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Simplified Comparison Diagrams for Special Steels　　　　Material Properties Guide 　　

 

Simplified Comparison Diagrams for Special Steels

The comparison diagrams below show carbon steels such as JIS S45C and carbon tool steels such as JIS SK-5 (SK85).

Click the name of a particular grade to see a detailed specifications page.

To see general properties, refer to the Material Properties Guide below.

 

Carbon Steels (S**C)

 

 

Carbon Tool Steels (SK**)

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Material Properties Guide

1. Features	1.1. Steel grade chart	1.2 Finish definitions and finish chart
2. Workability	2.1 Bending	2.2 Drawing
3. Heat treatment	3.1 Heat treatment environment	3.2 Temperature of furnace and material	3.3 Pre-treatment and atmosphere
	3.4 Quenching	3.5 Tempering

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1.1. Steel grade chart

Type		Grade	Property data
Carbon steel (JIS G 3311) (JIS G 4051) (JIS G 4802)	S15C S45C S50C S55C S60C		Carbon steels have lower carbon content than carbon tool steels, and have less-strict regulations on impurities. They are used in applications that require a certain amount of strength and toughness. Carbon steels with low carbon content offer better raw-material workability, but are susceptible to uneven quenching, so care must be taken with regard to temperature management, cooling methods, and the like. Carbon steel applications include office appliances, electrical and mechanical components, springs, washers, clutch parts, Thomson blades, and bearing parts. > See detailed specifications page for information on chemical composition and mechanical properties
Razor steel	TE-2 (SKS81M)		By adjusting the chemical composition and quality control in the manufacturing process, the hardenability of razor steel can be increased. Refining the carbide enables us to improve sharpness and wear resistance. Razor steel is used for razor blades, long edged tools, high-grade knives, etc. > See detailed specifications page for information on chemical composition and mechanical properties
Carbon tool steel (JIS G 3311) (JIS G 4401)	SK2 (SK120) SK4 (SK95) SK5 (SK85) SK6 (SK75) SK7 (SK65)		Due to their workability, hardenability, product performance, affordability, and other characteristics, carbon tool steels are the most widely used cold-rolled special steel strips. Carbon tool steel is used in a wide range of fields from hard applications including blades, cutting tools, and regular tools to applications that require elasticity and toughness including regular springs, spiral springs, knitting needles, horns, measuring tapes, and washers. > See detailed specifications page for information on chemical composition and mechanical properties
Alloy tool steel (JIS G 4404)	SKS2 SKS51 SKS7		SKS2 and SKS7 are produced by adding tungsten and chromium to high carbon steel and scattering tiny, hard complex-carbides. Due to their excellent wear resistance and high-temperature strength, they are used for cutters, hacksaws, metal band saws, and similar products. SKS51 contains nickel and chromium for increased toughness, and is used for hand saws, utility knives, and other products.
High cleanliness steel	M2 (Corresponds to SK4)		M2 is high in carbon (C), manganese (Mn), and chromium (Cr) for increased wear resistance, and low in phosphorus (P) and sulfur (S) for a high degree of cleanliness and durability. M2 has good properties for heat treatment, a high degree of cleanliness, and a well conditioned surface. It is mainly used for knitting needle parts, where a high degree of reliability is required.
Chromium molybdenum steel (JIS G 4105)	SCM415		Chromium–molybdenum steels are typically used for structural applications. They can be quenched and tempered to provide mid-level strength and toughness. They have low hardness and good workability. Moreover, their alloy content gives them good hardenability and allows them to be quenched even if cooled at a slower rate. They are also not very susceptible to deformation. SCM415 is case hardened steel, so it is usually used after the surface has been hardened via carburization. Chromium–molybdenum steel applications include office appliances, electrical and mechanical components, Thomson blades, and chain components.

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1.2 Finish definitions and finish chart

Tokkin uses the following finishing definitions:

Finishing condition	Finishing rolling reduction
Annealed	—— (As annealed)
Skin passed (lightly rolled)	Up to 5%
Rolled	15%–40％
Full hardened	35% or higher

The table below is a finish chart for various steel grades.

