Bainidur 1300 – Special Steel for Distortion-free, Cost-efficient Forgings

Forged components for the automotive industry are often affected by distortion. This is a well-known issue in the drop forging industry for the fabrication of forged components such as steering knuckles, pistons, and common rail systems. A common solution to compensate for this distortion is over-dimensioning and removal of excess material, which results in an increase in production time and cost.

Bainidur 1300 is a low-alloyed bainitic stainless steel developed by Deutsche Edelstahlwerke, which is optimised to minimise the risk of such distortion.

The composition of Bainidur 1300 is specifically selected to provide an expanded cooling range for the bainite phase. Bainite is a steel phase which exhibits a plate-like microstructure that forms at temperatures of 125–500 °C, depending on the chemical composition of the steel. Alloys based on bainite, unlike martensitic stainless steels, usually do not require further heat treatment after transformation in order to optimise strength and toughness.

Properties of Bainidur 1300

Bainidur 1300 exhibits excellent mechanical properties, with the absence of distortion and uniform hardness. This is brought about by its homogeneous, 100 % bainitic microstructure. This is achieved through a unique composition.

Drastically simplified cooling

Bainidur 1300 is composed of the following elements:

This composition results in the range for the cooling rate required to achieve a homogeneous microstructure becoming significantly larger. The steel can thus be cooled in a more unregulated manner, similarly to conventional forgings, without the risk of distortion.

For conventional bainitic stainless steels, larger forgings are more difficult to cool in a precisely controlled manner. An additional advantage of Bainidur 1300 over these other bainitic steels is that the bainitic microstructure can be controlled consistently and reliably even for large components (> 60 mm rd.).

This simpler cooling process enables greater cost-effectiveness and more efficient production processes for distortion-free, lightweight, high-strength and ductile components.

Mechanical properties

Bainidur 1300 exhibits exceptional mechanical properties. It possesses a tensile strength of 1000 – 1300 MPa, the value of which can be tailored to specific applications. The yield strength lies at 600 – 900 MPa. Bainidur 1300 also exhibits a high Charpy notched impact strength at room temperature of 20 – 50 kJ/m2. It exhibits a high toughness without significant nickel content.

A major advantage of Bainidur 1300, is the homogeneity of its hardness profile for big cross-sections. Both after austenitisation and after a subsequent tempering, a homogeneous hardness is observed across bar sections from 20 mm up to 120 mm in diameter.

Hardness profile across cross-section (incremental turning test sample) made from Bainidur 1300

Bainidur 1300 enables distortion-free forged components thanks to its homogeneous microstructure. 

Comparison with other steels for die-forging

When compared with other steels, the advantages of Bainidur 1300 are clear.

Precipitation hardened ferritic-pearlitic (APF) steel grades are often used to overcome distortion, however, exhibit lower toughness and strength as well as low nitridability in comparison to Bainidur 1300. This limits their application for lightweight components in the automobile industry.

Quenched and tempered steels, in comparison to Bainidur 1300, after machining, undergo distortion and have higher processing costs.

Bainitic steels can exhibit extremely high strength, however, achieving the correct microstructure requires a high level of technological precision. This is especially true for large and complex components. This is because of an extremely tight range for the cooling rate. Imprecise control of cooling results in a mixed microstructure and inferior properties, including inhomogeneous distribution of residual stresses, resulting in distortion. Nitridisation of conventional bainitic steels results in an associated loss of strength and machinability, but not for Bainidur 1300.

Comparison of engineering steels for die forging.

Processing

The drawbacks of conventional steels have been overcome with the development of Bainidur 1300. The unique composition of this steel means that a homogeneous bainite microstructure can be formed in a larger processing window than for conventional bainitic steels. This allows for much more cost-efficient production of distortion-free forgings.

Continuous time-temperature-transformation diagram 

Applications

Bainidur 1300 is ideal for components exposed to heavy loads and can thereby allow for significant reductions in material usage compared to conventional steel parts. It is therefore ideally suited for various lightweight parts in the automobile industry. The lack of distortion in components made from Bainidur 1300 makes the steel ideal for forged components such as steering knuckles, pistons and common rail systems. 

Alternative and trade names

Bainidur 1300 can also be found under the trade names 1.7979 and 18MnCrMoV6-4-8.

Explore the properties of Bainidur 1300 and many other steels supplied by Deutsche Edelstahlwerke.