Fatigue tests of heat-treated rails in the R350HT grade

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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)
	C	Si	Mn	P max	S max	Cr
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 m1/2)	9.32	9.39	9.27
Initial K max (MPa m1/2)	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
	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
	(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 m1/2)	Average value K Ic (MPa m1/2)	Standard deviation K Ic (MPa m1/2)
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 m1/2	Average value min 32 MPa m1/2

Results of testing the fatigue crack growth rate_

Sample no.	da/dN = C (ΔK) m		Indicator m/Gc ΔK = 10, MPa m1/2	Indicator m/Gc ΔK = 13.5, MPa m1/2
	C	m
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 m1/2)		39.2	40.27	37.59	41.27	40.97
Rate test (MPa m1/2/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 m1/2)	22.08	22.2	22.2	22.1	22.1
	0.6 K Q (MPa m1/2)	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
	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
	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
	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
	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