Post by khatunejannat on Feb 15, 2024 1:45:10 GMT -5
Any experienced welder knows well the “golden rule” for selecting the electrode or wire to use to weld any metallic material. This rule says that the filler material must have a “similar” chemical composition to that of the base material and its mechanical resistance must be slightly higher than that of the base material. Although the criterion of mechanical resistance is equally applicable to stainless steels, what has been said regarding its chemical composition is not so applicable, since it must be interpreted as being “compatible” with that of the base metal. In this way, the Schaeffler diagram becomes an extremely useful graphic tool , since it allows you to determine if a certain electrode or wire is compatible with the base material that you want to weld. If you want to become an excellent welding technician, it is advisable that you know how it is used and how said diagram should be interpreted. First of all, we must remember that stainless steels are alloys of iron and carbon (just like any other steel), but with one more important alloying element, such as chromium , and also in a high percentage (at lea.
This element is what gives it its stainless property. In addition, it can contain other alloys that provide additional properties, such as resistance to cryogenic temperatures Cocos Islands Keeling Email List below zero). Depending on their chemical composition and properties, 4+1 (four plus one) types of stainless steels can be differentiated : ferritic, austenitic, martensitic, duplex (austeno-ferritic) and, finally, a special group of hardenable stainless steels. precipitation. In this way, the first use that the Schaeffler diagram offers us is to determine the type of stainless steel we have in hand. If we look at the appearance of said diagram, we can see that the X axis (horizontal) shows the value of Chromium Equivalent , while the Y axis (vertical) shows the value of Nickel Equivalent . Both the Chromium Equivalent (Cr eq ) and the Nickel Equivalent (Ni eq ) of a certain stainless steel are calculated using the following expressions, in which the chemical composition of the steel must be entered: Cr eq.
Defects in the weld based on the resulting structure in the bead. These defects are represented in the diagram by colored areas that correspond to: -Red zone: Risk of hot cracking above 1250°C -Green zone: Risk of fragility (due to sigma phase) between 500 and 900°C -Blue zone: Grain growth above 1150°C -Purple zone: Cracking due to quenching below 400°C Fig.2. Identification of defect areas during welding on the Shaeffler diagram To do this, we must calculate and represent the equivalent chromium (Cr eq ) and the equivalent nickel (Ni eq ) of the filler metal . That is, the same expressions are used as before, but in this case the chemical composition of the electrode, wire or rod used in welding is introduced. Suppose we use a type 316L coated electrode with the following chemical composition: This point has been represented in the previous diagram, noting that it is an austeno-ferritic stainless , with approximately 7% ferrite. Next, to predict the resulting structure in the welded bead, we join both points obtained on the diagram using a straight line, as seen in the following figure (where the enlarged area can be seen conveniently). The resulting point is located on said line, more displaced towards one end or the other depending on the dilution achieved in the bead, which is valued at 30-40% for the covered electrode welding process. Fig.3. Enlarged area of the Schaeffler diagram with the point corresponding to the welded bead In conclusion , it is observed that the structure of the resulting bead will be austeno-ferritic, with 5% ferrite, and without risk of serious defects during the welding process, since it is not located on any of the colored areas, which is a good result.
This element is what gives it its stainless property. In addition, it can contain other alloys that provide additional properties, such as resistance to cryogenic temperatures Cocos Islands Keeling Email List below zero). Depending on their chemical composition and properties, 4+1 (four plus one) types of stainless steels can be differentiated : ferritic, austenitic, martensitic, duplex (austeno-ferritic) and, finally, a special group of hardenable stainless steels. precipitation. In this way, the first use that the Schaeffler diagram offers us is to determine the type of stainless steel we have in hand. If we look at the appearance of said diagram, we can see that the X axis (horizontal) shows the value of Chromium Equivalent , while the Y axis (vertical) shows the value of Nickel Equivalent . Both the Chromium Equivalent (Cr eq ) and the Nickel Equivalent (Ni eq ) of a certain stainless steel are calculated using the following expressions, in which the chemical composition of the steel must be entered: Cr eq.
Defects in the weld based on the resulting structure in the bead. These defects are represented in the diagram by colored areas that correspond to: -Red zone: Risk of hot cracking above 1250°C -Green zone: Risk of fragility (due to sigma phase) between 500 and 900°C -Blue zone: Grain growth above 1150°C -Purple zone: Cracking due to quenching below 400°C Fig.2. Identification of defect areas during welding on the Shaeffler diagram To do this, we must calculate and represent the equivalent chromium (Cr eq ) and the equivalent nickel (Ni eq ) of the filler metal . That is, the same expressions are used as before, but in this case the chemical composition of the electrode, wire or rod used in welding is introduced. Suppose we use a type 316L coated electrode with the following chemical composition: This point has been represented in the previous diagram, noting that it is an austeno-ferritic stainless , with approximately 7% ferrite. Next, to predict the resulting structure in the welded bead, we join both points obtained on the diagram using a straight line, as seen in the following figure (where the enlarged area can be seen conveniently). The resulting point is located on said line, more displaced towards one end or the other depending on the dilution achieved in the bead, which is valued at 30-40% for the covered electrode welding process. Fig.3. Enlarged area of the Schaeffler diagram with the point corresponding to the welded bead In conclusion , it is observed that the structure of the resulting bead will be austeno-ferritic, with 5% ferrite, and without risk of serious defects during the welding process, since it is not located on any of the colored areas, which is a good result.