**2. Experimental Procedure**

1Cr12Mo stainless steel was used as the base metal, with the chemical composition in weight percent of Cr (11.50~13.00), Ni (0.30~0.60), Mo (0.30~0.60), Mn (0.30~0.50), C (0.10~0.15), Si (0.05), P (0.035), S (0.030), and Fe (balance) according to the national (Chinese) standard GB8732. A nickel-based filler metal, BNi-2, containing in weight percent Cr (6.0~8.0), B (2.75~3.5), Si (4.0~5.0), Fe (2.5~3.5), Ni (balance) was chosen. The filler metal was in powder form with the granule size about 400 mesh. The base metal was processed to shear specimens described in the national (Chinese) standard GB11363-89, then cleaned using an ultrasonic bath and acetone solvent, and dried with hot air. Before brazing, the shear specimens were assembled as shown in Figure 1. The gap between brazed materials was 2 μm and sufficient filler metal was put on the packing place. To prevent the powder from running away, some alcohol was used during brazing. Figure 2 shows a schematic illustration of the induction brazing. A HX-GP-25 type high-frequency inductor was used as the heating equipment, and the heating current was 600 A. A high speed infrared temperature measuring instrument (Kleiber KMGA740, Kleiber, Allgäucity, German) was used to measure and record the brazing temperature. Due to the low content of Cr elements in BNi-2, to prevent oxidation the induction brazing was performed in an Ar atmosphere, and the Ar gas flow rate was 25 L/min. The brazing temperatures were 1050, 1080, 1120 and 1150 ◦C. The holding times were 10 s, 30 s, 50 s, and 90 s respectively.

**Figure 1.** The brazed specimen for shear strength test (units: mm).

The brazed samples were cut using a metallographic sample cutting machine, then executed in accordance with the standard metallographic procedure. The cross section of the brazed joint was examined using the JSM-7600 UHR thermal field emission scanning electron microscope (JEOL, Tokyo, Japan) with an operating voltage of 15 kV. To evaluate the bonding strength of the base metal and the filler metal, the shear test was conducted. The shear test piece was drawn by a universal testing machine (Zwick, Ulm-Einsingen, German) with a constant speed of 1 mm/min at room temperature.

**Figure 2.** Schematic illustration of the induction brazing.
