Application
Preheating
Thermal Preparation for Welding, Forging and Coating
Preheating is a thermal pre-treatment that brings the workpiece to a defined temperature before the main process (welding, forging, forming or coating). It protects against thermal shock, prevents cold cracking and significantly improves workability and final product quality.
NTH Therm offers preheating furnaces for all scales, from compact chamber furnaces for machine tool components to large bogie-hearth furnaces for multi-tonne forgings.
Process Parameters at a Glance
| Application | Temperature | Purpose |
|---|---|---|
| Preheat before welding | 80–400 °C | Cold crack prevention, stress relief |
| Preheat before forging | 900–1200 °C | Formability, scale control |
| Preheat before coating | 60–200 °C | Adhesion, surface drying |
| Post-weld heat treatment | 200–700 °C | Residual stress relief after welding |
Typical Materials and Components
- High-strength structural steels (S690, S960), creep-resistant steels (P91, P22)
- Heavy forgings, crankshafts, pressure vessels, turbine housings
- Dies and hot-work tooling before operation
- Pipe components and flanges before welding
Recommended NTH Therm Furnace Systems
- Bogie-Hearth Furnace IWF: for very heavy charges up to several tonnes, to 1300 °C
- Bogie-Hearth Furnace IWO: for medium-weight charges, flexible loading
- Chamber Furnace ICF: for smaller components, to 1300 °C
- Chamber Furnace ICO: for low-temperature preheating with excellent uniformity
Frequently Asked Questions
Why does steel need to be preheated before welding?
Preheating reduces the cooling rate of the weld and heat-affected zone. This prevents cold cracking caused by hydrogen embrittlement, reduces thermal stresses and improves the toughness of the welded joint, particularly important for high-strength steels and large wall thicknesses.
What preheat temperatures are typical for welding?
The minimum preheat temperature depends on the steel grade, wall thickness and hydrogen content of the electrodes. For high-strength structural steels (S690, S960) and creep-resistant steels, typical values range from 80 °C to 250 °C; for high-alloy steels up to 400 °C.
How long does preheating large forgings take?
Through-heating time depends on component cross-section. As a rule of thumb: 1 hour per 25 mm wall thickness in the furnace. NTH Therm bogie-hearth furnaces enable preheating of very large forgings weighing several tonnes.