CN103866190B - Low fragility 650MPa level steel for automobile crossbeam and manufacture method thereof - Google Patents

Abstract

The invention discloses a kind of low fragility 650MPa level steel for automobile crossbeam and manufacture method thereof.C0.06～0.08%, Si < 0.1%, Mn1.40～1.60%, P < 0.012%, S < 0.005%, Al0.020～0.070%, Nb0.035～0.050%, Ti0.05～0.075%, N < 0.005%%, surplus is ferrum and inevitable impurity.By desulfurizing iron, converter smelting, application of vacuum, continuous casting, slab inspection and cleaning, heating of plate blank, hot continuous rolling, section cooling, batch, finishing is sequentially carried out prepared.Intensity of the present invention is high, at Vehicle Frame Design weight loss effect up to 10%～25%；Good moldability, it is adaptable to the techniques such as punching press, roll-in, bending；Low-temperature flexibility is good, it is adaptable to the transport of cold district.

Description

Low fragility 650MPa level steel for automobile crossbeam and manufacture method thereof

Technical field

The invention belongs to metallurgical technology field, relate to a kind of vehicle beam steel, be specifically related to a kind of low fragility 650MPa level steel for automobile crossbeam and manufacture method thereof.

Background technology

Alleviate tare by improving armor plate strength, reach energy-conservation of consumption reduction, reduce the important topic that environmental pollution is current auto industry research.At home and abroad, mostly present stage is that employing is added certain microalloy element and strengthened the intensity of steel.Performance and formability, as the safety load-bearing part of passenger-cargo carriage, are had significantly high requirement by beam steel.Domestic each steel mill is all carrying out the research work of related fields.But alloying element used, consumption, which kind of technique are all not quite similar, and the equipment of each factory, technology, raw material etc. are relevant.At present, the production technology of below 650MPa rank beam steel is quite ripe, also wide in the application of auto industry.It is limited to the backward molding equipment of domestic automobile industry, commonly use below 650MPa rank steel grade at present and manufacture heavy truck crossbeam, working strength scope is concentrated mainly on 510MPa～600MPa, and the range of application of higher intensity rank crossbeam is less or is in the industrial certification stage.

The vehicle frame on heavy truck chassis adopts hot rolling automotive frame steel to make, and its frame assembly is divided into longeron, lining beam, crossbeam, reinforcement and strengthens plate etc., and each parts are to adopt cold stamping shaping or rolling forming mode, and its assembling mainly adopts riveting method.

Namely automotive frame is the supporting part of passenger-cargo carriage, is also the safety member in vehicle traveling process.In order to improve lifting capacity, heavy truck crossbeam is generally adopted the hot rolled steel plate manufacture of 6～12mm.Tonnage according to heavy truck and application scenario, heavy truck crossbeam adopts single-beam or twin beams design.By improving intensity rank, it is possible to reduce the thickness of crossbeam, or twin beams change in design is designed for single-beam, bring multiple benefits, while alleviating car weight, it is possible to reduce oil consumption or increase cargo dead-weight.The intensity increasing steel for automobile crossbeam when prior art condition further is the problem that people are studying always.

CN200910272678.4 discloses a kind of tensile strength in 590MPa level steel for automobile crossbeam and manufacture method thereof, its gained steel grade intensity is relatively low, in chemical composition, adopting Trace Titanium Treatment, titanium Main Function is to make the inclusion modifications such as S, P in steel, reduces the harm of field trash, its shape is made to change, thus improving the formability of steel, for reaching this purpose, its content is typically in about 0.03%.This steel grade intensity is relatively low, can not meet modern heavy-duty commercial car manufacturing enterprise steel are high-strength thinning to adapt to day by day harsh day environmental regulation requirement.

Summary of the invention

It is an object of the present invention to provide a kind of tensile strength at 650MPa level steel for automobile crossbeam, while there is higher intensity and good mouldability, it may have excellent low-temperature flexibility.

