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Hot-rolled chassis steel with optimized hole expansion

For economical, lightweight, high-strength chassis parts

Chassis steels CH-W® are ideal for complex cold-formed chassis parts.

As a further development of our proven complex-phase steels, the new chassis steels CH-W® offer significantly improved formability with otherwise comparable properties.

CH-W® permits than hitherto larger openings with tighter flange radii. The chassis grades are also characterized by very good surfaces. The CH-W® steels are available uncoated and in strength class 800 MPa hot-dip galvanized.

New: The new ultra-high-strength hot-rolled multiphase steels CH-W® 700Y950T and CH-W® 700Y950T promises maximum weight-saving potential and maximum service life in the chassis. The chassis grades with a strength of almost 1,000 megapascals and optimized hole expansion offers not only a significant weight reduction but also high fatigue strength for complex chassis parts. Due to the high strength with reserves in the elongation, a high crash deformation resistance and thus a high crash energy absorption is given.

Chassis steel CH-W® is ideal for use in the chassis.
Chassis steel CH-W® is ideal for use in the chassis.

With its property profile, the bainitic chassis steel CH-W® is particularly suitable for complex chassis components such as single-skin control arm, axle beams, bumpers and similarly challenging components.

Hot-rolled chassis steel

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Steel grade
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Reference grade
VDA 239-100
Reference grade
DIN EN 10338,
DIN EN10346
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Thickness1
from _ to in mm
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Width1
from _ to in mm
CH-W® 660Y760T-UC HR660Y760T-CP HDT760C 1.80 – 5.00 940 – 1,360
CH-W® 660Y760T+Z HR660Y760T-CP-GI HDT760C+Z 1.80 – 3.00 970 – 1,330
CH-W® 700Y950T-UC 2.00 – 4.00 900 – 1,400
CH-W® 750Y950T-UC
(On request)
HR750Y950T-CP-UC

2.00 – 4.00
900 – 1,400
1. Not all thickness and width combinations possible.

Mechanical properties

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Steel grade
Yield
strength

Rp0.2 [MPa]
Tensile
strength

Rm [MPa]
Elongation
A80 [%] min.
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A5 [%] min.
Hole
expansion

Thickness [mm]
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λ [%] min.
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λ [%] typ.
CH-W® 660Y760T 660 – 820 760 – 960 12 14 1.80 – 4.20 60 90
4.21 – 5.00 50 80
CH-W® 700Y950T 700 – 850 950 – 1,100 10 12 2.00 – 4.00 35
CH-W® 750Y950T-UC 750 – 920 950 – 1,100 8 10 2.00 – 4.00 35
Test direction in rolling direction.

Notes on applications and processing

Material characteristics

Microstructure

Due to its selected chemical composition and the special rolling process, the bainitic chassis steel has a very fine microstructure. The desired properties of the steel are created by the specific microstructure with nanoprecipitations. The low Si content guarantees a flawless surface.

Microstructure of CH-W®

Forming

Hot-rolled bainitic chassis steel is often used in the vehicle chassis area. It offers high resistance to local necking thanks to favorable work hardening behavior. Due to its extremely fine and homogeneous microstructure, CH-W® steel also exhibit guaranteed hole expansion properties of at least 60% to ISO 16630. Furthermore bainitic chassis steel provides a favorable bending behavior, bending angles of well over 130° (to VDA 238-100) are typically possible.

Joining

Bainitic chassis steel is very suitable for welding both same-grade joints and hybrid joints with other common steel grades. The precondition is welding parameters matched to the material. Test results in accordance with SEP 1220-x are available and attest CH-W® good ability to join in any joining process. Of particular note are the excellent results of the typically even and fine-flaked MAG welding seams without cracking tendency or significant hardening. Consequently, the high demands placed on the fatigue strength of the seams are fulfilled.

Fatigue strength

The bainitic chassis steel CH-W® 660Y760T displays a comparably good fatigue strength like standard chassis grades.

