After mechanical processing such as drawing, blanking, welding and bending, substantial residual internal stress remains inside steel materials. Minor consequences include workpiece deformation and dimensional deviation, while severe cases trigger late-stage cracking and scrapping, directly impairing finished product quality and service life. Stress-relief annealing temperatures vary drastically across different steel grades; improper temperature control either leaves residual stress unremoved or damages steel hardness and mechanical properties.
Listed below are standard stress-relief annealing temperatures for commonly used steel grades:
1. Low-carbon carbon steel (Q235, Q195)
Widely applied for racking, supports, general sheet metal parts and welded frames, these steels feature good ductility and relatively low tensile strength. Their standard stress-relief annealing temperature ranges from 550℃ to 620℃. Keep temperature constant for 1 to 2 hours (extend holding time for thick workpieces accordingly), then cool down gradually inside the furnace. Never exceed 650℃, as excessive temperature causes coarse grain growth, resulting in reduced rigidity and excessive softening of steel.
2. Medium-carbon steel (Grade 45#, 50# steel, etc.)
Mainly used for shafts, fasteners and mechanical components, medium-carbon steel generates extremely high internal stress after machining and quenching & tempering treatment. Recommended stress-relief annealing temperature: 600℃～650℃. Inadequate low-temperature annealing for Grade 45# steel leaves persistent residual stress, which causes shaft vibration, unbalance and premature failure during operation. Slow cooling is mandatory; rapid air cooling induces secondary residual stress and invalidates prior processing procedures.
3. Low-alloy structural steel (Q355, 16Mn, Q690 high-strength steel plate etc.)
Commonly adopted for construction machinery, pressure vessels and load-bearing steel structures, high-alloying elements make stress elimination more difficult. Suggested annealing temperature: 620℃～680℃. For thick plates and welded assemblies, calculate holding duration at 1 hour per 25mm plate thickness; apply staged heating for oversized components to avoid deformation caused by excessive temperature difference.
4. Stainless Steel
Classified into austenitic, ferritic, martensitic and duplex stainless steel based on metallographic structure, stainless steel requires differentiated stress-relief annealing parameters accordingly.
4.1 Austenitic stainless steel (304, 304L, 316)
Standard stress-relief annealing range: 800℃～850℃ followed by forced air cooling, effectively eliminating residual stress from welding and bending while retaining corrosion resistance. Thin-wall and high-precision components are prone to structural distortion at such high temperatures; low-temperature stress relief below 400℃ is preferred to avoid subsequent structural deformation.
4.2 Ferritic & Martensitic stainless steel
Controlled annealing temperature: 700℃～780℃; high temperature leads to material embrittlement requiring strict temperature monitoring.
4.3 Duplex stainless steel (2205, 2507)
Recommended annealing temperature: 300℃～350℃, removing 50%~70% residual stress with minimal risk of component deformation.
5. Die & tool steel (Cr12, Cr12MoV, T8/T10)
High-carbon high-alloy steel easily cracks due to processing residual stress. Optimal stress-relief annealing temperature: 650℃～700℃ with slow heating and cooling rates, a critical procedure for die manufacturing.
Summary
Two core principles govern steel stress-relief annealing: set temperature per steel grade and determine holding time based on workpiece thickness. Improvisational annealing parameters based on personal experience are the primary cause of high deformation and rework rates in most manufacturing workshops. All above parameters follow industrial universal standards and can be directly used for on-site workshop production and outsourced heat treatment coordination.
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