Fueled by the automotive industry’s desire to improve crash protection while reducing vehicle weight and increasing fuel economy, the steel industry has been highly successful at developing new high-strength and advanced-high-strength steels over the past two decades. Those alloys are steadily finding applications outside the automotive sector and working their way into service center inventories. But this new generation of steel calls for a new generation of processing equipment.

“It’s a trend that’s catching on. If they see it in the automotive area, it’s only a matter of time before it’s wanted in appliance, heavy truck, heavy equipment or agriculture,” says Tom Bell, vice president of business development for Bohler-Uddeholm Corp., Elgin, Ill. “Anytime a part can be made thinner and stronger, there’s an advantage to that. It will certainly catch on.”

For service center operators, the market appeal of the material is offset somewhat by the challenges it poses in processing. While those challenges are significant, experts say, they can be managed.

Though high-strength steel is not a brand new concept, there remains much uncertainty about leveling, slitting and shearing the stronger steels, says Eric Theis, who spent 30 years in the equipment-manufacturing sector before becoming a consultant to the metals industry. “I’m making a living answering those questions.”

When mild steel was the common option, with a 60,000 psi tensile strength and 40,000 yield, running a leveler was pretty easy, Theis explains. “When I started in the flat-rolled business in the 1960s, we’d tell the leveler operators to get a little black book. See what settings worked and write them in the book—the entry setting, the entry gap setting and the exit gap setting. They didn’t even know what the yield was because nobody told them,” Theis recalls.

(In simple terms, yield is the force needed to overcome metal’s elasticity or tendency to return to its original shape, which is the minimum pressure that must be applied by a leveler. Tensile strength is the amount of force a material can withstand without snapping or breaking, which is the maximum pressure that can be applied by a coil straightener or stretcher leveler.)

“Today, the settings for high-yield, high-strength are altogether different than the settings were for low-yield, low-strength. When the managers grew up, that wasn’t the case because there was no high-yield. To ask the operators to figure it out by the seat of their pants by writing in a little black book is not fair,” Theis says.

The consequences for processors running the levelers on the wrong settings are considerable, he says. On low-yield material, the equipment will overwork the metal and miss the desired flatness by adding stresses to the surface. On high-yield material, the equipment will underwork the metal and fail to make it flat, while running the risk of breaking the machine.

“Without giving the operator some [standard] go-to information, he winds up by trial and error spoiling the first couple hundred feet of coil and wasting 20 minutes trying to get it right,” Theis says. “If he had the proper data given to him for each coil—the tensile and the yield, which are right on the test reports—he’s in the right ballpark. He’s not trying to swing at softballs with a hardball bat.”

Mark Menego, director of technical sales for Herr-Voss Stamco, agrees that the high-strength materials pose a serious leveling challenge.

“If you look at the leveling capacity chart, as the yield strength goes up, the minimum thickness increases and the maximum decreases,” Menego explains. “The workable range gets smaller and smaller, and you finally get to a point where the minimum and the maximum are the same.”

This condition calls for processing equipment that is more powerful and durable. “We’re doing new backup designs to withstand the greater separating loads on the levelers. We’re looking for new materials for rolls and backups. The days are gone when you can make everything on a machine out of mild steel. You have to look at better alloys in order to make the parts stand up.”

The challenges involved in leveling high-strength materials have driven demand for Red Bud Industries’ stretcher leveler, says Dean Linders, vice president of marketing and sales for the Red Bud, Ill.-based equipment manufacturer.

“If you go back to some of the smaller machines, like the 10-gauge lines rolling cold-rolled and galvanized, it was not unusual to have a maximum yield of about 40,000 and a maximum tensile of about 50,000. If you ran material such as stainless steel, it was very common to have a tensile strength of 90,000 and a yield of 50,000 to 60,000. When you get into hot-rolled steels today, the yields are equivalent, if not higher, than what we see in stainless steels. At a quarter inch, the machine has to have a capacity of around 100,000 yield,” Linders says.

In response to the increasing yield and tensile strengths of high-strength steels, service centers and toll processors have been investing in coil processing equipment with more horsepower.

Red Bud has seen growing interest in its stretcher leveler technology over the past five years, largely because of the proliferation of high-strength steels and how they react in laser-cutting operations. “Even if the material looks flat, when you cut it with a laser, plasma or even a shear, it will frequently spring back. It hurts the quality of the product and can also damage the lasers or other machines they use,” Linders says.

McNeilus Steel Inc., Dodge City, Minn., is among those who have invested in a new stretcher leveler. The company was handling an increasing amount of high-strength material and had difficulty getting a level of flatness that was acceptable to today’s quality-conscious customers.

“Not only has the grade of the material changed, but the material once had a much wider tolerance. When you look at ASTM flatness tolerances, they’re wide-open at three-quarters to one inch. That was acceptable when the standard was written, but that isn’t the unwritten standard in the industry today,” says Paul Blaisdell, materials director for McNeilus. “Nobody wants any kind of flatness issues, especially with lasers that run lights-out without operators. You can’t have any deviation from flat.”

While mills have been delivering high-strength steels in varying grades for some time, the push is even greater, especially from automakers, for further development of advanced-high-strength steels. The Brussels-based International Iron and Steel Institute reports that up to 40 percent of the cars on the road now contain parts made of advanced-high-strength steels. 

