CN101597716A - A kind of low carbon bainite type cold work reinforced non-hardened/tempered steel - Google Patents
A kind of low carbon bainite type cold work reinforced non-hardened/tempered steel Download PDFInfo
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- CN101597716A CN101597716A CNA2009100881770A CN200910088177A CN101597716A CN 101597716 A CN101597716 A CN 101597716A CN A2009100881770 A CNA2009100881770 A CN A2009100881770A CN 200910088177 A CN200910088177 A CN 200910088177A CN 101597716 A CN101597716 A CN 101597716A
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Abstract
The invention belongs to field of alloy steel, particularly have a kind of low carbon bainite type cold work reinforced non-hardened/tempered steel of good plasticity and cold-forming property, mainly be applicable to and make 10.9 above grade high-strength bolts of tensile strength 1000MPa.The concrete chemical ingredients (weight %) of this steel is: C 0.06～0.15%, Si≤0.20%, and Mn 1.80～2.40%, P≤0.015%, S≤0.010%, Cr 0.10-0.50%, B 0.0005～0.003%, Ti 0.01～0.10%, RE 0.005～0.04%, and Nb 0.01～0.10%, and Al 0.005～0.05%, N 0.004～0.01%, and surplus is Fe and other unavoidable impurities.In addition, the Zr of adding 0.01～0.10% in the concrete chemical ingredients (weight %) of this steel.The present invention compared with prior art has plasticity and cold-forming property is good and the low advantage of cost, can be used to make 10.9 grade high-strength bolts.
Description
Technical field
The invention belongs to field of alloy steel, particularly a kind of have the good plasticity and a low carbon bainite type cold work reinforced non-hardened/tempered steel of cold-forming property, mainly is applicable to make 10.9 above grade high-strength bolts of tensile strength 1000MPa.
Background technology
Fastening pieces such as high strength bolt are widely used in industries such as machinery, automobile, bridge fine strain of millet, building, generally adopt low, medium carbon structural alloy steel or medium carbon steel to make.In the manufacturing processed of high strength bolt, to carry out at least once softening usually or the Spheroidizing Annealing processing, behind a small amount of drawing and cold upset forming, finally carry out modifier treatment again, to obtain required intensity and toughness.Soften or Spheroidizing Annealing and the modifier treatment heat treatment step that all the genus cycle is long, energy consumption is big.To this, people have developed the non-hardened and tempered steel wire rod that can omit softening or Spheroidizing Annealing and modifier treatment, the i.e. wire rod of producing by controlled rolling and controlled chilling, produce work hardening by a certain amount of cold deformation again, its intensity is further improved, under the situation of modifier treatment, can reach desired performance index.
Some cold work reinforced non-hardened/tempered steel wire rods of present exploitation, its tissue mostly is ferrite+perlite, is used for making 8.8 grades and 9.8 grade high-strength bolts after cold work reinforced; And for 10.9 grade high-strength bolts cold work reinforced non-hardened/tempered steel wire rod, it is organized then and to be bainite substantially, with obtain required strength level (Hui Weijun etc. mechanical engineering material, 2002,26 (11): 1-4,38; Boratto F et al.Wire J.Inter., 1992, (9): 129-134).10.9 grade bolts of China's exploitation are higher owing to Si content with low-carbon Mn-V-Ti-B serial cold working reinforced non-hardened/tempered steel, and the thick non-metallic inclusion in the steel is not carried out spheroidizing, cause the cold-workability of wire rod relatively poor, having limited it applies, add in the steel simultaneously the cost that expensive microalloy element V improved steel (Yan Zhen Qi etc. steel vanadium titanium, 1992,13 (3): 1-8,74).Document (Boratto F et al.Wire J.Inter., 1992, (9): a kind of 10.9 grade bolt bainitic steels of introducing 129-134), then because higher Cr (0.60%) content is not only unfavorable to cold-forming property, and can improve the cost of steel, thereby weakened the economy of this class steel.Japanese Patent JP9-291312 proposes a kind of non-modified bolt wire rod of high strength with good workability, can be used to make 10.9 grade bolts, but the anneal that higher Cr (0.50 ~ 1.50%) content and wire rod need carry out 500 ~ 700 ℃ in the steel, can significantly improve steel product cost and reach the manufacturing cost of bolt subsequently, limit its industrial application in enormous quantities.
Summary of the invention
The object of the present invention is to provide a kind of have good plasticity and cold-forming property, the low carbon bainite type cold work reinforced non-hardened/tempered steel of low cost of manufacture can be used to make 10.9 grade high-strength bolts simultaneously.
According to above-mentioned purpose, the technical solution adopted in the present invention is: (1) reduces constituent contents such as Si, P, S, and is poly-partially with the crystal boundary that reduces steel inclusion quantity and inhibition impurity element, improves cold-forming property, plasticity and the toughness of steel; (2) add micro-B, when guaranteeing to obtain bainite structure, particularly the crystal boundary of P is poly-partially to suppress impurity element, improves the toughness of steel; (3) add the proper amount of rare-earth element, inclusion is carried out denaturing treatment, make the inclusion in the steel have certain plasticity, further improve the steel cold-forming property; (4) add microalloy element Nb, form the carbonitride of the Nb of small and dispersed,, further improve the plasticity and the cold-forming property of steel with crystal grain thinning.
