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GRADI

BUMAX Product portfolio

All values are nominal unless stated otherwise

Grades Trade name EN UNS Micro structure C max Cr Ni Mo Other Max temp¹ Pre²
A2: Widely used grade for moderate corrosive environments. AISI 304 1.4301 S30400 Austenitic 0.07 17-19.5 8-10.5 - 300ºC (570ºF) 25
A4: Widely used grade with good corrosion resistance in chloride-bearing media. AISI 316 1.4401 S31600 Austenitic 0.08 16.5-18.5 10.5-13 2-2.5 300ºC (570ºC) 25
BUMAX 88, 109: BUMAX 88 and 109 offers higher mechanical properties and better corrosion resistance than standard A4 due to higher Molybdenum content.
Generally tighter tolerances on all elements as well as lower max limit of trace elements compared with standard A4.
AISI 316L, 316LHigh Mo 1.4432 S31603 Austenitic 0.03 16.5-18.5 11-13 2.5-3 300ºC (570ºC) 27
BUMAX SuperAustenite: High-alloy austenitic stainless steel for use in seawater and other aggresive chloride bearing medias. High resistance to general crevice, pitting and stress corrosion. 254SMO 1.4547 S31254 Austenitic 20 18 6.2 N, Cu 300ºC (570ºC) 43
BUMAX Duplex: Bumax Duplex is characterized by excellent strength, ductility and fatigue resistance in combination with good general, pitting, crevice and stress corrosion properties. SAF2205 1.4462 S31803
S32205
Ferrite-Austenitic 22 5.2 3.2 N 0.18 300ºC (570ºC) 36
BUMAX SuperDuplex: Bumax SuperDuplex is characterized by excellent mechanical properties and very good corrosion resistance. Excellent resistance to general crevice, pitting and stress corrosion in chloride bearing medias. SAF2507 1.4410 S32750 Ferrite-Austenitic 0.03 25 7 4 N 0.3 300ºC (570ºC) 42
BUMAX HyperDuplex: Bumax Hyperduplex is a groundbreaking alloy used in the most demanding applications. Suited for use in severe environments such as hot chlorinated sea-water and for aggressive acidic chloride containing media in chemical, oil, gas and petrochemical industry. SAF2707HD 1.4658 S32707 Ferrite-Austenitic 0.03 27 6.5 4.8 N 0.4, Co 300ºC (570ºC) 49
BUMAX Ultra: BUMAX Ultra is a unique precipitation hardenable stainless steel that can be delivered in Ultra high strength levels. Strongest stainless steel on the market. Good corrosion resistance in chloride environments. Sandvik Nanoflex S46910 Martensitic 0.02 12 9 4 Al, Ti, Cu 350ºC (840ºF) 25
A286: High temperature resistant material for applications requiring high strength and god oxidation resistance at temperatures up to 700ºC. Can be precipitation hardened. Alloy 286, AISI 660 1.4980 S66286 Austenitic 0.08 15 26 1.5 Ti, V 700ºC (1300ºF)
Nimonic80A: Precipitation hardenable high temperature resistant material with good oxidation resistance and high tensile and creep properties at temperatures up to 815ºC. Nimonic80A, Alloy 80A 2.4952 N07080 Austenitic 0.10 19 >65 - Al, Ti, Co 815ºC (1500ºF)

¹ Max recommended service temperature. Mechanical properties are affected by cryogenically and elevated temperatures, for more information see chapter: “Temperature effect on the mechanical properties”.

² A parameter for comparing the resistance of different steels to pitting corrosion is the PRE number (Pitting Resistance Equivalent).
The PRE is defined as, in weight-%:PRE= % Cr + 3.3 x % Mo + 16 x % N

Other grades can be offered on request: AISI 302, 310, 321, 904L, LDX 2101, Hastelloy ®, Inconel ® Alloy 600, 601, X750, 625, 718, Incoloy ® Alloy 800HT, 825, 28, Monel ® Alloy 400, 253MA.

