, the duplex stainless is very brittle.

 

Machining duplex stainless steel may require specialized tools due to their brittle nature. Similarly, both types of these alloys can undergo a welding process. However, the high alloy steel types may require special attention during the process. Likewise, stainless steel undergoes a welding process. However, the ease of weldability is higher in austenitic than in other types.

 

7- Lifespan & Aesthetic Preferences

 

As I said earlier, stainless steel is excellent in rust protection. It contains a higher quantity of chromium. This chromium reacts with oxygen and makes a chromium oxide layer, which acts as a shield. So, rust and other environmental factors cannot affect the quality of this material. So, products made with stainless steel have a long life.

 

Chromium oxide is not handy just for protecting the product against rust. Instead, it plays a key role in enhancing the look and aesthetics of a product. The chromium oxide layer on the surface gives the product a shiny and more polished look. Therefore, I recommend choosing stainless steel when aesthetics are your preference.

 

8- Cost & Applications

 

The cost of materials is an essential factor everyone considers before choosing it. Right? Stainless steel is a more precious and costly material. However, it offers excellent rust protection, which is a big plus. On the flip side, alloy steel is inexpensive but has compromised rustproofing. You’ll have to apply additional coating or paint to make their product rustproof.

 

However, you get high tensile strength and fatigue resistance of alloy steel. It means compromised rustproofing doesn’t stop people from using alloy steel. It ultimately comes down to individual choices and decisions. Both of these steel alloys have their unique value proportions. Stainless steel is premium mainly due to rust protection.

 

Here is the table showing the application of alloy steel and stainless steel:

 

Application Area	Alloy Steel	Stainless Steel
Automotive Industry	Gears, shafts, crankshafts, springs	Exhaust systems, fuel tanks, and body panels
Aerospace Industry	Aircraft components, turbine blades.	Aircraft parts and fuel tanks due to better corrosion resistance
Construction	Beams, columns, reinforcement bars	Corrosion-resistant fixtures, railings
Marine Applications	Ship propellers	Boat fittings and underwater structures
Energy Sector	Power plant components, turbines, and reactors	Oil rigs, nuclear power plants, and wind turbines

 

Stainless steel is also used to make cookware and medical instruments. The primary reason behind making cookware is its high temperature-bearing ability. Similarly, the higher-strength alloy steel makes them perfect for creating different tools. Remember, both of these steel alloys are very diverse. You’ll see them used in almost every industry to meet their needs.

 

Frequently Asked Questions

 

What is better, alloy steel or stainless steel?

I consider stainless steel a superior option due to its rustproofing. Its durability and strength are also optimal. Moreover, it has a high tempering bearing ability. Last but not least, products made of stainless steel look aesthetically pleasing. 

 

Is alloy steel rustproof?

It depends on the alloy steel types. Generally, they have lower chromium concentration, and their corrosion resistance is compromised. You might need additional treatment, such as painting, to make your product rustproof.

 

Alloy steel vs stainless steel: which is suitable for making knives?

Stainless steel is a better option for manufacturing knives. It will make the knife corrosion-resistant and very sharp and shiny. Additionally, the knife will be easy to clean and have better longevity.

 

Conclusion

 

Deciding which material you should use depends on many factors. I recommend analyzing your needs and then making a final call. Do you need rustproofing? If so, stainless steel is the best option. If you can compromise on rustproofing, alloy steel may be a fit. Remember, stainless steel material comes with a higher cost and perks. It can be a big drawback if you want to keep product prices low.