Concrete scheme is as follows:

Low fragility 650MPa level steel for automobile crossbeam, its chemical composition is by mass percentage:

C0.06～0.08%, Si < 0.1%, Mn1.40～1.60%, P < 0.012%, S < 0.005%, Al0.020～0.070%, Nb0.035～0.050%, Ti0.05～0.075%, N < 0.005%%, surplus is ferrum and inevitable impurity.

By such scheme, described low fragility 650MPa level steel for automobile crossbeam, through desulfurizing iron, converter smelting, application of vacuum, continuous casting, slab inspection and cleaning, heating of plate blank, hot continuous rolling, section cooling, batches, and finishing prepares；

Wherein, tap after converter smelting 1/3 time start to add ferroalloy, tap 2/3 time add complete, and alloying order be followed successively by ferro-aluminum, ferromanganese, ferro-niobium；Use adds aluminum machine and adds aluminum steel and carry out final deoxidizing, adds ferrotianium, Ferrotitanium particle diameter≤30mm during application of vacuum；

In Hot Strip Rolling, continuous casting steel billet being first heated in 160～240min 1230～1280 DEG C and carry out roughing, roughing end temp controls to carry out finish rolling again at 1040～1140 DEG C, and finishing temperature is 780～880 DEG C.

By such scheme, described section cooling is back segment cooling, and the water temperature < 35 DEG C of cooling water controls rate of cooling >=10 DEG C/s.

By such scheme, coiling temperature is 500～580 DEG C.

The preparation method of above-mentioned low fragility 650MPa level steel for automobile crossbeam, including desulfurizing iron, converter smelting, application of vacuum, continuous casting, slab inspection and cleaning, heating of plate blank, hot continuous rolling, section cooling, batches, the processing step of finishing；It is characterized in that:

Tap after converter smelting 1/3 time start to add ferroalloy, tap 2/3 time add complete, and alloying order be followed successively by ferro-aluminum, ferromanganese, ferro-niobium；Use adds aluminum machine and adds aluminum steel and carry out final deoxidizing, adds ferrotianium, Ferrotitanium particle diameter≤30mm during application of vacuum；

In described Hot Strip Rolling, continuous casting steel billet being first heated in 160～240min 1230～1280 DEG C and carry out roughing, roughing end temp controls to carry out finish rolling again at 1040～1140 DEG C, and finishing temperature is 780～880 DEG C.

By such scheme, section cooling requires back segment cooling, the water temperature < 35 DEG C of cooling water, and controlling rate of cooling is >=10 DEG C/s.

By such scheme, coiling temperature is 500～580 DEG C.

Carbon is cheap solution strengthening element.If its content is more than 0.08%, then press formability can reduce；If its content is less than 0.06%, then can not meet the material requirement to intensity, so, its content is limited to 0.06%～0.08% scope.

Element silicon promotes the generation of iron scale in the hot rolling, worsens surface quality, easily comes off in follow-up punching course, causes use difficulty, so its content is limited to < 0.1%.

Manganese is to improve intensity and the maximally effective element of toughness, can improve the intensity-extension balance of steel.But add the manganese of volume, the quenching degree increasing steel can be caused, in consideration of it, it will be defined to 1.60%, so, its content is limited to 1.40%～1.60% scope.

Phosphorus is the harmful element in steel, easily causes center segregation of casting blank, in order to avoid cold bending performance, toughness worsen, sets its upper content limit as 0.012%.

Sulfur is very harmful element.Sulfur in steel often exists with the oxide morphology of manganese, the impact flexibility of steel is very disadvantageous by this sulphide inculsion, and causes the anisotropy of performance, along with the raising of beam steel intensity, the extension of micro-crack is very sensitive to field trash, so sulfur content in steel being controlled below 0.005%.

Aluminum adds for deoxidation, when Als content is less than 0.020%, it is impossible to play its effect；On the other hand, the aluminum owing to adding volume easily forms aluminium oxide agglomerate, so, it is stipulated that the Als upper limit is 0.070%.Therefore, Als content is limited to 0.020%～0.070% scope.