 

Physical properties

All values are nominal unless stated otherwise

Grades *20 to 100ºC
(86 to 200ºF)
*20 to 200ºC
(86 to 400ºF)
*20 to 300ºC
(86 to 600ºF)
Resistivity
µΩm (µΩin.)
20ºC (86ºF)
Modulus of Elasticity
GPa (10³ ksi)
20ºC (86ºF)
Max relative
permeability
20ºC (86ºF)
A2 16.5 (9.5) 17.0 (9.5) 17.5 (10) 0.80 (31) 190 (27.7) 1.800
A4 16.5 (9.5) 17.0 (9.5) 17.5 (10) 0.80 (31) 190 (27.7) 1.03
BUMAX 88, 109 16.5 (9.5) 17.0 (9.5) 17.5 (10) 0.80 (31) 190 (27.7) 1.007
BUMAX SuperAustenite 16 (9) 16 (9) 16.5 (9.5) 0.84 (33) 195 (28) 1.003
BUMAX Duplex 12.5 (7) 13 (7.5) 13.5 (7.5) 0.84 (33) 200 (29) 50
BUMAX SuperDuplex 12.5 (7) 13 (7.5) 13.5 (7.5) 0.83 (32.7) 200 (29) 50
BUMAX HyperDuplex 12.5 (7) 13 (7.5) 13.5 (7.5) 0.75 (29.5) 200 (29) 50
BUMAX Ultra 11.5 (6.5) 12 (6.5) 12 (7) 0.83 (32.7) 190 (27.5) 1000
A286 16.5 (9.5) 16.5 (9.5) 17 (9.5) 0.91 (35.8) 200 (29.5) 1.007
Nimonic80A 13 (7.5) 13.5 (7.5) 13.5 (7.5) 1.24 (48.8) 210 (30) 1.001

 

* Thermal expansions, mean values in temperature ranges (x10-6) per °C (ºF)

 

 

Croce selezione Gradi

 

 

Corrosion resistance

The corrosion properties of a stainless steel are defined mainly by the ability to form a protective passive layer of Chromium Oxide, and to remain in the passive state in the actual environment. When passivity cannot be maintained, due to a too aggressive environment, the metal will be exposed to the surrounding environment and corrosion will occur.

The Pitting Resistance Equivalent value (PRE1)) gives a good indication of the pitting and crevice corrosion resistance as a function of the alloying content. The corrosion resistance of a stainless steel fastener is not only defined by the chemical composition of the steel, but by many other factors such as, fastening design, surface quality, stresses and presence of crevices. Environmental factors as concentration of chloride ions, chemical composition of the corrosion environment, temperature, pH, pressure and oxidizing agents is important information to determine the material resistance and selecting the right material.

Many forms of corrosion exists, the most common types are described below.

General corrosion: Characterized by a uniform corrosion over the surface. It is therefore common to define a corrosion rate as mean metal lost per unit time, mm/year or milli-inch/year (mpy).

Pitting corrosion: Localized to a small area and creates pits in the metal. Pitting corrosion is often much more insidious than general corrosion as a single pit can be starting point of a failure.

Crevice corrosion: Same corrosion principle as pitting corrosion but occurs in crevices. Crevice corrosion can occur in concealed places such as small gaps and contact areas between parts and spaces where corrosive deposits can be retained. Correctly selected material in combination with a good design and cleaning will reduce the risk of crevice corrosion.

Galvanic corrosion: Two different metals in the same corrosive environment, in which the less noble metal corrodes. The potential difference between the two metals produces a flow of electron from the less noble metal (anodic) to the noble metal (cathodcic). Several factors determine galvanic corrosion potential, the electrochemical potential difference between the two metals, the presence of moisture and the relative surface area ratio. The ranking of materials with regard of potential can be found in galvanic series. The relative surface area of the two metals is very important. When the surface of the noble metal is large relative to the less noble metal, there is an increase in corrosion rate of the less noble material. For an example, carbon steel bolt in stainless steel sheet has a higher corrosion rate than stainless steel bolts in carbon steel sheet, when used in the same environment. Coupling different stainless steel grades together is rarely a problem as the potential difference is too small.

Stress corrosion: Stress Corrosion Cracking (SCC) can occur when the metal is exposed to tensile stresses in a corrosive environment, often at elevated temperatures above 60°C. It is an insidious corrosion type as it can lead to unexpected sudden failure of normally ductile metals. The most common media type where SCC occurs is chloride containing solutions. Grades such as BUMAX SA, SD or HD is a must in sever condition such as swimming pool suspended ceilings and corrosive petrochemical, industrial environments.

 

Practical guidelines

  • Evaluate the environment and the likelihood of accumulated deposits.
  • Use a design that minimizes crevices and allows rain to rinse away deposits
  • Use a stainless steel fastener with equivalent or higher corrosion resistance than the component being fastened

 

1)  PRE = % Cr + 3.3 x %  Mo + 16 x % N