AISI 4130 (aircraft) Alternatives

by Jan Zumwalt - 2013.12.11

Referances

"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
1"x10' .080
Condition Tensile strength Yield strength Elongation Hardness
(Rockwell)
AISI 4130
ASTM A519
$60.00 Cold drawn - normalized 85,000–110,000 psi
(590–760 MPa)
70,000–85,000 psi
(480–590 MPa)
20–30% B 93
AISI 4130
ASTM A519
Cold drawn - annealed 150,000–170,000 psi
(590–760 MPa)
130,000–150,000 psi
(480–590 MPa)
20–30% B 93
AISI 4142
ASTM A519
Hot rolled - annealed 90,000–100,000 psi
(620–690 MPa)
60,000–70,000 psi
(410–480 MPa)
20–30% B 93
AISI 4142
ASTM A519
Cold drawn - annealed 105,000–120,000 psi
(720–830 MPa)
85,000–95,000 psi
(590–660 MPa)
15–25% B 98
AISI 4150
ASTM A519
Hot rolled - annealed 90,000–110,000 psi
(620–760 MPa)
65,000–75,000 psi
(450–520 MPa)
20–30% B 93
SAE 1020 $35.00 Hot rolled 55,000 psi
(380 MPa)
30,000 psi
(165 MPa)
20% B 66
SAE 1020
A513
$35.00 Cold rolled 60,000-80,000 psi
(420 MPa)
50,000–70,000 psi
(165 MPa)
15% B 73
SAE 1030 $20.00 Hot rolled 68,000 psi
(470 MPa)
38,000 psi
(260 MPa)
20% B 75
SAE 1030 $25.00 Cold rolled 76,000 psi
(525 MPa)
64,000 psi
(440 MPa)
12% B 80
SAE 1090 Hot rolled 95,000 psi
(650 MPa)
52,000 psi
(360 MPa)
15% B 91
SAE 1090 Cold rolled 103,000 psi
(710 MPa)
88,000 psi
(605 MPa)
10% B 93
SCH 40 $20.00 48,000
30,000
SCH 80 $50.00 48,000
30,000

CARBON STEEL

Described below are the five types of common carbon steel tubing primarly used for mechanical applications.

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.