Stress Relieving
in India
Precision sub-critical thermal cycles to relax residual stresses and guarantee dimensional stability in critical metal parts.
The Process
What is Stress Relieving Heat Treatment?
Stress Relieving is a thermal conditioning process used to eliminate residual internal stresses in steel and alloy parts. These internal elastic strains are introduced during manufacturing operations like welding, casting, rough machining, or forging. If left unmanaged, the relaxation of these stresses during subsequent precision turning or service leads to structural warping.
By heating the steel to a sub-critical temperature below Ac1 (typically 550°C to 650°C), the yield strength of the material drops temporarily, permitting micro-plastic relaxation of internal strains. Crucially, the parts are cooled very slowly down to 250°C in the furnace. This prevents thermal gradients from reintroducing new internal stresses.
Sub-Critical Thermal Path (Stress Relief)
Metallurgical Outcomes
Elastic Stress Relaxation
Sub-critical thermal relief relaxes internal material stresses without altering the base core mechanical properties.
Zero warpage on CNC lines
Dimensional Integrity
Relieves machining stresses, preventing the component from bending or warping when subsequent precision dimensions are turned or ground.
Sub-critical heat limit
Preserved Base Hardness
Because heating takes place below phase change Ac1, hardness, core strength, and yield profiles of pre-hardened steels remain unchanged.
Stress reduction in weldments
Relieved Weld Zones
Reduces critical tensile stresses created at weld junctions during fast solidification, preventing micro-crack development.
Homogenized micro-strain
Casting Stress Release
Relaxes internal tension resulting from uneven solidification rates in thick-walled cast steel valve bodies and housings.
Uniform lattice structure
Symmetrical Micro-Strains
Restores crystal lattice balance, resulting in uniform tool cutting pressure and consistent tool wear during finish machining.
Environmental integrity
Stress Corrosion Resistance
Lowers vulnerability to stress corrosion cracking (SCC) in components exposed to aggressive chemical or marine environments.
OUR PROCESS
How we stress relieve
at Tapovan
Inspection & Loading
Components checked for heavy oils. Racked flatly with uniform support to prevent sagging during heating.
Gradual Ramp Heating
Parts heated slowly to sub-critical temp (550-650°C) to avoid inducing thermal shock stresses.
Soak holding phase
Temperature stabilized and held for 1-3 hours, allowing mechanical stress relaxation to occur.
Controlled Slow Cool
Slow cooling inside furnace down to 250°C. Prevents re-introduction of residual surface tensions.
Final Air Cool
Parts safely removed from the furnace below 250°C and allowed to cool in still air to ambient temp.
QC Audit & Dispatch
Dimensions verified against target margins. Time-temperature furnace charts logged and batch dispatched.
STANDARDS WE WORK TO
Applications in India
Specified Components
Critical for welded frames, cast valves, forgings, and machined shafts requiring strict dimensional compliance before final assembly.
Cast Valve Components
- Large pump body castings
- Valve gate housings
- Impeller castings
- Flanged pipe junctions
Welded Structural Parts
- Heavy machinery beds
- Crane boom assemblies
- Welded frames and brackets
- Press frames
Precision Shafting
- CNC turned engine shafts
- Steering system gears
- High-speed rotative spindles
- Hydraulic cylinders
Cold Worked Tooling
- Heavy stamping dies
- Forming dies
- Bending plate structures
- Cold extruded components
Frequently Asked
Common questions
Find technical answers about sub-critical thermal cycles.
The primary purpose is to remove internal residual stresses that accumulate in steel parts during manufacturing processes such as cold rolling, welding, casting, heavy machining, or forging. If left unresolved, these stresses can cause the component to distort (warp or twist) during subsequent machining stages or during its service life under load.
Unlike hardening or normalizing, stress relieving is a sub-critical thermal process, meaning the steel is heated to a temperature below its lower critical limit (typically 550°C-650°C). Since no microstructural phase change occurs, the process does not significantly alter the material's bulk mechanical properties, such as tensile strength or hardness, but successfully relaxes internal elastic stresses.
Components are typically heated slowly to 550°C-650°C, soaked for 1 to 3 hours, and then cooled very slowly in the furnace down to approximately 250°C. Slow cooling is critical — cooling too rapidly at this stage would introduce new thermal stresses, defeating the entire purpose of the treatment.
If a heated metal part is cooled rapidly (e.g. by air blasting or quenching), the outer surface cools and contracts faster than the hot core. This temperature gradient creates localized elastic strains, introducing fresh residual stresses. Slow furnace cooling down to 250°C ensures a highly uniform temperature across the cross-section, keeping the material stress-free.
It should be scheduled after heavy rough machining, welding, or rough grinding, but before final finish machining or grinding. This ensures that any distortion caused by the release of machining stresses happens during the stress relieving furnace cycle and can be machined out during final precision sizing.
Yes, it is highly recommended and often mandatory for heavy welded fabrications. The extreme thermal cycles of welding create massive localized tensile stresses near the weld seam. Stress relieving relaxes these areas, preventing weld-crack propagation and improving structural reliability.
We supply a time-temperature digital furnace cycle log, confirming the slow ramp-up, controlled soak period, and slow ramp-down cooling profile, along with a batch certificate of compliance.
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