CN103331390B - Manufacturing method of automotive U-shaped beam - Google Patents

Abstract

The invention provides a manufacturing method of an automotive U-shaped beam. The method comprises the steps that a steel plate is heated to a temperature between Ac1 transformation temperature and Ac3 transformation temperature and then stays for 1-2 min under the temperature; the steel plate is cooled to a temperature higher than the martensite transformation starting temperature Ms point at a cooling speed of 9-11 DEG C / s; the steel plate is placed into a U-shaped beam die and is formed for 1.9-2.1 s after spotting, and the forming termination temperature is controlled to be higher than the martensite transformation starting temperature Ms point; the circulating cooling speed inside the die is set to be 25 DEG C / s, and stamp-forming of the U-shaped beam is achieved after spotting pressure maintaining is kept for 10 s. According to the manufacturing method of the automotive U-shaped beam, cracks or wrinkles will not appear in the forming process, the Rm value reaches more than 948 MPa, the Rp0.2 value reaches 518 MPa, the A value reaches 12.33%, and therefore the automobile U-shaped beam with high strength, good forming property and good malleability is obtained.

Description

A kind of production method of automobile U-shaped beam

Technical field

The invention belongs to compression molding technology field, particularly relate to a kind of production method with the automobile U-shaped beam of good ductility.

Background technology

In field of car body structure, lightweight more and more obtains the attention of industry personnel, alleviates the security performance that tare not only can improve complete automobile collision effectively, and every loss of weight 100kg, fuel consumption per hundred kilometers on average can reduce 0.5L, and CO2 emissions reduce 12g/km.In order to realize lightweight, thinning along with part material thickness, in order to ensure that collision safety performance just must improve part strength.

Automobile U-shaped beam adopts the method for Steel Sheet to obtain usually, but in employing high-strength steel sheet cold forming process, when the strength of materials is more than 800 ~ 1000MPa, material forming becomes very difficult, and very large to mould damage.Because the cost of mould is very high, therefore greatly add stamping risk.

For above-mentioned situation, research staff takes the method be shaped in a heated state to steel plate, the method improves the formability of metal material, also prevent the appearance producing the fault in material such as resilience, delayed fracture due to residual stress.When tensile strength is used as U-shaped beam material more than the steel plate of 1000MPa, the method can obtain the part with respective strengths and favorable forming property, and these high-strength steel sheets almost do not form by traditional cold manufacturing process.

But, in heat forming processes, owing to needing the transition temperature of blank heating to more than Ac3, therefore after being shaped, the microstructure of product just becomes major part is martensitic structure, although can obtain the steel plate with 1270MPa or more high strength, the ductility of U-shaped beam is poor, even may occur the situation of breaking, thus thermoformed parts is never widely used, its main cause is just the U-shaped beam that cannot simultaneously obtain having high strength and favorable forming property.

Summary of the invention

Object of the present invention is intended to overcome above-mentioned defect, and then provides a kind of without resilience defect, and has the production method of the automobile U-shaped beam of high strength and good ductility.

For this reason, the solution that the present invention takes is:

A production method for automobile U-shaped beam, its concrete grammar and step are:

1, steel plate heating:

Steel plate is heated to after between Ac1 transition temperature ~ Ac3 transition temperature, insulation 1 ~ 2min;

Ac1 and Ac3 transition temperature pH-value determination pH formula is:

Ac1=723-10.7Mn+29.1Si+16.9Cr-16.9Ni+290Als+6.38W℃

Ac3=910-203sqr（C）+44.7Si-15.2Ni+31.5Mo+104V+13.1W℃

2, steel plate cooling:

According to the cooling velocity of 9 ~ 11 DEG C/s, being cooled to by steel plate is shaped starts temperature, is shaped and starts temperature higher than Ms (martensite start) point Ms point;

The beginning temperature that is shaped should meet:

Ms point≤shaping starts the heating-up temperature of temperature≤0.75 × steel plate;

For the Ms point of C-Mn-Si system steel plate, the calculating according to chemical composition obtains:

