Illustrative image: a Vickers hardness indentation; the test force and measurement location are specified for each order.
Testing services · Bolts and screws · Hardness
Hardness testing of bolts and screws: core, surface and hardness profiles
Do you need to test the hardness of bolts or screws, assess a heat treatment or investigate differences between batches? Testawell offers Vickers, Rockwell and Brinell testing, as well as core and surface hardness measurements. We measure hardness profiles on ground and polished cut surfaces, known as metallographic sections. What you need to check determines the method and sample preparation.
Testawell offers Vickers, Rockwell and Brinell hardness testing, as well as core hardness, surface hardness and hardness profiles on prepared metallographic sections. Testawell is currently not accredited to DIN EN ISO/IEC 17025. If you require an accredited test report, this must be agreed with a laboratory accredited for the relevant scope before placing the order.
Which hardness tests can you request from Testawell?
We can examine individual accessible locations or prepared sections. Do you need to measure hardness, or also check whether the values meet specific requirements in a standard? To compare the results with limits, we need the requirements that apply to the fastener, such as the product standard and its edition.
Typical reasons for testing include suspect batches, a change in heat treatment, deviations found during incoming inspection or a complaint. The results help assess the material. They do not by themselves show that the bolt or screw meets every requirement for acceptance.
Vickers hardness testing, for example HV 0.3 and HV 10, suited to the agreed test objective.
Rockwell hardness testing at suitable locations with stable support for the sample.
Brinell hardness testing where dimensions, material and applicable requirements permit.
Core hardness and surface hardness as separate measurement tasks.
Hardness profiles on prepared sections: a series of measurements showing differences between the surface region and core.
Why are core hardness and surface hardness reported separately?
Manufacturing and heat treatment can produce differences between the core and the surface region. A measurement on the easily accessible head surface does not automatically replace the required core hardness measurement. The test location, sample preparation and requirements for the fastener all matter.
A documented section shows where in the fastener each measurement was taken. Cutting and polishing should leave the material condition and the edges under investigation as unchanged as possible. Mike Keeble specifically discusses these sample preparation issues for fasteners. [1]
For coated bolts and screws, we first establish whether the coating itself or the steel beneath it is to be examined. This matters especially for small indentations. Where coating removal is required, it must not cause uncontrolled changes to the near-surface region being assessed.
Vickers, Rockwell or Brinell: which method suits your fastener?
All three methods measure hardness. They use different test tips or balls, called indenters, and evaluate the resulting indentations in different ways. The suitable and permitted method depends on the product requirements, expected hardness, available test cross-section and test objective. Converting a hardness value to another scale does not replace a measurement using the required method.
Measurement with a larger indentation where the component and standard permit
Ball, test force and available area; not intended for closely spaced measurements near the edge.
Which standards are relevant to bolt and screw hardness?
For many bolts and screws made of carbon steel and alloy steel, DIN EN ISO 898-1 sets the product requirements. Separate test method standards describe how to measure hardness. For stainless steel fasteners, we need to establish which part of the ISO 3506 series applies. [2][3]
ISO 6507-1 describes Vickers testing, ISO 6508-1 Rockwell testing and ISO 6506-1 Brinell testing. Before accepting an order, we clarify which product requirements, method and standard editions apply. A hardness limit can only be set once this information is available. [4][5][6]
What does a near-surface hardness profile show?
A hardness profile shows how hardness changes from one measurement location to the next. Significant differences may be a reason to investigate decarburization or carburization in bolts and screws more closely. The spacing between measurements and the sample preparation also affect how thin a surface layer can be examined.
Hardness values do not directly measure carbon or hydrogen content. In a failure investigation, we therefore also consider heat treatment, coating and, where needed, other examinations. A hardness value within the expected range does not explain the cause of failure or rule out possible damage.
In 2018, John S. Medcalf, Brian G. Thomas and Salim V. Brahimi investigated susceptibility to hydrogen embrittlement in case-hardened fasteners. Their work considers the condition of the core and hardened surface layer together with the shape and dimensions of the parts. It shows why these factors should be examined together. It does not provide an acceptance limit that applies to all bolts and screws. [7]
What information belongs in the test report?
The agreed test report identifies the samples and records the method used, test conditions and measured values. For core, surface-region or profile measurements, it should also show where the measurements were taken. We can agree in advance which images or diagrams are needed.
We can only judge whether a result passes or fails against specific requirements. Without these, we document and explain the measurements but cannot confirm that the fastener meets a standard. Hardness testing alone does not replace the other evidence required for a property class.
What do we need to prepare a quotation?
Send a drawing or photograph, material and property class, dimensions, coating details and the number of available parts. Describe the unusual property or the evidence you need. State whether the samples may be cut and ground for examination.
The work involved depends on the number of measurement locations, sample preparation and level of detail in the report. We therefore agree the price, number of samples needed and schedule based on your fastener. If your customer requires accredited testing, include that requirement in the initial enquiry.
Can Testawell perform HV 0.3 and HV 10 testing on bolts and screws?
Yes. You can request Vickers testing including HV 0.3 and HV 10. We select the test force and measurement location to suit the shape and dimensions of the fastener and the applicable requirements.
Can hardness be measured directly on the bolt or screw head?
A head measurement is possible if the surface, shape and dimensions are suitable and the fastener is stably supported. However, it is not automatically the core or surface hardness measurement required by the standard. The measurement location must match the test objective.
Can a bolt or screw still be used after hardness testing?
A hardness indentation alters the surface. If the fastener is cut or ground for examination, it can no longer be used as a component. Continued use cannot be guaranteed as a general rule even without cutting.
Can hardness testing certify a bolt as property class 10.9 or 12.9?
A hardness value alone does not show that the fastener meets all requirements of a property class. The other required properties must also be checked under the prescribed test programme.
Will I receive an accredited test report?
Testawell is currently not accredited to DIN EN ISO/IEC 17025. If an accredited report is required, this must be agreed in advance with a laboratory accredited for the relevant scope.
Request hardness testing for your bolts and screws
Tell us the material, property class, thread, coating and required measurement locations. We will clarify sample preparation, the test method and the report scope.
