CN1152148C

CN1152148C - High-strength bolt steel

Info

Publication number: CN1152148C
Application number: CNB011295120A
Authority: CN
Inventors: 翁宇庆; 惠卫军; 董瀚; 王毛球; 陈思联; 时捷
Original assignee: Central Iron and Steel Research Institute
Current assignee: Central Iron and Steel Research Institute
Priority date: 2001-06-22
Filing date: 2001-06-22
Publication date: 2004-06-02
Anticipated expiration: 2021-06-22
Also published as: CN1329179A

Abstract

The present invention belongs to the field of alloy steel, which is applicable to high-strength bolt steel whose tensile strength is from 1400 to 1600Mpa with good delayed fracture resistance performance. The steel contains the following specific components (weight %): 0.35 to 0.5 wt% of C, 0.01 to 0.09 wt% of Si, at most 0.30 wt% of Mn, at most 0.010 wt% of P, at most 0.008 wt% of S, 0.5 to 1.5 wt% of Cr, 0.7 to 1.5 wt% of Mo, 0.20 to 0.50 wt% of V, 0.01 to 0.08 wt% of Nb, 0.002 to 0.04 wt% of RE, 0.005 to 0.05 wt% of Al, 0.006 to 0.015 wt% of N, 0.01 to 0.15 wt% of Ti or Zr or Ti and Zr and Fe and inevitable impurities as the rest. Under the air pressure of 1400 to 1600Mpa, the delayed fracture resistance performance of the steel in the present invention is increased obviously, and other kinds of integrative performance is also favorable compared with that of the steel in the prior art.

Description

High-strength bolt steel

Technical field

The invention belongs to field of alloy steel.Be applicable to that mainly tensile strength is 1400～1600MPa, require high-strength bolt steel simultaneously with good delayed fracture drag.

Background technology

High strength bolt is widely used in industries such as machinery, automobile, bridge fine strain of millet, building.When the tensile strength of the bolt made from the low alloy steel of modifier treatment surpassed about 1200MPa, it is very outstanding that the delayed fracture problem just becomes.Therefore, the strength level basic controlling of the high strength bolt that uses at present is below 1200MPa.Along with the development of each production department, the material of making all kinds of fastening pieces (as bolt, screw, nut etc.) use has been proposed more and more high requirement, some automobiles, construction implement are more than the 1400MPa with bolt even desired strength.In recent years, the research and development of delayed fracture resistance high strength bolting steel have been carried out in the world.Cr-Mo-V high-strength bolt steel as among the Japanese Patent JP1-96354 has the tensile strength of 1400～1600MPa, has resistance for delayed fracture preferably simultaneously.But its Si content higher (0.50%～1.50%, weight percent, down with), significantly worsen the cold heading performance of steel, simultaneously higher Cr content (1.50%～3.50%) is not only unfavorable to cold-forming property, and can improve the cost of steel.Cr-Ni-Mo-V high-strength bolt steel among the Japanese Patent JP8-225845 then contains the noble element Ni (0.8%～2.4%) of high level, makes that the cost of steel is higher.The high strength bolting steel ADS3 of the 1300MPa level delayed fracture resistance of Sumitomo Metal Industries' exploitation of Japan, because C content higher (0.49%), the toughness of steel is relatively poor, the processing characteristics of bolt worsens simultaneously.These all are restricted in actual applications.

Summary of the invention

The objective of the invention is to propose a kind of tensile strength is 1400～1600MPa and the high-strength bolt steel with good resistance for delayed fracture.

According to above-mentioned purpose, main technical schemes of the present invention is: (1) adds the strong elements Mo of anti-temper softening ability, V etc., improves tempering temperature and grain-boundary strength; (2) content of reduction impurity element P, S reduces Mn, Si content simultaneously, the cold-forming property that gathers and improve steel altogether partially of Mn and P when suppressing the hardened steel high tempering; (3) add the proper amount of rare-earth element, inclusion is carried out sex change and hydrogen is played the trap effect, further reduce hydrogen gathering partially and improve toughness at crystal boundary; (4) add microalloy elements such as V, Nb, generate the tiny carbonitride of disperse, improve the intensity and the toughness of steel with refine austenite crystal grain.

The concrete chemical ingredients (weight %) of steel of the present invention is as follows: C 0.35～0.50, Si≤0.01-0.09, Mn≤0.30, P≤0.010, S≤0.008, Cr 0.50～1.50, Mo 0.70～1.50, V 0.20～0.50, and Nb 0.01～0.08, and RE 0.002～0.040, Al 0.005～0.05, N 0.006～0.015, can add 0.01～0.15 Ti, any one or two kinds among the Zr according to demand, and surplus is Fe.

The effect of each element and proportioning are according to as follows:

C: quench, after the tempering in order to obtain required high strength, C content must be more than 0.35%, but too much C content can worsen the toughness and the manufacturability of steel, and increases the susceptibility of delayed fracture, thereby C content is controlled to be 0.35～0.50%.

