The present work describes the study on influence of modifying steel with rare-earth metals on metallurgical quality of ingots and finished steel. To achieve the assigned task, the laboratory melting of 08G2NMDFBT (Х100) pipe steel was carried as in open (UIP 100 – 2,4), so in vacuum induction furnace (ISV-0,01 - PI) with use of conditioning agents, which contain rare-earth metals. Next materials were used as conditioning agents: mischmetal (MM), which contain total amount of rare-earth metal (REM) up to 93 %, АlPCIr and RENTN which contain total amount of from 31 to 32,6 %

A. Z. Issagulov

P. V. Kovalev

S. D. Popova

Sv. S. Kvon

V. Yu Kulikov

English

Directory of Open Access Journals

Investigation of the effect of high strength strips steel modification with rare-earth metal (REM)

Hrčak - Portal of scientific journals of Croatia

393METALURGIJA 56 (2017) 3-4, 393-395P. V. KOVALEV, S. D. POPOVA, A. Z. ISSAGULOV, V. YU. KULIKOV, SV. S. KVONINVESTIGATION OF THE EFFECT OF HIGH STRENGTH STRIPS STEEL MODIFICATION WITH RARE-EARTH METAL (REM)Received – Primljeno: 2016-12-05Accepted – Prihvaćeno: 2017-03-10Preliminary Note – Prethodno priopćenjeP. V. Kovalev, S. D. Popova, A. Z. Issagulov, V. Yu. Kulikov, Sv. S. Kvon, Saint-Petersburg State Polytechnic University, Russia, Karagan-da State Technical University, Karaganda, Kazakhstan.The present work describes the study on influence of modifying steel with rare-earth metals on metallurgical quality of ingots and finished steel. To achieve the assigned task, the laboratory melting of 08G2NMDFBT (Х100) pipe steel was carried as in open (UIP 100 – 2,4), so in vacuum induction furnace (ISV-0,01 - PI) with use of conditioning agents, which contain rare-earth metals. Next materials were used as conditioning agents: mischmetal (MM), which contain total amount of rare-earth metal (REM) up to 93 %, АlPCIr and RENTN which contain total amount of from 31 to 32,6 %. Key words: steel, modification, REM, structure,stripINTRODUCTIONToday many issues of creating pipe steels of different strength category are solved as in terms of chemical com-pound, so in terms of their smelting technology, second-ary processing, teeming, thermo-mechanical processing and accelerated cooling. But the problem of structural and chemical inhomogeneity of smelted metal, which oc-cur during plastic processing of inhomogeneity of sheet structure and anisotropy of mechanical properties at its cross-section, remains unsolved in general. One of the main directions of improving quality of flat products for high-strength pipe steels is providing metallurgical heredity of continuous casting, which in-cludes forming a homogeneous fine-grained structure of ingot, minimizing central segregation inhomogeneity, also preventing formation of surface defects and defects of macrostructure. The presence of hereditary bounda-ries, residual dendritic segregation, structural inhomoge-neity, segregation streamer, non-metallic inclusion with unfavorable morphology in structure of metal sheet can be considered as the hereditary development of structural parameters of continuous casting (CC) [1]. The possible method of improving quality of cast and strained metal is an active forming their structure and properties by adding the conditioning agents and microalloying additives in melt before ingoting [2,3].MATERIAL AND EXPERIMENTAL METHODSMelting and holding of liquid metal for all vacuum melting were performed in vacuum with residual pres-sure equal to 2·10-3 mmHg. And the process of smelting steel in open induction furnace was next. After smelting ISSN 0543-5846METABK 56(3-4) 393-395 (2017)UDC – UDK 669. 15. 001/.43: 669. 85/.86: 620. 18: 621. 