ALTERNATIVES TO HEAT TREATMENT OF STEELS FOR THE FORMING INDUSTRY

Improved usability with DEW RC+T and Steeltec XTP-Technology

Cold forming is a proven process for the production of rotationally symmetrical components. For good formability, case hardening steels are ferrite-pearlite or GKZ-annealed. However, this type of heat treatment is very time-consuming and requires extensive post-treatment. Our Deutsche Edelstahlwerke (DEW) business unit, together with cold formers, has developed RC+T (Rapid Cooling + Tempering), an alternative process to conventional heat treatment. The result: significantly leaner process chains and improved material properties.

Making better use of savings potential

Another innovation is the XTP steels from our Steeltec business unit. Solid forming, which conserves resources in every respect, has by no means exhausted the potential for savings coupled with the high performance of the end product. Dynamically highly stressed components require extremely high toughness and strength of the base material. Up to now, there has been no solution with which the product properties could be adjusted to customer-specific requirements, efficiently and thus more competitively. Now, with XTP steels the solution is at hand.

 

RAPID COOLING + TEMPERING TECHNOLOGY

The innovative process of Deutsche Edelstahlwerke for improved material properties in case steels

In order to ensure good formability of steel, not only heat treatment is necessary. In addition, complex, time-consuming and cost-intensive subsequent treatments are required, for example for a microstructure that meets the requirements, straightness and surface quality of the steel.

A hard shell and a soft core in the component are important properties for case-hardened components such as drive shafts or drive trains. Because long service life and process reliability is a combination of wear resistance of the surface and ductility of the product core under dynamic load. The more homogeneous and fine-grained the steel structure, the more precisely the mechanical-technological product properties can be adjusted.

Increasing efficiency and component quality with the new process

To ensure that the material condition of the starting material meets the requirements of the processing process and end product, several heat and after-treatments are necessary. To meet the increasing demands, Deutsche Edelstahlwerke and its customers developed a technological alternative to classical heat treatment with significant added value throughout the entire process chain: DEW RC+T. With the temperature-controlled rolling process and subsequent tempering, the classic ferrite-pearlite or GKZ annealing is replaced. Cold formers save time-consuming process steps and simultaneously optimize the steel properties for increased component quality.

Advantages of Rapid Cooling + Tempering compared to FP and GKZ annealing

The integration of heat treatment into the rolling process allows material properties that cannot be achieved by conventional annealing processes alone.

  • Microstructure is fine-grained and resembles a GKZ-annealed structure
  • Uniform hardness over the entire cross-section
  • Better formability
  • Smooth and score-free surface in rolled condition
  • Lower decarburization tendency compared to FP-annealed material
  • Increased output due to reduced scale formation
  • Better initial structure for further surface treatments

Contact

 
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Heating to 1,160 °C
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Hold for 30 minutes and cool in air
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60 percent of grains with size from 8 to 10

Convincing results with Rapid Cooling + Tempering

A comparison of the microstructure, the forming behaviour and the fine-grain stability of formed components made of classic FP-annealed and DEW RC+T treated steel shows clear differences. Classically annealed case-hardened steel, e.g. 20CrMo5, requires a high effort during forming due to its linear structure. In comparison, the temperature-controlled rolled and tempered variant is characterized by a finer grain and evenly distributed spherical carbides. The analysis proves the fine grain resistance: After heating to 1160 °C, holding for 30 minutes and cooling in the air, over 60 percent of the grains have a size between 8 and 10 (according to ISO 643).

XTREME PERFORMANCE TECHNOLOGY

The thermomechanical process from Steeltec opens up new potential for standard materials

Cold and warm forming is used for customer-specific high demands on the end product: close geometric tolerances, high surface quality, a uniform and defect free material structure and excellent toughness and strength. The steel with its structure and its toughness and strength ratio has a decisive influence on the efficiency of the manufacturing process and the achievement of the product attributes desired for the specific component.

Exploiting material potentials

One way to increase cold and semi-heat formability, toughness and fatigue strength of steel materials and to produce more competitive end products is the novel thermomechanical process in combination with controlled, accelerated cooling in the production of the starting material: Xtreme Performance Technology (XTP) from Steeltec. XTP has been proven to open up new degrees of freedom in order to exploit the property potential of standard materials in a targeted manner and to save process steps along the value chain from the starting material to the end product.

Advantages of steel with XTP technology (Example 7MnB8 XTP)

  • Saving of additional heat treatment processes
  • Medium strength and high-strength variants possible
  • Medium strength: High notched bar impact values for cold forming
  • High strength: Very good toughness properties for mechanical processing

 

Potential application example: ball stud

Ball studs are a classic application example for a cold-formed component. These are located in steering rods, tension and compression struts and tie rods of motor vehicles. The component is loaded statically, cyclically and dynamically in many ways. The dynamic loads are short, hard shocks, such as those caused by crossing a threshold or kerbstone, for example. Case-hardened or quenched and tempered steels are used as standard for the production of ball studs.

INFORMATION AND DOWNLOADS

 

Steeltec:

(Contact details can also be found in the brochures)

XTP broschure: Xtreme Performance Technology
Data sheet: Micro-alloyed steel 7MnB8 XTP

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