Though the Si:Si element can deoxidation, therefore grain boundary oxidation and promote that the crystal boundary of impurity element P and S is poly-partially when its promotes steel high temperature austenite worsens the resistance for delayed fracture of steel.Simultaneously, the Si element also significantly worsens the cold heading performance of high-strength steel, thereby controls its content and be no more than 0.09%.

Mn:Mn is the effective element of deoxidation and desulfurization, can also improve the hardening capacity and the intensity of steel, but during the hardened steel high tempering, Mn and P have the poly-partially altogether tendency of intensive crystal boundary, promote temper brittleness, thereby control Mn content are below 0.30%.

P:P can form microsegregation when solidification of molten steel, gather partially at crystal boundary when austenitizing temperature heats subsequently, and the fragility of steel is enlarged markedly, thereby increases the delayed fracture susceptibility of steel, so the content of control P is below 0.010%.

S: inevitable impurity forms that MnS is mingled with and gets together partially at crystal boundary and worsen the cold-forming property and the resistance for delayed fracture of steel, thereby controls its content below 0.008%.

Cr: can improve the hardening capacity and the resistance to tempering of steel effectively, to obtain required high strength.Content is difficult to function as described above less than 0.50%, but content surpasses 1.50% toughness and cold-workability that can worsen steel.

Mo:Mo can also strengthen crystal boundary in hardening capacity that improves steel effectively and resistance to tempering.Content is not obvious less than 0.70% effect, but content is saturated above 1.50% above-mentioned action effect, and cost is higher.

V:V can crystal grain thinning, the carbon vanadium nitride of separating out when the comparatively high temps tempering also because the carbon vanadium nitride has stronger trap energy, can capture hydrogen and make it be evenly dispersed in intracrystalline except that the intensity that can further improve steel, suppress the diffusion of hydrogen, thereby improve the resistance for delayed fracture of steel.V content is difficult to function as described above less than 0.20%, but content effect above 0.50% is saturated.

Nb: crystal grain thinning, the toughness of raising steel, content does not have above-mentioned effect less than 0.01%, but content effect above 0.08% is saturated.

RE: show by the systematic study that for many years the RE element is acted in steel, the RE element is except that having deoxidization desulfuration and the effect to the non-metallic inclusion denaturing treatment, can also capture hydrogen effectively, reduce hydrogen and other harmful element gathering partially on crystal boundary, reduce the infiltration diffusion of hydrogen, can further reduce the susceptibility of high-strength steel delayed fracture.RE content does not have above-mentioned effect less than 0.002%, but content surpasses 0.040%, then because inclusion increases, worsens the resistance for delayed fracture of steel on the contrary.Control its content 0.002～0.040%.

Al: deoxidation and crystal grain thinning effectively, content does not have above-mentioned effect less than 0.005%, easily forms thick alumina inclusion but content surpasses 0.05%, worsens the toughness of steel.

N:N can form tiny nitride crystal grain thinning with Al, Nb, V etc., but excessive N can be gathered partially in crystal boundary and the thick inclusion of formation, so its content should be controlled at 0.006～0.015%.

Ti: except that the effect of crystal grain thinning, precipitation strength and fix N, S, the TiC that disperse is separated out is the highest hydrogen trap of trap energy in the steel, can capture hydrogen and make it be evenly dispersed in intracrystalline, suppresses the diffusion of hydrogen, thereby improves the resistance for delayed fracture of steel.Ti content does not have above-mentioned effect less than 0.01%, but content effect above 0.15% is saturated.

Zr: its effect and Ti are similar.

Steel of the present invention can adopt electric arc furnace+external refining to smelt, and is cast into steel ingot or continuous casting becomes base, is rolled into products such as excellent wire rod then.Heat Treatment Of Steel system of the present invention is similar to prior art, and steel of the present invention detects behind 850～950 ℃ of high temperings of 500 ℃ of quenching and be higher than again and delivers goods.

Steel of the present invention compared with prior art, not only tensile strength increases, and excellent in resistance to delayed fracture, good economical benefit.

Embodiment

The embodiment of the invention is according to above-mentioned designed chemical ingredients scope, has smelted 4 stoves steel of the present invention and 1 stove compared steel on the 50kg vacuum induction furnace, also has the commercial steel 42CrMo of 1 stove steel as a comparison in addition, and its concrete chemical ingredients is as shown in table 1.Molten steel casting becomes ingot, and makes bar through forging.Through 900 ℃, 30 minutes normalizing treatment, be processed into normal room temperature tension specimen (L subsequently before the sample processing ₀=5d ₀, d ₀=5mm) the WOL type sample (blank of 15mm * 37.2mm * 48mm).Said sample through the Q-tempering post-treatment to final size.Heat treating regime and corresponding performance perameter see Table 2.

Sample at room temperature carries out Erichsen test.Behind the fatigue cracking of the sample prefabricated 1～2mm of improved WOL type, load the back with screw and immerse in the 3.5%NaCl aqueous solution of room temperature.Measure crack length a with reading microscope, when crack growth rate da/dt≤1.0 * 10 ^-9Stop experiment during m/s.Add permanent displacement according to the crack length after the crack arrest with institute and just can obtain critical stress intensity factor of stress corrosion cracking K _ISCCTest is carried out with reference to GB12445.3-90.The gained result has listed table 2 in.