Niobium is indispensable element in cerium sulphate crystal rolls, in thermomechanical is processed crystal grain thinning, reduce austenite to ferritic transition temperature and precipitation strength, therefore steel adds trace alloying element niobium and can be easy to the carrying out of controlled rolling, and improve intensity and the toughness of steel plate.So, the consideration of the aspects such as comprehensive mechanical property of steel plate and cost, its content is limited to 0.035～0.050% scope.

Titanium is cheap alloy strengthening element, precipitates out with carbon and nitrogen compound, not only crystal grain thinning, and hinders dislocation to move in deformation process.For making full use of the invigoration effect of titanium, it is stipulated that its lower limit is 0.05%, for avoiding too high titanium to cause that toughness worsens, it is stipulated that its upper limit is 0.075%.So, its content is limited to 0.05～0.075% scope.

Nitrogen element is very strong with the affinity of titanium elements, in order to avoid nitrogen is combined formation large scale metallic inclusion with titanium, is limited to < 0.005%.

In patent of the present invention, on composition designs, raising due to steel-making level, S, P content itself can be controlled in very low level, steel becomes purer, Ti adds primarily as alloy strengthening element, simultaneously, in order to ensure effective precipitation of Ti element, N element is had strict requirement, N element and Ti is avoided to form large-sized TiN metallic inclusion, on hot rolling technology designs, in order to ensure that the Ti compound in steel billet fully dissolves, in heating steel billet process, heating-up temperature and heat time heating time there is special requirement, simultaneously in order to fully improve the formability of steel plate, section cooling mode does not adopt leading portion cool down, but use the back segment type of cooling.

Along with Ti content increases, slab heating temperature needs to improve, in order that ensure that the compound of titanium fully dissolves, this patent requires 1230～1280 DEG C, if lower than 1230 DEG C, titaniferous compound dissolves insufficient in heating process, exists with large-sized titaniferous compound in rolling process, affects its precipitating reinforcing effect.

Upper limit heat time heating time is required, and heat time heating time, more than 240 minutes, makes austenite crystal too grow up, causing that intensity reduces, simultaneously billet surface forms excessive iron scale, not easy-clear in de-scaling process, during steel rolling, iron scale is rolled into steel plate, forms hole shape defect on surface.

Section cooling adopts the back segment type of cooling, compares the leading portion type of cooling, and back segment cooling cools down after first passing through a period of time air cooling again, and therefore the intensity of cooling of back segment cooling is relatively low, can improve the elongation percentage of steel, can reduce steel plate internal stress simultaneously, improves toughness.

Coiling temperature is set in 500～580 DEG C, is beneficial to the formation of bainite structure, and the toughness of bainite structure is better than pearlitic structrure.

Beneficial effects of the present invention:

1) intensity is high, at Vehicle Frame Design weight loss effect up to 10%～25%；

2) good moldability, it is adaptable to the techniques such as punching press, roll-in, bending；

3) low-temperature flexibility is good, it is adaptable to the transport of cold district.

Detailed description of the invention

Following example are for being further appreciated by technical scheme, not as limiting of its scope.

Low fragility 650MPa level steel for automobile crossbeam, its chemical composition is by mass percentage:

C0.06～0.08%, Si < 0.1%, Mn1.40～1.60%, P < 0.012%, S < 0.005%, Al0.020～0.070%, Nb0.035～0.050%, Ti0.05～0.075%, N < 0.005%%, surplus is ferrum and inevitable impurity.

It, through desulfurizing iron, converter smelting, application of vacuum, continuous casting, slab inspection and cleaning, heating of plate blank, hot continuous rolling, section cooling, batches, and finishing prepares.

Preparation process control to tap after converter smelting 1/3 time start to add ferroalloy, tap 2/3 time add complete, and alloying order is followed successively by ferro-aluminum, ferromanganese, ferro-niobium；Use adds aluminum machine and adds aluminum steel and carry out final deoxidizing, adds ferrotianium, Ferrotitanium particle diameter≤30mm during application of vacuum.In Hot Strip Rolling, continuous casting steel billet being first heated in 160～240min 1230～1280 DEG C and carry out roughing, roughing end temp controls to carry out finish rolling again at 1040～1140 DEG C, and finishing temperature is 780～880 DEG C.

