Low-carbon microalloyed steel high-heat input weldability evaluation method based on flux-cored wire
阅读说明：本技术 基于药芯焊丝的低碳微合金钢高热输入焊接性评估方法 (Low-carbon microalloyed steel high-heat input weldability evaluation method based on flux-cored wire ) 是由 刘硕 于 2020-05-27 设计创作，主要内容包括：本发明涉及一种基于药芯焊丝的低碳微合金钢高热输入焊接性评估方法,其步骤依次包括：选用试验板为低碳微合金钢板；选用直径为1.2mm的气体保护药芯焊丝；所述一对试验板进行平焊位置对接焊,其坡口形式为正面为一侧带直边的V型坡口,正面坡口的直边侧底部带圆弧倒角,背面为V型坡口并设置陶瓷衬垫,当钢板厚度t＞25mm时,正面的坡口面向外偏折构成双V型坡口；采用熔化极气体保护焊接的方式对试验板进行焊接,热输入为3.0～4.0kJ/mm；完成焊接后,观察和检测焊接接头裂纹倾向以评估材料工艺焊接性,并通过焊接接头力学性能检测以评估材料使用焊接性。本发明兼顾工艺焊接性和使用焊接性评估需求,对不同领域使用的低碳微合金钢焊接性评估具有普适性。(The invention relates to a method for evaluating the high-heat input weldability of low-carbon microalloy steel based on a flux-cored wire, which sequentially comprises the following steps: selecting a test plate as a low-carbon microalloy steel plate; selecting a gas shielded flux-cored wire with the diameter of 1.2 mm; the pair of test plates are subjected to butt welding at flat welding positions, the groove form is a V-shaped groove with a straight edge on one side, the bottom of the straight edge side of the groove on the front side is provided with an arc chamfer, the back side is a V-shaped groove and is provided with a ceramic liner, and when the thickness t of the steel plate is more than 25mm, the groove face on the front side deflects outwards to form a double V-shaped groove; welding the test plate by adopting a gas metal arc welding mode, wherein the heat input is 3.0-4.0 kJ/mm; after welding is completed, the crack tendency of the welding joint is observed and detected to evaluate the process weldability of the material, and the mechanical property detection of the welding joint is used to evaluate the service weldability of the material. The method gives consideration to both the requirements of process weldability and use weldability evaluation, and has universality for evaluation of the weldability of the low-carbon micro-alloy steel used in different fields.)
1. A method for evaluating the high heat input weldability of low-carbon microalloyed steel based on a flux-cored wire is characterized by comprising the following steps: the method comprises the following steps:
selecting a test plate as a low-carbon microalloy steel plate;
selecting a gas shielded flux-cored wire with the diameter of 1.2 mm;
step three, butt welding the flat welding positions of the pair of test plates, wherein the groove form is as follows: the front surface of the test plate is a V-shaped groove with a straight edge on one side, an angle alpha is formed between a groove opening surface and the central axis of the groove, the bottom of the straight edge side of the groove on the front surface is provided with an arc chamfer, one end of an arc is vertical to the straight edge, the other end of the arc is tangent to the straight edge, the back surface of the groove is a V-shaped groove, an angle theta is formed between the groove opening surface and the central axis of the groove, a ceramic gasket is arranged on the back surface of the groove, wherein alpha is 50-65 degrees, theta is 40-60 degrees, the minimum clearance a of the test plate is 4-7 mm, the height b of the V-shaped groove on the back surface is 2-3.5 mm, and the radius R of the arc is 3-8 mm; when the thickness t of the steel plate is larger than 25mm, the front bevel face deflects outwards and forms an angle beta with the central axis of the bevel to form a double V-shaped bevel, wherein the angle beta is 15-35 degrees, and the height c of the lower bevel and the thickness t of the steel plate satisfy the relation: t is 1/3 and c is 3/5;
step four, welding the test board in a consumable electrode gas shielded welding mode, wherein: the protective gas is a mixed gas of argon and carbon dioxide; the root welding adopts ceramic liner auxiliary forming; the welding technological parameters used for root welding and filling cover surface welding are as follows: the welding heat input E is 3.0-4.0 kJ/mm; the welding current is 260-320A, the welding voltage is 26-31V, the welding speed is 110-140 mm/min, and the combination of the welding current, the welding voltage and the welding speed can be matched with the welding heat input value required by the test on the premise of ensuring the welding seam forming quality; the swing width of the welding gun is within 3-5 mm from the edge of the groove; in the welding process, an included angle delta formed between a welding gun and the straight side of the groove is 3-25 degrees along the width direction of the groove;
and step five, obtaining a welding joint after welding, observing and detecting the crack tendency of the welding joint to evaluate the technological weldability of the material, and evaluating the service weldability of the material through the mechanical property detection of the welding joint.