Grade	Finishing condition	Hardness test	Tensile test
		HV	Tensile strength N/mm2	Elongation %
TE-2 SK-2	Annealed	170–210	520–685	20–32
	Skin passed	190–230	570–715	10–28
	Rolled	250–290	735–980	2–15
	Full hardened	280–320	835–1080	1–3
	See also detailed specifications pages for high carbon steels and stainless steels for blades. > High carbon steels and stainless steels for blades (TE-2, SK-5, RB-S, & SUS420J2)
SK4 M2	Annealed	160–200	490–645	24–35
	Skin passed	175–215	540–695	12–32
	Rolled	245–285	725–970	2–15
	Full hardened	270–310	825–1040	1–4
	See also detailed specifications pages for carbon tool steels and high cleanliness steels. > Carbon tool steels (SK2, SK4, SK6, & SK7) > High cleanliness steel (M2)
SK5	Annealed	150–190	460–625	26–37
	Skin passed	170–210	510–685	15–35
	Rolled	240–280	725–930	3–16
	Full hardened	260–300	805–1000	1–5
	See also detailed specifications pages for carbon tool steels and gauge steel plates. > Carbon tool steels (SK2, SK4, SK6, & SK7) > Gauge steel plates (SK5)
SK6 S70C	Annealed	145–185	440–615	27–38
	Skin passed	160–200	490–665	15–35
	Rolled	235–275	715–920	3–16
	Full hardened	255–295	795–990	1–5
	See also detailed specifications page for carbon tool steels. > Carbon tool steels (SK2, SK4, SK6, & SK7)
SK7 S60C S55C S50C S45C S15C	Annealed	140–180	410–610	28–39
	Skin passed	155–195	460–655	16–36
	Rolled	230–270	705–900	3–17
	Full hardened	250–290	775–970	1–5
	See also detailed specifications pages for carbon tool steels and carbon steels. > Carbon tool steels (SK2, SK4, SK6, & SK7) > Carbon steel (S15C, S45C, S50C, S55C, & S60C)
SKS2	Annealed	190–230	615–715	20–30
	Full hardened	280–320	835–1080	1–3
SKS7	Annealed	200–240	645–735	20–28
	Full hardened	300–340	880–1125	1–3
SCM415	Annealed	125–165	335–540	28–50
	Full hardened	200–240	655–735	1–8
Grade	Finishing condition	Hardness test	Tensile test
		HV	Tensile strength N/mm2	Elongation %

 

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2.1 Bending

1. While a rolled finish is sometimes used for bent products, we normally use an annealed or skin-passed finish for such products. 　

2. Steel strips generally have directional properties. As products with a rolled finish in particular have strong directional properties, it is better to avoid bending parallel to the rolling direction. It is therefore necessary to think of a layout that will ensure that the bending direction is perpendicular or cross to the rolling direction.

3. After cutting, shearing, or processing, if a bend is made so that the burred surface is on the outer face of the bent section, cracks may propagate from the burred edge. Therefore, the burred surface should be positioned so that it is on a section that will not be bent, or the burrs should be removed before bending.

4. When bending, spring back differs according to the extent of processing and finish of the material. It is necessary to make appropriate corrections depending on the shape and processing method.

5. Bendability differs according to grade and processing conditions, but it is possible to process materials with different finishing conditions as shown below.

　　(These conditions mainly apply to low carbon steel strips of grade SK5 or below)

 

Finishing condition	Thickness of under 1 mm	Thickness of 1 mm or greater
Annealed
Skin passed
Rolled

Note: t = thickness, R = internal bend radius 　　

Reference: Approximation of bending power

　

V-shaped die	P = 0.6bt2σB/L
U-shaped die	P = 0.6bt2σB (1 + t/L)

Note: t = thickness, b = width, L = width of die channel, σB = tensile strength of material 　

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2.2 Drawing

1. Except for minor drawing processes, the product usually needs to have the same drawability for all directions. For this reason, products with an annealed or skin-pass finish are used.

 

1. Even though cold rolled special steel strips are not susceptible to significant stretcher-strain marks in the way that soft steels are, they have a low drawing limit. Therefore, when deep drawing, we perform intermediate annealing, and then re-draw the product.

 

 

We use a drawing rate of 0.4 for drawing a regular flat sheet and 0.6 for re-drawing.

