Selecting the suitable filler metal is crucial when welding abrasion-resistant (AR) plate to equipment, whether it’s for repair purposes or fabricating a new plate onto a structure.
AR plates possess exceptional hardness and are specifically designed to offer extended durability in challenging environments. As a result, they are commonly employed in critical equipment components that frequently encounter impacts or sliding contact with abrasive substances. Examples of such applications include backhoe buckets and teeth, bulldozer blades, dump truck beds, and other components that require protection against excessive wear.
Abrasion resistant steel is widely used in industries where the protection of critical components against wear and impact is essential. Welding abrasion resistant steel requires careful consideration of specific procedures to maintain the material’s integrity and ensure optimal performance.
In this blog post, we will delve into the detailed welding procedure for abrasion resistant steel, highlighting key considerations and best practices to achieve durable and strong welds.
Abrasion Resistant Steel Welding Consideration
Pre-heat the base material
Pre-heating the base material helps prevent rapid cooling, reduce hydrogen levels, and minimize cracking. Follow the recommended pre-heating guidelines provided by the AR plate manufacturer.
Consider joint and weld designs
Avoid locating the weld joint in highly restrained areas that restrict the expansion and contraction of the base material, AR plate, or weldment. Welding shorter and smaller fillet welds reduces heat input and residual stresses on the AR plate.
Choose the appropriate filler metal
Select a filler metal based on the tensile strength of the base metal. Opt for a filler metal with low hydrogen content and the lowest tensile strength that still meets the required impact value. Check the manufacturer’s recommendations for filler metal selection based on the grade of the base metal.
Refer below chart for welding rod selection based on Abrasion resistant steel strength or grade. (Image- JFE Steel)
Utilize low-hydrogen stick electrodes for field repairs
For repairing or replacing AR plate equipment in service, consider using a low-hydrogen stick electrode with a basic slag system, such as AWS E7016 & E7018. These electrodes offer excellent as-welded mechanical properties, toughness, and resistance to hydrogen pickup.
They can weld through contaminants like mud, rust, dirt, and oil commonly found on used equipment. Note that stick electrodes may be inefficient for large AR plate repairs and require frequent electrode changes.
Leverage flux-cored wires
Gas-shielded flux-cored wire is recommended for welding AR plates due to its toughness, resistance to hydrogen pickup, and ability to weld through light rust and mill scale. It provides versatility for welding AR plates to heavy equipment, whether for fabrication or repair work.
Self-shielded (gasless) flux-cored wire is suitable for outdoor repairs but may have reduced impact properties. Consult a trusted filler metal manufacturer for the best recommendation. Both types of flux-cored wires require slag removal between passes and after welding.
Use solid wire indoors on new equipment
When welding AR plates onto clean, new heavy equipment structures indoors, solid wire like AWS ER70S-3 or ER70S-6 is suitable, especially if the base material is A36. Solid wire offers a clean bead appearance and does not require slag removal.
Improve productivity and quality with metal-cored wire
Metal-cored wire increases travel speeds, minimizing heat input and the risk of rapid cooling and cracking when welding AR plates. It provides excellent toughness properties, minimal spatter, and performs well on clean base materials or those with light mill scale or rust. Metal-cored wire is particularly useful for bridging gaps in poor fit-ups and offers higher deposition rates than solid wires, increasing production.
Post-Weld Heat Treatment
Some abrasion resistant steels may require post-weld heat treatment to relieve residual stresses and enhance the material’s properties. Consult the material manufacturer or relevant standards to determine if post-weld heat treatment is necessary.
AR400 Abrasion Resistant Steel Welding Procedure
- AR400 steel is a quench and tempered steel known for its high strength and hardenability, which can make welding challenging.
- Welding AR400 steel results in a heat-affected zone (HAZ) with high hardness due to rapid heating and cooling of the base steel during the welding process.
- Hydrogen in the weld metal can diffuse into the HAZ, potentially causing hydrogen embrittlement and delayed under-bead or toe cracks.
- To minimize heat-affected zone cracking, consider the following tips:
- Use low hydrogen consumables with an -H4 or -H2 designation (non-stainless steel filler rod) and ensure proper shielding gas for the consumable and material combination.
- Select the lowest strength filler metal that meets the design requirements.
- If making fillet welds, consider oversizing the weld to achieve the specified strength.
- Minimize weld restraint to control cracking by considering the significant difference in yield strength between the AR400 plate and the filler material.
- Preheat the material to a temperature of 150°F-300°F (66°C-149°C) to slow down the cooling rate.
- Note that excessive preheating may anneal the base material, so be cautious.
- The maximum temperature allowed between passes is 400°F (204°C).
