TWI761714B - Welding process with controlling temperatures of welding pool and heat affected zone - Google Patents

Abstract

A welding process with controlling temperatures of welding pool and heat-affected zone (HAZ) includes the following steps. First, the process is fixing the welded part to a welding machine. Next, the process is welding the welded part in a circular arc path to form a welding pool, which subsequently solidifies to be a welding bead. Finally, the process is setting a temperature measuring instrument within a certain distance from the weld bead, controlling the welding process at a sampling rate. It intends to achieve the positive-negative ratio of the instantaneous temperature change rates, i.e. a difference between the two measured temperatures divided by the time difference, to be one, and the absolute value of the instantaneous temperature change rate over 250 ℃ per second. The invention is suitable for improving the weld microstructure of all the fusion welding processes, which can reduce not only the welding defects but also the nonuniform distribution of the grain orientation to improve the mechanical properties of the welds as a result.

Description

Welding process to control the temperature of the molten pool and heat affected zone

The present invention relates to a welding process, in particular to a welding process for controlling the temperature of the molten pool and the heat affected zone.

The conventional welding process is only suitable for the grain refinement and weld bead of the electromagnetic device used in arc welding processes such as Gas Tungsten Arc Welding (GTAW, Gas Tungsten Arc Welding) and Gas Metal Arc Welding (GMAW, Gas Metal Arc Welding). Defect improvement. This method cannot improve the segregation structure and grain isotropy in the weld bead, and cannot be used to improve the weld bead structure of non-magnetic arc laser weld bead.

In order to solve the above problems, a welding process that controls the temperature of the molten pool and the heat-affected zone is required. This process can produce instantaneous cooling and heating effects in the molten pool to refine the grains and reduce the proportion of the base metal integrated into the weld bead. That is, the dilution rate to avoid weld stress induced cracks. At the same time, the periodic change of the heat source position is used to avoid the fixed direction of the maximum temperature inclination of the weld bead, which causes the solid-liquid interface of the weld bead to advance in the same direction, so that the grains grow in the same direction, resulting in the directionality and composition of the weld bead. Homogeneity (formation of coarse segregation), which affects the mechanical properties of the weld bead.

The purpose of the present invention is to provide a welding process for controlling the temperature of the molten pool and the heat-affected zone, and a method for improving and controlling the weld bead structure suitable for all fusion welding processes, so as to refine the weld bead grains, reduce the segregation structure and disperse the grains directional distribution.

The present invention provides a welding process for controlling the temperature of the molten pool and the heat-affected zone in order to achieve the above object. First, a piece to be welded is fixed on a welding machine. Next, the parts to be welded are welded in a circular arc path to form a weld bead with a molten pool. Finally, a temperature measuring instrument is set within a specific distance from the weld bead, and the welding process is controlled at a temperature measuring rate of the temperature measuring instrument to achieve the difference between the two measured temperatures in the heat-affected zone The ratio of the positive and negative instantaneous temperature change rates divided by the time difference approaches 1, and the absolute value of the instantaneous temperature change rate of the difference between the two measured temperatures divided by the time difference exceeds 250°C per second.

Compared with the conventional welding process, the present invention has the following advantages: 1. Change the frequency and amplitude of the arc path according to the different materials to be welded, so as to control the temperature of the molten pool and the heat affected zone, so as to refine the weld bead structure, reduce the segregation structure, uniform grain orientation and reduce welding defects. benefit. 2. The present invention is applicable to the improvement of the weld bead structure in all fusion welding processes, which can not only reduce weld bead defects, but also promote the uniform distribution of grain orientation and improve the mechanical properties of the weld bead.

The present invention moves the welding heat source forward in a circular arc path, and sets the temperature control measurement value at a specific distance, such as within 2 mm from the welding bead, the temperature sampling rate needs to be more than 100 points per second, and the two measurements are calculated at high speed in real time. The temperature change rate is used to control the temperature change rate of positive and negative weld bead above the material transformation temperature of the weld bead and heat affected zone (stainless steel is above 800 degrees Celsius). above 250°C per second.

FIG. 1 shows a schematic diagram of the welding process for controlling the temperature of the molten pool and the heat affected zone according to the present invention. As shown in Fig. 1, the pretreatment before the welding process of the present invention needs to fix a piece to be welded on a fixture on a welding machine, then clean the grooved surface with alcohol, and then use argon welding with a DC negative electrode process for welding. The welding current is 180A. Under the condition that the distance between the electrode and the base metal is fixed (the voltage control is about 11V), a commercially available electromagnetic stirring module is used. For stainless steel, such as ER308L, the stirring frequency is 3 Hz. For nickel-based alloys, such as The stirring frequency of Alloy 52, Alloy 52M and Alloy 52MSS is 7Hz for welding. The parts to be welded can be barrels or various mechanical components.

