Microhardness and Stress Analysis of Laser-Cladded AISI 420 Martensitic Stainless Steel
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JMEPEG (2017) 26:1076–1084 DOI: 10.1007/s11665-017-2541-x
Microhardness and Stress Analysis of Laser-Cladded AISI 420 Martensitic Stainless Steel Mohammad K. Alam, Afsaneh Edrisy, Jill Urbanic, and James Pineault (Submitted September 28, 2016; in revised form December 13, 2016; published online February 14, 2017) Laser cladding is a surface treatment process which is starting to be employed as a novel additive manufacturing. Rapid cooling during the non-equilibrium solidification process generates non-equilibrium microstructures and significant amounts of internal residual stresses. This paper investigates the laser cladding of 420 martensitic stainless steel of two single beads produced by different process parameters (e.g., laser power, laser speed, and powder feed rate). Metallographic sample preparation from the cross section revealed three distinct zones: the bead zone, the dilution zone, and the heat-affected zone (HAZ). The tensile residual stresses were in the range of 310–486 MPa on the surface and the upper part of the bead zone. The compressive stresses were in the range of 420–1000 MPa for the rest of the bead zone and the dilution zone. The HAZ also showed tensile residual stresses in the range of 140–320 MPa for both samples. The post-cladding heat treatment performed at 565 °C for an hour had significantly reduced the tensile stresses at the surface and in the subsurface and homogenized the compressive stress throughout the bead and dilution zones. The microstructures, residual stresses, and microhardness profiles were correlated for better understanding of the laser-cladding process. Keywords
AISI 420, cladding, heat treatment, laser, martensitic, microhardness, microstructure, residual stress, stainless steel
1. Introduction Martensitic stainless steel grade 420 powder is considered to be one of the potential alloys for creating additive manufacturing functional components (Ref 1). This alloy is also used for coating and surface repair applications in the tool and die industry because of its high resistance to wear, corrosion, and degradation (Ref 1). Unlike other stainless steels, martensitic stainless steels are heat treatable, and properties can be tailored for specific applications such as steam generators, mixer blades, cutting tools, and medical application (Ref 2). The use of laser cladding as an additive manufacturing process has been growing as it has many unique advantages over conventional cladding done through welding or metal deposition in terms of low dilution, less heat-affected zone (HAZ), less distortion to the substrate, and overall quality of the deposited materials (Ref 1, 2). Laser cladding provides a localized and relatively low heat input to produce a clad with perfect diffusion bonding to the substrate (Ref 3). Hence, it reduces undesired major deterioration of the desired mechanical properties of the substrate as well as the bead layers. However, despite having a relatively low heat input, a significant amount of internal residual stresses and minor distortions are developed M
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