FAQ

What is a stainless steel?

Stainless steel is a steel alloy that contains at least 10.5% chromium. The chromium and oxygen form a passive chromium oxide layer that protects the metal from corrosion.

What is ‘acid-proof’ steel?

Acid-proof steel is a layman term that is used to describe steel that is alloyed with molybdenum to provide improved corrosion resistance. The most common acid-proof steel is ASTM 316 and most of the grades in the BUMAX® range can be considered as acid-proof steel. It is however important to point out that the term “acid-proof steel” does not necessarily mean that the material is corrosion resistant to acids, it is more complicated than that. The chemical composition, concentration and temperature of the solution must be considered. BUMAX can help you to select the best possible material for each environment.

What is duplex stainless steel?

Duplex stainless steel, also known as Ferrite-Austenitic stainless steel, has a mixed microstructure of austenite and ferrite. It is a steel type that consists of high strength corrosion resistant grades and is characterized into groups based on their alloy content and corrosion resistance.

Types of duplex stainless steel:

  • Lean duplex – similar or lower corrosion resistance than ASTM 316.
  • Standard Duplex – most common type of duplex stainless steel, with better corrosion resistance than ASTM 316.
  • Super Duplex – PRE >40, material for severe corrosive environments such as petrochemical, oil/gas and marine.
  • Hyper Duplex – PRE >48, better corrosion resistance than all super duplex stainless steel grades available on the market.

What is PRE?

PRE stands for Pitting Resistance Equivalent. It is a theoretical way of ranking different stainless steel grades in terms of pitting corrosion resistance, mainly in saltwater or chloride bearing environments. The most common PRE equation is:

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

Are all BUMAX products of European origin?

Yes, all BUMAX raw materials (wire rod, bars and sheets) are sourced from European premium manufacturers and our fasteners are made in Europe.

Why should I use BUMAX 88 instead of an ordinary A4-80?

BUMAX 88 is a premium product within the A4 standard. BUMAX 88 offers many advantages compared with the vast majority of A4 fasteners:
• BUMAX 88 is a 316LHigh Mo grade, meaning that we guarantee a minimum quantity of 2.5% molybdenum compared to a standard A4 which is 2.0%. This enhances the PRE value and corrosion resistance.
• BUMAX 88 is sourced solely from premium European stainless steel manufacturers according to rigid specifications. The tight tolerance on each element, controlled process and the best available metallurgical process gives very clean steel with a low amount of inclusions and slags. This results in a consistent material with very little variation from batch to batch and much better fatigue and corrosion resistance.
• BUMAX 88 has higher yield strength than A4. BUMAX 88 offers a minimum yield strength of 640 MPa, compared with a minimum of 600 MPa for A4.
• BUMAX 88 offers traceability throughout the entire production process, from melting to finished fastener.
• BUMAX 88 offers excellent surface quality and hard threads. Many customers appreciate the anti-galling properties of BUMAX 88 compared with A4.

What is the difference between cut and rolled thread?

Cut threading is a process that normally takes place in a lathe where steel is cut away from a round bar to form the threads. Roll threading is a process by which the material is extruded with threading dies to form the thread, instead of being removed. There are several benefits with rolled threading and it is used whenever possible on BUMAX fasteners. The strain hardening that takes place during roll threading will increase the strength of the fastener and is beneficial for the fatigue resistance. Furthermore, rolled threads are often smoother than cut threads. There are some products where rolled threading cannot be used and cutting is needed, particularly for very large dimensions.

Can BUMAX be manufactured according customer specific drawings and requirements?

Yes. We specialize in offering custom solutions to specific customer requirements. We have an engineering department that is dedicated to offering design guidance, calculation support, testing and material selecting support.

What is the maximum service temperature for BUMAX?

Recommended maximum service temperature for each grade can be found in the section Technical information. All steels are affected by higher temperatures, which can lead to reduced strength, fatigue resistance and corrosion resistance. Long-term exposure can also cause creep deformation, relaxation and brittleness due to over-aged material. The thermal expansion that occurs at elevated temperatures must also be considered, especially if material with a different Constant of Thermal Expansion is combined. There have been cases where BUMAX fasteners have successfully been used in temperatures exceeding the recommended maximum service temperature, but this must be evaluated on a case by case basis with good understanding of the effect it will have on the fastener properties.

Are BUMAX products non-magnetic?

We have grades that are optimized to have very low magnetic permeability, and are therefore considered to be non-magnetic. Austenitic stainless steel generally has very low magnetic permeability although this is affected by chemical composition, metallurgical process, residual stresses and the amount of deformation martensite that is created during cold working. Our BUMAX 88 is well suited for applications with high demands on low magnetic permeability, such as in the electrical nuclear power sectors. BUMAX 88 offers lower magnetic permeability than standard A4, with less variation in properties from batch to batch. See Magnetic permeability or contact us for more information.

BUMAX is available worldwide

Our extensive network of sales offices and distributors makes it easy to get in touch with us. Find your local sales office or distributor below. For other countries not represented, please contact our Main Sales Office.

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