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1. 45 steel before quenching without tempering, hardness greater than HRC55 (up to HRC62) as qualified.
The highest hardness for practical application is HRC55 (high-frequency hardening HRC58).
2. 45 steel should not use carburizing and quenching heat treatment process.
The quenched and tempered parts have good overall mechanical properties and are widely used in a variety of important structural parts, especially connecting rods, bolts, gears and shafts that work under alternating loads. However, the surface hardness is low and it is not wear resistant. Can be quenched and tempered + surface hardening to improve the surface hardness of parts.
Carburizing treatment is generally used for heavy-duty parts with surface wear resistance and core impact resistance, and its wear resistance is higher than quenched and tempered surface quenching. The surface carbon content of 0.8 - 1.2%, the core is generally 0.1 - 0.25% (0.35% in special circumstances). After heat treatment, the surface can obtain high hardness (HRC58--62), low hardness of the core, and impact resistance.
If 45 steel is carburized, hard and brittle martensite will appear in the core after quenching, losing the advantage of carburizing. Carburizing technology is now used in the material, the carbon content is not high, to 0.30% of the core strength can be achieved very high, the application is rare. 0.35% has never seen an instance. It is only introduced in textbooks. Can use quenched and tempered + high frequency surface quenching process, wear resistance is slightly worse than carburizing.
Q235 is a carbon structural steel, yield strength of 235MP, carbon content of 0.14 ~ 0.22% Although the mechanical properties are not good, but the price is cheap, previously called A3 steel, welding is quite common, but can only be used in Some unimportant structures.
Q235 is made up of the Q+ number + quality class symbol + deoxy method symbol. Its steel number is marked with "Q", which represents the yield point of the steel. The following figures indicate the yield point value in MPa. For example, Q235 indicates carbon structural steel with a yield point (σs) of 235 MPa.
What is the difference between Q235 boiling steel and stabilization steel? How do you distinguish the mechanical properties? What should you watch out for when using it?
In the later stage of smelting, the steel is calmed by ferromanganese, ferrosilicon and aluminum. The molten steel is solidified in the ingot mold. Its chemical composition is uniform, the structure is dense, and the quality is high, but there are shrinkage holes.
The former has better impact toughness than the latter, but the strength and elongation are not much different.
The difference between 45# steel and Q235 steel
45# steel is a carbon structural steel with a carbon content of 0.45%. It is widely used in machinery manufacturing. The mechanical properties of this steel are very good. However, this is a medium carbon steel and the quenching performance is not good. 45 steel can be hardened to HRC42~46. Therefore, if the surface hardness is required, and the superior mechanical performance of 45# steel is desired, the surface of 45# steel is often carburized and quenched so that the required surface hardness can be obtained.