The welding process for controlling the temperature of the molten pool and the heat-affected zone of the present invention is to weld the weld bead 90 , the welding heat source 23 advances along the direction A, and the arc path C is a circular arc path. The winding frequency of the welding heat source 23 is changed according to the material of the welding bead 90 , and a molten pool 92 will be formed on the welding bead 90 during welding. A temperature measuring instrument 34 is disposed in the heat-affected zone D within a certain distance, eg, within 2 mm from the edge of the weld bead 90 . The range of the heat affected zone D is determined by the material and size of the parts to be welded. The measurement rate of the temperature measuring instrument 34 can be set to more than 100 temperature values per second for effective control. The welding heat source 23 may be gas tungsten arc welding (GTAW, Gas Tungsten Arc Welding), gas metal arc welding (GMAW, Gas Metal Arc Welding), gas metal arc welding (GMAW, Gas Metal Arc Welding), laser welding (LAW) , Laser Welding). The temperature measuring instrument 34 is a thermocouple combined with a high-speed data recorder or a high-speed pyrometer. The arc path B in FIG. 1 is a commonly used arc path, and the welding heat source 23 performs welding along the direction A in the manner of the arc path B.

In the present invention, whether the welding bead 90 is heated by heating or cooling by temperature, it must be ensured that when the position of the heat affected zone D is in a temperature range above 800°C, the difference between the two measured temperatures is divided by the time difference. The positive and negative of the instantaneous temperature change rate The ratio can be close to 1:1. The temperature rise means that the welding heat source 23 is gradually approaching the welding position, and the welding bead 90 is in the welding state. Cooling means that the welding heat source 23 gradually leaves the welding position, and the welding bead 90 is in a cooling state. Among them, the optimal ratio of the instantaneous temperature change rate of the molten pool 92 during heating is positive:negative=2:1, and the optimal ratio of the instantaneous temperature change rate of the heat-affected zone D is positive:negative=1:1. The optimal ratio of the instantaneous temperature change rate of the molten pool 92 during cooling is positive:negative=1:2, and the optimal ratio of the instantaneous temperature change rate of the heat-affected zone D is positive:negative=1:1. In addition, the absolute value of the instantaneous temperature change rate of the difference between the two measured temperatures divided by the time difference, that is, the magnitude of the positive and negative temperature change rates must exceed 250°C per second, and the best is more than 300°C per second. The direction of the maximum temperature inclination of the weld pool of the weld bead 90 can be changed, which further refines the grains of the weld bead, reduces the segregation structure and disperses the directional distribution of the grains. Among them, the magnitude of the positive and negative temperature change rate mainly changes with the ratio of the temperature change rate, but the larger the better. The following examples illustrate all the actual temperature values in the welding process of the present invention. In the welding process, a High Speed Pyrometer is used to measure and control the temperature change with 100 values per second. , 52 temperature values are respectively 760 ℃, 765 ℃ and 762 ℃, then: 1. The temperature of the two measured values: The 50th and 51st temperature values in the first second are 760 ℃ and 765 ℃ respectively. 2. The difference between the two measured temperatures: the temperature difference between the 50th and 51st points in the first second is 5℃; the temperature difference between the 51st and 52nd points in the first second is -3℃. 3. The instantaneous temperature change rate of the difference between the two measured temperatures divided by the time difference: the time difference between the two temperature points is 0.01 seconds, and the temperature difference between the 50th and 51st points in the first second is divided by The time difference is 500°C per second, and the temperature difference between the 51st and 52nd points in the first second divided by the time difference is -300°C per second. 4. The positive and negative ratio of the instantaneous temperature change rate of the difference between the two measured temperatures divided by the time difference: After collecting the temperature data from 800 ℃ to the highest temperature, after calculation, there are 800 positive instantaneous temperature change rates, while the negative There are 400 instantaneous temperature change rates in total, so the positive and negative ratio of the instantaneous temperature change rate is 2:1. 5. The temperature rise means that the heat source gradually approaches the welding position and the weld bead is in the welding state. The optimal ratio of the instantaneous temperature change rate in the molten pool is positive:negative=2:1, and the optimal ratio of the instantaneous temperature change rate in the heat-affected zone at the same time is positive:negative=1:1. 6. Cooling means that the heat source gradually leaves the welding position, and the weld bead is in a cooling state. The optimal ratio of the instantaneous temperature change rate in the molten pool is positive:negative=1:2, and the optimal ratio of the instantaneous temperature change rate in the heat-affected zone is positive:negative=1:1. 7. The absolute value of the instantaneous temperature change rate of the difference between the two measured temperatures divided by the time difference, the temperature difference between the 50th and 51st points in the first second divided by the time difference is 500 ℃ per second , its absolute value is 500 °C per second; and the temperature difference between the 51st and 52nd points in the first second divided by the time difference is -300 °C per second, and its absolute value is 300 °C per second.

