FEM-Based Thermogram Correction for Inconel 625 Joint Hardness Clustering.

Wojciech Jamrozik,Jacek Górka,Bernard Wyględacz,Marta Kiel-Jamrozik

doi:10.3390/ma15031113

Wojciech Jamrozik, Jacek Górka + Show 2 more

Open Access

https://doi.org/10.3390/ma15031113

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Abstract

Assessing the temperature of the joint in on-line mode is a vital task that is demanded to characterize the formations of terns formations that are taking place in a joint and result in reaching necessary properties of the joint. Arc welding generates a high amount of heat that is reflected by the metallic surface of the welded object. In the paper, a temperature measurement credibility increase method is described and evaluated. The proposed method is used to reduce the influence of the reflected temperature of the hot torch and the arc on the temperature distribution observed on the surface of the welded joint using an infrared camera. The elaborated approach is based on comparison between infrared observation of the solidifying weld and precisely performed finite element method (FEM) simulation. The FEM simulations were calibrated according to the geometry of the fusion zone. It allows to precisely model heat source properties. The best-reflected temperature correction map was selected and applied to obtain a temperature representation that differs from the FEM baseline by less than 10 °C. Precise temperature values allowed us to cluster welded joints in 3D feature space (temperature, hardness, linear energy). It was found that by using the k-means clustering method it is possible to distinguish between correct and faulty (in terms of too low mechanical properties) joints.

Highlights

Inconel nickel-chromium superalloys contain approximately 15 to 20% chromium and iron additives up to approximately 18%, molybdenum up to approximately 16%, niobium up to approximately 5% and other elements (Co, Cu, W)
Inconel 625 (EN 2.4856-NiCr22Mo9Nb) being a trademark of the Special Metals Corporation group [2] is a nickel-chromium-molybdenum alloy with an addition of niobium that acts with the molybdenum to stiffen the alloy matrix and thereby provide high strength without strengthening heat treatment
As the vast majority of new metallic materials, alloys and superalloys are used in harsh environments, are characterized by low thermal expansion coefficients, have relatively good weldability and have low emissivity in the wavelength band used mainly by longwave infrared (LWIR) cameras (8–14 μm), so there is a constant demand for novel acquisition and processing methods that will limit these drawbacks

Summary

Introduction

Inconel nickel-chromium superalloys contain approximately 15 to 20% chromium and iron additives up to approximately 18%, molybdenum up to approximately 16%, niobium up to approximately 5% and other elements (Co, Cu, W). The use of an infrared camera for welding process monitoring is relatively simple, but it is a non-trivial task to get measurement results that are valid. As the vast majority of new metallic materials, alloys and superalloys are used in harsh environments, are characterized by low thermal expansion coefficients, have relatively good weldability (cobalt, titanium, and nickel) and have low emissivity in the wavelength band used mainly by longwave infrared (LWIR) cameras (8–14 μm), so there is a constant demand for novel acquisition and processing methods that will limit these drawbacks. According to well calibrated FEM simulation results, a valid ground truth temperature distribution was generated Based on those distributions, a method of reflected temperature correction was proposed. Using corrected IR images, the condition of welded joints was clustered to differentiate the correct and incorrect joints from the hardness point of view

Materials and Methods

Metalographic Examination

FEM Modelling