Metallographic ：
a. Purpose: Applying microscope (optical, SEM, EDS) to investigate the metal microstructure which cause by manufacture process or in-service.
b. Application: Using the optical microscope or electron microscope are used to examine the microstructure of metal materials at different magnifications, such as sensitization, creeping, fatigue, phase change, crystal size, intermediates, decarburization, carburizing, hardening depth, or material properties and damage analysis.
Hardness Test ：
a. Purpose: To measure the variation of the hardness condition of a material before and after heat treatment, processing, and in-service.….etc. With the information, we can understand the results of processed for our evaluation
b. Principle: There are several hardness test methods such as Brinell (HB), Rockwell (HR), Shore (HS), Vickers (HV) and Leeb (HL). All methods use a probe (steel ball, indenter, or diamond tip) at a rated load on the test surface, after release the load the diameter of indentation, diagonal length, and rebound height is investigated, and then calculates into a hardness value.
A latest hardness test method applied the ultrasonic impedance. It uses a metal rod with a diamond tip at front to excite into longitudinal oscillation by a ceramic piezoelectric transducer at an ultrasonic frequency. When the test load is applied, a frequency shift occurs as proportional to diamond penetrates the metal. Then electronic detected by piezoelectric receiver measures the shift of an ultrasonic frequency and convert to hardness value.
c. Application:
1) To examine the results after heat treatment of steel.
2) To evaluate the hardness after hardening and hardening depth.
3) To evaluate the hardness variation at the weld of in-service pressure vessel and piping
