KnE Materials Science | Theoretical and practical conference with international participation and School for young scientists | pages: 221–230

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1. Introduction

Being one of the most promising alloying elements, vanadium has acquired particular importance as a micro-alloying element capable of significantly increasing the performance of steel, as early as in the 60s of the last century.

The properties of vanadium, large mineable reserves of vanadium-containing ores in Russia determine the wide range of applications for vanadium-containing steels: railway rails, wheels and rings/tires, oil and gas pipes, and complex civil structures.

The use of vanadium as a micro-alloying additive allows to obtain a consistently high level of mechanical properties and performance characteristics of railway steel, traditionally manufactured by JSC “EVRAZ NTMK”. Rails, wheels, rings/tires manufactured by the company, proved to be excellent among consumers both in Russia and abroad.

Table 1 shows the analysis of rail steel manufactured by EVRAZ NTMK, Table 2 shows the mechanical properties of the finished rails.

Table 1

The analysis of rail steel K76F.


Main elements, %
C Mn Si V
GOST R 51685-2013 0.71-0.82 0.75-1.25 0.25-0.60 0.03-0.15
Actual values Mean 0.78 0.90 0.36 0.036
Minimum 0.76 0.85 0.30 0.030
Maximum 0.80 0.98 0.44 0.045
Table 2

Mechanical properties of rails type R65 of OT350 category.


Growing rail freight turnover has tasked to develop a railcar of a new generation. For these purposes, the specialists of the company developed a technology and learned to manufacture the steel grade of strength class 390 micro-alloyed with vanadium, intended for rolled products for car building (Z-profile, I-beams, etc.), in substitution for the conventional steel grade 09G2S (09G2SD), which could offer maximum strength class 345.

Table 3 shows the analysis of steel grades 09G2S and 12G2FD manufactured by EVRAZ NTMK, and Table 4: the mechanical properties of the Z-section from steel grades 09G2S and 12G2FD.

Table 3

The analysis of steel grades 09G2S and 12G2FD for car building.


Reference Main elements, %
C Mn Si P S V
345 (09G2S) GOST: 19281-2014 0.12 1.30-1.70 0.50-0.80 0.030 0.035 0.12
390 (12G2FD) TU 14–1–5391–99 0.09-0.15 1.30-1.70 0.17-0.37 0.040 0.035 0.02-0.10
Table 4

Mechanical properties of Z-section from steel grades 09G2S and 12G2FD.


Section Class Of strength (steel grade) Indicator σ т , N/mm 2 σ B , N/mm 2 δ 5 , %, % <Impact strength, KCU, J/cm2, C
+20, After mechanical aging -60
Z section Z–310 390 (12G2FD) Minimum 390 530 26 198 152
Maximum 482 599 39 379 373
Mean 419 543 31 297 278
345 (09G2S) Minimum 370 483 30 152 201
Maximum 431 539 37 373 349
Mean 399 514 33 279 284

In recent years, the company has learned to manufacture a wide range of pipe steel grades with vanadium, including those for large diameter pipes X70 and X80.

Construction in different climatic zones requires the use of high-strength steels for the manufacture of structures. The required properties are achieved by introducing various alloying elements into the steel, however the microalloying of steel by carbon and nitride-forming elements, primarily vanadium, is a better tool to improve the quality of steel. In this context, the modern development of the construction industry, primarily in the direction of high-rise construction, involves the use of I-beams made of high-strength steels of classes 390, 440, 460, micro-alloyed with vanadium and nitrogen (Table 5).

Table 5

Analysis of steel for I-beam manufacturing.


Reference Steel grade Main elements, %
C Mn Si P S N Ni V Ceq
EN 10025 S450J0 0.20 1.70 0.55 0.035 0.035 0.025 0.13 0.47
ASTM A 572 Grade 65 0.23 0.50-1.65 0.40 0.030 0.030 0.003 - 0.015 0.06
JIS G 3101:3106 SM 570 0.18 1.70 0.55 0.035 0.035 0.44
GOST R 57837 S390B 0.16 1.30-1.70 0.15-0.50 0.020 0.010 0.020 0.50 0.12 0.46
S440B 0.17 0.015 0.14

In 2017 EVRAZ NTMK started to improve liquid steel and rolled steel manufacturing processes to obtain the properties of these strength classes. To obtain the properties of rolled products, the steel analysis variants were set, which offered varying amounts of alloying elements, including vanadium and nitrogen (Table 6).

