Texas A&M researchers uncover the art of printing extremely hard steels flawlessly

April 17, 2020

For millennia, metallurgists have been meticulously tweaking the ingredients of steel to enhance its properties. As a result, several variants of steel exist today; but one type, called martensitic steel, stands out from its steel cousins as stronger and more cost-effective to produce. Hence, martensitic steels naturally lend themselves to applications in the aerospace, automotive and defense industries, among others, where high-strength, lightweight parts need to be manufactured without boosting the cost.

However, for these and other applications, the metals have to be built into complex structures with minimal loss of strength and durability. Researchers from Texas A&M University, in collaboration with scientists in the Air Force Research Laboratory, have now developed guidelines that allow 3D printing of martensitic steels into very sturdy, defect-free objects of nearly any shape.

"Strong and tough steels have tremendous applications but the strongest ones are usually expensive -- the one exception being martensitic steels that are relatively inexpensive, costing less than a dollar per pound," said Dr. Ibrahim Karaman, Chevron Professor I and head of the Department of Materials Science and Engineering. "We have developed a framework so that 3D printing of these hard steels is possible into any desired geometry and the final object will be virtually defect-free."

Although the procedure developed was initially for martensitic steels, researchers from the Texas A&M said they have made their guidelines general enough so that the same 3D printing pipeline can be used to build intricate objects from other metals and alloys as well.

The findings of the study were reported in the December issue of the journal Acta Materialia.

Steels are made of iron and a small quantity of other elements, including carbon. Martensite steels are formed when steels are heated to extremely high temperatures and then rapidly cooled. The sudden cooling unnaturally confines carbon atoms within iron crystals, giving martensitic steel its signature strength.

To have diverse applications, martensitic steels, particularly a type called low-alloy martensitic steels, need to be assembled into objects of different shapes and sizes depending on a particular application. That's when additive manufacturing, more commonly known as 3D printing, provides a practical solution. Using this technology, complex items can be built layer by layer by heating and melting a single layer of metal powder along a pattern with a sharp laser beam. Each of these layers joined and stacked creates the final 3D-printed object.

However, 3D printing martensitic steels using lasers can introduce unintended defects in the form of pores within the material.

"Porosities are tiny holes that can sharply reduce the strength of the final 3D-printed object, even if the raw material used for the 3D printing is very strong," said Karaman. "To find practical applications for the new martensitic steel, we needed to go back to the drawing board and investigate which laser settings could prevent these defects."

For their experiments, Karaman and the Texas A&M team first chose an existing mathematical model inspired from welding to predict how a single layer of martensitic steel powder would melt for different settings for laser speed and power. By comparing the type and number of defects they observed in a single track of melted powder with the model's predictions, they were able to change their existing framework slightly so that subsequent predictions improved.

After a few such iterations, their framework could correctly forecast, without needing additional experiments, if a new, untested set of laser settings would lead to defects in the martensitic steel. The researchers said this procedure is more time-efficient.

"Testing the entire range of laser setting possibilities to evaluate which ones may lead to defects is extremely time-consuming, and at times, even impractical," said Raiyan Seede, a graduate student in the College of Engineering and the primary author of the study. "By combining experiments and modeling, we were able to develop a simple, quick, step-by-step procedure that can be used to determine which setting would work best for 3D printing of martensitic steels."

Seede also noted that although their guidelines were developed to ensure that martensitic steels can be printed devoid of deformities, their framework can be used to print with any other metal. He said this expanded application is because their framework can be adapted to match the observations from single-track experiments for any given metal.

"Although we started with a focus on 3D printing of martensitic steels, we have since created a more universal printing pipeline," said Karaman. "Also, our guidelines simplify the art of 3D printing metals so that the final product is without porosities, which is an important development for all type of metal additive manufacturing industries that make parts as simple as screws to more complex ones like landing gears, gearboxes or turbines."
-end-
Other contributors to the research include Austin Whitt and Dr. Raymundo Arróyave from the Texas A&M Department of Materials Science and Engineering; David Shoukr, Bing Zhang and Dr. Alaa Elwany from the Texas A&M Department of Industrial and Systems Engineering; and Dr. Sean Gibbons and Dr. Philip Flater from the Air Force Research Laboratory, Florida.

Texas A&M University

Related Steel Articles from Brightsurf:

How soft hair deforms the sharpest steel blades
Why do the edges of a steel razor dull from cutting far softer materials?

HKU super steel project attains major breakthrough
The Super Steel project led by Professor Huang Mingxin at the Department of Mechanical Engineering of the University of Hong Kong (HKU), with collaborators at the Lawrence Berkeley National Lab (LBNL), has made important breakthrough in its new super D&P steel (produced using a new deformed and partitioned method) to greatly enhance its fracture resistance while maintaining super strong in strength for advanced industrial applications.

Making stronger concrete with 'sewage-enhanced' steel slag
Researchers examined whether steel slag that had been used to treat wastewater could then be recycled as an aggregate material for concrete.

Buildings can become a global CO2 sink if made out of wood instead of cement and steel
A material revolution replacing cement and steel in urban construction by wood can have double benefits for climate stabilization.

Finding out the factors that most influence the steel corrosion in reinforced concrete
This process causes structures to deteriorate internally and can even cause buildings to collapse.

Corrosion resistance of steel bars in concrete when mixed with aerobic microorganisms
Dissolved oxygen in pore solution is often a controlling factor determining the rate of the corrosion process of steel bars in concrete.

Scientists invented how to improve steel properties by 100 times
Scientists from Tomsk Polytechnic University developed a new method of ion implantation that dramatically expands the application of the alloying process in the industry.

C. difficile resists hospital disinfectant, persists on hospital gowns, stainless steel
Surgical gowns and stainless steel remained contaminated with the pathogen Clostridium difficile even after being treated with the recommended disinfectant.

30 shades of steel: Scientists develop 'cheat sheet' for the creation of new steels
Researchers from the National University of Science and Technology 'MISIS' developed a database that will help create new grades of steels.

Metal foam stops .50 caliber rounds as well as steel -- at less than half the weight
Researchers have demonstrated that vehicle armor using composite metal foam (CMF) can stop ball and armor-piercing .50 caliber rounds as well as conventional steel armor, even though it weighs less than half as much.

Read More: Steel News and Steel Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.