Crack specimens, hardness tests, and machine images are all right in front of us. The issue is not whether there is a number, but whether that single number can replace the entire judgment.
Cold-headed screws with obvious head cracks
On-site workpiece: Some visible cracking at the head. The image is used to illustrate the abnormal morphology; it should not be used alone to determine the root cause.
The screw heads already show cracks after cold heading. Faced with such parts, many people's first reaction is: Is the material too hard?
A hardness test was indeed conducted on site, and the reading shown in the image is about 185 HV0.2. But this is precisely where the problem lies: Can a single hardness value answer why the material cracked?
The answer is no.
The crack has already appeared; we cannot focus solely on one number
Detail of the screw head crack
The crack is already visible at the head. Its location and shape are important clues, but they do not yet reveal the cause.
From the workpiece, the crack has already emerged at the head. This tells us that during this forming process, the conditions experienced by the material and the product were not fully matched.
However, the crack itself does not directly tell us which stage caused it. To pin all judgments on "whether the hardness is high or low" is like assuming someone is healthy just because their blood pressure is normal.
Hardness is important, but it mainly answers how hard the material is at a specific point. It cannot independently substitute for an overall assessment of the material's condition, surface state, and actual forming performance.
Crack locations marked on-site
The crack locations marked on-site. The lines are original field markings.
Hardness testing provides clues, not a verdict
Hardness tester on-site
Hardness testing in progress.
Hardness testing software interface
The testing interface shows a reading of approximately 185 HV0.2.
The hardness test gives us a very important clue and also demonstrates that discussions about the material are not based on mere intuition.
But "measuring a reading" is different from "having found the cause of the cracking."
Just as a normal result in one item of a medical checkup report does not validate the entire examination, the same applies to materials: hardness results can help with the assessment, but they cannot replace other facts, nor can they bypass the defective part itself.
Therefore, what truly needs discussion in this case is not whether 185 is high or not, but rather: Why did cracks still appear after forming despite a seemingly acceptable hardness reading?
The material ultimately faces inspection on the production line
Cold-heading machine production site
Scene at the cold-heading machine. The actual performance of the material in production is what the customer ultimately experiences.
Material test results are important, but when delivered to the customer, the final outcome depends on the actual machine, the finished product, and continuous production.
The same hardness value does not guarantee identical behavior when the material is used in different products or subjected to different deformation processes. Product structure, forming conditions, and other intrinsic properties of the material all influence the final result.
This is not to say that hardness is useless, but rather that it should not bear the full burden of judgment alone.
What customers really need is not just a statement that "hardness is qualified"
What customers truly care about is whether this batch of material can consistently produce qualified products.
When cracking has already occurred, a more valuable approach is to examine the defective parts, on-site tests, and actual usage together. Only then can we clearly define the scope of the problem, instead of endlessly speculating over a single number.
Creation Group pays attention to both material specifications and their actual performance on the customer's equipment. If you also encounter situations where "hardness appears fine, but abnormalities occur during forming," please feel free to contact us with photos of the defective parts, material specifications, and details of your application.
Image notes: All images in this article are provided by users. Crack images are used to illustrate abnormal morphologies; hardness test images demonstrate the existence of hardness records on-site; machine images depict the actual forming environment. Apart from the factual observations explicitly described in the text, this article does not draw definitive conclusions regarding the root cause of the cracks, the correspondence between material batches, or the effectiveness of any improvements. Specific process parameters, acceptance thresholds, or corrective measures are not disclosed.