CN101215680A

CN101215680A - Aluminum alloy die-casting die steel surface shot blasting strengthening treatment method

Info

Publication number: CN101215680A
Application number: CNA2008100323939A
Authority: CN
Inventors: 吴晓春; 陈玉华; 闵永安; 汪宏斌
Original assignee: University of Shanghai for Science and Technology
Current assignee: University of Shanghai for Science and Technology
Priority date: 2008-01-08
Filing date: 2008-01-08
Publication date: 2008-07-09

Abstract

The invention relates to a method for shot peening strengthening the surface of aluminum alloy die casting die steel, and belongs to the field of surface strengthening treatment technology of alloy steels. The invention has the characteristics that the surface of die steel is done with shot peening, through controlling the hardness, particle size and injection pressure and direction of projectiles, the surface of die steel is obtained ideal residual compressive stress distribution, through changing hot cracking formation and distribution of a die, the thermal fatigue resistance of the die steel is improved, thereby increasing the life and the reliability of the die. The process parameters of the shot peening are that the particle sizes of injection cast steel projectiles are 0.20-0.30mm, the injection pressure is 0.3-0.6 MPa, an injection angle is continuously changed between 30 degree and 60 degree, the hardness of the projectiles is controlled between 44 HRC and 52HRC, and the shot peening time is 20-60 minutes. After being treated by shot peening, the maximum compressive stress of the surface of steel is capable of being 600 MPa, the surface coverage of the shot peening is 200 percent, after being treated by the shot peening, thermal fatigue crack of the die steel is of a reticular dispersion fine distribution state.

Description

The method that aluminum alloy die-casting die steel surface shot blasting strengthening is handled

Technical field

The present invention relates to the method that a kind of aluminum alloy die-casting die steel surface shot blasting strengthening is handled, belong to steel alloy surface strengthening treatment technology field.

Background technology

Along with the fast development of society, the industrial scale of modern industry has been emerged in large numbers large quantities of alloy products in continuous expansion, Just because of this demand of aluminum alloy die-casting die is more and more come manyly, and the requirement of quality is also more and more high.

Aluminum alloy die-casting die contacts with the alloy of the condition of high temperature in the process under arms repeatedly, and under periodic alternating thermal stress effect, the moulding stock especially structure property on top layer progressively develops, and finally causes losing efficacy.Thermal fatigue is the topmost failure mode of aluminum alloy die-casting die steel, and thermal fatigue is meant metallic substance under the cold cycling alternating action, and the surface can form the phenomenon of map cracking.In order to improve the thermal fatigue property of mould, improve the life-span of mould, introduced process for treating surface.

Process for treating surface is mainly to be to change material surface pattern, chemical ingredients, phase composite, microtexture, defect state or stressed condition by applying methods such as various coverings or employing machinery, physics, chemistry, thereby improves the ability that material is resisted environmental activity.Shot-peening is a kind of widely used material surface cold working method in the various surface treatment methods, and shot peening can improve die surface layer hardness and intensity, causes the fatigue strength of part to improve prolongs life then.Fatigue cracking all is from the surface mostly, the development of crackle is mainly by tensile stress, and shot peening strengthening is handled and can be produced residual compressive stress at upper layer, makes to add tensile stress and the reduction of residual compressive stress synthetic total stress approach of shear strength, thereby can improve the fatigue strength of material and prolong fatigue lifetime.In addition, the die surface roughness increases after the shot peening, more helps improving the anti-stick film properties of mould.

Someone success shot peening is applied to made on the ultrahigh-strength steel and stainless steel of load-carrying member, reaches the purpose that improves its mechanical fatigue performance, but for shot peening being applied to research that aluminum alloy die-casting die steel improves its thermal fatigue property also seldom.In addition, in relevant document, mention and conventional shot peening is applied to die-casting die steel can improves the die steel surface compress residual stresses, play and suppress crackle and produce, reduce the effect of crack growth rate; But it is all not mentioned for the form of crackle behind concrete blasting technology method and the shot-peening and characteristic distributions etc.Because the use hardness height of die-casting die steel, it is big that it is carried out conventional shot peening technical difficulty, and effect is limited.

