In the presence of water most metals corrode:  iron and steel rust, galvanized steel forms “white rust” when the zinc coating is exposed to moisture in the absence of air, copper turns green, and aluminum will stain under certain conditions.  Sources of moisture can be external (obvious sources such as precipitation and water leaks) or related to humidity causing condensation.

Humidity is a measure of the amount of water vapour in the air.  Specific humidity is expressed as grams of water vapour per kilogram of air.  In the atmosphere the ratio can vary from nearly zero (in deserts or polar regions) to as much as 30 grams per kilogram (in warm, tropical climates).

Relative humidity, expressed as a percent, also measures water vapour, but relative to the temperature of the air.  In other words, it is a measure of the actual amount of water vapour in the air compared to the total amount of water vapour that can exist in the air at a given temperature.  Warm air can possess more water vapour than cold air, so with the same amount of humidity, air will have a higher relative humidity if the air is cooler and a lower relative humidity if the air is warmer. 

The Dew Point Temperature is the temperature to which the air must be cooled in order for that air to be saturated and for condensation to start to form. Condensation will form on any object when the temperature of the object is at or below the dew point temperature of the surrounding air.   

Dew point, relative humidity and temperature are all related.  There are extensive tables, easily accessible on the internet, that provide the specifics.  An example:

• At 27°C, and relative humidity of 75%, the dew point is 22°C
• At 27°C, and relative humidity of 45%, the dew point is 13°C

The most reliable way to anticipate conditions conducive to condensation is to measure the dew point temperature in the area of interest.  There are units that will do this using full time monitoring and portable indicators that can be utilized on a spot basis.

Fundamentally, controlling condensation can be done by heating the ambient area to keep the objects above the dew point temperature or by reducing the dew point temperature of the air by implementing an air-drying system.  Airflow helps by reducing layers of stagnant cool air surrounding cold objects and raising their surface temperature.  It can also help to replace humid air with drier air from outside under appropriate conditions.  When condensation can’t be prevented elevated airflow can dry the water that forms on surfaces. 

In practical terms, when storing metal, it is detrimental to leave warehouse doors open especially during the spring and fall months when there may be significant differences in temperature between day and night. During the night, cold air enters and starts cooling the metal. During the day, if the temperature of the air increase rapidly the dew point rises quickly. But the temperature of the metal increases at a much slower rate and this sets up the condition where water begins to condense.  Similar circumstances can occur during loading and unloading. If wrapped material is being transported it is prudent to leave the wrapping on until the material has reached ambient temperature.

Dessicants are substances which draw and retain moisture from the environment and prevent it from reacting with the metal surface. VCI’s (volatile corrosion inhibitors) are substances that slowly release a corrosion preventative compound that is capable of protecting metal surfaces. The suitability of these methods depends on the application and the circumstances.

What does 1008/1010 mean?

• SAE International (formerly Society of Automotive Engineers) is a professional association and standards developing organization in various disciplines.
• J403 is the SAE standard which governs the chemical composition of SAE Carbon Steels, including the grades 1008 and 1010.

• It is very common for some users to specify 1008/1010 but this is, at the very least, confusing. As can be seen from the above table there is an overlap in the required chemical composition of 1008 and 1010 but they are not the same thing.  

Are 1010 and CS Type B the same?

• 1010 is a low carbon grade specified in SAE J403 to have the chemical composition shown above.
• CS Type B is a low carbon grade specified by ASTM (formerly American Standards for Testing and Materials) in various product standards (e.g. A653 for Galvanized or Galvanneled, A1008 for Cold Rolled, A792 for 55% Aluminum-Zinc Alloy-Coated, A1011 for Hot Rolled).
• More often than not, a 1010 is a subset of CS Type B, i.e. 1010 will generally meet CS Type B but not vice versa.  However, there are differences between the two grades in terms of requirements governing residual elements so a detailed review is required in order ensure a successful cross application.

What is the difference between 1018, 1020, 1021 and 1022 and what are the mechanical properties of these grades?

• 1018, 1020, 1021 and 1022 are grades specified in SAE J403 that are commonly referred to as mid-carbon grades.

• As can be seen from the above table there are overlaps between 1018, 1021 and 1022.  However these three grades can be quite different from each other depending on where in the allowable chemical composition range the steel mill aims to produce and because there are unique allowances for residual elements and additional elements in J403.
• These grades are often ordered with the expectation of meeting certain mechanical properties, e.g. 50 KSI minimum yield strength.  Care must be taken to ensure that the applied chemical composition is compatible with the mechanical properties required.

What are 44W and 50W?

• Canadian Standards Association (operating as “CSA Group”) is a Canadian organization which develops standards globally in multiple areas.
• 44W and 50W are two common grade designations under CSA G40.20/G40.21: General Requirements for Rolled or Welded Structural Quality Steel/Structural Quality Steel.
• These grades have chemical and mechanical property requirements similar to some in ASTM standards (e.g. in ASTM A1018 Structural Steels and High Strength Low Alloy Steels) but this CSA standard is intended for discrete lengths, either produced as plate or cut from coil.  As such 44W and 50W require test certification from the body of a coil if produced this way.
• Often the mid-carbon grades identified under SAE J403 will meet both the chemical and mechanical requirements of CSA G40.20/G40.21 but, due to differences between the standards, compliance to specification must be ensured by reading “the fine print”.

Many breakage problems are created by tension along a sheared edge or flange.  Some of these problems are caused by a burr due to stamping dies that are dull or have incorrectly set clearances.  When the burr, which has low ductility, is subjected to high strain, as can occur during forming, a crack may develop.  If the crack occurs in an area that is not subsequently trimmed off the result is scrap or rework. Removing the burr will reduce the length of the crack but may not eliminate it.  This is because even though the area where the greatest amount of cold work, the burr, has been removed, severe deformation of the grain structure may extend well into the base metal and reduce the ductility of that area as well.  To eliminate tearing of the blank during forming, the burr and cold worked area must be completely removed or, preferably, be prevented from developing.  This can be done by keeping the dies sharp and adjusted.

Sometimes even good edges are susceptible to splitting.  In this case it is worth reviewing the part and blank design.  Part designers often have latitude in specifying the final shapes of stampings but even where that is not possible blank shape optimization may be possible by conducting a forming severity analysis.  Based on the part geometry and material properties a finite element model can be developed for the forming stage and analyzed to assess the effect of blank shape redevelopment in minimizing edge strain at the location of the splits.

Examples of splitting at a stretched edge or flange

Schematic cross section of a sheared or blanked edge


Photomicrograph showing a cold worked microstructure in the fracture portion of the blanked edge