Selection of electrodes for welding low-alloy steel grade 4140

Low alloy steel grade 4140 (Low Alloy Steel 4140) is well known in the steel market in Thailand as “Fah Iron”. This type of steel, if referring to international standards, then Classified in the AISI 4140 standard, which is equivalent to ASTM A29/A29M or the Japanese standard, JIS G4053:SCM440. Classified in medium carbon steel. 

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In the high strength low alloy group (High Strength Low Alloy; HSLA), the carbon content is approximately 0.38 – 0.43 percent, making it possible to harden and temper (Quenched and Tempered) with a thermal process. To achieve the required strength and properties. Grade 4140 steel is one of the low alloy steels used in many industrial applications such as mechanical parts that require high strength. crankshaft steering column joints, wheel shafts, connecting rods, oil well drill bits gear or shaft Hydraulic jack prestressing core Oil industry screws and nuts Including machine parts that need strength and when these parts need to be connected It is often difficult for users to decide on the design of the welding process. due to consideration of the selection of welding wire heat treatment before and after welding, hardness and strength of the seam to be obtained, etc.

the ability to harden It is the heart of 4140 low-alloy steel obtained by heat treatment. It can be difficult to select the welding wire that meets the required strength under given conditions. for that reason There are several ways to weld 4140 low-alloy steel, depending on the application and desired effect. For example, welding thin-walled tubing for racing cars with 4140 steel will have different welding requirements than using steel. this group to make a large valve For heavy duty use in the petrochemical industry or the mechanical parts of the oil drilling industry.

This article provides best practices. in selecting the appropriate welding wire with additional instructions and preheating temperature before welding For welding low-alloy steel grade 4140 as follows

Principles of welding of low-alloy steel grade 4140

Low-alloy steel grade 4140 is characterized by increased carbon content. including molybdenum and chromium Elemental enhances the ability to harden. It makes it possible to increase hardness and mechanical strength by using heat treatment. Material strength can vary greatly. Depending on the nature of heat treatment, including annealing (Annealing), normal baking to improve properties (Normalizing) Quenched and Tempered For example, the estimated strength of 4140 low-alloy steel when annealed is 90 ksi, while in the normal annealed condition it is about 100 ksi. Quenched and tempered 4140 has the highest mechanical strength. with strength up to 200 ksi

For this reason, we can use many different types of welding electrodes or electrodes. in welding 4140 steel with success Although the welder may want a wire with better properties. (Overmatching) or just equivalent (Matching) with the mechanical properties of 4140 steel only.

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