- Allow for slow cooling, as more time at elevated temperatures helps the dissolved hydrogen escape.
- Consider peening the weld beads to minimize residual weld stresses.
AR500 Abrasion Resistant Steel Welding Procedure
When welding AR500 abrasion-resistant steel, it is important to follow a proper welding procedure to ensure quality and integrity. Here are some general guidelines to consider:
- Preheating: Preheating the AR500 steel before welding can help reduce the cooling rate and minimize the risk of cracking. Generally, preheating to a temperature between 200°F and 400°F (93°C to 204°C) is recommended. However, it’s important to refer to the specific welding procedure or manufacturer’s recommendations for the exact preheating temperature.
- Filler Metal Selection: Choose a filler metal that matches or closely matches the properties of the AR500 steel. The filler metal should have sufficient strength and toughness to withstand the high-stress conditions. Consult the welding consumable manufacturer’s recommendations or refer to the welding procedure specification for the appropriate filler metal selection.
- Welding Technique: Employ proper welding techniques to achieve sound and strong welds. Some common techniques used for welding AR500 steel include:
- Short-circuiting Transfer: This technique involves using lower heat input, lower welding current, and shorter arc length. It helps reduce the heat-affected zone (HAZ) and minimize the risk of cracking.
- Pulse Welding: Pulse welding can be beneficial for controlling heat input and reducing distortion. It allows for better control of the weld pool and helps prevent excessive heating of the base metal.
- Backstep Technique: When making multiple passes, consider using the backstep technique. This involves welding in a reverse direction, moving back towards the completed weld, to help minimize the build-up of residual stresses.
AR600 Abrasion Resistant Steel Welding Procedure
When welding AR600 abrasion-resistant steel, it is crucial to follow a proper welding procedure to ensure the quality and integrity of the welds. Here are some key guidelines to consider:
- Preheating: Preheating the AR600 steel before welding is recommended to reduce the cooling rate and minimize the risk of cracking. The preheating temperature should be between 300°F and 500°F (149°C to 260°C) to achieve optimal results.
- Filler Metal Selection: Select a filler metal that closely matches the properties of AR600 steel, considering its strength and toughness. For welding AR600, a low hydrogen electrode, such as AWS E7018, is commonly used. However, it is essential to consult the welding consumable manufacturer’s recommendations or welding procedure specification for the appropriate filler metal selection.
- Welding Technique: Employ appropriate welding techniques to achieve sound and strong welds. Techniques such as short-circuiting transfer, pulse welding, and backstep technique can be used to minimize the heat-affected zone and control distortion.
- Post-Weld Heat Treatment (PWHT): Depending on the requirements and application, post-weld heat treatment may be necessary to relieve residual stresses and improve the overall properties of the welded joint. The recommended PWHT temperature for AR600 steel is typically around 1100°F (593°C), followed by slow cooling in still air.
- Quality Control and Inspection: Ensure thorough quality control and inspection during and after welding. Visual inspection, non-destructive testing, and destructive testing should be performed according to applicable codes and standards.
Cold Cracking issue when Welding Abrasion Resistant Steel
Cold cracking, also known as delayed cracking, is a common issue that can occur when welding abrasion-resistant steel. These cracks typically appear after the weld has cooled to less than 150°C.
To prevent cold cracking, it is necessary to control three key factors: hydrogen content, hardenability of the steel material, and restraint stress.
- Hydrogen Content: Elevated hydrogen levels in the welding consumables can contribute to cold cracking. Moisture absorption by the consumables is the primary cause of increased hydrogen content. To mitigate this, it is crucial to ensure that the welding consumables are properly stored and handled to prevent moisture absorption. Dry storage and suitable handling practices can help reduce the hydrogen content.
- Hardenability of Steel Material: The hardenability of the steel material, often indicated by the weld crack sensitivity composition (PCM), is closely related to the susceptibility of cold cracking. Materials with higher hardenability are more prone to cold cracking. Therefore, selecting steel materials with lower weld crack sensitivity composition can help reduce the risk of cold cracking.
- Restraint Stress: Restraint stress refers to the stress imposed on the weld due to the joint’s design and the plate thickness. Thicker plates generally result in higher restraint stress. Controlling restraint stress is crucial to prevent cold cracking. Techniques such as proper joint design, weld sequencing, and the use of fixtures or jigs to minimize the restraint stress can be employed.
Determining the optimum preheating temperature (T0) plays a crucial role in preventing cold cracking. Experimental methods have been used to establish a recommended minimum preheating temperature. By considering the three factors mentioned above, including hydrogen content, hardenability of the steel material, and restraint stress, the appropriate preheating temperature can be determined to prevent cold cracking.