20G steel is boiler steel, which is similar to No. 20 carbon steel. The difference is that 20G steel has higher and stricter inspection standards than ASTM A29 4140 structural steel, No. 20 carbon steel for harmful impurities and internal defects. That is to say, 20G steel is specially produced for boiler pressure vessels. It is special purpose "No. 20 carbon steel". The use of 20G steel to make boilers is not because it is more resistant to burning than other steels such as ASTM A29 4140 structural steel, but because of its strength, toughness, ductility, weldability, temperature influence, fatigue fracture, price and cost, etc. 20G steel is most suitable for use in medium and low pressure boilers.
No. 45 steel is commonly used medium carbon quenched and tempered structural steel. The cold plasticity of No. 45 steel is generally better than ASTM A29 4140 structural steel. Annealing and normalizing are better than quenching and tempering. No. 45 steel has higher strength and better machinability than Q345 steel. After proper heat treatment, it can obtain certain toughness, plasticity and wear resistance. No. 45 steel ASTM A29 4140 structural steel is suitable for hydrogen welding and argon arc welding, but not suitable for gas welding. Preheating is required before welding, and stress relief annealing shall be conducted after welding.
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The strip steel thickness is generally below 6mm, which is convenient for crimping and processing. You should choose the ASTM A29 4140 structural steel, strip steel specifications according to your own purposes. The specifications and materials used for different purposes are different, so you must confirm it before buying. It is best to ask professionals to give advice before purchasing strip steel, and purchase the specifications and types you need according to the corresponding requirements.