2. The method for evaluating the high heat input weldability of low-carbon microalloyed steel based on flux cored wire as recited in claim 1, wherein: and in the fifth step, the mechanical property detection comprises the detection of the low-temperature impact and the fracture toughness of the coarse crystal area of the welding heat affected zone adjacent to the single-side straight-edge fusion line.
3. The method for evaluating the high heat input weldability of low carbon microalloyed steel based on flux cored wire as recited in claim 1 or 2, characterized in that: and an arc-shaped groove is formed in the back of the ceramic liner, which is opposite to the groove.
4. The method for evaluating the high heat input weldability of low carbon microalloyed steel based on flux cored wire as recited in claim 1 or 2, characterized in that: and the swing path of the welding gun in the fourth step is zigzag, the time of the welding gun staying on the straight side of the groove is 50-150 ms, and the time of the welding gun staying on the oblique side of the groove is 30-80 ms.
5. The method for evaluating the high heat input weldability of low carbon microalloyed steel based on flux cored wire as recited in claim 1 or 2, characterized in that: the protective gas in the fourth step is the mixed gas of argon and carbon dioxide, and the mixing ratio is Ar to CO2The gas flow rate is 20-27L/min when the ratio is 80: 20.
Technical Field
The invention relates to a microalloy steel welding technology, in particular to a method for evaluating the high heat input weldability of low-carbon microalloy steel based on a gas shielded flux-cored wire.
Background
For an important engineering structure using low-carbon microalloy steel, welding is a key process of field installation and construction, the welding quality and efficiency also determine the quality and efficiency of an engineering project, and the quality of the field weldability of the low-carbon microalloy steel material directly influences the quality and safety service of a welded joint. Generally, the weldability of a material includes process weldability, which mainly refers to the ability to avoid welding defect problems (including various types of welding crack sensitivity) and obtain a continuous and complete welding joint during welding, and use weldability, which mainly refers to the use properties (including mechanical properties such as strength, plasticity, toughness and the like) of the welding joint.
Recently, foreign high-grade pipeline pipe users put forward pipeline steel pipe field weldability evaluation requirements under certain welding heat input conditions, including process weldability and use weldability, particularly the welding heat affected zone coarse grain zone (CGHAZ) which is the weakest theoretically is required to be located at the test position of low-temperature impact and fracture toughness of a welded joint, and therefore embrittlement tendency of materials under certain welding heat input conditions is evaluated systematically. Here, for low-carbon microalloy pipeline steel with a certain specification, welding heat input has important influence on solid-state phase change and microstructure evolution of a welding joint, and further influences integral embrittlement and service safety of the joint. Therefore, low carbon microalloyed pipeline steel tends to exhibit different weldability under different welding heat input conditions.
At present, many methods for evaluating weldability, i.e. weld crack sensitivity, of a steel material process are available, such as: the ISO17642-2 standard provides a TEKKEN test for evaluating the cold crack sensitivity of a plate, which is similar to the oblique Y-shaped groove welding crack test method described in GB 4675.1, welding of a small-scale test welding seam is carried out under a high constraint condition, so that the cold crack sensitivity of a material under a certain welding condition is evaluated, however, the constraint condition of the test method is too harsh, and the test welding seam is a single welding seam with an irregular shape, so that high welding residual stress exists, and cold cracks are more favorably induced. GB/T13817 provides a rigidity restraint welding crack test method, which completely fixes a test steel plate on a bottom plate with a very large thickness, residual stress cannot be released in the welding process, cold cracks are easily induced in a joint area, the method is also conservative, and the welding joint form is also greatly different from the common joint form of a low-carbon microalloy steel structure, and has no direct field construction welding guidance function. An improved oblique Y-shaped groove welding crack sensitivity test specimen disclosed in Chinese patent 201611208203.5 and a manufacturing method thereof, and a constrained weld manufacturing method for an oblique Y-shaped groove welding crack test disclosed in Chinese patent 201510012348.7 can only solve the problem of indirect evaluation of weldability under certain conditions. The above-mentioned patent and non-patent documents both focus on indirect evaluation of process weldability, and have a certain referential significance for on-site welding construction of low-carbon microalloy steel structures, but have no direct guidance, and mainly the use weldability cannot be considered, and the design form of joints and implementation details of welding process methods are greatly different from the construction welding conditions of the mainstream low-carbon microalloy steel structures.
