Welding Guidelines for Q&T Plates

Overview – Why Q&T Plates Need Special Welding Guidelines

What Are Q&T Plates?

Quenched and Tempered (Q&T) steel plates such as S690QL, A514, Dillimax, and HITEN are high-strength structural steels that achieve their mechanical properties through a dual-stage heat treatment: rapid quenching followed by controlled tempering.

This process makes them exceptionally strong, yet tough — ideal for cranes, military vehicles, trailers, and mining equipment.

⚠️ Why Welding Requires Precautions

The same hardness and yield strength that make Q&T plates valuable also make them sensitive to heat input during welding.

Incorrect welding can cause:

• 🔥 Softening in the heat-affected zone (HAZ)
• ❌ Cold cracking due to residual stress
• 💥 Hydrogen-induced cracking
• 🛑 Loss of mechanical strength near the weld
• 💧 Loss of impact resistance at low temperature

✅ Correct welding practice ensures the plate retains its full performance.

Pre-Welding Preparation – Surface, Preheat & Edge Prep

Before welding Q&T plates, proper preparation is critical. This step helps avoid weld defects, cracking, and property loss in the heat-affected zone (HAZ).

🔹 1. Surface Cleaning

✅ Remove rust, paint, oil, and mill scale near the weld zone.

• Use a grinder or wire brush
• Clean at least 25–50 mm around the joint
• Avoid contamination from cutting fluids or oils

🔹 2. Edge Preparation

Depending on the plate thickness and joint type, prepare the edges for full penetration welds:

Plate Thickness	Recommended Edge Prep
6–12 mm	Square or single-V joint
12–30 mm	Single-V or double-V joint
>30 mm	Double-V or compound bevel

📌 CNC beveling or machining ensures better fit-up and weld strength.

🔹 3. Preheat Temperature Guidelines

Preheating helps prevent cold cracks and hydrogen embrittlement. Always match preheat to plate grade and thickness.

Plate Thickness	S690QL / A514	S960QL / Dillimax 965T
6–20 mm	75–100°C	100–120°C
20–50 mm	100–150°C	120–160°C
50–100 mm	150–180°C	160–200°C

⚠️ Do not exceed interpass temperature of 250°C unless approved.

🧠 Pro Tip:
Measure preheat using a contact thermometer or temp stick, not by feel. Uneven preheat leads to weld cracking later.