In Conclusion

Answers

1.) What metal is inherently brittle with natural occurring defects?

Cast Iron is brittle and has graphite (flakes) that occur naturally in great abundance in the casting that lowers the strength and prevents the cast iron from being stretchable (ductility) giving it a brittle property.

2.) What is the most common carbon steel found in boilers, pressure vessels, tanks, and piping?

Low carbon steel is the answer because it has relatively good strength and ductile. Low carbon steel is easily weldable and significantly cost effective when compared to other metals like stainless steel, alloy steels, non-ferrous metals.

3.) Do all stainless steels have the same corrosion resistance?

No. The level or concentration of chromium in the stainless steel determines the level of corrosion resistance. The amount of chromium is one of the principal chemical components of stainless steel that provide a naturally occurring protective layer of chromium oxide when the stainless steel is exposed to our atmosphere.

4.) Why will a weld fail?

The answer is 'All the above.' Stress risers in the weld geometry can initial a weld failure and this includes too much weld and an undersized weld. Impurities in the weld will cause internal stress risers. Also, if the chemistry of the weld is different than the (base) metal the two will not mix and essentially behave like to separate metallic pieces and fail early. Finally, when both weld and (base) metal have two different physical properties early failures or premature failures will occur from fatigue or cyclic stresses. Of course there are other reasons for weld failures like weld machine settings and qualifications of the welder and these are beyond the scope of this simple tutorial.

5.) What is the general cause of corrosion of low carbon steel?

Answer is 'All the above.' Using two-dissimilar metals together causes a difference on the natural electrical charge of the two-different metals. Being in the presence of moisture (+60% RH) or in water will cause corrosion. Finally, stray electric currents in even very small amounts can accelerate corrosion of metals. The sources of these stray electric currents can be near by transformers or a lighting circuit that is leaking stray current on the neutral or ground.

Congratulations

You now have a better understanding of metallurgy and a basic metallurgical understanding of metals.

We hope in some way that your view of life is now enhanced with an appreciation of how metals affect our activities everyday.

We are not here to make you into a metallurgist or metallographer. Understandably this introductory tutorial cannot possible address every requirement and was never intended to. It does highlight important and key issues.  More in-depth training courses are available at AIS Technical Training

If you would like further reading materials please visit our sister company AIS Engineering Books.

Please email us your suggestion or comment to info@ais-metallurgical-testing.com. This will help other students in developing a better tutorial.

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