 

Drawing rate = d/D 　

d = diameter of product to be drawn, D = diameter of circular plate before drawing

 

Reference: Formula for approximate calculation of drawing power

P = ndtσBm

Note: t = thickness, m = correction factor (normally 0.4–1.0), σB = tensile strength of material

 

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3.1. Precautions regarding heat treatment

Almost all cold rolled special steel strips are quenched and tempered as appropriate depending on the application.

The most important considerations when performing these heat treatment processes are:

 

(1) to heat and cool the product evenly using suitable conditions,

(2) to prevent decarburization, scaling, and high temperature corrosion as much as possible, and

(3) to choose a quenching method that will minimize quenching deformation.

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3.2 Temperature of furnace and material

When performing heat treatment, the temperature of the heat treatment furnace is measured and used as the temperature to which the material is heated. However, sometimes there may be a large difference or variation between the material’s actual temperature and the measured furnace temperature. It is therefore necessary to thoroughly investigate temperature properties, and control the temperature and alter the heat treatment process accordingly.

 

3.3 Pre-treatment and atmosphere

When treating cold rolled special steel strips, the higher the carbon content, the easier decarburization occurs. In particular, the risk becomes greater in in high-temperature heating processes like quenching. If the material is contaminated with dirt or foreign substances then high temperature corrosion may occur. Therefore it is necessary to pre-treat material surfaces by cleaning them and adjust the atmosphere of the furnace before heat treatment. RX gas is used as a standard furnace atmosphere during quenching, NX gas during tempering, but N2, H2, AX gases, and others are also used. In some cases, neutral salt-bath furnaces, metal bath furnaces, furnace tubes, cases, and other equipment is used to ensure that the material does not come into direct contact with the air.

 

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3.4 Quenching

In most cases, a value around the midpoint of the quenching temperature range in the table above is used as the quenching temperature. This temperature is maintained for anywhere from several tens of seconds to several minutes depending on the material grade, dimensions, shape, required properties, and quenching method. Quenching conditions have a significant influence on the properties of the product. If the quenching temperature is too high or is maintained for too long, grains become larger, toughness is reduced, and the risk of decarburization increases. On the other hand, if the quenching temperature is too low or is not maintained for long enough, the product does not harden and soft spots may occur. It is therefore important to select appropriate quenching conditions.

 

Normally oil or water is used to cool materials down. Water-quenched products harden better than products oil-quenched products, but are more susceptible to problems such as quenching deformation and cracking. For this reason, except in some special cases, oil quenching is used for cold-rolled special steel strips.

 

To avoid quenching deformation, the oil temperature is increased and martempering is performed. In special cases, quenching is performed in a salt bath or metal bath (austempering). For ribbon shapes or simple shapes, stool quenching, press quenching, and other methods are employed.

Grade	Quenching temperature (°C)
TE-2	790–850 oil quenching (760–820 water quenching)
SK4	790–850 oil quenching (760–820 water quenching)
SK5	790–850 oil quenching (760–820 water quenching)
SK6	790–850 oil quenching (760–820 water quenching)
SK7	790–850 oil quenching (760–820 water quenching)
SKS51	790–850 oil quenching (760–820 water quenching)
SKS2	830–880 oil quenching
SKS7	830–880 oil quenching
S70C	790–850 oil quenching
S60C	800–860 water quenching
S55C	800–860 water quenching
S45C	800–850 water quenching
S15C	800–860 water quenching

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3.5 Tempering

In spite of their hardness, quenched materials lack toughness and are brittle. To be finished into materials that possess toughness and strength, they must therefore must be tempered. Tempering conditions are determined depending on the required properties of each material by considering test results, the steel grade's quenching and tempering properties, and other factors. For cold-rolled special steel strips, long tempering time is used for certain cases (particularly when toughness is required) because the amount of material used is small and tempering work is often carried out consecutively. However, it would seem that most manufacturers often use a short tempering time of no longer than a few minutes. Moreover, due to the nature of the consecutive tempering process, if time is short then the temperature is set a little higher and products are tempered repeatedly. However, as a general rule, materials that are tempered at low temperature for a long time have more toughness than those that are tempered at high temperature. Care is therefore taken to avoid making the tempering furnace shorter, the tempering temperature higher, and the tempering time shorter than necessary. Using an oil, metal, or salt bath for tempering makes it possible to reduce time compared to open-air tempering. Quenching and tempering properties for common steel grades are shown in the graphs below.

 

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