Summary of the invention

The purpose of this invention is to provide a kind of brand-new ball blasting method, be applied to aluminum alloy die-casting die steel surface and handle, with thermal fatigue property, the physical strength of raising mould, and the life-span and the reliability of raising mould.

The method that a kind of aluminum alloy die-casting die steel surface shot blasting strengthening of the present invention is handled is characterized in that having following technological process and step:

A. at first aluminum alloy die-casting die steel is heat-treated, under 1020 ℃ of conditions, carry out a vacuum hardening, under 560 ℃, 610 ℃, 560 ℃, carry out three tempering subsequently, make its Hardness Control in the 42-50HRC scope;

B. described die steel is placed on the Stage microscope of shotblast unit and carries out shot peening; Stage microscope at the uniform velocity rotates with the rotating speed of 3-5rad/min; The jet angle of shot-peening changes between 30 °-60 °; Spraying pressure is 0.3-0.6MPa; The particle diameter of cast steel bullet is 0.20-0.30mm; The bullet Hardness Control is between 44-52HRC; The shot-peening time is 20-60 minute.

The inventive method adopts the mechanism of above-mentioned technological process and acts on as described below:

Aluminum alloy die-casting die steel is adjusted to its hardness in the certain rigidity scope through quenching temper.Adopt three tempering process of quenching not only to make die steel obtain required hardness but also changed the stressed condition of mould.

Shot peening focuses on the hardness and the diameter of control base steel bullet, and the Stage microscope of placement mould at the uniform velocity rotates with certain speed in the shot-peening process, and spray angle also constantly changes.The Hardness Control of bullet is in the scope than the high 1-3HRC of die steel, if bullet hardness is lower than this scope, shot blasting effect is not obvious; If bullet hardness is higher than this scope, the bullet that hardness is high will damage die surface, influence die life.The bullet diameter is controlled in the scope of 0.20-0.30mm, does the homogeneity that not only can improve shot-peening like this; And, the mould at R angle is arranged particularly for complicated die, and can improve the shot-peening fraction of coverage, reduce damage to mould R angle region.In addition, the at the uniform velocity rotation of sample bench cooperates the variation of spray angle can make shot-peening more even.

Characteristics of the present invention and advantage are as follows:

Pill spraying surface reinforcing treatment process of the present invention, hardness, particle diameter, spraying pressure and direction by the control bullet can reach surface treatment effect preferably.Compare with the shot peening method of routine, shot-peening fraction of coverage height of the present invention is little to the mould damage; The die steel surface not only can obtain higher stress, and its effective stress layer depth also increases greatly; It is tiny a lot of that the die steel that handle without bead blasted surfaces on die steel surface after treatment, its heat fatigue cracking is wanted, and is netted disperse and distributes.The inventive method is by the life-span and the reliability that change and control die steel surface heat crackle forms, distribution improves mould.

Description of drawings

Fig. 1 is the synoptic diagram of the shotblast unit of the inventive method.

Among the figure: 1-mould, 2-Stage microscope, 3-motor, 4-bullet case, 5-air compressor, 6-nozzle.

Fig. 2 is through shot peening with without the change curve of the die steel surface compress residual stresses of shot peening.

Fig. 3 is the transmission electron microscope photo on the H13 steel surface before and after the shot-peening.

Wherein Fig. 3 (a) is the surface of shot-peening H13 steel not submicroscopic structure, and Fig. 3 (b) be the surperficial submicroscopic structure of shot-peening H13 steel.

Fig. 4 is shot peening die steel thermal fatigue test surface crack figure not.

Fig. 5 is shot peening die steel thermal fatigue test surface crack figure.

