Types of Steel Alloy

TYPES OF ALLOY STEEL

Common Steel Alloys and Typical Uses

1010:This is one of the most widely used low

carbon steels for low strength applications. It is best suited for parts whose fabrication involves moderate to severe forming and

some machining. Its weldability is excellent and it can be case hardened for wear

resistance by cyaniding.

1018:

Is a popular carburizing grade of steel. It can be strengthenedby cold working or surface hardened by carburizing or cyaniding. It isrelatively soft and has good weldability and formability.

1020:

Is a general-purpose low-carbon “mild” steel. It is easy to fabricateby the usual methods such as mild cold or hot forming and welding.It is weldable by all processes and the resulting welds are of extremelyhigh quality.

4130:This chromium-molybdenum alloy is one of the most widelyused aircraft steels because of its combination of weldability, ease offabrication and mild hardenability. In relatively thin sections, it may beheat treated to high strength levels. In the normalized condition it hasadequate strength for many applications. It may be nitrided for resistanceto wear and abrasion.

4140:

This chromium-molybdenum alloy is a deep hardening steelused where strength and impact toughness are required. It has highfatigue strength making it suitable for critical stressed applications. Itmay be nitrided for increased re sis tance to wear and abrasion.

4340:This chromium-nickel-molybdenum alloy is a widely used deep hardeningsteel. It possesses remarkable ductility and toughness. Withits high alloy con tent uniform hardness is developed by heat treatmentin relatively heavy sections. Its high fatigue strength makes it ideal forhighly stressed parts.

6150:

This chromium-vanadium alloy steel is similar to 4340. It hasgood hardenability, good fatigue properties and excellent resistance toimpact and abrasion.

8620:This is a “triple alloy” chromium-nickel-molybdenum steel.It is readily carburized. It may be heat treated to produce a strong,tough core and high case hardness. It has excellent machinability andresponds well to polishing operations. It is easily welded by any of thecommon welding processes, although the section should be heated andstress relieved after welding.

9310:

This chromium-nickel-molybdenum alloy is a carburizing steelcapable of attaining high case hardness with high core strength. It hasexcellent toughness and ductility.

4620:

This nickel-molybdenum alloy is a carburizing steel capable ofdeveloping high case hardness and core toughness. It can be forgedsimilarly to the other carburizing grades. Because of its relatively highnickel content, it is not as readily cold-formed.

5160:This carbon-chromium grade of spring steel has a high yield/tensile strength ratio, excellent toughness and high ductility. It is verydifficult to ma chine in the as-rolled condition and should be annealedprior to machining. It is not readily welded, but it can be welded by eitherthe gas or arc welding proc esses if the section involved is preheatedand stress relieved after welding.

52100:This high carbon-high chromium alloy is produced by theelectric furnace process and then vacuum degassed to meet the rigidstandards of the aircraft industry for bearing applications. It developshigh hardness and has exceptional resistance to wear and abrasion.

The first two digits indicate the type of alloy according to alloying elements as follows:

13xx Manganese 1.75 per cent 40xx Molybdenum 0.20 or 0.25 per cent 41xx Chromium 0.50, 0.80 or 0.95 per cent — Molybdenum 0.12, 0.20 or 0.30 per cent 43xx Nickel 1.83 per cent—Chromium 0.50 or 0.80 percent Molybdenum 0.25 percent. 44xx Molybdenum 0.53 per cent 46xx Nickel 0.85 or 1.83 per cent—Molybdenum 0.20 or 0.25 percent 47xx Nickel 1.05 per cent Chromium 0.45 per cent 48xx Nickel 3.50 per cent Molybdenum 0.25 per cent 50xx Chromium 0.40 per cent 51xx Chromium 0.80, 0.88, 0.93, 0.95 or 1.00 per cent 5xxxx Carbon 1.04 per cent -- chromium 1.03 or 1.45 per cent 61xx Chromium 0.60 or 0.95 per cent -- Vanadium 0.13 per cent or 0.15 per cent min.

General representation of steels:

EFFECTS OF COMMONALLOYING ELEMENTS IN STEEL

CARBON (C), although not usually considered as an alloying element, isthe most important constituent of steel. It raises tensile strength, hardnessand resistance to wear and abrasion. It lowers ductility, toughnessand machinability.

MANGANESE (Mn) is a deoxidizer and degasifier and reacts with sulphurto improve forge ability. It in creases tensile strength, hard ness, hardenabilityand resistance to wear. It de creases tendency toward scaling anddistortion. It in creases the rate of carbon-penetration in carburizing.

