41xx steel is a family of SAE steel grades, as specified by the Society of Automotive Engineers (SAE). Alloy

Alloy

An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...

ing elements

Chemical element

A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...

 include chromium

Chromium

Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...

 and molybdenum

Molybdenum

Molybdenum , is a Group 6 chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek , meaning lead, itself proposed as a loanword from Anatolian Luvian and Lydian languages, since its ores were confused with lead ores...

, and as a result these materials are often referred to as chromoly steel or CRMO. They have an excellent strength to weight ratio, are easily welded

Welding

Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...

 and are considerably stronger

Strength of materials

In materials science, the strength of a material is its ability to withstand an applied stress without failure. The applied stress may be tensile, compressive, or shear. Strength of materials is a subject which deals with loads, deformations and the forces acting on a material. A load applied to a...

 and harder than standard 1020 steel.

While these grades of steel do contain chromium, it is not in great enough quantities to provide the corrosion

Corrosion

Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...

 resistance found in stainless steel

Stainless steel

In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....

.

Examples of applications for 4130 and 4140 include structural tubing, bicycle frame

Bicycle frame

A bicycle frame is the main component of a bicycle, on to which wheels and other components are fitted. The modern and most common frame design for an upright bicycle is based on the safety bicycle, and consists of two triangles, a main triangle and a paired rear triangle...

s, firearms receivers, clutch

Clutch

A clutch is a mechanical device which provides for the transmission of power from one component to another...

 and flywheel

Flywheel

A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have a significant moment of inertia, and thus resist changes in rotational speed. The amount of energy stored in a flywheel is proportional to the square of its rotational speed...

 components, and roll cage

Roll cage

A roll cage is a specially constructed frame built in the cab of a vehicle to protect its occupants from being injured in an accident, particularly in the event of a roll-over. Roll cages are used in nearly all purpose-built racecars, and in most cars modified for racing...

s. 4150 stands out as being one of the steels accepted for use in M16 rifle and M4 carbine barrels by the United States military. These steels are also used in aircraft

Aircraft

An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

 parts and therefore 41xx grade structural tubing is sometimes referred to as "aircraft tubing".

Properties

Alloy composition (by weight)

SAE grade	% Cr Chromium Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...	% Mo Molybdenum Molybdenum , is a Group 6 chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek , meaning lead, itself proposed as a loanword from Anatolian Luvian and Lydian languages, since its ores were confused with lead ores...	% C Carbon Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...  *	% Mn Manganese Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...	% P Phosphorus Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...  (max)	% S (max)	% Si Silicon Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
4118	0.40–0.60	0.08–0.15	0.18–0.23	0.70–0.90	0.035	0.040	0.15–0.35
4120	0.40–0.60	0.13–0.20	0.18–0.23	0.90–1.20	0.035	0.040	0.15–0.35
4121	0.45–0.65	0.20–0.30	0.18–0.23	0.75–1.00	0.035	0.040	0.15–0.35
4130	0.80–1.10	0.15–0.25	0.28–0.33	0.40–0.60	0.035	0.040	0.15–0.35
4135	0.80–1.10	0.15–0.25	0.33–0.38	0.70–0.90	0.035	0.040	0.15–0.35
4137	0.80–1.10	0.15–0.25	0.35–0.40	0.70–0.90	0.035	0.040	0.15–0.35
4140	0.80–1.10	0.15–0.25	0.38–0.43	0.75–1.00	0.035	0.040	0.15–0.35
4142	0.80–1.10	0.15–0.25	0.40–0.45	0.75–1.00	0.035	0.040	0.15–0.35
4145	0.80–1.10	0.15–0.25	0.43–0.48	0.75–1.00	0.035	0.040	0.15–0.35
4147	0.80–1.10	0.15–0.25	0.45–0.50	0.75–1.00	0.035	0.040	0.15–0.35
4150	0.80–1.10	0.15–0.25	0.48–0.53	0.75–1.00	0.035	0.040	0.15–0.35
4161	0.70–0.90	0.25–0.35	0.56–0.64	0.75–1.00	0.035	0.040	0.15–0.35
* The carbon composition of the alloy is denoted by the last two digits of the SAE specification number, in hundredths of a percent

Mechanical properties

Material	Condition	Tensile strength Tensile strength Ultimate tensile strength , often shortened to tensile strength or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract...  [psi (MPa)]	Yield strength Yield (engineering) The yield strength or yield point of a material is defined in engineering and materials science as the stress at which a material begins to deform plastically. Prior to the yield point the material will deform elastically and will return to its original shape when the applied stress is removed...  [psi (MPa)]	Elongation in 2" [%]	Hardness (Rockwell Rockwell scale The Rockwell scale is a hardness scale based on the indentation hardness of a material. The Rockwell test determines the hardness by measuring the depth of penetration of an indenter under a large load compared to the penetration made by a preload. There are different scales, denoted by a single... )
4130	Cold drawn Drawing (manufacturing) Drawing is a metalworking process which uses tensile forces to stretch metal. It is broken up into two types: sheet metal drawing and wire, bar, and tube drawing. The specific definition for sheet metal drawing is that it involves plastic deformation over a curved axis... —normalized	85000–110000 psi (586.1–758.4 MPa)	70000–85000 psi (482.6–586.1 MPa)	20–30	B 90–96
4142	Hot rolled—annealed Annealing (metallurgy) Annealing, in metallurgy and materials science, is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness. It is a process that produces conditions by heating to above the recrystallization temperature, maintaining a suitable temperature, and...	90000–100000 psi (620.5–689.5 MPa)	60000–70000 psi (413.7–482.6 MPa)	20–30	B 90–95
	Cold drawn—annealed	105000–120000 psi (723.9–827.4 MPa)	85000–95000 psi (586.1–655 MPa)	15–25	B 96–100
4150	Hot rolled—annealed	90000–110000 psi (620.5–758.4 MPa)	65000–75000 psi (448.2–517.1 MPa)	20–30	B 90–96

Other characteristics

One of the class of steels is their ability to be case hardened

Case hardening

Case hardening or surface hardening is the process of hardening the surface of a metal, often a low carbon steel, by infusing elements into the material's surface, forming a thin layer of a harder alloy...

 by carburization

Carburization

Carburizing, spelled carburising in the UK, is a heat treatment process in which iron or steel is heated in the presence of another material which liberates carbon as it decomposes. Depending on the amount of time and temperature, the affected area can vary in carbon content...

 of the surface. The core of the material retains its bulk properties, while the outside is significantly hardened to reduce wear and tear on the part. This makes this grade of steel an excellent material for such uses as gear

Gear

A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine....

s, piston pins, and crankshaft

Crankshaft

The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...

s.