Abstract
4Cr14Ni14W2Mo is a duplex stainless steel demonstrates great corrosion resistance, heat resistance and oxidation resistance, which makes it widely used in engines, valves and any situations require small deformation in severe environments. We choose this material cut off in valve manufacturing as a representation of complex stainless steel. In this website, we lead you to explore its chemical components and unique duplex microstructure, use tables with data to show properties and evaluate what offers it these advantages. Based on them, we would demonstrate applications, and analysis its manufacture process from multiple aspects.
Keywords: S32590, Duplex, Heat and corrosion resistance,
Figure1. Two pieces of 4Cr14Ni14W2Mo
Introduction
As the engineering and technology progresses, the complexity and difficulty increase in all aspects of construction and manufacture, more materials with specific properties that can stand in severe conditions are of great demand. For traditional materials, the original properties should remain but other properties are expected to enhance and improve. Here we present a special stainless steel: 4Cr14Ni14W2Mo which not only remains the great mechanical properties as a steel, also has great corrosion resistance and heat resistance which make it can be applied in server conditions like engine and valves.
Properties
Composition(mass fraction)(wt.%)(9)
Max: 0.50%C, 0.80%Si, 0.70%Mn, 0.35%P, 0.03%S, 15.00%Ni, 15.00%Cr, 0.40%Mo, 2.75%W
Mechanical properties(9)
|
Young’s modulus |
243 kN/mm2 |
|
Tensile strength(after annealing） |
817 MPa |
|
Proof strength Rp0.2(after annealing） |
363 MPa |
|
Elongation(at fracture) |
44% |
|
Reduction in cross section on fracture Z |
43% |
Thermal properties(9)
|
Melting point |
5989 - 6128 °C |
|
Thermal conductivity |
23 - 98 W/m*K |
|
Specific heat capacity |
450 - 460 J/kg*K |
|
Thermal expansion |
70 - 57 e-6/K |
Electric properties(9) (10)
|
Electrical conductor or insulator |
Poor conductor |
|
Resistivity |
8708 - 8515 Ω*m |
Resistance properties (11)
|
Corrosion resistance |
Great |
|
Oxidation resistance |
Great |
Eco properties (12)
|
CO2 footprint(without recycle) |
2.9 kg/kg |
|
Recycle |
√(100% recyclable) |
Reflection
Through the whole project, all group numbers show their greatest enthusiasm and efforts. We studied the material by variety approaches, which increases our knowledge in not only one specific material, but the ferritic metal family. We maintain smooth and clear communication despite the difficulties in online working, which contributes to the conducting of the project. We improved our literature researching ability as the information about this material is limited. We maintained impeccable group management and shared work equally.
Literature review
4Cr14Ni14W2Mo, or S32590, is a kind of special austenite stainless steel with duplex (1) structure, it has become a widely applied material in conditions requires high temperature strength and heat resistance (2).
- Classification:
- Stainless steel: 13%-15% Ni and 13%-15% Cr components (3)
- Duplex: two primary phases: f.c.c austenite and b.c.c. ferrite, often seen as austenite steel
Chemical components (2)(4)(5)
- 5% max Carbon: Medium carbon steel, good strength and toughness.
- 13%-15% Chromium: greatly improve strength, corrosion resistance and heat resistance
- 13%-15% Nickel: increase strength, corrosion resistance and toughness,
- form solid solution strengthen, form austenitic
- 8% max Silicon: improve strength and acid resistance by enlarge ferrite grain size.
- 2.5%-0.4% Molybdenum 2%-2.75% Tungsten: improve strength, corrosion resistance and oxidation resistance.
- Form carbide, which reduces Cr carbide, increased the corrosion resistance and heat resistance given by Cr.
- Not solute able carbide: grain boundary pinning effect, which prevent austenitic grain size grow, refining grain, thus makes solid solution better, contribute to tenacity of the steel
Microstructure
- Duplex : steel combain two phases: ferritic (b.c.c) and austenitic (f.c.c) . (6)
- Crystallize by fully ferritic or ferritic–austenite solidification with the austenite precipitation due to the solid solution(7)
Figure 2. Distribution of ferritic (black phase) and austenitic (white phase)(7)
Formation process
Figure 3. Phase diagram of Fe-Ni-Cr (6)
- The austenitic as γ, ferritic as α, initially solidify as σ.
- Cr in favor of solidification of ferritic, Ni in favor of austenitic, as the concentraction of Ni and Cr are similar, the distribution of two phase do not shows obvious difference
- By recrystallization and deformation to refine crystal, S32590 obtain typical pancake-like structure, which greatly increased strength and toughness based on the Hall-Patch principle.
- The two-phase microstructure inhibits grain growth during deformation and heat treatment. The ferritic phase tend to coalesce while due to the rapid diffusion processes in f.c.c. lattice, while the austenite phase coarsens slowly
- The solubilities for interstitial elements in ferrite are approximately 100 times lower while the diffusion rates are 100 times lower than those in austenite. Which causes that the formations of carbides, nitrides, and intermetallic phases is easy and occur in the ferritic phase only. (8)
- The formation of chromium carbides has a significant negative influence on the oxidation resistance and corrosion resistance.
References
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[2]4Cr14Ni14W2Mo forging [Internet]. Tool & Die Steels. 2020 [cited 4 March 2020]. Available from: https://www.tool-die-steels.com/products/forging-rolling/46/139/45Cr14Ni14W2Mo-forging.html?tdsourcetag=s_pcqq_aiomsg
[3]Chan W, Kwok C, Lo K. Effect of laser surface melting and subsequent re-aging on microstructure and corrosion behavior of aged S32950 duplex stainless steel. Materials Chemistry and Physics. 2018; 207:451-464.
[4]Christian Doppler Laboratory for Early Stages of Precipitation The Effects of Alloying Elements on Steels (I) [Internet]. Technische Universität Graz; 2020 [cited 19 March 2020]. Available from: https://online.tugraz.at/tug_online/voe_main2.getvolltext?pCurrPk=32837
[5]Effect of alloying elements on steel properties [SubsTech] [Internet]. Substech.com. 2020 [cited 20 March 2020]. Available from: https://www.substech.com/dokuwiki/doku.php?id=effect_of_alloying_elements_on_steel_properties
[6]Weber J. Encyclopedia of Materials - Science and Technology, Stainless Steels: Duplex, Volumes 1-11. 2nd ed. Knovel; 2001.
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[8]Knyazeva M, Pohl M. Duplex Steels. Part II: Carbides and Nitrides. Metallography, Microstructure, and Analysis. 2013;2(5):343-351.
[9]Steels T. 4Cr14Ni14W2Mo - Stainless Steel,Heat-Resistant Steel and Special Alloy Steel - steel, 4Cr14Ni14W2Mo Datasheets, Supplier, Chemical composition, properties [Internet]. Tool-die-steels.com. 2020 [cited 28 May 2020]. Available from: https://www.tool-die-steels.com/grades/Stainless-Steels-Special-Steel/31/140/4Cr14Ni14W2Mo.html.
[10]CES EduPack 2018, Granta design, level 3, MaterialUniverse, Austenite steel, Cambridge UK. [Cited 28 May, 2020].
[11]Chan W, Kwok C, Lo K. Effect of laser surface melting and subsequent re-aging on microstructure and corrosion behavior of aged S32950 duplex stainless steel. Materials Chemistry and Physics. 2018; 207:451-464.
[12]Sandberg, H., Lagneborg, R., Lindblad, B., Axelsson, H. and Bentell, L., 2001. CO2 emissions of the Swedish steel industry. Scandinavian Journal of Metallurgy, 30(6), pp.420-425.