Embodiment

After now specific embodiments of the invention being described in.

Embodiment 1

Adopt aluminum alloy die-casting die steel H13 commonly used to do surperficial shot peening strengthening and handle, its technological process and step are as follows:

(1) at first the H13 steel is heat-treated, carry out a vacuum hardening under 1020 ℃ of conditions, carry out three tempering subsequently under 560 ℃, 610 ℃ and 560 ℃, its hardness is all adjusted to 47～48HRC;

(2) described die steel H13 is carried out surface grinding earlier, be placed on then on the Stage microscope of shotblast unit and carry out shot peening.Referring to Fig. 1, Fig. 1 is the synoptic diagram of shotblast unit.Die steel 1 is placed on the Stage microscope 2, is provided with a motor 3 below the Stage microscope 2, drive Stage microscope 2 and at the uniform velocity rotate with the rotating speed of 4rad/min; Simultaneously by air compressor 5 with the bullet force feed in the bullet case 4 to nozzle 6, between 30 °-60 °, constantly change and carry out the shot-peening action with jet angle by nozzle 6; Spraying pressure is 0.45MPa; Bullet is the cast steel bullet, and its particle diameter is 0.2-0.3mm; The bullet Hardness Control is at 48-49HRC; The shot-peening time is 30 minutes.

To doing to observe and detect as follows through the die steel of shot peening:

(1) after testing, the H13 steel after the shot peening, its shot-peening fraction of coverage reaches 200%.

(2) to the shot peening and the simultaneous test of the die steel H13 surface compress residual stresses of shot peening not: test-results is seen Fig. 2, Fig. 2 is the change curve of its surface compress residual stresses, as seen from the figure, die steel surface maximum residual stress reaches-600MPa, and the stress zone of influence reaches case depth 300 μ m places.

(3) transmission electron microscope observing on H13 steel surface before and after the shot-peening: observations is seen Fig. 3 (a) and the Fig. 3 (b) among Fig. 3; Fig. 3 (a) is the surface of shot-peening H13 steel not submicroscopic structure, and Fig. 3 (b) be the surperficial submicroscopic structure of shot-peening H13 steel.Steel surface a large amount of high density dislocations of generation and dislocation become cell structure after the shot peening.

(4) H13 die steel carries out the thermal fatigue simultaneous test respectively before and after the shot-peening: thermal fatigue test the results are shown in Figure 4 and Fig. 5.Fig. 4 makes surface crack figure after the thermal fatigue test for shot peening die steel not, and Fig. 5 is the surface crack figure after shot peening die steel is done thermal fatigue test.

The condition of thermal fatigue test is: maximum heating temperature is 700 ℃, and be 7.5s the cooling time of heat treatment process setting, and the cycle index that colds and heat succeed each other is 1200 times.Then steel is taken out, carry out pickling, scale removal; Observing its crackle then under the continuous zoom stereoscopic microscope compares.As seen from the figure, its heat fatigue cracking of steel after shot peening surface is tiny, and disperse is evenly distributed, and illustrates that shot peening has improved the thermal fatigue property of die steel.

Claims

1. the method handled of an aluminum alloy die-casting die steel surface shot blasting strengthening is characterized in that having following technological process and step:

A. at first aluminum alloy die-casting die steel is heat-treated, under 1020 ℃ of conditions, carry out a vacuum hardening, under 560 ℃, 610 ℃ and 560 ℃, carry out three tempering subsequently, make its Hardness Control in the 42-50HRC scope.

B. described die steel is placed on the Stage microscope of shotblast unit and carries out shot peening; Stage microscope at the uniform velocity rotates with the rotating speed of 3-5rad/min; The jet angle of shot-peening constantly changes between 30-60 °; Spraying pressure is 0.3-0.6Mpa; The particle diameter of cast steel bullet is 0.20-0.30mm; The bullet Hardness Control is between 44-52HRC; The shot-peening time is 20-60 minute.