Abstract
The paper presented the findings obtained by industrial research and experimental development on the use of rare earth metals (REMs) in the production of heavy steel ingots and their impact on the internal quality of the 42CrMo4 grade steel forging. REMs alloying was carried out after vacuuming the steel. A relatively large melting loss of cerium (about 50%) and its further decrease in casting due to reoxidation were observed. Refinement of structure and better mechanical properties of forged bar containing about 0.02 wt.% of Ce compared to that of the standard production were not achieved. The wind power shaft with content of about 0.06 wt.% of Ce showed high amount of REM inclusions, which were locally chained, and in some cases, initiated cracks. Four stoichiometrically different types of REM inclusions were detected in forgings, namely (La-Ce)2O2S + (La-Ce)O2 + SiO2 (minority); oxygen, phosphorus, arsenic, and antimony bound to lanthanum and cerium probably bonded with iron oxides La + Ce, MgO, Al2O3 a SiO2; (La-Ce)2O2S, FeO, SiO2, and CaO or CaS.
Highlights
Supervision of the quality of products in metallurgical production imposes on the company the obligation to comply with numerous standards and procedures—which results from the specificity of metallurgical processes determined by thermal processes and chemical dependencies of components
The results showed that after modification with Ce/La, the morphology, size, and distribution of Cr7C3 carbides change greatly
Experiments were realized in two stages, when two trial heats of low-alloy structural Cr-Mo steels, which were alloyed by rare earth metals (REMs) in the form of Mischmetal with a composition of 59.3 wt.% of Ce, 36.5 wt.% of La, 0.2 wt.% of Fe, and 0.4 wt.% of Mg, were gradually produced in the electrical steel plant
Summary
Supervision of the quality of products in metallurgical production imposes on the company the obligation to comply with numerous standards and procedures—which results from the specificity of metallurgical processes determined by thermal processes and chemical dependencies of components. Metallurgical processes such as casting, forging, and rolling, etc., are classified as special processes. Large steel products produced by complex open-die forging processes are widely used in industries with high quality demands on structural and mechanical properties. The input semifinished product for the production of these shafts is heavy steel ingots, in which there may be problems with achieving the required internal quality due to the occurrence of a very inhomogeneous and coarse-grained structure [15,16,17,18]
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