As cast CC slabs of microalloyed steels are prone to surface cracking. Precipitation phenomena, initiated during solidification, reduce ductility at high temperature. The size, morphology and distribution of precipitates in as cast semis depend on solidification rate, on secondary cooling, straightening and cooling off the caster. Microsegregation of the microalloying additions to the interdendritic boundaries during solidification increases precipitation temperature. Results are presented concerning the effect of solidification and cooling on precipitates characteristics in semis. The characterization of precipitates is quite satisfactory although it could not be clearly correlated with surface quality.


The main components of the Castrip facility at Nucor are presented and the specific features of the twin-roll casting are highlighted with reference to conventional and thin slab casting. Nucor expected in February 2005 a monthly production of 25,000 tons of strips with an average thickness of 1.4 mm and a minimum thickness of 0.84 mm. Most products are utilized in construction application as light gauge hot rolled low carbon steel grades.
Nucor is now in the planning stages for a second Castrip facility in the United States and is exploring opportunities for utilizing the technology internationally through joint ventures.

High carbon and chromium martensitic stainless steels are used when hardness and corrosion resistance are essential. Their mechanical properties and cold workability are impaired by large Cr carbides formed during solidification. This can be overcome by a nitrogen addition as a substitute for high carbon. Results are reported about 0.080% N addition to a 1.4116 grade (C=0.47%, Cr=14.5%, Mo=0.5%). The new grade offers a better combination of hardness, toughness and corrosion resistance than the three higher carbon grades 1.4109, 1.4112 or 1.4125.

Exhaust systems are submitted to ever more severe service conditions, high temperature thermomechanical fatigue in particular. A numerical method is proposed for the design and the lifetime prediction of stainless steel exhaust manifolds submitted to a thermal fatigue load that is deducted from motor bench tests. The method relies on behaviour and damage models and on finite element analysis design of stainless steel exhaust manifolds. A dedicated damage criterion is proposed on the basis of the peak temperature and plastic strain amplitude reached during a thermal cycle. A more general thermomechanical fatigue damage model is also discussed.

Stainless steel forming processes require simple laboratory simulation tools to save production costs. Although reliable numerical tools are available, there is still a need for appropriate constitutive laws. Stainless steel is characterized at high strain rates with an instrumented impact test machine. This allows determining the rheological parameters of different grades to be fitted in a simple constitutive law. Accurate results are thus obtained that afford an effective simulation of the stainless steel forming process with FE-analysis (Forge3).
This is illustrated with the development of a new austenitic stainless steel grade for cold heading applications.