Steel Weldability
Welding of metallic materials at a certain conditions, the emergence of weld defects (particularly crack) and use the degree of reliability, referred to as metal solderability. Carbon steel and alloy steel elements for truck and auto assessed solderability. Selection of drug-coated electrode
In addition to weld performance status depends on the joints and welding process parameters, the main depends on the welding rod coating transition heart and the composition of alloying elements. Therefore should be based on repair parts and technical requirements for materials selection electrode, the following principles should in general be selected electrode.
① general requirements for mechanical properties are as follows:
i. Welding low, medium carbon steel and low alloy steel may make use of the same strength of welding rod;
ii. Welding alternating load or impact load of spare parts, should use coated metal strength is slightly lower than the strength of base metal electrode;
iii. The solderability of bad materials, such as the application of high-carbon steel welding Interlayer law. Advised to pay attention to high-carbon steel Welding and surfacing, are not suitable for structural welding;
iv. Different materials of welding materials, should be based on low-intensity materials prevail.
v. Parent material of high carbon content, S, P content is high, should select crack resistance and anti-gas-strong electrode, such as low hydrogen sodium (potassium) electrode.
② physical and chemical properties in general requirements are as follows:
i. At high temperature or low temperature conditions of the welding parts, should use the corresponding electrode temperature varieties, such as heat-resistant steel electrodes, high-alloy austenitic-type low-temperature electrode;
ii. Optional surfacing electrode, it is important to distinguish the type of wear and corrosion medium category, choose the appropriate composition and performance (especially hardness) of the electrode.
③ welding parts status in general requirements are as follows:
i. Parts of complex shape, or structural rigidity Heavy large, the larger the residual stress after welding, easy to crack, crack resistance must be in good low hydrogen type electrodes, high toughness electrodes, or iron oxide-based electrode.
ii. Weldment groove for oil there is, rust can not be in addition to the net, we should choose a strong acid oxidizing electrode, such as Fe-Ca-type electrode.
iii. Of large parts not easily overturned, weld in a Yang-welding, welding position should be used all-position welding electrode Shi.
3. Welding repair process elements
Mechanical parts welding repair welding difficult than steel, because welded repair parts not only to ensure strength and stiffness requirements, but also to ensure that the overall size, shape and relative position accuracy and revised requirements of machinability. Of large complex parts welding for repair parts must be wear and tear, damage to the development of welding repair technology, and strictly enforced. Normal circumstances, spare parts welding repair process as follows.
① preparation before welding. Preparation before welding equipment in addition to job preparation, the major groove are welded Weldment Preparation and preheat.
Single-sided welding (thickness ≤ 30mm) with Y-shaped groove, two-sided welding (thickness> 30mm) with double V-shaped groove, butt welding axis pieces with U-shaped groove [. Groove machining best shape, can also use gas cutting or gouging, but must to remove oxide. Groove to clean, non-greasy dirt and corrosion. Butt welding of the groove should be symmetrical in order to ensure good positioning. Crack groove with the crack depth and length, should ensure that measures to facilitate and minimize welding filler metal.
Welding repair parts in accordance with the preheating temperature to determine the carbon content of parent material. Maintained at ambient temperature under certain austenite steel types of non-hardening case, do not preheat.
② positioning welding. Welding repair and docking at the shaft parts or some parts of the local time has been cut from the whole shall be guaranteed to be accurate position butt welding parts in order to prevent excessive welding deformation generated. To this end, it should first conduct a positioning welding: welding with a diameter less than the facilities to carry out spot welding electrodes, and then again Calibration position, in a number of symmetrical positioning small welding.
③ Weld Road, a few with the choice of electrode diameter. Wide or deep weld required to complete multi-layer welding, weld staggered procedures, and can improve performance, and Shi welding weld annealing. Road surfacing welding to symmetric intervals. Cladding layer thick first part of the general good toughness of austenitic stainless steel welding rod or electrode welding job near the post size, and then be welded to the surfacing requirements of size, if necessary, set aside allowance. Multi-channel welding, the first 1 ~ 3 optional small diameter electrode penetration angle can then use the rough track to complete the remaining weld rod. Article surfacing in diameter than the average should be smaller welding electrode to control the welding temperature at the time of parts.
④ line matching energy. Hardened steel welding, the weld cooling faster than the critical quenching rate hardening and cracks appear. Line energy (welding heat input per unit length of weld on effective energy) input, and preheat temperatures are high, weld joints, slow cooling, quenching tendency to smaller, less cracks appeared. But enhance the energy lines cause deposited metal burning, high preheating temperature will expand the base metal heat affected zone. Therefore, the input line match the energy and preheating temperature to ensure that welded joints quenching cooling rate no greater than the critical cooling rate, while simultaneously deposited metal welding normal melting.
⑤ PWHT. Welding parts in order to eliminate residual stress and reduce the crack after welding, heat treatment after welding must be carried out.
About the Author
Haven Frbiz has a rich database comprising of manufacturers, traders, exporters, importers and products . Frbiz.com is the Stainless Steel Industry's most effective search engine that provides Industry professionals with global Stainless Steel and related hot news, trade shows , latest buying leads and latest products.