PHOSPHORUS (P) increases strength and hardness and improvesmachinability. However, it adds marked brittleness or cold-shortnessto steel.

SULPHUR (S) Improves machinability in free-cutting steels, but withoutsufficient manganese it produces brittleness at red heat. It decreasesweldability, impact toughness and ductility.

SILICON (Si) is a deoxidizer and degasifier. It increases tensile and yieldstrength, hardness, forge ability and magnetic permeability.

CHROMIUM (Cr) increases tensile strength, hardness, hardenability.toughness, resistance to wear and abrasion. resistance to corrosion andscaling at elevated temperatures.

NICKEL (Ni) increases strength and hard ness without sacrificing ductilityand toughness. It also increases resistance to corrosion and scalingat elevated temperatures when introduced in suitable quantities in highchromium (stainless) steels.

MOLYBDENUM (Mo) increases strength, hardness, hardenability andtoughness, as well as creep resistance and strength at elevated temperatures.It improves machinability and resistance to corrosion and itintensifies the effects of other alloying elements. In hot-work steels, itincreases red-hard ness properties.

TUNGSTEN (W) increases strength, hard ness and toughness. Tungstensteels have superior hot-working and greater cutting efficiency atelevated temperatures.

VANADIUM (V) increases strength, hard ness and resistance to shockimpact. It retards grain growth, permitting higher quenching temperatures.It also enhances the red hardness properties of high speed metalcutting tools and intensifies the individual effects of other major elements.

COBALT (Co) Increases strength and hard ness and permits higherquenching temperatures. It also intensifies the individual effects of othermajor elements in more complex steels.

ALUMINUM (Al) is a deoxidizer and degasifier. It retards grain growthand is used to control austenitic grain size. In nitriding steels it aidsin producing a uniformly hard and strong nitrided case when used inamounts 1.00% - 1.25%.

LEAD (Pb), while not strictly an alloying element, is added to improvemachining characteristics. It is almost completely in soluble in steel, andminute lead particles, well dispersed, reduce friction where the cuttingedge contacts the work. Addition of lead also improves chip-breakingformations.

Common Steel Alloys and Typical Uses

Alloy Application Alloy Application

1020Structural steel, bars,

plates4130

General purpose, high strength steel shafts, gears, and pins

1040 Machinery parts, shafts 4140 Same as 4130

1050 Machinery parts 4150 Same as 4130

1095 Tools, springs 5160High strength gears,

bolts

1137Shafts, screw machine

parts (free-cutting alloy)

8760 Tools, springs, chisels

1141Shafts, machined

parts

Principal effects of major alloying elements for steel[8]

Element Percentage Primary function

Aluminium

0.95–1.30 Alloying element in nitriding steels

Bismuth - Improves machinability

Boron 0.001–0.003 A powerful hardenability agent

Chromium

0.5–2 Increases hardenability

4–18 Increases corrosion resistance

Copper 0.1–0.4 Corrosion resistance

Lead - Improved machinability

Manganese

0.25–0.40 Combines with sulfur and with phosphorus to reduce the brittleness. Also helps to remove excess oxygen from molten steel.

>1 Increases hardenability by lowering transformation points and causing transformations to be sluggish

Molybdenum

0.2–5Stable carbides; inhibits grain growth. Increases the toughness of steel, thus making molybdenum a very valuable alloy metal for making the cutting parts of machine tools and also the turbine blades of turbojet engines. Also used in rocket motors.

Nickel2–5 Toughener

12–20 Increases corrosion resistance

Silicon

0.2–0.7 Increases strength

2.0 Spring steels

Higher percentages

Improves magnetic properties

Sulfur 0.08–0.15 Free-machining properties

Titanium - Fixes carbon in inert particles; reduces martensitic hardness in chromium steels

Tungsten

- Also increases the melting point.

Vanadium

0.15Stable carbides; increases strength while retaining ductility; promotes fine grain structure. Increases the toughness at high temperatures

Steel classes

Crucible steel Carbon steel (≤2.1% carbon; low alloy) Spring steel (low or no alloy) Alloy steel (contains non-carbon elements) Maraging steel (contains nickel) Stainless steel (contains ≥10.5% chromium) Weathering steel Tool steel (alloy steel for tools)

2.Cutting alloy steel

Cemented Carbides Steel Stellites Steel

Cutting alloy steel used on tools that operated high cutting speeds with high temperature up to 1000 C developed in the cutting edge.

Powdery mixture of Tungsten (W) & Titanium carbide (TiC) with metallic cobalt which is 1st compacted & then sintered.

In their finished form cemented carbides consists of extremely fine grains of tungsten &Titanium carbide with cobalt binder.

