Ploughs have been used in agriculture for thousands of years. Today they are larger and more sophisticated than the wooden implements that were once harnessed behind horses and cattle but their task has hardly changed: turning, loosening, and mixing the soil. The plough blades dig deep into the soil, crush the roots of harvested plants, or spread manure.

Modern ploughs are made of steel because they are exposed to immense stresses. They constantly collide with stones in the soil. The force of the collisions has been increasing for years, as soil tillage equipment is being pulled over the fields more and more rapidly for economic reasons. They can therefore cultivate around 10,000 hectares – their so-called service life. After that the steel wears out, it cracks or breaks and has to be replaced.

“This is a waste of energy and material,” says Maik Kunert, professor of materials engineering at the University of Applied Sciences Jena. “Calculated over the lifetime of agricultural equipment, 65 per cent of the energy is consumed during its fabrication because steel production is very energy-intensive.” In contrast, assembly, transport, and use of the equipment only account for about a third of the total energy consumption.

Wanted: a durable, resource-saving, and cost-effective steel

That is why Kunert started “VeraMAG” at the beginning of 2019: a research project that aims to improve the eco-balance of ploughs by extending their service life. “We wanted to find a steel that is harder and more durable,” says the 52-year-old. Moreover, the steel was to be produced in a resource-friendly and cost-effective way.

According to materials expert Kunert, tillage equipment is particularly well suited for a research project like this: “There is a good leverage for changes in this industry, as there is generally a high demand for ploughs and the production chain is short.” Accordingly, the project only has two industry partners: a steel manufacturer, the Saarland-based company Dillinger (AG der Dillinger Hüttenwerke), who produces the innovative steel. And the BBG (Bodenbearbeitungsgeräte Leipzig GmbH & Co. KG), who uses it to build a plough prototype. The new plough is to be tested before the end of the year.

Nine theses resulted from the project

As with all projects in the IngenieurNachwuchs funding, young scientists played an important role in VeraMAG. “We tried to involve many students. The results of their work were directly used in the project. Thus, a great group was formed that is lots of fun to work with,” Kunert says. “Nevertheless, we have serious problems recruiting young talent in our department. Yet materials science and engineering offer everything from atomic scale to component size. The subject is just right if you are interested in science but don't want to commit yourself to a certain topic yet – so please apply!”

VeraMAG has produced a total of nine theses – including that of Jerome Ingber. The 26-year-old has been part of the project since the beginning and wrote his master thesis in materials engineering on the “alloy design” of the novel steel.

VeraMAG was set up like a funnel: The team aimed to find the perfect steel for agriculture from a sheer endless number of potential alloy mixtures. This steel was to have improved wear properties, lose less mass in use, be harder and have the greatest possible toughness. At the same time, all the elements that are added during production were to be readily available and crisis-proof. Despite these requirements, there were still too many “recipes” to consider, so the team further narrowed down the options based on the following consideration: “We knew from preliminary tests that certain metastable-austenitic steels have good wear properties,” says Ingber.

When mechanical forces act on metastable-austenitic steel, the relatively soft austenite transforms into hard martensite on the surface. The steel parts therefore become harder and more wear-resistant during use – whereas conventional steel is made as hard as possible right from the start. When the metastable-austenitic steel has completed the “phase transformation” to martensite its wear resistance decreases again. Such steels are also called TRIP steels (transformation induced plasticity). They are often used in car body construction, as they provide a good combination of strength and formability. However, the requirement profile for soil tillage equipment is completely different. In this area, steels with TRIP effect are a novelty.

The tougher a steel is, the more energy it can absorb before it breaks

To narrow the funnel further, Ingber modelled different alloys on the computer. He wanted to find out which elements can be melted into the starting steel in what quantity to obtain the desired properties. The steel had to remain in its austenitic phase after heating in the blast furnace and cooling to room temperature, and not change back to its ferritic phase. At the same time, it was to be very tough.

The tougher a steel, the more energy it can absorb before it breaks. Toughness means that a crack does not expand and result in the fracture of the whole component – which is an important property when the steel is constantly hitting stones. “We were able to increase the toughness by adding aluminium,” Ingber explains. The main challenge of his model calculations was that with each alloy addition, the temperature shifted at which the lattice structure of the steel changed and it switched phases. “With each degree Celsius, the wear properties of the final product changed,” the 26-year-old explains, “it was very complex.”

Nonetheless, Ingber found a number of promising alloys and the funnel narrowed further: “I identified 15 to 20 potential steel recipes that worked well in calculations. These we were able to produce in small quantities in our experimental melts,” he says, “and set up a series of tests.”

The steel for the first prototype is ready

To determine the wear properties, the VeraMAG team processed small steel samples – the plates measured only 15 by 20 millimetres – with sandpaper, using a specific force and defined speed. Before and after this treatment, the steel samples were weighed to see how much material the sandpaper had removed. The lighter the samples were at the second weighing, the lower the wear resistance of the steel.

The second property to be determined was toughness. To this end, the steel samples had to go through the notched-bar impact test. “Casually speaking, a big hammer hits our sample steel with great force,” says Professor Kunert. The test setup consists of a weight hanging from a pendulum that is then dropped. At the lowest point, it hits the steel sample and penetrates it. “The higher the hammer swings up on the other side, the less energy was consumed in the process,” says Kunert. The team looked for the steel that took as much momentum away from the weight as possible.  

The numerous preliminary considerations, modelling, steel samples, and tests finally led to the end of the funnel: The result was a high-carbon steel, mixed with a few mass percentages of aluminium, silicon, and manganese. It combined the best wear properties, the lowest mass loss, and the highest toughness. This steel has already been cast in a large-scale implementation for the plough prototype.

From the lab to the field

“In the lab, our results are promising,” says Ingber: “We achieve a six-fold improvement in mass loss.” This means that the innovative steel is six times as wear-resistant as conventional steel. If the result could actually be transferred to the field, tillage equipment could be used six times longer – “which would save a corresponding amount of energy”, adds Kunert. The field test will also show whether the toughness of the steels is sufficient, as the laboratory values for toughness were not yet quite in the range the team had hoped for.

VeraMAG will run until the end of the year, and in late summer or autumn the last milestone will be reached: the field test. Project partner BBG maintains a field in Saxony-Anhalt where innovations can be tested under realistic conditions. Professor Kunert says: “If possible, we will be on site and hopefully toast to the success of the project – provided our steel delivers what it promises.”