What is the reasonable hardness range?

There are some customers would ask the precise hardness.  Too precise sometime "my target is HRC 48, if HRC 47, it is defective and I will not accept that"

Well, this kind of request would only confuse our engineer.  The problem is how to explain it is technically impossible to do so in mass production.  During heat-treatment process, every item in the furnace would has some difference, such as material component, position by temp, position by up or down…etc.  All these thing will slightly affect the hardness.

Additionally, Rockwell hardness test, the HRC inspection machine, is with tolerance.  The tolerance of machine itself may be +/- 1-2 HRC.

The quote from ASTM E18-15 :

3.1.7.2 Rockwell hardness standardizing machine- a Rockwell ….. The standardize machine differs from a regular Rockwell harness testing machine by having tighter tolerance on certain parameters.

So if someone claimed he can make the tools with the precise hardness, I am quite curious what black box of that heat-treatment is.  In other words, when there is tighter range of tolerance of harness request, the total cost is higher.  Because it is not only the request of more precise control on heat-treatment but also the previous machine processes such as forge, machine, quality material selection…etc.  However, back to the original goal, why do you need such precise hardness?  Is it for rocket or aircraft?

If our customers have special demand for durability and torque loading performance, we usually suggest them to consider to set up the reasonable range of hardness by changing the right material as well as right heat-treatment machine in order to stably increase the quality performance in terms of durability and torque loading.

If the part broken, is it due to low quality heat-treatment?

When product is broken or deforming, it is risky to jump into conclusion.  From bad design, wrong material, insufficient machining, or not long enough heat-treatment will be part of reasons.  Heat-treatment is no doubt one of them.  If we don't set up the time right or temperature right, there would be defective.  This kind of defective can be determined by observation from piece to piece among the mass production.  Check individual and then check the production history is how our QC would look.

For example, in forging process, annealing is to make the material soft to forge, but if annealing adjustment is bad, the material would be excessively carbonized, and the subsequent heat treatment process will cause excessive embrittlement of the material, resulting in poor torsion.  Now in this example, it is hard to blame heat-treatment.

That's the reason why our QC look closely on material component, forging process and heat-treatment, because these 3 parts are critical to the quality hand tools performance.  If you want to dig further about how Tien-I make the quality socket and impact socket for pro brands around the world, please read below link:

"from concept to quality tools"

Tien-i is Taiwan’s leading manufacturer of professional hand tools.  We welcome requests from various field industries and brands who are interested in quality hand tools. If you have any questions, please contact our helpful team of experts.