Table 6

Chemical analysis of trial steel grades for testing of the I-beam process at EVRAZ NTMK.


Option Main elements, %
Carbon (C) Manganese (Mn) Silicon (Si) Vanadium (V) Nitrogen (N) Carbon equivalent:
1 0.10 1.45 0.46 0.10 0.013 0.41
2 0.11 1.55 0.30 0.08 0.011 0.42
3 0.11 1.57 0.39 0.09 0.015 0.44

The heats were intended for manufacturing of three I-beam section types: 40K2, 40K4, 40K5 with different flange thicknesses. They were rolled at the universal beam mill of the H-beam plant using the current process.Samples for mechanical tests were taken at the hot saws to measure the quality characteristics of the rolled steel. Tensile tests were performed on proportional flat specimens.Impact toughness was tested on Charpy V-notch specimens, KCV, at temperatures of minus 40 C, minus 60 C. See Table 7 for test results.

Microstructure of an 40K5 I-beam specimen (flange thickness is 35.5 mm) was studied, which was made from steel with the analysis of variant №3. Steel structure: pearlite and ferrite, grain size number seven through nine.

The test results showed:

  • The mechanical properties of I-beams made from steel grade of the variant two and three analyses comply with the requirements of GOST 27772–2015 for steel C390 and GOST R57837–2017 for steel S390B if the material thickness is up to 35.5 mm.

  • The mechanical properties of I-beams made from steel grade of the variant three analysis comply with the requirements of GOST R57837–2017 for steel C440B with a thickness of rolled products up to 35.5 mm.

  • The impact strength values in all variants significantly exceed the requirements of the standards. A high level of impact strength at test temperatures of minus 40 C and minus 60 C ensures proper I-beam performance in civil structures and in any climate zone.

Table 7

Mechanical test results of the I-beams manufactured from the trial heats.


Section Flange thickness mm Analysis variant σ т , N/mm 2 σ B , N/mm 2 δ 5 , %, % <Impact strength, KCV, J/cm2, C
-40 -60
40К2 21.0 1 373 503 33 205
2 413 560 31 265
3 473 600 26 245 175
40К4 28.0 1 354 491 32 119
2 437 572 25 208
3 471 585 25 247 150
40К5 35.5 1 334 495 28 155
2 429 569 27 143
3 454 582 29 235 81
GOST 27772- 2015 C390 at least
370 490 20 34
GOST R 57837- 2017 S390B at least
375 520 20 34 34
S440B at least
425 580 18 34 34
legend: σ т – tensile strength; σ т – ultimate resistance; δ 5 – percent elongation; Note: The reference mechanical property values are shown for the rolled steel products over 20 through 40 mm thick.

Noteworthy that, having many years of experience in the production of steel grades with vanadium, specialists at JSC “EVRAZ NTMK” have developed several technological methods for obtaining the required vanadium and, if necessary, that of nitrogen using different types of vanadium ferroalloys:

  • lumpy (FeV80, FeV50, nitrided ferrovanadium quality FeV45N10, ferrovanadium nitride FV45N9);

  • cored wire with fillers FeV80 and ferrovanadium nitride FV37N9.

Furthermore, various methods of nitrogen micro-alloying of steel are used to obtain target nitrogen both through the use of nitrogen ferroalloys and nitrogen gas as a purge gas during metal treatment at the ladle metallurgy furnaces or as a carrier gas during metal treatment at the RH vacuum degassers.

To date, the grade mix of JSC “EVRAZ NTMK” shows over 200 successfully manufactured vanadium micro-alloyed steel grades, which is over 20 percent of the total steel produced by the company.

2. Conclusions

The use of different combinations of micro-alloying of steel with vanadium and nitrogen enables obtaining of the target amounts of these elements in a preset range, which guarantees consistent quality and the required strength characteristics of the rolled steel products.

References

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ISSN: 2519-1438