Questions:
We make steel shackles for padlocks, and the material we use is 15B21H steel. The parts are carbonitrided, and we need to achieve a 40+ HRC core hardness. We also must comply with SAE J1268. My questions are as follows:

1. What does it mean to specify an H-band steel?

2. By not designating the "H" on 15B21, is it possible that our commercial heat-treat source would not be able to achieve the core-hardness specification?

3. Are all boron steels H-band steels?

4. Should 15B21H be certified from the raw-material supplier, and do I need to provide this information to my heat treater?

Answers:
SAE J1268 is a specification for all carbon and alloy H-band steels along with their corresponding minimum and maximum hardenability limits (based on Jominy testing).

In answer to your questions:

1. H-band steels have wider chemistry limits so that the raw-material supplier can achieve specific hardenability ranges. For example, with 15B21H the typical hardness limits for specification purposes are (Jominy values in mm):
  • J1.5 = 48 maximum, 41 minimum
  • J3 = 48 maximum, 40 minimum
  • J5 = 46 maximum, 36 minimum
  • J7 = 43 maximum, 27 minimum
  • J9 = 38 maximum
  • J11= 30 maximum
Oil quenching, such as commonly follows carbonitriding may not result in values over 40 HRC in the core unless the part section thickness is thin.

2. The addition of boron to this steel is intended to enhance hardenability, especially in the core. See the references below. Boron in combination with manganese will aid hardenability, and if the manganese levels are toward the high end of the range for 15B21H (nominally 0.70-1.20%Mn), it will provide even a greater hardenability and give you an edge when heat treating. Oftentimes you can request/specify higher manganese levels at no additional cost from your steel supplier.

3. All boron steels are not H-band steels.

4. You should call out the material as 15B21H to your heat treater and provide him with a copy of your material certification sheet. In this way he will know the material chemistry, including trace elements, hardenability values, grain size and prior heat treatments performed.