The great debate? Is stainless steel best classified as a ferrous or a nonferrous metal? The answer isn't so simple

Recycling Today, July, 2002 by DeAnne Toto

Some things can't be neatly classified, such as that jock from your English lit class who wore sweater vests, listened to Devo and Loretta Lynn and knew everything there was to know about Fellini. He moved from clique to clique; and while he wasn't rejected, he wasn't completely accepted either because no one could quite figure him out. In high school, where stereotypes reign, someone who doesn't fall neatly into a clique tends to puzzle his classmates.

Stainless steel can elicit the same sort of befuddlement. Until asked the question, "Is stainless steel a ferrous or a nonferrous metal," you probably never gave it much thought. But once confronted with the question, you may begin to realize a lot of factors have to be considered before answering. And some may ask: Is the question ultimately even important?

DEFINING CHARACTERISTICS

According to the Specialty Steel Institute of North America (SSINA), [Web site www.ssina.com], stainless steel is a low carbon steel containing chromium levels of 10 percent or more by weight, while the carbon content is less than one percent.

Stainless steel is available in more than 60 grades, which are divided among five classes defined by the alloying elements.

Basic stainless steel, or maretensitic, contains 12 percent to 18 percent chromium, according to the SSINA. These stainless steels are magnetic, hardened by heat treatment and have poor welding characteristics and often are used in knife blades and surgical instruments. The grades include 410, 420 and 440C.

Ferritic stainless steels contain less than 0.2 percent carbon, though their chromium content remains in the range of 12 percent to 18 percent. Ferritic grades are magnetic, though they are not heat-hardened, and are used in automotive exhaust lines, architectural trim and cooking utensils, according to the SSINA. Grades include 409 and 430.

Austenitic stainless steels contain nickel as well as a higher chromium level. These grades are not magnetic, are hardened by cold working, are highly corrosion resistant and are easily welded. Austenitic grades, such as 304, 310, 316 and 317, are used in roofs and gutters, kitchen sinks and chemical vessels, according to the SSINA.

Duplex stainless steels have chromium content in the 18 percent to 26 percent range, with nickel ranging from four percent to seven percent. According to the SSINA, most grades also contain two percent to three percent molybdenum. These grades are weldable. They are highly resistant to stress corrosion cracking and higher tensile and yield strengths than ferritic and austenitic grades and are used in heat exchangers and food pickling plants. A popular grade is 2205.

How would you define stainless steel? Are you not so sure after the introductory science lesson? Keep reading, but I can't promise you things will get any clearer.

ONE OR THE OTHER

Gerry Stewart, executive vice president of ELG Metals, McKeesport, Pa., says without hesitation, "I consider it a ferrous grade. The benchmark grade, 304, is 75 percent ferrous. In the ferritic grades, the ferrous content can be as high as 85 percent to almost 90 percent."

Bill Heenan of the Steel Recycling Institute, Pittsburgh, agrees. "Anywhere from 70 percent of stainless steel typically is iron. If it's iron, how can it be anything but ferrous?

Chalk up another vote on the ferrous side from Michael Marley, secondary metals editor for American Metal Market, Philadelphia, who also says iron's predominance in the metallurgy qualifies stainless steel as a ferrous metal.

"Most of the guys who are the consumers from my perspective tend to be members or the steel industry or are to be found on the steel industry side," Marley says. He adds that the stainless steel production process is similar to electric arc furnace steel production. "They may require some additional secondary treatment depending on whether it's a argon-oxygen decarburisation process that they are using or just some form of ladle metallurgy which most steel companies use now whether producing stainless or carbon steels."

Heenan says the biggest factor in classifying stainless steel as a ferrous metal is its consumption of about two million tons of steel scrap every year. "Now, that's not much considering the 60-plus million tons ... that the carbon steel industry [consumes]."

Randy Castriota of Castriota Metals & Recycling, Pittsburgh, says he considers stainless steel to be nonferrous, though the question caught him off guard. "Most of the nonferrous metals are nonmagnetic, such as copper, brass, aluminum, and most of--I'm not sure on a percentage basis--of stainless is nonmagnetic." In scrap yards, stainless steel is almost never placed in the same pile as scrap iron and carbon steel.

Stewart says, "The national association ISRI (Institute for Scrap Recycling Industries Inc., Washington) has two categories: nonferrous and ferrous. It's always very confusing where we fit as stainless processors."

Marley has found little consensus on the topic among members of the industry. "I've talked to guys who consider it a nonferrous metal in part because of the nickel being such a significant driver or the price--primary nickel price, anyway--which is their focus and their interest they way they see it."