SU1636462A1 - Method of weld joints thermomechanical treatment - Google Patents

Abstract

The invention relates to the thermomechanical treatment of welded joints and can be used in the production of sheet metal from martensitic stainless steels that undergo quenching during the welding process. The purpose of the invention is to reduce the duration of the process and increase plasticity. The method includes local heating to 720 - 750 ° C, compression of the seam by punches with radii R

Description

(Ls

The invention relates to the field of thermomechanical treatment of welded joints and can be used in the manufacture of rolled sheets of chromium stainless steels of the martensitic class, which undergo quenching during the welding process.

The aim of the invention is to reduce the duration of the process and increase the ductility of welded joints.

Figure 1 shows the curves of C from T; Fig. 2 is a flow chart of the method.

The method of thermomechanical processing includes the operations of local heating, pulse revolving and subsequent tempering of the weld metal and heat affected zone. In the process of deforming the treated zone, the curve of the cavity with radius R WV (8 - 10) Ј, where is the thickness of the welded metal, and the compression of the molds by the value of (0.17 - 0.2) oЈ along the recess axis with a deformation rate} of not less than 22 mm / s, the heating temperature is set in the interval 720 - 750 ° before the compression C, and the temperature of the subsequent vacation is deformed as specified Nomu zone mode is maintained in accordance with the dependence

And l p meni t

 T (M

WITH)

9

when holding time (70 - 90) o and speed

 - vi silt

cooling 5 - 7 ° C / s, where Tmn is the temperature of the onset of martensitic transformation

31

Scheni, C - carbon content in this steel.

A decrease in the deformation temperature below 600-6509C cannot serve as a condition for obtaining plastic structures during metal compression. Increasing iagreva to 780

temperature

800 C in steels x containing 0.2–0.8% C, quenching structures in the weld, and c.t. not completely eliminated, which requires a further increase in the holding time during tempering. At a heating temperature of 600-700 ° C, large internal stresses in the metal of the compound remain, which often causes microcrack nucleation and, in some cases, the appearance of tears in the edge regions of the joint.

With decreasing radius R. (8-10) it is dangerous not to embrace the process of deformation of the areas of the heat-affected zone that have an increased hardness. And an increase in the radius R (8 - - 10) is impractical, since with an increase in the treatment area, it is required to significantly increase the crimping mechanism's power and involve metal parts that are not subject to embrittlement to the crimping process, as well as unproductively increase the power to heat the metal lying outside embrittlement.

If the amount of compression deformation along the recess axis for martensitic high-chromium steels is less than 0.17 from the initial thickness of the metal being welded, then the plasticity of the metal is no more than 55–60% of the base metal level with all the other process parameters. Starting from about a reduction area of at least 0.17, a monotonous increase in plasticity with an increase in compression makes a qualitative change in the increase in plasticity of a deformable metal. When compressed within (0.17-0.20) 5, the metal has plasticity and viscosity already about 70% of the properties of the base metal. A further increase in compression does not significantly affect the increase in plasticity — a linear relationship is again observed between deformation and plasticity increase (starting with a reduction of 30%, it remains almost unchanged, and with a further increase in deformation, the opposite effect occurs due to the work hardening). When this should be noted that the achievement of pain

The degree of reduction causes certain technical difficulties.

In order to determine the limits of the strain rate during the TMT process, the range of strain rates was varied from 15 to 250 mm / s. The results of the experiments show that an increase in this parameter above the established limit does not provide a noticeable increase in plasticity. The graph for determining the tempering temperature (Fig. 1) in a simplified form shows the optimal values of Tetp, determined more precisely by the dependencies:

off

 TMN (1

9)

2 b

0

five

0

five

0

five

0

five

There is an area of permissible deviations from this temperature of + 20 ° C.

The magnitude of the exposure is determined by the initial thickness of the product and satisfies the dependencies

about

Where

Sturn - (60 - 90),

thickness of the metal being welded, mm.

An increase in the exposure is impractical, since the reduction of residual stresses (measurements by X-ray diffraction) has time to occur within a specified period of time. When reducing the exposure time, the residual stresses do not have time to relax. If the cooling is delayed for a while at a temperature below the austenite, which remains unchanged when cooled to this temperature, it becomes more stable. And residual austenite, as a softer component, lowers hardness., Fatigue limit, and elastic limit of steel. Similar stabilization of austenite has a very favorable effect on the metal structure. The amount of residual austenite is greatly affected by the cooling rate below TMI (, with slower cooling, the amount of residual austenite increases.

The cooling rate of the treated metal after tempering was established experimentally, satisfying the amount of residual austenite in the structure in the range of 4-6. This rate is a cooling interval of 5-7 ° C per second. At a higher cooling rate, new thermal stresses are generated, which are identified on the radiographs as residual. With a decrease in the cooling rate of less than 5 ° C / s, the amount of residual austenite increases (more than 8%), which, under unfavorable conditions of the heat treatment mode, causes a decrease in ductility.

The diagram (figure 2) shows the punches 1, the welded joint 2 and the seam 3.

Example. Characteristic of hardenable stainless steels with a carbon content of 0.6–0.7% st.65X13 4 mm thick, used for cutting tools, are used as the metal being welded.

Based on the thickness of the metal, the radius of the punch is chosen for surface treatment. Using the dependence R (8-10) o, take a radius of 36 mm.

The process of thermal mechanical processing begins with heating the weld zone (for example, by induction) to 750 ° C. Then the heated metal is subjected to impact compression by punches having a surface radius of 36 mm, with a deformation rate of 22 mm / s, and a residual amount of reduction at the site of the seam and heat-affected zone corresponding to 0.20 or 0.8 mm.

After the operation of the high-temperature reduction, low-temperature tempering of the deformed metal is required. For this, an optimum tempering temperature is selected in accordance with the dependence

Torn + С / 2) Substituting the T value (tabular data) and the carbon content in steel C {%), the optimum tempering temperature T is found.-345 ° C (J50 ° C).

To simplify the search for tempering temperatures, generalized results are given on the choice of martensite points and their corresponding optimum tempering temperatures depending on the carbon content of the steel.

The temporal time delay during tempering corresponds to the empirical dependence

tOTn (70 -90) Ј

and is chosen to be 300 seconds. The cooling rate after tempering is also regulated and corresponds to l 5 C / s.

Claims (1)

Invention Formula The method of thermomechanical treatment of welded joints. Mostly from high-chromium stainless. steels of the martensitic class with a carbon content of 0.2-0.8%, including local heating to a given temperature, plastic deformation of the welds and tempering, characterized in that, in order to shorten the process time and increase ductility, heating is carried out to 720 - 750 ° С, 0 deformation is performed by crimping punches with radii R (8 - 10) ff, where about the thickness of the metal being welded, mm, by the value (0-, 17 - 0.20) about with a speed of at least 22 mm / s , and tempering is carried out at a temperature Totp, determined by the dependence TotO TMH where T W (j is the temperature of the onset of the marten – Qsite transformation; C is the carbon content in steel, with an exposure for a period of time t OTL five (J 1 f I (70 - 90) o and a cooling rate of 5 - 79 ° / s. WO 0.1 0.2 0.3. OM 0.5 0.6 0.7 03 C,% 7