A Comprehensive Guide to Stainless Steel: EN 1.4313 (UNS J91540)

What is EN 1.4313 (UNS J91540)?

“Super martensitic stainless steel” is made by improving the smelting process of martensitic stainless steel, reducing carbon content, and adding nickel-molybdenum alloy elements. Its performance is better than conventional martensitic stainless steel. It not only has better corrosion resistance and weldability, Moreover, it has the characteristics of high strength and good low temperature toughness, and it has great application potential in the fields of hydropower, mining equipment, chemical equipment, food industry, transportation and high temperature pulp production equipment.

UNS J91540 (S-135/00Cr13Ni5Mo), also known as 04Cr13Ni5Mo, is an ultra-low carbon martensitic stainless steel developed on the basis of CA-6NM cast steel. It is a typical steel grade of super martensitic stainless steel.

M.-NR. / EN	DIN	AISI	UNS	BS	AFNOR	GOST
1.4313	X3CrNiMo13-4	F6NM430	J91540	425 C 11	Z 6 CN 13-04	03X13H4M

Standard of UNS J91540

China	Taigang	00Cr13Ni5Mo S-135
	GB/T 20878-2007 GB/T 3280-2015 GB/T 4237-2015	04Cr13Ni5Mo S41595
	JB/T 7349-2002	ZG06Cr13Ni5Mo
USA	ASTM A182-10a	F6NM,S41500
Japan	JIS G 3214:2009	SUS F6NM
	JIS G 5121:2003	SCS6
Germany	DIN EN 10088-2:2005	X3CrNiMo13-4 1.4313

Composition specification (%) of UNS J91540

Standards	Steel Grades
	Chemical Composition %
	C:	Mn:	Si:	P:	S:	Cr:	Ni:	Mo:	N:
EN	1.4313 – X3CrNiMo13-4
	<0.05	<1.5	<0.7	<0.04	<0.015	12.0 – 14.0	3.5 – 4.5	0.3 – 0.7	>0.02
ASTM	UNS S41500 – F6NM – F 6NM – 13Cr-4Ni – AISI 415
	<0.05	0.5 – 1.0	<0.6	<0.03	<0.030	11.5 – 14.0	3.5 – 5.5	0.5 – 1.0	–
ASTM	UNS J91540 – CA6NM – CA-6NM
	<0.06	<1.0	<1.0	<0.04	<0.030	11.5 – 14.0	3.5 – 4.5	0.4 – 1.0	–
AF	Z6CN13-04 – Z 6 CN 13-04
	<0.06	<1.0	<0.75	<0.04	<0.015	12.0 – 13.5	3.5 – 4.5	0.3 – 0.5	–
BS	425C11 – 425 C 11
	<0.1	<1.0	<1.0	<0.04	<0.03	11.5 – 13.5	3.4 – 4.2	<0.6	–
SNV   VSN	X5CrNi13-4 – X 5 CrNi 13-4
	<0.07	<1.5	<1.00	<0.035	<0.025	12.0 – 13.5	3.5 – 4.5	0.4 – 0.6	–
JIS	SCS5 – SCS 5
	<0.06	<1.0	<1.0	<0.040	<0.040	11.0 – 14.0	3.5 – 4.5	–	–

Mechanical properties of 1.4313, X3CrNiMo13-4 steel

Delivery condition +A: 

• Tensile strength, Rm: <1100 MPa

• HBW Hardness: <320

Delivery condition +QT650 

• Tensile strength, Rm: 700 – 850 MPa

• Yield point, Re: >520 MPa

• Elongation, A: > 15%

• Impact resistance, KV: >70 J

Delivery condition +QT780 

• Tensile strength, Rm: 780 – 980 MPa

• Yield point, Re: >620 MPa

• Elongation, A: > 15%

• Impact resistance, KV: >70 J

Delivery condition +QT900 

• Tensile strength, Rm: 900 – 1100 MPa

• Yield point, Re: >800 MPa

• Elongation, A: >12%

• Impact resistance, KV: >50 J

Delivery condition +QT according to EN 10028-7 

• Tensile strength, Rm: 780 – 980 MPa

• Yield point, Re: >650 MPa

• Elongation, A: >14%
• Impact resistance, KV: >70 J

Characteristics of UNS J91540

UNS J91540 (S-135/00Cr13Ni5Mo) steel abandons high-carbon martensite and the strengthening means of forming carbides, and uses the formation of low-carbon martensite with high toughness and supplementary strengthening with nickel and molybdenum alloy elements as the main strengthening means. Through appropriate heat treatment, it has a composite structure of low-carbon lath martensite and reverse transformed austenite, which not only retains a high level of strength, but also has good toughness and weldability. In addition, this steel grade also has excellent erosion resistance, abrasion resistance, and corrosion resistance, which can meet the long-term requirements of water conservancy projects to withstand sediment erosion.

