No abstract

roughing reductions are used and the transfer time to finishing is shorter, making it easier to tolerate higher A comparison of the metallurgical principles of reheating temperatures. thermomechanical processing (TMP) on plate andThe finish rolling pass schedule and temperature range hot strip mills is given together with a discussion of control the amount of strain accumulation (pancaking) some important factors influencing its practical achieved as well as the driving force and nucleation site implementation. This is followed by a description of density for microalloy precipitation in the austenite. On the economic benefits of TMP to the customer.the strip mill, partial interpass recrystallisation may occur Some illustrative examples of TMP plate and strip in the finishing train, which is not ideal from a micromill products are given, covering steels for offshore, structural point of view as it can lead to inhomogeneous shipbuilding, engineering, construction, and austenite and ferrite grain size distributions3 with a detrilinepipe applications. Finally, the suitability of TMP mental influence on product toughness. In both strip and steel to laser cutting and welding is discussed.plate mills, the austenite grain size distribution at the start I&S/1587 of pancaking and the size of the pancaking reduction influence toughness through the homogeneity of the final The author is with Rautaruukki Oyj, Corporate R&D, PO Box 93, ferritic microstructures. Finishing rolling slightly below the FIN-92101 Raahe, Finland

Increasing demands for ultrahigh-strength steels in commercial as well as military applications have raised interest in finding alternatives to the high-cost high-alloyed steel and super-alloys currently used, e.g. the use of economic low-alloy compositions processed via low-cost air induction melting and electroslag refining (ESR). In this work the yield of alloying elements and the removal of the impurities nitrogen, sulphur and phosphorus as a result of electroslag refining (ESR) in a newly developed CrNiMoWMnV ultrahigh-strength steel (UHSS) have been studied in relation to their activities in the molten metal pool. Six experimental heats of CrNiMoWMnV UHSS with different chemical compositions were designed, melted in an induction furnace (IF) and refined using ESR. This was followed by hot forging of the ingots at 1100˚C to 950˚C. ESR using a CaF 2 -CaO-Al 2 O 3 slag system led to a high yield in Cr, Ni, Mo, W, Mn and V, while the yield of Si is low. The desulphurization of all six UHSS grades was pronounced with most of the sulphur removed either to the slag or by gas reactions. The degree of dephosphorization was only 5% irrespective of the steel composition. On the other hand, denitrification (removal of nitrogen) was achieved. It ranged from 8% to 63% depending on the steel composition. The yield of the alloying elements and removal of impurities from the steel during ESR depends on the chemical and physical properties of the ESR slag and the activity of the elements in the molten state, taking into account elemental interactions.

The mechanism of solid solution decomposition within the chemj.cal spinodal boundary was investigated for the tungsten-chromium system. Two alloys were solution treated, quenched, and aged at various temperatures inside the chemical spinodal boundary. It w·as concluded from x-ray and metallographic evidence that tungsten-chromium alloys do not decompose by a spinodal mechanism. The decomp(,)sition process was found to be one of nucleation and growth. This observation is in agreement with Cahn's 4 theory of the effect of strain energy on the occurrence of spinodal decomposition~