Powder-Added Overlay Welding Process and Application of Wear-Resistant Clad Steel Plate

Literature Overview and Process Description

Powder-added overlay welding, also known as flux-cored arc welding with externally fed alloy powder, is a versatile and cost-effective technique for depositing wear-resistant overlay layers on carbon steel substrates. The literature under review provides a comprehensive examination of the process parameters, metallurgical behavior, and practical applications of powder-added overlay welding in the manufacture of wear-resistant clad steel plates. This technique is particularly attractive for large-area overlay applications where the combination of high deposition rate and precise alloy composition control is required.

The process operates on the principle of a submerged arc or flux-cored arc welding configuration where a consumable electrode delivers base metal filler while a separate powder feed system introduces alloy powder into the arc. The powder particles melt in the arc plasma and are transferred to the weld pool, where they dissolve into the molten metal and are incorporated into the solidifying overlay. This dual-feed mechanism allows independent control of the base metal dilution and the alloy composition of the final overlay layer.

Key Process Parameters and Their Influence

The performance and quality of the powder-added overlay layer are governed by several critical process parameters. The powder feed rate determines the alloy content of the overlay, with typical values ranging from 50 to 200 grams per minute depending on the desired alloy concentration and the specific application requirements. The welding current, typically in the range of 350 to 550 amperes for submerged arc configurations, controls the penetration depth and the size of the weld pool, which in turn affects the dilution ratio and the metallurgical bonding between the overlay and the base metal.

The travel speed is a critical parameter that directly influences the heat input per unit length. Lower travel speeds result in higher heat input, which increases the weld pool volume and promotes better mixing of the alloy powder with the base metal. However, excessive heat input can lead to grain coarsening and reduced hardness in the overlay. A balance must be struck between achieving sufficient alloy incorporation and maintaining a fine microstructure.

Metallurgical Characteristics of the Overlay Layer

The metallurgical examination of the powder-added overlay layer reveals a complex microstructure that is characteristic of rapidly solidified alloy deposits. The overlay typically exhibits a columnar dendritic structure growing from the fusion interface toward the surface, with the dendrite spacing decreasing with increasing cooling rate. In high-alloy wear-resistant overlays containing chromium, molybdenum, and tungsten, the microstructure is dominated by hard carbide phases embedded in a martensitic or austenitic matrix. The hardness of the overlay layer can range from 45 HRC to 70 HRC depending on the specific alloy composition and the cooling conditions.

The dilution rate in powder-added overlay welding is generally lower than in conventional submerged arc welding, typically ranging from 15 to 35 percent. This lower dilution is advantageous for maintaining the intended alloy composition and hardness profile. The dilution rate can be further reduced by using multiple passes with decreasing powder feed rates in the upper passes, creating a graded composition profile that transitions from high dilution at the fusion line to low dilution at the surface.

Application of Wear-Resistant Clad Steel Plates

The wear-resistant clad steel plates produced using powder-added overlay welding find extensive application in mining, cement, coal handling, and material processing industries. In mining applications, the clad plates are used for conveyor chutes, hopper linings, and crusher walls where abrasive wear from ore and rock particles is the primary degradation mechanism. In cement plants, the overlay plates line kiln discharge chutes and grinding mill liners, providing extended service life compared to unclad carbon steel components.

The overlay thickness for wear-resistant applications typically ranges from 3 to 8 millimeters, depending on the severity of the wear environment and the expected service life. For severe abrasion conditions, multi-pass overlay with a total thickness of 6 to 8 millimeters is recommended, while moderate wear applications can be adequately served by a 3 to 5 millimeter overlay. The overlay layer is usually deposited in 2 to 4 passes, with each pass having a thickness of 2 to 3 millimeters, to ensure adequate metallurgical bonding and minimize cracking susceptibility.

Quality Control and Inspection

Quality control of the powder-added overlay clad plates involves a combination of visual inspection, dimensional measurement, hardness testing, and non-destructive testing. Visual inspection checks for surface defects such as undercut, porosity, and incomplete fusion at the fusion line. Dimensional measurement verifies that the overlay thickness meets the specified requirements at multiple locations across the plate surface. Hardness testing is performed at the surface, mid-thickness, and near the fusion line to confirm the hardness profile and detect any soft zones that may result from excessive dilution or improper heat treatment.

Non-destructive testing by magnetic particle inspection or ultrasonic testing is recommended for critical applications to detect subsurface cracks and lack of fusion defects. The acceptance criteria typically follow relevant standards such as GB/T 11345 for ultrasonic testing and GB/T 15858 for magnetic particle inspection. The overlay layer should be free of cracks, and any porosity detected should be below the acceptance threshold specified in the applicable quality standard.

Study Insights and Recommendations

This literature provides valuable guidance on the optimization of powder-added overlay welding for wear-resistant applications. The key insight is that the powder feed rate and welding current must be carefully balanced to achieve the desired alloy composition while maintaining acceptable dilution levels. Engineers should conduct welding procedure qualification tests to establish the optimal parameter window for their specific consumable combination and application conditions. The graded composition approach, using decreasing powder feed rates in successive passes, is a practical and effective strategy for improving the overall performance of the overlay layer. Regular monitoring of powder composition and feeding consistency is essential to maintain overlay quality throughout the production run, as even minor variations in powder alloy content can significantly affect the hardness and wear resistance of the final overlay.