How do I know if preheating is required for a steel joint?

Calculate the Carbon Equivalent (CE) of the steel and note the thickness of the thicker part. Refer to Table 1 for the minimum preheat temperature required.

What is the purpose of preheating steel before welding?

To slow down the cooling rate of the weld and heat-affected zone (HAZ), which reduces hardness, minimizes distortion, and helps prevent hydrogen-induced cracking. (Clause 8.1)

Can I weld if the outside temperature is very cold?

Welding should not be done when the parent metal temperature is below 5°C, unless it is preheated to the required temperature as per Table 1. (Clause 7.2)

What is the Carbon Equivalent (CE) and why is it important?

CE is a value calculated from the chemical composition of steel that indicates its weldability. A higher CE means a higher tendency to form hard, crack-susceptible structures upon cooling, thus requiring more stringent controls like preheating.

IS 9595

: 1992

Recommendations for Metal Arc Welding of Carbon and Carbon Manganese Steels

CurrentFrequently UsedCode of PracticeMaterials Science · Steel and Reinforcement

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This standard provides recommendations for the manual metal arc welding (MMAW) of carbon and carbon-manganese steels. It covers parent materials, selection of welding consumables, joint preparation, preheating requirements based on Carbon Equivalent (CE) and thickness, welding procedures, and inspection to ensure sound weld quality.

Provides recommendations for manual, semi-automatic, and automatic metal arc welding of carbon and carbon manganese steels.

Quick Reference Values

Minimum ambient temperature for welding without preheat5 °C

Carbon Equivalent (CE) limit for no preheat (thickness < 25mm)0.41

Typical max interpass temperature for general C-Mn steels250 °C

Recommended minimum preheat for CE 0.45 & thickness >50mm150 °C

Maximum allowable hydrogen content for 'Very Low Hydrogen' electrodes5 ml/100g

Key Formulas

CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15 — Carbon Equivalent Formula

Practical Notes

This standard is superseded; always refer to the latest version, IS 9595:2021. However, the principles of CE calculation and preheating remain fundamental.

The Carbon Equivalent (CE) formula is the most critical calculation from this code. It dictates the entire welding procedure, especially preheat requirements.

Proper control of electrode moisture is non-negotiable to prevent hydrogen-induced cracking. Always use baked, low-hydrogen electrodes from a heated quiver for critical joints or thick materials.