Microstructure–properties relationships in martensitic stainless steel resistance spot welds

Abstract

The paper addresses the phase transformations and mechanical response of martensitic stainless steel resistance spot welds. The fusion zone microstructure consists of carbon-rich martensite together with a relatively high amount of retained delta ferrite along the grain boundaries with a transition in solidification mode from equiaxed to columnar dendritic grains across the fusion zone. The heat affected zone microstructure is featured by martensitic matrix together with carbide precipitation. The very high hardness of the fusion zone and the heat affected zone, the sharpness of the notch at sheet/sheet interface, which is located in the hard microstructural zone, and the presence of delta ferrite in the weld nugget play important roles in failure characteristics and mechanical performance of the joint.

Welding metallurgy of stainless steels during resistance spot welding Part II –heat affected zone and mechanical performance

“…Figure 13 shows the energy capability versus load bearing capacity of stainless steels RSWs. The mechanical properties of a martensitic stainless steel from a previous work 17 is also included. The inset of Fig.…”

“…There are limited works on the resistance spot weldability of stainless steels. [15][16][17]25 Part I of this work 26 addressed the solidification and post-solidification phase transformations in the FZ of three types of stainless steels, including austenitic, ferritic and duplex steels. Part II is focused on the phase transformations in the HAZ and mechanical properties of stainless steels spot welds.…”

“…Generally, spot welds fail at four different modes ( Fig. 1): 1,[10][11][12][13][14][15][16][17] (i) interfacial failure mode in which fracture propagates through the FZ (ii) pullout failure (PF) mode in which failure occurs via withdrawal of the weld nugget from one sheet; in this mode, fracture may initiate in the BM, HAZ or HAZ/FZ depending on the metallurgical and geometrical characteristics of the weld zone and the loading conditions (iii) partial interfacial failure mode in which the fracture first propagates in the FZ and is then redirected towards the thickness direction (iv) partial thickness-partial pullout (PT-PP) mode in which fracture initiates in a manner similar to PF mode; however, some part of mating sheet thickness is removed by a slant crack through the FZ during final crack propagation around the circumference of the weld nugget. Generally, the pullout mode is the preferred failure mode due to its higher associated plastic deformation and energy absorption.…”

Investigation of the Failure of Advanced High Strength Steels Heterogeneous Spot Welds

“…Numerous authors use them directly to express the spot weld strength [5][6][7][8][9]. Others insist also on the role of the steel microstructure in the spot weld zone [10][11][12]. The weld nugget size is in fact the main varying parameter with the increase of welding current intensity during the determination of the welding range for a given sheet configuration.…”

Welding metallurgy of stainless steels during resistance spot welding Part I: fusion zone

“…17,18 However, there are limited publications on resistance spot weldability of stainless steels. [22][23][24][25][26][27] The current understanding of the processstructure-property relationships is limited for RSW of stainless steels. Therefore, improving the knowledge regarding the microstructural characteristics and failure behaviour of stainless steels is a priority for the successful implementation of new design in vehicle applications.…”