Why Do Razor Blades Get Dull So Quickly?

Some work-from-homers may have abandoned daily shaving in recent months, but who wouldn’t want a longer-lasting razor? Multiblade cartridges usually last only a week or two before they begin to grab at the skin, then get tossed in the garbage. But what if someone could invent a razor that stays sharp for six months, or even a year?

That’s the thinking behind a recent experiment by researchers at the Massachusetts Institute of Technology, who tried to find out why steel razor blades go dull so quickly, especially when they are just cutting soft human hair. By observing and recording the cutting process under a scanning electron microscope, the team noticed that the hairs created small chips in the blade surface. These microscopic chips wreck the blade’s ability to cut hair, according to Cem Tasan, professor of materials science at MIT and an author on the study published today in the journal Science, a finding that nobody expected.
“We want to design new materials that are better and go longer,” says Tasan. “This problem of the blade is an excellent example. We are so used to it, you don’t think about it. You use the razor for a few weeks and then move on.”Tasan says razor blades are made of martensitic steels, some of the toughest materials known to mankind. Martensitic steel (named for a 19th-century German metallurgist) is a super-hard alloy, honed through heat and tempering, that is used in commercial razors, surgical instruments, ball bearings, and bicycle disc brakes. What Tasan and his colleagues found is that, despite this strength, the blades fatigued rather quickly after multiple shaves.
Tasan and graduate student Gianluca Roscioli devised an experiment to examine the progress of wear and tear on a blade after each shave. After examining several different commercial razors, the team found that they all were made from a similar hardened steel-carbide alloy. Because the materials were similar, the experiment used only one brand of razor.Roscioli shaved every three days for a month with the same razor, then brought it into the Cambridge lab. The researchers set up a device to take images of the blades under the microscope, which bounces a beam of electrons off the surface to gain information about the blades’ molecular structure.

“Our initial thought was that this was a wear problem, that material was being removed from the razor,” Tasan says. “We were expecting to see that over time the blade gets rounder and rounder. We didn’t see it.”

Instead, he continues, “we saw fracturing and chipping of the blade that is forming this C-shaped crack.”

This video shows how the tiny chips form in the blade after slicing through human hair.

Tasan says commercial disposable razors—those marketed to both men and women—typically use the same type of steel but have different coatings and numbers of blades in the cartridge. (Razors marketed to men and women are similar except for handle design and the number of blades. Single-blade razors, often sold to women, don’t stay sharp as long as multiblade shavers, says Tasan.)