Good and Bad Electropolishing

Electropolishing Introduction

Electropolishing streamlines the microscopic surface of a metal object. The process removes metal from the object’s surface through an electrochemical process which is similar to, but the reverse of, electroplating.

Electropolishing effectively removing stainless steel by shedding the metal peaks or high points of the treated surface. The benefits of electropolishing are numerous, including:

• Better physical appearance
• Enhanced mechanical properties
• Better corrosion resistance

Since 2015, ICS have had Western Australia’s largest Electropolish bath for the treatment of stainless steel.

ASTM standard B912 recommends, as a pre-treatment process, the pickle and passivation of stainless steel to ASTM A380. Our facility is the only facility in Western Australia able to facilitate this large-scale service.

Good and Bad Electropolishing

To achieve a high quality Electropolishing result, starting materials with superior electropolishing properties are required. If client-supplied materials are very good quality, combined with your quality procedures throughout the ICS process, the result will be excellent.

Despite our best efforts on all projects, occasionally Electropolishing doesn’t produce the desired results. This can occur if a stainless steel part has been produced from an alloy or batch which may have inherent qualities making it impossible to achieve the desired result – e.g., pits, exposed seams, grainy, dull or ‘patchy’ luster or a generally ‘unfinished’ look are some examples of problems that may be rooted in the material.

Some of these problems can be attributed to non-metallic inclusions which can trace back to:

• Hot-rolling of slabs
• Under- or over-pickling
• Excessive or undue temperature rise (during cold rolling)
• Under- or over-annealing
• Surface decarburization during annealing
• Excessive grinding prior to cold-rolling
• Burnishing action during the last stage of cold rolling
• Contamination from exposure to industrial process materials
• Pollutants, lubricants or other materials used during manufacture

Additionally, end-grade surfaces of free-machining stainless steel grades, such as Types 303 and 416, will have a ‘frosty’ appearance after the electropolishing process due to the removal of sulfide inclusions.

Stainless steel with a fine, uniform crystal homogeneous structure will provide the best electropolishing results. While some structural characteristics can exist in stainless steel without affecting the nominally specified properties, they can still influence the electropolishing results. Some of the characteristics which may influence the electropolishing result include:

• Broken down, highly oriented structures
• Grain boundary precipitation of carbides
• Other non-homogeneities

All of these characteristics can cause a lower quality electropolishing finish.

Electropolishing Dimensions

Our electropolish bath is 6.5m long, 1.5m deep and 1.3m wide. However, pieces larger than this can be treated using a double dip method, which may result in a slight demarcation line where there is overlap.

ICS Acceptance Criteria

The electropolishing process reveals imperfections in the structure of stainless steel. It will accentuate any existing welding flaws, with a non-uniform appearance indicating a high volume of inclusions or a large-grained grade of stainless steel.

Mechanical buffing may occasionally be required to achieve the desired result, but as this service is imprecise, ICS does not include it as default, as the result varies on all pieces.

ICS’ acceptance criteria includes the following:

• Overall finish to appear with maximum brightness, luster and reflectivity on required surfaces
• Surfaces free of frosting, shadows, streaks, erosion, stains, water spots and irregular patterns in the finish
• Specified surfaces are to be free of pebbly, orange peel or pitted appearance

Contact Us

Our facilities, located in Forrestdale, Western Australia are available Monday through Friday. We can be contacted on  (0)8 9497 3500 or via our website.