MTI

Lab 2 - Welding

This lab exercise is based on a lab from MET E 421 - Metallurgy Processes taught at the University of Washington. In this lab we will evaluate the Charpy impact strength and tensile strength of five different weld types. At a later lab we will observe the microscopy of the welded samples.

Today’s lab session is in three parts: 

  1. Welding demonstration by Dave Demaray
  2. Charpy impact testing of welded samples
  3. Instron tensile testing of welded samples.

The base metal for all samples is mild steel.

The five welding processes used and the filler material are as follows:

Welding Category

Specific Process

Filler Material
Shielded Metal Arc Welding (SMAW) Stick Welding space.gif (335 bytes)
Oxyfuel Gas Welding (OFW) Oxy-acetylene space.gif (335 bytes)
Gas Metal Arc Welding (GMAW) Metal Inert Gas (MIG) space.gif (335 bytes)
Gas Tungsten Arc Welding (GTAW) Tungsten Inert Arc (TIG) space.gif (335 bytes)
Hard Solder Silver Solder space.gif (335 bytes)

The Charpy impact samples were prepared following ASTM E 23 - 94b Standard Test Methods for Notched Bar Impact Testing of Metallic Materials.

The Charpy impact test is a method for determining behavior of materials under conditions favorable to brittle fracture. The test is used where results of a tension impact test would not be significant. It is the most popular impact test. The test is performed by striking a notched specimen supported as simple beam with a falling weight. Results are reported as energy absorbed in fracture and a description of the fracture.

The following ASTM standards describe the Charpy impact test for various materials:  

Discussion Questions from MET E 421 Lab

  1. Composition of the 304 and 308 (weld filler) metal.

    2.  

  2. Analysis of stress-strain curves

    3.  

  3. Brief description of the welding processes and how the samples were prepared. Test parameters: crosshead speed, specimen geometry. Basically think of those things which a person would need to know in order to repeat the experiment.

    4.  

  4. Rank the usefulness of the MIG, TIG, Base metal, in terms of strength and ductility. Don’t look for huge differences, I’m not sure they exist, but come to some conclusion and argue the point persuasively. See also the question below. Perhaps there will be some experiment that would help prove or disprove your point.

    5.  

  5. Describe any additional experiments, which might be performed in order to evaluate the relative merits of MIG with filler metal versus TIG fusion versus base metal. For example, any additional tensile tests or hardness tests or how the tests that were performed might be improved upon (improvement of specimen geometry, additional measurements of the samples, etc.) Include your reasons for including the additional tests.

    6.  

  6. Describe (perhaps with a schematic sketch) the two samples of the weld (TIG, MIG) that were prepared for optical microscopy. Which method do you think produced the larger heat effected zone and larger grain growth? What does this tell you about the relative heat input of the two processes?

 

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