Thp CarbonTheo thnh phn carbon th thp c chia thnh bn nhm : thp carbon thp,

thp carbon thp x l nhit c hm lng carbon > 0.10 n khng qu 0.30%C,

thp carbon trung bnh hm lng trn 0.30 n di 0.60%C) v

thp carbon cao c hm lng >0.60%C.

Ty thuc vo mc x l kh oxy khi luyn thp cn chia ra: Thp Rimmed 1Tn gi chnh xc l thp vnh, song tn ny khng c dng ph bin.

c rt trc tip t l luyn khng thm cc cht kh oxy (ch mt lng nh c thm vo dt). Mt lng d oxy va tip tc duy tr phn ng t carbon khi thp lng trong dt bt u ngui v ng rn. Kt qu l phn v bn ngoi ca dt c hm lng carbon rt thp. Thp si (phn vnh bn ngoi) c dng lm phi ko li que hn, dy hn, nguyn liu luyn thp khng g, thp HSLA, thp tm cn ngui dng ch to thn xe t, thit b dn dng.

Thp Capped qui trnh tng t nh thp si, ngoi tr cng on dt thp s c y kn ngay khi qu trnh si kt thc phi thp bt u ngui t bn ngoi t mi hng. Thp capped thng dng lm phi cn nng , cc tp cht, bng kh cn li s c p dnh, ko di v phn tn ra ton b thnh phm. Thp Capped thng c hm lng carbon >0.15%.

Thp bn lng (Semi-killed) qu trnh kh oxy c tng cng song cha n mt trit nh thp lng (fully-killed), lng oxy cn li va bin lng carbon d thnh oxt carbon phn tn cn bng vi cc bng, hc co rt do ng rn. Thp bn lng thng dng lm phi thp hnh cn nng c hm lng carbon t 0.15 n 0.30%.

Thp lng (Fully-killed), m thp c x l kh oxy v kh (CO) trit trc khi ng rn. Thp ny thng dng lm phi liu cn nng thp dy c yu cu ng nht cu trc cao s dng lm v bn b p lc, ng dn p sut cao, chi tit nh hnh bng pgu7o7ng php rn. dp nng.

Thp carbon thp, thp carbon thp x l nhit Cn c tn khc l thp carbon thng (mild steel), in hnh l thp l cn ngui c do cao, kh nng nh hnh tt, thng c hm lng carbon khng qu 0.10%C v Mnggan di 0.50%Mn. Thp l cn ngui cng c th c m nng (galvanised) vi km / hoc nhm, hoc trng thic (thp l bao b) hoc sn ph. Ferrite l cu trc ch yu vi mt lng nh carbide c cu ha.Both rimmed steel and aluminum-killed steel can be used for low carbon sheet, with the latter having become the norm. Low carbon sheet steel is also available as dual-phase steel which has a desirable combination of strength and formability due to processing which provides a microstructure consisting of islands of martensite in a ferrite matrix. Typical applications are in consumer products, notably automotive body panels and appliances.Rolled structural steel plates and sections typically have higher carbon contents, up to 0.3% with manganese up to 1.5%. These are used for such applications as forgings, seamless tubing and boiler plate, usually in the as-rolled or normalized conditions.Heat treatable (hardenable) low carbon steel products have carbon contents in the range 0.10-0.30%C. These have increased strength and reduced cold formability and although they can be directly quenched and tempered, they are more generally used in the carburized condition, with higher carbon contents used for thicker sections where increased hardenability is necessary.Medium Carbon SteelMedium carbon steels containing 0.30 to 0.60%C and 0.60 to 1.65%Mn are normally used in the quenched and tempered condition. Oil quenching can be used if section size is not too great. These steels, normally produced in the killed condition, are versatile since the balance between strength and ductility can be controlled by adjusting the tempering time and temperature. For example tempering a quenched AISI/SAE 1040 steel at 200C (400F) results in a tensile stress of about 830 MPa (120,00 psi) and a ductility of 18% elongation, whereas raising the tempering temperature to 650C (1200F) lowers the tensile strength to 650 Mpa (94,000 psi) while raising the ductility to 28% elongation. Quenched and tempered medium carbon steels are used for such applications as automotive engine, transmission and suspension components, for example axles, gears and crankshafts. Railway applications include rails, railway wheels and axles.High Carbon SteelHigh carbon steel containing 0.6% to 1.0%C finds applications as springs and as high strength wires. These steels have lower ductility than the medium carbon steels as well as restricted formability and weldability. High carbon steels are normally processed by quenching and tempering, with oil quenching common except in heavy sections and for cutting edges.High Strength Low Alloy (HSLA) SteelsHSLA steels offer improved mechanical properties and in some cases improved resistance to atmospheric corrosion in the as-rolled or normalized condition without the necessity of going to a quenched and tempered product. They are not characterized as alloy steels, rather they can be considered to be carbon steels with enhanced properties resulting from a combination of small alloying element additions and, usually, special processing methods. The HSLA steels are generally produced to mechanical property specifications (e.g. ASTM A 242), with quality descriptors (e.g. structural quality or pressure vessel quality) and less emphasis on chemical composition. They are capable of highly attractive combinations of strength and toughness at a reasonable cost. Many are described in SAE specification J410.There are many categories of HSLA steels. One of the common ones is the microalloyed steels, so named because they contain alloying elements such as Nb (Cb), V, Ti or Mo in amounts rarely exceeding 0.1%. Manganese levels are generally high, in the vicinity of 1.5%.

