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 strengthened by cold working or surface hardened by carburizing or cyaniding. It is relatively soft and has good weldability and formability. 1020 is a general-purpose low-carbon “mild” steel. It is easy to fabricate by the usual methods such as mild cold or hot forming and welding. It is weldable by all processes and the resulting welds are of extremely high quality. 4130 This chromium-molybdenum alloy is one of the most widely used aircraft steels because of its combination of weldability, ease of fabrication and mild hardenability. In relatively thin sections, it may be heat treated to high strength levels. In the normalized condition it has adequate strength for many applications. It may be nitrided for resistance to wear and abrasion. 4140 This chromium-molybdenum alloy is a deep hardening steel used where strength and impact toughness are required. It has high fatigue strength making it suitable for critical stressed applications. It may be nitrided for increased resistance to wear and abrasion. 4340 This chromium-nickel-molybdenum alloy is a widely used deep-hardening steel. It possesses remarkable ductility and toughness. With its high alloy content uniform hardness is developed by heat treatment in relatively heavy sections. Its high fatigue strength makes it ideal for highly stressed parts. 6150 This chromium-vanadium alloy steel is similar to 4340. It has good hardenability, good fatigue properties and excellent resistance to impact 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 and responds well to polishing operations. It is easily welded by any of the common welding processes, although the section should be heated and stress relieved after welding. 9310 This chromium-nickel-molybdenum alloy is a carburizing steel capable of attaining high case hardness with high core strength. It has excellent toughness and ductility. 4620 This nickel-molybdenum alloy is a carburizing steel capable of developing high case hardness and core toughness. It can be forged similarly to the other carburizing grades. Because of its relatively high nickel 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 very difficult to machine in the as-rolled condition and should be annealed prior to machining. It is not readily welded, but it can be welded by either the gas or arc welding processes if the section involved is preheated and stress relieved after welding. 52100 This high carbon-high chromium alloy is produced by the electric furnace process and then vacuum degassed to meet the rigid standards of the aircraft industry for bearing applications. It develops high hardness and has exceptional resistance to wear and abrasion.
ENDING OF 4130 STEEL Specification MIL-S-18729C states that 4130 steel .749 inch and less in thickness shall withstand bending without cracking at room temperature, with the axis of bending transverse to the direction of rolling, through an angle as indicated in the table. Condition N materials shall be bent around a diameter three times the thickness of the material. Test samples are bent cold either by pressure or blows. In the event of dispute, bending shall be by pressure. Paragraph 4.5.3 of the specification states that the formation of cracks not over 1/16" in aggregate lengths at the corners on the outside of the bend shall not be cause for rejection.
Thickness of Material Inches	Min. Angle of Bend Cond. N Degrees
Under .090 .090 to .187, Incl. Over .187 to .249, Incl. Over .249 to .749, Incl.	180 135 90 90

