Quality assessment of heat-treated rails in the R350HT grade

Żak, Sylwester

doi:10.2478/msp-2025-0042

Figures & Tables

Image of the microstructure at the corner of the rail heads after heat treatment: (a) rail from melt no. 321036, and (b) rail from melt no. 321037.

Hardness distribution on the cross-section of the rail head for the R350HT grade according to the standard [2] (a), hardness distribution on the cross-section of the rail head – sample 4 (b).

Spacing of supports and force application points for fatigue strength in the vertical plane.

Microstructure of R350HT steel in the cross-section of the rail head corner – sample no. 2 after industrial head hardening tests: (a) and (b) near-surface area, (c) and (d) area 10 mm below the surface; pearlitic structure, light microscope.

Microstructure in the cross-section in the area of the foot centre (5 mm below the surface) – sample 2 after industrial tests; pearlitic structure, light microscope.

Schematic representation of the areas of the tested microstructure from Figures 6 and 7.

Fracture of sample numbers 4–3 for determining the fatigue crack growth rate.

Baumann’s print: (a) sample 7 – pattern D2, (b) sample 7 – pattern D2. The area of positive sulphur segregation with a small amount of negative sulphur segregation in the rail web is marked.

Rail sample 60E2 R350HT in the vertical fatigue strength test.

Schematic diagram of the arrangement of strain gauges on the perimeter of the 60E2 rail.

Distribution of residual stress on the perimeter of the rail from test no. 8.

Fracture toughness tests [21]_

Number of specimens		Fracture toughness K _Ic, MPa m^1/2	Average value K _Ic, MPa m^1/2	Standard deviation K _Ic, MPa m^1/2
1	1–1	46.2	43.0	2.7
	1–2	45.4
	1–3	40.3
	1–4	40.7
	1–5	42.3
2	2–1	39.9	40.1	1.1
	2–2	40.8
	2–3	40.4
	2–4	38.3
	2–5	41.2
3	3–1	39.2	39.9	1.5
	3–2	40.3
	3–3	37.6
	3–4	41.3
	3–5	41.0
Requirements according to EN13674-1 for the R350HT grade		Single min. value 30 MPa m^1/2	Average value min 32 MPa m^1/2

Fatigue strength test results [21]_

Sample No.	Strain amplitude	Force, kN	Result
1a	0.00135	10.78	No cracks
1b	0.00135	10.88	No cracks
1c	0.00135	10.75	No cracks
2a	0.00135	10.83	No cracks
2b	0.00135	10.83	No cracks
2c	0.00135	10.88	No cracks
3a	0.00135	10.83	No cracks
3b	0.00135	10.76	No cracks
3c	0.00135	10.57	No cracks

Averaged results of mechanical properties tests and hardness measurements on the running surface of industrially manufactured 60E1/60E2 profile rails made of R350HT steel_

Number of samples	Cooling start temperature, °C	R _p0.2, MPa	R _m, MPa	A, %	Z, %	Impact strength KV₂ at 20°C, J/cm²		HBW hardness on the rolling surface – (RS)*
Number of samples	Cooling start temperature, °C	R _p0.2, MPa	R _m, MPa	A, %	Z, %	Head	Foot	HBW hardness on the rolling surface – (RS)*
1	830	724	1,228	10.2	19.4	12.7	10.1	362.1
1	810	732.2	1239.2	10.3	17.5	10.3	10.7	361.0
2	790	699.7	1264.3	9.7	17.1	10.7	10.7	367.1

Results of the measurement of residual stress in the rail foot_

Number of sample	Residual stress value (MPa)
1	96.9
3	66.4
2	84.9
2	104.9
3	116.7
4	114.3
Mean value	97.3

Results of the Baumann test_

Number of sample	Number of pattern
5	D2, D2, D2, D2, D2, D2
6	D2, D2, D2, D2, D2, D4
7	D2, D2, D2, D2, D2, D2

Basic properties of the tested rail steel for individual rail types [21]_

Number of sample	Basic mechanical properties
Number of sample	Tensile strength, R _m, MPa	Yield strength R _p0.2, MPa	Elongation A, %	Necking Z, %	Hardness, HB
1	1,286	881	9.1	18	376
2	1,249	854	10.3	22	365
3	1,238	875	10.9	23	363
4	1,262	877	10.7	22	366
5	1,284	904	11.2	23	364
6	1,270	899	10.4	23	367
7	1,293	885	11.5	21	370
8	1,273	880	10.9	19	366

Summary of average fatigue test results and residual stress in the rail foot from tests 1 and 2_

Type of study	Obtained result (average value)	Requirements according to EN 13674-1
K _Ic coefficient	41 MPa m^1/2	32 MPa m^1/2
27 samples 60E1, 54E4, 49E1	41 MPa m^1/2	32 MPa m^1/2
Fatigue tests	10 × 10⁶ cycles	5 × 10⁶ cycles
27 samples 60E1, 54E4, 49E1	10 × 10⁶ cycles	5 × 10⁶ cycles
Fatigue tests	50 × 10⁶ cycles	—
1 sample 60E1	50 × 10⁶ cycles	—
Fatigue crack growth rate	6.12 m/Gc	17 m/Gc for ΔK = 10 MPa m^1/2
27 samples 60E1, 54E4, 49E1	6.12 m/Gc	17 m/Gc for ΔK = 10 MPa m^1/2
Fatigue crack growth rate	15.02 m/Gc	55 m/Gc for ΔK = 13.5 MPa m^1/2
27 samples 60E1, 54E4, 49E1	15.02 m/Gc	55 m/Gc for ΔK = 13.5 MPa m^1/2