In order to improve the utilization rate of effective titanium, Ferrotitanium particle diameter≤30mm.Owing to the affinity of titanium Yu oxygen is very strong, it is necessary to the application of vacuum link after deoxidation adds titanium in molten steel, it is to avoid titanium forms compound with oxygen, float and enter covering slag.Hot continuous rolling controlling of production process is critically important, for realizing ferrite and the bainite structure of low-alloy steel of the present invention, the present invention adopts reheating original austenite structure refinement to control, complex chemical compound is formed with carbon, nitrogen respectively by niobium and titanium, rolling and cooling procedure precipitate out, its precipitate hinders grain growth, thus realizing grain refinement.

Along with Ti content increases, slab heating temperature needs to improve, in order that ensure that the compound of titanium fully dissolves, this patent requires 1230～1280 DEG C, if lower than 1230 DEG C, titaniferous compound dissolves insufficient in heating process, exists with large-sized titaniferous compound in rolling process, affects its precipitating reinforcing effect.Upper limit heat time heating time is required, and heat time heating time, more than 240 minutes, makes austenite crystal too grow up, causing that intensity reduces, simultaneously billet surface forms excessive iron scale, not easy-clear in de-scaling process, during steel rolling, iron scale is rolled into steel plate, forms hole shape defect on surface.

Laminar cooling process cools down the water temperature < 35 DEG C of water, controls rate of cooling >=10 DEG C/s, adopt the back segment type of cooling.Comparing the leading portion type of cooling, back segment cooling cools down after first passing through a period of time air cooling again, and therefore the intensity of cooling of back segment cooling is relatively low, can improve the elongation percentage of steel, can reduce steel plate internal stress simultaneously, improves toughness.

Coiling temperature is 500～580 DEG C.Being beneficial to the formation of bainite structure, the toughness of bainite structure is better than pearlitic structrure.

Metallographic testing result shows, this steel be organized as ferrite and bainite.Tension test shows, this hardness of steel is high, and yield tensile ratio is high, has good non-deformability.Wide cold bending test shows, even if still check qualified when d=0, has good cold forming performance.

Embodiment

Low fragility 650MPa level hot rolling automotive frame steel is prepared by the specific chemical composition shown in table 1.Preparation process is as follows:

90 tons and 250 tons converters of steel mill carry out top bottom blowing, adopts Desulphurization of Pig Iron, make S≤0.005% in molten iron；Furnace rear tap 1/3 time start to add ferroalloy, tap 2/3 time add complete, alloying order: ferro-aluminum → ferromanganese → ferro-niobium, use adds aluminum machine and adds aluminum steel and carry out final deoxidizing, titanium is added when application of vacuum, and to carrying out trimming, making the chemical composition in steel meet the requirement of table 1, surplus is Fe and is inevitably mingled with；The pouring molten steel of composition shown in table 1 is become the slab of 230～250mm × 1050～2150mm section again；Then slab is delivered to hot rolling mill, 2250mm milling train carries out hot continuous rolling, is rolled into hot-rolled sheet coil, then carries out finishing；First continuous casting steel billet is heated in 160～240min 1230～1280 DEG C and carries out roughing, end temp is 1040～1140 DEG C, carry out finish rolling again, finishing temperature is 780～880 DEG C, strip steel roll after control cooling adopt back segment section cooling mode, the water temperature < 35 DEG C of cooling water, controlling rate of cooling is >=10 DEG C/s, and coiling temperature is 500～580 DEG C.Rolling coil of strip carries out surface quality inspection at finishing line, and controls plate shape further well, finally gives the hot rolled coil of 3～8mm.