SHEET GAUGES
Gauge No.	STEEL SHEETS		GALVANIZED SHEETS		STAINLESS STEEL SHEETS			ALUMINUM SHEETS
	Weight Lbs. per Square Foot	Thick- ness in Inches	Weight Lbs. per Square Foot	Thick- ness in Inches	Weight Lbs. per Square Foot		Approx. Thick- ness in Inches	Weight Lbs. per Square Foot (1100)	Thick- ness in Inches
					Straight Chromium (400 Series)	Chromium Nickel (300 Series)
38 37 36 35 34 33	.25000 .26562 .28125 .31250 .34375 .39500	.0060 .0064 .0067 .0075 .0082 .0090						.0558 .0627 .0705 .0791 .0888 .0998	.00396 .00445 .00500 .00561 .00630 .00708
32 31 30 29 28	.40625 .43750 .50000 .56250 .62500	.0097 .0105 .0120 .0135 .0149	.56250 .59375 .65625 .71875 .78175	.0134 .0142 .0157 .0172 .0187	.3708 .4506 .5150 .5794 .6438	.3780 .4594 .5250 .5906 .6562	.010 .011 .013 .014 .016	.1121 .1259 .1410 .1593 .1777	.00795 .00893 .0100 .0113 .0126
27 26 25 24 23	.68750 .75000 .87500 1.0000 1.1250	.0164 .0179 .0209 .0239 .0269	.84375 .90625 1.03125 1.15625 1.28125	.0202 .0217 .0247 .0276 .0306	.7081 .7725 .9013 1.0300 1.1587	.7218 .7875 .9187 1.0500 1.1813	.017 .019 .022 .025 .028	.2002 .2242 .2524 .2834 .3187	.0142 .0159 .0179 .0201 .0226
22 21 20 19 18	1.2500 1.3750 1.5000 1.7500 2.0000	.0299 .0329 .0359 .0418 .0478	1.40625 1.53125 1.65625 1.90625 2.15625	.0336 .0366 .0396 .0456 .0516	1.2875 1.4160 1.5450 1.8025 2.0600	1.3125 1.4437 1.5750 1.8375 2.1000	.031 .034 .038 .044 .050	.3567 .4019 .4512 .5062 .5682	.0253 .0285 .0320 .0359 .0403
17 16 15 14 13	2.2500 2.5000 2.8125 3.1250 3.7500	.0538 .0598 .0673 .0747 .0897	2.40625 2.65625 2.96875 3.28125 3.90625	.0575 .0635 .0710 .0785 .0934	2.3175 2.5750 2.8968 3.2187 3.8625	2.3625 2.6250 2.9531 3.2812 3.9375	.056 .063 .070 .078 .094	.6387 .7163 .8051 .9038 1.015	.0453 .0508 .0571 .0641 .0720
12 11 10 9 8	4.3750 5.0000 5.6250 6.2500 6.8750	.1046 .1196 .1345 .1495 .1644	4.53125 5.15625 5.78125 6.40625 7.03125	.1084 .1233 .1382 .1532 .1681	4.5063 5.1500 5.7937 6.4375 7.0813	4.5937 5.25OU 5.9062 6.5625 7.2187	.109 .125 .141 .156 .172	1.139 1.279 1.437 1.613 1.812	.0808 .0907 .1019 .1144 .1285
7 6 5 4 3	7.5000 8.1250 8.7500 9.3750 10.0000	.1793 .1943 .2092 .2242 .2391						2.035 2.284 2.565 2.881 3.235	.1443 .1620 .1819 .2043 .2294

STANDARD AISI and SAE STEELS

Studies have been made in the steel industry for the purpose of establishing certain “standard” steels and eliminating as much as possible the manufacture of other steels which vary only slightly in composition from the standard steels, These standard steels are selected on the basis of serving the significant metallurgical and engineering needs of fabricators and users of steel products.

STANDARD CARBON STEELS

Definition. By common custom. steel is considered to be carbon steel when no minimum content is specified or required for aluminum, boron. chromium, cobalt, columbium, molybdenum. nickel, titanium, tungsten, vanadium or zirconium, or for any other element added to obtain a desired alloying effect; when the specified minimum for copper does not exceed 0.40 per cent; or when the maximum content specified for any of the following elements does not exceed the percentages noted: m7anganese 1.65, silicon 0.60, copper 0.60.

Numbering System. In the AISI system of identification. the prefix “B” is used to designate acid bessemer steel. The letter “L’’ within the grade number is used to identify leaded steels.

A four-numeral series is used to designate graduations of chemical composition of carbon steel. The last two numbers of which are intended to indicate the approximate middle of the carbon range. For example, in the grade designation 1035, 35 represents a carbon range of 0.32 to 0.38 per cent.

It is necessary, however. to deviate from this rule and to Interpolate numbers in the case of some carbon ranges and for variations in manganese, phosphorus or sulphur with the same carbon range.

The first two digits of the four-numeral series of the various grades of carbon steel and their meanings are as follows:
10xx Nonresulphurized carbon steel grades
11xx Resulphurized carbon steel grades
12xx Rephosphorized and resulphurized carbon steel grades
I5xx Nonresulphurized high manganese carbon steels.

