Welding the HY steels refers to the process of welding a family of high yield strength metals. These metals were created in the form of thick plates at the request of the United States Navy for use in the fabrication of ship hulls and submarines. Submarines need to operate 100 meters or below the Sonic Layer Depth to avoid sonar detection which is why they need to be constructed using high yield strength metals.
This class of metals, which includes HY 80, HY100, HY 130, and HY 180, is high strength. The materials are represented by their associate number which refer to their yield strength in KSI, or kilograms per square inch.
What to Avoid
There are a few precautions when welding the HY steels that should take precedent. These classes require stricter than normal welding conditions in order to optimize their characteristic potential. Low hydrogen electrodes are recommended but with the warning that they should be kept dry as well as heating them before hand to rid them of any moisture. The welds should be done will minimal heat input as well. Lower yields, or welds with minimum yield strength, are welded with low hydrogen electrodes whereas higher yield steels are better welded using plasma arc welding with metals of very low impurity levels. Preheating will be needed for thicker plates in an effort to slow the cooling rate after the weld.
There are different types of cracking that can happen when welding the HY steels, including HAZ cracking and hydrogen induced cracking. HAZ cracking refers to cracks appearing in the heat affected zone (HAZ) and can be avoided by preheating the plates before welding. Hydrogen induced cracking occurs mainly in high yield steels able to form high-carbon twinned martensite should these conditions be also present:
- Dissolving hydrogen
- Microstructure that’s susceptible
- High residual tensile stress
- Insufficient temperature scope
- Hydrogen accumulation in the internal flaws of the steel
Preheating and interpass temperature control along with post welding heating operations are effective methods in reducing the dissolved hydrogen content. This then minimizes the chances of heat affected zone cracking.
If you are attempting to weld HY steels, you should be familiar with the restrictions and procedures involved.