The concrete chemical ingredients (weight %) of steel of the present invention is as follows: C 0.06～0.15%, Si≤0.20%, Mn1.80～2.40%, P≤0.015%, S≤0.010%, Cr 0.10～0.50%, and B 0.0005～0.003%, Ti 0.01～0.10%, RE 0.005～0.04%, and Nb 0.01～0.10%, and Al 0.005～0.05%, N 0.004～0.010%, and surplus is Fe and other unavoidable impurities.
In addition, the Zr of adding 0.01～0.10% in the concrete chemical ingredients (weight %) of this steel.
The effect of each element and proportioning are according to as follows:
C: in order to obtain required strength level after hot rolling attitude and drawing, C content must be more than 0.06%.But increase C content to the moulding of steel, toughness, and cold-forming property will there be bigger infringement.In addition, increase C content, will make the continuous cooling transformation curve of steel, particularly bainite partly moves to right, and forms the granular bainite tissue when being unfavorable for air cooling.Therefore, C content should be controlled at below 0.15%.
The Si:Si element significantly worsens the cold-forming property of steel, promote to promote also that simultaneously the crystal boundary of impurity element P and S is poly-partially, worsens the resistance for delayed fracture of steel, thereby controls its content and be no more than 0.20%.
Mn: except that C, Mn forms the most effective cheap alloying element of bainite structure, and plays the solution strengthening effect.At C content one regularly, increase Mn content, the quantity of bainite increases thereupon in the steel, particularly under the less situation of speed of cooling, and increase more remarkable.Mn content can not obtain full bainite structure less than 1.80% o'clock, but the then above-mentioned effect above 2.40% o'clock of Mn content is saturated, and segregation is serious, increased to smelt difficulty and cost, thereby controlled its content 1.80～2.40%.
P:P can form microsegregation when solidification of molten steel, gather partially at crystal boundary when heat subsequently, and the fragility of steel is enlarged markedly.In addition, reduce the resistance to deformation that P content can reduce steel, so the content of control P is below 0.015%.
S: inevitable impurity, form that MnS is mingled with and get together partially and worsen the cold-forming property of steel at crystal boundary, S content can improve the deformability of steel and the non-metallic inclusion in the minimizing steel in the reduction steel, also can reduce S simultaneously and alleviate embrittlement of grain boundaries the poly-partially of crystal boundary, improve the cold-forming property and the plasticity of steel, thereby control its content below 0.010%.
The Cr:Cr element promotes the formation of acicular ferrite; to obtain to have the low-carbon bainite tissue of excellent toughness; thereby guarantee to obtain required intensity and toughness, but too high levels can worsen the cold-forming property and the increase cost of steel, thereby control its content 0.10～0.50%.
B: micro-B can significantly postpone ferrite and begin to separate out line, increases the possibility that obtains air-colled bainite.It is poly-partially that B can also suppress the crystal boundary of impurity element P, works to purify crystal boundary, improves grain-boundary strength, can also suppress the oxidation and decarbonization of steel when heat simultaneously, thereby improve the toughness of steel.For above-mentioned effect, B content needs more than 0.0005%, but B content surpasses at 0.003% o'clock, and superfluous B can form thick BN, and steel easily produces hot-short, influences hot workability, and worsens the toughness of steel, therefore controls its content 0.0005～0.003%.
Ti:Ti is the N in the steel fixedly, suppresses the generation of thick BN, guarantees the above-mentioned good action of B.In addition, Ti also plays crystal grain thinning and precipitation strength.Ti content does not have above-mentioned effect less than 0.01%, but content effect above 0.10% is saturated, and easily forms the cold-forming property that thick TiN worsens steel on the contrary.
RE:RE has deoxidization desulfuration and to the effect of non-metallic inclusion denaturing treatment, makes the inclusion in the steel have certain plasticity, improves the cold-forming property of steel.RE content does not have above-mentioned effect less than 0.005%, but content surpasses 0.04%, then because inclusion increases, worsens the cold-forming property of steel on the contrary, thereby controls its content 0.005～0.04%.
Al: deoxidation effectively, fix N and crystal grain thinning, content does not have above-mentioned effect less than 0.005%, but content effect above 0.05% is saturated, and the thick AlN that forms is mingled with the toughness and the cold-forming property that can worsen steel.
N:N can form tiny nitride with crystal grain thinning with Al etc., but excessive N can gather in crystal boundary partially and form thick inclusion, so its content should be controlled at 0.004～0.01%.
Nb: crystal grain thinning, the plasticity and the cold-forming property of raising steel, content does not have above-mentioned effect less than 0.01%, but content effect above 0.10% is saturated.