Stress-strain curve of CH-W® 660Y760T compared to HR660Y760T-CP and S700MC

Stress-strain curve of CH-W® 660Y760T compared to HR660Y760T-CP and S700MC

In service: new chassis steel for high flexibility and production reliability

Good cooperation, successful development: the new hot-rolled chassis steel is a product of the close cooperation between Gestamp and thyssenkrupp Steel.
Good cooperation, successful development: the new hot-rolled chassis steel is a product of the close cooperation between Gestamp and thyssenkrupp Steel.

With its new CH-W® 660Y760T product, thyssenkrupp Steel is offering the automotive industry a high-strength multiphase steel ideally suited for meeting highly demanding requirements, especially in the chassis area. The cooperation partner Gestamp, an internationally renowned supplier to the automotive and commercial vehicle industry, is the first customer to successfully use the material for producing complex chassis parts.

There is hardly any other area of production today where the formability of materials plays such an important role as in the chassis. The increasingly complex components used in automotive chassis require not only very robust, but also high-strength steels with good formability. Tight bending radii or good hole expansion properties are just two examples among many showing how the automotive industry is placing increasing demands on modern chassis steel. thyssenkrupp Steel developed hot-rolled CH-W® 660Y760T chassis steel in close cooperation with its customer Gestamp.

The new grade guarantees a hole expansion of at least 60 percent and is ideal for complex, cold-formed chassis components. The targeted coordination of chemical analysis and production in our modern hot strip mills results in a particularly homogeneous microstructure, with a positive effect on processing in the customer's stamping shop.

As part of this practically oriented work conducted jointly, intensive trials were carried out over a period of months both at our Duisburg location and at the Gestamp development centers in Bielefeld and Bilbao. Initially on a laboratory scale, then later on the prototype die and, finally, on the series production die.

Melanie Dinter, thyssenkrupp Steel, Sales Engineer
Close and successful cooperation: Alexander Lange (left) and Melanie Dinter from thyssenkrupp Steel together with Dr. Mehdi Asadi, Material Engineering Manager at Gestamp.
Close and successful cooperation: Alexander Lange (left) and Melanie Dinter from thyssenkrupp Steel together with Dr. Mehdi Asadi, Material Engineering Manager at Gestamp.

Many advantages and a robust process

Several trial runs in a production die showed that CH- W® 660Y760T can reliably handle even critical forming stages as well as accommodating large openings and the tightest of radii. Both in component design and during subsequent processing by the customer: the hot strip in the 800 strength class promises the greatest possible flexibility with guaranteed high production reliability. Also an advantage: The material meets the requirements of VDA grade HR660Y760T-CP and DIN EN grade HDT760C, and offers significant reserves in elongation at break compared with established complex-phase steels of this class.

The chemistry is also right: The coordinated chemical analysis indicates a low carbon equivalent, which leads to excellent MAG welding properties. Welding tests, for example, confirmed an extremely low hardening in the heat-affected zone. This is a considerable advantage, and not only for components subjected to vibration.

Alexander Lange, thyssenkrupp Steel, Product Manager Hot strip

After a final check of the fatigue endurance properties on the real component, the material was approved by Gestamp and is now being used in various chassis components made by a well-known German OEM.

We are very satisfied: With the new chassis steel grade from thyssenkrupp Steel, we are in the best possible position to meet our customers' requirements for complex, high-strength chassis parts, and set up a robust production process.

Dr. Mehdi Asadi, Gestamp, Manager Material Engineering

About Gestamp

Gestamp is one of the largest and most eminent suppliers to the international automotive and commercial vehicle industry, with a presence in more than 24 countries. Headquartered in Madrid, the company currently employs around 40,000 people at more than 100 locations. The broad portfolio includes, among other things, the design, development and production of chassis and body parts as well as mechanical and mechatronic components.

www.gestamp.com

General inquiry

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Contact

thyssenkrupp Steel Europe AG

Kaiser-Wilhelm-Strasse 100

47166 Duisburg, Germany

+49 (0)203 52-0

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