Thermal Processing That Determines Field Performance
Heat treatment is not a finishing step — it is the stage at which the mechanical properties that determine how a component performs in service are established. A manganese steel jaw plate that has not been correctly solution annealed and water quenched will not work-harden in the crusher and will wear out in a fraction of its design life. An alloy steel planetary carrier that has not been austenitised and tempered to the correct hardness range will either be too brittle or too soft for the torque loads it carries. Getting heat treatment right is not optional; it is where the engineering work becomes real.
Our heat treatment capability covers the principal thermal processes required for wear-resistant and structural components in mining and bulk handling applications. Each process is executed to documented parameters, recorded per batch, and verified by mechanical testing before components proceed to machining or final inspection.
Furnace Capability
Our bogie hearth furnaces provide an effective working volume sufficient for large structural castings and assembled component groups. Working dimensions accommodate components up to approximately 6–8 metres in length and 3 metres in width, with hearth load capacity up to 50 tonnes per charge. This range covers the majority of mining machinery components — from crusher wear parts and conveyor structural castings through to large gear blanks and heavy housing assemblies.
Temperature uniformity across the working zone is verified periodically against thermocouple survey data. For large or thick-section components, furnace loading arrangements are specified to ensure adequate heat penetration and uniform temperature distribution through the full section before the soak period begins.
Temperature and time are recorded digitally on modern equipment; older furnaces in the network retain chart recorder documentation. All records are retained as part of the batch traceability file regardless of recording method.
Process Routes by Alloy Type
Manganese Steel — Solution Annealing and Water Quenching (Water Toughening)
Austenitic manganese steel (Mn13, Mn14, Mn18 and alloyed variants) is supplied in the solution-annealed and water-quenched condition. The as-cast microstructure contains carbides at grain boundaries that embrittle the material and prevent the work-hardening response that gives manganese steel its wear resistance. Solution annealing dissolves these carbides into the austenitic matrix; water quenching retains the single-phase austenite at room temperature.
The process requires heating to the solution temperature range (typically 1,050–1,100°C depending on composition and section thickness), holding for sufficient time to achieve complete carbide dissolution through the full section, and rapid water quenching. The time between furnace exit and full immersion in the quench tank is critical — for most components, this must be achieved within 30 seconds. Delay allows carbide re-precipitation to begin, which cannot be reversed without re-treatment.
Quench tank specification: Dedicated water quench tanks with forced circulation (propeller agitators or high-pressure pump jets) to break the steam film at the component surface and maintain consistent cooling rate. Tank volume and heat exchanger capacity are sized to maintain water temperature below 30°C throughout the quench cycle. Mechanical handling — overhead crane with rapid descent — ensures consistent transfer time from furnace exit to full submersion. These are not shared or general-purpose tanks; the cooling performance of the quench medium is part of the process specification.
Verification: Hardness (Brinell) on representative surfaces after quenching. Microstructure examination by metallographic section where specified or where hardness results indicate a deviation. Chemical composition is confirmed before heat treatment — a correctly heat-treated casting from an out-of-specification heat will still underperform in service.
Alloy Steel — Austenitising and Quench-Temper
Chromium-molybdenum and other low-to-medium alloy steels for structural and wear applications are heat-treated by austenitising followed by quenching (oil or water, depending on alloy hardenability and section size) and tempering to the specified hardness or strength range.
Tempering temperature is the primary variable controlling the final hardness-toughness balance. Higher tempering temperatures reduce hardness and increase toughness; lower tempering temperatures retain hardness at the cost of some impact resistance. For components subject to cyclic loading — planetary carriers, industrial housings, track shoes — the temper is specified to achieve the hardness range that balances wear resistance against fracture risk under the operating load cycle. This specification is set at the engineering review stage, not chosen arbitrarily.
Verification: Hardness testing (Brinell or Rockwell as appropriate to the component) after tempering, against the specified acceptance range. Tensile and impact testing on separately heat-treated test bars from the same batch where mechanical property certification is required by the client.
High-Chromium White Iron — Destabilisation Treatment
As-cast high-chromium iron (GX260Cr27 and related grades) contains chromium carbides in a martensitic or austenitic matrix depending on cooling rate during solidification. Destabilisation heat treatment heats the casting to a temperature at which secondary carbides precipitate from the matrix, reducing carbon and chromium content in the matrix and allowing it to transform to martensite on air cooling. The result is a significant increase in hardness — typically to 58–65 HRC depending on composition and treatment parameters — while retaining the carbide volume fraction that provides abrasion resistance.
Destabilisation temperature and time are critical: too low or too short, and insufficient secondary carbide precipitation occurs; too high, and carbide dissolution reduces the volume fraction of hard phases. These parameters are established per alloy composition and section thickness and are not transferred between different heats without review.
Verification: Hardness (Rockwell C) after treatment. Microstructure examination for carbide morphology and matrix condition where specified.
Normalising and Stress Relief
Structural cast steel components (connecting housings, frames, pan sides) are normalised after casting to refine grain structure and reduce residual casting stress before machining. Stress relief annealing is applied after welding operations or after rough machining of precision components where residual stress could cause distortion during finish machining or in service.
Documentation
Heat treatment records are generated for every batch and retained as part of the order documentation. Records include furnace identification, charge composition (component batch numbers), set point and actual temperatures, soak time, quench method, and post-treatment hardness results. Records are supplied to the client as part of the delivery documentation where specified or where the component type warrants it.
For clients whose quality management systems require heat treatment records in a specific format — time-temperature curves, signed batch records, or third-party witness — we accommodate these requirements at the order confirmation stage.
For heat treatment specifications, process queries, or component-specific thermal processing requirements, contact our engineering team.