Translation of "Austempering" in German

The high yield ratio is especially attained by specific method steps after austempering.

After the end of the austempering period, the formed steel part is cooled down to room temperature.

Austempering of previously austenitized steels has previously been performed in baths referred to as hot salt baths.

The present invention is explained using the example of austempering of a type 100Cr6 steel, material No.

In the production of this material, unalloyed or only low-alloy cast iron containing spheroidal graphite is subjected to a subsequent heat treatment referred to as bainitizing or austempering.

Isothermal transformation such as austempering and patenting - and thus the combination of all 4 processes in a single line - is possible by changing the configuration of the facility components.

Austempering produces a good combination of the component properties of hardness and strength in steel materials and cast-iron.

The screw of claim 14, wherein the yield ratio after austempering is realized by heat treatment of the screw at a temperature of between 350° C. and 600° C.

The novel high strength screw has a bainite structure which at least partly has been produced by austempering.

In contrast thereto, austempering means that hardening is instead realized by rapid cooling from the austenite phase due to an isothermal structural transformation in the bainite phase.

Due to austempering, the direct structural transformation from martensite and thus the abrupt lattice transformation resulting in great lattice tensions is omitted.

The method according to claim 1, wherein the total of the ferrite and bainite portions in the structure of the formed steel part is at least 90% at the end of the austempering period (tB).

The method according to claim 10, wherein the austempering period (tB) is shorter than the tool closing time (tW).

The total pressing time comprised the cooling period tK, in which the steel blank SP1 was cooled down from the tool entry temperature TW to the bainite forming temperature TB, and the austempering period tB, in which the bainite structure was produced in the steel component hot-press-formed in the press-form tool.

Since martensite formation is prevented as completely as possible according to the invention, in principle it is advantageous if at the end of the austempering period the martensite portion of the formed steel part is less than 1%, in particular is limited to only traces.

Accordingly a particularly advantageous variant of the invention proposes that after the primary material has been press-formed, the formed steel part then obtained remains in the press-form tool and there is brought to the bainite forming temperature and maintained for the austempering period.

Alternatively to bainitising in the press-form tool, it is also conceivable after press forming to remove the steel part press-formed out of the primary material from the mould and bring it in a separate process step to the bainite forming temperature and to maintain this for the austempering period.

The procedural effort associated with executing the inventive method can also be reduced to a minimum if, after the end of the austempering period, the formed steel part obtained is cooled in a simple manner in air.

The method according to claim 1, wherein after press forming, the formed steel part is removed from the press-form tool and brought in a separate process step to the bainite forming temperature (TB) and maintained for the austempering period (tB).

As soon as the bainite forming temperature TB is reached, the steel component still held in the press-form tool is maintained for an austempering period tB at the bainite forming temperature TB in an isothermic manner.

In this case the austempering period tB is limited such that, at its end, the austenitic structure of the steel component is essentially entirely transformed to a bainitic structure.