Another type is the acicular ferrite HSLA steels which contain less than 0.1% carbon, with additions of manganese, along with such elements as molybdenum and boron. This material finds wide application in linepipe for low temperature service.

These HSLA steels obtain their high strengths through a combination of mechanisms including extremely fine grain size, with precipitation hardening by carbide, nitride and carbonitride particles. To achieve the desired microstructure and properties it is necessary to carefully control the processing of these steels with emphasis on the temperature and deformation during the final stages of rolling, and the cooling conditions after finish rolling.There are also dual-phase HSLA steels whose microstructures consist of small, uniformly distributed islands of high-carbon martensite in a ferrite matrix. Martensite typically accounts for about 20% of the volume. These materials have the excellent formability of low strength steel but can yield a high strength in the finished component, because they are greatly strengthened by the plastic deformation during forming.Alloy SteelsAlloy steels are more expensive and can be more difficult to weld than carbon steels but have many attractive characteristics. Firstly, the alloying elements increase the hardenability so that thicker sections can be through hardened. Furthermore, the increased hardenability means that lower quench rates can be utilized, (e.g. oil quenching rather than water quenching) with consequent lower distortion and less susceptibility to quench cracking. The hardenability provided by the alloying elements also means that a lower carbon content can be used, giving a lower hardness martensite after quenching, further reducing the risk of quench cracking. In addition, the effectiveness of the alloying elements in retarding tempering permits the use of higher tempering temperatures with a consequent improvement in toughness. In some cases the alloying elements also provide resistance to environmental degradation under particular service conditions.As mentioned in Chapter 1, it is important to distinguish the difference between hardness and hardenability. The principal purpose of adding alloying elements to make alloy steel is to increase hardenability. While carbon by itself controls the maximum attainable hardness for any standard steel (see discussion of martensite in Chapter 1), the carbon content has only a minor effect on hardenability.Low carbon alloy steels (0.10 to 0.25%C) are used primarily as carburizing steels, the alloying elements giving improved mechanical properties in the core in comparison with corresponding carbon steels, as well as the other advantages discussed in the previous paragraph. Examples include alloy steels AISI/SAE 4023 and 5015 (UNS G40230 and G50150), which are used for such applications as shafts and other automotive components.

Low alloy higher carbon steels are used in (non-carburized) applications involving small sections and severe service conditions, such as high strength bolts and small machinery axles and shafts. Examples include manganese alloy steels such as AISI/SAE 1345 (UNS G13450), the molybdenum alloy steels AISI/SAE 4037 and 4047 (UNS G40370 and G40470) and the low nickel-chromium-molybdenum alloy steels AISI/SAE 8630-8650 (UNS G86300-G86500).

The higher strengths of these materials are also used to advantage in reducing the size and weight of components. Higher levels of alloying element are used in carburizing steels where superior properties of case or core are necessary. The nickel-molybdenum alloy steel AISI/SAE 4620 (UNS G46200), the chromium steel AISI/SAE 5120 (UNS G51200) and the low nickel-chromium-molybdenum alloy steel AISI/SAE 8620 (UNS G86200) find applications as small hand tools, automotive gears and bearings for relatively severe service. The higher alloy nickel-molybdenum steel AISI/SAE 4815 (UNS G48150) and the nickel-chromium-molybdenum steels AISI/SAE 9310 and 94B17 (UNS G93100 and G94171) are used in severe service applications such as truck transmissions and differentials and in rock bit cutters. Non-carburizing high alloy constructional steels such as AISI/SAE 4340 and 86B45 (UNS G43400 and G86451) find applications in heavy aircraft and truck components where service conditions are severe and/or where quench distortion must be minimized.Specialized alloy steels include the AISI/SAE 52100 (UNS G52986) ball bearing steel and the AISI/SAE 5155 and 5160 (UNS G51550 and 51600) spring steels.There are also low carbon quenched and tempered constructional alloy steels which are not included in the AISI/SAE designation system. These have good toughness and weldability as a result of their low carbon levels. Included here are the T1 steels (UNS K11576, K11630, K11646) which find uses in pressure vessels, in mining equipment and as structural members in buildings.