The Influence of Vanadium Microalloying on Voids Occurence in Low-Alloyed Cr-Mo Steels After Continuous Casting

Abstract

We discuss the correlation between segregation of carbide forming elements (vanadium) and void initiation and propagation in low-alloyed Cr-Mo steels. The internal defects are created during blooms straightening in radial type of casting machine due to strain deformation field in the temperature range characteristic for vanadium nitride, carbide or carbonitride precipitation. Based on the statistical analysis (1097 continuously cast blooms) of three low-alloyed Cr-Mo steel variants with different vanadium content, we conclude that the void occurence is strongly associated with the level of vanadium content. The experiments performed by means of microstructural, fractographic investigations and microchemical point analysis proved that preffered areas for void initiation are interdendritic segregations in the core of bloom. We observed vanadium carbide precipitates that are situated close to the cracks, whereas the content of vanadium was 7,5 times more then in an average smelt composition. The further development of defects is connected with fast heating up to the austenization temperature in soaking pit. Our results confirm that marked decrease of defects can be achieved by optimization of production process, i. e. optimized casting speed, steel overheat above the liquidus temperature and/or application of M-EMS.

Comparative strain analysis of 34CrMo4 steel and Inconel 738LC

“…Good performance of the 34CrMo4 steel at high pressures enables its application to gas cylinders. The steel is primarily produced as blanks -wire, universal mill plates, forgings, seamless tubes, hot-rolled billets, rolled bars, hot-rolled strips or steel for refining [1][2][3][4]. The heat-treatable steel could be in different thermal treated stages, as austenitized and quenched or austenitized, quenched and tempered.…”

Continously Cast Bloom With Internal Defect - Fem Model Optimization

“…It is generally known that niobium and vanadium microalloyed steels are very sensitive to surface and internal defect occurence after continuous casting. It was found that it is caused by suboptimal casting conditions setting such as steel superheat, casting speed, secondary cooling intensity in combination with blooms straightening in temperature range where NbC, NbN, Nb(C,N), VC, VN and V(C,N) precipitates [1][2][3][4][5][6][7]. It was also found that proper heating strategy preceding the hot rolling process is necessary to prevent excessive internal defects grow [8][9][10].…”

Simulation of the Carbides Precipitation Mechanism in 34CrMo4 and 42CrMo4 Steels

“…The only relevant difference among these steel grades is vanadium content. Based on the manufacturing experience it was discovered that 24CrMo4 and 34CrMo4 steels are significantly more sensitive to the cracks that occurred after continuous casting and/or heating in the soaking pit [1][2][3][4][5]. Critical points of the manufacturing process were already identified.…”

“…In terms of the VC, VN and V(C,N) precipitation mechanism it is possible to state that the precipitation occurs in the stable austenite through heterogeneous nucleation of the VC, VN and V(C,N) on the dislocations, austenite grain boundaries and the MnS particles [2,3]. In many cases it can arise even complex multiphase inclusions, it is possible to observe multiphase inclusions such as MnS, (Ti,V) (C,N) and AlN [14].…”

“…The negative effect of precipitation of carbides, nitrides and carbonitrides of vanadium is realized during the continuous casting, if the proper casting conditions are not guaranteed. Continuously cast blooms straightening within the critical temperature range (1073 -1273 K) on the radial casting machines creates unfavourable stress-strain conditions that contributes to the initiation and propagation of the internal cracks [1][2][3]. Typical internal defect present in 34CrMo4 steel after hot-rolling is shown on Fig.1.…”