Application of UNS J91540

UNS J91540 (S-135/00Cr13Ni5Mo) steel is mainly used for high-strength load-bearing parts that need to be welded. The most common is as hydroelectric steel, used to manufacture the wear-resistant runner and runner lower ring of hydraulic turbine equipment; in the petroleum industry, it is used as a pipeline that is resistant to CO₂, H₂S and needs to be welded on site; in the nuclear industry, it is used The drive shaft and control rod drive mechanism of PWR 2 and 3 auxiliary pumps.

Heat treatment process and microstructure properties of 04Cr13Ni5Mo steel

04Cr13Ni5Mo steel belongs to the Cr Ni series of low-carbon martensitic stainless steel, which was developed in the 1960s. Due to the addition of Ni element, although the C content was reduced, its strength was not reduced, and the plasticity, toughness, and corrosion resistance were improved, resulting in better performance than Fe-Cr-C martensitic stainless steel. It also has excellent low-temperature mechanical properties, good hardenability, casting, forging, welding, machining and other process properties, as well as service performance such as cavitation resistance and wear resistance.
Through proper heat treatment of 04Cr13Ni5Mo steel, it can have the dual phase structure of low-carbon lath martensite and inversion austenite so as to achieve the goal of maintaining a high strength level and improving toughness and weldability of the steel. Therefore, this article focuses on studying the effect of tempering heat treatment system after quenching at 1050 ℃ on the microstructure and mechanical properties of 04Cr13Ni5Mo steel, selecting the optimal heat treatment system, and studying the high-temperature tensile properties under this system, providing reference basis for subsequent workers.

1. Test materials and methods

The material used in this experiment is 04Cr13Ni5Mo martensitic stainless steel, with the main chemical composition shown in Table 1.
Table.1 Chemical Composition of 04Cr13Ni5Mo Steel (Mass Fraction, %)

Element	C	Si	Mn	P	S	Ni	Cr	Mo
Requirement	0.05	0.6	0.50-1.00	0.03	0.03	3.50-5.50	11.50-14.00	0.50-1.00
Actual Measurement	0.03	0.27	0.74	0.008	0.002	4.47	12.6	0.59

Heat treatment of 04Cr13Ni5Mo steel was carried out in a box-type resistance furnace, with a specific system of holding at 1050 ℃ for 1 hour, oil cooling to room temperature, and then holding at 620, 650, and 700 ℃ for 2 hours for tempering treatment. The cooling method was air cooling. Conduct microstructure observation, tensile test, impact test, and hardness test on three types of tempered samples, compare the test results to determine the optimal heat treatment system, and conduct high-temperature tensile test. The sample was polished, polished, and corroded (with corrosive agents HCl, HNO₃, and H₂O in a ratio of HCl: HNO₃: H₂O=1:1:1), and the microstructure was observed under the OLYMPUS-GX71 large metallographic microscope; On a universal tensile testing machine, according to the requirements of GB/T 228-2002 “Metallic Materials – Room Temperature Tensile Testing Method”, test M12 mm × Perform tensile testing on 80mm standard specimens; Conduct impact tests on the JB-300B impact testing machine in accordance with GB/T 229-2007 “Metallic Materials Charpy Pendulum Impact Test Method”; Perform hardness testing on the HB-3000 Brinell hardness testing machine in accordance with GB/T 231-2009 “Metallic Materials – Brinell Hardness Testing – Part 1: Test Method”; Perform high-temperature tensile tests at 100, 200, 300, and 400 ℃ on the CMT 5205 tensile testing machine in accordance with GB/T 8653-1988 “Metallic Materials – Test Methods for Young’s Modulus, Chord Modulus, Tangent Modulus, and Poisson’s Ratio (Static Method)”.

