If the material is low on hardness or even totally soft, it is usually incorrect material. This can have occurred either by selection at the merchant or mixed at the purchaser’s operation. The method of steel identification can either be by spectrographic analysis or by spot chemical grinding into the surface of the steel to get into the “clean steel.”

If the component has failed completely, then the tree diagram shown in Fig. 2 should be considered. In the case of component failure, you should consider: 

  • Checking the quality of the furnace atmosphere
  • Checking if sufficient stock has been removed prior to heat treatment to remove any mill decarburization
  • Checking the salt analysis if salt-bath heat treated (salt could possibly be in a decarburizing condition)
  • Checking for discoloration after pressure quench if the part has been vacuum heat treated (this is an indication of either a leak in the furnace at a seal or in the vessel itself)
  • Checking for the possibility of contaminated quench gas

If the steel is only 3-6 HRC points lower than required after quenching, there is the probability of retained austenite being the root cause. The retained-austenite phase is usually found in the higher-alloyed steels, such as tool steels (O series, H series, HSS series and D series), but it can also be seen as a result of minimal control on carburizing steels.

Read part 1 here.