Metallurgical Design of High-Performance GMAW Electrodes for Joining HSLA-65 Steel

Abstract

A C++ algorithm was used to metallurgically design high-performance GMAW electrodes for joining HSLA-65 steel. The electrode design was based on: (1) a carbon content ≤0.06 wt.% for improved weldability, (2) a 5-15% lower A_r3 transformation temperature than HSLA-65 steel for enhanced strength and toughness, and (3) a desirable range of carbon equivalent number (CEN) for consistently overmatching the minimum specified tensile strength of HSLA-65 steel. The algorithm utilized a set of boundary conditions that included calculated A_r3, B_S, B_F, and M_S transformation temperatures besides CEN. Numerical ranges for boundary conditions were derived from chemical compositions of commercial HSLA-65 steel, substituting thermomechanical effects with weld solidification effects. The boundary conditions were applied in evaluating chemical composition ranges of the following three prospective welding electrode specification groups that offered to provide ≤0.06 wt.% carbon, a minimum transverse-weld tensile strength of 552 MPa (80 ksi), and a minimum CVN impact toughness of 27 J at −29 °C through −51 °C (20 ft lbf at −20 °F through −60 °F) in the as-welded condition: (1) ER80S-Ni1, (2) E90C-K3, and (3) E80C-W2. At ≤0.06 wt.% carbon, the algorithm returned over 3100 results for E90C-K3 that satisfied the boundary conditions, but returned no acceptable results for other two electrode specification groups. Results revealed that welding electrode designs based on an Fe-C-Mn-Ni-Mo system, containing 0.06 wt.% C, 1.6 wt.% Mn, 0.8 wt.% Ni, and 0.3 wt.% Mo that provide weld metals characterized by an A_r3 of 690 °C, a CEN of 0.29, and a (B_F − M_S) of 30 °C are expected to consistently overmatch the minimum specified tensile strength of HSLA-65 steel while offering a minimum CVN impact toughness of 41 J at −40 °C (30 ft lbf at −40 °F).

Appendix A: An Algorithm for Evaluating Chemical Composition Limits of Welding Electrode Specifications Suitable for HSLA-65 Steel in Nonlanguage Specific “Pseudo Code”

• 1) Define new variables as real numbers for Carbon, Manganese, Nickel, Chromium, and Molybdenum content in wt.% as well as maximum and minimum values.

• 2) Define new variables as real numbers representing mean values of Silicon, Copper, Titanium, Vanadium, Niobium, and Boron content in wt.%.

• 3) Define new variables as real numbers for CEN, A_r3, B_S, B_F, M_S, and B_F-M_S maximum values, minimum values, and calculated values.

• 4) Assign values for variables based on relevant electrode and base metal specifications.

• 5) Display on screen: “Welding Electrode Composition Evaluation”.

• 6) Display on screen: “Enter integer difference in temperature between calculated B_F & calculated M_S”.

• 7) Receive value for B_F-M_S.

• 8) If B_F-M_S is less than 0 or greater than 50 display on screen “Range incorrect. Enter value between 0 & 50”.

• 9) Else display on screen “filename name to store weld metal chemical compositions. Filename with .csv (comma separated values) would be best for viewing”).

• 10) User enters file name.

• 11) If Filename is NULL display “Error! The file could not be opened”

• 12) Else filename is OK then continue calculations

  •      a) Print Carbon, Manganese, Nickel, Chromium, and Molybdenum minimum and maximum wt-%, CEN, A_r3, B_S, B_F, M_S, and B_F-M_S values to spreadsheet (.csv)

  •      b) For loop: Increment C wt-% until it hits the maximum defined.

    •        i) For loop: Increment Mn wt-% until it hits the maximum defined.

    •           (1) For loop: Increment Ni wt-% until it hits the maximum defined.

    •               (a) For loop: Increment Cr wt-% until it hits the maximum defined.

    •                    (i) For loop: Increment Mo wt-% until it hits the max defined.

    •                          1. Calculate CEN.

    •                          2. If CEN is between max and min values

    •                               a. Calculate A_r3

    •                               b. If A_r3 is between max and min values

    •                                   i. Calculate B_S

    •                                   ii. If B_S is between max and min values

    •                                       1. Calculate B_F

    •                                       2. If B_F is between max and min values

    •                                           (a) Calculate M_S

    •                                            (b) If M_S is between max and min values

    •                                                 (i) If M_S + B_F-M_S is less than B_F

    •                                                      (1) Print C, Mn, Ni, Cr, Mo, Cu, Si, Ti, Nb, B, V, CEN, A_r3, B_S, B_F, M_S values to spreadsheet

• 13) Close all statements