2. Results and Analysis

2.1 Microstructure

The microstructure of the original state (annealed state), 1050 ℃ quenched state, and 620, 650, and 700 ℃ tempered state samples of 04Cr13Ni5Mo steel were observed, as shown in Figure 1. It can be seen from Figure 1 that the microstructure of 04Cr13Ni5Mo steel in the annealed state and the quenched state at 1050 ℃ are relatively coarse low-carbon lath martensite, and large angle grain boundaries separate Flat noodles bundles. After tempering, the coarse martensite Flat noodles become thinner.
From Figure 1 (c), it can be seen that after 620 ℃ × After 2h tempering, the tempered martensite in the structure maintains the orientation of Flat noodles more obviously than the other two tempering temperatures and the Flat noodles bundles are also relatively wide, short, and the structure is more uniform. At 650 ℃ × After 2h tempering, the microstructure of 04Cr13Ni5Mo martensitic stainless steel is lath tempered martensite + reversed austenite + granular carbide, as shown in Figure 1 (d), and 620 ℃ × Compared with 2h tempering structure, its Flat noodles bundles are more slender and dense. After 700 ℃ × After 2h tempering, the microstructure of 04Cr13Ni5Mo martensitic stainless steel is lath tempered martensite + a small amount of reversed austenite + granular carbide, as shown in Figure 1 (e), its Flat noodles beam ratio is 650 ℃ × When tempered for 2 hours, the martensite becomes more dense and slender, with almost no small bright white strip like inverted austenite visible, indicating that the amount of inverted austenite is gradually decreasing.
Comparing the three heat treatment processes, it was found that as the tempering temperature increased, the microstructure of 04Cr13Ni5Mo martensitic stainless steel became finer. This is because as the tempering temperature increased, the amount of martensite decomposition increased, and dispersed small carbides were precipitated.

Figure.1 Microstructure of 04Cr13Ni5Mo Steel under Different Heat Treatment States
(a) Annealed; (b) Quenched; (c, d) tempered at 620 ℃; (e, f) tempered at 650 ℃; (g, h) tempered at 700 ℃

2.2 Mechanical properties

Room temperature tensile, impact, and hardness tests were conducted on 04Cr13Ni5Mo martensitic stainless steel in three different tempering states. The specified nonproportional elongation strength, tensile strength, elongation after fracture, cross-sectional shrinkage, impact absorption energy, and Brinell hardness of 04Cr13Ni5Mo martensitic stainless steel were obtained under three different heat treatment states, as shown in Figure 2. From Figure 2 (a-c), it can be seen that under a certain quenching temperature (1050 ℃), as the tempering temperature increases, the specified nonproportional elongation strength and tensile strength gradually increase while the plastic toughness decreases to varying degrees. From Figure 2 (d), it can be seen that after 700 ℃ × After 2 hours of tempering, the hardness of 04Cr13Ni5Mo steel is the highest because a portion of the newly formed reverse austenite (different from induced austenite) in the microstructure undergoes martensitic transformation during the tempering process, which increases the tempering hardness during the subsequent cooling transformation process.

Figure.2 Mechanical properties of 04Cr13Ni5Mo steel tempered at different temperatures
In summary, the optimal heat treatment process among the three heat treatment processes is: 1050 ℃ × 1 hour of oil cooling quenching + 620 ℃ × 2 hours of air cooling tempering. Under this heat treatment condition, the strength, plasticity, and toughness of the material have reached the optimal combination.

2.3 High temperature tensile properties

Under optimal heat treatment conditions (1050 ℃ × 1 hour quenching + 620 ℃ × The samples prepared for 2 hours of tempering were subjected to tensile tests at 20, 100, 200, 300, and 400 ℃. The average of the three effective values of the specified nonproportional elongation strength R_p0.2, tensile strength Rm, and elongation after fracture A at each temperature, which differ by less than 10%, can be obtained. The variation of strength and elongation with temperature can be obtained as shown in Figure 3.
From Figure 3 (a), it can be seen that during the high-temperature tensile test, the tensile strength and yield strength of 04Cr13Ni5Mo steel continue to decrease with the increase in temperature, and the decrease begins relatively slowly at 200 ℃. From Figure 3 (b), it can be seen that the elongation after fracture of 04Cr13Ni5Mo steel reaches its maximum at around 100 ℃ and then gradually decreases with the increase of temperature until it remains basically unchanged.

Figure.3 High temperature tensile properties of 04Cr13Ni5Mo steel
(a) Strength; (b) Elongation

3. Conclusion

• 1) After quenching and tempering, the microstructure of 04Cr13Ni5Mo steel is mainly fine-lath tempered martensite.
• 2) As the tempering temperature increases, the strength of 04Cr13Ni5Mo steel gradually increases, and the plasticity and toughness decrease to varying degrees. The hardness increases with the increase of tempering temperature.
• 3) After heat treatment, 04Cr13Ni5Mo steel undergoes tensile tests at high temperatures, and its strength decreases with increasing temperature. The elongation after fracture first increases and then decreases with the increase of temperature.

Author: Zhi Jinhua