41 = 111a furnace charge at 1630 – 1650 °C degrees alloying materials and deoxidizing agents (FeMn, FeSi, FeTi, FeV, FeNb and Al) were added in furnace. The tapping of metal from furnace was held at 1600 – 1650 °C de-grees into two molds with use of intermediate ladle, which was heated up to 500 – 750 °C degrees. The first mold was filled with metal without conditioning agent; the second mold was filled with metal with condition-ing agent. The experiments on the hot simulation of controlled rolling were carried on LPS-210 laboratory rolling mill by modes applied for low-carbon high-strength pipe steels. A quantitative metallographic analysis of macro- and microstructure of cast and strained metal was held with use of Axiovert 200 MAT motorized light micro-scope and Meiji RZ stereoscopic microscope, equipped with Thixomet image analyzer. Electron micro probe analysis (EMPA) was performed on Zeiss Supra 55VP electron microscope with Inca attachment (Oxford In-struments).The results of studying influence of conditioning agents on structure cast grain shown on Figure 1. The Figure 1 shows the all-round images of macro-structure of cast metal of ingots from one smelting: non-modified and modified RZNTB in amount of 2,0 kg/t of steel. The average diameter of austenitic grain in pre-sented structures decrease from 1 110 microns to 670 microns. Thus it was established that adding the condi-tioning agents, containing REM, into steel contributes to decrease of transcrystallization zone (up to 100 %) and refinement of cast austenitic grain (on the average up to 40 %), the size of which defines the further struc-ture, obtained during the controlled rolling. RESULT AND DISCUSSIONAnalyzing results of conditioning agents’ influence on dendritic strucutre of ingot showed that modifying 394P. V. KOVALEV et al.: INVESTIGATION OF THE EFFECT OF HIGH STRENGTH STRIPS STEEL MODIFICATION... METALURGIJA 56 (2017) 3-4, 393-395increase of dispersion of dendrite structure leads to more homogeneous distribution of alloying and doping elements by cross-section of ingot. This type of dendrite structure wil contribute to obtaining more homogene-ous and dispersed structuresduring controlled rolling.The impurity of steel with non-metallic inclusions was defined according to ASTM E 1245. It is found that modifying pipe steel with REM leads to significant de-crease of its impurity with non-metallic inclusions: from 0,03 – 0,08 % for non-modified steel and up to 0,01 – 0,02 % for modified steel. The results of electron micro probe analysis of non-metallic inclusions, which were found in modified met-al, allowed to identify next types of inclusions: 1) glob-ular compounds (Ce,La)AlO3, (Ce,La)Al11O18 of mi-cron, submicron and nanometric size; 2) sharply angu-lar inclusions of (Ce,La)2O3; 3) compounds of Al2O3 - FeO system, also 4) titanium nitride TiN. The formation of these inclusions was proved by the results of thermo-dynamic simulation, except (Ce,La)2O3 particles, which are formed at non-equilibrium conditions of salvo input of modifiers. Oxides of rare earth metals are often substrates for the precipitation of titanium nitride on them by hetero-geneous mechanism resulting in formation of mul-tiphase compounds such as (Ce, La) Al11O18 + TiN. In the process of plastic deformation inclusions are trans-formed to relatively large multiphase aggregates mainly consisting of inclusions of rare earth metal oxides and system FeO - Al2O3. It is found that the steel produced in vacuum is characterized by a uniform distribution of inclusions by volume of the metal. This is due to  the fact that in vacuum melts modifier was added directly in a furnace, with the melt homogenization processes by chemical composition occurring more completely un-like open melts at which ligature was introduced to the flow during intermediate ladle pouring. Using the software package Fact Sage we did ther-modynamic modeling of the formation of non-metallic inclusions upon introduction of REM-containing liga-tures into the liquid melt. Immediately upon entering of the modifier, compounds of the following type are formed as primary inclusions: LaAl11O18, AlLaO3 and AlCeO3. Next, during the cooling and crystallization secondary and tertiary inclusions are formed: Al2O3 and CeAl11O18. In other words, in view of high reactivity, lanthanum and cerium immediately after adding the ligature precipitate as non-metallic inclusions of the fol-lowing type: RAl11O18, RAlO3. This process is accom-panied by the release of considerable heat, active spray-ing of molten metal and sparks-release. It should be noted that the most favorable morphol-ogy of nonmetallic inclusions is characteristic for ingots modified by mischmetal. In these ingots are found ex-clusively nanometric inclusions such as RAl11O18, whereas multi-phase TiN-containing inclusions reach relatively small size (up to 5 microns). In ingots modi-fied by AKCeZh and RZNTB are found similar types of with rare-earth metals leads to formation of dendrites of spherulitic type instead of dendriform ones. The Figure 2. shows image of dendritic strucutre of experimentally melted ingots. In case of modifying macrostructure across the whole cross-section of ingot, it consists of spherulitic dendrites with size of primary grain from 0,40 mm in transcrystallization zone to 1,2 mm in the middle. At the same time, the macrostructure of non-modified ingots represent mixture of dendriform and spherulitic dendrites, where dispersion of primary grain decrease from surface to core from 5 to 3-4 mm. The Figure 1  Macrostructure of cast metal a) without adding conditioning agents, b)  with adding conditioning agent RZNTB in amount of 2,0 kg/t steelDav = 1 110 micronsDav  = 670 micronsa)b)a)b)Figure 2  Dendritic (а) and spherulitic (b) structure of cast metal: а) no conditioning agents added, b) with adding conditioning agent MM 0,2 kg/t395P. V. KOVALEV et al.: INVESTIGATION OF THE EFFECT OF HIGH STRENGTH STRIPS STEEL MODIFICATION...METALURGIJA 56 (2017) 3-4, 393-395providing morphologically similar highly dispersed structure. Figure 3 shows the panoramic images and fragments of microstructure of strained metal modified by REE and without modifiers added.Furthermore, it was found that after hot strain the dendritic structure of the ingot persists acquiring band-ed nature and direction corresponding to the lines of plastic flow during rolling. This fact demonstrates the inheritance of chemical heterogeneity of the cast den-dritic structure of a starting ingot. Use of modifiers pro-vides better dispersion and uniformity of the resulting deformed dendritic structure (Figure 4).In this regard, within this work we tested in a labora-tory the technology of introducing modifying additives to molten steel both in open melting and vacuum melt-ing which ensures rare earth metals recovery within 0,003 – 0,0052 %. It is found that modification of pipe steel grades by rare earth metals reduces metal contam-ination by nonmetallic inclusions 3-4 times, provides, under certain conditions, the formation of dispersed nonmetallic inclusions up to nanometric dimensions, and increases the uniformity and dispersion of the cast and strained structure.REFERENCES[1] P. V. Kovalev, S. V. Ryaboshuk, A. Z. Issagulov, V. YU. Kulikov, SV. S. Kvon,  Y. P. Chsherbakova, G. I. Sultamu-rat, M. V. Jironkin Improving production technology of tube steel grades in converter process, Metalurgija 55(2016) 4, 715-718.[2] Ya. I. Goldstein, V.G. Mizin. Modification and micro-al-loying of iron and steel. M.: Metallurgiya, 1986, 272.[3] Golubtsov V. A., Lunev V. V. Modification of steel for ca-stings and ingots, Chelyabinsk - Zaporozhye: ZNTU 2009, 356.Note:  The responsible for England language is Nataliya Drag, Kara-ganda Kazakhstaninclusions, but their dimensions are several microns whereas dimensions of multiphase conglomerates may reach several dozens of microns. In this regard, in terms of influence on the size and morphology of the inclu-sions formed, modifiers can be conventionally arranged in the following order in priority of use: ММ→ RZNTB → AKCeZh. CONCLUSIONSResults of studying the microstructure of strained metal resulting from controlled rolling process simula-tion showed that the modified samples after deforma-tion are characterized by fine-grained polygonized fer-ritic-bainitic structure with the actual ferrite grain equal to 13 and above. When rolling modified ingots, final structure of the sheet is characterized by higher disper-sion (increase in grain number by ½), decrease in the volume fraction (by 2-10%) and the length of bainite zones of rack morphology (by 100 - 250 microns) thus a)b)Figure 3  Microstructure of the strip after controlled rolling: a) no modifiers added,b) modified by RZNTB 2,0 kg/ta)b)Figure 4  Dendritic structure of the strip after controlled rolling: а) no modifiers added; b) modified by AKCeZh 2,3 kg/t 

Investigation of the effect of high strength strips steel modification with rare-earth metal (REM)

Abstract

Similar works

Full text

Available Versions

Directory of Open Access Journals

Hrčak - Portal of scientific journals of Croatia