FIG. 2 shows a flow chart of the welding process for controlling the temperature of the molten pool and the heat affected zone according to the present invention. First, a piece to be welded is fixed on a welding machine, as shown in step S10. Next, a welding bead is formed by welding the to-be-welded member in a circular arc path, as shown in step S20. Finally, a temperature measuring instrument is set within a specific distance from the weld bead, and the welding process is controlled at a temperature measuring rate to achieve the difference between the two measured temperatures in the heat-affected zone divided by the time difference. The ratio of the instantaneous temperature change rate approaches 1:1 and the absolute value of the instantaneous temperature change rate of the difference between the two measured temperatures divided by the time difference exceeds 250° C. per second, as shown in step S30 .

The analysis results after the actual implementation of the welding process for controlling the temperature of the molten pool and the heat-affected zone of the present invention, Figure 3 shows the grain direction distribution of the cross-section of the CF8A duplex cast stainless steel weld bead (the reverse pole figure result of the back-trans electron scattering analysis) . In arc path B, the grains of the Wostian iron and the fertile iron are concentrated in the [001] direction. Figure 4 shows the phase distribution of the CF8A duplex cast stainless steel weld bead cross-section (the results of the microstructure phase analysis by back-trans electron scattering analysis). The iron phase of Wostian is white, and the iron phase of fertilizer grain is black. The ferrite iron in arc path B is relatively coarse. Figure 5 shows a secondary electron image of an intermediate pass of a nickel-based alloy Alloy 52MSS weld pass. The size of the segregation structure of the arc path B bead is significantly larger than that of the path C weld bead. Figure 6 shows the hardness distribution of the CF8A duplex cast stainless steel bead. The bead hardness of arc path C is slightly higher than that of arc path B. Figure 7 shows the intermediate pass average hardness of a nickel-based alloy weld bead. The bead hardness of arc path C is slightly higher than that of arc path B.

90: weld bead 92: Molten Pool C: arc path B: arc path D: heat affected zone 23: Welding heat source 34: Temperature measuring instrument

FIG. 1 shows a schematic diagram of the welding process for controlling the temperature of the molten pool and the heat affected zone according to the present invention. FIG. 2 shows a flow chart of the welding process for controlling the temperature of the molten pool and the heat affected zone according to the present invention. Figure 3 shows the grain direction distribution of the CF8A duplex cast stainless steel bead profile. Figure 4 shows the phase distribution of the CF8A duplex cast stainless steel weld bead profile. Figure 5 shows a secondary electron image of an intermediate pass of a nickel-based alloy Alloy 52MSS weld pass. Figure 6 shows the hardness distribution of the CF8A duplex cast stainless steel bead. Figure 7 shows the intermediate pass average hardness of a nickel-based alloy weld bead.

S10-S30: Welding process for controlling the temperature of the molten pool and heat affected zone

Claims (7)

A welding process for controlling the temperature of a molten pool and a heat-affected zone includes the following steps: fixing a piece to be welded on a welding machine; The weld bead of the pool; and a temperature measuring instrument is arranged within a specific distance from the weld bead, and the welding process is controlled above the material transformation temperature of the to-be-welded part under a temperature measuring rate of the temperature measuring instrument, so as to The ratio of the positive and negative instantaneous temperature change rates of the difference between the two measured temperatures divided by the time difference when the heat-affected zone is reached is close to 1, and the difference between the two measured temperatures divided by the time difference The instantaneous temperature change rate of The absolute value exceeds 250°C per second, wherein the temperature measurement rate is more than 100 temperature values per second. The welding process for controlling the temperature of the molten pool and the heat-affected zone according to claim 1, further comprising, using gas tungsten arc welding (GTAW, Gas Tungsten Arc Welding), gas metal arc welding (GMAW, Gas Metal Arc Welding), Gas metal arc welding (GMAW, Gas Metal Arc Welding) or laser welding (LAW, Laser Welding) are used as welding heat sources. The welding process for controlling the temperature of the molten pool and the heat-affected zone according to claim 1, further comprising: when the welding heat source is close to the weld bead, controlling the instantaneous temperature change ratio of the molten pool to be 2. The welding process for controlling the temperature of the molten pool and the heat-affected zone according to claim 1, further comprising: when the welding heat source leaves the weld bead, controlling the instantaneous temperature change ratio of the molten pool to be 0.5. The welding process for controlling the temperature of the molten pool and the heat-affected zone as claimed in claim 1, further comprises, using an electromagnetic stirring module, the stirring frequency for stainless steel is 3 Hz, and the stirring frequency for nickel-based alloys is 7 Hz for welding. The welding process for controlling the temperature of the molten pool and the heat-affected zone according to claim 1, wherein the specific distance is the heat-affected zone, and the range of the heat-affected zone is determined by the material and size of the parts to be welded. The welding process for controlling the temperature of the molten pool and the heat-affected zone according to claim 1, wherein the temperature measuring instrument is a thermocouple combined with a high-speed data recorder or a high-speed pyrometer.

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