Weldability and Its Test Evaluation

1. Welding: The process of forming an inseparable whole by heating or pressurizing, with or without filler material, so that two objects are combined between atoms.

2. Weldability: refers to the homogeneous or heterogeneous materials in the manufacturing process conditions, the ability to weld to form a complete joint and meet the expected use requirements.

3. The four major factors affecting weldability are: material, design, process and service environment.

4. The principles of assessing weldability include: ① assess the tendency of welded joints to produce process defects, to provide a basis for the development of a reasonable welding process; ② assess whether the welded joint can meet the requirements of structural performance; design new welding test methods to meet the following principles: comparability, relevance, reproducibility and economy.

5. Carbon equivalent: the content of the alloying elements in the steel is converted and superimposed on the equivalent of a number of carbon content, as a rough assessment of the steel cold cracking tendency of the parameter index.

6. Oblique Y-bevel butt crack test: The purpose is mainly used to identify the first layer of low-alloy high-strength steel weld and HAZ formation of cold cracking tendency, can also be used to develop the welding process.

(1) test preparation, the welded steel plate thickness δ = 9-38mm. butt joint bevel with mechanical processing, test plate at each end of the 60mm range in the application of constrained welds, using double-sided welding. Attention to prevent corner deformation and not welded through. Ensure that the middle to be welded specimen weld at 2mm gap.

(2) test conditions: test welding seam selected welding rod to match the parent material, the welding rod should be strictly dry, the diameter of the welding rod 4mm, welding current (170 ± 10) A, welding voltage (24 ± 2) V, welding speed (150 ± 10) mm / min. test welding seam can be applied at various temperatures, test welding seam only one, not fill the bevel. After welding and natural cooling 24h after the interception of specimens and crack detection.

3) Detection and cracking strip rate calculation. With the naked eye or handheld 5-10 times magnification to detect the surface and section of the weld and heat-affected zone whether there are cracks. It is generally believed that low-alloy steel "small iron research" test surface cracking rate of less than 20%, generally do not produce cracks.

7. pin test: the purpose, the main assessment of steel hydrogen delayed cracking tendency, additional equipment, can also determine the reheat cracking sensitivity and laminar sensitivity.

(1) specimen preparation, the welded steel will be processed or cylindrical pin test bar, sampling along the rolling direction and indicate the location of the pin in the thickness direction. The test bar has a ring or screw-shaped notch near the upper end. Insert the pin test rod into the corresponding hole in the base plate so that the notched end is flush with the surface of the base plate. For the ring-shaped notch pin test rod, the distance between the notch and the end surface a should make the weld depth of fusion and the notch root intercept plane tangent or intersection, but the notch root circumference is melted through the part of not more than 20%. For low-alloy steel, a value of 2mm in the welding heat input for E = 15KJ/cm.

(2) test process, according to the selected welding method and strict control of the process parameters, the base plate melt a layer of overlay welding channel, the center line of the weld channel through the center of the specimen, the melt depth should be so that the tip of the notch is located in the heat-affected zone of the coarse crystal zone, the length of the weld channel L about 100-150mm. application of welding should be measured 800-500 ℃ cooling time value t8/5 value, not preheat welding, after welding cooling to 100- 150 ℃ when loading; preheating before welding, should be loaded at 50-70 ℃ above the preheating temperature. The load should be applied within 1min and before cooling to 100℃ or 50-70℃ above the preheating temperature. If it is post-heat, it should be loaded before post-heat. When the test bar is loaded, the pin may break during the load duration, note down the bearing time.