Is all 4140 alloy steel the same?
It is common for 4140 alloy steel to be supplied in either the annealed (soft) condition, or Quench & Tempered (Q & T), the hardened condition. The hardened condition is used where added strength or resistance to wear is desired. The softer condition is used where considerable machining may be required, or where more ductility is required. And then of course there are different surface conditions, shapes, etc. What we will be addressing here will be something a bit less obvious.
Quality varies from mill to mill, and within even one mill, quality will depend on the specification the customer is having it made to. The number one cause of shaft failure in heavy industry is fatigue related failure. “Toughness” resists fatigue, and “cleanliness” increases toughness. Cleanliness in steel is a result of refinement process incorporated in the melting of the steel. (electric furnace melt, vacuum degassing, small grain refinement, etc.). Each process may contribute to the quality of the steel. Each has a cost to the service center requesting it. When all of the available cleanliness processes are incorporated, the collective cost of those extras could be near, or may even exceed the base cost of the steel grade.
I have always considered the steel making process to be more of an art form than merely a manufacturing effort. Very much the same as; there are certified welders, and then there are certified welders. There is often a big difference from one to another. Or, as the age old adage points out; “What do you call a doctor who graduates last in his/her class? The answer is still Doctor. It is the same with steel; who makes it and how is it made?
Often, we encounter a situation where a grade of steel has failed in service. It is common for the customer to consider changing the grade of steel. In many instances it would be more appropriate to retry the recommended steel again, but perhaps investigate purchasing from a higher quality resource.
If you believe on specific grade of steel has identical attributes to that same grade from any source, you are likely to encounter some surprises along the way. Don’t get bit by an insufficient piece of steel because you misunderstood the situation.
“A man walks up to a woman waiting at the bus stop. Next to her is a large friendly looking dog. The man asks if her dog bites. She smiles and says, “No. He is very friendly and loves people.” The man reaches to pet the dog and is immediately bitten. “I thought your dog didn’t bite!”, he exclaims. “That’s not my dog.”
An old experienced business associate of mine would often comment on something I did that did not come out as planned. He would simply say; “Well kid, you almost had it right.”
Don’t be that kid. Pay attention to the details and make your life easier.
-Howard Thomas, Nov 25th, 2019