For safety reasons, the demands made on line pipe steels have been continuously increasing in recent years. The focus is on the steels’ mechanical, weldability and toughness properties, in particular. In addition to this typical pattern of increasing demands, it is also observable that customers increasingly require an integrated process and quality control system, from the steel-making process right through to ultimate plate production. Awareness of the potentials available in the production of the steel and of the plate, and their interaction in process improvement, is an essential factor in the meeting of such demands for comprehensive process control.
Both steelmaking plant and rolling-mill processes are increasingly being automated via the incorporation of sophisticated control and instrumentation technology. This creates optimum conditions for precise adjustment of these processes on the criteria of product quality.
The methods of process adjustment using the latest quality-evaluation tools, such as SILENOS (Steel Inclusion Level Evaluation by Numerical Optical Systems) and THEMiS (Testing for Heterogeneous Microinclusions and Segregation) are examined here. SILENOS is a new procedure for the assessment of steel cleanliness in which particle diameters of above 20 micron are analysed using computer-tomographic images.
A special CNC milling machine, a high-resolution scanner and a laser spectrometer examine the layers of metal by removing a large number of 10 μm layers in order to obtain a statistically correct evaluation. An automated procedure determines the concentration, size, geometry and chemical composition of the particles.
THEMiS was developed for assessment of the quality of the centre zone of slabs. Centre segregation in slabs is monitored and non-metallic inclusions evaluated simultaneously. A large number of spark-spectrometric analyses are performed perpendicular to the centreline segregation for this purpose. The classical spectrometric analyses and individual sparks are evaluated. This permits precise description of centre segregation by measurement, and also assessment of non-metallic inclusions of between 1 and 10 μm in the centre zone. The cleanliness and quality of the centre zone can then be described with very great accuracy and a new confidence level.
These specific measuring instruments are used for control of the steel-making processes at HKM (Hüttenwerke Krupp Mannnesmann) and at SMGB (Salzgitter Mannesmann Grobblech) in order to accommodate end-customers’ requirements and are directly correlated to production data and can be used for a product improvement.
This paper’s topic is the evaluation of an integrated improvement and quality assurance process extending from the very start of steel production, and including the interlinking of the properties of the cast slabs and the ultimate outcome in the form of the final plate. The benefits for the end customer and milestones along this evaluation route are examined and discussed.