Results of testing the fatigue crack growth rate [21]_

Sample No.		da/dN = C (ΔK)^m		Indicator m/Gc ΔK = 10, MPa m^1/2	Indicator m/Gc ΔK = 13.5, MPa m^1/2
Sample No.		C	m	Indicator m/Gc ΔK = 10, MPa m^1/2	Indicator m/Gc ΔK = 13.5, MPa m^1/2
1	1–1	1.4207 × 10⁷	1.9498	12.66	22.72
	1–2	1.1649 × 10⁷	2.0288	12.45	22.88
	1–3	2.8016 × 10⁷	1.6677	13.03	21.50
2	2–1	2.0673 × 10⁷	1.9153	17.00	30.22
	2–2	4.8851 × 10⁸	2.4538	13.78	28.77
	2–3	8.5625 × 10⁸	2.2583	15.52	30.57
4	4–1	1.3571 × 10⁷	2.1066	17.00	32.64
	4–2	1.4220 × 10⁷	2.0735	16.84	31.38
	4–3	1.4038 × 10⁷	2.0718	16.56	30.84
Average value				14.98	27.95
Requirements of the EN13674-1 standard				max 17 m/Gc	max 55 m/Gc

Rail steel grades_

Grade	Hardness, HBW	Type of steel	Condition of the rail
R200	200 ÷ 240	Carbon–manganese (C–Mn)	Raw
R220	220 ÷ 260	Carbon–manganese (C–Mn)	Raw
R260	260 ÷ 300	Carbon–manganese (C–Mn)	Raw
R260Mn	260 ÷ 300	Carbon–manganese (C–Mn)	Raw
R320Cr	320 ÷ 360	Alloyed (≤1.2% Cr)	Raw
R350HT	350 ÷ 390	Carbon–manganese (C–Mn)	Heat treated
R350LHT	350 ÷ 390	Low alloy (≤0.3% Cr)	Heat treated
R370CrHT	370–410	Alloyed (≤0.6% Cr)	Heat treated
R400HT	400–440	Carbon–manganese hypereutectoid (≤1% C)	Heat treated

Rail steel parameters_

Parameter	Condition of the rails
Parameter	Raw*	Heat treated
Austenite grain size	100 ÷ 120 µm	20 ÷ 25 µm
Interlamellar spacing	0.20 ÷ 0.25 µm	0.09 ÷ 0.12 µm
HBW hardness	270 ÷ 290	340 ÷ 390

Result of staircase method at vertical loading on rail profile 60E2-R350HT_

Number of samples	Maximum stress (MPa)	Minimum stress (MPa)	Stress range σ _o (MPa)	Executed load cycles	Result
8–1	400	40	360	5,000,000	Positive
8–2	420	42	378	5,000,000	Positive
8–3	440	44	396	5,000,000	Positive
8–4	460	46	414	619,397	Failure
8–5	440	44	396	5,000,000	Positive
8–6	460	46	414	5,000,000	Positive
8–7	480	48	432	562,692	Failure
8–8	460	46	414	717,294	Failure
8–9	440	44	396	5,000,000	Positive
8-10	460	46	414	716,943	Failure

Chemical composition for individual melts [21]_

Number of		Content mass in liquid state (%)								10⁻⁴ % (ppm)
Sample	Melt	C	Mn	Si	P	S	Cr	Al max	V max	N max	O max	H max
1	321,036	0.79	1.09	0.36	0.008	0.017	0.069	0.004	0.001	56	18	2.00
2	321,037	0.77	1.07	0.35	0.008	0.017	0.077	0.004	0.001	55	18	1.83
3	321,038	0.77	1.08	0.39	0.009	0.014	0.076	0.004	0.001	54	18	1.29
4	331,713	0.78	1.12	0.37	0.016	0.017	0.078	0.004	0.003	50	18	1.50
5	331,823	0.77	1.10	0.38	0.012	0.012	0.08	0.003	0.002	40	14	1.3
6	331,824	0.78	1.13	0.38	0.011	0.019	0.08	0.003	0.002	49	20	1.1
7	331,991	0.79	1.13	0.36	0.012	0.011	0.08	0.003	0.002	43	19	1.4
8	430,499	0.78	1.08	0.34	0.010	0.014	0.08	0.003	0.003	70	13	0.8

Results of residual stress measurements in the rail section taken from test 2_

Number of sample	Strain gauge location
Number of sample	Foot	Head	Web point 1	Web point 2
2	Deformation value after 1 cut, μm
	−375	−983	12	29
	Deformation value after 2 cut, μm
	−422	−1,225	36	51
	Residual stress value, MPa
	87	254	−7	−11

Quality assessment of heat-treated rails in the R350HT grade

Figures & Tables

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Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

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Figure 12

Figure 13

Figure 14

Figure 15

Fracture toughness tests [21]_

Fatigue strength test results [21]_

Averaged results of mechanical properties tests and hardness measurements on the running surface of industrially manufactured 60E1/60E2 profile rails made of R350HT steel_

Results of the measurement of residual stress in the rail foot_

Results of the Baumann test_

Basic properties of the tested rail steel for individual rail types [21]_

Summary of average fatigue test results and residual stress in the rail foot from tests 1 and 2_

Results of testing the fatigue crack growth rate [21]_

Rail steel grades_

Rail steel parameters_

Result of staircase method at vertical loading on rail profile 60E2-R350HT_

Chemical composition for individual melts [21]_

Results of residual stress measurements in the rail section taken from test 2_

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