Mild steel is widely selected as the base plate for hardfacing because the substrate does not need to be as hard as the wear layer. Its main job is to provide toughness, structural support, and a weldable foundation for the hardfacing deposit. Low carbon content generally improves weldability, lowers carbon-equivalent-related cracking risk, and makes thermal control easier than with high-carbon or highly alloyed substrates.

Why Low-Carbon Steel Wins as a Hardfacing Base

Hardfacing creates a special material combination: the surface needs high hardness and wear resistance, while the base plate needs adequate ductility and weldability. Using a highly hardenable substrate can make the welding operation unnecessarily difficult because the heat-affected zone may become susceptible to hard, brittle microstructures and hydrogen-assisted cracking.

Mild steel provides a practical balance of plasticity, toughness, strength, and weldability. Its relatively low carbon content also helps limit the formation of excessively hard heat-affected-zone structures when the correct welding procedure is followed.

Carbon Equivalent: The Link Between Chemistry and Preheat

Carbon equivalent (CE) is used to estimate the weldability and hardenability of steel from its chemical composition. Different CE formulas exist, so the calculation method should be identified when a specification requires a particular value.

A commonly used expression for carbon-manganese and low-alloy steels is the IIW-style formula:

As CE increases, the heat-affected zone generally becomes more hardenable and the risk of hydrogen-assisted cold cracking can increase. Preheating is one of the methods used to control cooling rate and reduce this risk.

CE and Preheat: A Practical Decision Logic

These ranges are useful for preliminary screening rather than replacing a qualified welding procedure. Hardfacing itself can introduce significant thermal and residual stresses, so the substrate chemistry should be evaluated together with the consumable and deposition method.

Common Mild Steel Base Plates

Several familiar structural steels can serve as base materials for hardfacing, provided their thickness, chemistry, strength, and welding requirements match the application.

These grades should not be assumed to be interchangeable simply because they are all described as mild or structural steel. Chemical composition, yield strength, impact requirements, thickness range, applicable standard, and delivery condition should be confirmed on the material certificate.

Why High-Carbon and Highly Alloyed Bases Can Be Difficult

A high-carbon or highly alloyed substrate may develop a harder heat-affected zone during welding. If the component is thick or highly restrained, rapid cooling can increase the risk of hydrogen-assisted cracking. The hardfacing layer itself may already have high hardness and substantial residual stress, so adding a crack-sensitive substrate can make the complete system harder to control.

Potential problems include:

• Higher heat-affected-zone hardness
• Greater sensitivity to rapid cooling
• Higher preheat requirements
• Increased hydrogen-assisted cracking risk
• More difficult repair welding
• Greater sensitivity to restraint and residual stress

This does not mean high-alloy substrates cannot be hardfaced. They can be processed successfully with an appropriate qualified welding procedure. The point is that their chemistry should be treated as a welding-engineering input rather than assuming the same procedure used for mild steel will work.

Surface Preparation: Clean Steel Before Hardfacing

Even an excellent low-carbon base plate can produce a poor overlay if the surface is contaminated. Before hardfacing, the substrate should be prepared to provide a clean, sound surface for welding.

A clean surface reduces the chance of porosity, lack of fusion, inclusions, and unstable arc behavior. Rust or oil should not be treated as harmless surface discoloration when the overlay is expected to carry demanding wear service.

Mild Steel Base vs Stainless Steel Base

A stainless steel substrate changes the welding problem considerably. Stainless steel is not simply a corrosion-resistant version of mild steel; its thermal properties, alloy chemistry, heat-affected-zone behavior, and welding requirements can be very different.

For a wear component where the environment does not require corrosion resistance through the entire thickness, mild steel can provide a more practical structural foundation while the specialized alloy is concentrated at the working surface.

The Base Plate and Hardfacing Heat Cycle

The substrate experiences several thermal effects during hardfacing. The weld pool partially melts the base metal, creating a dilution zone. Heat then travels into the surrounding base plate and forms a heat-affected zone. As the deposit cools, thermal contraction creates residual stresses.

A low-carbon base generally provides a more forgiving foundation for this thermal cycle. Nevertheless, thick plates, high restraint, high-carbon-equivalent material, low ambient temperature, and hydrogen-sensitive welding consumables can still require controlled preheat and cooling.

Mild Steel Base Plate Procurement Checklist

Teda Ganghua Hardfacing Material Selection

When a project needs a tough structural substrate combined with a high-wear surface, the base plate should be selected together with the hardfacing chemistry and deposition process. For severe abrasive applications, buyers can also compare the required mild-steel substrate configuration with a chromium carbide overlay plate solution, considering wear mechanism, total thickness, backing material, fabrication method, and service conditions together.

Providing the base grade, thickness, working environment, and required wear-layer thickness at the quotation stage allows Teda Ganghua to evaluate the material combination rather than treating the surface alloy as an isolated specification.

FAQs About Mild Steel Base Plates for Hardfacing

Why is mild steel commonly used as a hardfacing base plate?

Mild steel generally offers good ductility, toughness, weldability, and relatively low carbon equivalent. These characteristics provide a practical foundation for depositing a much harder wear-resistant layer.

Does CE below 0.40 mean preheating is never required?

No. CE below 0.40 generally indicates relatively good weldability, and preheat may often be unnecessary under suitable conditions. However, thickness, restraint, hydrogen level, ambient temperature, heat input, and the qualified welding procedure must also be considered.

Why avoid high-carbon steel as the hardfacing substrate?

High-carbon steel can have greater hardenability and may develop a hard, crack-sensitive heat-affected zone. This can increase preheat requirements and the risk of hydrogen-assisted cracking, particularly in thick or highly restrained components.

Can Q235B, A36, and St37 all be used as base plates?

They can represent common low-carbon structural-steel choices, but they should not be treated as automatically identical. The applicable standard, chemistry, thickness, strength requirements, and material certificate should be verified before welding.

Why must the surface be free of rust and oil?

Contamination can contribute to porosity, inclusions, lack of fusion, and unstable welding conditions. A clean substrate provides a more reliable metallurgical foundation for the hardfacing layer.