CN103331390A - 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 the compression molding technology field, relate in particular to a kind of production method with automobile U-shaped beam of good ductility.

Background technology

In the automotive body structure field, lightweight more and more obtains industry personnel's attention, alleviates the security performance that tare not only can improve the car load 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, along with the attenuate of part material thickness, just must improve part strength in order to guarantee the collision safety performance.

Automobile U-shaped beam adopts the method for steel plate drawing to obtain usually, yet in adopting high-strength steel sheet cold forming process, when the strength of materials surpassed 800～1000MPa, it is very difficult that material forming becomes, and very big to the mould damage.Because the cost of mould is very high, therefore greatly increased the risk of drawing.

At above-mentioned situation, the research staff has taked the method that is shaped to steel plate under heated condition, and this method has been improved the formability of metal material, has also prevented from producing owing to residual stress the appearance of faults in material such as resilience, delayed fracture.The steel plate that surpasses 1000MPa when tensile strength is during as U-shaped beam material, and this method can obtain to have the part of respective strengths and favorable forming property, and these high-strength steel sheets almost can not form by the traditional cold manufacturing process.

Yet, in the hot forming process, because need be with blank heating to the transition temperature more than the Ac3, therefore it is martensitic structure that the microstructure of back product of being shaped just becomes major part, although can obtain to have 1270MPa or more high-intensity steel plate, the ductility of U-shaped beam is relatively poor, even the situation that may occur breaking, thereby the hot forming part never is widely used, and its main cause just is can't obtain simultaneously having the U-shaped beam of high strength and favorable forming property.

Summary of the invention

Purpose of the present invention is intended to overcome above-mentioned defective, and then a kind of no resilience defective is provided, and has the production method of the automobile U-shaped beam of high strength and good ductility.

For this reason, the solution taked of the present invention is:

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

1, steel plate heating:

After being heated to steel plate between Ac1 transition temperature～Ac3 transition temperature, insulation 1～2min;

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

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 ℃/s, steel plate is cooled to the beginning temperature that is shaped, the beginning temperature that is shaped is higher than Ms (martensite start) point Ms point;

The beginning temperature that is shaped should satisfy:

The heating-up temperature of Ms point≤shaping beginning temperature≤0.75 * steel plate;

Be the Ms point of steel plate for C-Mn-Si, obtain according to the calculating of chemical composition:

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, drawing:

After steel billet temperature reaches the beginning temperature that is shaped, steel plate is put into the U-shaped beam mould, stamping machine is started working, the descending matched moulds of patrix; Curring time is 1.9～2.1s, and the control of shaping final temperature is being higher than martensite transformation temperature Ms point; The circulation cooling velocity is set in 25 ℃/s in the mould, behind the matched moulds pressurize 10s, finishes the drawing 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 the hot forming process, by the reasonable control to forming process, not only can guarantee in forming process, can not occur crackle or defective such as wrinkling, and can effectively control the heterogeneous microstructure of U-shaped beam, thereby obtain to have the automobile U-shaped beam of high strength and good formability and ductility, after testing, its Rm value reaches more than the 948MPa, and Rp0.2 reaches 518MPa, the A value reaches 12.33%, makes the U-shaped beam have wider range of application.

The specific embodiment

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

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

After being heated to steel plate between Ac1 transition temperature～Ac3 transition temperature, insulation 1～2min.Ac1, Ac3 and Ms point temperature according to composition measurement are: Ac1 is 720 ℃, and Ac3 is 830 ℃, and the Ms point is 415 ℃.

Embodiment forming process control parameter is as shown in table 1:

Table 1 embodiment forming process control parameter list

During whole drawing, the circulation cooling velocity is set in 25 ℃/s in the mould.The result proves, defective such as when steel plate was shaped under these conditions, to break can not appear in steel plate, wrinkling, resilience.Although in traditional thermo shaping method, think that always beginning to be shaped is technology general knowledge under high heating-up temperature, high forming temperature, but can find from the mechanical property testing result of final U-shaped beam, steel plate after the heating is cooled to form when 75% temperature of heating-up temperature is following, and 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. the production method of an automobile U-shaped beam is characterized in that, concrete grammar and step are:

(1), steel plate heating:

After being heated to steel plate between Ac1 transition temperature～Ac3 transition temperature, insulation 1～2min;

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

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

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

(2), steel plate cooling:

According to the cooling velocity of 9～11 ℃/s, steel plate is cooled to the beginning temperature that is shaped, the beginning temperature that is shaped is higher than Ms (martensite start) point Ms point;

The beginning temperature that is shaped should satisfy:

The heating-up temperature of Ms point≤shaping beginning temperature≤0.75 * steel plate;

Be the Ms point of steel plate for C-Mn-Si, obtain according to the calculating of chemical composition:

Ms=540-420［C］ ℃

(3), drawing:

After steel billet temperature reaches the beginning temperature that is shaped, steel plate is put into the U-shaped beam mould, stamping machine is started working, the descending matched moulds of patrix; Curring time is 1.9～2.1s, and the control of shaping final temperature is being higher than martensite transformation temperature Ms point; The circulation cooling velocity is set in 25 ℃/s in the mould, behind the matched moulds pressurize 10s, finishes the drawing of U-shaped beam.