AISI 4130 (aircraft) Alternatives
by Jan Zumwalt - 2013.12.11
"Metallic Materials and Elements for Aerospace Vehicle Structures," Military Handbook, MIL-HNBK-5
"Aerospace Structural Metals Handbook," Battelle’s Columbus Laboratories
"Steel, Sheet, Strip, and Plate," AMS 6345, Nov 1996, SAE
""Steel Sheet, Strip, and Plate," AMS 6350 Rev H, 1990-10-01, SAE
" Steel Sheet, Strip, and Plate," AMS 6351 Rev E, 1990-07-01, SAE
Steel Tubing Properties
Structural steel tubing is formed by rolling a strip of sheet
stock into a tube and roller-welding the edges. Several alloys are available
that is superior to the SAE 1020 mild steel tubing used in tens of thousands
of early airframes and is legal for use in repair work on rag & tube airframes.
(The details are covered in a CAA bulletin posted in the mid-1950's.)
AISI 4130 is called "4130" or "chro-moly" (chrome-moly or chromium-molybdenum
alloy) tubing. It is recommended for use at temperatures up to 700° F The 30
in 4130 represents a value of 0.30 percent carbon content. This steel is not
subject to temper embrittlement, and can be nitrided. It is a general
cut-off value for weldability. Alloys with more than 0.30 percent carbon are
not as easily weldable.
The Pietenpol or Cub style aircraft are proven designs that use about 10ea 20ft
pieces of tubing. Perhaps 30' is wasted so the design actually uses 170' or so,
mostly 1/2 and 5/8 inch. A 20' piece of 5/8" x .042, for example, is about $15.
And of course there will be a few brackets, axles, struts, etc. So lets be
generous and double the material cost. Still, the whole fuselage can be built
for about 2x $150 or a total of $300.
Whats the penalty for using structural steel instead of 4130? Structural steel
is 10-15% weaker so we could use the next larger size wall thickness. Yikes! That
might weigh a lot! Lets see... if we used 4130 tubing the weight comes in at about
43-lbs and structural steel is 48-50 lbs... Who cares? For 6 lbs of extra metal we
saved ourselves $600 dollars.
Wood aircraft weigh approximately 1/3 more so a wood aircraft would weigh 70-75 lbs.
Using structural steel is only slightly heavier than 4130 and 1/3 lighter than wood.
Oh! I forgot to mention that according to testing by the
American Welding Institute
4130 is more prone to crack than 1020 structural steel. They also mention that welders
should preheat 1020 100° less than 4130.
|Steel Tubing Properties|
|Material ||Approx Price |
|Condition ||Tensile strength ||Yield strength ||Elongation ||Hardness|
| $60.00 ||Cold drawn - normalized ||85,000–110,000 psi |
|70,000–85,000 psi |
|20–30% ||B 93 |
| ||Cold drawn - annealed ||150,000–170,000 psi |
|130,000–150,000 psi |
|20–30% ||B 93 |
| ||Hot rolled - annealed ||90,000–100,000 psi |
|60,000–70,000 psi |
|20–30% ||B 93 |
| ||Cold drawn - annealed ||105,000–120,000 psi |
|85,000–95,000 psi |
|15–25% ||B 98 |
| ||Hot rolled - annealed ||90,000–110,000 psi |
|65,000–75,000 psi |
|20–30% ||B 93 |
|SAE 1020 || $35.00 ||Hot rolled ||55,000 psi |
|30,000 psi |
|20% ||B 66 |
| $35.00 ||Cold rolled ||60,000-80,000 psi |
|50,000–70,000 psi |
|15% ||B 73 |
|SAE 1030 || $20.00 ||Hot rolled ||68,000 psi |
|38,000 psi |
|20% ||B 75 |
|SAE 1030 || $25.00 ||Cold rolled ||76,000 psi |
|64,000 psi |
|12% ||B 80 |
|SAE 1090 || ||Hot rolled ||95,000 psi |
|52,000 psi |
|15% ||B 91 |
|SAE 1090 || ||Cold rolled ||103,000 psi |
|88,000 psi |
|10% ||B 93 |
|SCH 40 || $20.00 || ||48,000 |
| || |
|SCH 80 || $50.00 || ||48,000 |
| || |
Described below are the five types of common carbon steel tubing primarly used for
COLD DRAWN SEAMLESSis is made from 1026 (UNS G10260) steel in sizes through 9 ½” OD,
from .28 wall thickness. Furnished in “as drawn” condition. Cold Drawn
seamless offers good surface quality and increased mechanical properties over hot
finished seamless tubing. No color identification. Meets ASTM A519. Stocked in
lengths of 8 to 24 ft.
HOT FINISHED SEAMLESSis made from 1026 (UNS G10260) steel. It is lower in cost
than cold drawn and most applicable where precise dimensions and surface quality
are of secondary importance. As an industry standard, HF seamless is manufactured
to OD and wall dimensions. Identification color: green. Meets ASTM A519. Stocked
in lengths of 8 to 24 ft.
DOM (Drawn–Over-Mandrel) is a cold drawn electric resistance welded tube with all
flash removed. Each tube is tested for soundness of weld. Preferred over seamless
tubing for its excellent OD & ID tolerance. Normalizing and cold drawing over a
mandrel makes DOM a uniform and precision product. Made from 1020 (GNS G10200)
steel in walls 10 ga. and lighter; from 1026 (GNS G10200) steel in walls heavier
than 10 ga. Furnished in “as drawn” condition. Manufactured to OD and ID dimensions.
Identification color:gold. Meets ASTM A513 Type 5. Stocked in
random lengths of 8 to 24 ft.
RY-STAR 512 EXTRAis electric resistance welded tubing (produced from 1020 SRA
(UNS G10200 steel) which is normalized and cold drawn over a mandrel for improved
mechanical properties, surface finish and controlled tolerances. Although not
recommended for pressure applications, Ry-Star has many of the advantages of DOM
at a price comparable to butt weld tubing. Furnished in stress-relief annealed
condition. Produced to OD and ID dimensions. Identification color: pink. Meets
ASTM A512(ERW). Stocked in random lengths of 8 to 24 ft.
BUTTWELD is similar to Ry-star (above) but produced from continuous welded pipe.
Does not offer the inherent strength in the weld area of an electric resistance
welded product. Made from low carbon SRA steel. Machinability and mechanical
properties are reduced as a result of lower carbon content. Identification
colors: pink and white. Meets ASTM A512. Stocked in random lengths of 8 to 24ft.
ELECTRICAL RESISTANCEWELDED is produced from low carbon steel. Tubing with walls
heavier than 18ga. Is produced from hot rolled steel; tubing with walls 18 ga. and
lighter is produced from cold rolled steel. Furnished in “as-welded” condition. OD
flash removed on all sizes. For round tubing 1” OD & larger ID flash controlled to
.010” to .015” (depending on O.D.) Sizes under 1” OD and all square and rectangles
are flash-in. ERW is the lowest cost of all mechanical tubing. Manufactured to OD
and wall dimensions. No color identification. Meets ASTMA513 Type 1 (HR) or Type
2 (CR). Stocked in 20 ft. random lengths.