Mapping and Analyzing the Hardness Testing Process of Steel to Understand the Cause of Variation and Lack of Precision : A Case Study of Industrial Testing and Hardness Measurement System at Ovako Sweden AB

Sammanfattning

Hardness testing is a critical activity in steel manufacturing because hardness is closely linked to mechanical performance and suitability for certain applications. Steel producers rely on hardness measurements to make decisions about acceptance, rework, and heat treatment. If the measurement system is unreliable, a well-produced material can be wrongly rejected, or a defective material can be wrongly accepted. This thesis investigates the hardness testing process at Ovako Sweden AB with the aim of understanding why measurements show unwanted variation and lack of precision. The study focuses on the complete measurement system rather than the testing machine alone. The process is examined across three main stages: sampling, sample preparation, and hardness testing. A case study approach is applied using process mapping, interviews, historical data analysis, measurement system analysis and a series of controlled experiments. The results show that variation arises from all three stages of the process. Cutting induced heat during sampling and sectioning alters the surface hardness of steel. Differences in sample preparation procedures introduce additional variation. At the testing stage, unstable focus position of the microscope of the machine, improper setup conditions such as nonperpendicular sample positioning, edge indentation, and loose anvil fixation lead to systematic errors in measured hardness. The study concludes that improving hardness measurement reliability requires controlling the entire process rather than focusing only on the testing machine. A structured Measurement System Analysis framework adapted for an active industrial environment is proposed. The findings support improved consistency between laboratories and provide practical guidance for reducing measurement variation and non-conformance costs.