By contrast as can be seen, steel of the present invention is the intensity height not only, and significantly improving than the resistance for delayed fracture of compared steel under the same intensity level under the strength level of 1400～1600MPa, presents good resistance for delayed fracture.

In embodiments of the present invention, table 1 is the composition contrast table of the embodiment of the invention and prior art steel, and table 2 is the comparison of embodiment of the invention properties of sample and prior art rigidity energy.

The chemical ingredients of table 1 embodiment of the invention and compared steel is (weight %) relatively

Heat (batch) number	Steel grade	C	Si	Mn	P	S	Cr	Mo	V	Al	RE	Ti	Nb	N	Fe
Heat (batch) number	Steel grade	C	Si	Mn	P	S	Cr	Mo	V	Al	RE	Ti	Nb	N	Fe	1	The invention steel	0.45	0.09	0.29	0.005	0.003	1.09	0.71	0.23	0.02	0.005	-	0.08	0.008	Surplus
2	The invention steel	0.38	0.08	0.23	0.003	0.004	1.26	0.94	0.31	0.01	0.020	-	0.04	0.006	Surplus	1	The invention steel	0.45	0.09	0.29	0.005	0.003	1.09	0.71	0.23	0.02	0.005	-	0.08	0.008	Surplus
2	The invention steel	0.38	0.08	0.23	0.003	0.004	1.26	0.94	0.31	0.01	0.020	-	0.04	0.006	Surplus	3	The invention steel	0.42	0.05	0.20	0.002	0.001	0.92	0.80	0.25	0.02	0.008	0.014	0.05	0.010	Surplus
4	The invention steel	0.39	0.07	0.28	0.009	0.006	1.23	1.23	0.20	0.03	0.038	Zr 0.011	0.03	0.014	Surplus	3	The invention steel	0.42	0.05	0.20	0.002	0.001	0.92	0.80	0.25	0.02	0.008	0.014	0.05	0.010	Surplus
4	The invention steel	0.39	0.07	0.28	0.009	0.006	1.23	1.23	0.20	0.03	0.038	Zr 0.011	0.03	0.014	Surplus	5	Compared steel	0.41	0.29	0.30	0.006	0.003	1.22	0.32	0.26	0.02	-	-	-	0.007	Surplus
6	Commercial steel	0.39	0.30	0.80	0.025	0.019	1.08	0.22	-	0.03	-	-	-	0.008	Surplus	5	Compared steel	0.41	0.29	0.30	0.006	0.003	1.22	0.32	0.26	0.02	-	-	-	0.007	Surplus

The comparison of the heat treating regime of table 2 embodiment of the invention and compared steel, tensile strength and resistance for delayed fracture

	Heat (batch) number	Quenching temperature ℃	Tempering temperature ℃	Tensile strength Mpa	Yield strength Mpa	Unit elongation δ ₅ ％	Relative reduction in area %	K _ISCC MPa·m ^1/2
	Heat (batch) number	Quenching temperature ℃	Tempering temperature ℃	Tensile strength Mpa	Yield strength Mpa	Unit elongation δ ₅ ％	Relative reduction in area %	K _ISCC MPa·m ^1/2	Steel of the present invention	1	860	590	1460	1350	15.0	61	34.0
2	900	600	1510	1400	14.5	59	33.5			1	860	590	1460	1350	15.0	61	34.0
2	900	600	1510	1400	14.5	59	33.5	3		880	610	1520	1420	14.0	58	34.2
4	880	550	1580	1460	14.5	58	35.7	3		880	610	1520	1420	14.0	58	34.2
		550	1580	1460	14.5	58	35.7	630		1500	1420	15.0	59	38.3
		650	1430	1360	16.0	59	42.9	630		1500	1420	15.0	59	38.3
		650	1430	1360	16.0	59	42.9	Compared steel		5	860	480	1410	1300	13.0	59	28.1
425	1530	1410	12.0	57	20.6							480	1410	1300	13.0	59	28.1
425	1530	1410	12.0	57	20.6	6	860		380			1520	1370	9.0	45	16.3
430	1420	1290	11.0	49	22.5				380			1520	1370	9.0	45	16.3
430	1420	1290	11.0	49	22.5				500	1260	1170	12.0	50	43.2

Claims

1, a kind of high strength bolting steel with resistance for delayed fracture is characterized in that the concrete Chemical Composition of this steel is (weight %) C 0.35-0.5, Si 0.01-0.09, Mn≤0.30, P≤0.010, S≤0.008, Cr 0.5-1.5, Mo 0.7-1.5, V 0.20-0.50, Nb 0.01-0.08, RE 0.002-0.04, Al 0.005-0.05, N 0.006-0.015, among Ti and the Zr any one or two kinds of sums are 0.01-0.15, and all the other are Fe.