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Remember, 90%+ of a component's fatigue life is realized before a detectable crack is formed. Increased notch sensitivity certainly reduces the time from when a detectable crack forms and final failure, notch sensitivity does not seem to have a direct effect on the 90%.

If the composition limits that are out of spec are the Nb levels, what is being reported and what are the limits? Have you performed analysis on the components to verify what your reports are telling you?

What they mean by soundness is lack of imperfections, particularly near the center of the bar. What type of imperfections? That is why you need to know the acceptance criteria. Presumably, they mean any imperfections that may affect their ability to process the bar. That is too vague...

Your client's requirements should include some standard for taking and evaluating these specimens. Typically it would be an ASTM or ISO standard. You can take, and examine, all the samples you want, but without a specific acceptance criteria for evaluating these samples, you will not be able to...

You don't mention what the original heat treatment was nor what your proposed heat treatment would be. For the original heat treatment, you need to find out the tempering temperature (if there was one). For the original heat treatment, the product shape (OD, ID, an length) are all important...

The nominal weight is just a name used to designate the product. The differences could be used to denote different collapse ratings, different applications, or perhaps just rounding issues, it is hard to tell. Your screenshot did not make it to the post, so I cannot see your example.

I am not sure that switching to 4340 is going to solve your problem. While what WKTaylor has posted is accurate, it does not address the cracking issue and 4340 has just about the same quench crack sensitivity as 4140. Now, you may find that it solves your issue if the root cause in in the...

A few things I would check out First, how is the stock is cut into lengths. From the photo, it appears to be cut by a band saw. How are the lengths cut by the mill? If they are cold sheared, it is possible that the ones that are cracking are the ones from the end of the cold sheared bars and...

Are you obtaining mechanical properties in the as-cast condition, or has it been previously heat treated? If the material is in the as-cast condition, then, yes, the properties can be improved with proper heat treatment. If those are the properties after heat treatment, then it would seem...

Do you have any idea how your customer is going to use the material? That is, are they planning on performing additional machining and heat treatment? The specification you gave in your OP suggests they probably will. This is because 23-34 is a very wide hardness range to insure mechanical...

Just to take a wild stab at it, I'd guess somewhere between 80,000-100,000 PSI. Maybe as high as 115,000, particularly at the higher end of the hardness range. I'll assume quenched and tempered. A lot will depend on section size and tempering temperature.

I don't know you are asking for. API K-55 is a casing grade, not a material. Sure, API makes some material requirements for that grade of casing, but it also requires dimensional, weight, and marking requirements to be met to be considered K-55. If you want to know what steel grade would be...

Well, picral isn't all that finicky as it is just a bit tricky to get the hang of it. With low P steels, you need to be using an as-quenched sample. A drop of dishwashing liquid helps, along with some water; maybe even a drop or two of HCl. Submerge the sample for a while; I'd start with 10...

Do you have any flexibility in the material? You will get better results with heats that are higher in carbon and higher chrome and moly. What material form are you using (bar, sheet, tube)? Timken has a material called Impact7 which should be available from warehouses in bar form. This...

The drillstring is generally run box up/pin down because it is easier to stab the pin connection into a stationary box connection. Generally, your point of view is above the connection so stabbing the pin into the box allows the operator a better view of what is going on. This results in...

I always viewed the minimum tempering temperature as a way to insure adequate quenching response. If you are not meeting the minimum hardness when tempered at the minimum tempering temperature, your quench is not effective. While lowering the tempering temperature will raise the hardness, it...

Take one sample per heat as-quenched and etch with picral. Even with low P & S, the GB will show up well. It takes a bit of fussing with the picral (try adding a drop of dishwashing liquid) and don't throw it out when it turns black. I was getting the steel suppliers to certify the heat as...

Ding! Ding! Ding! We have a winner! The location of the bulb in the housing can be very important. Usually, there is an adjustment so the bulb can be moved forward, backward, up, and down. You need to adjust the bulb so the filament is "out of focus" with respect to the focal plane of the...

As israelkk has inferred, the use of statistical methods will only be valid if the specimens were obtained from truly random samples. This is unlikely to be the case. Depending on the material and form, it can difficult to obtain a random sample. For example, if the tests were performed to...

As I mentioned above, you need to make sure you are watching the temperature of the part as it leaves the quench. Also, the temperature of the quenchant is very important. The polymer has an inverse solubility with temperature in water, meaning if the quenchant is too hot, it is almost just...