Fatigue tests of heat-treated rails in the R350HT grade

Żak, Sylwester

doi:10.2478/msp-2025-0024

Figures & Tables

Image of the microstructure at the corner of the rail heads after heat treatment: (a) rail from melt no. 1 and (b) rail from melt no. 2.

Baumann’s print: (a) Sample 5 – pattern D2 and (b) sample 5 – pattern D2. The area of slight negative and positive sulphur segregation in the rail web is marked.

Baumann’s print: (a) Sample 6 – pattern D4 and (b) sample 6 – pattern D2. The area of slight negative sulphur segregation in the rail web is marked.

Baumann’s print: (a) Sample 7 – pattern D2 and (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.

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

Dimensions of the sample for testing the fatigue crack growth rate.

Dimensions of the sample for determining the K
Ic factor. — Dimensions of the sample for determining the K Ic factor.

Sample fractures for determining the fatigue crack growth rate representing. The photos represent the following samples: (a) sample 2a, (b) sample 2b and (c) sample 3c.

Graph showing the dependence of da/dN on ΔK determined for the sample 2a.

Graph showing the dependence of da/dN on ΔK determined for the sample 2b.

Graph showing the dependence of da/dN on ΔK determined for the sample 2c.

View of fractures for samples (a) 3c and (b) 3d.

Sample number 2a in the holders after fatigue testing.

Chemical composition for individual melts_

	Number	Mass in liquid state (%)									10⁻⁴ % (ppm)
of samples	of melts	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	0.0056	18	2.00
2	321,037	0.77	1.07	0.35	0.008	0.017	0.077	0.004	0.001	0.0055	18	1.83
3	321,038	0.77	1.08	0.39	0.009	0.014	0.076	0.004	0.001	0.0054	18	1.29
4	331,713	0.78	1.12	0.37	0.016	0.017	0.078	0.004	0.003	0.0050	18	1.50
5	331,823	0.77	1.10	0.38	0.012	0.012	0.08	0.003	0.002	0.0040	14	1.3
6	331,824	0.78	1.13	0.38	0.011	0.019	0.08	0.003	0.002	0.0049	20	1.1
7	331,991	0.79	1.13	0.36	0.012	0.011	0.08	0.003	0.002	0.0043	19	1.4

Basic range of chemical composition and mechanical properties of rail steel grades for heat treatment_

Steel grade	Mass (%)						R _m (MPa)	A (%)	Hardness (HBW)
Steel grade	C	Si	Mn	P _max	S _max	Cr	R _m (MPa)	A (%)	Hardness (HBW)
R260	0.60–0.82	0.13–0.60	0.65–1.25	0.030	0.030	≤0.15	880	10	260–300
R350HT	0.70–0.82	0.13–0.60	0.65–1.25	0.025	0.030	≤0.15	1,175	9	350–390
R350LHT	0.70–0.82	0.13–0.60	0.65–1.25	0.025	0.030	≤0.30	1,175	9	350–390
R370CrHT	0.68–0.84	0.38–1.02	0.65–1.15	0.025	0.025	0.35–0.65	1,280	9	370–410
R400HT	0.88–1.07	0.18–0.62	0.95–1.35	0.025	0.025	≤0.30	1,280	8	400–440

Conditions for determining the fatigue crack growth rate_

Fatigue crack growth rate
Sample no.	2a	2b	2c
Load rate R	0.5	0.5	0.5
Amplitude type	Sinusoidal	Sinusoidal	Sinusoidal
Load frequency (Hz)	15	15	15
Initial ΔK (MPa m^1/2)	9.32	9.39	9.27
Initial K _max (MPa m^1/2)	18.64	18.78	18.54
Initial ΔP (kN)	6605.00	6600.00	6608.00
Final crack length (mm)	27.26	26.93	27.75
Temperature (°C)	Room temp.	Room temp.	Room temp.
	Measurement of the crack front
Average a (mm)	25.24	24.47	24.69
Standard deviation (mm)	1.0041	1.1314	0.3606
Paris’ law (da/dN) = C(ΔK)^m
C	2.0673 × 10⁷	4.8451 × 10⁸	8.5625 × 10⁸
m	1.92	2.45	2.26
R _m (MPa)	1,292
R _p0,2 (MPa)	894

Condition check P max/P Q ≤ 1_1_

Sample	P _Q (N)	P _max (N)	P _max/P _Q
3a	17,810	18,344	1.03
3b	18,390	18,574	1.01
3c	17,240	18,274	1.06
3d	18,560	18,746	1.01
3e	18,560	18,746	1.01

Fatigue strength test results_

Sample no.	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

Checking the validity criterion K Ic_

Sample	Check the conditions
Sample	a ≥ 2.5 K Q R p 0.2 2 \hspace{1em}{\left(\frac{{K}_{{\rm{Q}}}}{{R}_{{\rm{p}}0.2}}\right)}^{2} , [m]	B ≥ 2.5 K Q R p 0.2 2 \hspace{1em}{\left(\frac{{K}_{{\rm{Q}}}}{{R}_{{\rm{p}}0.2}}\right)}^{2} , [m]
	Steel – R350HT
3a	0.01981 > −0.0079	0.02498 > −0.0079
3b	0.01983 > −0.0084	0.02502 > −0.0084
3c	0.01991 > −0.0073	0.02498 > −0.0073
3d	0.02011 > −0.0088	0.02505 > −0.0088
3e	0.01993 > −0.0087	0.02496 > −0.0087

