Study on fracture toughness evaluation method of SA738Gr.B steel heat affected zone in ductile-brittle transition region

Figures & data

Figure 1. Microstructure of SA738Gr.B steel.

Table 1. SAW experiment scheme of SA738Gr.B

Weld bead	Current A	Voltage V	Welding speed	Weld bead temperature °C	Heat input KJ/cm	Preheating Temperature °C
Bottoming	320–450	26–30	35–45	≤200	9.6–10.2	100–200
Filling	400–500	26–32	40–55	≤200
Cover	400–500	26–32	40–55	≤200
Remarks: Welding material	Welding wire ：CHW-S62HRF
	Specification：Φ2.4 mm
	Welding flux：CHF102HRF

Figure 2. Schematic diagram of double-Y groove.

Table 2. Fracture toughness test data

State	Temperature(°C)	J-integral (KJ/m^2)	KJc(0.5T) (MPa√m)	KJc(1T-converted) (MPa√m)	KJc(limit) examination (MPa√m)
PWHT	−130	45.8	101.1	88.2	Valid
	−130	166.7	192.8	165.3	Valid
	−130	85.8	138.3	119.5	Valid
	−130	115.3	160.4	138.1	Valid
	−130	18.0	63.4	56.5	Valid
	−130	12.7	53.1	47.9	Valid
	−140	23.5	72.4	64.1	Valid
	−140	31.2	83.4	73.3	Valid
	−140	15.1	58.1	52.0	Valid
	−140	162.0	190.1	163.1	Valid
	−140	60.2	115.9	100.6	Valid
	−140	55.1	110.9	96.5	Valid
AW	−130	37.1	91.0	75.8	Valid
	−130	93.9	144.7	118.0	Valid
	−130	139	175.8	142.5	Valid
	−130	97.4	147.4	120.2	Valid
	−130	89.5	141.3	115.4	Valid
	−130	51.3	106.9	88.3	Valid
	−130	21.2	68.9	58.4	Valid
	−130	23.8	73.0	64.5	Valid
	−130	26.4	76.9	67.8	Valid
	−130	34.6	87.9	77.1	Valid
	−130	101.5	150.5	129.7	Valid
	−130	34.4	87.6	76.8	Valid
	−130	61.6	117.3	101.8	Valid
	−130	21.5	69.2	61.4	Valid
	−130	50.0	105.6	92.0	Valid
	−130	186.1	203.8	174.5	Valid
	−130	107.3	154.7	133.3	Valid
	−130	120.4	163.9	141.0	Valid

Figure 3. HAZ specimen sampling diagram. (a) Schematic diagram of 0.5T-C(T) specimen sampling in HAZ, (b) Heat-affected zone range metallographic map, (c) Machining groove in HAZ schematic, and (d) HAZ prefabricated fatigue crack specimen.

Figure 4. Fracture toughness test environment.

Table 3. Standard MC method to obtain the characteristic parameters

	K0(MPa·m^1/2)	T0(°C)
AW	119.1	−137.3
PWHT	132.8	−145.0

Figure 5. MC method results of SA738Gr.B HAZ. (a) AW and (b) PWHT.

Figure 6. Weibull plots of fracture toughness data (Weibull slop fixed at 4).

Table 4. BMC method characteristic parameters fitting values

	pa	K01(MPa·m^1/2)	K02(MPa·m^1/2)
AW	0.527	81.0	138.8
PWHT	0.365	73.2	151.0

Figure 8. Weibull distribution fitting (Weibull slop fixed at 4). (a) AW and (b) PWHT.

Figure 7. BMC model master curve and its 5% and 95% upper and lower boundary curves.

Figure 9. SPE model master curve and its 5% and 95% upper and lower boundary curves. (a) AW and (b) PWHT.

Table 5. BMC method characteristic parameters fitting values

		K0(MPa·m^1/2)			T0 (°C)
Datum	r	Stage1	Stage 2	Stage 3	Stage 1	Stage 2	Stage 3
HAZ-AW	18	119.1	100.1	106.7	−137.3	−124.5	−129.3
HAZ-PWHT	12	130.1	94.9	77.6	−143.5	−120.4	−103.8

Remarks: The results of all sample data converted to 1T specimens, the corresponding temperature is -130°C.

Table 6. SINTAP inhomogeneity screening results

Heat treatment state	β(°C)	r	T0(step1)-T0(step2) (°C)	ΔT0	Inhomogeneity screening result
AW	18	18	12.8	6.10	Inhomogeneous
PWHT	18	12	23.1	7.48	Inhomogeneous

Figure 10. SINTAP model master curve and its 5% and 95% upper and lower boundary curves.

Table 7. HAZ fracture toughness characteristic parameters

	MC	BMC	SPE	SINTAP
HAZ-AW-K0（MPa·m^1/2）	119.1	91.1 (K01) 138.8 (K02)	107.4	100.1
HAZ-PWHT-K0（MPa·m^1/2）	132.8	73.2 (K01) 151.0 (K02)	99.8	77.6
HAZ-AW-T0(°C)	−137.3	−128.2	−129.8	−124.5
HAZ-PWHT-T0(°C)	−145.0	−144.8	−124.2	−103.8