ESW Cladding of High-Chromium Cast Iron Interface Temperature Field and Microstructure Properties

Literature Overview

This study investigates the temperature field distribution at the interface during electroslag welding (ESW) cladding of high-chromium cast iron, and examines the resulting microstructure and mechanical properties across the bond line. High-chromium white cast iron (typically 12–30 wt% Cr) is widely used in severe abrasive environments such as coal handling, mining, and cement grinding equipment, but its brittleness limits direct welding. ESW cladding offers a practical route to combine the wear resistance of high-Cr cast iron with the toughness of a low-carbon or low-alloy steel base. The paper employs both numerical simulation and experimental validation to characterize the thermal cycle, solidification behavior, and final property profile of the cladding system.

Core Technical Points on Interface Temperature Field

The ESW process generates a deep, narrow slag pool that maintains a stable molten zone for extended periods. The study highlights that the peak temperature at the interface can exceed 1700 °C during welding, while the cooling rate at the bond line typically ranges from 5 to 25 °C/s depending on the number of passes and current settings. The thermal gradient perpendicular to the interface is steep, creating a narrow transition zone (TZ) of approximately 0.5–2 mm where dilution between the high-Cr overlay and the steel substrate occurs.

The numerical model reveals that the first pass produces the highest thermal gradient because the base metal acts as a heat sink. Subsequent passes benefit from the preheating effect of previously deposited layers, reducing the thermal gradient and thereby limiting the formation of brittle martensite in the transition zone.

Microstructure and Properties Analysis

Metallographic examination of the cladding interface reveals a layered microstructure consisting of the high-Cr white cast iron overlay (with Cr7C3 and M7C3 carbides), a narrow transition zone, and the base steel. The transition zone is critical because it is where dilution introduces carbon and chromium into the steel matrix, potentially forming hard, brittle phases. The study reports that the overlay hardness reaches 600–800 HV due to the dense distribution of Cr-rich carbides, while the base steel retains 200–250 HV. The transition zone hardness typically falls between 400–600 HV, creating a gradual hardness gradient that is beneficial for wear resistance without introducing severe stress concentrations.

Tensile testing of the interface region shows that the bond strength is adequate for most service conditions, with failure typically occurring in the overlay rather than at the interface. However, the study notes that excessive dilution (above 35%) can lead to the formation of untempered martensite in the TZ, which significantly reduces impact toughness and increases susceptibility to cracking during cooling or subsequent thermal cycling.

Engineering Practice Implications

From a fabrication standpoint, this study reinforces several key process recommendations. First, preheating the base steel to 200–300 °C is essential to reduce the cooling rate at the interface and minimize martensite formation. Second, controlling the dilution ratio through careful selection of ESW current (typically 800–1200 A) and travel speed is critical; lower current with slower travel tends to increase dilution. Third, post-weld heat treatment (PWHT) at 600–650 °C for 1–2 hours per 25 mm thickness can effectively temper any retained martensite in the transition zone, improving toughness without significantly reducing overlay hardness.

A practical concern that arises from this work is the potential for thermal cracking in the overlay itself, particularly at the grain boundaries where Cr7C3 carbides concentrate. The study suggests that adding small amounts of sulfur or selenium to the consumable can modify carbide morphology from angular to more rounded shapes, reducing crack initiation sites. This is a valuable insight for engineers selecting or developing consumables for ESW cladding applications.

Study Insights and Reflections

The most valuable contribution of this literature is the quantitative mapping of the temperature field and its direct correlation with the observed microstructure. In engineering practice, engineers often rely on empirical rules for ESW cladding parameters, but this study provides a physics-based framework that can guide parameter optimization for new material combinations. The emphasis on the transition zone as the critical region for performance evaluation is a reminder that the bond line, not just the overlay or the base, must be the focus of quality control. Non-destructive testing of the bond line, such as ultrasonic examination for lack of fusion or hot cracks, should be mandatory for any safety-critical cladding application.