Zr: its effect and Ti are similar.Zr is the N in the steel fixedly, suppresses the generation of thick BN, guarantees the above-mentioned good action of B.In addition, Zr also plays crystal grain thinning and precipitation strength.Zr content does not have above-mentioned effect less than 0.01%, but content effect above 0.10% is saturated.
The preparation method that employing of the present invention is similar to prior art:
Steel of the present invention can adopt electric arc furnace or converter+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.Steel wire rod of the present invention has certain intensity and good cold-workability rolling attitude, produce work hardening by a certain amount of cold deformation more subsequently, its intensity is further improved, last ageing treatment of carrying out stabilization again, plasticity is recovered to some extent, promptly, just can reach the desired performance index of 10.9 grade bolts under the situation of modifier treatment.
The present invention compared with prior art, steel of the present invention has the low advantage of good plasticity, cold-forming property and cost, can be used to make 10.9 grade high-strength bolts.
Embodiment
According to chemical ingredients scope of the present invention, on the 50kg vacuum induction furnace, smelted 5 stoves steel of the present invention and 4 stove compared steel, its concrete chemical ingredients is as shown in table 1.Wherein heat (batch) number 1～5# is a steel of the present invention, and heat (batch) number 6～9# is a compared steel.Molten steel casting becomes ingot, and makes bar through forging.The part bar carries out the drawing of different drafts subsequently, and carries out ageing treatment.Be processed into normal room temperature tension specimen (L from stocking and the sampling of drawing material
0=5d
0, d
0=5mm) and cold deformation sample (diameter d=10mm, height h=20mm).
Sample at room temperature stretches and the cold deformation test.The gained result has listed table 2 in.
As can be seen from Table 2, all more than 700MPa, relative reduction in area is all more than 65% in the tensile strength of rolling attitude for steel of the present invention; Then owing to fail to obtain wholegrain shape bainite structure, tensile strength is lower for compared steel.Steel of the present invention is after suitable drawing and stabilizing aging processing, all can obtain the above tensile strength of 1000MPa level, have good plasticity and excellent cold-forming property (with cold deformation time critical pressure compression deformation scale levy) simultaneously, promptly satisfy the intensity of 10.9 grade bolts and the requirement of cold-workability; And compared steel is after drawing and ageing treatment, although the intensity that has satisfies the requirement of 10.9 grade bolts, because soft mutually ferritic existence, cold-workability is poor, and the then intensity that has does not satisfy the requirement of 10.9 grade bolts.
Claims (2)
1, a kind of low carbon bainite type cold work reinforced non-hardened/tempered steel, it is characterized in that the concrete chemical ingredients (weight %) of this steel is: C 0.06～0.15%, Si≤0.20%, Mn 1.80～2.40%, P≤0.015%, S≤0.010%, Cr 0.10～0.50%, B 0.0005～0.003%, and Ti 0.01～0.10%, RE0.005～0.04%, Nb 0.01～0.10%, Al 0.005～0.05%, and N 0.004～0.010%, and surplus is Fe and other unavoidable impurities.
2, low carbon bainite type cold work reinforced non-hardened/tempered steel according to claim 1 is characterized in that this steel adds 0.01～0.10% Zr.
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| Application Number | Priority Date | Filing Date | Title |
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| CNA2009100881770A CN101597716A (en) | 2009-07-10 | 2009-07-10 | A kind of low carbon bainite type cold work reinforced non-hardened/tempered steel |
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| CNA2009100881770A CN101597716A (en) | 2009-07-10 | 2009-07-10 | A kind of low carbon bainite type cold work reinforced non-hardened/tempered steel |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101880826A (en) * | 2010-07-08 | 2010-11-10 | 安徽工业大学 | Non-hardened bainite cold heading steel for fastener and manufacturing method thereof |
| CN101935806A (en) * | 2010-09-10 | 2011-01-05 | 钢铁研究总院 | Low-carbon bainitic cold-work-strengthened non-quenched and tempered steel with excellent delayed fracture resistance |
| CN102181619A (en) * | 2011-02-18 | 2011-09-14 | 济钢集团有限公司 | Method for manufacturing non-tempering low-carbon bainite type high-strength steel plate of 1000Mpa grade |
-
2009
- 2009-07-10 CN CNA2009100881770A patent/CN101597716A/en active Pending
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101880826A (en) * | 2010-07-08 | 2010-11-10 | 安徽工业大学 | Non-hardened bainite cold heading steel for fastener and manufacturing method thereof |
| CN101935806A (en) * | 2010-09-10 | 2011-01-05 | 钢铁研究总院 | Low-carbon bainitic cold-work-strengthened non-quenched and tempered steel with excellent delayed fracture resistance |
| CN102181619A (en) * | 2011-02-18 | 2011-09-14 | 济钢集团有限公司 | Method for manufacturing non-tempering low-carbon bainite type high-strength steel plate of 1000Mpa grade |
| CN102181619B (en) * | 2011-02-18 | 2013-02-13 | 济钢集团有限公司 | Method for manufacturing non-tempering low-carbon bainite type high-strength steel plate of 1000Mpa grade |
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Open date: 20091209 |