STANDARD ALLOY STEELS

Definition. Steel is considered to be alloy steel when the maximum of the range given for the content of alloying elements exceeds one or more of the following limits: manganese, 1.65 per cent; silicon, 0.60 per cent; copper, 0.60 per cent; or in which a definite range or a definite minimum quantity of any of the following elements is specified or required within the limits of the recognized field of constructional alloy steels: aluminum, boron, chromium up to 3.99 per cent, cobalt, columbium, molybdenum, nickel, titanium, tungsten, vanadium, zirconium or any other alloying element added to obtain a desired alloying effect.

Numbering System. In the AISI numbering system, the prefix letter E is used to designate steels normally made only by the basic electric furnace process. Steels without a prefix letter are normally manufactured by the basic open hearth or basic oxygen processes, but may be manufactured by the basic electric furnace process with adjustments in phosphorus and sulphur limits.

The last two digits of the four-numeral series are intended to indicate the approximate middle of the carbon range. For example, in the grade designation 4142, 42 represents a carbon range of 0.40 to 0.45 per cent. (Where a five-numeral series occurs, the last three digits indicate the carbon content.) It is necessary, however, to deviate from this rule and to interpolate numbers in the case of some carbon ranges, and for variations in manganese, sulphur, chromium, or other elements.

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 per cent — Molybdenum 0.25 per cent
44xx Molybdenum 0.53 per cent
46xx Nickel 0.85 or 1.83 per cent — Molybdenum 0.20 or 0.25 per cent
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.
86xx Nickel 0.55 per cent --Chromium 0.50 per cent-- Molybdenum 0.25 per cent
87xx Nickel 0.55 per cent -- Chromium 0.50 per cent -- Molybdenum 0.35
88xx Nickel 0.55 per cent --Chromium 0.50 per cent -- Molybdenum 0.35
92xx Silicon 2.00 per cent

EFFECTS OF COMMON
ALLOYING ELEMENTS IN STEEL

By definition, steel is a combination of iron and carbon. Steel is alloyed with various elements to improve physical properties and to produce special properties, such as resistance to corrosion or heat. Specific effects of the addition of such elements are outlined below:

Carbon (C), although not usually considered as an alloying element, is the most important constituent of steel. It raises tensile strength, hardness and resistance to wear and abrasion. It lowers ductility, toughness and machinability.

Manganese (Mn) is a deoxidizer and degasifier and reacts with sulphur to improve forgeability. It increases tensile strength, hardness, hardenability and resistance to wear. It decreases tendency toward scaling and distortion. It increases the rate of carbon-penetration in carburizing.

Phosphorus (P) increases strength and hardness and improves machinability. However, it adds marked brittleness or cold-shortness to steel.

Sulphur (S) Improves machinability in free-cutting steels, but without sufficient manganese it produces brittleness at red heat. It decreases weldability, impact toughness and ductility.

Silicon (Si) is a deoxidizer and degasifier. It increases tensile and yield strength, hardness, forgeability and magnetic permeability.

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

Nickel (Ni) increases strength and hardness without sacrificing ductility and toughness. It also increases resistance to corrosion and scaling at elevated temperatures when introduced in suitable quantities in high chromium (stainless) steels.

Molybdenum (Mo) increases strength, hardness, hardenability and toughness, as well as creep resistance and strength at elevated temperatures. It improves machinability and resistance to corrosion and it intensifies the effects of other alloying elements. In hot-work steels, it increases red-hardness properties.

Tungsten (W) increases strength, hardness and toughness. Tungsten steels have superior hot-working and greater cutting efficiency at elevated temperatures.

Vanadium (V) increases strength, hardness and resistance to shock impact. It retards grain growth, permitting higher quenching temperatures. It also enhances the red hardness properties of high speed metal cutting tools and intensifies the individual effects of other major elements.

Cobalt (Co) Increases strength and hardness and permits higher quenching temperatures. It also intensifies the individual effects of other major elements in more complex steels.

