Schaeffler Diagram and its practical uses


What is Schaeffler Diagram?

The Schaeffler diagram is an important tool for predicting the constitution of your stainless steel weld deposits. Depending on the alloying elements present in the weldment, the Schaeffler diagram gives predictions about the various phases (structures) present in the weld. The diagram is an effective tool for phase predictions for austenitic stainless steels having carbon contents up to 0.12%.


In stainless steel welds (predominately austenitic types- SS316L, SS321, for example), ferrite plays a crucial role by eliminating the hot cracking during weld solidification. ‘Constitution diagrams’ such as the Schaeffler diagram is very helpful in such situations to accurately predict the ferrite level in the weld deposit based on the chemical composition.

This prediction is based on the ferrite and austenitic stabilizers present in the weldment. Schaeffler’s diagram is useful in estimating the microstructure of the weld deposit and the filler metal composition required to produce the prescribed amount of ferrite in the weld deposit.

The chromium equivalent (Drawn on the horizontal line) is calculated from the weight percentage of ferrite-forming elements (Cr, Si, Mo, Nb, W) and the nickel equivalent (drawn on the vertical line) is calculated from the weight percentage of austenite-forming elements (C, Ni, Mn, Cu, N).

The position in the Schaeffler diagram defined by the Cr- and Ni-equivalents gives the proportions of martensite, austenite, and ferrite in the resulting microstructure.

Read more about Constitution Diagrams:

  1. Delong Diagram & its practical uses.
  2. WRC-1992 Diagram & its practical uses.
Figure 1. Microstructures plotted on Schaeffler Diagram

A Schaeffler diagram can be used to shows the influence of the proportion of two alloying elements (and therefore the composition of the alloy) on the structure achieved after fast cooling from 1050°C to room temperature. The diagram shows how the microstructure of the weld is affected by the alloying elements in the stainless steel, base don those like Nickel (Ni- austenitic stabilizer) and those act like Chromium (Cr- Ferrite stabilizer).

The Nickel equivalent (Ni- Eq) group includes Ni and the effect of C and Mn. Chromium Equivalent (Cr-Eq) includes the effects of Cr, Mo, Si, and Cb. To estimate the microstructure of a deposit the Cr and Ni Equivalents are calculated using the following equations:

• Cr equivalent = %Cr + %Mo + 1.5(%Si) + 0.5(%Cb)
• Ni equivalent = (%Ni)+30(%C+%N)+0.5(Mn+%Cu+%Co)

The Schaeffler diagram is very useful for austenitic base weld metals to predict the final deposit weld structure. Below Schaeffler Diagram shows the positions of various welding consumables with their respective weld deposit microstructure.

Figure 2. Most common welding electrode metallurgy on Schaeffler Diagram

A practical example for Schaeffler Diagram for Dissimilar Welding

As we learned that the position of the weld microstructure in the Schaeffler diagram is located using the Cr-Eq and Ni-Eq of the base metals. The value obtained is marked on the coordinates of the diagram and a point is located. The microstructure of the point is the one predicted for a deposit of that composition. It is possible to plot the composition of the filler wire and the composition of the base metal and connect them with a line and the resulting weld would be along the line.

By the use of the Schaeffler Diagram, it is possible to select a filler metal that will avoid ferrite or martensite, as desired in the stainless steel weld deposit. The Schaeffler Diagram can also be used to predict the composition of the weld deposit when welding dissimilar stainless steel materials.

The Schaeffler diagram in the above Figure represents an example of the above for the case of a low-alloy steel grade C15 (EN 1.0401), (A), being welded to stainless steel AISI 304 (1.4301), (B), using  ER309LMo (ER 23 12 2 L) filler wire (D). The resultant weld deposit at location E, Close to B (304) will have ferrite value in the range of 10%.

Chemical compositions of the above three materials in the discussion are given below:

Chemical composition % of steel C15 (1.0401): EN 10277-2-2008

CSiMnPS
0.12 – 0.18max   0.40.3 – 0.8max   0.045max   0.045

             Chemical composition % of steel  X5CrNi18-10 (1.4301): EN 10088-2-2005

CSiMnNiPSCrN
max   0.07max   1max   28 – 10.5max   0.045max   0.01517.5 – 19.5max   0.11

Chemical composition % of grade 309LMo ( 309LMo )

CSiMnNiPSCrMoCu
max   0.03max   0.651 – 2.512 – 14max   0.03max   0.0323 – 252 – 3max   0.75

Watch our You Tube video for interactive animation learning on Schaeffler Diagram & its importance.

Figure 3. Distribution of phases on Schaeffler Diagram

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