At Euroblech 2004, Edelstahl Witten-Krefeld GmbH will be presenting among other things cold rolls made of the material Thyrodur 2362. The rolls have proven themselves in processing difficult-to-form materials such as electrical sheet. Used as work rolls in a four-high mill to produce cold-rolled sheet, they last more than 20% longer than comparable products on the market.

The rolls are used in the production of non-grain-oriented electrical sheet in the Bochum plant of ThyssenKrupp Stahl AG. Electrical sheet is alloyed with silicon and with a strength of 680 megapascals, rising to up to 1,200 megapascals in the course of the rolling process, is a difficult-to-form material that places heavy demands on the cold rolls. Around 1,500 tons of roll pressure are applied in up to seven passes to reduce the two to three millimeter thick hot rolled strip to a final thickness of 0.2 to 0.5 millimeters.

Rolls from Edelstahl Witten-Krefeld owe their performance capability to the fact that all the processes decisive to the quality of the end product, from primary and secondary metallurgy to near-net-shape forging and basic heat treatment, are carried out in one place at Edelstahl Witten-Krefeld. Key factors in the quality of Thyrodur 2362 cold rolls are their high alloy content and the targeted heat treatment that takes place during the partial hardening of the roll work surfaces.

Thyrodur 2362 contains five percent chromium and 1.4 percent molybdenum. Its hardening and tempering temperatures are therefore higher than those of medium-alloyed steels, and multiple tempering in a range above 500 degrees Celsius is necessary to develop the roll`s optimum properties.

For the partial hardening of the roll work surfaces, Edelstahl Witten-Krefeld has a vertical induction hardening unit whose frequency can be varied from 300 to 2000 Hertz to meet the individual requirements of the roll. Hardening is carried out in a continuous feed movement. The feed rate and the pressure of the water cooling jets are also variable. Subsequent tempering of the hardened roll takes place in conventional furnaces.

A roll treated in this way has an absolute surface hardness of approximately 62HRc (Rockwell hardness), very high compressive strength, and higher toughness than rolls of conventional cold roll steels.

Contact:

Dietmar Stamm
Phone: +49 203 / 52 - 2 62 67
Fax: +49 203 / 52 - 2 57 07
E-mail: dietmar.stamm@tks.thyssenkrupp.com

Bernd Overmaat
Phone: +49 203 / 52 - 4 51 85
Fax: +49 203 / 52 - 2 57 07
E-mail: bernd.overmaat@tks.thyssenkrupp.com