Chinese patent 201410516996.1 discloses a method for welding steel plates for ocean platforms, which adopts a general K-shaped groove form, if the implementation process of the welding process is properly controlled, a fusion line with certain straightness on one side can be obtained after welding, and the requirements of CGHAZ position impact and fracture toughness sampling are met, but the method aims at the specific product structure of a super-thick plate (such as 50-150 mm), has no universality in various industrial fields, and does not relate to the straightness guarantee measure of the fusion line with straight edges on one side, the straightness of the fusion line after welding is easily guaranteed when the steel plate is thick, and the straightness of the fusion line is easily damaged by a welding pool when the steel plate is thin. Chinese patent 201510385434.2 discloses a CTOD test method for a large thick plate welding repair joint, and chinese patent 201510605044.1 discloses a welding repair CTOD test method, both of which have certain characteristics of a single-side straight-edge weld line even when the plate thickness is thick, but both of which belong to repair processing measures after defects are found in a finished product welded part, and cannot meet the requirements of low-carbon microalloyed steel with universality in a certain welding heat input range for simultaneously evaluating technological weldability and using weldability.
Disclosure of Invention
The invention aims to provide a method for evaluating the high-heat input weldability of low-carbon microalloy steel based on a gas shielded flux-cored wire, which is characterized in that a welding joint with a good straightness of a single-side fusion line is obtained by optimally designing the groove form of a single-side straight edge, constructing welding process parameter combinations, welding gun inclination angles, welding process quality control and the like under the condition of high heat input, and the process weldability and the use weldability of materials are evaluated by observing and detecting the welding joint.
The invention is realized by the following steps:
a method for evaluating the high-heat-input weldability of low-carbon microalloyed steel based on a flux-cored wire comprises the following steps:
selecting a test plate as a low-carbon microalloy steel plate;
selecting a gas shielded flux-cored wire with the diameter of 1.2 mm;
step three, butt welding the flat welding positions of the pair of test plates, wherein the groove form is as follows: the front surface of the test plate is a V-shaped groove with a straight edge on one side, an angle alpha is formed between a groove opening surface and the central axis of the groove, the bottom of the straight edge side of the groove on the front surface is provided with an arc chamfer, one end of an arc is vertical to the straight edge, the other end of the arc is tangent to the straight edge, the back surface of the groove is a V-shaped groove, an angle theta is formed between the groove opening surface and the central axis of the groove, a ceramic gasket is arranged on the back surface of the groove, wherein alpha is 50-65 degrees, theta is 40-60 degrees, the minimum clearance a of the test plate is 4-7 mm, the height b of the V-shaped groove on the back surface is 2-3.5 mm, and the radius R of the arc is 3-8 mm; when the thickness t of the steel plate is larger than 25mm, the front bevel face deflects outwards and forms an angle beta with the central axis of the bevel to form a double V-shaped bevel, wherein the angle beta is 15-35 degrees, and the height c of the lower bevel and the thickness t of the steel plate satisfy the relation: t is 1/3 and c is 3/5;
step four, welding the test board in a consumable electrode gas shielded welding mode, wherein: the protective gas is a mixed gas of argon and carbon dioxide; the root welding adopts ceramic liner auxiliary forming; the welding technological parameters used for root welding and filling cover surface welding are as follows: the welding heat input E is 3.0-4.0 kJ/mm; the welding current is 260-320A, the welding voltage is 26-31V, the welding speed is 110-140 mm/min, and the combination of the welding current, the welding voltage and the welding speed can be matched with the welding heat input value required by the test on the premise of ensuring the welding seam forming quality; the swing width of the welding gun is within 3-5 mm from the edge of the groove; in the welding process, an included angle delta formed between a welding gun and the straight side of the groove is 3-25 degrees along the width direction of the groove;
and step five, obtaining a welding joint after welding, observing and detecting the crack tendency of the welding joint to evaluate the technological weldability of the material, and evaluating the service weldability of the material through the mechanical property detection of the welding joint.
