We may not spend much time pondering how dense a substance is, but metallurgists and engineers probably think about density more than most consumers realize.
The density of an object determines whether it will float or sink. Do you know why a tiny pebble will drop to the bottom of a glass of water while a giant log will float on the surface of a river? Density. The pebble is more dense than the water while the tree is less dense.
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Like the pebble, steel is also more dense than water, but ships crafted from tons of steel carry cargo and passengers on top of the ocean all the time. How does density explain that? And why are we discussing density anyway?
As researchers have learned more about density, they’ve also discovered how to harness the concept in order to advance technology. To return to the example of the ship, we know that the air inside the vessel’s buoyancy chambers is less dense than the water below it. That’s why a steel ship floats — and a steel submarine sinks.
Density matters to manufacturers because it’s linked to a product’s mass and volume. These factors together determine size and buoyancy, which affect a metal product’s transportation, weight, and usefulness in a given environment.
What is density?
In general terms, the word density refers to the amount of something within a defined space. When we say Manhattan is densely populated, we mean that a lot of people live inside the borough’s limits.
More scientifically, density is defined as mass per unit volume. Expressed algebraically, the formula looks like this:
In this calculation, density (p) equals mass (m) divided by volume (V).
Density is also an intensive property, which means that the density of an object never changes no matter how much of it is present.
Consider the old question: Which weighs more, a ton of bricks or a ton of feathers? The answer, of course, is that both weigh the same — one ton. The power of the joke lies in the concept of density not weight. A brick’s density is 1.992 grams per cubic centimeter while a feather’s density is about 0.0025 grams per cubic centimeter. That’s why one square inch of brick weighs more than one square inch of feathers, about 800 times more in fact.
Speaking of units of measure, density can be measured in kilograms per meter cubed (kg/m3), grams per centimeter cubed (g/cm3), grams per meter cubed (g/m3), or pounds per inches cubed (lb/in3). To calculate the density of a stainless steel object or to convert density from one unit of measure to another, you can our metal calculator to calculate the weight and density of stainless steel.
Why does density matter?
Industrial designers include several factors about metal when they develop their concepts. Density is one of those factors. One metal may be much more dense than another. If you’re designing a lamp to sit on a table, for instance, the density of the material used may not matter much. If you are designing an airplane that has to get off the ground and stay in the air, density suddenly becomes very important indeed.
Density also matters when metallurgists blend one metal with another to make an alloy. Steel is an alloy of iron, carbon, and other chemicals. Different types of steel are composed of various blends of chemical elements. Stainless steel, for example, contains at least 10.5% chromium while carbon steel has a lower chromium content. Consequently, the density of plain steel is slightly different from the density of stainless steel.
When creating a new grade of steel or welding one kind of steel to another, density affects the strength, hardness, and malleability of the material produced.
By comparison to many other metals, steel is an extremely dense material. Titanium, for instance, has a density about half that of steel, and aluminum has about one-third the density.
Plain steel’s density is about 490 pounds per cubic foot, which can also be expressed as 7.85 g/cm3. Carbon steel’s density is about 7.84 g/cm3, pure iron’s density is around 7.86 g/cm3, and stainless steel’s is about 8.03 g/cm3. The particular grade and chemical composition of the steel makes its density vary slightly.
Stainless steel is the most dense variety of steel, but how does density vary among the different types of stainless steel?
Let’s look at the two most commonly used grades of stainless steel — 304 stainless steel and 316 stainless steel. The density of grade 304 stands at 7930 kg/m3 while the density of grade 316 is about 7980 kg/m3. The two grades’ different chemical composition and content determine the difference in their densities. Stainless steel 304 is less dense than 316, but has slightly higher density than stainless steel 430 at 7750 g/m3.
Density affects weight. (Remember the example of the bricks and feathers?) Thus, a stainless steel item weighs more than a carbon steel item of the exact same size, and a grade 316 stainless steel product weighs more than the same product made with grade 304 stainless steel.
In general, however, one cubic foot of stainless steel weighs about 490 pounds.
How to use your knowledge of density while selecting materials
What should you keep in mind about density when choosing material for fabrication or construction?
Consider several factors when determining the metal that’s right for your project. You should think about both the physical properties of the metal — its melting point, conductivity, and (yes) its density. You should also consider its mechanical properties such as strength, ductility, and resistance.
When crafting their inventions, engineers weigh the relative benefits of each property as they determine what materials should compose their new product.
Density is particularly important to projects where weight is a critical consideration. Engineers will try to find a low density product if they need to control an object’s weight. That said, they also have to consider strength-to-weight ratio so the product’s material is strong enough to do the job.
A highly dense alloy such as steel is much stronger than many other metals. And since stainless steel is also corrosion resistant and attractive to the eye, it’s the popular choice for everything from kitchenware to surgical supplies.
Due to stainless steel’s high relative strength ratio, engineers can use thinner versions of the material to fashion various products. That’s why a surgical blade can be micro-thin and simultaneously very strong.
To learn more about stainless steel’s composition and uses, visit other articles on our site.
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Natalie Spira is Kloeckner's Acquisition Marketing Manager. Previously, she was the Founder and CEO of Fraction Marketing, a marketing agency providing fractional support to scaling startups with a focus on acquisition marketing and demand generation. Natalie holds a MBA from Tel Aviv University with concentrations in entrepreneurship and marketing and a BA in English from UCLA.