Case Hardening

HTA offers Case hardening, Carburising and Carbo Nitriding of alloy and mild steel components utilizing the latest online carbon diffusion software from SCR Europe.

The company has four sealed quench furnaces of various sizes to accommodate most engineering components whether it is a large gear weighing 100 Kilogram or small rollers weighing less than one kilogram.

The furnace software gives ultimate control from atmospheres to soak time and quench speeds and temperatures.

Components are protected from the outside atmosphere by using a protective endothermic gas. This gas can also control the level of carbon in the atmosphere allowing the carbon potential to be changed in order to suit the material and the customer specification. Carburising temperatures ranging from 790 C to 960 C can be used to achieve customer requirements. Our extensive stock of fixtures and jigging ensures minimum distortion during treatment and maximum hardness and case depth penetration.

The treatments we offer include carbo-nitriding, case hardening and carburising to depths from as little as 0.1mm (0.004″ ) to depths in excess of 3mm (0.120″)

Treatments are fully computer controlled to ensure repeatability and process conformity each and every time.

Carburising and carbo-nitriding case-hardening treatments offer a means of enhancing the strength and wear properties of parts made from relatively-inexpensive easily worked materials. Generally applied to near-finished components, the processes impart a high-hardness wear resistant surface which, with sufficient depth, can also improve fatigue strength. Applications range from simple mild steel pressings to heavy-duty alloy-steel transmission components.

Low-carbon / non-alloy (mild) steels can be case hardened by carburising or carbo-nitriding, but do not develop significant care strength. Thus they are normally treated for increased wear resistance only

Low-carbon alloy case-hardening steels, intrinsically higher-strength materials, can be carburised to yield a high surface hardness whilst developing significant strength and toughness in the core. They are not normally carbo-nitrided.

Case Depth

Depending upon process temperature, duration and media, case depths can be produced within a wide range, from less than 0.1 mm where some wear resistance is the only requirement (e.g. thin-section pressings), increasing where fatigue resistance is needed (e.g. carburised case depths of the order of 1 mm in automotive gears) up to total depths of some 7.5mm (e.g. heavy transmission gearing).

Case depths imparted by carbo -nitriding, generally used for small components, are limited to no more than 0.75mm by practical considerations.

It should be noted that maximum hardness of a case hardened part is not maintained throughout the full depth of the case: part-way through the case, hardness begins to reduce progressively until it reaches the core hardness. It is therefore important not to grind a case-hardened part excessively, otherwise the resulting surface hardness and strength will be significantly diminished.

Core properties

Core properties are predominantly determined by the type of steel section/size and can only be changed marginally without adversely affecting surface hardness.

Component size and shape

The size and shape of a component that can be carburised/carbonitrided depends on the type of equipment operated by the heat treater. Overall, items that can be handled within the contract heat treatment sector range from those of a few grams to components weighing several tonnes each.

Changes in size or shape can arise in case-hardened components from a variety of causes, some inherent in these high-temperature/rapid-cool processes, some attributable to component design shortcomings, and others relating to earlier manufacturing steps (e.g. thermal relief of stresses introduced by prior forming). It is important to consider if preliminary Normalising before finish machining will be an advantage in reducing distortion during subsequent treatment.

Close tolerance components must be ground (with care) after treatment. The case depth specification must allow for this. (Shallow-case carbonitriding components are not normally ground).

All of the following information should be included if possible. If uncertain, ask your heat treater before producing a specification:

  • The process: case harden, carbo nitride or carburize only.
  • Material: type, grade, and the standard from which it is drawn, with drawing, composition and mill certificate where available.
  • Any general standards applicable (national, international or company) that contain relevant details which must be adhered to.
  • Existing condition; e.g. details of any prior heat treatment, such as hardening and tempering, solution treatment and ageing, intended to establish mechanical or other properties.
  • The level of mechanical properties required. Generally a hardness range . A maximum hardness level is often requested.
  • The type(s) of testing required; e.g. hardness (Vickers, Brinell), tensile etc. and any special locations for testing or the removal of samples for test pieces.
  • Requirements for any special certificates or data to be provided by your heat treater.

Guidance and information is always available from our experience heat treatment professionals.

Our procedures and work instructions are fully documented under our AS 9100 and ISO 9001 quality