And in the fifth step, the mechanical property detection comprises the detection of the low-temperature impact and the fracture toughness of the coarse crystal area of the welding heat affected zone adjacent to the single-side straight-edge fusion line.
And an arc-shaped groove is formed in the back of the ceramic liner, which is opposite to the groove.
And the swing path of the welding gun in the fourth step is zigzag, the time of the welding gun staying on the straight side of the groove is 50-150 ms, and the time of the welding gun staying on the oblique side of the groove is 30-80 ms.
The protective gas in the fourth step is the mixed gas of argon and carbon dioxide, and the mixing ratio is Ar to CO2The gas flow rate is 20-27L/min when the ratio is 80: 20.
The low-carbon microalloy steel high heat input weldability evaluation method based on the flux-cored wire, firstly, for the condition that the high heat input is 3.0-4.0 kJ/mm, the method actually exceeds the optimal application range of the 1.2mm thin-diameter gas shielded flux-cored wire, but because of good operability and heat input adaptability of the gas shielded flux-cored wire, the stability and the forming quality of the welding process can still be ensured under the condition of higher heat input, and the method is used as an alternative welding method different from field construction to carry out weldability evaluation test under the condition of high heat input, has the advantages of convenience in implementation, flexibility in operation, low requirement on hardware equipment, low implementation cost and good reproducibility, and has direct guiding significance for weldability evaluation in different fields. Secondly, a welding joint with a single-side weld line with good straightness can be obtained by optimally designing a special single-side straight-edge welding joint groove form and constructing and matching a scientific and reasonable welding process parameter combination (comprising welding current, welding voltage, welding speed and welding gun swing mode), a welding gun inclination angle and welding process quality control, and the single-side straight-edge groove form is matched with the back surface to add a ceramic liner to assist in forming root welding, so that the defect that the penetration capacity of a gas shielded flux-cored wire is weak can be overcome, the advantages of high welding current density and high heat capacity of the flux-cored wire are fully utilized, the back surface weld is ensured to be uniformly spread and formed, and the proper groove width and welding gun swing can ensure the quality of straight-edge fusion.
The present invention can evaluate the technological weldability of the material by observing and detecting the crack tendency of the welded joint. Through the detection of mechanical properties of a welding joint, particularly the detection of low-temperature impact and fracture toughness of a coarse grain zone (CGHAZ) of a welding heat affected zone adjacent to a single-side straight-edge fusion line, and the straightness of the single-side straight-edge fusion line can ensure that 80% of impact toughness sampling notch grooves are positioned in the CGHAZ, the use weldability of the material under the condition of high heat input can be evaluated, namely, the evaluation requirements of process weldability and use weldability are considered at the same time, and the method has universality for the evaluation of the weldability of low-carbon microalloy steel used in different industries and fields in a given high welding heat input range. Meanwhile, the characteristic of the single-side straight-edge fusion line ensures that the CGHAZ which is the weakest theoretically is positioned at the test position accurately in the impact toughness and fracture toughness sampling process, and compared with the actual welding condition of field installation construction, the invention has high safety margin and has important reference value for field safety construction and operation.
Compared with the prior art, the invention has the following beneficial effects: the method has universal applicability, can simultaneously meet the evaluation requirements of process weldability and use weldability under the condition of high heat input, and has the advantages of convenient implementation, flexible operation, low requirement on hardware equipment, low implementation cost and good reproducibility.
Drawings
FIG. 1 is a schematic structural diagram of a groove form of a welding joint with a steel plate thickness of more than 25mm according to the method for evaluating the high heat input weldability of low-carbon micro-alloy steel based on a flux-cored wire;
FIG. 2 is a schematic structural view of the present invention in the form of a weld joint groove having a steel plate thickness of not more than 25 mm;
FIG. 3 is a schematic view of the inclination angle of the welding gun of the present invention in the direction along the width of the bevel;
FIG. 4 is a schematic diagram of a specific weld joint groove form employed by an embodiment of the present invention.
In the figure, 1 test panel, 2 welding torch.
Detailed Description
The invention is further described with reference to the following figures and specific examples.
