A special steel grade for the agricultural and forestry industry
Agricultural machines are expensive and should therefore be hard wearing, as they are subject to extreme wear. The steel used for the construction of those machines needs to be especially wear-resistant. Moreover, the steel should be easy to process, allowing manufacturers to form, weld, and thermal cut the material in all commonly used methods.
The hardenable TBL boron steels made by thyssenkrupp provide the material solution meeting all these needs for high-wear components in the agricultural industry. TBL combines an especially high final hardness level achieved after processing, and high ductility. Owing to these characteristics, TBL has long been used for the construction of agricultural and forestry vehicle components. TBL steel features a high purity degree and close-analysis tolerances, thus ensuring consistent behavior in the quenching and hardening process.
Boron steels TBL and TBL Plus according to DIN EN ISO 683-2 (previously DIN EN 10083-3)
| Steel grade designation | Reference grade | THICKNESS1 from _ to in mm |
WIDTH1 from _ to in mm |
|---|---|---|---|
| TBL | Special mill grade | 2.50 – 15.00 | 1,000 – 2,000 |
| TBL Plus | Special mill grade | 2.50 – 15.00 | 800 – 1.630 |
Chemical composition
| Steel grade | C [%] |
Si [%] max. | Mn [%] |
P [%] max. | S [%] max. | Cr [%] max. | B [ppm] | Typ. CEV |
Typ. CET |
|---|---|---|---|---|---|---|---|---|---|
| TBL | 0.24 – 0.31 | 0.40 | 1.10 – 1.40 | 0.020 | 0.010 | 0.50 | 8 – 40 | 0.55 | 0.41 |
| TBL Plus | 0.32 – 0.38 | 0.40 | 1.10 – 1.40 | 0.020 | 0.005 | 0.50 | 8 – 40 | 0.60 | 0.49 |
Mechanical properties, typical values in delivery condition at room temperature
| Steel grade | Thickness [mm] |
Yield strength Re [MPa] |
Tensile strength Rm [MPa] |
Elongation A5 [%] |
Hardness indelivery condition |
|---|---|---|---|---|---|
| TBL1 | 3.00 – 8.00 | 400 | 620 | 22 | 180 |
| TBL Plus | 4 | 430 | 680 | 22 | 200 |
Impressive final hardness
TBL is a boron steel with a carbon content of 0.24 to 0.31% – the carbon content of TBL Plus being even slightly higher. During the quenching and tempering process, the combination of carbon, manganese and the smaller boron content ensures that the steel can be hardened easily in different media. The maximum attainable hardness depends on the type of process applied and is about 500 HBW for TBL and 560 HBW for TBL Plus. The subsequent tempering, i.e. renewed heating of the component, reduces the stresses in the material caused in the hardening process.
Application examples of boron alloyed quenched and tempered steels
Hardened TBL steel is especially well suited for the construction of wear-resistant welded parts with complex geometries. Exemplary use cases within the agricultural sector are the shares and waves of ploughs. Due to its very high durability, this steel grade also lends itself well for the construction of coupling elements and chains of construction vehicles. Even unhardened, TBL is suitable for applications subject to moderate wear, such as cement mixers.
Excellent processing properties
Our TBL steels offer a wide range of processing possibilities. TBL and TBL Plus can be hot formed, but also be cold formed and used unhardened. This is an option for concrete mixers, which are subject to minor abrasive wear. Even unhardened, boron steel offers good wear properties owing to its fine-grained microstructure.
The fine-grained microstructure is obtained by settings made during the rolling process: In the as-delivered condition, the steel contains ferrite and perlite, i.e. both hard and soft microstructure elements. After the hardening the microstructure displays a 100% martensite content, which is an indicator of an extremely strong material. That is why we recommend a combination of hot forming between 900 and 1050 °C, followed by quenching and tempering, where intricate geometries are concerned and high demands are to be met.
TBL steel has excellent processing properties, both in cold and in hot forming. It can be welded or cut in all commonly used processes, both automatic and manual. In order to avoid cold cracks, the steel should be preheated. Our technical customer advisory service is available to answer any questions you may have regarding the processing of TBL steels. We will be just as happy to advise you on all joining and forming technology issues.