Aluminum (Al) is a deoxidizer and degasifier. It retards grain growth and is used to control austenitic grain size. In nitriding steels it aids in producing a uniformly hard and strong nitrided case when used in amounts 1.00% - 1.25%.

Lead (Pb), while not strictly an alloying element, is added to improve machining characteristics. It is almost completely insoluble in steel, and minute lead particles, well dispersed, reduce friction where the cutting edge contacts the work. Addition of lead also improves chip-breaking formations.

HEAT TREATMENT OF STEEL
By thermal treatment, steel may be made harder or softer, stresses induced or relieved, mechanical properties increased or decreased, crystalline structure changed, machinability enhanced, etc. The terms used to describe such heat treatments and their effects are listed below.

NORMALIZE
Normalizing consists of uniform heating to a temperature slightly above the point at which grain structure is affected (known as the critical temperature), followed by cooling in still air to room temperature. This produces a uniform structure and hardness throughout.

ANNEAL
When not preceded by a descriptive adjective, annealing consists of heating to and holding at a suitable temperature, then allowing to cool slowly. Annealing removes stresses, reduces hardness, increases ductility and produces a structure favorable for formability.

Full Anneal - This term is synonymous with annealing and is used to differentiate anneal from bright anneal, stress relief anneal, etc.

Spherodize Anneal - This treatment is similar to full annealing except the steel is held at an elevated temperature for a prolonged period of time, followed by slow cooling in order to produce a microstructure where carbides exist in a globular or spheroidal form.

Soft Anneal - When maximum softness and ductility are required without change in grain structure, steel should be ordered soft annealed. This process consists of heating to a temperature slightly below the critical temperature and cooling in still air.

Stress Relief Anneal - Stress relieving is intended to reduce the residual stresses imparted to the steel in the drawing operation. It generally consists of heating the steel to a suitable point below the critical temperature followed by slow cooling.

Bright Anneal - This process consists of annealing in a closely controlled furnace atmosphere which will permit the surface to remain relatively bright.

QUENCH
Quenching consists of heating steel above the critical range, then hardening by immersion in an agitated bath of oil, water, brine or caustic. Quenching increases tensile strength, yield point and hardness. It reduces ductility and impact resistance. By subsequent tempering some ductility and impact resistance may be restored, but at some sacrifice of tensile strength, yield point and hardness.

TEMPER
Tempering is the reheating of steel, after quenching, to the specified temperature below the critical range, then air cooling. It is done in furnaces, oil or salt baths, at temperatures varying from 300 to 1200°F. Low tempering temperatures give maximum hardness and wear resistance. Maximum toughness is achieved at the higher temperatures.