Referring to fig. 1 to 3, a method for evaluating the high heat input weldability of low-carbon microalloyed steel based on a flux-cored wire, mainly aiming at the occasions with a high welding heat input range of 3.0 to 4.0kJ/mm involved in various arc welding processes in various industrial fields, applying a gas shielded flux-cored wire with the diameter of 1.2mm, combining the characteristics of a welding arc and a molten pool under the condition of high heat input, and constructing and matching a welding process parameter combination (including welding current, welding voltage, welding speed and welding gun swinging mode), a welding gun inclination angle and welding process quality control, particularly a weld line straightness control technology and the like by optimally designing a groove form of a single-side straight-edge welding joint suitable for the welding conditions to obtain a welding joint with good quality, wherein the method comprises the following steps:
step one, selecting a test plate 1 as a low-carbon microalloy steel plate.
And step two, selecting a gas shielded flux-cored wire with the diameter of 1.2 mm.
Step three, performing butt welding on the flat welding positions of the pair of test plates 1:
referring to fig. 1, when the thickness t of the steel plate is more than 25mm, the groove form is as follows: the front is the two V type grooves of one side banding straight flange, the bevel face of downside and groove central axis angulation alpha, the bevel face of downside outwards deflects and with groove central axis angulation beta, the straight flange side bottom of front groove takes the circular arc chamfer, the one end of circular arc is perpendicular with the straight flange, the other end of circular arc is tangent with the straight flange, the back is V type groove and its bevel face and groove central axis angulation theta, and the groove back sets up ceramic liner, wherein, alpha equals 50 ~ 65, beta equals 15 ~ 35, theta equals 40 ~ 60, the minimum clearance of test plate a is 4 ~ 7mm, the V type groove height b of back is 2 ~ 3.5mm, downside groove height c and steel sheet thickness t satisfy the relational expression: t is not less than 1/3, c is not less than t is 3/5, and the radius R of the circular arc is 3-8 mm.
Referring to fig. 2, when the thickness t of the steel plate is less than or equal to 25mm, the groove form is as follows: the front surface of the V-shaped groove is provided with a V-shaped groove with a straight edge on one side, an angle alpha is formed between a groove opening surface and the central axis of the groove, the bottom of the straight edge side of the groove on the front surface is provided with an arc chamfer, one end of an arc is vertical to the straight edge, the other end of the arc is tangent to the straight edge, the back surface of the groove is provided with a V-shaped groove, an angle theta is formed between the groove opening surface and the central axis of the groove, a ceramic gasket is arranged on the back surface of the groove, wherein alpha is 50-65 degrees, theta is 40-60 degrees, the minimum clearance a of the test plate is 4-7 mm, the height b of the V-shaped groove on the back surface of the groove is 2-3.5 mm, and the radius R of the arc is 3-8 mm.
By adopting the optimally designed welding joint groove form, the design requirement of a straight edge on a single side is ensured, and meanwhile, the auxiliary forming root welding method of adding the ceramic liner on the back surface of the groove is adopted, so that the defect of weaker penetration capability of the gas shielded flux-cored wire can be overcome, and the advantages of large welding current density and large heat capacity of the gas shielded flux-cored wire are fully utilized, so that the welding heat input of the gas shielded flux-cored wire with the diameter of 1.2mm can also reach a higher numerical range of 3.0-4.0 kJ/mm, the uniform spreading and forming of a back welding seam can be controlled, the swinging requirement of a welding gun during higher heat input can be met through the proper width of the groove of the welding joint, the fusion quality of the straight edge side is ensured, and the arc-shaped transition structure at the bottom of the straight edge side can avoid slag inclusion of the corner under the condition of high heat input.
And step four, welding the test plate 1 by adopting a gas metal arc welding mode, and constructing a welding process parameter combination according to the welding heat input E of 3.0-4.0 kJ/mm and the characteristics of large current density, high deposition speed, wide welding pool and weak penetration capacity of the gas-shielded flux-cored wire. The welding protective gas is a mixed gas of argon and carbon dioxide, and the mixing ratio is Ar to CO2The gas flow rate is 20-27L/min when the ratio is 80: 20.