Even though U.S. auto production is plummeting due to the weak economy and record high gas prices, consumption of advanced-high-strength steels continues to rise, notes Roger Lidgren, U.S. geographical sales manager for Swedish steelmaker SSAB. “[Automakers] are swinging as quickly as possible to manufacture cars instead of trucks. This is where our material fits. Even though the number of vehicles produced is going down, the users of the new materials are going crazy.”

While some toll processors have jumped on board, upgrading to more heavy-duty equipment, service centers have been slower to adapt. In fact, the reluctance of many service centers to dive into higher-strength materials has been puzzling to Lidgren.

Since coming to the United States in 2000, Lidgren has visited over 200 service centers, big and small, to promote the new steel alloys and help operators understand the challenges in processing the material. But the message has not been well received.

“Most service centers do not know the limitations on their equipment. They fall into the same trap, saying they can’t [slit high-strength steels] because the wear and tear is too much on their knives. They need to be educated on how to set the knives and what types of knives to use.”

Theis has seen the same attitude. “Slitting or shearing is a different ballgame [than leveling]. That’s not an issue of yield, but tensile strength,” Theis says. A slitter actually breaks the steel along the knife-edge, rather than cutting it. “It’s an absolute issue, because the fracture angle is a function of tensile. It controls the clearance between the upper and lower knife blades.”

When processors try to run the advanced-high-strength steels as they would other materials, it results in damaged knives and poor edges, says Al Zelt, director of sales and marketing for slitter knife manufacturer ASKO Inc., Homestead, Pa. “It’s a different animal than the normal stuff they process.”

Zelt counsels slitter operators on the appropriate knives and clearances for the material at hand. “Each one’s different. I can’t give a general rule of thumb. Our shimless tooling and the program that comes with it is designed to help.”

Toll processor Voss Industries, Taylor, Mich., has had few issues with slitting high-strength material, but has spent considerable time getting comfortable pickling it. “When you’re dealing with advanced-high-strength steels, you realize the power requirements are going to be greater, because the bending force is higher. You have to look at it with respect to what your line is capable of, in terms of gauge and width,” says Ed Sikina, Voss quality manager. “You don’t want to overextend yourself then find out you can’t keep the line tension because you don’t have enough power to overcome the bending force, plus satisfy the tension requirements to keep the material tracking well through the line.”

Additionally, possible head end or tail end irregularities due to uneven cooling of the coils must be cropped off before putting it on the pickling line. “Otherwise, going through all the different bridle sets, it can snap. If you have a break in your line, that’s a big problem on a continuous pickler,” Sikina says.

Cutting high-strength steel is also spurring interest in laser and plasma cutting equipment, which is largely unaffected by the toughness of the material. “There are a lot of processes it does affect, but fortunately it doesn’t affect our thermal cutting process. The plasma cutting process doesn’t really know the difference between the high-strength and high-alloy steels compared to the regular steels,” says Jim Colt, strategic account manager for Hypertherm, Hanover, N.H.

For manufacturers of saw blades, the increasing use of the new high-strength steels calls for continuous product development. “They keep putting out tougher materials, and the saw blade people keep putting out tougher saw blades, different grinds and carbides. The saw people and the coolant people are the same way,” says Frank Truckly, inside sales engineer for Behringer Saws, Morgantown, Pa.

For those sawing the material, care is required. “You need a good sturdy machine. You need a good feed control on the saw and you need a blade that will take the abuse some of these tough materials will give it,” Truckly says. “It’s a challenge. We’re doing it everyday, but it’s one of those things where you have to be very careful.”

Al Terronez, in charge of solutions and applications for DoALL Sawing Products, Elk Grove Village, Ill., agrees that heavy-duty machinery, good blades and proper coolant is the first step. From there, the operator must use his eyes and ears to determine if the high-strength material is being cut efficiently.

“The harmonics should be pleasant sounding. If the operator can’t hear himself, there’s too much vibration,” says Terronez. “And he needs to look at the chips. If they’re flaky, he’s not using enough feed pressure. If they’re thick to the point of turning blue, he’s burning up the blade. They should have a nice curl to them and be the same color as the material being cut.”

Benefiting from these new materials and the challenges they pose are tool steel manufacturers such as Bohler-Uddeholm. “High-strength steel is thinner and much more difficult to form, flange, trim, pierce, punch, whatever. We try to identify potential problems customers might have on the tooling side and offer some suggestions on how to maximize the tooling performance, or at a minimum eliminate down time,” says Bell.

Another resource, the Washington, D.C.-based American Iron and Steel Institute, in cooperation with the IISI, offers extensive information about the performance of the material on its web site and through other sources. “Part of our strategy is to build a better knowledge base so that everyone who has to deal with these steels has a better chance to be successful, instead of having to recut dies over and over until they get something that works,” says Ron Krupitzer, vice president of AISI’s Automotive Applications Committee. “We had the same kind of learning curve with HSLA steels in the 1970s. It took us 10 or 15 years to learn how to build dies for them. With these materials, we’re trying to accelerate the process so it doesn’t take 15 years to make everyone successful using them.”