Rockwell Hardness number up to 85 & even higher &they retain his hardness @ temperature up to 1000 C.

Most widely used grade of cemented carbide contain 2-15% Cobalt .

Cemented carbides steel is extremely resistance to wear .

They contain large amounts of metal like cobalt and tungsten have high hardness (RHN 60-65) melt at high temperature.

Tips or rods from 5-10 mm thick cast of this alloy s are used in hard facing of tools by welding technique to increase the life of the cutting edges.

High speed steel(HSS or HS) is a subset of tool steels, commonly used in tool bits and cutting tools. It is often used in power saw blades and drill bits. It is superior to the older high carbon steel tools used extensively through the 1940s in that it can withstand higher temperatures without losing its temper (hardness). This property allows HSS to cut faster than high carbon steel, hence the name high speed steel. At room temperature, in their generally recommended heat treatment, HSS grades generally display high hardness (above HRC60) and a high abrasion resistance (generally linked to vanadium content often used in HSS) compared to common carbon and tool steels.

M2M2 is a high speed steel in tungsten-molybdenum series. The carbides in it are small and evenly distributed. It has high wear resistance. After heat treatment, its hardness is the same as T1, but its bending strength can reach 4700 MPa, and its toughness and thermo plasticity are higher than T1 by 50%. It is usually used to manufacture a

variety of tools, such as drill bits, taps and reamers. Its decarburization sensitivity is a little bit high.

M35M35 is similar to M2, but with 5% cobalt added. The addition of cobalt increases heat

resistance.M42

M42 is a molybdenum series high speed steel alloy with an additional 8% cobalt. It is widely used in metal manufacturing because of its superior red-hardness as compared to more conventional high speed steels, allowing for shorter cycle times in production environments due to higher cutting speeds or from the increase in time between tool changes. M42 is also less prone to chipping when used for interrupted cuts and cost

less when compared to the same tool made of carbide. Tools made from cobalt-bearing high speed steels can often be identified by the letters HSS-Co.

Alloying compositions of common high speed steel grades (by %wt)

Grade C Cr Mo W V Co Mn Si

T1[7] 0.65–0.80 3.75–4.00 - 17.25–18.75 0.9–1.3 - 0.1–0.4 0.2–0.4

M2 0.95 4.2 5.0 6.0 2.0 - - -

M7 1.00 3.8 8.7 1.6 2.0 - - -

M35 0.94 4.1 5.0 6.0 2.0 5.0 - -

M42 1.10 3.8 9.5 1.5 1.2 8.0 - -

Note that impurity limits are not included

3.Special alloy steel

Heat resisting steels Magnet steels Shock resisting steels Stainless steels High speed Stainless steels

Plain carbon steels, if used for cutting tools, lack certain characteristics necessary for high-speed production, such as red

hardness and hot -strength toughness. The effect of alloying elements in steel is of great advantage and yields tool steels that overcome many of the shortcomings of the plain carbon steels.

Tool steels are defined by U.S. steel producers as "carbon or alloy steels capable of being hardened and tempered". Many alloy steels

would fit this loose definition. Tool steels usually contain significantly more alloying elements than alloy steels.There are six major categories one of which contains grades intended for special purposes. A prefix letter is used in the alloy identification system to show use category, and the specific alloy in a particular category is

identified by one or two digits.

Tool steels:

Tool Steel Type Prefix Specific Types

Cold Work W = Water HardeningO = Oil HardeningA = Medium alloy Air

HardeningD = High Carbon, High

Chromium

W1, W2, W5O1, O2, O6, O7A2, A4, A6, A7, A8, A9, A10,

A11D2, D3, D4, D5, D7

Shock Resisting S S1, S2, S4, S5, S6, S7

Hot Work H H10-H19 Chromium typesH20-H39 Tungsten typesH40-H59 Molybdenum types

High Speed M T

Molybdenum types (M1, M2, M3-1, M3-2, M4, M6, M7, M10, M33, M34, M36, M41, M42, M46, M50

Tungsten types (T1, T4, T5, T6, T8, T15)

Mold Steels P P6, P20, P21

Special Purpose L and F series L2, L6

The following are some of the characteristics of tool steels:Composition and physical properties vary significantly (some tool steels have compositions that fit into the composition ranges of carbon and alloy steels, but most tool steels have alloy concentrations that are significantly higher than the carbon and alloy steels),One important factor that should be kept in mind is that the alloy additions do not improve corrosion resistance even though some grades have as much chromium as stainless steels. The reason for this is that alloy elements are usually combined with carbon to form carbides.The most significant metallurgical difference between tool steels and the other steels is their microstructure.