The root welding adopts the special ceramic liner that has the arc recess to assist the shaping, and the arc recess is just to groove back center department, and the welding process parameter of root welding is the same with the used welding process parameter of filling the capping welding, and the welding process parameter includes welding current, welding voltage, welding speed and welder swing mode etc. wherein: the welding current is 260-320A, the welding voltage is 26-31V, the welding speed is 110-140 mm/min, and on the premise that the forming quality of a welding seam is guaranteed, the combination of the welding current, the welding voltage and the welding speed can be matched with a welding heat input value required by a test. The welding gun is adopted to swing to improve the spreading and forming quality of the welding seam, and meanwhile, the heat under the condition of high heat input can be dispersed, so that the problems of welding beading, local cold welding and slag inclusion caused by the fact that molten slag cannot float upwards in time due to the fact that a welding pool is not in time to solidify and the aggregation and the flowing are avoided. The swing path of the welding gun is in a zigzag shape, the swing width of the welding gun is within a range of 3-5 mm from the edge of the groove, the stay time of the welding gun 2 on the straight side of the groove is 50-150 ms, and the stay time of the welding gun 2 on the bevel side of the groove is 30-80 ms, as shown in fig. 3. The optimized welding gun swinging mode can ensure the sufficient fusion of the edge of the groove of the welding joint and the forming quality of a welding seam, and can not cause the molten pool to destroy the straightness of the straight side after welding.
Referring to fig. 3, in view of the sensitivity of the straight-side unfused defect in the form of a single-side straight-side bevel, the welding gun is tilted during root welding and fill-cap welding in the following manner: along the width direction of the groove, the welding gun 2 and the straight side of the groove form an included angle delta of 3-25 degrees. Considering that the size of a molten pool is increased under the condition of higher heat input welding of 3.0-4.0 kJ/mm, the edge fusion capability is enhanced, the inclination angle of a welding gun is not too large, otherwise, the straightness of a fusion line after welding is damaged by the shape of the molten pool induced by the position of the welding gun. Meanwhile, in order to ensure that the straightness of the single-side fusion line of the welding joint is good, the position of a welding gun in a welding bead needs to be monitored in real time in the welding process, if the welding gun deviates from the original setting position due to the problems of groove processing and group assembling precision, the position of the welding gun needs to be adjusted rapidly and timely, otherwise, the probability of the lack of fusion defect on the straight side is increased, and the straightness of the fusion line after straight-side welding can be damaged.
And fifthly, obtaining a welding joint after welding, observing and detecting the crack tendency of the welding joint to evaluate the technological weldability of the material, and evaluating the use weldability of the material by detecting the mechanical properties of the welding joint, particularly detecting the low-temperature impact and the fracture toughness of a coarse crystal area of a welding heat affected area adjacent to a single-side straight-edge fusion line.
Examples
The test plate 1 is made of typical X70 pipeline steel with the thickness t being 26.2mm, a ceramic liner is added to the back of a groove to assist in forming a root welding method, based on the fact that welding heat input is within the range of 3.0-4.0 kJ/mm and the diameter is 1.2mm, gas shielded flux-cored wires are adopted, and welding shielding gas is 80% Ar + 20% CO2And (4) carrying out weldability evaluation test on the mixed gas with the flow of the shielding gas of 20-27L/min. Referring to fig. 4, the specific weld joint groove form is: the front is the two V type grooves of one side straight flange, and the straight flange side bottom of front groove takes the circular arc chamfer, and the back is V type groove, wherein: α is 60 °, β is 30 °, θ is 50 °, a is 6mm, b is 3mm, c is 11mm, and R is 5 mm.
Table 1 lists specific welding process parameters, torch tip angles, and corresponding weld heat input values for examples 1-5, as follows:
table 2 lists the results of the defect inspection and evaluation of the straight-side CGHAZ impact toughness for examples 1-5, as follows:
as can be seen from tables 1 and 2, the X70 pipeline steel process shown in different examples has good weldability, no weld cracks and other weld defects, the impact toughness at the CGHAZ position of the straight side at-10 ℃ is higher than the general acceptance standard requirement, namely the minimum impact work requirement is 34J (refer to NB/T47016: mechanical property test of welded test pieces of pressure-bearing equipment products), and the impact toughness is reduced along with the increase of welding heat input.
The method for evaluating the high-heat-input weldability of the low-carbon microalloy steel based on the gas shielded flux-cored wire considers the technological weldability of the material in the welding process and the using weldability of the material after welding, and has universality and universality for evaluating the weldability of low-carbon microalloy steel materials used in different industries and fields in a given higher welding heat input range.
The present invention is not limited to the above embodiments, and any modifications, equivalent replacements, improvements, etc. within the spirit and principle of the present invention should be included in the protection scope of the present invention.