An iron-carbon alloy containing no other alloying elements, except for impurities such as silicon, manganese, phosphorus, and sulfur, which are less than 2.11% of carbon, except iron, carbon, and a limited amount. The carbon content of industrial carbon steel is generally 0.05% to 1.35%. The performance of carbon steel depends mainly on the carbon content. As the carbon content increases, the strength and hardness of the steel increase, and the ductility, weldability and weldability decrease. Compared with other steels, carbon steel is the earliest used, low cost, wide performance range and maximum dosage. Applicable to medium, such as water, steam, air, hydrogen, ammonia, nitrogen and petroleum products, with nominal pressure PN��32.0MPa and temperature -30-425��C. Commonly used grades are WC1, WCB, ZG25 and high quality steel 20, 25, 30 and low alloy structural steel 16Mn.

Folding chemical influence

The performance of carbon steel depends mainly on the carbon content and microstructure of the steel. In the annealed or hot rolled state, as the carbon content increases, the strength and hardness of the steel increase, while the ductility and impact toughness decrease, and the weldability and cold bendability deteriorate. Therefore, the steel used in engineering structures often limits the carbon content. Residual elements and impurity elements such as manganese, silicon, nickel, phosphorus, sulfur, oxygen, nitrogen, etc. in carbon steel also have an effect on the properties of carbon steel. These effects sometimes reinforce each other and sometimes offset each other. For example: 1 sulfur, oxygen, nitrogen can increase the hot brittleness of steel, and the right amount of manganese can reduce or partially offset its hot brittleness. 2 Residual elements reduce the impact toughness of steel and increase the cold brittleness except manganese and nickel. 3 In addition to reducing the strength of sulfur and oxygen, other impurity elements increase the strength of the steel to varying degrees. 4 Almost all impurity elements can reduce the plasticity and weldability of steel.

Hydrogen can cause many serious defects in steel, such as white spots, point segregation, hydrogen embrittlement, surface bubbling and cracks in the weld heat affected zone. In order to ensure the quality of the steel, it is necessary to reduce the hydrogen content of the steel as much as possible (see stress corrosion cracking and hydrogen embrittlement). The residual elements brought by deoxidation, such as aluminum, can reduce the aging tendency of low carbon steel, and can also refine the grains and improve the toughness of the steel at low temperatures, but the balance should not be excessive. The residual elements brought in by the charge, such as nickel, chromium, molybdenum, copper, etc., can increase the hardenability of the steel when it is high, but it is disadvantageous for special steels requiring high plasticity, such as deep-drawn steel sheets.

Folding processing performance

Carbon steel is mostly smelted by oxygen converter and flat furnace, and high quality carbon steel is also produced by electric arc furnace. According to the degree of deoxidation in the steelmaking process, carbon steel can be divided into killed steel, boiling steel and semi-killed steel between the two. The effect of the smelting method on the properties of the steel is mainly due to the purity of the steel. Through the vacuum treatment, refining and blowing technology, higher purity steel can be obtained, which significantly improves the quality of carbon steel.

The plastic working process of carbon steel is usually divided into thermal processing and cold working. After hot working, defects such as small bubbles and looseness in the ingot are welded together to make the structure of the steel dense. At the same time, thermal processing can destroy the as-cast microstructure and refine the grains. The wrought steel has better mechanical properties than the as cast. The cold-worked steel increases in strength and hardness as the degree of cold plastic deformation increases, and the ductility and toughness decrease. In order to improve the yield, the continuous casting process is widely used.

Folding purpose

The Q195 is used to make smaller parts, wire, iron rings, horns, split pins, tie rods, stampings and weldments.

Q215 A is used in the manufacture of tie rods, ferrules, gaskets, bleed rings, carburized parts and welded parts.

Q235 AA, B grade for the manufacture of metal structural parts, carburizing parts or carbonitriding parts, tie rods, connecting rods, hooks, couplers, bolts, nuts, sleeves, shafts and fittings with low core strength requirements Class C and D are used to manufacture important welded structural parts.

Q255 A is used to make parts with low strength requirements such as shafts, spindles, hooks, tie rods, rockers, wedges, etc. This negative weldability is acceptable.

Q275 is used to manufacture parts with high strength requirements such as shafts, sprockets, gears and hooks.

Folding impurities

Effect of Mn

Common impurities in steel include: Si, Mn, S, P and gases such as oxygen, hydrogen, and nitrogen. Mn is an element which is deoxidized by ferromanganese to steel after steelmaking and remains in steel. It has strong deoxidation ability, and most of manganese is dissolved in F to strengthen steel. At the same time, manganese can reduce the damage of S to steel. Generally, carbon is controlled in the range of 0.25% to 0.8% of carbon steel.

The influence of Si

Si is mainly derived from raw iron and ferrosilicon deoxidizers. Stronger than manganese deoxidation, silicon dissolved in F, can increase the strength and hardness of steel, but will reduce plasticity and toughness. Silicon can promote the decomposition of Fe3C into graphite. If graphite appears in the steel, the toughness of the steel will be seriously degraded, resulting in so-called "black brittleness". Silicon is generally controlled in the range of 0.17 to 0.37% in carbon steel.

The influence of S

S can increase the "hot brittleness" of steel. (S is insoluble in ��-Fe, but exists in the form of compound FeS, its melting point is 1190, and FeS can form a eutectic on Fe on the grain boundary, and its melting point is only 985 .). S also has an adverse effect on the welding performance of steel, which easily leads to thermal cracking of the weld. Therefore, S is a harmful impurity in steel, and its content is generally required to be no more than 0.05%. However, S can improve the cutting performance of steel.

The influence of P

P will cause "cold brittleness" of steel. (P is all dissolved in ��-Fe in steel, which increases the strength and hardness of steel, and at the same time, the plasticity and toughness are significantly reduced. When the amount of P in the steel reaches 0.3%, the steel becomes completely brittle, and this brittleness phenomenon It is more severe at low temperatures.). P also reduces the weldability of steel. Therefore, P is a harmful impurity in steel, and its content is generally required to be no more than 0.045%. However, P can improve the cutting performance and corrosion resistance of steel.

Gas effect

Oxygen reduces the mechanical properties of steel, especially fatigue strength. It is not good for steel, the less the better.

N will precipitate in the form of nitride, increasing the strength and hardness of the steel, but will reduce the plasticity and toughness of the steel, making the steel brittle.

H will increase the brittleness of steel significantly, called "hydrogen embrittlement". At the same time, H causes cracks in the steel, called "white spots."