Doktorand/Ph.D. student -- continuous hardening

Hardening of thin Martensitic Carbon and Stainless Steel strip

A continuous hardening line includes components that are responsible for austenitising, controlled cooling, rapid cooling, flattening and tempering. All of these components have an effect on the strip flatness, microstructure and mechanical properties of the steel strip produced.
Because of the integrated nature of the line, a line speed change (for example) has a number of competing metallurgical influences i.e. it changes the austenitising time, the cooling rate in two main cooling media and the tempering time.
Therefore, it is difficult to predict the effect it will have on such things as microstructure, the phase change related expansion, mechanical properties, internal stresses, secondary precipitation hardening and importantly flatness. In addition, the as-rolled cross-sectional profile / shape, the internal stress patterns and degree of prior cold reduction play a role in the strip’s response to hardening.

Project Aims

To develop a comprehensive theoretical understanding of the parameters within the continuous hardening process that affect strip flatness, microstructure and mechanical properties, which can then be used to modify the steel and their properties to provide superior performance in subsequent applications.

Research

Phase I

Establish a benchmark of existing production in terms of:

• As-rolled flatness
• As-rolled residual stress distribution
• incoming secondary carbide size and distribution
• Surface roughness and reflectivity.
• Degree of carbide dissolution
• Retained austenite volume fraction and distribution.
• Final hardened flatness
• Hardened residual stress distribution
• Standard mechanical properties
• Fatigue strength

Modify the different process variables in a controlled way, assessing the effects of the changes on the above characteristics to develop a fundamental understanding of the key elements that need to be controlled to optimise and control the hardening process.

Phase II

Use the fundamental knowledge from Phase I to establish a model for further development of the performance of the strip by:

• Enhanced mechanical properties from the existing grades that give superior performance, or
• Enhanced chemical compositions that allow superior performance from the existing equipment.

Phase III

Validate the model by producing trial quantities of the modified strip products and characterise them in a similar manner to Phase I.
Once characterised, undertake trials in collaboration with reference customers to assess the suitability of the new products in the target applications.

Researcher requirements

An interest in:

• Heat treatment
• Cold rolling
• Material characterisation
• Practical application of structure:
  property relationships
• Alloy development