Table 1

Composition	C	Si	Mn	P	S	Als	Nb	Ti	N
										1	0.06	0.08	1.42	0.011	0.003	0.047	0.035	0.053	0.004
2	0.063	0.03	1.47	0.009	0.004	0.045	0.037	0.062	0.0034
										3	0.067	0.05	1.55	0.008	0.001	0.051	0.041	0.071	0.0035
4	0.073	0.05	1.60	0.011	0.002	0.060	0.048	0.69	0.0021
										5	0.080	0.04	1.58	0.010	0.002	0.042	0.050	0.075	0.0037

In above-mentioned table 1, five groups of each constituent contents of embodiment are all calculated in mass percent, and the performance of its corresponding product is shown in Table 2.Wherein, lower yield strength, tensile strength, percentage elongation, 180 ° of wide clod washes ,-60 DEG C of ballistic works all perform according to national standard.

Table 2

By table 2 it can be seen that the lower yield strength of embodiments of the invention steel product is between 600～720MPa, tensile strength is between 680～780MPa, and percentage elongation is between 18%～27%.Its tensile strength minimum is 680MPa, the average strength 655MPa higher than patent CN200910272678.4 noted earlier, it was shown that the intensity rank of steel grade improves a grade.By the adjustment of each composition, the technique that design and composition adapt so that the intensity of steel grade is significantly improved, and elongation percentage is substantially reduced, and has good low-temperature flexibility, and-60 DEG C of ballistic works are 70J, it is achieved that the matched well of intensity and toughness simultaneously.

Claims (2)

1. one kind low fragility 650MPa level steel for automobile crossbeam, it is characterised in that chemical composition is by mass percentage:

C0.06～0.08%, Si < 0.1%, Mn1.40～1.60%, P < 0.012%, S < 0.005%, Al0.020～0.070%, Nb0.035～0.050%, Ti0.05～0.075%, N < 0.005%, surplus is ferrum and inevitable impurity；

Described low fragility 650MPa level steel for automobile crossbeam by desulfurizing iron, converter smelting, application of vacuum, continuous casting, slab inspection and cleaning, heating of plate blank, hot continuous rolling, section cooling, batch, finishing is sequentially carried out and prepares；

Wherein, tap after described converter smelting 1/3 time start to add ferroalloy, tap 2/3 time add complete, and alloying order be followed successively by ferro-aluminum, ferromanganese, ferro-niobium；Use adds aluminum machine and adds aluminum steel and carry out final deoxidizing, adds ferrotianium, Ferrotitanium particle diameter≤30mm during application of vacuum；

In described Hot Strip Rolling, continuous casting steel billet being first heated in 160～240min 1230～1280 DEG C and carry out roughing, roughing end temp controls to carry out finish rolling again at 1040～1140 DEG C, and finishing temperature is 780～880 DEG C；

Section cooling is back segment cooling, and the water temperature < 35 DEG C of cooling water controls rate of cooling >=10 DEG C/s；

Coiling temperature is 500～580 DEG C.

2. the preparation method of the low fragility 650MPa level steel for automobile crossbeam described in claim 1, including desulfurizing iron, converter smelting, application of vacuum, continuous casting, slab inspection and cleaning, heating of plate blank, hot continuous rolling, section cooling, batch, the processing step of finishing；It is characterized in that:

Chemical composition is by mass percentage:

C0.06～0.08%, Si < 0.1%, Mn1.40～1.60%, P < 0.012%, S < 0.005%, Al0.020～0.070%, Nb0.035～0.050%, Ti0.05～0.075%, N < 0.005%, surplus is ferrum and inevitable impurity；

Tap after described converter smelting 1/3 time start to add ferroalloy, tap 2/3 time add complete, and alloying order be followed successively by ferro-aluminum, ferromanganese, ferro-niobium；Use adds aluminum machine and adds aluminum steel and carry out final deoxidizing, adds ferrotianium, Ferrotitanium particle diameter≤30mm during application of vacuum；

In described Hot Strip Rolling, continuous casting steel billet being first heated in 160～240min 1230～1280 DEG C and carry out roughing, roughing end temp controls to carry out finish rolling again at 1040～1140 DEG C, and finishing temperature is 780～880 DEG C；

Section cooling is back segment cooling, and the water temperature < 35 DEG C of cooling water controls rate of cooling >=10 DEG C/s；

Coiling temperature is 500～580 DEG C.