Ms=540-420［C］℃

$\begin{array}{ccccc}\left[C\right]=C& \frac{\mathrm{Mn}}{12}+\frac{\mathrm{Cr}}{35}& \frac{\mathrm{Ni}}{21}+\frac{\mathrm{Mo}}{20}& \frac{\mathrm{Si}}{40}+\frac{V}{3}& \frac{\mathrm{Al}}{21}\end{array}$

3, stamping:

After steel billet temperature reaches the beginning temperature that is shaped, steel plate is put into U-shaped beam mould, stamping machine is started working, the descending matched moulds of patrix; Curring time is 1.9 ~ 2.1s, and shaping final temperature controls higher than martensite transformation temperature Ms point; Mould Inner eycle cooling velocity is set in 25 DEG C/s, after matched moulds pressurize 10s, completes the stamping of U-shaped beam.

Beneficial effect of the present invention is:

The present invention adopts the mode of warm forming to make automobile U-shaped beam, and in heat forming processes, by the conservative control to forming process, not only can guarantee to there will not be crackle or the defect such as wrinkling in forming process, and effectively can control the heterogeneous microstructure of U-shaped beam, thus obtain the automobile U-shaped beam with high strength and good formability and ductility, after testing, its Rm value reaches more than 948MPa, and Rp0.2 reaches 518MPa, A value reaches 12.33%, makes U-shaped beam be provided with wider range of application.

Detailed description of the invention

Below, the present invention will be further described in conjunction with the embodiments.

The chemical composition wt% that embodiment makes U-shaped beam steel plate used is: C0.19, Si0.18, Mn1.2, P0.015,0.015, C0.35, B0.002, Ti0.019.

Steel plate is heated to after between Ac1 transition temperature ~ Ac3 transition temperature, insulation 1 ~ 2min.Ac1, Ac3 and Ms point temperature according to composition measurement is: Ac1 is 720 DEG C, and Ac3 is 830 DEG C, and Ms point is 415 DEG C.

Embodiment forming process controling parameters is as shown in table 1:

Table 1 embodiment forming process controling parameters table

In whole stamping period, mould Inner eycle cooling velocity is set in 25 DEG C/s.Result proves, when steel plate is shaped under these conditions, steel plate there will not be break, the defect such as wrinkling, resilience.Although in traditional thermo shaping method, think that under high heating-up temperature, high forming temperature, start shaping is technology general knowledge always, but can find from the mechanics properties testing result of final U-shaped beam, form when being cooled to below the temperature of 75% of heating-up temperature by the steel plate after heating, the forming property of U-shaped beam will be greatly improved.

The mechanical performance index testing result of embodiment U-shaped beam is as shown in table 2.

Table 2U ellbeam mechanical performance index testing result

Claims (1)

1. a production method for automobile U-shaped beam, is characterized in that, concrete grammar and step are:

(1), steel plate heating:

Steel plate is heated to after between Ac1 transition temperature ~ Ac3 transition temperature, insulation 1 ~ 2min;

Ac1 and Ac3 transition temperature pH-value determination pH formula is:

Ac1＝723-10.7Mn+29.1Si+16.9Cr-16.9Ni+290Als+6.38W℃

Ac3＝910-203sqr(C)+44.7Si-15.2Ni+31.5Mo+104V+13.1W℃

(2), steel plate cooling:

According to the cooling velocity of 9 ~ 11 DEG C/s, being cooled to by steel plate is shaped starts temperature, is shaped and starts temperature higher than Ms (martensite start) point Ms point;

The beginning temperature that is shaped should meet:

Ms point≤shaping starts the heating-up temperature of temperature≤0.75 × steel plate;

For the Ms point of C-Mn-Si system steel plate, the calculating according to chemical composition obtains:

Ms＝540-420[C]℃

[C]＝C+Mn/12+Cr/35+Ni/21+Mo/20+Si/40-V/3-Al/21

(3), stamping:

After steel billet temperature reaches the beginning temperature that is shaped, steel plate is put into U-shaped beam mould, stamping machine is started working, the descending matched moulds of patrix; Curring time is 1.9 ~ 2.1s, and shaping final temperature controls higher than martensite transformation temperature Ms point; Mould Inner eycle cooling velocity is set in 25 DEG C/s, after matched moulds pressurize 10s, completes the stamping of U-shaped beam.