CN103105477A - Method for predicting forge crack initiation of forged steel - Google Patents

Abstract

The invention discloses a method for predicting forging crack initiation of forged steel, which belongs to the technical field of forging technology. The characteristics are: by doing high-temperature tensile experiments under different temperature and strain rate conditions, the flow stress curve of the material, crack initiation strain and its corresponding diameter value are obtained; using finite element software to simulate high-temperature tensile tests under different temperature and strain rate conditions Based on the critical damage value, the basic forging process is simulated by finite element method to obtain the critical deformation of forging; the critical deformation data verified by the forging reduction experiment is drawn to draw the critical deformation surface. All points below the surface are points where no cracks are initiated, all points above the surface are points where cracks are initiated, and all points on the surface are critical points. The advantage is that a simple and convenient method can be used to determine the amount of deformation that does not cause cracks in the forging during forging.

Description

A method for predicting forging crack initiation in as-forged steel

technical field

The invention belongs to the technical field of forging technology, and in particular relates to a method for predicting the initiation of forging cracks in forged steel.

Background technique

At present, there are two ways to solve forging cracks at home and abroad: one is to find the cause of the cracks after the forging process produces cracks in production, and to solve the specific reasons instead of predicting the forging cracks before they are formed. , which brings great economic losses to factories and enterprises; the other is theoretical research, which is to establish a fracture criterion, obtain a fracture damage factor based on the fracture criterion, and use the damage factor to predict the occurrence of cracks, but this method It has poor operability in actual production and cannot be applied in actual forging process.

Contents of the invention

The purpose of the present invention is to provide a method for predicting the initiation of forging cracks in forged steel under different temperature and strain rate conditions in order to provide a basis for formulating a reasonable forging process in view of the shortcomings of the prior art.

The object of the invention is achieved in that it is characterized in that the implementation steps are:

(1) Do material performance experiments: conduct material performance experiments according to actual deformation conditions, and obtain material flow stress curves.

(2) Do high-temperature tensile test: take the forging temperature range and strain rate range of steel, do high-temperature tensile test on a thermal simulator, stretch until the sample breaks, and obtain the true stress-true stress under different temperature and strain rate conditions. For the strain curve, read the peak strain, which is the crack initiation strain.

(3) Determination of the diameter of the sample corresponding to the crack initiation strain: do a high-temperature tensile test under the same deformation condition on a thermal simulator, stretch until the crack initiation strain stops, and then measure the minimum cross-sectional diameter of the necking area of the sample. The value is the diameter value corresponding to the crack initiation strain.

(4) Finite element simulation: input the flow stress curve into the finite element software, simulate the high temperature stretching process under different temperature and strain rate conditions through the finite element software, and simulate stretching to the diameter corresponding to the diameter of the sample and the crack initiation strain Similarly, at this time, read the damage value corresponding to the center point of the sample from the simulation software, and this damage value is the critical damage value for crack initiation.

(5) Determination of the critical deformation of forging: according to the critical damage value of crack initiation, simulate the actual forging basic process of upsetting and elongation on the flat anvil, conical anvil and spherical anvil respectively, and obtain different anvil shapes and different deformation conditions. Forging critical deformation.

(6) Verification of the critical deformation of forging: the critical deformation is verified by forging reduction experiments under different anvil shapes and different deformation conditions to ensure that the critical deformation is correct and reliable.

(7) Drawing of the critical deformation surface: use drawing software to draw the critical deformation surface under different anvil shapes and different deformation conditions during upsetting and elongation, as shown in Figure 1.

(8) Prediction of forging crack initiation: According to the critical deformation surface diagram, all points below the critical deformation surface are safe points, and no cracks will initiate at this point; all points above the critical deformation surface are crack initiation points; all points on the surface are critical points.

The advantages and positive effects of the present invention are: the method is simple and convenient to apply, and has good operability in factories and enterprises, as long as the corresponding deformation is determined according to the given deformation conditions and corresponding to the critical deformation diagram under the corresponding conditions can. This method can well predict the initiation of steel cracks in the forging process, thereby avoiding cracks in the forging process, which provides a reference for formulating a reasonable forging process, brings great economic benefits to enterprises, and has great application prospects.

Description of drawings

Fig. 1 is a surface diagram of the critical deformation amount of the present invention.

Fig. 2 is the surface diagram of the critical deformation of 316LN steel when the temperature is 900℃-1250℃ and the strain rate is 0.005s ^-1 -1s ^-1 flat anvil upsetting.

A in Figure 1 and Figure 2 represents the critical deformation; B represents the strain rate; T represents the temperature.

Detailed ways

Taking the upsetting of 316LN austenitic stainless steel flat anvil as an example, the deformation conditions are: temperature: 900°C-1250°C, strain rate: 0.005s ^-1 -1s ^-1 , and the critical deformation surface is obtained according to the implementation steps of the method of the present invention. as shown in picture 2.

When formulating the upsetting process of 316LN steel flat anvil, firstly, according to the combination of temperature and strain rate, corresponding to Figure 2, the critical deformation under this condition is determined, and the deformation during actual upsetting should be less than the critical deformation. For example: To determine the critical deformation of upsetting under the condition of temperature 1200 ℃ and strain rate 0.005s ^-1 , corresponding to Figure 2, it can be seen that the critical deformation value under this condition is 0.58, so the upsetting deformation under this condition The amount should be less than 58%. If it is greater than 58%, cracks will initiate on the surface of the forging.

Claims (1)

1. a kind of method for predicting the germinating of forged steel forge crack, it is characterised in that implementation steps are as follows：

（1）Do material property experiment：Material property experiment is done according to practical distortion condition, material flowing deformation stress curve is obtained；

（2）Do tensile test at high temperature：The forging range and strain rate scope of steel are taken, tensile test at high temperature is done on thermal simulation machine, sample fracture is stretched to, the true stress-true strain curve under the conditions of different temperatures and strain rate is obtained, peak strain is read, the strain is exactly crack initiation strain；

（3）The determination of crack initiation strain correspondence specimen finish：The tensile test at high temperature under same deformation condition is done on thermal simulation machine again, crack initiation strain stopping is stretched to, sample constriction smallest cross-sectional diameter is then measured, the diameter value is exactly that crack initiation strains corresponding diameter value；

（4）Finite element modelling：Flow stress plots are inputted in finite element software, the drawing by high temperature process under the conditions of different temperatures and strain rate is simulated by finite element software, it is identical that simulation is stretched to specimen finish diameter corresponding with crack initiation strain, now, the corresponding impairment value of sample central point is read from simulation softward, this impairment value is exactly the critical damage value of crack initiation；

（5）Forge the determination of critical strain amount：According to crack initiation critical damage value, actual forging basic working procedure jumping-up and pulling are simulated on flat anvil, taper anvil and spherical anvil etc. respectively, the forging critical strain amount under the conditions of different anvil shapes, different distortion is obtained；

（6）Forge the checking of critical strain amount：Critical strain amount is verified by the forging small scale test under the conditions of different anvil shapes, different distortion, to ensure the correct reliability of critical strain amount；

（7）The drafting of critical strain amount curved surface：Using mapping software, critical strain amount curved surface when drawing jumping-up with pulling under the conditions of different anvil shapes, different distortion；

（8）The prediction of forge crack germinating：According to critical strain amount surface chart, all points below critical strain amount curved surface are all safe points, and this puts not crack initiation；All points above critical strain amount curved surface are all the points of crack initiation；All points on curved surface are critical points.

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