How case hardening improves steel performance, process and benefits from an expert perspective
How case hardening improves steel performance, process and benefits from an expert perspective
Over 43 years of precision work in metals
Located in Muurame, about 15 kilometres south of Jyväskylä, Sten Teräs’ heat treatment facility has been operating since 1982. Over the decades, the nearly 3,000-square-metre facility has grown from a small hardening shop into a full-scale production unit supported by modern automation.
In addition to high-quality heat treatment, customers receive technical guidance and planning support tailored to their materials and application needs. Ilkka Harri, Technical Director, has worked at Sten for eight years and also supports technical customer service in steel sales.
“I work as Technical Director and am responsible for the heat treatment business. I also support technical customer service in steel sales, so I see customer needs from both perspectives,” Harri explains.
Case hardening ensures quality and a better surface
Case hardening is a heat treatment method used to improve hardness, wear resistance and mechanical properties. The component is heated to around 930 °C in a carbon-rich atmosphere and then rapidly quenched in oil or nitrogen gas.
The method is widely used in applications such as machine components, gears and shafts.
“In case hardening, the entire process takes place in a protective atmosphere. This prevents oxidation and scaling. There is no decarburization, and the result is a clean surface ready for further processing,” Harri says.
At Sten, components are always heat treated according to customer requirements. Some applications require extremely hard and wear-resistant surfaces, while others demand toughness and good formability. Case hardening allows precise control of surface hardness and case depth.
Technology supports quality and the environment
Sten has invested in technologies that support both high quality and responsible production. The gas optimization system automatically adjusts the amount of protective gas, which also significantly reduces carbon dioxide emissions.
“Customers are increasingly interested in carbon footprint. Our technology enables CO₂ emission reductions during the hardening process,” Harri explains.
The quenching oil is continuously filtered throughout the process. This ensures a cleaner and more uniform surface without unnecessary post-processing.
“Continuous oil filtration results in cleaner components. The surface looks better and overall quality improves,” Harri says.
The facility also uses CO₂-free electricity, and heat is recovered from both cooling water and exhaust air. ISO 9001:2015 certification and long-term cooperation with furnace supplier Ipsen International GmbH ensure the use of modern technology and consistent high quality.
How the process works in practice
Heat treatment begins by placing the customer’s components into a heat-resistant steel basket, which is then moved into a glowing furnace. The programmed furnace control raises the temperature to the austenitizing level and maintains it precisely for a defined time.
After that, the batch is transferred by lift directly into quenching oil in a protective atmosphere. The oil is continuously filtered to ensure a cleaner surface and higher-quality result.
“Filtered oil means a cleaner end result. The component surface is more even and free from defects,” Harri explains.
After quenching, the components are washed in an alkaline solution in an industrial washing machine, where oil residues are removed in a closed-loop system without burdening the environment.
Finally, the components are tempered to achieve the required mechanical properties for industrial use.
“Once the components are ready, their hardness is measured by a skilled professional to ensure they meet the specified values. Only then are they packed and delivered,” Harri says.