Validity check K Ic_

Sample	Check the conditions
Sample	(W – a) > 2.5 K Q R p 0.2 2 {\left(\frac{{K}_{{\rm{Q}}}}{{R}_{{\rm{p}}0.2}}\right)}^{2} , [m]
	Steel – R350HT
3a	0.02013 > −0.0079
3b	0.02020 > −0.0084
3c	0.02017 > −0.0073
3d	0.01993 > −0.0088
3e	0.02003 > −0.0087

Results of determining the stress intensity factor_

Sample no.	K _Ic (MPa m^1/2)	Average value K _Ic (MPa m^1/2)	Standard deviation K _Ic (MPa m^1/2)
3a	39.20	39.86	1.50
3b	40.27
3c	37.59
3d	41.27
3e	40.39
2a	39.95	40.12	1.09
2b	40.77
2c	40.38
2 d	38.35
2e	41.16
1a	46.24	42.97	2.70
1b	45.36
1c	40.32
1d	40.67
1e	42.28
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

Results of testing the fatigue crack growth rate_

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
2a	2.0673 × 10⁷	1.9153	17.00	30.22
2b	4.8851 × 10⁸	2.4538	13.78	28.77
2c	8.5625 × 10⁸	2.2583	15.52	30.57
1a	1.4207 × 10⁷	1.9498	12.66	22.72
1b	1.1649 × 10⁷	2.0288	12.45	22.88
1c	2.8016 × 10⁷	1.6677	13.03	21.50
4a	1.3571 × 10⁷	2.1066	17.00	32.64
4b	1.4220 × 10⁷	2.0735	16.84	31.38
4c	1.4038 × 10⁷	2.0718	16.56	30.84
	Requirements of the EN13674-1 standard		Max 17 m/Gc	Max 55 m/Gc

Validation requirements for 321038 A101 rail (samples 3)_

Determining K _Ic
Sample no.		3a	3b	3c	3d	3e
R _m (MPa)		1,331
R _p0.2 (MPa)		696
Test temperature (°C)		−20	−20	−20	−20	−20
P _max (kN)		18.3443	18.5739	18.2744	18.7456	18.7456
P _Q (kN)		17.81	18.39	17.24	18.54	18.56
Time test (s)		35.21	61.15	71.01	76.27	69.1
K _Q (MPa m^1/2)		39.2	40.27	37.59	41.27	40.97
Rate test (MPa m^1/2/s)		1.11	0.66	0.53	0.54	0.59
Mean value of a		19.81	19.83	19.91	20.11	19.53
Standard dev. of a		1.1066	1.1580	0.9459	0.8739	1.2609
0.45 ≤ (a/W) ≤ 0.55		0.50	0.50	0.50	0.50	0.50
P _max/P _Q < 1.1		1.03	1.01	1.06	1.01	1.01
K _max < 0.6 K _Q	K _max (MPa m^1/2)	22.08	22.2	22.2	22.1	22.1
K _max < 0.6 K _Q	0.6 K _Q (MPa m^1/2)	23.52	24.162	22.554	24.762	24.582

Validation requirements for 321038 A101 rail (samples 3) – the criterion 2_5(K Q/R p0_2)_

Determining K _Ic
Sample no.		3a	3b	3c	3d	3e
2.5 (K _Q/R _p0.2)² < a ₀	2.5 (K _Q/R _p0.2)²	0.0079	0.0084	0.0073	0.0088	0.0087
2.5 (K _Q/R _p0.2)² < a ₀	a ₀	19.81	19.83	19.91	20.11	19.93
2.5 (K _Q/R _p0.2)² < B	2.5 (K _Q/R _p0.2)²	0.0079	0.0084	0.0073	0.0088	0.0087
2.5 (K _Q/R _p0.2)² < B	B	24.98	25.02	49.98	25.05	24.96
2.5 (K _Q/R _p0.2)² < W − a	2.5 (K _Q/R _p0.2)²	0.0079	0.0084	0.0073	0.0088	0.0087
2.5 (K _Q/R _p0.2)² < W − a	W − a	20.13	20.20	20.17	19.93	20.03
K _Ic results		39.2	40.27	37.59	41.27	40.97

Basic properties of the tested rail steel for individual rail types_

Sample no.	Basic mechanical properties
Sample no.	Tensile strength, R _m (MPa)	Yield strength R _p0.2 (MPa 20°C)	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

Fatigue tests of heat-treated rails in the R350HT grade

Figures & Tables

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Figure 13

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Figure 15

Chemical composition for individual melts_

Basic range of chemical composition and mechanical properties of rail steel grades for heat treatment_

Conditions for determining the fatigue crack growth rate_

Condition check P max/P Q ≤ 1_1_

Fatigue strength test results_

Checking the validity criterion K Ic_

Validity check K Ic_

Results of determining the stress intensity factor_

Results of testing the fatigue crack growth rate_

Validation requirements for 321038 A101 rail (samples 3)_

Validation requirements for 321038 A101 rail (samples 3) – the criterion 2_5(K Q/R p0_2)_

Basic properties of the tested rail steel for individual rail types_

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