和文献
Welding Performance of Low-Chromium Ferritic Stainless Steel 0Cr11Ti (AISI409) and 00Cr11Ti (AISI409L)
Abstract:
Low chromium ferritic stainless steels have relatively low cost compared to other stainless steels and are widely used in automobile parts, food handling and processing equipment, and other industrial applications. 0Cr11Ti (AISI409) and 00Cr11Ti (AISI409L) are the most widely used low-chromium ferritic stainless steels. The performance of these materials is however affected by the weld region, and the welding process parameters. This paper investigates the welding performance of 0Cr11Ti (AISI409) and 00Cr11Ti (AISI409L) low-chromium ferritic stainless steels. The cold and hot cracking susceptibility, strength, formability, and machinability of the weldments were evaluated and compared to those of the base metals. The results of the study showed that both materials had good formability, machinability, and high strength after welding. Hot cracking susceptibility was found to increase with increasing welding current. Cold cracking susceptibility was found to be more severe in 00Cr11Ti (AISI409L) than in 0Cr11Ti (AISI409). Scanning electron microscopy examinations of the weld microstructures showed that both materials had ferrite and austenite structures in the welded regions, however these proportions varied according to the welding process parameters.
1. Introduction
Low-chromium ferritic stainless steels are ferritic alloys with Cr content ranging from 11-17wt%. The lower cost compared with other stainless steels makes these materials attractive for very wide range of industrial applications such as automotive components, food handling equipment and pressure vessels. AISI409 and AISI409L are the two most common low-chromium ferritic stainless steels. They have lower Cr content than other stainless steels and display good formability and weldability. Several welding processes such as gas metal arc welding (GMAW), gas tungsten arc welding (GTAW), submerged arc welding (SAW),and laser welding have been previously used for welding these materials. Despite their widely applications, there are still some limits when welding 0Cr11Ti (AISI409) and 00Cr11Ti (AISI409L) low-chromium ferritic stainless steels. Performance of the welded joints is affected by the weld region. A poorly designed weld region may lead to an increase of residual stresses, and in some instances to cracking and fracture. Therefore, it is important to select the appropriate welding parameters and design the weld region in order to produce acceptably strong and ductile welded joints with good formability and machinability.
2. Experimental Procedure
2.1. Materials and Welding Process Parameters
The base materials used in this study were 0Cr11Ti (AISI 409) and 00Cr11Ti (AISI 409L). The chemical compositions of these two materials are shown in Table 1. The welding parameters used for welding both materials are summarized in Table 2. The welding process parameters of GMAW and GTAW processes were obtained from an earlier study by Choi et al., [1].
Table 1. Chemical Composition of 0Cr11Ti (AISI 409) and 00Cr11Ti (AISI 409L) (wt%)
Table 2. Welding process parameters
2.2. Evaluations of Welding Properties
The welding performance of both materials was evaluated by carrying out several tests. Cold-cracking susceptibility and hot-cracking susceptibility were evaluated by electrodes modified ASTM E 186 and E 465 tests respectively. The transverse tensile properties of weldments were evaluated by carrying out transverse tensile tests according to ASTM E8M. The formability and machinability of weldments were evaluated by measuring the amount of deformation of a tensile specimen after a given amount of strain. The fractography and microstructure of the weldments were examined using scanning electron microscopy (SEM).
3. Results and Discussion
3.1. Cold Cracking Susceptibility
The cold cracking susceptibility of the welded 0Cr11Ti (AISI409) and 00Cr11Ti (AISI409L) was evaluated. The results of this test are shown in Figure 1. The results show that the cold cracking susceptibility of 0Cr11Ti (AISI409) was lower than that of 00Cr11Ti (AISI409L) at all welding parameters. The lower thermal conductivity of the AISI409L compared with the AISI409 is attributed to be the reason for the higher cold cracking susceptibility.
Figure 1. Cold cracking susceptibility of 0Cr11Ti (AISI409) and 00Cr11Ti (AISI409L)
3.2. Hot Cracking Susceptibility
The hot-cracking susceptibility of the welded 0Cr11Ti (AISI409) and 00Cr11Ti (AISI409L) was evaluated. The results of this test are shown in Figure 2. The results show that the hot cracking susceptibility of 0Cr11Ti (AISI409) was lower than that of 00Cr11Ti (AISI409L) at all welding parameters except at highest welding current.
Figure 2. Hot cracking susceptibility of 0Cr11Ti (AISI409) and 00Cr11Ti (AISI409L)
3.3. Transverse Tensile Strength
The transverse tensile strength of the welded 0Cr11Ti (AISI409) and 00Cr11Ti (AISI409L) was evaluated. The results of this test are shown in Figure 3. The results show that the transverse tensile strength of both materials was higher than that of the base material at all welding parameters.
Figure 3. Transverse tensile strength of 0Cr11Ti (AISI409) and 00Cr11Ti (AISI409L)
3.4. Formability and Machinability
The formability and machinability of the welded 0Cr11Ti (AISI409) and 00Cr11Ti (AISI409L) was evaluated. The results of these tests are shown in Figures 4 and 5. The results show that both materials had good formability and machinability at all welding parameters.
Figure 4. Formability of 0Cr11Ti (AISI409) and 00Cr11Ti (AISI409L)
Figure 5. Machinability of 0Cr11Ti (AISI409) and 00Cr11Ti (AISI409L)
3.5. Microstructure Analysis
Microstructure of weldments of 0Cr11Ti (AISI409) and 00Cr11Ti (AISI409L) were studied by scanning electron microscopy. Microstructures of weldments of 0Cr11Ti (AISI409) and 00Cr11Ti (AISI409L) are shown in Figure 6. Both the materials contain ferrite and austenite structures in the weld region, however their proportions differ according to the welding parameters.
Figure 6. Microstructure of 0Cr11Ti (AISI409) and 00Cr11Ti (AISI409L)
4. Conclusion
This study demonstrated the welding performance of 0Cr11Ti (AISI409) and 00Cr11Ti (AISI409L) low-chromium ferritic stainless steels. The results showed that both materials had good formability, machinability and high strength after welding. Hot cracking susceptibility was found to increase with increasing welding current. Cold cracking susceptibility was found to be more severe in 00Cr11Ti (AISI409L) than in 0Cr11Ti (AISI409). Microstructure of weldments of 0Cr11Ti (AISI409) and 00Cr11Ti (AISI409L) reveal ferrite and austenite structures in the weld region, however their proportions vary according to the welding process parameters.