A fully hardened carbon steel or alloy steel would have only martensite as the predominant phase. Most tool steels have a hardened structure of martensite and alloy carbides.Require special heat treatment processes ,Higher cost than alloy steels,Better hardenability than most carbon and alloy steels,High heat resistanceEasier to heat treat,More difficult to machine than carbon and alloy steelsMost tool steels are sold as hot-finished shapes such as rounds and bars,Cold-finished sheets are not available because it is difficult to cold roll or cold finish these materials.

Water Hardening Tool Steels

(W series)

Oil Hardening Tool Steels

(O-Series)

Medium Alloy Air Hardening

Steels(A-series)

High Carbon High Chromium

Steels(D-series)

Essentially these are carbon steels with 0.60 to 1.10 % carbon.

Lowest cost tool steels.Soft core(for toughness)

with hard shallow layer (for wear resistance).

Use of w-series steels is declining.

0.90 to 1.45 % Carbon with Mn, Si, W, Mo, Cr.

They contain graphite in the hardened structure along with martensite. (Graphite acts as a lubricator and also makes machining easier.

Tungsten forms tungsten carbide which improves the abrasion resistance and edge retention in cutting devices.

5 to 10 % alloying elements (Mn, Si, W, Mo, Cr, V, Ni) to improve the hardenability, wear resistance, toughness.

All D-series contain 12% Cr and over 1.5 % C.

Air or oil quench.Low distortion, high

abrasion resistance. 

SAE - AISI Number Classification

1XXX Carbon steelsLow carbon steels: 0 to 0.25 % CMedium carbon steels: 0.25 to 0.55 % CHigh carbon steels: Above 0.55 % Carbon

2XXX Nickel steels5 % Nickel increases the tensile strength without reducing ductility.8 to 12 % Nickel increases the resistance to low temperature impact15 to 25 % Nickel (along with Al, Cu and Co) develop high magnetic properties. (Alnicometals)25 to 35 % Nickel create resistance to corrosion at elevated temperatures.

Table 1. Classification of steels

3XXX Nickel-chromium steelsThese steels are tough and ductile and exhibit high wear resistance , hardenability and high resistance to corrosion.

4XXX Molybdenum steelsMolybdenum is a strong carbide former. It has a strong effect on hardenability and high temperature hardness. Molybdenum also increases the tensile strength of low carbon steels.

5XXX Chromium steelsChromium is a ferrite strengthener in low carbon steels. It increases the core toughness and the wear resistnace of the case in carburized steels.

86XX87XX93XX94XX97XX98XX

Triple Alloy steels which include Nickel (Ni), Chromium (Cr), and Molybdenum (Mo).These steels exhibit high strength and also high strength to weight ratio, good corrosion resistance. 

Element Effect

Aluminum Ferrite hardenerGraphite formerDeoxidizer

Chromium Mild ferrite hardenerModerate effect on hardenabilityGraphite formerResists corrosionResists abrasion

Table 2. The effect of alloying elements on the properties of steel

Cobalt High effect on ferrite as a hardenerHigh red hardness

Molybdenum Strong effect on hardenabilityStrong carbide formerHigh red hardnessIncreases abrasion resistance

Manganese Strong ferrite hardener

Nickel Ferrite strengthenerIncreases toughness of the hypoeutectoid steelWith chromium, retains austeniteGraphite former

Copper Austenite stabilizerImproves resistance to corrosion

Silicon Ferrite hardenerIncreases magnetic properties in steel

Phosphorus Ferrite hardenerImproves machinabilityIncreases hardenability

Red Hardness: This property , also called hot-hardness, is related to the resistance of the steel to the softening effect of heat. It is reflected to some

extent in the resistance of the material to tempering.Hardenability: This property determines the depth and distribution of hardness

induced by quenching.Hot-shortness: Brittleness at high temperatures is called hot-shortness which is usually caused by sulfur. When sulfur is present, iron and sulfur form iron

sulfide (FeS) that is usually concentrated at the grain boundaries and melts at temperatures below the melting point of steel. Due to the melting of iron sulfide, the cohesion between the grains is destroyed, allowing cracks to

develop. This occurs when the steel is forged or rolled at elevated temperatures. In the presence of manganese, sulfur tends to form manganese

sulfide (MnS) which prevents hot-shortness.

Cold-shortness: Large quantities of phosphorus (in excess of 0.12%P) reduces the ductility, thereby increasing the tendency of the steel to crack when cold worked. This brittle condition at temperatures below the recrystallization temperature is called cold-shortness.