RELATIONSHIP OF HARDNESS TO TENSILE
STRENGTH OF CARBON & ALLOY STEEL

Brinell Indentation Diameter mm	Brinell Hardness Number		Rockwell Hardness Number		Tensile Strength (Approx. 1000 psi)
	Standard Ball	Tungsten Carbide Ball	B Scale	C Scale
2.45 2.50 2.55 2.60 2.65	-- -- -- -- --	627 601 578 555 534	-- -- -- -- --	58.7 57.3 56.0 54.7 53.5	347 328 313 298 288
2.70 2.75 2.80 2.85 2.90	-- -- -- -- --	514 495 477 461 444	-- -- -- -- --	52.1 51.0 49.6 48.5 47.1	274 264 252 242 230
2.95 3.00 3.05 3.10 3.15	429 415 401 388 375	429 415 401 388 375	-- -- -- -- --	45.7 44.5 43.1 41.8 40.4	219 212 202 193 184
3.20 3.25 3.30 3.35 3.40	363 352 341 331 321	363 352 341 331 321	-- -- -- -- --	39.1 37.9 36.6 35.5 34.3	177 171 164 159 153
3.45 3.50 3.55 3.60 3.65	311 302 293 285 277	311 302 293 285 277	-- -- -- -- --	33.1 32.1 30.9 29.9 28.8	149 146 141 138 134
3.70 3.75 3.80 3.85 3.90	269 262 255 248 241	269 262 255 248 241	-- -- -- -- 100.00	27.6 26.6 25.4 24.2 22.8	130 127 124 120 116
3.95 4.00 4.05 4.10 4.15	235 229 223 217 212	235 229 223 217 212	99.0 98.2 97.3 96.4 95.5	21.7 20.5 -- -- --	114 111 104 103 100
4.20 4.25 4.30 4.35 4.40	207 201 197 192 187	207 201 197 192 187	94.6 93.8 92.8 91.9 90.7	-- -- -- -- --	99 97 94 92 90
4.45 4.50 4.55 4.60 4.65	183 179 174 170 167	183 179 174 170 167	90.0 89.0 87.8 86.8 86.0	-- -- -- -- --	89 88 86 84 83
4.70 4.80 4.90 5.00 5.10	163 156 149 143 137	163 156 149 143 137	85.0 82.9 80.8 78.7 76.4	-- -- -- -- --	82 80 73 71 67
5.20 5.30 5.40 5.50 5.60	131 126 121 116 111	131 126 121 116 111	74.0 72.0 69.0 67.6 65.7	-- -- -- -- --	65 63 60 58 56
* This table, which is based on ASTM A 370-68, Table lll, lists the approximate relationship of hardness values to corresponding approximate tensile strength values of steels. Some compositions and processing histories may deviate from these relationships. The data in this table do not represent hardness-to-tensile strength conversions for austenitic, ferritic, and martensitic stainless steel. If more precise conversions are required, they should be developed for each specific composition and heat treatment. Related Rockwell superficial hardness numbers, if of interest, may be found in ASTM A 370-68.

METAL FINISHING DATA

Cadmium Plating - a nonporous electrolytically deposited layer of cadmium that offers better corrosion resistance for steel than zinc coating. Plating is per specification MIL-P-416A ( or equivalent commercial specification QQ-P-416A). Three types of cadmium plating are considered in this specification:
Type I – Pure silver-colored cadmium plate, without supplementary treatment. This type of cadmium coating was used on all steel aircraft hardware in the past.
Type II – This consists of Type I plating followed by a chromate treatment. Type II plating is a light to dark gold color. It has improved corrosion resistance. Procurement specifications for aircraft hardware now specify Type II plating.
Type III – This is Type I coating followed by a phosphate treatment. It is used mainly as a paint base.
In addition to the type of plating, MIL-P-416A also defines the plating thickness in terms of the following classes:
Class 1 - .0005" minimum, Class 2 - .0003" minimum, Class 3 - .0002" min.
Steel parts with a Rockwell hardness greater than Rc40 (approx. 180,000 PSI tensile strength) must be stress relieved before cleaning and plating, and if they are subject to flexure (springs, etc.) they must be baked at 375°F. within 30 minutes after plating to prevent hydrogen embrittlement.

Anodizing - This finish, applied to aluminum by an acid plating process, hardens the surface, reduces porosity, increases abrasion resistance and has high dielectric strength. Anodized aluminum can be dyed almost any color. Specification MIL-A-8625B covers three types of anodizing:

Type I – Chromic anodize coating will vary from a light to a dark gray color, depending on the alloy. Coating is given a chromate treatment to seal surface.
Type II – Sulfuric anodize coating is the best coating for dying (Class 2). Non-dyed (Class 1) coatings will have a dull yellow-green (gold) appearance when sealed with a chromate treatment.
Type III – Hard anodize coating can be used as an electrical insulation coating or as an abrasion resisting coating on devices such as hydraulic cylinders, wear surfaces and actuating cams.

Bonderizing - a chemical process which rust proofs steel and supplies a base for paint or enamel. This treatment is used on AN301 steel aircraft nails.
Phosphate Coating - is a light coating applied to steel parts as a paint base. Most Tinnerman speed nuts are phosphate coated before painting with olive drab paint.